Uptime: December 2008 Archives

Squirrel Stores

user-pic
Vote 0 Votes
& Why You Would Be Nuts to Keep Them
by Phillip Slater

Breaking the locks was the only option. It was 2:00am and Line 1 had stopped completely.

The good news was that we knew exactly what the problem was and how to fix it. We also knew that the spare part we needed had been in the storeroom earlier in the day - I had seen it there myself.

 

The bad news was that it was no longer there. And although we didn't know with certainty where the part was, we were pretty sure that one of the dayshift crew had taken it and put it in his locker.

 

Waiting was not an option so locks had to be broken. We just hoped that we found the part before doing too much damage.


Sound familiar?

This scene is played out in maintenance workshops all over the world. Maintenance team members take parts and put them away in their own stores and sometimes, when really needed, the part cannot be found. The team members do this either because they think it is 'convenient' or that it 'saves time'. Convenient and time saving for them but what about the rest of us!

Let's face it, reliability and maintenance people are different. They have a unique position in the world. We all know that when things go wrong maintenance gets the blame. But when things go right, production gets the credit. As a result, some maintenance folk hoard spare parts, like squirrels keeping nuts for the winter. That's why these unofficial stores are often referred to as 'squirrel stores'. Look around almost any workshop and you will find spare parts that are being held in private stores, 'just in case'.

The problem with this, as demonstrated above, is that when parts are held outside of the official storeroom or inventory management system, they actually impact the rest of your inventory holding for that part. Not only in the obvious ways of poor availability and access, but also in less obvious ways relating to inventory levels, operational expenditure and even your reliability program - more on that in a moment.

First, let's understand why these stores exist. One reason is trust. That is, the trust that your official store will actually have the required parts when they are needed. If your storeroom management is unreliable, this erodes trust in the system. Also, if team members know that other team members are 'squirreling away' parts then they might do the same - just in case. No one wants to be caught short. Not only does it let the plant down but it is personally inconvenient.

Second, more than just being inconvenient, not having the spare part can be a real hassle. If the plant is down at 2:00am, it's your job to fix it and there is no spare, then you get the hassle from production - even though it is not your fault. Better to avoid all that and keep your own little emergency squirrel store - just in case.

A third reason is a rationalization that squirrel stores improve service (or at least reduce downtime) by reducing the time needed to go and get the spare from the official store. Squirrel stores are usually held closer to the plant (or at least closer to the team member) than the official store, hence, the time to access the store is reduced.

No matter what the reason, squirrel stores are ultimately a cultural issue, and they need to be managed on that basis. This requires building trust in the system, communicating the negative impact of 'squirreling', modeling and encouraging the right behavior, and not allowing any exceptions.

Now, how do squirrel stores really impact your inventory levels, operational expenditure, and reliability program? And why would you be nuts to allow your team to keep squirrel stores? Here are six reasons:

1. You Will Hold More Inventory

Duplicating the parts being held in your official store by holding parts in a squirrel store obviously adds to your inventory but it is the flow on effect that can be much, much worse. You might be surprised to realize that in addition to duplicating your inventory, squirrel stores can also significantly increase the level of spares held in your official store. How? Through a mechanism that I call Induced Demand Volatility (IDV). IDV occurs when your team takes more spares than actually required so that they can put some into their squirrel store. This behavior produces false data on usage and shows higher volatility than is really the case. This higher volatility then results in a need to hold more safety stock - after all safety stock is held to account for volatility. The breakout box shows a situation where induced demand volatility could increase spares holdings by 264%!

2. You Will Spend More Money

Obviously, the parts in the squirrel store and the extra parts in the official store have to be paid for. Therefore, this ties up much more money than would otherwise be the case. What many people don't consider is that this diverts funds from other and more useful purposes. Still waiting for the money to buy that tool to make your life easier? Perhaps the money is tied up in your squirrel store!

3. You Will Spend More on Your Operating Budget and Skew Your Reporting

When your team removes more items from the store than they really need, the costs have to be charged somewhere. Guess where - one of your operating budgets! Not only does this limit your ability to manage and improve your reliability (with what will already be a tight or underfunded budget), but it skews your reporting of costs by bringing forward costs that you could have incurred later. In many cases you may even be paying for parts that never get used, which leads to the next point.

4. You Will Have Increased Obsolescence

Is anyone really keeping track of those squirrel stores? Of course not. So, you have spent the money and when the item eventually becomes obsolete (as everything does) the squirrel stores will contain items that should have been used or should not even have been purchased! The only time they will be cleaned out is when someone decides to tidy up their squirrel store or workshop and you know that they will then just throw the parts in the trash.

5. You Will Increase Your Downtime

This is perhaps the worst part of the squirrel stores phenomenon. If the 'unofficial' parts are held in a locker or tool kit so that only the 'owner' can access them, then the rest of your team cannot access them. If you have a breakdown and need that part right away, you might not be able to get to it or might not even know that it is there! The irony here is that the part was being held in order to improve service and the squirrel approach actually made things worse. The result of this scenario is an increase in 'official' holdings, increasing expenditure even further.

6. Your Reliability Program Will Be Endangered.

As mentioned previously, when your team keeps squirrel stores they skew the data on usage. But this doesn't just impact your expenditure. It also means that your official records will show higher demand than actual at some times and lower demand than actual at others. If you are trying to perform any sort of analysis to understand your failure patterns, this data will be useless at best, and at worst, misleading. All that money spent on reliability training, software, gadgets and cultural change could be wasted because of a failure to control squirrel stores.

Unfortunately squirrel stores are almost a fixture of maintenance departments. They result from the mindset of reliability and maintenance professionals that are passionate about reducing downtime and take equipment failure personally. This drives them to hoard items that they can use later and to 'short cut' the system to try to improve response times. However, this approach does not work. Squirrel stores are a blight in your system and can have a significant and detrimental impact on your expenditure and your reliability program. In fact, you would be nuts to allow or endorse them.

Phillip Slater is an Inventory Process Optimization Specialist and is widely known as 'The Inventory Guy'. He is the author of a number of books, including Smart Inventory Solutions and The Optimization Trap, both of which deal directly with MRO and engineering spares inventory. For more information visit www.InitiateAction.com 

 Click Here for the Case Study

PrecMaint_Dec_Jan_2009 - Squirrel Stores.pdf

Research Brings Results

user-pic
Vote 0 Votes
Defining Mean Time Between Pump Failures
by Heinz P. Bloch, PE

In September 2008, we were contacted by a Mechanical Engineering student. He was close to completing an internship with a major U.S. oil refinery and had been asked to set up a system allowing the refinery to monitor its pump mean-time-between-failures (MTBF).

Since being given the assignment, the young man had encountered serious roadblocks. His first question was how MTBF was being calculated in the oil refining industry. He advised that some people just take the number of months in service and divide by the number of repairs during that time; while others apparently perform a Weibull analysis. The Weibull analysis sounded much more accurate to him, but he wanted to stay with industry standards.

He ran into a second roadblock when attempting to define what a failure is. The refinery was currently contemplating a definition of "anything costing over $1,000", but he wanted to know what the standard was. Using the all-pervasive and now rather customary (and generally inadequate!) Internet search method, he found many articles that talked about MTBF studies. He did not, however, uncover any articles that shed useful light on how such studies were to be set up. Finally, he asked for help in finding some of the answers.


No Standard, Just Choices

There is no written standard on MTBF, but McKenna and Oliverson's "Glossary of Reliability and Maintenance Terms" (ISBN 0-88415-360-6) neatly defines it as:

"A basic measure of reliability for repairable items; the mean life during which all parts perform within their specified limits, during a particular measurement interval under stated conditions; an index of reliability calculated by dividing the total number of stoppages (outages) by operating time; the number of hours or cycles an item or items operated divided by the number of failures that occurred; commonly expressed as a six or 12 month rolling average; also expressed as one over the failure rate."

That pretty much explains what is common practice. By deviating from common practice, perhaps doing a Weibull plot, one achieves another benchmark. A Weibull plot is a reliability prediction technique used to evaluate the reliability parameters of components (e.g. bearings), and the data from it is more precise than MTBF calculations. These plots are also valuable during the development phase of a component. While Weibull plots are possible for failed pumps, the specialist using them will give up the straightforward comparison with others that use MTBF. That should be a concern for us.

More About Weibull For definitions of failures/metrics, etc., go to Paul Barringer's reading list for reliability1. Select an old document, MIL-STD-721. This is one of many military documents Paul has accumulated on his website. Specifically, go to page 11 for the words, which he has reduced to the equations below:



The MIL-STD-721 document reaches way back to the 1970's, and has now become obsolete. Better modern documents such as MIL-HDBK-338 are available today.

Quoting Paul Barringer, "The practice of summing the life of active units plus dormant units is a poor (lazy) engineering practice in calculating MTBF & MTTF metrics. It is poor because it overstates the results by including so-called life of dormant units. This sets a trap for naive people building RAM models of system performance because the flawed metrics will overstate system performance."

The military documents, such as DoD Ram Guide, RAM primer, MIL-STD-785, NASA-Std 8729.1, and other documents listed on the Barringer website, provide some excellent guides for building RAM models.

For Weibull analysis of components:

Reliability02DecJan09.jpg

Here, h is the characteristic life (i.e., the life at 63.2% of the cumulative distribution function, as this is a mathematical property of the distribution--in short, it's the single point representation of durability that you discuss without all of the if/and/buts). The b is the shape factor. For components, b tells you how things died (i.e., b<1 infers infant mortality, b~1 infers chance failures, and b>1 infers wear-out failure modes)--it is important to let the data speak rather than pontificating about how things died.

The term G(1+1/b) is called the Gamma function. For b = 0.5 the Gamma function is 2, for b = 1 the Gamma function is 1, and for b>1 it may be as small as 0.87 or as large as 1, so as a rough rule of thumb, the MTTF is roughly equal to h. You need to know the beta values to get the correct medicine because everyone will tell you things wear out, although, unfortunately, we kill more things than ever live long enough to wear out. (Note: On another website2, Dr. Robert Abernethy provides additional insight into the differences between MTBF and MTTF. Consulting his website may be important for students of the Weibull method.)

MIL-HDBK-338 on page 46 gives you a simple and clear definition of failure: "The event, or inoperable state, in which any item or part of an item does not, or would not, perform as previously specified." Reliability (lack of failures) always terminates in a failure (loss of the function when you needed it). Many other details about failures are also included in pages 46-47.

Finally, download the technical paper #2 from Paul Barringer's website at the bottom of the page called: Where Is My Data For Making Reliability Improvements. It gives other source documents and shows how to make the calculations.


Consider Feedback from an Asset Management Expert

Several comments were also obtained from John S. Mitchell, a self-described "advocate of change" whose "Asset Management Handbook" (ISBN 0-971-7945-1-0) is listed in our essential library3. John believes a meaningful comparison of MTBF must consider the service. Some, because of the fluid and/or operating conditions, will have shorter life expectancies than others. Mitchell uses the analogy of a coal miner who smokes; the miner probably has a shorter lifetime than a non-smoker office worker.

John Mitchell has been trying -- without success so far -- to find a parameter that will, with one number, describe the distribution around an average. Distribution around an average might be the percentage or number of the total population more than 20% below the average MTBF. As an example, suppose a plant reports an MTBF of 48 months. This would be showing performance a bit below best in class in Table 1, from "Pump User's Handbook: Life Extension" (ISBN 0-88173-517-5), but doesn't say much beyond that. Knowing also that 2% of the total population was below 36 months would be useful information because it would tell us that the plant was aware of certain pumps that failed more often than others. (In many refineries that number is somewhere between 7 and 10 percent). However, suppose one found out that the MTBF of 25% - 30% of the population was below 36 months, our diagnosis might be quite different and the opportunities for improvement would be shifting to a new focus.


Reliability03DecJan09.jpg

More Experience-based Advice You Can Use Today

The explanations offered by Paul Barringer and John Mitchell will have to be weighed by serious reliability professionals. Some of their suggestions were certainly considered in the mid- 1970's when we wrote about calculating pump MTBF based on actual operating time. Yet, industry soon decided that the numbers looked better when the calculation encompassed all installed pumps, irrespective of running or not running. Moreover, we have always advocated picking first the ripe, low-hanging fruit and hasten to note that not everyone has heeded this advice. We are where we are and the picture is not rosy. Repeat failures abound and continue to be tolerated. Repeat failures are warning signs; they are the inevitable precursors to extreme failures which very often kill people. To this day, we see CMMS (computerized Maintenance Management Systems) software that allows log entries in words such as "bearing replaced." To be of use to devotees of equipment uptime, a system must recognize that accurate failure analysis is required for failure avoidance. The entries must properly identify why a bearing failed and diligent failure analysis is absolutely necessary. Failure avoidance should be the ultimate goal because it means asset preservation and curtailment of money wasted on repeat repairs, not to mention costly remedial action after an extreme failure. All too often, persistent repeat failures are evidence of seriously flawed reasoning.

The engineering student employed as an intern at that refinery probably would not wish to lose the opportunity for easy tracking of pump failures. He was probably searching for answers to tasks assigned to him by others. We can only speculate that "persons unknown" are often looking for ways to bury the unacceptable performance of their refinery pumps. They would be delighted to obfuscate the issue by arguing over the most precise numerical evaluation. We, for our part, believe the most productive choice to reduce pump failures is to compare one's pump MTBF against other refineries and to itemize and comprehend what "others" do differently. Note that we are not advocating that you compare your refinery against any non-refineries, but you could make a relevant comparison between a given process unit at your refinery against a like process unit at another refinery.

Although such comparisons are usually made on the basis of MTBF, they are still more useful than anything else. They lead to the next and most important step towards implementing the necessary changes, i.e. intelligently upgrading pumps or systems that fail frequently. Typically, and with few exceptions, these changes must be made on pumps with low MTBF. The simple MTBF roadmap has been followed for the past 35 years; its relative success makes us comfortable with the McKenna-Oliverson definition mentioned earlier. In stark contrast, we consider endless debates over more precise or limited definitions both unproductive and all too often diversionary. In this context, debates generally solve nothing, they are mere exercises in bureaucracy. Exploring the failure history of a given pump in a given service in YOUR refinery and then comparing its reliability with that of a pump in the same service at SOMEONE ELSE'S refinery is of real value. It points out the way to lasting improvement.


How to Recognize a Good Pump MTBF

Examining pump repair records (and the admittedly imperfect MTBF metric) is deemed useful for responsible and conscientious pump users. In view of that fact, the preface to the 2006 Pump User's Handbook (ISBN 0-88173-517-5) alludes to pump failure statistics. Again, and for the sake of convenience, these failure statistics are often translated into MTBF. Agreeing with McKenna and Oliverson and because they wanted to avoid arguments on statistics, many of the best practices plants in the time period of the early 2000's simply took all their installed pumps, divided this number by the number of repair incidents, and multiplied it by the time period being observed. For a wellmanaged and reasonably reliability-focused U.S. refinery with 2,400 installed pumps and 312 repair incidents in one year, the MTBF would be (2,400/312) = 7.7 years. The refinery would count as a repair incident the replacement of parts, any parts, regardless of cost. In this instance, a drain plug worth $2.90 or a casing costing $8,000 would show up the same way on the MTBF statistics. Only the replacement of lube oil, a routine maintenance task, would not be counted as a repair.

Using the same bare-bones measurement strategy, and from published data and observations made in the course of performing maintenance effectiveness studies and reliability audits in the late 1990's and early 2000's, the mean-times-between-failures of Table 1 have been estimated. As of 2008, we have reason to believe the figures are valid within a 10% range of accuracy.

It should again be emphasized that many plants are achieving these mean times before a failure occurs. Why, then, the difference between a "best-of-class" U.S. refinery and a somewhat mediocre performer? There are many reasons that account for the difference. An unsuitable seal with a lifetime of just two or three months will have a catastrophic effect on pump MTBF, as would a badly-performing coupling or bearing. A good refinery frowns upon pulling piping towards the nozzle of a fluid machine, a mediocre refinery permits these disastrous procedures to continue for decades. One refinery supports its machine baseplates with epoxy grout, another refinery not only uses an inferior grout system, but might also allow it to soak with oil, degrade, and deteriorate. It is those types of things, and in areas of lube application, bearing housing protection, mechanical seal selection, installation methods and so forth, that the "best-of-class" differ from the weak performers.


What Constitutes a "Failure"

Finally, we were asked what constitutes a failure. In particular, we would like to comment on the sordid implications of limiting the term "failure" to events costing over $1,000.

In "Glossary of Reliability and Maintenance Terms" , McKenna and Oliverson defined a failure as:

"The termination of the ability of a functional unit to perform its required function; loss of function when the function is needed; the event, or inoperable state, in which any item or part of an item does not, or would not, perform as specified; any event that results in work performed on equipment, rather than scheduled preventive or predictive maintenance that requires the equipment to be shut down for repair or whose lack of repair could ultimately lead to an equipment shutdown. Synonym: malfunction."

We are much indebted to Paul Barringer for providing the many links that will facilitate serious research on reliability subjects. The "Essential Reliability Library, 2008" is the author's own recommendation. We consider it rather elementary, but representing a good first step for machinery engineers.

We accept this definition without qualification or reservation, and offer two examples that illustrate why. Years ago, a plant decided to count failures as only pumps that were taken to the shop for repair. One day, a badly mangled pump was being parked on a flatbed trailer near the shop. Because the pump never entered the shop, it did not appear on the failure record kept by this facility. Another plant decided that "rework" should not be counted as a failure. The facility defined as rework any successive event, occurring within three days of repair completion and restart. This plant then counted the second, or third, or fourth event as part of the same repair and made it show up only once on the refinery's failure log. Those were the games we have seen played when industry deviated from the definitions crafted by people with common sense and logic.

So, again answering the intern's question with an example: If an O-ring worth $2.20 allows oil to leak, it must be counted as a failure. If an impeller replacement were to cost $100,000 plus labor, it would also be called a failure. The most crucial issue identified here is the huge problem many refineries have today: It's a people and people-management problem. It's a problem with setting the wrong priorities. An individual tasked with managing equipment reliability must have the time and the motivation to read, to assemble a reference library (see below), to engage in effective root cause failure analysis, and to improve specifications for both new (future) and present (existing) equipment installed at his plant. He must also mentor others, and do so with knowledge and wisdom. If he neglects any of these duties, he should be viewed like a medical doctor lacking in those traits - society would deny him the title MD. Likewise, a mere dabbler in reliability engineering may not deserve to be called a professional. The medical analogy could also be extended to reliability practitioners that feed their minds only on the Internet. Reasonable people would never entrust life and health to a medical doctor whose knowledge was derived solely from the Internet, from its sales-driven advertisers and from conversations with the purveyors of anecdotal knowledge. Needless to say, a medical professional is being taught by other experienced professionals and will consult relevant texts. It should be no different with reliability engineers working in industry.

I have compiled an essential reference library for those who wish increase their knowledge, which can be found at the link listed in Reference 3 below. Rest assured that research via exclusively consulting the Internet will, at best, uncover disjointed pockets of information. The information so found will not follow a logical progression and will not even come close to conveying the coherent picture needed by true professionals.


References

  1. Paul Barringer's complete reading list can be found at the following link: http://www.barringer1.com/read.htm
  2. Dr. Bob Abernethy's website: http://www.bobabernethy.com
  3. The Essential Reliability Library 2008, a reading list compiled by Heinz P/ Bloch: www.uptimemagazine.com/reading.htm
Heinz P. Bloch (hpbloch@mchsi.com) is a professional engineer with offices in West Des Moines, Iowa. He advises process and power plants worldwide on reliability improvement and maintenance cost reduction opportunities. Heinz is the author of 17 full-length texts and over 400 papers and technical articles. His most recent texts include "A Practical Guide to Compressor Technology" (2006, John Wiley & Sons, NY, ISBN 0-471-727930-8); "Pump User's Handbook: Life Extension," (2006, Fairmont Publishing Company, Lilburn, ISBN 0-88173-517-5) and "Machinery Uptime Improvement," (2006, Elsevier-Butterworth-Heinemann, Stoneham, MA, ISBN 0-7506-7725-2)

Measuring Performance

user-pic
Vote 0 Votes
The Need for Metrics Standardization
by Walter Nijsen, CMRP

Understanding how our plants perform and how well we perform in relation to others often reveals opportunities for improvement, at least in principle. The key question first raised is often, "Are we comparing apples with apples?" If not (as in many cases), the whole exercise of comparison, and to some extent, measurement, becomes somewhat (or completely) meaningless.

On top of that, a question that really should be answered first is, "WHY should we measure?", along with, "WHAT should be measured and HOW?"

The measures we believe are truly important are often referred to as Key Performance Indicators (KPI's), since, apparently, as the wording implies, those contain key information on performance. But does it, and if so, what precisely is it indicating?

When measuring true performance, a number of questions and preliminary steps need to be taken first:

  • Which KPI's are useful at what stage?
  • Is this a leading or a lagging indicator?
  • What is the correct definition?
  • How will we interpret the results?
  • How will you benchmark KPI's?

Why Should We Measure?

Joseph Juran famously said, "If you don't measure it, you can't manage it."

Ron Moore said, "Your measurements should expose your weaknesses - those are your improvement opportunities."

When asking this question to several persons in an organization, you will typically get different answers. An operational leader or business leader could answer: "to measure our profit and losses, or to understand if we are achieving our goals". A reliability improvement leader could answer: "to identify opportunities for improvement, or to measure the improvement progress".

Both answers are correct and make sense, depending on your role and interests, because you want to measure and trend the results or the improvements at your facility.

"To compare and benchmark between industries or within the company" is also an expected answer. On top of this, there is another important, and mostly forgotten, or at least not identified, reason why we should measure: "To share success, which encourages changes and improvements".

To achieve reliability excellence many changes and improvements need to be made. Some are easy, and some are more difficult, but sharing success will help drive forward these changes. Benchmarking at a facility level, company level or industry level is a part of sharing those successes.


What Should We Measure?

If the "Why should we measure question?" is clear and understood, the answer to "What should we measure?" is simple. Lets focus only on the maintenance and reliability process. At the end of the day, the financial results, product quality and availability will determine your profit and losses and your business growth. So KPI's such as, OEE, maintenance cost as a percent of replacement asset value, quality index, on time delivery, production cost per unit produced need to be in place.

However, these indicators are lagging indicators, or results indicators, which give a snapshot or update for the moment, but will not tell you what the future results will be, nor if these results are sustainable. Further, many persons or processes can influence these KPI's. For example, maintenance cost is influenced by many things, e.g., amount of unplanned breakdowns, amount of pro-active work executed, quality of the executed work, efficiency of the executed work, etc. Therefore, it is important to also implement KPI's, which tell you something about your potential performance in the future, or so-called leading or process indicators. These indicators are typically used to measure the process improvements that bring us to our new goals.

The leading indicators should show us the direction of future results, or in other words, the leading indicators will tell us if the lagging indicators will get better or worse.

There are three sets of measurable components that make up the maintenance and reliability process at Cargill (See Figure 1: Components of the Maintenance and Reliability Process).

  • Behaviors and management processes (people skills, mission and vision)
  • Operational execution (operations, design and maintenance)
  • Manufacturing performance (availability, quality, cost and benefits)

Each component is a process on its own, which can be measured using both leading and lagging indicators. To determine the quality of each process, the results of each process need to be measured using lagging indicators. To assure good results, we must have good leading indicators - if you do the right things, the right things will happen for the business.

The components of the maintenance and reliability process can also be explained as: approach, deployment and results. Manufacturing performance is a (end) result of the (correct) deployment of operational execution. Operational execution is, in part, the deployment of maintenance planning and scheduling, defect elimination, predictive and preventive measuring and follow up.

To understand if these manufacturing performance (results) are sustainable, it is important not only to measure the deployment (operational execution) but also the approach (behaviors and management process). Without having a clearly defined approach, the result can be, and often times is, based on individuals deploying to their best effort, but without any vision and strategy for the future.

In this context, and as a supply chain, the components of the maintenance and reliability process are both leading and lagging indicators depending on where in the process the indicators are being used.

This simplified view of leading and lagging measures betrays the full value the definition can have. There is a cause and effect relationship between leading and lagging; the action being measured will cause a resulting action or effect, which is also being measured. This means that a given measure could be both a lagging measure for a previous cause in the chain, and a leading measure for a following effect. There are a series of causes and effects in the chain until the final lagging measures are reached.

The Leading and Lagging Indicator Mapping in Figure 2 shows the concept of an indicator being both leading and lagging. Preventive Maintenance (PM) Compliance is a lagging indicator, or a result of how much PM work is completed when viewed in the context of work execution. However, when viewed as an indicator of equipment reliability, PM compliance is a leading indicator of the reliability process. The better or higher an organization's PM compliance, the more likely this will lead to or predict improved equipment reliability. Similarly, improved equipment reliability will lead to reduced Maintenance Costs, which is a lagging indicator of the maintenance process.

Before applying and implementing leading and lagging indictors, the maturity of the facility or company needs to be understood. For example, if you are in a transition stage from reactive to pro-active, then KPI's like training compliance and percent pro-active work completed are more applicable to use than inventory turns increasing, or maintenance rework reducing, which are typically results of a more mature reliability process.


MaintMgmt01DecJan09.jpg

To implement which KPI at which particular moment is unique for each business or location. Some ground rules need to be considered:

  • Focus on leading and lagging indicators for each reliability process component, see Figure 1
  • Provide clear definitions and examples
  • Assets the operational readiness to implement the KPI.

How Should We Measure? When implementing key performance indicators and setting goals, it is a natural human behavior to produce the results you are aiming for. This induces a natural bias to get the results you are targeting. For example, at our company we are measuring percent pro-active work completed, and we are aiming to achieve 80% pro-active work. Clear definitions with examples are set and the unit of measure is hours.

When starting the measurement, plants were only asked to report the percent pro-active work done, and within several months, almost all plants were achieving this number, even though we knew it could not be possible considering the maturity stage of some plants. A thorough review showed that not all plants used "work hours complete" as a unit of measure; that is, some used number of work orders complete, some used actual cost, some included contractors, and some not.


MaintMgmt02DecJan09.jpg

So, we made a change in the reporting. Instead of asking plants to report the percent pro-active work completed, we asked them to report actual hours spent on pro-active work and the total actual hours worked. This changed the results completely; some plants captured only 60% of the total hours, which were typically the hours spent on proactive work. The hours on reactive work were not included in the total hours show, and thus a much higher percentage of proactive work was reported done than actual. Plants not capturing hours at all actually failed to report anything.

Lessons learned on how we should measure are:

  • Provide clear definitions and examples, in multiple languages if applicable
  • Understand the unit of measure and report the raw data, not the end results
  • Use uniform reporting systems

Benchmarking and Standardization

Cargill is a leading company in the food industry with over 1500 locations in more than 80 countries. Comparing and benchmarking within the company and with other industries is a challenge. During the last 10 years, a major change has been made within the company, from a focus on traditional lagging indicators to more leading indicators.

Cargill has learned a great deal in the last 10 years, and many others can learn and benefit from both these lessons learned and from Cargill's experience. In fact, these lessons learned drive the process of standardization of key performance indicators.


MaintMgmt03DecJan09.jpg


Figure 3 - SMRP Developed Key Performances Indicators

Acronyms
SMRP - Society for Maintenance and Reliability Professionals KPI - Key performance Indicators
OEE - Overall Efficiency Effectiveness BoK - body of Knowledge

The Society for Maintenance and Reliability Professionals (www.smrp.org) is a group "by practitioners for practitioners", who in the last year, has developed standardized Maintenance and Reliability Key performance indicators. Each of these indicators have a clear definition, objective, formula, component definition, qualification and sample calculation developed by experts from several industries world wide, validated and evaluated by practitioners, and are ready for use.

A total of 77 key performance indicators are identified and under development, 21 KPI's are finished and will be published soon by SMRP. Figure 3 provides several examples of the key performances indicators from the body of knowledge (BoK), including the reliability process component upon which they can be used.

Worldwide adoption of these metrics will benefit Cargill, but also all other industries. It will also create transparency and unique benchmarking opportunities within the maintenance and reliability industry.

Walter Nijsen, CMRP, holds the position of Asst M&R Leader for Cargill grain and oilseeds in Europe. Based in the Netherlands, he is responsible for developing and implementing the maintenance and reliability strategy for about 40 locations across West and East Europe. During the last 5 years Walter has implemented maintenance best practices, and has been instrumental in building the overall reliability culture and vision for Cargill worldwide by actively participating in maintenance steering committees, conferences, facilitating trainings, developing systems and procedures. He holds a degree in Chemical Engineering and joined Cargill in 1995. He is certified in several predictive technologies, is a certified maintenance and reliability professional since 2003. He is an active member of the SMRP Best Practice Committee.

Original article in PDF Format:

MaintMgmt_Dec_Jan_2009.pdf



Building A Lubrication Program

user-pic
Vote 0 Votes
By Using the Five Rights, You Won't Go Wrong

by Ray Thibault, CLS, OMA I & II

This article will examine the use of the five rights of lubrication - which are Right Type, Right Quality, Right Amount, Right Place and Right Time - all of which are important in the development of a highly effective lubrication program. Many companies fail to realize the importance of lubrication and the application of these five basic concepts to achieve world class machinery reliability. Each will be examined in detail, along with a summary of best practices, including procedures in the selection of the optimal lubricant supplier.


Right Type

As a first step in the lubrication of equipment, refer to the OEM manual. The OEM should be contacted if there are any questions. With old equipment the OEM manual may be outdated and better lubricants may be available. When in doubt, utilize your lubricant supplier along with the OEM.

Two major classes of lubricants are oil and grease. The selection of the type is based on the application. Greases are used extensively in the lubrication of small bearings. As a rule of thumb use oil where possible because it can be cooled and filtered but this is not possible for many applications where grease is the better choice. The following are applications for grease:

  • To decrease drippage and splattering, as the grease acts as an additional seal to reduce leakage
  • To reach hard to get to lubrication points where lubrication frequency is important and when oil circulation is impractical
  • To seal in the lubricant and assist in sealing out contaminants such as water, dirt and damaging corrosives
  • To protect metal surfaces from rust & corrosion
  • To lubricate machines with intermittent operation
  • To suspend solid additives such as moly or graphite
  • To lubricate sealed-for-life applications
  • When extreme or special operating conditions exist
  • When machine parts are badly worn
  • When noise reduction is important

Greases are composed mainly of oil dispersed in a thickener with additives. Typical grease is about 85% oil. It is the oil which does the lubricating in grease. The NLGI classifies greases according to consistency with the following grades increasing in hardness: 000, 00, 0, 1, 2, 3, 4, 5, and 6. The most common NLGI grade is #2. At high speeds #3 may be used and at low temperatures and in centralized systems a 0 or 1 is used.

Most large equipment is oil lubricated and selection of the right type is critical to reliability. Two major factors in selection of an oil based lubricant are the correct viscosity and additives in the formulation. For a more complete discussion of viscosity please refer to Basic Principles of Viscosity and Proper Selection Techniques published in Lubrication & Fluid Power (LFP). For a more complete discussion of additive types, please refer to All Lubricants are not Created Equally (Basic Concepts in Formulation of Finished Lubricants) which was published in LFP in 2006.

OEM's will recommend the correct ISO viscosity grade for their equipment based on the operating temperature. Table 1 classifies kinematic oil viscosity in centistokes for industrial lubricants based on the ISO grade which is the midpoint of a viscosity range +/- 10%.


Since grease is primarily oil which does the lubricating; the correct viscosity must be selected in the grease formulation. Table 2 provides guidelines on the selection of the correct viscosity in grease.

Once the correct viscosity has been determined, the correct lubricant type based on additive composition needs to be selected. Lubricant formulations consist of a base stock and additives. Most base stocks are mineral oils from refining of crude oil. Table 3 summarizes lubricant composition in various lubricant types.

Lubricants in Table 3 with 'o' signify the additive is not in all formulations but is optional for specific applications.


Right Quality

Once the right type of lubricant has been selected, it is important to select a high quality lubricant. Quality is both the ability of the lubricant to meet OEM specifications based on performance on ASTM tests and the cleanliness of the fluid which is delivered. You can have the highest quality lubricant, but if is not handled properly during delivery or storage it will not perform as expected.

lubrication02decjan09.jpg
Table 3 - Lubricant Composition by Additive Type

Product data sheets provide useful information on lubricants and their behavior on ASTM tests which provides information on their performance on equipment. The best test for a lubricant is how it has performed in your plant, but there are some situations where a lubricant is selected only on specification tests. A series of articles was published in 2005 in LFP on turbine, hydraulic, and gear oil specification tests. Please refer to these articles for an in-depth coverage of lubricant specification tests and how they can help in the selection of the right quality lubricant.

The following summary is best practices to apply in maximizing lubricant quality:

  • Utilize specification tests on product data sheets to compare lubricants
  • Contact OEM's for minimum specification requirements
  • Set minimum lubricant specifications with suppliers
  • Set standards on new lubricant deliveries but be reasonable. During the delivery process it is difficult to maintain high levels of cleanliness. Most hydraulic oils need to filtered before use
  • Utilize certificates of analysis for water content and viscosity on delivered lubricants
  • Routinely run more extensive tests with an oil analysis laboratory to determine if supplier is meeting minimum requirements
  • Don't utilize price as main criteria in supplier selection
  • Establish return criteria in lubricant contracts

lubrication03decjan09.jpg

Right Amount

Grease Lubrication - More is not better. Too much lubricant in a system can be as destructive as not enough, as evidenced by the over greasing of electric motors, which happens to be a major failure mode. The use of the formula in Figure 1 will assist in greasing rolling element bearings with the correct amount.

This calculation will give you the number of ounces to add to a bearing during greasing. This is especially important when greasing electric motors because of the tendency to over grease. In order to add the correct amount, grease guns need to be calibrated on their delivery of number of shots /ounce. This can be completed by using a postage scale to weigh out one ounce of grease. An easier method is to count the number of shots to fill a 35 mm film canister, which is approximately one ounce of grease. Once the guns have been calibrated, try to use the same grease gun type consistently for the same application. Some of the newer guns will indicate the amount being added.

Oil Lubrication - Centralized oil systems add the right amount at the right time. This discussion will focus on the having the correct level in oil baths and splash lubricated gear boxes.

Many small pumps are lubricated by oil baths as illustrated in Figure 2. The correct level for a bottle oiler bath should be at the middle of the lowest ball.

lubrication04decjan09.jpg
Figure 2 - Oil Bath Illustration
Courtesy Trico Mfg


lubrication05decjan09.jpg
Figure 3 - Slinger Ring
Courtesy Matthews Royal Purple


Large pumps and process steam turbines which have journal bearings are often lubricated with the use of slinger rings as illustrated in Figure 3. The oil level with slinger rings should be set at 1/8 to 3/8 inches from the bottom inside edge of the ring. The faster the speed the lower the level should be.

Splash lubricated gear boxes are very common where both gears and bearings are lubricated. Enough oil needs to be splashed up for cooling and for lubrication. An oil level too high will cause churning, which will over heat the oil, while a level too low will not provide proper oil cooling and lubrication for bearings and gear teeth. Spur helical, bevel and spiral bevel gears are lubricated with the gears dipping into the oil at twice the tooth depth. The OEM will provide information on the correct oil level.

lubrication06decjan09.jpg

Worm gears consist of a steel worm and a bronze wheel with either the worm being above or below the wheel. Figure 4 illustrates a worm below the wheel, where the oil level is normally set just below the worm center line. With the worm above the wheel, as illustrated in Figure 5, the oil depth ranges from just above the wheel tooth depth to the center line of the wheel. The oil level is dictated by the speed. The higher the speed, the lower the oil level to minimize churning.


Right Place

Once we have selected the right type of lubricant and the quantity to be added, we need to apply it at the proper location. Adding the wrong oil to a lubrication point is not uncommon. It will usually go undetected until a problem occurs or, with an oil analysis program, detection can be at an early stage, avoiding possible equipment damage.

All lubrication points should be properly labeled as to the lubricant to be added. Lubricant manufactures provide lube tags for proper identification of the proper lubricant to be used at the lube point. A typical tag is illustrated in Figure 6.

lubrication07decjan09.jpg

Figure 6 - Typical Lubrication Tag.


A good practice is to use separate containers for different lubricant types, as mixing lubricants with different additive packages is not recommended. Normally each lubricant supplier color codes their tags by lubricant types. In Figure 6, all of their hydraulic oils would be red tags, but with different ISO numbers such as ISO 46 and 68. Containers should also be properly tagged, along with the drums or totes where the oil is transferred to the container. This will minimize the possibility of adding the wrong oil. The following is a summary of best practices for the addition of lubricant at the right place:

  • Become acquainted with lubrication points on new equipment through the OEM manual
  • Train personnel on correctly adding lubricants to equipment
  • Label all equipment lube points with color coded lube tags, which contain ISO viscosity, obtainable from lubricant supplier. Type of lubricant based on color
  • Lube containers should be used for only one type of lubricant and should have a color coded tag for lubricant type. Ideally use only one container per lube type and ISO viscosity
  • Apply label to lube containers
  • Apply tags to totes and drums

Right Time

Grease - Once we have established our program with the right type, quality, amount, and place, we need to establish proper lubrication intervals. Grease frequencies can be determined by using charts, but the following easy calculation is also is used:
lubrication08decjan09.jpg

Oil - The frequency of changing lubricants depends upon the type of system and size of the reservoir. Initial guidance is provided by the OEM and should be adjusted based upon the environmental conditions.

Small reservoirs (<50 gallons) in non-circulated systems are often changed on a certain frequency based on OEM recommendations and experience. As an example, small ANSI centrifugal pumps in plants hold less than two quarts of oil and the oil is changed over a wide range of intervals. I know one plant that will change every quarter while another using the same type of pumps will change every two years. The environmental conditions dictate the change frequency. The plant changing quarterly has to deal with difficult conditions on water ingression and contamination, while the plant changing biannually has much more favorable conditions. This also applies for splash lubricated gear boxes or any bath lubricated system. To determine the correct change frequency for similar equipment under similar conditions, statistically evaluate the condition of the oil through oil analysis tests. This can provide useful information on establishing change frequency.

Change frequency for large systems (>50 gallons) should be established with oil analysis condition monitoring tests. Two major failure mechanisms for lubricants are contamination (particles/water) and oxidation. Routine visual monitoring of the oil is important. Oils that are getting darker indicate possible oxidation and should be further evaluated. Oils appearing hazy or having suspended solids indicate excessive contamination and should also be further evaluated.

Oxidation is one of the primary reasons lubricants fail, and it's temperature dependent. For every 18°F increase in temperature the oxidation rate doubles which cuts the oil life in half. This is noticeable over 140°F. When oils oxidize they produce sludge, varnish, and acids all, of which can cause equipment damage. A very useful test is to monitor the increase in the acid number of a lubricant through oil analysis and to set condemning limits for the oil.

Excessive water contamination can be determined with a Karl Fisher test, and particle counting can measure the cleanliness of oil. Both of these tests can be included in an oil analysis testing program.

The following is a summary of best practices for oil change frequency:

  • Utilize OEM recommendations for change frequency
  • Set frequencies for small systems based under high operating temperature
    conditions
  • Cost of changing lubricant is minimal compared to potential equipment damage and downtime; therefore err on the side of changing too frequently 

Summary of Lubrication Best Practices

  • Assign lubricant program to one person
  • Conduct lubrication survey on equipment and keep updated
  • Develop lubrication scheduling through CMMS or other electronic program
  • Keep records of lubrication activities
  • Utilize OEM and lubricant supplier to ensure use of correct lubricant
  • Consolidate lubricants without compromising performance
  • Utilize competent personnel for lubrication and provide adequate training
  • Set equipment cleanliness as goal to proactive maintenance
  • Establish an effective oil analysis program for proactive and predictive maintenance
  • Practice continuous improvement with lubrication program

Lubricant Supplier Selection An effective lubrication program is a partnership between the lubricant supplier and the end user. This includes both the lubricant manufacturer and distributor/marketer. Selecting the correct supplier is a very important step in establishing a world class lubrication program and should not be taken lightly. Don't select or change suppliers based strictly on price.

lubrication09decjan09.jpg

The criteria in Table 4 should always be used in selecting a lubricant supplier. No one single factor such as price should determine the supplier selection.

The following is a summary of each of the selection factors:

Product Quality

  • Lubricants are not all created equal
  • Set minimum specifications through ASTM tests
  • Adhere to OEM guidelines
  • Request data from suppliers not reported on product data sheets where needed
  • Utilize outside laboratories to evaluate suppliers when appropriate

Price
  • Never base selection of a lubricant supplier solely on price
  • Utilize high price synthetics where appropriate to extend equipment reliability and drain intervals
  • Don't let purchasing make final decision

Logistics
  • Most deliveries, especially packaged items, are provided by lubricant distributors
  • Proximity and response time are important factors in selection of supplier
  • Require cleanliness and dryness in oil deliveries, but don't be unreasonable
  • Utilize Just-In-Time where appropriate

Technical Service
  • Evaluate potential suppliers based on innovative approaches for lubricant program improvement
  • Utilize lubricant suppliers expertise in troubleshooting lubricant related equipment problems
  • Consolidate lubricants without compromising performance
  • Request that the supplier run compatibility tests before changing suppliers

Conclusion

Establishing a world class lubrication program, through applying the five rights of lubrication, will pay dividends in the long run by enhancing equipment reliability resulting in major bottom line savings. Establishing the right program requires planning and work and the lubricant supplier and OEM should be utilized when needed. The first step is to recognize and promote the importance of a well designed lubrication program to management and then implement the program. Of course, implementation is the most difficult step, but you will find it is well worth the effort.

References
1. Bannister, Kenneth (2nd edition) Lubrication
for Industry, Industrial Press, 2007
2. Lansdown, A.R. Lubrication and Lubrication Selection, Mechanical Engineering
Publications, 1996
3. Neale, M.J. Lubrication and Reliability Hand
book, Butterworth and Heinemann, 2001


Ray Thibault owns Lubrication Training & Consulting (LTC), and is based in Cypress (Houston), TX. In 2001, he retired from the Exxon Company after 31 years of developing lubrication programs and providing technical support for customers such as Dow Chemical, Koch Refining, Chevron, Texaco, Sinclair, Eastman Chemical, and many others. He has conducted extensive training in different industries and is a STLE-Certified Lubrication Specialist and Oil Monitoring Analyst. Ray currently conducts numerous training classes throughout the U.S. and Canada preparing individuals for the Certified Lubrication Specialist (CLS) exam sponsored through the Society of Tribologist and Lubrication Engineers (STLE), and for both OMA and MLT certification. Ray holds both B.S. and M.S. degrees in Chemistry.


 

Lubrication_Dec_Jan_2009.pdf


A Study of a Positive, and Growing, Return on Investment
by Martin Robinson

A paper mill in South Carolina had a very successful infrared inspection program that management wanted to expand. However, the requirements of NFPA 70E were causing them to re-think their strategy since inspections of energized equipment was becoming more restrictive, more time consuming and more costly. Furthermore, 8% of the mill's applications had never been surveyed due to either switched interlocks (which automatically deenergize the equipment upon opening, thereby preventing access to energized components), or to incident energy calculations in excess of 100 cal/cm2 on certain equipment (which exceeds personal protective equipment [PPE] ratings, and would place personnel in extreme danger and open the company to OSHA fines).

In search of alternative methods of conducting safer, standards- compliant inspections, the corporate Reliability Engineer investigated how infrared inspection windows (commonly referred to as IR windows, viewports or sightglasses) might be utilized. It was determined that:

  • Use of Infrared Windows for routine inspections of healthy equipment did not require the elevated levels of PPE required in 70E, since as stated in 70E 100: "Under normal operating conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard." In NFPA terms, an IR window maintains an "enclosed" state for the switchgear, MCC, Transformer, etc., and maintains energized components and circuit parts in a "guarded" condition. Therefore, the hazard/risk category would be equal to that of reading a panel meter, using a visual inspection pane for lockout/tagout confirmations, or walking past enclosed, energized equipment.
  • Use of infrared windows would provide an efficient method to perform inspections. This would make more frequent inspections feasible for critical or suspect applications to ensure plant uptime.

  • Use of IR windows would provide non-intrusive access to electrical applications; therefore, surveys could be conducted without elevating risk to plant assets and processes, meaning that inspections could be conducted during peak hours for the best diagnostic data.

  • Use of IR windows and closed panel inspection would eliminate high-risk tasks during inspections and thereby increase safety for thermographers.

The focus of the mill's initiative was to facilitate inspection of the primary switchgear in their electrical distribution system which feeds one paper machine and several smaller operations within the plant. An impending ten-day shutdown increased the sense of urgency since all windows could be fitted for one machine during that period.

IRISS, inc. was commissioned by the paper mill to conduct a pre-site inspection to ascertain the optimal position and quantity of windows which would give thermographers thorough visibility of desired targets. The conclusions from the initial inspection are noted in Table 1.


Table 1 - Equipment List

The customer ordered 200 units of assorted 3-inch diameter and 4-inch diameter Infrared Inspection Windows to complete the installation. 197 windows were later installed.

Investment

197 infrared inspection windows totaled $42,050.00. IRISS was also retained to supply an installation team to perform the installation of the IR windows. Installation costs sited in Table 2 were calculated using the following assumptions:

  • Two-man installation team at $625.00 each per day
    (total cost $1,300 per day) x 10 Days = $13,000.00
  • $30.00 per window installation charge x 197
    Windows = $5,910.00

infrared02decjan09.jpg
Table 2 - Total Costs

The Installation Installation of the infrared inspection panes was conducted during three nights and three days during the ten-day shutdown. Some installations were completed on live gear using additional safety measures; however, the vast majority were conducted on deenergized equipment in what NFPA terms an "electrically safe work condition."

Although the plan allowed for twelve-hour shifts, installers were quickly and safely moving at a rate of approximately six window installations per hour, and were finishing the plant on the night shifts within six hours. Installations during normal business hours allowed much more flexibility; therefore all "live works" were completed during these periods. When the clients' electricians assisted with the installations, the installation rates were also faster than originally planned (7 to 8 windows per hour). All window installations were completed well within the allotted timelines.

infrared03decjan09.jpg
Figure 1 - Installation of IR Window

Inspection Cost Analysis

Prior to the installation of the IR windows, all infrared inspections were completed on open, energized gear. Therefore, PPE, live works procedures, risk assessments, permits, etc. were required for all inspections, and as noted earlier, several applications had never been surveyed due to safety restrictions.

The paper mill had previously invested in its own infrared camera and an on-staff thermographer. The thermographer was trained and "qualified" to assist in opening panels on energized gear. Therefore, some efficiencies were already in place when compared to a typical crew of a single thermographer + two electricians. Consequently, the man-hour calculations for the "traditional inspection" are actually conservative.

Table 3 details the man-hour costs for infrared surveys using in-house staff without infrared windows or viewports. The following assumptions are made:

  • Total man-hours per inspection of "inspectable" equipment: 331 hours (23 days)

  • Staff electrician internal charge-out rate $125.00 per hour

  • Staff thermographer assists with panel removal, etc... (two-man task)

  • PPE suit-ups twice per day, per man (30 minutes per man per suit-up)

  • One man-hour per compartment panel for safe removal, etc. (x two for two-man team)

  • 147 individual panels to inspect (per Table 1)


infrared04decjan09.jpg

Table 3 - Costs for Traditional Infrared Surveys


After the infrared windows were installed and there was no requirement to remove panels or wear increased levels of PPE, the task became a one-man job. The increased efficiency and economies of motion and man-power, which infrared windows provided, significantly decreased the time required to complete a survey to just two, eight-hour days for a total of just 16 man-hours. The costs associated with an infrared survey using the IR windows are detailed in Table 4.

infrared05decjan09.jpg
Table 4 - Costs for Infrared Surveys
Using IR Windows


Compared to the costs of traditional inspections (Table 3), the paper mill now saves $39,375 per inspection cycle because of the efficiencies they have gained through the use of infrared windows.

infrared06decjan09.jpg
Figure 2 - Traditional inspection using PPE


Return On Investment


Table 5 combines the data from the previous tables to illustrate the ROI for the paper mill based on the initial investment of the IR windows, the investment in installation and the costs to perform surveys using the windows, compared with the mill's traditional costs of using their in-house team while not using any windows.

Using infrared windows is shown in this example to pay dividends as early as mid-way into the second inspection cycle, yielding almost $18,000 in savings which can be put back into the budget by the end of the second cycle. In just five inspection cycles the mill shows a savings of over $135,000.

Moreover, because inspections can be completed with greater ease and without increased risk to personnel, plant and processes, the frequency of inspection cycles has been increased to quarterly, reflecting best-practices recommendations which were previously not feasible, and thought to be unattainable. The new inspection cycle brings ROI to the plant in just one quarter, while reducing the risk of catastrophic failure among the plant's critical power distribution systems, which will, in turn, minimize production losses due to equipment failure.


Future Installations

Additional window installations have been planned and scheduled to occur during the facility's next shutdown. Because the customer's in-house electricians were trained to install infrared windows, the installation costs for future installations will be a fraction of the cost paid for the original installation, saving even more money and accelerating the ROI for additional windows.

infrared07.jpg


Conclusion

This mill realized a return on investment very quickly while benefitting from the other intangibles of infrared windows. Specific achievements are:

  • The ability to inspect the previously un-inspectable equipment
  • The ability to inspect critical applications more frequently
  • The ability to more aggressively monitor any applications which are suspected to be running to failure
  • Increase in safety for personnel
  • Decrease in risk to plant assets and operations due to non-invasive nature of inspection - safeguarding profitability
  • Freeing up critical personnel who can be utilized for other valuable jobs in the plant rather than removing and reinstalling panels
A portion of the financial savings were used to continue to build and strengthen the PdM Program through the purchase of a second IR camera for the maintenance electricians, further underscoring the mill's commitment to practical use of technology to ensure uptime while enhancing the safety of its workers. Infrared windows provide a cost-effective and safer alternative to traditional inspections.

Martin Robinson, I Eng, MInstD, is a highly sought after trainer and speaker for topics including infrared windows and general thermography, electrical preventative maintenance, condition based monitoring, "green energy," and electrical safety standards. With over 15 years of practical field experience, Martin's expertise is also valued on various committees, such as the British Institute for Non- Destructive Testing - InfraRed Training Working Group (which for establishes the training standards and working practices for Thermographers in the UK). In 1997, he founded Global Maintenance Technologies, which provides Condition Monitoring, and energy management services to some of the most recognizable and prestigious landmarks, organizations and businesses in London and Southeast England. Martin also formed IRISS, Inc, which produces the world's only industrial-grade infrared windows capable of passing durability and impact requirements, the world's first ultrasound ports; emissivity standardization "landmarking" tags, and the world's only transmissive PDU panels; and other groundbreaking solutions released continually. Residing in Sarasota, FL, Martin is a devoted husband and the proud father of 8.

Original PDF Format: Infrared_DecJan_2009.pdf

One Out of Many...

user-pic
Vote 0 Votes

Pointing the Whole Organization in the Same Direction

By: Dr. Peter G. Martin

Although huge quantities of technology and intellectual property have been invested into the efficient and effective operation of industrial plants over the past century, many plants are still not operating to full potential. At least part of the reason for this has been the lack of focus on the value that the human assets can generate given a supportive, collaborative and empowering environment in which to perform. Mobilizing the valuable human assets to approach their full performance potential has been proven to result in a new operational paradigm which maximizes the business performance through all plant assets. This new paradigm is labeled "asset performance management".

Dealing with Labor

A considerable contributing factor in the engine that can drive toward effective asset performance management is a fundamental change in mindset and culture that is a holdover from the industrial revolution. Changing such a mindset requires that we first understand what it is and where it originated. As industrialization started to ramp up in North America and Western Europe, one resource that was abundant was people to work the plants and factories. Unfortunately, the vast majority of the available human resources were uneducated and unskilled. From the perspective of today's culture it may be hard to relate to how uneducated these people really were.

Most could not read, write or do even basic arithmetic. This led to a huge industrial challenge - how to take advantage of such a resource. This challenge was met by Frederick Taylor, who developed an approach called Scientific Management, which focused on gaining maximum value from an uneducated workforce. In today's vernacular, Scientific Management essentially turned people into minimally functional robots, each performing a well contained and well defined function within the context of the operation of the entire plant or factory. For example, a person may have been trained to watch a gauge and keep it in a certain range. When the needle moved out of the range, the worker would turn a hand valve in one direction. When the needle moved out of range in the other direction, he turned the valve in the other direction. This person might join the workforce of the factory at 16 years old and retire 50 years later having performed that contained task his entire career. This led to the concept of a labor force in industrial companies which was so unskilled that management believed it could not be trusted to perform duties beyond menial tasks. In essence, the laborers were almost treated as a kind of industrial slave.

 
This view of the labor force was exacerbated with the introduction of automation technologies. In many cases, the automation technologies were developed to perform the same functions laborers had performed. For example, automatic controllers providing direct manipulation of control valves essentially were replacing the laborer who had previously been stationed at that valve. Early automation advancements may have allowed a single laborer to perform the scope of functionality that six or eight laborers had previously been doing. As computer-based automation systems were introduced, single operators may have been able to oversee functionality that single operators may have been able to oversee functionality that would have required fifty people in the past. The basic value proposition for the introduction of automation technology was typically based on headcount reductions that could be achieved. Many manufactures seem to have viewed these reductions as a double benefit to the company. First was the cost reduction for not having to pay the displaced laborers. But second was the thought that there would be less of the low-level laborers to have to manage and worry about.

The culmination of the technology replacing people trend took place in the 1980s when a number of management scientists and engineers supported a notion referred to as "lights-out manufacturing." The thought process behind this trend was that technology may have advanced to the point at which no front line workers would be required at all, and without people in the plants there would be no need to turn on the lights. This was a short-lived movement due to the fact that the technologists found they could not anticipate every possible issue or problem that may arise in a plant and that at least some number of people must be in the plant, if for nothing else, at least contingency responses.

All of this has left a residual mindset in both industrial management and engineering that frontline personnel are a necessary evil that would be eliminated if possible. This has further led to an attitude prevalent across industry that the actions and activities of these frontline laborers have to be contained to only those essential to keep the plant operating. A good example of this mindset can be found in the design approach taken to the software in industrial workstations. This software is designed around the concept of "operation by exception," which basically means that the process operator is not supposed to do anything if the process is operating in a reasonable manner (except, perhaps read the sports page). When something unexpected happens, an alarm will cause the operator to follow a predefined procedure that should bring the alarm condition under control. Once the alarm condition has been addressed, the operator goes back to the newspaper. Additionally, engineers have developed and deployed advance control and other advanced techniques designed to operate the plant better than the operators could by themselves. The attitude of protecting the plant from the frontline laborers has continued, even while the average education and skill level of the labor force has been steadily rising. I have been in control rooms in which the frontline process operators all had college educations, and were still viewed as the unskilled, uneducated laborers of the early industrial revolution.

Organizational Silos

Having worked with industrial organizations for over three decades, I have frequently heard the rejoinder that "islands of automation" are to blame for the difficulties in developing higher performing operations. Although there is certainly much truth to this, I have found that "islands of organization" within industrial companies present a much more formidable barrier to performance improvement. As industrialization took hold and grew, the complexities introduced to manufacturing businesses became very challenging. In early industrial plants the same person might operate and maintain the equipment, design and commission new production areas and even account for the business. As more complex manufacturing systems have evolved, this level of generalization is just not feasible, which has led to the era of specialization.

Professionals specialized in engineering, accounting, management, purchasing of materials and shipping of finished products while frontline labor specialized in operations and maintenance of the equipment. This naturally resulted in separation of departments by function which, in turn, led to organizational silos. The development of specialists was necessary to the operation of the increasingly complex plants, but the development of organizational silos resulted in huge inefficiencies across organizations. Today it is not unusual to find maintenance departments that never directly communicate with operations or production teams. In some organizations they don't even like or trust each other. Adding to this, many IT organizations don't like or trust engineering, and the feelings are mutual. And nobody seems to get along well with accounting.

In many cases, the performance measures used to evaluate the performance of one group are in direct conflict with those of a second group. For example, maintenance teams are often measured on the availability of critical equipment assets while operators are measured on the utilization of the assets. Asset availability and asset utilization are inverse functions. That is, to increase utilization often requires the sacrifice of some availability and vice versa. Under this scenario, it is no wonder operations and maintenance teams seldom get along well.

As industry has invested huge amounts of capital into efficiency-increasing automation and information technologies, organizational silos have worked to destroy any potential value that may have been created by the technology. I was recently attending an industrial conference in which an engineer estimated that over 80% of all advanced control that has been implemented in industrial plants has been turned off by the process operators because the operators don't trust it. If engineering and operations had a better working relationship, based on common goals and objectives, this might not be the case. Organizational silos have tended to sub-optimize plant performance by sub-optimizing the human performance within the plants. Perhaps it is time for industry to start moving away from long over-worn prejudices and consider using the valuable human resources more effectively to drive better plant performance.

Measuring Performance

You are probably familiar with the common adage is: "people perform to their measures." I believe that this is very true. Most people want to be evaluated positively, and if they know that measures of performance exist for which they will be held accountable, they will strive to make those measures move in the correct direction. This is true whether the measures are driving desired behaviors or not. For example, measuring maintenance on asset availability and operations on asset utilization does not encourage the cooperative behaviors most industrial leaders would like to see.

In the early periods of industrialization, prior to the many inventions that drove the industrial revolution, most shops measured performance as each product was produced. Production was so slow that accounting for the business on the basis of piecemeal production was easily achieved. Management and operators of these firms knew exactly how they were performing compared to their plan at all times. But with the introduction of tools, such as the power loom in the textile industry, the pace of production increased to the point that piecemeal accounting was no longer feasible. The result was that industrial operations compromised and began measuring the business performance through monthly accounting methods. The primary output of these systems for measuring manufacturing performance was, and in most cases today still is, the variance report. Variance reports basically report the cost per unit product made for each product produced over the past month and displays this against a previously predicted expected value, referred to as the standard cost for the product class. This information may be acceptable for reporting manufacturing performance, but it has little value in enabling the plant personnel to change their behaviors to improve the performance of the operation. The information in the variance reports is both too little (providing a broad plant-wide perspective) and too late (after the month is over) to be of any value to the people actually working to keep the plants operating.

Monthly accounting systems for reporting of manufacturing and business performance represented a compromise introduced to industry out of necessity. The tools just did not exist to measure plant performance as the plant was running. Over many years, industry got lulled into believing that monthly financial reporting was a best practice that should never be challenged. Accounting professionals earned Masters Degrees on how to do monthly accounting. Once degrees are conferred on how to do any practice, it is very challenging to ever question the validity of the practice again. Therefore, when digital computers were generally introduced into industrial operations during the 1960s and 1970s, nobody seemed to raise the question as to whether accounting and performance measurement systems might be able to be developed to account for operations as originally intended - as the products are made - in real time.

Since monthly accounting measures from in cost accounting systems proved to be fairly useless in directing the actions of the operations and maintenance teams, a number of leading industrial companies started to develop a different set of operations performance measurements to supplement the accounting systems by providing more actionable feedback to plant personnel. The measures produced by these systems are commonly referred to as key performance indicators (KPIs). These KPIs were not developed to replace the accounting measures, rather they were developed because engineers and managers did not view the measures produced in the accounting systems as adequate for directing performance and improving actions in the plant. KPIs were typically developed to measure different operational silos within plants, such as maintenance, operations and engineering. By focusing on specific functions, they tend to offer better resolution, as well as better timeliness, than accounting measures. However, by being functionally focused, they also tend to discourage cooperation between organizational groups. Even though daily measures provided a great leap forward from traditional monthly measures, frontline personnel often find daily measures too long a timeframe to offer actionable feedback. A single operator may make hundreds of specific actions each day, and an overall daily measure does not provide the timeliness for them to understand the performance impact of any specific action.

To make matters worse, KPIs tend to have little credibility with accountants, whose job it is to measure the business performance. Although many KPIs may report in monetary terms, accountants often have great difficulty reconciling the values reported though the KPIs with the values in the accounting reports. When this happens, the accounting information clearly takes precedent. I actually heard one CFO say, "If one more engineer comes to me with one more KPI telling me how much value he has created, I'll fire his $&*!"

Dynamic Performance Measures

The value of an effective and comprehensive performance measurement system cannot be overstated when it's working to drive increased levels of performance from plant assets. Industry has reached the point where the performance measures that encourage the organizational silo mentality have to be abandoned in favor of measures that drive collaboration between traditionally competing functions. A new approach to performance measurement is required that combines the goodness of accounting and operational measures, provides performance measures for every person in the operation, within the time frame in which they do their job and for the same domain for which they are responsible. Such performance measures are referred to as dynamic performance measures (DPMs, See Figure 1).

The first issue that has to be addressed in developing a DPM approach is the availability of a database that provides real time input data. Fortunately, in most industrial plants, such a database is readily available in the form of plant sensors. Plant sensors continually measure physical and chemical properties, such as flow, level, temperature, pressure, speed and composition of process variables in real time. They are typically accessible by the installed automation systems and are used to monitor and control the process. Since both accounting and operational measures can be defined via equations, an experienced engineer can develop models of the equations in the automation system and determine which sensors can be used to populate the models needed to calculate the DPMs. The net result is a set of performance measures for each process unit or work cell in the plant.

martin01decjan09.jpg

In most plants there are simply too many measures for any one frontline person to deal with in real time. When working in real time environments, such as driving a car or operating a plant, ergonomic research has determined that most people can only consider up to four competing measures at a time. The question is which four measures are most appropriate for each person in the operation. This can be determined by taking the current manufacturing strategy into consideration. Dr. Thomas Vollmann developed a strategy analysis approach that can be very helpful in determining the DPMs for each person in the operation. The Vollmann Triangle diagram (See Figure 2) is helpful in understanding his approach. He points out that every plant should be working to a strategy designed to maximize the economic value of the plant output within the external and internal environment in which the plant is operating. Each manufacturing strategy should be defined by a set of actionable strategic objectives for the plant. An action plan, in which each action step is measurable, should be developed for each objective. The measures that fall out of the action steps are the strategic performance measures of the plant. These measures can be decomposed through the physical areas, units and major assets of the plant to determine the most important measures for each process unit according to the current strategy. This can then be used to prioritize the real time KPI and accounting measures for each person that impacts the performance of the operation. This information can then be presented on a performance dashboard contextualized to each person's responsibility. These are the DPMs of the frontline operators.

martin02decjan09.jpg

Developing these DPMs requires a real time computer engine that has builtin modeling capability. This is exactly what a standard automation system is. These DPMs must then be aggrandized to provide performance measures in real time for every other function within the plant. This can easily be accomplished by using a standard process historian which can also develop hourly, shift, daily, weekly and monthly accumulations of the DPMs. The availability of a comprehensive, real time, bottom to top performance measurement system provides the potential to drive improved performance in a number of ways previously unavailable to industrial operations. The basic value improvement that can be realized through better individual performance of frontline personnel, who can immediately see how their actions impact plant performance, has been proven to provide huge performance gains. However, this is only a starting point.

A New Perspective on Asset Performance Management

The availability of DPMs enables asset performance management in ways previously unavailable. As previously mentioned, traditional asset management involves operators driving the assets to maximize asset utilization and maintenance maintaining the assets to drive maximum asset availability. It is important to understand that neither asset availability, nor asset utilization, is a measure of the business objectives of any plant. Since they are inverse functions, operators and maintenance teams are frequently at odds with each other. So, in essence, traditional performance measurement systems tend to discourage cooperation and collaboration.

It's quite useful to use an analogy from the world of sports since nearly all professional sports are performance- driven. In automobile racing, the driver is analogous to the operators in industrial plants and the pit crews are analogous to the maintenance teams. In interviewing a NASCAR driver and a pit crew chief, I noticed how well they tended to cooperate. I asked them if, as is common in industrial plants, the pit crew was measured on the availability of the car and the operator measured on the utilization. They told me that although utilization and availability (or maintained state, which may be a much better measure than classic availability) are important, the primary measure of both is winning the race. I asked the pit crew chief if, upon detecting a problem with the car that might negatively impact the maintained state, he would call the car into the pit. He said, "Only if the problem means we won't win the race." Then I asked the driver if he would refuse to come into the pit if called in by the crew chief. He said, "no way, I know he is calling me in because I'll lose the race if something is not done." You see, for both parties, the primary focus is winning. And since they have a shared focus, they not only trust each other, but they cooperate extremely well. So how can we define "winning" for frontline maintenance teams and operators in industrial plants to engender the same level of cooperation and even collaboration?

Most plant management teams are measured on driving the maximum production value from the plant assets over an extended period of time. Certainly the utilization and availability of each plant asset impacts business value, but neither should be treated as the primary measure of performance of any industrial operation. The real victory in industrial plants is driving the maximum business value from each plant asset over time. If every operator and maintenance person has a primary measure based on this win, the behaviors of each will change drastically and the behavior of the plant will follow suit. Industrial companies must empower frontline teams with the information, in the form of DPMs, which will drive both collaboration and continuously improving business value from all plant assets.

martin03decjan09.jpg

Asset Performance Management (APM) driven by DPMs results in operations and maintenance working together to balance plant operations for optimal business value in all circumstances. The primary measure of both frontline teams is business value. Secondary measures for maintenance include the maintained state of the equipment and the probability of a failure over time. Secondary measures for operations include operation to maintained state and the probability of a failure over time. With all DPMs prioritized to the manufacturing strategy in place, every person in the organization will be pulling in the same direction. They will all be focused on "winning." They will all be focused on doing their part, but, even more productively, doing it within the context of the overall performance of the operation.

An interesting symmetry develops between operations teams and maintenance teams when a true asset performance management approach is taken. Both operations and maintenance have advanced in three steps with the evolution of technology in each area over time. Technology impacted operations by first providing regulatory control, followed by advanced control, then followed by process optimization. Maintenance had a similar progression from reactive, to preventive and then to predictive maintenance. As each progression was underway, the KPIs for each function were used to measure progress. The next step, asset performance management, occurs when the two frontline functions converge around new measures of performance that combine accounting and operational measures into a comprehensive, prioritized performance measurement system called DPM. This is the point at which cross silo collaboration takes hold and breakthrough levels of performance are attained.

Summary

Industry is on the verge of a major new wave in performance improvement driven by collaboration across organizational silos guided by Dynamic Performance Measures. For this new wave to really take hold, industrial management and engineering have to escape from the residue of the industrial revolution and stop thinking of operations and maintenance teams as an unskilled, uneducated labor force.

Frontline personnel are responsible for making, or losing, most industrial operations more money minute by minute than any other group in industry. It is time we start treating them as the performance managers they are by empowering them with DPMs.

On top of this, industrial management must start to break down the organizational silos that have existed in plants for decades while simultaneously preserving the specialized knowledge and capability of each team in the plant. Again, this can be achieved by empowering the teams with the correct performance measures that define the "win" for the business. When this is accomplished, the result is a new performance-generating collaborative approach to plant operation called asset performance management. Asset performance management is the industrial performance wave that is just starting to crest. Those industrial concerns that catch this wave will be the performance leaders of this new millennium.

Peter G. Martin, PhD, D. Eng., joined The Foxboro Company in the 1970's and has worked in a variety of positions in training, engineering, product planning, marketing and strategic planning. He left Foxboro to become Vice President at Intech Controls and also at Automation Research Corporation before returning to Invensys in 1996. Since his return, he has been VP of Marketing for Foxboro and Chief Marketing Officer for Invensys Manufacturing and Process Systems prior to moving into his current position, VP Strategic Ventures. He has written two books: Bottom Line Automation and Dynamic Performance Management: The Pathway to World Class Manufacturing. Dr. Martin holds multiple patents, including the patent for Dynamic Performance Measures, Real-Time Activity-Based Costing, Closed-loop business control, and Asset and Resource Modeling, which are the basis for Fortune recently naming him a Hero of U.S. Manufacturing. He was also recently named as one of the 50 Most Influential Innovators of All Time by the Instrument, Systems and Automation Society (ISA). Dr. Martin has BA and MS degrees in Mathematics, an MA degree in Administration and Management, a Master of Biblical Studies degree, and a D. Eng in Industrial Engineering and a PhD in Biblical Studies.

Click Here for the Case Study

Feature_Dec_Jan_2009.pdf


A Tough Diagnosis

user-pic
Vote 0 Votes
The Saga of the Never Ending Problem
by Greg Davison

You are often told that there is never just one problem with a machine. My very first vibration class taught me that a phase and magnitude vector was a combination of all the vibration from all of the forces acting upon the machine. Likewise, a spectrum also contains all of the frequencies from all of the forces acting upon a machine. So, it is never just imbalance, or just misalignment. It is always some combination of many forcing frequencies. This is precisely why wall charts and cookie cutter solutions do not always work. What follows is a story of multiple problems of mythical proportions.

The story begins along the east bank of the Arkansas River at Oklahoma Gas and Electric's Muskogee Generating Station, about three miles east of Muskogee, Oklahoma. The station consists of three large coal fired units, each producing approximately 505 net megawatts, and one smaller 180 net megawatt gas fired unit.

On Muskogee Unit 4, one of the coal fired units, condensate is pumped by two 60% capacity pumps driven by two identical Westinghouse 1000 HP condensate pump motors. The motors are vertical Westinghouse 6808 P30 frame, 4160 Volt, 3 Phase, 60 cycle motors with a 1.15 service factor.

In October of 2006, Operations alerted the Reliability Technician of a potential problem with the MK4B Condensate Pump. The technician proceeded immediately to the pump to determine if the vibration had increased. Indeed, the vibration level had doubled since the last monthly route data had been uploaded two weeks earlier. A doubling of the amplitude was an obvious indication that there had been a change in machine condition. Was the change in the pump, or the motor, or both? This is usually the first question asked, quickly followed by, "How long will it last?"

One of the easiest ways to answer the first question is to divide and conquer. Uncouple the motor. Run the motor solo and see if the vibration goes away. If the vibration goes away, the problem is most likely in the pump. If the vibration is still higher than normal, the problem is probably in the motor.

If Dispatch could allow the unit to come to half load, this fairly common troubleshooting technique could cut the problem in half. As luck would have it, system needs required the unit to remain at full load, if at all possible. So, other methods had to be devised to diagnose the problem.

The top of the vertically mounted motor is approximately ten feet above floor level (see Figure 1). The bottom of the pump is almost twenty feet below floor level. Figure 2 shows a multi-stage pump being lowered into position. Without permanently mounted vibration probes, it was impossible to get direct measurements from the pump. We took several readings on the motor and along the motor base, and we used a fishtail to obtain shaft readings adjacent to the coupling and stuffing box.

The highest readings were from the motor outboard. The amplitudes gradually decreased as the probe was moved from the top of the motor to the floor, which might lead one to conclude that the problem was in the motor, since this was where the highest readings were. But, past experience had shown that sometimes the tail wags the dog. In this particular arrangement, a vibration caused by forces in the pump can cause the top of the motor to move back and forth as the whole assembly pivots about the floor, similar to a lever and a fulcrum. Or, could it be just something terribly wrong in the top of the motor? Frequency analysis would help to identify the problem.

The spectra contained a peak close to 0.5x running speed that was higher than the running speed peak (see Figure 3). There was also what appeared to be a harmonic at 1.5 x running speed. These ½ harmonics are often associated with rubs. The most likely place for a rub would be the impeller rubbing in the pump. Perhaps, there was some debris in the suction?


vibration02decjan09.jpg

The sub-synchronous frequency was 750 cpm, or .4x running speed. The upper frequency of interest was 2825 cpm, or 1.6x running speed. Neither was an exact ½ multiple. The possibility remained that this might be the cage frequency of the lower bearing in the motor. However, since most of the vibration was in the top of the motor, this theory was discounted.

Another possibility was that the frequencies in question were non-synchronous vibration being excited by the pump or the motor. Researching the OEM manuals revealed the pump natural frequency between 500 cpm and 800 cpm. This could actually be a resonance.

vibration03decjan09.jpg

There were now three clues leading us to the conclusion that the problem was with the pump, possible resonance, possible rub, and possible fulcrum effect. The next day the vibration doubled again and Dispatch agreed to allow the unit to come to half-load and remove the pump from service.

The pump inspection revealed extensive damage. It was a complete wreck. Something had apparently gone through the pump and destroyed several impellers (see Figure 5). The first stage cast iron housing was broken off of the pump. All of the cutlass bearings were in need of replacement and one had seized to the journal and was spinning in the housing. Due to the machine work on the journals and bearing housings and the lead time to order impellers, we decided to send the motor in for a routine clean, dip, and bake.The motor inspection revealed no obvious defects. All clearances and run-outs were within acceptable tolerances. There were no rub marks or evidence of any shorting on the rotor or in the winding. The bearings had only normal wear and the journals were in good shape.


vibration04decjan09.jpgThe motor inspection revealed no obvious defects. All clearances and run-outs were within acceptable tolerances. There were no rub marks or evidence of any shorting on the rotor or in the winding. The bearings had only normal wear and the journals were in good shape.

The motor was steam cleaned, and the winding dipped and baked. The rotor went through the balance machine before reassembly. The motor was test run on a test pad at full voltage. The vibration amplitude exceeded acceptance standards. Trim balancing was attempted and the test run repeated without improvement. At this point, there was a pause to take another look at the data and develop a new plan of action.

Not only were the overall levels too high, there was a significant 2x component with some 3x in the spectrum. Looseness was an immediate speculation. The carrier bearing in the outboard of the motor is a critical fit, and any taper in the journal or looseness in this fit will cause excessive vibration in the top of the motor. The carrier bearing had not been removed during disassembly due to the meticulous effort required to maintain this critical fit.

We decided to pull the rotor and remove the carrier, but the journal and bearing were well within tolerances. All clearances and run-outs were re-checked and found to be acceptable. We found nothing to explain the high vibration. The motor was carefully reassembled and test run.

Vibrations were still high, with a 2x running speed frequency that was higher than the running speed component and there was still some 3x. Knowing that the motor had been scrutinized with a fine tooth comb twice, suspicion shifted to the shaft. Since the pump had suffered such a catastrophic failure, perhaps some of the energy transferred through to the shaft and damaged it. If nothing else, maybe a few simple tests would eliminate the possibility of a bad shaft.

The first thing was a simple bump test. To everyone's surprise, it rang like a bell around running speed and at two times running speed, (Figure 6). This natural frequency had not always been present. Where did it come from? What had changed? Either the mass or stiffness had to change in order to shift the natural frequency. A crack in the shaft could possibly explain a change in stiffness resulting in a change of the natural frequency. However, neither dye penetrant nor ultrasonic testing uncovered any evidence of a crack in the exposed portion of the shaft. If there were a crack, it was where these tests could not detect it.

Any further testing would require pressing the iron off of the shaft. Besides being expensive, this could easily ruin the shaft. Well, either the shaft was already ruined, or it was going to be ruined in order to find out if it was ruined. We decided to stop doing any more testing and not take excessive care to save the shaft (see Figure 7). Instead, we would just build a new shaft.

vibration05decjan09.jpgMeasurements were taken from the old shaft and a new one was turned from similar materials. The new one was bump tested before the rotor iron was pressed on, and again after the assembly was complete. These tests showed no natural frequencies near running speed or running speed harmonics. The rotor was balanced. The motor was assembled, once more placed on the test pad, and, after a slight trim balance, the motor passed acceptance testing. The motor was finally placed on a truck, the rotor blocked to prevent any movement, and shipped back to the Muskogee Power Plant to be placed in service.

Motors are routinely run uncoupled for ac-ceptance testing before placing them in service. This establishes a chain of quality custody and a new baseline data for future comparison. If the motor does not pass acceptance, either something happened during transit, the motor base has a problem, or there is some on-site assembly problem because the shop tests prove the motor to be fine.

Well, as you might have already guessed, when this motor was run uncoupled for acceptance, it failed. Normally, a slight balance adjustment will allow a rebuilt motor to meet the acceptance criteria. This motor did not respond predictably to weight movements., and further diagnosis discovered symptoms other than imbalance. There was still some 2x and a little 3x in the spectrum, with the majority of vibration at running speed. Figure 8 shows the motor being tested on its own base and foundation.

vibration06decjan09.jpg

There was no obvious shipping damage. The motor was uncoupled, so there was no misalignment. Imbalance had been ruled out by process of elimination. The base and/or the foundation were really all that were left. A visual inspection of the base revealed that a couple of nuts were not even touching the base. In fact, the blade of a pocket knife could fit in between the nut and the base. The grouting was also cracked and deteriorating. A machinist's level placed on the base determined a severe out of level condition, so 40 mils of shims were required to level the base. After this temporary repair, the motor was once more run uncoupled. Figure 9 on the next page shows the shim pack under the bottom right hand corner of the base plate.

The vibration was greatly reduced, but not yet within expected readings for an unloaded motor. Most of the vibration was now at running speed, and phase analysis indicated ac ouple imbalance. Correcting the couple imbalance would require weights to be placed in both ends of the rotor.

vibration07decjan09.jpg

Even though this rotor had been balanced at the motor shop in a balancing machine, all symptoms suggested imbalance. Experience has shown that this is not uncommon in a vertical machine. In the balancing machine, the rotor is balanced when mounted horizontally. Then, when it's turned upright to the vertical position, a couple imbalance is often observed. This, plus the fact that the motor is now sitting six feet above the floor on a base that allows much more movement, means much less force is needed to create unacceptable levels of vibration.

Removing a cover allows easy access to the outboard end of the motor, where there are provisions for balance weights. However, access to the lower end of the motor is rather difficult. The only way to attach weights is to worm a hand and arm through and around to gain access to the cooling fan. Dispatch was now calling for load. Luckily, with historical balancing data in hand, one run was all that was needed to balance the rotor.

The vibration was now at or below historical levels, so the motor was coupled to the pump. A performance test was conducted to evaluate the pump repair. This test proved the pump to be in good shape. Baseline vibration data was collected and the machine was returned to service (see figure 10).


vibration08decjan09.jpg

The unit was given back to Dispatch 29 days after the first problem was discovered. The old grouting was removed, the base was leveled, and new grout poured at the next scheduled unit overhaul. While this was a very challenging case, not all machines are so difficult all the time. Rarely do so many problems exist at the same time on the same machine. Complex problems require complex problem solving. Each machine is different and that's what makes this job so rewarding and keeps life so interesting.

Greg Davison is the Supervisor of Reliability Technologies at Oklahoma Gas and Electric. He is an ISO Category III Vibration Analyst. He is a member of the Vibration Institute and the Oklahoma Predictive Maintenance User's Group. Greg graduated from Oklahoma Christian University with a Bachelor of Science degree in Organizational Management.


A Closer Look at Air Gap Eccentricity
by Douglas E. Swinskey & Peter M. Bechard

The first step in evaluating test data is understanding the relationship to the circuit's Fault Zones and how abnormalities in a specific Fault Zone affect the performance of the motor. The six Fault Zones (Power Quality, Power Circuit, Stator, Insulation, Rotor, and Air Gap) are derived from the most common electrically related motor failures in industrial environments. The Air Gap Fault Zone describes the measurable distance between the rotor and stator within the motor. Air gap eccentricity is a condition that occurs when a non-uniformity in the air gap between the rotor and stator exists.

During operation, several stresses are brought to bear upon key components of the motor. An air gap eccentricity results in increasing these stresses during operation. A motor operated with an eccentric air gap results in increased mechanical vibration, accelerated insulation degradation due to increased coil movement, and possible rotor/stator rubbing due to unbalanced magnetic pull. Types of air gap eccentricity are:

Static Eccentricity - which occurs when the centerline
of the shaft is at a constant offset from the centerline of
the stator. An example is a misaligned end bell.

Dynamic Eccentricity - which occurs when the centerline
of the shaft is at a variable offset from the centerline of
the stator, such as a wiped bearing.


Failure Mechanisms

By definition, air gap eccentricity is a mechanical fault with the motor. There are several possible causes for the presence of variances in the distance between a rotor and a stator. The five basic types of air gap eccentricities that can occur are:

  • Rotor O.D. is eccentric to the axis of rotation
  • Stator bore is eccentric
  • Rotor and stator are round, but do not have the same axis of rotation
  • Rotor and shaft are round, but do not have the same axis
  • Any combination of the above
The following are only a few of the possible causes of an air gap eccentricity:
  • Improper mounting of the motor to its bedplate can lead to an air gap distortion. A loose or missing bolt allows shifting of the motor's mounting foot during thermal expansion of the frame. This shifting over time could lead to a distortion of the frame and possible distortion of the stator bore. The common term for a motor incorrectly mounted is "soft-foot."

  • During construction of the motor, out-of-roundness of either the rotor or stator will lead to an air gap eccentricity. Industry standards recommend that measurements for total indicated roundness (TIR) should be performed at different locations along the length of each of these components. Couple these measurements with the circumferences of each component, and depending on the speed and size of the motor, there are recommended tolerances from 5 to 20 percent variation in the air gap.

  • Eccentricity can develop due to improper tensioning of drive belts coupled to a motor. One customer working with PdMA's technical support staff said that while they were releasing the tension on one set of belts, they measured the deflection of the motor shaft, only to find it had moved 1/8 an inch! Improper alignment could also lead to a situation similar to this with both leading to a bowing of the rotor during operation.

  • Distorted end bells, cocked bearings, or a bent shaft will all cause an air gap eccentricity. During the manufacturing of the rotor, uneven mechanical stresses could be introduced into the cage and lamination stack leading to bowing of the completed rotor.

  • An air gap eccentricity results in increased levels of vibration due to the uneven magnetic pull it creates between the circumference of the rotor and stator bore. Over time, these elevated levels of vibration can result in excessive movement of the stator winding, which could lead to increased friction and eventually a turn-to-turn, coil-to-coil, or ground fault. Increases in mechanical vibration accelerate bearing failure, which could seize the shaft and overheat the windings or allow additional movement of the shaft leading to a rotor/stator rub. The uneven magnetic stresses applied to the rotor, coupled with the increased vibration, will also contribute to mechanical looseness developing in the rotor assembly. Risk of rotor pull-over increases exponentially with the amount of air gap eccentricity.

  • Rotor pull-over is an example of rotor/stator rub that appears as random marks on both the stator bore and surface of the rotor. Pull-over describes the bending of the motor shaft allowing the rotor to come into contact with the stator. Pull-over most often occurs during start up when the magnetic forces pulling on the rotor are greatest. The magnetic pull acting upon the rotor varies as the square of the difference in the air gap (Figure 1). For example, when the air gap at the narrowest point between the rotor and the stator is one half that of the air gap at its widest, the magnetic force at the narrowest will be four times stronger than the widest point. Couple that with the in-rush current and the magnetic pull could flex the shaft leading to a rotor/stator strike.

motor01decjan09.jpg
Analysis
Testing a motor for air gap eccentricity can be easily accomplished using Motor Circuit Analysis (MCA) or Current Signature Analysis (CSA). The hardest part seems to be deciding what to do about it, after confirming that an air gap eccentricity exists. When performing CSA there is no absolute standard on how much eccentricity indicated on a current spectrum is too much. The same can be said for the results of a Rotor Influence Check (RIC). The graph may indicate the presence of an air gap eccentricity, but without historical results for comparison you really cannot develop a sense of how much eccentricity has developed and if it is getting worse with time.


MCE Analysis

Motor Circuit Analysis utilizes a combination of phase-to-phase resistance and inductance measurements to detect abnormalities in the motor's winding, rotor, and air gap. Positioning the rotor in specific mechanical increments and graphing the phase-to-phase inductance values results in a graph www.uptimemagazine.com 39 that allows air gap eccentricity analysis.

Air gap evaluation with the MCE is accomplished utilizing the Rotor Influence Check (RIC) test. The RIC is a graphical representation of the magnetic coupling between the rotor and the stator. The RIC test will be most successfully applied in troubleshooting and determining a course of action if pre-existing RIC data is available. However, even without a baseline test, the RIC test will give you definite indications of existing eccentricity.

The RIC test is conducted by positioning of the rotor in incremental steps through one or more pole groups and recording each of the three phase-to-phase inductance values at each increment. These readings of inductance are graphed allowing for analysis of the motor's winding, rotor, and air gap.

A pole group is the amount of mechanical movement of the rotor required to produce a 360-degree sine wave of the stator winding inductance values. For example, in a four-pole motor, the rotor would need to be positioned incrementally through 90 degrees mechanically to complete a 360-degree electrical sine for each of the three phases.

motor02decjan09.jpg

Figure 2 is an example for a two-pole motor. The rotor was positioned mechanically 180 degrees producing a 360-degree sinusoidal graph of inductance.

Analysis of phase-to-phase inductance for air gap eccentricity focuses on: Alignment, Minimum & Maximum Peak-to-Peak Inductance over two or more pole faces and Inductive Imbalance.


Alignment: Is there a level alignment of the graph across the chart?

To determine if the motor has an eccentricity in the rotor/stator air gap, evaluate the alignment of the RIC graph. Unevenness in the space between the rotor and stator will affect the alignment of the Rotor Influence Check (RIC) as the rotor is positioned during the test. An uneven alignment such as what is seen in Figure 3 indicates eccentricity exists between the rotor and stator. The more severe the air gap eccentricity, the greater the misalignment. Comparison to a previous RIC test allows for determining if the condition is worsening over time.


Peak-to-Peak Inductance: What are the minimum and maximum inductance values?

When air gap eccentricities exist in a motor, peak-to-peak inductance values for each individual phase will vary from one pole face to the next. To see this change in peak-to-peak inductance values, position the rotor through at least two pole faces. Figure 4 on the following page demonstrates how the peak-topeak inductance values vary from one pole group to another for an individual phase when there is an air gap eccentricity.

motor03decjan09.jpg

Remember, in a concentric wound motor each individual phase will have it's own minimum and maximum inductance values. An example of how a concentric wound motor develops uneven minimum and maximum inductance values between individual phases is shown later in this article.


Inductive Imbalance

Inductive Imbalance is a percentage calculated by dividing the average of the three phase-to-phase inductance readings into the value of the individual phase-to-phase inductance
furthest from the average and multiplying by 100. With the rotor removed from a threephase motor this imbalance is expected to be less than 1%. With a rotor installed this value varies and is determined by design considerations such as rotor skew, design air gap, and other factors that affect rotor/stator geometry. For a motor in satisfactory condition, this imbalance remains within a plus or minus window of 2 for any rotor position. Some motors may be 5.5% to 7.5%, for example. When performing a RIC, at the end of positioning the rotor through one pole face, check the highest and lowest calculated imbalance. If the difference is greater than 2%, positioning the rotor through a second pole face is recommended.


Concentric vs. Lap Wound

An important consideration when evaluating RIC data for indication of eccentricity is whether the motor is concentric or lap wound. If a motor is concentric wound, it may be built with a pre-existing offset between the stator windings and the rotor.

The concentric wound motor illustrated in Figure 5 has the stator windings inserted into the stator slots in a basket form or stacked configuration. Commonly all of the pole groups for phase A are laid into the slots, then all of the pole groups for phase B, then finally all of the pole groups for phase C. This results in a greater distance between the rotor and the phase A coils than exists between rotor and phase C coils. This results in a natural stair stepping indication of the phase-to-phase values seen in Figure 8.

Standard lap wound motor windings, which have each coil of every phase equally lapped over the surrounding coils, results in the three phases having equal high/low inductance vales.

How does a person identify a concentric or lap wound motor? There are only two absolute methods. One is by taking the end bell off and looking. The other is obtaining the information directly from the manufacturer. However, here are some rules of thumb that should help you distinguish between the two.

  1. If it is new and smaller than 50hp, it is very likely concentric wound.
  2. If it exhibits the pattern seen in Figure 8, it is very likely concentric wound.
  3. If it has been rewound at any size, it may be lap wound.

Note: These are not absolute, as several manufacturers design medium and high voltage concentric wound machines.

Figures 6 and 7 clearly illustrate the way windings are placed in a concentric wound stator. Note the different depths and locations of the coil groupings.

motor04decjan09.jpg

Due to design, concentric wound motors create RIC results that appear as though there may be an air gap eccentricity when the rotor is only positioned through a single pole face. Results of a RIC performed on a concentric wound motor can be seen in Figure 8. Notice on the blue phase indicator, that the peak amplitudes from one pole group to another are essentially the same, but different from the other two phases. The blue phase is always slightly lower than the red phase, but higher than the green phase.

In a case where concentric wound motors are identified or suspected, the RIC needs to be performed over two pole faces. Place the motor in observe and confirm any suspected eccentricity with correlating evidence, such as EMAX eccentricity analysis or vibration analysis.

Figure 9 shows an example of dynamic eccentricity. Notice how the peak amplitudes of the blue phase vary from pole group to pole group as the rotor is rotated. This is occurring for each of the three phases. Dynamic eccentricity is the more severe type of eccentricity due to the increased chance of a rotor/stator rub due to rotor pull-over.

To determine the severity of an eccentricity problem identified with the MCE, it is important to correlate with other technologies, which analyze the motor while it is in a dynamic condition. If the eccentricity is affecting the running characteristics, such as high eccentricity sidebands in the current spectrum of EMAX and higher than acceptable vibration levels at twice line frequency, then action should be taken to correct the eccentricity as soon as possible. If eccentricity is not evident in the RIC test with the motor de-energized, but the running tests do indicate eccentricity, then soft foot should be the first thing investigated.


EMAX Analysis

Eccentricity analysis using EMAX technology is performed through a high frequency spectrum
of current signature analysis. When air gap eccentricity exists in a motor, the air gap flux will  be off balance, causing different levels of voltage to be induced onto the rotor. This results in irregular current flow on the rotor and varying levels of counter electromotive force, which is felt by the stator. These varying forces on the stator winding produce changes in the amplitude of the current similar to a load change. By displaying the current in a spectrum format, the modulations can be seen as sideband activity around a location known as the Eccentricity Frequency (FECC). The FECC is the number of rotor bars multiplied by the shaft frequency (RPM/60) of the motor. The current modulations are seen as peaks on the spectrum, which will be odd multiple sidebands of the line frequency powering the motor. In a 60 Hz system, the 1st and 3rd sidebands will appear as 4 peaks, 120 Hz apart, and non-synchronous to line frequency. These peaks are seen in Figure 10 on the following page.

One advantage the EMAX offers when performing CSA is that the technician may use alarm set points to estimate the severity of the eccentricity and act accordingly. However, speed and rotor bar information is necessary for the technician to be able to confirm that the peaks identified on the spectrum are indeed eccentricity related. If the number of rotor bars and the speed are known, the MCEGold and WinVis software automatically places a red X at the four peak locations that identify eccentricity. Obtaining the speed from the Advance Spectral Analysis (ASA) current demodulation software, Low/High Resolution rotor tests, or via a strobe light is the easy part. The rotor bar count, however, is another matter. First, at the earliest opportunity you should verify that a rotor bar count request exists on each of your motor repair specifications. The report you get back from the shop should include how many rotor bars and stator slots exist in the motor. Second, utilize the vibration department to assist in the rotor bar count. They may have previously identified the number of rotor bars through spectrum analysis of the vibration signal. If neither of these methods work, reverse calculation as described later in this article may be required.

One of the most often overlooked tools is the caution and alarm set points, which are preprogrammed into the software. We often get information sent in for review on possible eccentricity and neither the eccentricity related peaks, nor any other peak for that matter, is close to the yellow caution line. Also remember when dealing with a VFD, no longer does 60 Hz line frequency necessarily apply. If the drive is operating at 40 Hz, rather than four peaks 120 Hz apart, you are now looking for four peaks 80 Hz apart and nonsynchronous to 40 Hz rather than 60 Hz. The MCEGold and WinVis auto frequency adjusts automatically and corrects for VFDs, and it will correctly identify peaks based on the measured fundamental frequency, as seen in Figure 11.

motor05decjan09.jpg

Whether across the line or powered from a VFD, if speed is known, but the number of rotor bars is unavailable, the following information will assist you in analyzing the eccentricity test's frequency spectrum. Eccentricity related peaks usually exist between 600 Hz and 2000 Hz on the current spectrum. This frequency range is based on the fact that the eccentricity peaks are odd multiple sidebands of the line frequency around the product of the number of rotor bars and the speed of the shaft (# of rotor bars x shaft speed). Commonly, the faster the motor, the lower the number of rotor bars. The slower the motor, the higher the number of rotor bars. When multiplied, the product is usually less than 2000 Hz. However, larger two pole motors may exceed the 2000 Hz mark. Eccentricity peaks cannot be harmonics of line frequency. As a result of slip being involved, the calculation of eccentricity prevents it mathematically from being a multiple of the line frequency. Therefore, running the harmonics marker, which places a small green x at each of the line frequency harmonic peaks, allows you to quickly remove the identified peaks from the suspect list. Line frequency harmonics are very common and often can look like eccentricity peaks.

If in a 60 Hz system you identify that four or more peaks exist between 600 and 2000 Hz,
which are 120 Hz apart and non-synchronous to line frequency, you can reverse calculate the number of rotor bars by highlighting the 2nd of the four peaks and clicking the estimate bars button on the screen. When using this feature to estimate the number of rotor bars you should always include a note with the test stating that the numbers of rotor bars is an estimate only until you can confirm the actual number of bars.


MCEMAX Helpful Hints

Rotor Influence Check

  • Slow motors require testing an additional pole face. When testing a slow speed motor, remember one pole face could equate to positioning the rotor 30 degrees or less. If there is an air gap eccentricity, a RIC, which only covers one pole face, will not have enough of a change mechanically in the rotor/stator relationship to cause the inductance readings to vary much, if at all.

  • Use the balance of inductance to determine if you should continue the test. The graph of inductance imbalance is produced during the RIC test to aid the operator in determining if a second pole face should be completed. If the balance of inductance changes by 2 or more, a second pole face should be performed. The extra data will facilitate the data interpretation.


Eccentricity Test

  • For VFD powered motors, strobe/tach speed. The added difficulty in determining the speed of a VFD powered motor from the High/Low Resolution or ASA means it is always better to be absolutely sure of motor speed. An external tachometer or strobe should be used to confirm speed and if the number of bars is known, the data analysis becomes automatic.

  • The X16 scale will fit 4 peaks. When manually searching (scrolling down from the higher frequency of the spectrum) the X16 scale display of the spectrum will give you just enough "window" to see four peaks 120 Hz apart. Keep this in mind and the manual search will become quicker.


Summary


Eccentricities in the air gap will develop uneven magnetic pull between the stator and rotor during operation. This uneven magnetic pull will lead to increased vibration, mechanical wear and tear, and possibly pull-over to the point of a rotor/stator rub. It is important to have equipment that provides you with the necessary information to make informed maintenance decisions concerning the severity of an air gap eccentricity. With the MCE RIC test and the EMAX eccentricity high frequency spectral analysis test, the MCEMAX provides one easy to operate package for comprehensive evaluation of air gap eccentricity during operation or when the motor is secured.

Doug Swinskey joined the PdMA Training & Technical support team in June 2005. Prior to joining PdMA Doug spent over ten years with a leading manufacturer of electronic motor speed controls. Before he began his work with variable frequency drives, he was the proprietor of an electric motor rewind and pump repair shop. Since joining PdMA Doug has had the opportunity to conduct training on the MCEMAX all over the United States and as far away as the Canary Islands. With all his travel he still finds time to operate a successful photography studio in historic Ybor City in Tampa, Florida. You can reach Doug at 813-621-6463, ext. 2.

By Phill Slater

 

The following example demonstrates the inventory effect of squirrel stores. For this example let's consider a part that is used weekly and therefore has an average demand of 1 unit per week. This type of part is a major target for squirrel stores as holding them reduces the number of trips to the storeroom.

Let's compare two situations:

1. No Squirrel Store: The item is removed from the storeroom as needed - 1 per week.

2. Squirrel Store: The item is removed two at a time with movement every two weeks.

The demand data for these two situations is shown in Figure 1.


Figure 1

The demand profile for these two different demand patterns is shown in Figures 2 & 3. It is clear from these two figures that, while in each case the average is one demand per week, the demand profile is not just different, it is completely opposite.

precmain02_decjan09.jpg
precmain03_decjan09.jpgNow, one way to calculate the inventory needs in this situation is by using a Gaussian distribution. This approach is familiar to most people as it can be represented by the formula:

Reorder =   (Usage rate x lead time)
Point                               +
                             safety stock


Alternatively:

              RP =           (D x LT) + csf x
                                 MAD x Sqrt(LT)


Where,
RP = reorder point

D = average demand per week (for
our example this is 1 per week)

LT = Lead time in weeks (let's
assume 4 weeks)

csf = customer service factor (or
availability factor) - here we
will use a csf of 2.56, this
assumes a 98% availability.

MAD = Mean Average Deviation - a
measure of demand variation.
In this example, with no squirrel store
this is 0 (there is no variation) and with
the squirrel store the MAD is 1.

Sqrt = square root

Results

Scenario 1: Using the above formula and data, Figure 4 shows the results for this scenario.

precmain04_decjan09.jpg

It is a surprise to most people when they see that when you hold inventory in a squirrel store the Reorder Point in your official store can be MORE THAN DOUBLE the Reorder Point without the squirrel store.

This result then means that the average level of inventory held in your official store, if you allow a squirrel store, is 264% greater than the average holding without the squirrel store (see Figure 5). This is not due to the items held in the squirrel store but due to the Induced Demand Volatility (IDV) that the squirrel store creates in your official store. The IDV changes the calculation of safety stock in the above formula and this is why you hold too much inventory.

Scenario 2: Over ride the calculation and manually set your reorder point to 4 for both scenarios.

precmain05_decjan09.jpg

Let's now assume that you understand the impact of the IDV on your calculation and decide to manually set the reorder level for both situations to 4, knowing that you only ever use 4 items during the lead time for supply. In this case the average inventory holding reduces to 3.5 items (including the items held in the squirrel store).

This is still 40% higher than the situation without the squirrel store!

Do you still think that squirrel stores don't cost much?

Click here for the Main Article

Expanding Your Senses

user-pic
Vote 0 Votes
The Synergy of Ultrasound and Vibration Analysis
by Leane Harris

Today's airborne ultrasound is a far more versatile technology than most people think. We can use ultrasound, together with vibration analysis and infrared thermography, to deepen our understanding of our machinery's condition. This article, which touches upon the use of airborne ultrasound and vibration, is the second of a three part series, in which we look at ultrasound, ultrasound/vibration and ultrasound/infrared.

ultrasound01decjan09.jpg

Similar beginnings, but different outcomes, and completely different roles in the greater scheme of things...We see these facets play out in many areas of everyday life. It happens in predictive maintenance as well, and it may surprise many of you to discover one scenario. Two technologies springing from similar beginnings, but moving into very different everyday uses in plants worldwide.

In predictive maintenance, we are blessed with technologies that help us transcend our senses' limitations. They allow us to see, hear, and feel events that give us the information about our machinery which we need in order to make informed decisions.

Infrared Technology allows us to see the spectrum of light that is invisible to our eyes. This capability becomes very useful if we want to know if there is a temperature variance between different objects or of the same object at different times.

Airborne Ultrasound extends our ability to hear sound waves that are above our hearing capability. There are many sources of high frequency sound waves: turbulent flow of material passing through a restricted opening is one, friction energy generated from the rolling elements of a bearing as it rotates inside the housing during operation is another, ionization energy also produces high frequency sound waves, and impact energy generates high frequency sound waves. Do the descriptions above give you some insights as to which areas in your plant may possibly have high frequency sound waves?

Vibration Analysis extends our sense of touch by a few leaps. It detects and measures vibration movements in machineries that are too small for us to feel, then allows us to identify the sources of these vibrations, which are then categorized according to severity. Informed decisions can then be made from there. We have made a few leaps from putting a coin on top of a motor to see how badly it is vibrating. Of course, with the coin, you'll see the coin vibrate, but you can't measure its vibration.

Oil Analysis gives us the ability to look at the chemical composition of used oil in the machines to see if it is normal or not. Any unacceptable deviation from the norm can give indications of problems.

Airborne Ultrasound has several applications in your plant. Based on the explanation above, this technology can be useful in locating air leaks (Turbulent Flow), checking for passing valves or steam traps (Turbulent Flow), managing bearing lubrication better (Friction), detecting flow or no flow situations (Turbulent Flow), detecting and locating sources of electrical discharge (Ionization), and in what I Call ultrasound PdM (Friction). For purposes of this article, I'll narrow the ultrasound discussion to the condition monitoring, or ultrasound PdM, application since that is also the area where machine vibration analysis is used. We'll talk about when to use each one by itself, and when to combine these two powerful technologies.


Similar Beginnings

Interesting enough, vibration analysis and ultrasound have similar beginnings. The accelerometers that vibration analysis uses rely on piezoelectric crystal to detect the changes in acceleration as a body oscillates or moves in a repetitive motion. The contact rod that airborne ultrasound uses in bearing inspection also has piezoelectric crystal that moves in response to the amount of ultrasonic signal generated from the friction energy as the bearing rotates in its housing. What differs is the specification of the crystal, the way the signal from the crystal is processed and the resulting information that comes out.

ultrasound02decjan09.jpg


Two (or more) is Better Than One

For Ultrasound PdM, or the bearing inspection application of ultrasound, the inspector gets a reading from his ultrasonic detector that relates to the amount of ultrasonic energy generated from the bearing. Care must be taken, and proper procedure should be followed, to ensure the validity of data. It is quite easy to get an erroneous reading. The inspector should always try to contact the spot closest to the bearing, because then it is likely that the reading is from the bearings and not from something else. What energy did he pick up? Friction? Impacting? Or Both?

For example, I recently conducted both a vibration and ultrasonic test on the outboard bearing of a pump for a customer. The ultrasonic reading was higher than normal. Sound quality was rough, similar to the sound produced when you have sand between your wet hands and you rub your hands together in a rotational motion instead of a back and forth movement. What could I deduce from this information? Namely, that there was more ultrasonic energy being produced than before, and that the sound was rougher than it used to be. Could I say that there was an outboard bearing problem based on the higher reading and the sound quality that I heard through the headphones? No, at least not yet.

Ultrasound will give an indication of the change in ultrasonic level and the quality of the sound heard (subjective information), but it cannot tell the specific cause of the change. Some highly experienced ultrasonic inspectors may be able to have a pretty good idea of the bearing condition based on the sound quality, but to transfer that experience to another ultrasonic inspector is difficult. This is when vibration tests come in. It is important to get more detailed information from another source in order to have a better picture as to the condition of this pump. And vibration analysis fits in perfectly in this type of situation.

Vibration Analysis detected that there was serious impacting happening in the bearing housing. Visual inspection showed grease coming out from the bearing seals, a similar situation to that in Figure 4. All three inspection methods - ultrasound, visual, and vibration - gave me much more comprehensive information to make the proper recommendation. This is a simple example of how the different condition monitoring technologies can be used together to increase effectiveness.


Sound Can Be Misleading

We live in a real and complicated world, and sometimes the real world gives us combinations of events that throws us for a loop and changes our perception.

One time I was in another customer's facility doing routine machine inspections. The ultrasonic reading was higher than normal on one pump in particular - high enough that ultrasonic guidelines called for possible incipient bearing failure. Spectra from machine vibration did not indicate any problem. I began scratching my head in thought. Hmmm, why was there so much more ultrasonic signal being generated from this pump?

I went to operations to ask a few questions. They told me that there was an increased flow going through the process. Of course, this meant that the machines were doing more work and, hence, a higher turbulence was being generated by the pumped liquid.

The machines were designed to handle the increased workload. So the ultrasonic energy level changed, but not because of a physical defect on the bearing. I learned the lesson that going back to the basic understanding of where and how ultrasonic energy can be generated is helpful, and important, when doing troubleshooting.

Spectra analysis of machine vibration is useful in identifying the different forcing frequencies that are affecting the machine. These forcing frequencies can be trended over time to establish the rate of machine deterioration due to the specific forcing frequency.

It is very important that a routine machine vibration analysis is performed to catch these changes as well as identify any new forcing frequencies that are attributed to machine problems.


ultrasound03decjan09.jpg

Trend

Airborne ultrasound is useful in two areas of machine condition monitoring. One is in the lubrication of bearings, and the second is in Ultrasound PdM, or condition monitoring. Integrating ultrasound in bearing lubrication is straightforward, as long as one follows the proper lubrication procedure to know when to stop adding grease. In Ultrasound PdM, one can do the comparison, or trending, method. This procedure is also straightforward, but the analysis of dB readings may not be. Inspector knowledge in ultrasound, as an inspection technique, process operation and machine operation comes into play in order to make sense of what the machine is actually telling you. Generally, relying only on Airborne Ultrasound for machine diagnostics will not be enough. Often, you will need to use another inspection tool, like a vibration test, to zero in on machine health condition.



ultrasound04decjan09.jpg


Do Vibration Analysis Diagnosis and Ultrasonic Readings Go Hand in Hand?

If vibration analysis identifies a fault, would you necessarily see a corresponding increase in ultrasonic readings of the machine (provided you have been doing a trending method)? And, conversely, would vibration analysis necessarily confirm a fault if you see an increased decibel reading through ultrasonic testing?

Not always, and that's just life in the real world. One of the reasons is the variety of ultrasonic sources that can exist in an operating machine. A pump is a good example. There is turbulent flow of the fluid being pumped, there is the possibility of cavitations, there is the metal to grease surface contact, there is the metal to metal surface contact in a bearing, there is the distinct possibility of transient ultrasonic signals - all of which carry ultrasonic energy that can be detected by the ultrasonic detector. Have you ever listened to a pump bearing with your ultrasonic detector and heard a sound like a bearing rotating, then moved your sensor away from the bearing and put it right on the pump and heard exactly the same sound quality? It can get confusing. That's where field experience, for which there really is no substitute, as well as vibration analysis, come into play.

In summary, using Airborne Ultrasound and Vibration Analysis together has its own strength. Many times, one technology can validate the other technology's findings. But, perhaps more importantly, the combination of technologies gives the inspector multiple sources of information, and a more comprehensive data set, in order to make the proper diagnosis and recommendations.

All photos used courtesy of ECS2, Group, Inc.

 

Liane Harris is the President of ECS2 Group Inc., a service and consulting company based in the Toronto, Ontario area. She has a BS in Chemical Engineering and MS in Engineering from McNeese State University in Louisiana. She is currently a Level 2 in Vibration Analysis, Level 2 in Airborne Ultrasound, and Level 1 in Infrared Thermography. 


 

Ultrasound_Dec_Jan_2009.pdf


About this Archive

This page is an archive of recent entries written by Uptime in December 2008.

Uptime: February 2009 is the next archive.

Find recent content on the main index or look in the archives to find all content.