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482

6:00 am
May 1, 2007
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Do We Really Know What We Are Measuring?

Inaccurate, unreliable partical counting can hamper your ability to make smart oil suitability decisions. That can cost your company considerably in tearms of time and money.

It’s no mystery to Maintenance professionals that clean oil promotes enhanced equipment performance and reliability. There is, however, something that many of them do not know. Today’s most commonly used particle counting tests for determining oil cleanliness—Filter & Count Method; Light Blockage Method—too often yield inaccurate and inconsistent results.

As detailed in this article, the inconsistency and lack of precision with these current practices can lead companies to waste considerable amounts of money and time developing maintenance plans based on inaccurate and unreliable information. But, by incorporating innovative methods to address sources of errors—including air entrainment, water content, and additive effects—particle counting precision and accuracy can be greatly improved. Maintenance professionals can then make better oil suitability decisions, garner a stronger return on their lubricant investment and enhance their equipment performance.

What is cleanliness?
Oil cleanliness can be defined as a measure of the level of dirt, other insoluble or hard particles in fresh or in-service oil. There are a number of factors that can impact a lubricant’s cleanliness, most notably contamination and harsh operating conditions, such as extremely high temperatures, pressures and operating speeds. To this end, maintenance professionals are implementing oil analysis programs with the desire to gain accurate readings on the cleanliness of their oil to support oil suitability decisions.

Oil cleanliness is typically determined by particle counting. The Filter & Count (ISO 4407) and Light Blockage or Extinction (ISO 11500) tests are the most widely used methods of particle counting. Thus, the results of these tests were used as the foundation for the discoveries detailed in this article.

Filter & Count Method–ISO 4407…
Particle counting using the Filter & Count Method is conducted exactly how it sounds. Oil samples pass through a fine-patch filter that captures particles that are greater than four microns (> 4μ) in size. After the sample has passed through the filter, the particles on the filter patch are counted and measured under a microscope. The Filter & Count Method is considered to be the most accurate method of particle counting because the test is not normally affected by fluid color, air or water.

There is, however, no precision statement for the test, so the accuracy of the measurements is unknown. In addition, agglomerated particles, particle coincidence (excessively high particle counts that prevent accurate detection by the instrument), sometimes emulsified water and even air bubbles can contribute to false readings. It also is important to note that this test is extremely laborintensive and expensive. Furthermore, human error and variability can contribute to inaccurate readings and low test precision.

0507_oilanalysis1Light Blockage (Laser) Method–ISO 11500…
The Light Blockage Method is the most commonly used particle counting test. For this type of test, a laser is focused on a capillary through which oil flows. As particles pass through the laser, the beam is partially blocked and the transmitted light is measured by a photocell detector. The amount of light blockage is related to the number and size of particles in the sample. Similar to the Filter & Count Method, there is no precision statement for this test, so the exactitude of the measurements is unknown. In addition, compounds such as air, water and some additives which refract or impede light, can cause false readings. This method also cannot effectively measure dark fluids.

ISO Classification…
Once these tests have been completed, oil analysis providers utilize ISO Cleanliness Code – ISO 4406 (see Fig. 1). This chart has been used to establish a standardized code for quantifying oil cleanliness. In essence, it is a counting tool. The ISO range code number, or simply the ISO code, represents the number of particles found per milliliter of oil, and a single ISO code increase represents (roughly) a doubling of particles in the fluid. Under ISO 4406, an ISO code is determined by measuring and grouping particles into three categories based on their size in microns (> 4μ, >6μ, and >14μ). (To put the size of the particles in perspective, the width of a human hair is about 40μ.) As an example, the results outlined in Fig. 2 indicate that the ISO cleanliness code of the oil is 21/17/12.

Maintenance professionals typically use particle counts—along with other in-service oil analysis results—to make oil suitability decisions, based on the fluid’s cleanliness rating and, consequently, its expected tendency to cause wear and premature failure. Recognizing the importance of oil cleanliness, equipment manufacturers have started to include limitations based on particle counts in their warranty specifications. A growing number of companies also include particle counting guidelines in their internal maintenance practices to ensure a strong return on their equipment investment. While monitoring oil cleanliness is geared toward improving equipment cleanliness and thus enhancing equipment reliability and life, both Maintenance professionals and Lubrication specialists have to be cautious when making decisions based on the results from these particle counting tests.

Comparison Study 1: Filter & Count Method
If samples of the same oil are tested using the Filter & Count Method with different operators, then all of the ISO cleanliness ratings should be exactly the same, right? Well, this hypothesis was dispelled when we evaluated the following four lubricant samples with increasing levels of particles at one lab with three different operators.

  • Sample A is a hydraulic fluid filtered through a 1μ filter
  • Sample B is a 50/50 mixture of Sample A and NIST SRM 2806a (a standard fluid with a known level of particles)
  • Sample C is NIST SRM 2806a
  • Sample D is Sample C spiked with 2 mg Medium Test Dust (a standard material used in the laboratory to generate fluid samples of increasing particulate levels)

Cleanliness values were assessed based on counts of particles with sizes greater than 5μ and 14μ.

For clarity, Fig. 3 shows the results for particles >14μ; particle counts for both >5μ and >14μ showed the same pattern. These results indicate that even though the Filter & Count Method was conducted on samples of the same oil, the values that were generated varied by as much as two ISO codes between operators, or roughly a factor of four in terms of particle counts.

0507_oilanalysis2Comparison Study 2: Laser Blockage Comparison
In a second experiment, the reliability of the results of the Light Blockage Method was investigated. Filter & Count tests also were conducted for comparison. Here, 100 ml samples of a lubricant, formulated with a medium amount of additives, no polymers and a silicon antifoamant, were taken from one batch and distributed to four different particle counting labs. Each lab was given the same instructions on how to handle the samples and run the Light Blockage tests. Particles with sizes greater than 5μ and 15μ were evaluated for each test. Fig. 4 plots the results generated from the four Light Blockage tests. There was a fluctuation of as much as two ISO codes generated from these tests.

Comparison Study 3: Filter & Count vs. Laser Blockage Methods
In light of the differences between the ISO cleanliness ratings generated by both the Filter & Count and Laser Methods, several comparative tests were conducted to determine if any correlation between the results could be established.

In each test, samples for multiple batches and package styles of the same lubricant were evaluated. To ensure that the results were unbiased, these tests were conducted by a third-party commercial lab and no special instructions were given. The lab only was directed to evaluate ISO cleanliness using both the ISO 4407 Filter & Count and ISO 11500 Laser Blockage Methods. For clarity, only counts of particles larger than 14μ are shown.

0507_oilanalysis3First, the Filter & Count Method and Laser Method were performed on 19 samples of a lubricant that was formulated with a medium amount of additives, a silicon antifoamant and no polymers. This formulation is representative of a commonly used hydraulic fluid. The average ISO Code of the lubricant was 11.

The results of the test generated a mean delta of the ISO codes between the two test methods of 1.7, with variations in results as high as four ISO Codes. In many of these cases, Maintenance professionals would be inclined to change an oil that still could be serviceable. There appears to be a bias toward the Filter and Count method giving a higher particle count than the Laser Blockage method.

To investigate this theory further, the same evaluation was conducted on 17 samples of oil that was formulated with a medium level of additives with polymers and a silicon antifoamant. The average ISO value of this lubricant also was 11.

For this series of tests, the mean difference of ISO Codes was 2.5. In contrast to the previous sample, the results of the microscope tests were lower than the laser method more than 82% of the time. Additionally, it should be noted that the Filter & Count and Laser Blockage Methods failed to give the same test results more than 87% of the time, with differentials as high as five ISO codes. Moreover, the measurements differed by greater than one ISO code more than 50% of the time.

These significant variations establish that there is no distinct correlation between the reported cleanliness of the oil and the method of testing. Not only was there no correlation between the two methods, the accuracy and precision of both methods are clearly in question.

Comparison Study 4: Rate of Cleanliness
A comparative study also was conducted to see if comparing the results of the Filter & Count and Laser Blockage tests would unveil a discernible pattern when analyzing oils of varying cleanliness levels. The samples included clean samples (IS0= 10), samples of medium cleanliness (ISO= 12) and relatively dirty samples (ISO= 15, 16, 17). Similar to previous tests, only particles larger than 14μ are shown.

When the 26 different samples of the cleanest lubricant were tested, the mean difference in test results was 1.7. The results of testing 23 lubricant samples with medium cleanliness generated an average difference in oil cleanliness rating of 2.1, with variations as high as 4 ISO codes between results. Finally, the average difference between the oil cleanliness values of the 15 samples of the dirtiest lubricant was 1.9.

0507_oilanalysis4

What do these results indicate? They indicate that there does not appear to be any consistency or pattern in the oil cleanliness results of oils with varying particle counts. Thus, Maintenance professionals need to be cautious when making oil suitability decisions based on particle counting results.

Sources of variation
The lack of standardization in the testing methods’ practices and instruments can explain some variation in the test results. This, however, is only part of the story. There are several other factors that lead to inaccurate results. These include:

  • Sample handling and storage
  • Emulsified water in oils
  • Air bubbles in oils
  • Aggregated particles in oils
  • Particle coincidence
  • Variability in additive chemistry (i.e., polymers, liquid dispersions, etc.)
  • Oil viscosity

During any particle counting test, sludge, emulsified water and fibers can all be interpreted as similarly sized particles. Additionally, black particles that absorb light and shiny particles reflecting light can affect the results of the oil cleanliness measurement. There are means by which to improve oil cleanliness testing, though.

Let’s now explore ways to increase test accuracy and precision, so that you can depend upon particle counting results more when making decisions about the health of, and investment in, your lubricant.

0507_oilanalysis5Minimizing test variability
As we’ve seen, significant sources of variation can occur from air bubbles, antifoam additives and water entrapped in the oil, and these “phantom particles” generate some of the largest spikes in ISO cleanliness values. With this in mind, many oil analysis companies are developing innovative ways to improve the repeatability and reproducibility of particle count tests.

The effects of air…
Because air has a different refractive index than oil, air bubbles can be measured as hard particles by Light Blockage particle counters. It has been discovered that by pre-treating the oil sample with an ultrasonic bath or a combination of ultrasonic bath and vacuum, inaccuracies in particle count as a result of air bubbles can be minimized. The ultrasonic treatment helps to remove the bubbles and provide more accurate particulate values.

Although there is not a significant change for particles greater than four microns, it is clear in Fig. 5 that by using this method, the particle count of the particles greater than six microns and particles above 14 μ has been signifi- cantly lowered after ultrasonic treatment. Thus, a more accurate assessment of an oil’s cleanliness can be determined by removing entrained air.

Using an antifoamant…
Foam is created by the combination of air and a lubricant and can compromise the performance of a product, possibly leading to equipment problems. Many lubricant manufacturers include antifoamants in the formulation of their products. Although these ingredients can improve equipment performance, they also can contribute to inaccurate particle counts when a sample is tested.

Fig. 6 illustrates how an antifoamant substantially increases the cleanliness rating of an oil and how this interference can be avoided through the use of a diluent—a miscible liquid or solvent used to dilute and lower the viscosity of the sample. By obtaining a more accurate value, Maintenance professionals will be able to make better decisions about whether or not they need to change their oil.

The effects of water…
Water tends to have a deleterious effect on lubricant and equipment performance, potentially leading to frequent component failure. When testing new or used oil, the water in a lubricant can increase the particle count in a laser particle counter.

Fig. 7 details the increase in the oil cleanliness rating (indicating “dirtier oil”) when water is added to a lubricant. Therefore, water is shown to affect the “hard particle” count, which we know should not be the case. Similar to the case of antifoamants, when a diluent is added to the same lubricant, the oil cleanliness rating is reduced, thus generating a more accurate particle count.

Summary
While there are currently no ASTM standard test methods for measuring the cleanliness of lubricating oils, innovative modifications to the Laser Blockage method can greatly increase the accuracy and repeatability of the results by eliminating test interference from entrained air, water and antifoamant additives. Armed with better in-service oil analysis results, Maintenance professionals can make better decisions about the suitability of an oil.

Bernie Koenitzer and Clint Smith are technical service advisors with Imperial Oil Ltd.

Alex Bolkhovsky and Dr. Tim Nadasdi are products technical advisors with ExxonMobil Lubricants & Specialties.

This article was the focus of a presentation at MARTS 2007. For more information, e-mail: tim.nadasdi@exxonmobil.com

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190

6:00 am
May 1, 2007
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The Inadequacy Of Learning By Phone And Surfing The Net

0507_profdevelopment1The story is true, the narrative real. Names have been changed so as not to touch too many raw nerves.

Played out over a recent several-day period, the following situation seems to be typical of how some industry specialists are attempting to acquire knowledge these days. The point is that phone calls and Internet searches should not be viewed as substitutes for the more traditional structured approaches to learning. These approaches include reading appropriate texts.

“Hi Heinz,” read the e-mail from a stranger. “I have read thru (sic) some of your articles I found at Magazine X and have learned quite a bit. How can I get in touch with you to discuss what levels of consultation you offer? If you could call me today or tomorrow, I’d appreciate it very much, as I am working on a short-fuse project. Thanks very much…Tommy”

So, I called Tommy, an engineer employed by a very large, well-known Engineering and Design firm involved in the construction and upkeep of nuclear power plants. I spent about 20 minutes on the phone, trying to steer him in the direction of reference material that would explain why one of the pumps he was concerned with seemed to always have an excessively high bearing housing oil level. Since he was interested in “solving” the problem by using sealed grease-lubricated bearings, I attempted to explain why this solution is certainly not worthy of being the first one to consider. It’s difficult, however, to download several decades of applicable pump experience to relative newcomers when virtually every question asked seems out of context, and would require a string of tie-in explanations. Therefore, for written backup, I mailed Tommy a list of applicable books and articles that would shed more light on the issue. He replied in writing:

“Heinz, thanks for your time & info yesterday. It was most helpful. I am looking forward to your recommendations for reading/reference material. I was hoping to ask—you wrote an article that appeared in Magazine X (in which) you created a subjective rating system for various configurations. I was trying to see how my system of questions would fall within the rankings. Would you be willing & interested in hearing my interpretation of what ranking my system has and offering your feedback & thoughts? Thanks, Heinz, looking forward to your recommended references…Tommy”

OK. I replied, “Try calling between 1 and 2 PM (CST) today.” Tommy acknowledged:

“Thanks, Heinz. I will call tomorrow. Thanks for your thoughts, I am going thru all of them. In your subjective ratings chart of lube systems, what is the “balance line” between bearings? I am not sure what it is, to figure out if the APS system has it or not. Thanks very much…Tommy.”

A second reply was needed to indicate that I would be available until 3 PM (CST) today, and that tomorrow I could be reached at and from—whatever. Tommy, though, apparently is busy. He e-mails back:

“Subject: RE: Pump bearing upgrades. Heinz—I actually have a meeting today from 1-2 with GOODANDBIG PUMP CORPORATION to discuss their recommended oil level, as well as discuss with them the feasibility of greased, sealed bearings. Can I call you afterwards? And, what is your phone number? I also have asked a pump & motors engineer here if they have your ‘Pump User’s Handbook’ so I can start using it today. By the way, from reading your writings, I would very much like to use a flinger disc, but it would not fit inside their housing. Thanks…Tommy.”

Although I promptly e-mailed the following information and questions to Tommy, I also recalled early in our communications that he had mentioned being on a “short fuse” project. In light of this, I assumed he probably would not see my reply prior to his meeting with GOODANDBIG. I wrote:

  • Greased, sealed bearings are suitable within a somewhat limited DN-range only. Therefore, what is your bearing DN (bore diameter times rpm)?
  • Once the grease is depleted (due to churning or oxidation or separation centrifugation) into oil and soap, the bearing will fail rapidly. Therefore, any non-regreasable “life-time” grease-lubricated bearings at a nuclear power plant will probably have to be replaced on a precautionary (safe) schedule. Does that imply that regreasable bearings are a wiser choice? Not necessarily, because regreasable bearings should be avoided at plants that disregard the critical nature of using correct regreasing procedures.
  • Does this plant use intelligent regreasing procedures? How do you know?
  • Also, regardless of bearing lubrication and application method, bearings with certain cage materials should not be used in your pumps.
  • Important: I believe it should be mandatory to (a) use a modern bearing protector seal on the bearing housings, and (b) only use pressure-balanced lubricators; i.e. you must disallow “open system” constant level lubricators.
  • Questions for GOODANDBIG CORPORATION:
    • What type of flinger disc doesn’t fit in their bearing housings?
    • What size doesn’t fit?
    • What material is used in flinger discs that DO fit elsewhere in industry?
    • What’s the constraint with the particular pump type that you seem to be dealing with?
    • Are any upgrade measures possible?
    • Have upgrade measures been implemented by Bestof- Class companies elsewhere?
    • Why don’t these other companies have the problem you seem to have?
    • What sense does it make to pursue a fundamental design change when others don’t seem to have the problem?
  • The pressure that exists behind a bearing is not always that existing in front of the (same) bearing, nor at the bearing at the far end of the housing. Sometimes, this unequal pressure is due to windage generation (fan effect) by an angularly arranged cage. At other times, it has to do with lack of a suitable drainage opening at the bottom of the bearing seat. This is shown on Fig. 7-22 of the “Pump User’s Handbook.” The area of the needed cross-sectional opening is determined from equation 7-6.
  • When unequal pressures are suspected, Best-of-Class users will install a “balance line” (tubing or pipe) that ensures that all spaces are at equal pressure.
  • I strongly suspect that the workers at the affected facility don’t understand that the laws of physics demand an air volume to exist at the top of the constant level lubricator bulb. This air will be at a slight vacuum and, together with the static pressure of the liquid column in the bulb, must equal the pressure in the air space floating above the liquid oil level in the bearing housing.
  • Based on what you have related to me so far, attempts to overfill the lubricator bulb are the most likely (although not the only possible) cause of the high oil levels.
  • Unfortunately, we are approaching a level of correspondence that goes beyond what I consider normal. Perhaps we might agree that my time, too, is valuable. Please honor my request to confine your call tomorrow to very brief essentials.…HPB

Tommy’s reply came the next day:

“Hello, Heinz, thank you for your commentary & explanations. I appreciate them very much! I actually don’t have any specific questions to ask, I was just seeking clarifications, which have been very helpful. Perhaps I don’t need to call today and would only touch base if I had another clarification to ask? I will pursue finding your book. Thanks very much, Heinz! I wish you had been teaching some of the classes I took…Tommy.”

That was the end of the story, or so I thought (see Sidebar). I might add that the classes I took in the 1950s didn’t teach the details outlined in my e-mails, either. On the other hand, they did teach the fundamentals of common sense and showed us students how to apply the basics of physics to hydraulics and general troubleshooting.

Collectively, common sense and physics were (and still are) the foundation of mechanical engineering. “Cold phone calls” were unheard of in the 1950s, and the Internet did not exist. But books did, and books were our prized possessions. Furthermore, the desire to read and educate oneself was there. Today, however, as evidenced by this round of communications between Tommy and me, whether that same desire to actually read and educate oneself still exists in some industrial environments is doubtful.

Tommy Wasn’t Done Yet…

A day or so after receiving what I thought had been Tommy’s last e-mail message to me, I find the following in my Outlook mailbox:

“Heinz, thanks for the info. You had asked me about the DN #—and I too wanted to verify the DN #, to apply it to your 1-100 scale of relative bearing housing scheme ratings. The shaft RPM is 3600. The shaft journal sizes are 2 5/8″ and 3 1/8” OD. Therefore the DN values are: 9,450 and 11,250. Or in mm (240,000 and 285,750). If you are using a DN value of 8,000 to “allow or disallow” slinger rings, is that in units of inch-rpm? Thanks very much…Tommy”

I reply. “Yes, it’s inches multiplied by rpm. Thus, I would allow slinger rings only if the installation were to positively meet “criteria of perfection” in terms of horizontality of shaft system, immersion depth, oil viscosity, ring concentricity and ring finish (RMS). That said, I would disallow them whenever the facility cannot: (a) ascertain that these criteria are met; but (b) expected me to give them advice on Best Available Technology. Slinger rings simply are not Best Available Technology at DN values exceeding 8000.”

Now, Tommy e-mails back:

“Thanks, Heinz. After our discussion last week, I asked Maintenance to verify concentricity of the ring. No results yet. As for horizontality, it’d be hard to make it ‘perfect’ within a very small tolerance, of course, however I’m looking into what features exist to mitigate this, such as running the slinger ring in an arced groove or groove or slot, etc. All the best, appreciate the food for thought as always. . .Tommy”

Exasperated, I vow to send Tommy one last e-mail. It reads as follows:

“In which case, (and assuming that the laws of gravity DO INDEED pertain at your plant), the slinger ring will make contact with the sides of the groove, and will slow down. Then, we’re right back to where we started and the whole exercise has been futile. At which time I anticipate you will suggest making the slinger ring cross-section trapezoidal. Note that the resulting sharper edges easily cut though the oil film and abrasive wear will take place. Wear particles (slivers of brass or bronze) will contaminate the oil, and on, and on and on. . . That, then, explains why Best-of-Class professionals do NOT consider slinger rings appropriate for the truly reliability-focused.”

…HPB

 

Frequent contributor Heinz Bloch is well-known to Maintenance Technology readers. The author of 17 comprehensive textbooks and over 340 other publications on machinery reliability and lubrication, he can be contacted directly at: hpbloch@mchsi.com

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105

6:00 am
May 1, 2007
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Solution Spotlight: Circuit Breaker Replacement & Retrofilling For Industrial Facilities

Electrical distribution is pretty simple in an industrial facility, at least for those who aren’t involved in MRO activities. As long as the lights are on and machinery is humming, everyone is generally happy. On the other hand, if the constant flow of electricity is interrupted for an extended period, it could lead to grave consequences like missed deadlines, lost sales and a tarnished reputation.

0507_solspotlight01

Circuit breakers are the linchpin of a facility’s electrical distribution system, so it’s probably not surprising that several warning signs of an aging system relate to these devices. That includes a steadily increasing amount of breaker nuisance tripping or failure of a main breaker. When these warning signs occur, it’s a message that breakers may need to be upgraded to help the power distribution system meet current and future needs.

Replacing and retrofilling
When an electrical distribution system is new, it doesn’t require a great deal of attention outside of routine maintenance. But loads increase over time, through expansion and other factors, and equipment ages, including circuit breakers. Nuisance tripping and minor outages become more common, translating to increased maintenance costs that strain budgets.

More ominous is the possibility of a massive power outage that could occur at any time. Suddenly, an entire system upgrade—including brand-new equipment purchases, short circuit coordination and revision of the facility’s single-line diagram, along with downtime and all the related labor issues—is required, costing thousands of dollars and potentially weeks to complete.

Replacing or retrofilling existing decades-old circuit breakers with the benefits of today’s devices can go a long way in modernizing a system and avoiding the problems associated with removing old switchgear and replacing it with new equipment. For example, fused switches and circuit breakers have provided arc flash protection in the past, but breakers have been introduced to the market that provide high interrupting ratings without fuses, up to 200,000A at 508Vac. Such breakers eliminate problems common to fused switches and breakers, including hazards associated with changing fuses and the need to stock/replace fuses, as well as dependence on related mechanical hardware that requires maintenance or replacement. Plus, they are built to trip faster in order to protect both equipment and workers nearby, and typically feature a smaller footprint than fused breakers.

Replacement and retrofilling options don’t require a major time commitment, either. For example, replacing a breaker may require a short 15- to 20-minute outage that can be done during off-hours. A retrofill process is a bit more extensive; it might take 8 to 10 hours per breaker section—but, that’s certainly more desirable than a complete system upgrade.

Consider the following information as a primer regarding replacement and retrofill processes for LV and MV circuit breakers.

Replacement circuit breaker
A replacement LV or MV power circuit breaker is a new breaker that uses a modern modular drawout assembly, designed and tested to interface with components inside the existing switchgear’s breaker compartment. An MV replacement breaker is simply a like-for-like replacement that requires no interface to rack into the existing cubicle. With the LV upgrade option, a new cradle interface is inserted into the existing breaker compartment. The cradle design typically includes a new racking mechanism, safety interlocks, primary and secondary disconnecting devices, truck operated contact (TOC) mechanisms, a new breaker compartment door and other provisions.

A replacement LV or MV power circuit breaker matches the original breaker in form, fit and function and is designed and tested in accordance with ANSI C37.59 and C37.09 standards. Because a number of breakers manufactured more than 50 years ago are still in operation but no longer supported, the replacement breaker provides facilities utilizing older switchgear with a viable alternative for increasing performance and reliability.

Another key benefit of LV breaker replacements is that they allow maintenance personnel to exchange older, existing breakers for one common breaker that is interchangeable throughout a facility’s power distribution system. Another advantage is that they allow for equipment upgrades without having to schedule a bus outage.

Circuit breaker retrofill
An LV or MV circuit breaker retrofill entails the replacement of the old breaker and related compartment components, such as the stationary primary and secondary disconnects, cell interlocks and racking mechanisms, with a drawout circuit breaker and cradle of a modern, previously qualified design.

During the retrofill design and installation, the existing switchgear cell is modified and equipped with a new drawout cradle assembly. Significant changes are made to the structural components of the existing circuit breaker compartment as well as to the line and load bus structure and bus bracing. New isolating barriers are installed to conform to the latest electrical switchgear industry standard requirements.

LV or MV circuit breaker retrofills are employed when and where a facility can afford modifications that require extended switchgear shutdown (minimum 8-10 hours). When the available fault current is higher than the withstand capabilities of the existing circuit breaker, a retrofill or replacement can upgrade the capacity of the existing system. In such cases, the entire switchgear bus structure and bus bracing must be evaluated and upgraded, which requires the switchgear to be de-energized during modifications.

Heed the warning signs
Confronted with the warning signs of an aging power distribution system, a maintenance organization should consider commissioning a facilities audit. Such a study includes evaluation of the entire electrical infrastructure, and can indicate if replacement or retrofill options are appropriate or if a more extensive upgrade is recommended.

The bottom line, however, is to do something if the warning signs are present. Doing nothing runs the risk of extended downtime and higher costs.

Joseph Weigel is a product manager for Square D Services marketing. He has been strongly involved in the development of the Arc Flash Safety program for Schneider Electric to educate customers on emerging arc flash safety standards.

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1097

6:00 am
May 1, 2007
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Problem Solvers

High-Speed Vision Sensors

0507_probsolvers_cognexCognex Corporation now offers the In- Sight® 5600 series of vision sensors. This new line features the same design as the In-Sight 5400 series, but has double the processing speed and memory. Included in the product line is the standard (640×480) resolution
as well as the two-megapixel (1600×1200) models for performance in high-speed applications. All sensors have an IP67 (NEMA 4) rating and advanced vision software for inspection, identifi cation, measurement and alignment tasks.

Cognex Corporation
Natick, MA

 

Better Safety Instrumentation Monitoring

0507_probsolvers_honeywellHoneywell says that its new SIS-Health Monitoring technology helps reduce maintenance and failures in safety instrumented systems. It includes the SIS-Health Monitoring Local Reliability Database module that stores all inventory information regarding a site’s safety instrumentation. The SIS-Health Monitoring Analysis Toolset lets operators analyze, validate and optimize these systems’ reliability and Safety Integrity Level (SIL). Operating as standalone units or together as an integrated system, the two modules can be used with any type or brand of safety instrumentation.

Honeywell
Phoenix, AZ

 

Lockout/Tagout Solutions0507_probsolvers_panduit

A new Lockout/Tagout and Safety Solutions Catalog, SA-IDCB33, is now available from Panduit Corp. The smallsized catalog covers the company’s lockout/tagout products, safety and facility identifi cation products and training materials. A convenient reference section on industry standards also is included. The free catalog can be requested through customer service or downloaded from the company’s Web site.

Panduit Corp.
Tinley Park, IL

 

 

 

 

0507_probsolvers_commtestState-of-the-Art Vibration Analysis

With the popularity of its vb3000™ portable vibration analysis tool in mind, Commtest has engineered its all-new vb7™ instrument’s electronics from the ground up. Designed by and for predictive maintenance professionals, the vb7 incorporates stateof- the-art components, sculpted into an especially comfortable, lightweight unit. The manufacturer notes that the all-in-one tool is suitable for every level of vibration analyst, from novice through expert. Its Ascent® software contains the collective experience of over 25 years of  expert in-depth machine fault analysis.

Commtest
Knoxville, TN

 

Centralized Mist Removal In A Box

0507_probsolvers_cecoAcid and other chemical mist can be removed with a minimal 99.5% effi ciency, using CECO Filters’ Mist Collector Systems (CMC). Mist cleaning is confi ned to a single room with this “boxed solution” design that can collect effl uent from several operations. According to the manufacturer, its fi ber bed fi lters provide up to 10 years of service life. Standard CMC units come in 18 sizes, with ACFM capacities ranging from 2,400 to 36,000.

CECO Environmental Corp.
Cincinnati, OH

 

Extreme Condition Computers

0507_problemsolvers6Glacier Computers notes that products in its new Everest series for harsh environments are ideal for both forklift and fi xed-mounted applications. These computers have passed thermal and reliability testing, have been HALT tested and have an MTBF of 40,000 hours. Screens are available in 10.4” and 12.1”. They also come with multiple processor options, a 6V to 60V isolated internal power supply and the ability operate in Linux and numerous Windows formats.

Glacier Computer
Amherst, NH

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147

6:00 am
May 1, 2007
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Viewpoint: Top Management Culture Change

My grandmother used to say “Nice words are seldom true and true words are seldom nice.” I do not sell engineering services, hardware or computer systems, so I do not need to be nice. In my role as an adviser and consultant, I must be honest. This means that I often must tell organizations what they need to hear and not what they want to hear—although I really try to do it in an as nice way as possible. Here are some true words to top management.

Anyone who has been involved in reliability and maintenance improvement initiatives for any length of time has heard that a culture change in work practices is necessary to deliver sustainable results. This is true—and these needed changes are the same as they were 30 years ago. So, why don’t all companies succeed with these types of improvement initiatives?

The culture change that is so talked about must first occur at the top level of the organization. If the president of a company tells the vice president of Manufacturing that he or she must cut the cost of manufacturing, this message will trickle down in the organization and the focus will be on cutting costs instead of doing something about measures that can drive down the cost. As many other contributors to this publication have noted, short-term savings followed by long-term losses will be the result of this culture. If a plant needs to save energy, no doubt heat recovery systems, better insulation, more efficient processes etc. will be considered and investments in these solutions will be made. Such investments, in turn, will drive down the use of energy. The only difference when it comes to maintenance cost reductions is that many of these do not require capital investments at all. It is more a matter of doing better with what you already have.

The resistance to accomplish more cost-effective maintenance is seldom in the Maintenance organization. Many Maintenance managers are in veritable “budget jails” built by management cultures that prioritize short-term savings ahead of long-term gains that can generate savings 10 to 50 times higher than the costs of deferring maintenance. To temporarily survive, these Maintenance managers will focus on cutting costs until such measures result in reduced reliability. As a consequence, he or she will be fired.

What a shame. We can’t afford not to implement measures that improve reliability, which, in turn, will drive down maintenance costs. It is, perhaps, the last significant improvement initiative we can make to stay competitive. The rest of the world buys modern equipment. With automation, it is easier than ever for anyone to learn how to operate this equipment. The real challenge lies in how well the equipment can be maintained and how reliable it will be.

Oh, yes, I generally get agreement from top management when I have the opportunity to talk with them. Agreeing with an idea and eagerly championing it, however, don’t necessarily go hand in hand. All too often, I hear the following: “We agree with you. Better reliability is our greatest improvement potential. But, we must first cut costs.”

The opinions expressed in this Viewpoint section are those of the author, and don’t necessarily reflect those of the staff and management of MAINTENANCE TECHNOLOGY magazine.

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6:00 am
May 1, 2007
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The Rise & Decline Of U.S. Auto Manufacturing

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Bob Williamson, Contributing Editor

While the U.S. automotive industry is enduring one of the most challenging eras in its history, foreign nameplate auto manufacturers in the U.S. appear to be flourishing. This reminds me of a similar situation: the rise and decline of the British automotive industry.

In the years following World War II (the very early ‘50s), the British automotive industry was the second largest in the world, and the largest exporter of automobiles and commercial vehicles. It exported more than the U.S. and was second only to the U.S. in auto manufacturing output. In fact, it out-produced any other country in Europe and any other industrialized country, save the U.S. Yet, by the late 1960s, it had embarked upon a precipitous decline, followed by “nationalization” in 1975.

In 2005, the last of the BIG British-owned auto plants, MG Rover, closed its doors, idling some 6,000 auto workers and severely undercutting another 20,000 supplier employees in the midlands of England. This sad event was punctuated with union leaders blaming mismanagement and the lack of government support—nevertheless, the doors still closed.

My lifelong fascination with British motorcars (especially the MG) sparked my interest in another story that made the news on March 28, 2007: The “First MGs Roll off Nanjing Automobile’s Production Lines.” Nanjing? As in China? Yes, China, the second largest, fastest growing automobile market in the world according to some sources…

Founded in 1947, Nanjing Automobile Group (NAG) is the oldest auto manufacturer in China. Today, it has 16,000 employees making cars, trucks and buses. The company clearly has big plans for its new acquisition, as evidenced by the fact that it produced its first MGs less than two years after purchasing the Brits’ ailing MG Rover firm and moving it to China!

NAG’s production goals include 200,000 MG cars plus engines and gearboxes in the High-Level New Technology Economic Development Zone located in a new $452 million manufacturing facility. The company has begun producing three models, among them the “MG-TF” reminiscent (by name only) of my own restored 1954 MGTF. While the original “MG” stood for “Morris Garage,” the new Chinese version stands for “Modern Gentleman,” which is meant to appeal to China’s rapidly emerging elite class. What’s even more interesting—especially for those of us in this country—concerns some other changes in the works. Apparently, NAG is planning to open an assembly plant in Ardmore, OK, USA.

Tough numbers Since the late ‘60s, in light of many historical labor, management and capitalization challenges, British auto-industry labor productivity had shrunk to only one-fourth that of the U.S. auto industry. Then, the reorganizing, nationalizing and dismantling began. Ford bought Aston Martin (recently sold), Daimler, Lanchester, Rover, Jaguar, Land Rover and Vanden Plas. BMW bought Riley, Standard, Dawson, Triumph, Autovia, MG Rover and Mini. Nanjing then bought Wolseley, Austin, Morris, Vanden Plas, MG Rover, American Austin, Princess and Sterling. What a list! Many of these names represent very strong brands, some them dating back to the late 1800s and early 1900s.

Speaking of past strength, for years, the MG Rover Longbridge plant was one of the most important factories in Europe, as well as one of the largest British-owned auto plants, employing over 22,000 workers in the mid ‘70s. In 1995, however, only 16,000 worked at the Longbridge plant. Ten years later, plant rolls had fallen to 6,000. Bankruptcy finally claimed MG Rover on April 7, 2005—just two years before NAG began rolling out MGs. Not too much left of the traditional British auto industry today…

Improving numbers
These days, a largely renewed British automobile industry is producing huge volumes of quality cars and trucks. In 2005, over 1.5 million cars and 200,000 commercial vehicles were produced with export sales of 74% and 63%, respectively. The Top Five auto makers in England today include: Nissan (The “Most productive car plant” in Europe for seven years running), Toyota, BMW (Mini), GM-UK and Honda.

  • GM and Ford are numbers one and two in commercial vehicle production.
  • Ford (including Land Rover) is the largest engine producer in the UK, more than double that of number two, Toyota.
  • Ford manufactures the largest number of cars and trucks sold in England ahead of Vauxhall (a GM company).

All of this proves that the auto workers in the UK today are capable of performing and producing at world-class levels, despite the decline and destruction of their traditional auto industry. We’ve been noticing similar trends on this side of the pond, too, for more than a decade.

I’ve seen it for myself, during a visit to the BMW plant in South Carolina, where two separate production lines (the BMW X-5 Sport Activity Vehicle [SAV] and the BMW Z4 sports car) recently were combined into a single line. In less than six weeks (over the Christmas/New Years break), the company literally gutted over a million square feet of this 11-year-old manufacturing facility and re-fitted an entirely new “single-line” process. Over the next 12 weeks, it ramped up to its current rate of 650 vehicles per day.

BMW undertook this radical modification to optimize production of the increasingly popular X5 SAV and adapt to changing seasonal demands for its Z4 model. Accordingly, I saw three to four X5s coming down the assembly line for every Z4. Almost every vehicle was different, too—different colors, wheels, interior and exterior trims, diesel or gas, basic or high-performance, domestic or export, left- or right-hand drive, coupe or convertible, etc. The combined line reflects an astonishing engineering and construction feat, as well as a significant logistical and workforce training success. This BMW plant is living proof that the U.S. workforce and leadership can do anything they put their minds to…certainly making us the most productive nation in the world. Refer to the following points to see how it works.

0507_uptime_img11U.S. productivity… Auto plant productivity is measured in a variety of ways across three operations: stamping, power-train and assembly. Let’s look at “hours per vehicle,” which includes ALL employees in the facility being measured—hourly, salary, direct and indirect.

In 2006 Nissan’s overall productivity per vehicle led the North American industry at 28.46 total labor hours/vehicle (HPV). Toyota’s was 29.40 HPV; Honda’s was 32.51; Chrysler Group’s was 33.71; GM’s was 33.19; and Ford’s overall productivity was 35.82 HPV. These types of statistics tell us that our auto industry can be competitive. Unfortunately, the cultures of some of our more traditional U.S. auto manufacturers significantly reduce their competitive edge.

0507_uptime2The most productive U.S. auto assembly plant (not including power-train and stamping) was Ford’s Atlanta operation, which turned out the Taurus and Mercury Sable (15.37 hours per vehicle). Ford, though, recently announced the closing of this plant. The second most productive plant was GM’s Oshawa #2 (16.08 hours per vehicle). But, like Ford, GM has announced plans to close this plant. The lesson here is that while “productivity” is essential, business success involves much MORE.

Additional factors pertaining to sustainable competitiveness include product sales volumes, operating costs, labor cost/hour, profit margins/ vehicle, production flexibility, future growth potential, labor relations, flexible work practices and distance from suppliers. Consider, too, the issues of “capacity utilization” and “profitability.”

Capacity utilization…
In 2005, in their North American operations, Toyota, Nissan and Chrysler were near full capacity (94%-100%), while Ford plants were only producing at 79% capacity.

Profitability…
Likewise, in 2005, Nissan, Toyota and Honda earned more that $1,200 pre-tax profit on every vehicle sold in North America, while Chrysler Group earned only $223. During the same period, though, Ford lost $590 and GM lost $2,496.

The rise and decline of the British automotive industry and the woes of the “Big Three” U.S. auto makers should provide some “lessons learned” for ALL U.S. manufacturers:

  • Market forces—Paying attention to customers and markets is as important as paying attention to the competition.
  • Business strategy—Manufacturing competitiveness demands that from time to time we fundamentally re-think how we perform work. (Design, build, work methods, marketing, sales, etc.)
  • Measures of success—Productivity, efficiency and quality are important, but are only part of a complex formula for business success. (Sales Revenue – Cost = Profit)
  • Hidden capacity—Capital asset utilization, or tapping the “hidden capacity” in a plant’s critical processes, must be a high priority. (Focus: Overall Equipment Effectiveness, MTBF, MTTR)
  • Equipment reliability—Poorly maintained, unreliable equipment can undermine almost all improvement initiatives in a capital-intensive business. (Higher costs, delayed shipments, interrupted flow, etc.)
  • Labor & management—Labor/management communications across and throughout the organization must be open, honest, continuous, and focused on business success, not individual or organizational agendas. (“We’re going to win or lose together.”)
  • Work methods—Restrictive work practices, outdated work rules and past practice can stifle creativity and innovation and lead to signifi- cant and irreversible losses. (“If you always do what you’ve always done, then you’ll always get what you’ve always got.”)
  • Standardized work—Consistent work procedures provide the basis for training and qualifying the workforce and drive out human variation shift-to-shift and crew-tocrew. (Drives out variation, improves efficiency, reduces errors, lowers cost, etc.)

Better numbers ahead
Historically, the auto industry has set the stage for manufacturing strategies across many other non-auto businesses. History repeats itself and history often tells us why things are the way they are today. Status quo, complacency and ignorance can kill a once thriving business. We can, and we should learn from history to avoid common pitfalls that have hurt businesses and their workforces. Successful businesses and workforces help communities and nations thrive. Let’s do our part in our businesses, plants, departments and crews to remain competitive and prosperous.

bwilliamson@atpnetwork.com

References

  1. The Rise and Decline of the British Motor Industry, 1995. Roy Church
  2. The Machine that Changed the World, (Chapter 2: “The Rise and Fall of Mass Production”), 1990. Womack, Jones, & Roos
  3. The Harbour Report 2006, Harbour Consulting
  4. The Society of Motor Manufacturers & Traders Limited (SMMT), the UK/England

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May 1, 2007
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Soution Spotlight: Zooming Technology

Municipal supervisors are increasingly turning to zooming, a pipeline inspection technique that delivers quick, comprehensive information about pipe condition using inexpensive equipment and few personnel. The goal of zooming is to rapidly classify infrastructure as either satisfactory or in need of maintenance, mapping, rehab or additional CCTV inspection. These classifications allow a supervisor to prioritize maintenance activities confidently, committing precious maintenance resources—inspection crawlers, cleaning trucks, cutters/rodders, GPS surveyors and grouting and relining crews—exactly where they’re needed most.

Very often, time, budget and resources keep a municipality from maintaining comprehensive, up-to-date information on the condition of pipeline infrastructure. Without a complete picture of infrastructure condition, however, it is difficult to prioritize and schedule maintenance activities. As a result, a vicious cycle of emergencies, including backups, collapses and overflows, can erupt unexpectedly. When this happens, these emergencies must be dealt with on a triage basis—often at great expense. Unfortunately, these incidents can detract from the inspection work that is meant to prevent them in the first place.

Zooming complements other inspection techniques, it doesn’t replace them. Inspection crawlers cannot be matched for their detailed, 360° inspection of pipe, but they move slower, require substantial investment and demand considerable manpower and overhead.

By contrast, zooming allows a single operator to make a rapid visual assessment of pipe using an inexpensive, ultra-portable zoom inspection camera. Such a camera identifies satisfactory regions of pipe, and also finds problem areas where detailed crawler inspection or other action must be taken.

Zooming’s simplicity is its power. A typical zoom inspection system consists of a camera, lamps, a positioning pole and a video display. Grasping the pole, an operator at street level lowers the camera into a manhole and orients it to look down an adjoining pipe. Starting with a wide-angle view, the operator slowly increases zoom so the camera’s view advances down the pipe. In this manner, an operator inspects the entire length of the pipe for anomalies, and then classifies its condition accordingly. With zooming, you don’t have to squander time and resources crawling every foot of pipe—you can deploy your crawler only where conditions warrant.

Sewer Technologies of Port Perry, ON—one of Canada’s leading trenchless sewer rehabilitation companies—finds that zooming with Envirosight’s QuickView and having the ability to conduct on-the-spot inspections affords it an edge on bid jobs with City of Toronto departments and agencies. The company’s estimates are much more accurate and it can assess job parameters very quickly. “We’ve used zooming technology to accurately assess infrastructure conditions without pulling in the big CCTV unit,” says Brent Giles, VP of sales and marketing at Sewer Technologies. “It allows us to rapidly assess the condition of the sewer lines in the contract and price them accordingly. The zoom camera is responsible for the increased growth of both our municipal and construction projects.”

Woolpert, Inc., a Dayton, OH-based engineering, geospatial and architectural consulting services firm, uses zoom cameras to keep abreast of manhole conditions. Zooming allows this company to capture unlimited digital images with greater magnification and illumination than a traditional camera. Woolpert also uses the QuickView to measures focal length, which is a helpful and accurate way to estimate the distance of a pipe defect from the camera. This ultimately allows crews to better estimate the location of needed repairs. Upon completion of the inspection, the operator classifies the pipe as “satisfactory,” or in need of additional CCTV inspection, new mapping, cleaning or rehabilitation.

Can it work for you?
Any operation with water systems to inspect can benefit from zooming technology. Although crawlers will always be essential to pipeline inspection, zooming simply helps you use your crawling capability more effectively and gives you an affordable option for maintaining a thorough, upto- date assessment of infrastructure condition. Savings in equipment costs, time, labor and resource allocation are all important factors for any organization, large or small. MT

Envirosight LLC
Randolph, NJ

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May 1, 2007
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Field Balancing

0507_field_balancing1For sure. It’s not good for every situation. When it is and when it’s done right, downtime can be reduced and dollars can be saved.

Today’s business environment, with its emphasis on maximizing plant output and efficiency, demands that machinery downtime be minimized. Excessive vibration adversely impacts the health of the affected machine and can shorten repair intervals, thus increasing downtime. The increased vibration also can lead to catastrophic failure, posing a threat to people and surrounding equipment. Unbalance is one cause of this vibration.

Most people observe the effects of unbalance in common rotating machinery like washing machines and ceiling fans. In these situations, restoring the proper balance may be as simple as rearranging a load of clothes or cleaning fan blades. Reducing or eliminating the unbalance in rotating plant equipment is usually more complex, however. Still, it often can be accomplished on site with the proper tools and techniques.

Is balancing the answer?
Attempting to balance a machine that has other problems may lead to unpredictable, possibly catastrophic results. Before attempting to balance a machine in the field, you need to determine the following:

  • Is unbalance the cause of the high vibration?
  • Is an in-place balance going to be sufficient, or does the rotor need to be removed for shop balancing, rebuilding or replacement?

A thorough inspection of the machine should be conducted and other causes of increased vibration should be corrected before balancing is undertaken. If the other defects are not corrected, satisfactory balancing may not be possible, or the correction may be short-lived. Some of the most common causes of increased vibration include:

  • Machinery support problems such as soft foot
  • Defects of mechanical transmission, such as loose or broken couplings, gear or pulley wobbles or cracked gear teeth
  • Bearing defects, including increased bearing clearances, non-uniform lubrication or non-uniform wear of friction surfaces
  • Shaft-line issues, such as misalignment or rubs (As we’ll discuss later, it is important to ensure the machine has reached thermal stability before measuring the effects of balance corrections.)
  • Rotor problems (Increased vibration can be the result of a shaft crack, machine fouling, or a broken or loose rotating component [i.e. blades, vanes, buckets, etc.].)

The best solution for conditions like these is to correct the root cause, rather than attempting to compensate for their effects by balancing.

Balancing the machine
Correcting unbalance is conceptually easy—place a corrective weight on the rotor to counter the effect of an excessive radial mass. Accomplishing this in the field, however, is usually less straightforward.

There are several software packages available to assist in developing balance solutions. They are particularly useful in solving complex, multi-plane balance problems or when the machine needs to be balanced for multiple operating speeds. Solving complex balance problems, though, is best left to properly trained and experienced technicians and is beyond the scope of this article.

Preparation…
Before the actual balancing begins, you must understand the machine’s normal mode of operation. The relationship of the machine’s normal operating speed to its “critical speed” is crucial to understanding the machine’s response to the unbalanced condition. Since we cannot directly identify the rotor’s “heavy spot, ” we must infer its location by observing the point of maximum radial displacement, the “high spot.” If a machine operates below its critical speed—that is, if it doesn’t go through a resonance point while accelerating to normal operating speed—the heavy spot will coincide with the high spot. As the rotor accelerates through the critical speed, the heavy spot and the high spot will separate until they are about 180o out of phase.

Measurements during balancing runs should be taken after the machine has reached thermal stability and when other conditions, such as load or bearing conditions, are as close to normal operation as possible. This minimizes the influence of other sources of vibration, such as a temporarily bowed rotor.

If the machine is to be balanced based on measurements at a single operating speed, the speed must be held steady during the balancing runs as the centrifugal force caused by the unbalance is proportional to the square of the shaft speed. If the machine is equipped with sensors to measure the shaft speed and determine the phase and amplitude of vibration, it is better to collect measurements over a transient event, especially if the operating speed is above the machine’s critical speed. The collection of transient measurements allows for better analysis of the influence of weight changes on the machine, particularly near resonance. (This article focuses on the constant speed method since many 0507_maintenancelog2common smaller machines are not equipped with permanently installed vibration monitoring equipment.)

For machines that lack installed vibration measurement equipment, you will need to measure vibration and shaft speed. Use the measurement points specified by the equipment manufacturer. If not specified, use a point, such as a bearing end cap where the vibrations are transferred from the shaft to the machine casing. A phase reference also will be needed to determine the angular position of maximum displacement.

Before taking measurements, the trial weights and attachments should be prepared. Again, the manufacturer will usually specify the weight placements and may even prepare locations, such as balance holes or dovetailed slots, on the rotor to place balance weights. If the weight placements are not specified, then the weights should be attached on an accessible rotating surface.

0507_maintenancelog3

All weights should be held rigidly in place to prevent them from shifting or flying off during operation. Either of these events will invalidate a balance run. Moreover, if a weight flies off, it may present a hazard to people or nearby equipment.

If you have no reliable prior balancing data, the first trial weight should produce a centrifugal force not greater than 10% of the weight of the rotor. This limit is imposed because the addition of weight to an unfamiliar rotor may cause undesirable vibration during startup, particularly near resonance.

If there is more than one balance plane, a separate trial run must be used for each plane. The required correction weights are calculated independently for each plane. The verification run is performed after all the individual correction weights have been calculated and applied.

Determination of baseline condition…
With the machine at normal operating conditions, measure the vibration. Determine the amplitude and phase of maximum vibration and plot on a polar plot. Furthermore, record the condition of the machine—temperatures, rotor speed, process state, etc. All information recorded during the balancing procedure should be retained to facilitate future balancing procedures.

Calibration or trial run…
Install a calibration weight (Wcal). Record the weight and position. Bring the machine up to normal operating conditions. The more closely you can duplicate the conditions of the baseline run, the better. Measure and record the machine’s vibration response to the weight. Plot the resulting response vector on the polar graph.

Calculation of balance weight…
Calculation of the balance weight is done with vectors. Subtract the baseline response vector O from the trial run response vector TR. The resultant vector C is the response due solely to the calibration weight. The correction weight should be placed to produce a desired response vector – O that is equal in magnitude and opposite in direction from the baseline response.

The size of the correction weight (Wcor) is calculated by multiplying the size of the trial weight by the ratio of the amplitude of the baseline run vector to the trial weight vector. The correction weight is placed at an angle equal to the angular difference of the desired response vector and trial weight vector. If the trial weight was placed at a position other than 0Y, add this angle to the angular difference to determine the correction weight position. Apply the correction weight to the machine (see Fig. 1).

Verification and documentation…
Bring the machine up to normal operating conditions, then measure and record its response to the correction weight. Verify that the vibration has changed as expected and is within tolerance.

One correction may not produce the desired results. There often are small errors in vibration measurements, differences in the parameters (size and placement) of the actual correction weights compared to the calculated ones or other influencing forces. These small variances may require the addition of a trim weight.

The size and position of the trim weight is calculated in the same manner as the correction weight. Another validation run is required after the trim weight has been applied. (Keep in mind that zero or near-zero vibration is not the end goal as achieving this state would usually involve several iterations. In most cases, there are some manufacturer- recommended or ISO-recommended acceptable vibration levels.)

Once the final weights are placed, document the steps of the balancing process. This documentation can serve to reduce the number of runs in future balancing events. In typical balancing events, the majority of time is spent either securing the machine to make the required adjustments or bringing the machine back up to speed and reaching thermal stability and normal operating conditions. Eliminating just one run can shave hours or even days off the balancing job—which means the machine can be returned to profitable operation more quickly.

A quick case study
The importance of having good machine balance data cannot be overstated—even if it’s not for the machine in need of balancing. Consider the following situation involving a gas turbine at an integrated cogeneration plant that powers a combined refinery and chemical complex. Downtime costs in such facilities are enormous, often several million dollars a day.

One of the two gas turbines in this facility began to exhibit high vibration levels. Unbalance was determined to be the most likely source of the problem. Since this machine was fairly new, there was no previous balance information associated with it.

This machine needs a two-plane balancing. With no balancing history, however, a two-plane balance would normally require at least three runs—one trial run for each plane and the correction verification run.

Fortunately, machinery diagnostic engineers and rotor dynamic experts were able to use a database of similar machines and calculate the required correction weights. This allowed the machine to be balanced in just one run. The owner/operator noted that the savings in this case were “…well over a million dollars.” [Ref. 1]

References

  1. Y. Lee and W.C. Foiles, “One-Shot Balancing for a Gas Turbine,” ORBIT Magazine, pgs. 5-13, Vol. 25, No. 1, 2005

Patrick Hamilton is a licensed Professional Engineer with 20 years of experience in plant operational and maintenance management. Prior to joining GE Energy, he spent 12 years in the U.S. Navy, which included service as the Engineer Officer of a nuclear submarine. GE Energy’s optimization and control group includes the Bently Nevada™ Asset Condition Monitoring and Optimization and Control Services product lines. In addition to providing hardware and software solutions, the company has an MDS (Machinery Diagnostic Services) group to assist in solving complex machinery problems.

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