Archive | Lubrication

172

7:29 pm
February 18, 2015
Print Friendly

The Inner Life of Bearings, Part 1: How Lubrication Really Works

What some personnel don’t know can hurt your equipment and processes. Expert advice bears repeating.

By Neville Sachs, P.E.

As a facility considers implementation of a sophisticated lubrication program, it’s not uncommon for someone to strongly insist that “oil’s oil,” and that “all our applications can be handled by one multi-purpose grease.” The numbers of mineral-based and synthetic lubricants in vendor catalogs run counter to those arguments. Manufacturers commonly list over 40 greases and lubricating oils, available in at least 10 viscosity ranges. Categories include aviation oils, automotive and light truck engine oils, gear oils, compressor oils, heavy-duty engine oils, gas engine oils, turbine oils and way oils, to name but a few.

Accounts of someone’s brother-in-law or friend who “never changed the oil in his truck,” or “used ATF (automatic transmission fluid) in his car engine,” may be more urban legend than truth—and they don’t reflect lasting solutions: Some oils will temporarily work in an incorrect application, but they won’t provide long, reliable service. Unproven theories and/or ill-informed theorists should carry no weight in a facility’s approach to lubrication, but often do.

Overcoming the harmful impact misinformation and flawed thinking can have in today’s industrial operations calls for continuous emphasis on correct information. This two-part article recaps lubrication fundamentals that have been covered in these pages before. But when it comes to the bearings in your plant’s critical equipment systems—and the ever-changing workforce that may be maintaining them—regular reinforcement of these principles is crucial.

Back to the basics

Friction, lubrication and wear (i.e., “tribology”) constitute a complex body of knowledge that involves, among other things, three basic types of bearings with very different “wear-prevention” mechanisms and critical point-of-contact temperatures.

For lubrication to be effective, a bearing’s mating pieces must be separated. In conventional plain bearings and rolling element designs, this separation depends on the lubricant’s viscosity. The success of a sliding application is governed by the lubricant’s additive package.

Screen Shot 2015-12-18 at 1.31.29 PM

One of the most important aspects of lubrication is relative lubricant film thickness. Figure 1 illustrates this film thickness by depicting two pieces of metal as viewed through a microscope. Note that these pieces are not perfectly flat: R1 and R2 refer to their average roughness measurements. Between the two pieces, h is a measure of the separation resulting from the lubricant. Represented by the symbol λ, relative film thickness is calculated as:

λ =  h/(R12 + R22)1/2

Within reason, the greater the λ value, the lower the wear rate.

Screen Shot 2015-12-18 at 1.31.42 PM

Another important principle of lubrication can be seen in the Stribeck Curve in Fig. 2. Developed in 1902 by the German engineer and scientist Richard Stribeck, it shows how the coefficient of plain-bearing friction varies with surface speed and lubricant viscosity. Referring to the diagram, we can see that when a lubricant is supplied and the surface speed between two properly designed parts increases, the friction first rapidly drops off,  then slowly increases. This curve is also helpful in that it shows the three lubrication zones—which basically equate to the three most common bearing types. Low-speed plain bearings and sliding applications fall into the boundary-friction zone; ball and roller bearings into the mixed-film (elastohydrodynamic) zone; and high-speed plain bearings into the full-film zone.

Screen Shot 2015-12-18 at 1.31.53 PM

The plot in Fig. 3 uses somewhat different terminology than the Stribeck Curve for the three lubrication zones. It also shows the effect of relative film thickness on wear rates. Hydrodynamic lubrication typically is seen in plain bearings, i.e., in automobile engines and large turbines and generators. Elastohydrodynamic refers to the lubrication mechanisms seen in higher-speed rolling element bearings. Sliding (boundary-friction) lubrication occurs in applications like piston rings, wire ropes and slow-speed rolling element bearings.

How different bearing types operate

Screen Shot 2015-12-18 at 1.32.07 PM

Lubrication occurs in the three categories of bearings by way of very different mechanisms. The diagram of a hydrodynamically lubricated plain bearing in Fig. 4 shows a journal that rotates inside the bearing. (The bearing can be made from any one of many materials, which will be discussed in Part 2 of this article.) Preferably, oil is fed into the gap at the unloaded area of the bearing, whereupon it is swept around the journal. In the process, the oil viscosity develops a wedge that separates the two pieces. The typical film thickness is in the order of 0.01 to 0.05mm (0.0004” to 0.002”). While this type of bearing can withstand tremendous pressures, as the load on it increases, internal shearing of the oil film increases the lubricant temperature, the viscosity drops and leakage increases.

Photo 1: As shown by the uneven wear pattern on this pair of gas-engine main bearing inserts, misalignment and excessive clearance will reduce the life of plain (i.e., hydrodynamically lubricated) bearings.

Photo 1: As shown by the uneven wear pattern on this pair of gas-engine main bearing inserts, misalignment and excessive clearance will reduce the life of plain (i.e., hydrodynamically lubricated) bearings.

Designing a hydrodynamically lubricated bearing primarily involves understanding operating temperatures and viscosities and the need to create a system that delivers more oil than can readily leak out from the edges of the bearing. Misalignment and excessive clearance will greatly reduce the bearing’s life. (As shown in Photo 1, the uneven wear pattern on a pair of gas-engine main bearing inserts contributed to their rapid degradation.)

Screen Shot 2015-12-18 at 1.34.50 PM

As can be seen in Fig. 5, rolling element bearings, ball and roller bearings, have vastly different lubrication mechanisms.

In the operation of a ball or roller bearing, as the element rolls along and traps that easy-flowing oil, viscosity changes significantly (increasing by a factor of 10,000 or more and becoming stiff enough to actually separate the rolling element from the ring). As this occurs, the mating areas of the element and ring flatten elastically to distribute the load across the film and support continued operation. While the lubricant film separation isn’t great (less than a micron [≈0.00004”]) and the pressure is tremendous (typically more than 2GPa [150,000 psi]), the overall effect is substantial: Contact forces are distributed over a much greater area, fatigue stresses are reduced and bearing life is increased.

Photo 2: The inner ring of this spherical roller bearing exhibits the fine-grained spalling that results from inadequate lubrication.

Photo 2: The inner ring of this spherical roller bearing exhibits the fine-grained spalling that results from inadequate lubrication.

Two important factors in this process are lubricant temperature—i.e., the lower the viscosity the thinner the film—and lubricant cleanliness: Because the lubricant film is so thin and the pressures so high, solid particles and water have huge effects on component lives. (Photo 2 shows the inner ring of a spherical roller bearing and the fine-grained spalling that results from inadequate lubrication.)

Photo 3: The dark bands alongside this bearing’s ball paths are oxidized oil deposits.

Photo 3: The dark bands alongside this bearing’s ball paths are oxidized oil deposits.

With the third lubrication mechanism, i.e., in sliding bearings, additives are more critical than oil viscosity. Some additives, such as oxidation inhibitors, are designed to improve oil life. Others, such as anti-wear and high-pressure (EP) additives, are designed to improve oil performance. (The dark bands alongside the ball paths shown in Photo 3 are oxidized oil deposits.)

Screen Shot 2015-12-18 at 1.32.13 PM

Although selection of the correct additive package is important for the lubrication mechanisms shown in Figures 4 and 5, with sliding applications (Fig. 6), the correct additive combination is the key to low wear rates and long component life.

The diagram of contacting metal pieces shown in Fig. 6 could represent piston rings or, alternately, rolling element bearings operating at a speed too low to generate a viscosity conversion. To reduce wear rates in these components, two general types of additives are used: anti-wear (AW) and, as they are known in North America, extreme pressure (EP). (Note: In the rest of the world, extreme pressure additives are characterized as “high pressure.”)

Anti-wear additives are almost always polar molecules—meaning they are compounds that have a positive charge on one end and a negative charge on the other. Because of their polar nature, they are attracted to the metals. An example of this is oleic acid, a fatty acid where one end of the molecule is attracted to the metal and the other end is repelled. With relatively low pressures and low contact temperatures below 100 C, these additives provide a cushion between the two sliding pieces. But at higher-point contact temperatures (and higher pressures), they lose strength and EP additives are needed.

There are two general types of EP additives: liquids and solids. Liquid additives in EP oils are generally compounds of sulfur and phosphorus, and sometimes chlorine, that, when heated, form hard semi-metallic coatings that provide the actual wear resistance. Solid additives found in greases commonly include molybdenum disulfide, graphite and other materials designed to slide between opposing metal parts to provide wear resistance. The proportion of solids varies with individual manufacturers. When using EP lubricants, keep these points in mind:

  • When water is present, some additives will form extremely corrosive chemicals.
  • Solid EP additives tend to disrupt the viscosity transformation that’s critical to higher-speed ball and roller bearing lubrication. (However, if those ball and/or roller bearings are in a gearbox, using EP additives to help preserve the gears is usually much more important than the life of bearings that can be easily monitored and replaced.)

Coming up

Part 2 of this article will focus on oil and grease selection for an application; why speeds and temperatures are important; and why operating environments are critical in determining lubrication frequency.

Neville Sachs has extensive experience in machinery reliability and lubrication. The author of two books on failure analysis and a contributor of sections to other books, he has also written more than 40 articles. A Professional Engineer, Sachs holds STLE’s CLS certification, among others. Contact him at sachscracks@att.net.

72

7:24 pm
February 18, 2015
Print Friendly

From Our Perspective: Revisiting the Power of Twofers and Threefers

kennewmugBy Ken Bannister, Contributing Editor
kbannister@engtechindustries.com

Prior to the Christmas break I was fortunate to visit England with my eldest son and spend quality time with my elderly parents who were celebrating their 60th wedding anniversary. Because geography has rarely favored such multi-generational get-togethers and, taking advantage of the situation as parents often do when grandchildren are around, they relished “spilling the beans” about my youthful traits and transgressions—much to the delight of my adult son! During one of their reminiscences, I experienced a “eureka moment,” recognizing a very specific trait instilled in me as a child that I still employ today. 

As a post-war-England baby boomer, I lived over half my childhood in a frugal world of government rationing with little money to spare for luxuries. With two competing siblings, I was taught that if I wanted something special, I had to present a rational reason for granting my request—essentially make a business case built on need first, want second—for the request to even be considered. In the early days, such prized requests included listening to a rock n’ roll radio program (and, later, television programs), staying up late, using the phone, borrowing the family car, etc.

I learned early on that success was more likely when I reasoned with a holistic view, which my parents called as my “twofer and threefer” approach. I always asked for something I thought was obtainable, and tried to make it easier for them to say yes by spelling out a minimum of two or three benefits for granting my request. For example, I recall my reasons for wanting to watch
Top of the Pops (Britain’s answer to The Ed Sullivan Show) as 1) it allowed me to watch and listen to musicians and study guitarists’ finger positions that would help me learn the guitar; 2) my siblings could watch it with me, and my parents could spend a half hour together in peace; and 3) music would help me become a better person. My approach usually worked. I loved that show!

Thus, it was interesting to see that when the ISO 55001 Asset Management Standard was released last year, it also looks for an asset-management program to deliver its own twofers and threefers. It tasks the organization with demonstrating proof of how its asset-management strategies, plans and objectives directly and holistically align with corporate objectives and culture. It also recommends the same program be designed to meet the identified needs of all program stakeholders.

When an industry employs mechanical equipment, one of the least expensive and most productive means of improving asset function and management is through the design and implementation of a best-practice asset lubrication-management program. This produces obvious internal benefits—increased asset availability, reduced downtime, reduced bearing failure, etc.—that result in a measurable twofer: one for maintenance (by reducing maintenance costs), and one for production (by increasing production throughput). There are other benefits, too,  which can include:

  • Reduced purchase costs through lubricant consolidation
  • Reduced lubricant and replacement-bearing inventory costs
  • Reduced lubricant stock-rotation requirement
  • Increased inventory real estate
  • Reduced lubricant waste
  • Reduced bearing friction
  • Reduced carbon footprint and emissions
  • Improved ability to meet ISO 55001 and other standards requirements

If you are looking to validate the implementation of an asset lubrication program, consider all your stakeholders and position your request based on how the intended program will benefit each. Make it easy for the corporation to say yes. I guarantee you will find more than the usual twofer or threefer in your reasoning, and will be more successful in future requests. Good luck!    

50

9:52 pm
December 14, 2014
Print Friendly

From Our Perspective: The Study

kennewmugBy Ken Bannister, Contributing Editor

In 1964, Professor H. Peter Jost published the results of the world’s first major study on the effects of “Lubrication, Friction and Wear.” His research had been commissioned by the British government, which was keenly interested in these effects on the nation’s Gross Domestic Product (GDP).

Jost’s study proved to be sensational. Industry was astounded by its documentation of the costs associated with poor or ineffective lubrication practices. He found that reversing the trend and making lubrication practices more effective could conservatively save British industry 20% in maintenance and repair costs; 20% in lubricant costs; 7.5% in energy costs; and significant downtime. For his part, Jost received a knighthood and, more important, assured his legacy by naming the study and practice associated with lubrication, friction and wear: He called it “Tribology.”

Six years later, in the hallowed halls of Massachusetts Institute of Technology (MIT), Dr. Ernest Rabinowicz built on Jost’s work and completed his formative study on the “Design, Friction, and Wear of Interacting Bearing Surfaces.” This led to his publication of the seminal tribology text Friction and Wear of Materials, and assurance of his legacy as a lubrication pioneer with the “Rabinowicz Law” that stated, “Every year, 6% of the GDP is lost through mechanical wear.” In his studies, Rabinowicz concluded that 70% of bearing-surface loss of usefulness (bearing failure) is attributed to mechanical wear (50%) and corrosion (20%). Both of these wear mechanisms, we now know, are entirely preventable with Good Lubrication Practices (GLP).

Fast forward 50 years: Great strides have been made in the science of Tribology, particularly in the fields of lubricants and bearing-surface technology—progress that has been driven primarily by the automotive industry and U.S. space program. Additionally, the past 10 years have witnessed significant growth in lubrication awareness through training and certification of lubrication-related personnel by the International Council of Machinery Lubrication (ICML), the Society of Tribologists and Lubrication Engineers (STLE), and the International Organization for Standardization (ISO). Lubrication-delivery systems have also greatly improved, especially in the area of electronic control and programming, and are now affordable to the point that their return on investment (ROI) can be measured in weeks and months in most cases.

Yet, despite our innovation and knowledge in these areas, in my capacity as an asset-management and lubrication specialist, I still see too many needless lubrication-related failures and ineffective lubrication practices in every type of industry. But why? Industry needs more than anecdotal information.

With that in mind, I recently worked with the editorial team at Maintenance Technology magazine to develop and conduct a comprehensive (37-question) online reader survey entitled “State of the Nation’s Lubrication Practices.” The Lubrication Nation’s response to it has been significant.

We asked the who, what, when, where, why and how pertaining to your lubrication practices and received a healthy number of fully completed responses from a variety of industry sectors, including manufacturing, automotive, natural resources, pharmaceutical, food and facility management. The results are telling.

In the next few pages, we share some of what our survey told us about North America’s lube practices and provide an initial explanation of what those responses indicate. Look for upcoming articles in Lubrication Technology and on LubricationTechnology.com that respond to and expand on the needs revealed by the study.

For now, please turn to page 4 to read this first article. Over time, I challenge survey respondents and those who were unable to participate in this study to use its findings as a lens through which to view your respective organizations’ states of lubrication; resolve to make positive changes in your practices; and always celebrate your lubrication-program successes. Good luck!    

56

9:49 pm
December 14, 2014
Print Friendly

Optimize Machine Health with Precision Lubrication

lt1214f2-1

By Jane Alexander, Managing Editor

Whether you call it world-class, best-practice or use the currently popular term—precision—the procedure is the same when it comes to lubrication: using the right lubricant for your equipment, in the right amount and at the right frequency. And it requires that lubricant condition be managed.

Jarrod Potteiger of Des-Case explains that the precision approach also excludes two common lubrication practices: the default use of high-quality lubricants and routine over-lubrication. Many steps are required to get a significant benefit from high-performance lubricants in most machines, and performing lubrication tasks at intervals shorter than those required is a waste of time and resources at best, and can lead to component failure at worst. Precision lubrication requires that lubrication PMs be rationalized and optimized to ensure that lubricant conditions and amounts will provide the most effective lubrication. Potteiger offers the following advice on developing and maintaining successful precision-lubrication programs.

Lubricant specs

Program success starts with having the right lubricant—oil and/or grease—in every component. This is probably the simplest precision-lubrication aspect to achieve, yet is rarely done right. Lubricants are often specified incorrectly due to initial misinterpretation of OEM specs or, over time, due to a misdiagnosed problem or misplaced perception of benefit. Whatever the reason, Potteiger says, it’s usually prudent to go through each lube point in a facility and verify or correct the lube specs if it has not been done recently. When specifying lubricants, however, he adds that it is important to not just create a proper spec, but to define the methods by which decisions are made. Doing so eliminates future questions about the accuracy of the selection.

With regard to accuracy, Potteiger notes that while it’s not uncommon for machines to have the wrong oil in them, grease is a different story. As he describes the situation, “Most maintenance professionals don’t really understand grease.” Rather, they tend to characterize different greases by the type of thickener they use or by vague terms such as “hi-temp.”

Grease, though, is actually just thickened lubricating oil. The purpose of the thickener is to hold the lubricating oil in place (like a sponge)—not to provide lubrication. For the most part, grease specification should use the same processes as oil, but with additional considerations.

According to Potteiger, the misunderstanding of grease runs so deep that many OEMs don’t provide adequate descriptions for grease specification. In a precision-lubrication program, each lubricated component should have a generic lube spec that identifies viscosity grade, base oil type and the proper additive system. Grease-lubricated components should have the same, and should include thickener type and NLGI grade.

Application amount and frequency

With the proper lubricant installed in every application, the rest of a precision-lubrication program is designed to ensure the proper condition of those lubricants. Lubricant condition has two components: 1) that the lubricant be suitably free of contaminants; and 2) that the lubricant be in acceptable condition from a chemical and performance standpoint. For oil, this means maintaining the proper oil level and replacing it at the right frequency. For grease, it means installing the correct amount initially, then replenishing with the correct amount at the right frequency going forward.

Oil-fill levels and replacement frequencies are typically pretty straightforward, Potteiger says. “OEM instructions usually cover this adequately.” Correct oil levels, however, can vary for similar components, based on factors such as their orientation or operating speed. OEM oil-level instructions should be reviewed carefully to determine that there is either a single, correct level or that the correct option has been chosen if there is more than one.

Oil-replacement frequencies can also vary. Typical recommendations are conservative because, to be on the safe side, the OEM must recommend for harsh operating conditions. Actual, useful oil service life, however, can vary dramatically. Factors such as high operating temperatures, wear debris, moisture and sludge can shorten oil life. In a given application, the severity of these items, or lack thereof, can alter useful service life by an order of magnitude. Nonetheless, most oil-change frequencies for similar equipment can fit into neat periods, such as three, six or 12 months, and should only be scrutinized when severe conditions exist. Use of oil analysis allows for oil to be replaced based on actual conditions, which, in turn, removes guesswork.

As with grease selection, grease application amounts and frequencies are often wrong. For grease-lubricated bearings, Potteiger says, the most common mistake is “too much grease too often.” This is especially true for electric motors. “The real problem,” he explains, “is that most people don’t realize they have a problem.” When the problem is recognized, correcting it is a simple, though time-consuming process that can depend on tapping several resources for information, including bearing manufacturers, electric-motor manufacturers and lubrication textbooks, among others.

To determine the proper initial fill amounts and replenishment rates for grease-lubricated bearings, one needs to know the bearing sizes, speeds and types. Secondary considerations such as temperature, vibration, contamination and bearing orientation are also important to know for fine-tuning default values. Whichever combination of factors is chosen, it is essential to use a consistent source for both amount and frequency determination.

Contamination control

While it’s a given that use of the correct lubricants—and ensuring that they are in suitable chemical condition—is a pre-requisite for success, Potteiger notes that big (i.e., positive) changes in the service-life of components can be achieved through the aggressive management of contamination. In most cases, he notes, the amount of particle contamination in oil is the single biggest factor that determines how long a lubricated component will last. “Many maintenance professionals,” he says, “don’t realize they have a problem with lubrication-related failures because they don’t properly characterize the failure or root cause. Most equipment failures are, in fact, lubrication-related.”

lt1214f1-2

The normal way in which most machines fail is to “wear out,” but wear rates can be controlled, and the primary purpose of lubrication is to do just that. Studies show that approximately half of lost machine life is due to mechanical wear—and, as shown in Fig. 1, approximately 80% of mechanical wear is caused by particle contamination in the oil. It therefore stands to reason that when particle contamination is reduced, wears rates go down and component service life goes up.

Effectively controlling contamination requires, among other things, a good strategy. Potteiger says that while implementing a contamination-control policy may take time and effort, developing the strategy is rather simple:

Step 1: Identify goals in the form of target-lubricant cleanliness and moisture limits for different types of machinery.

Step 2: Identify all potential measures to improve cleanliness.

Step 3: Verify the effectiveness of implemented measures with oil analysis.

The two basic approaches to controlling lubricant contamination are exclusion and remediation. Of these, contamination exclusion is typically the least costly and should always be the first—and sometimes only—measure taken. Improvements to contamination removal capabilities should be considered when exclusion measures prove inadequate.

Contamination exclusion

Preventing contamination in lubricated equipment starts with new oil. For several reasons, new oil from drums or bulk deliveries usually contains anywhere from 2 to 20 times the amount of particles that is acceptable for most lubricated equipment. This is not an indictment of lubricant suppliers, but a fact that must be addressed before cleanliness targets in machinery can be met.

In general, Potteiger says, it’s good practice to maintain the cleanliness of new oil at least two ISO codes cleaner than the targets for in-service oil. This will allow modest amounts of contamination to be introduced during transfer and application while still meeting the targets. Unfortunately, typical handling methods will add a lot more than a modest amount of contamination. Thus, for the average plant, lubricant-handling methods and equipment will need to be revised and upgraded to ensure oil cleanliness.

For small sumps that are filled from oil-cans, transfer containers should be made of plastic, sealed, marked for product type and maintained in a clean state. The use of funnels should be avoided when possible and separate handling equipment should be maintained for different lubricants. The simplest and most effective way to ensure that new oil additions are clean is to simply filter it as it is applied using portable filtration equipment. To do this, the reservoirs must be fitted with the proper fittings to effectively attach the transfer equipment.

Another effective and essential technique for preventing contamination is to stop airborne contaminants from entering machine reservoirs during service. Most reservoirs exchange air with the ambient environment regularly, and if that air is not filtered it can be a major source of contamination for both particles and moisture. “The good news,” Potteiger says, “is that this is one of the easiest problems to address through good headspace management.”

Headspace management is the process of managing the condition of the air that enters a sump when oil level is lowered or air pressure drops when the temperature goes down. Replacing typical OEM breathers with high-quality desiccant breathers will strip particles and moisture from the air as it enters the sump to a point where contamination is negligible. Other methods include purging reservoirs with clean, dry air or nitrogen to maintain positive pressure in the headspace, or using expansion chambers that effectively capture and re-circulate the air in the headspace.

For many common applications, such as small gearboxes and process pumps, contamination exclusion is the only practical approach. This makes good application practices and headspace management all the more crucial.

Contamination removal

Sometimes contamination exclusion is not enough. High ingression rates and/or sensitivity to contamination in some machines like hydraulics and those with circulating lube systems require improvements in contamination-removal capabilities as well. “When this is necessary,” Potteiger says, “the first step is to review existing filtration to see if the filters can be upgraded in terms of pore size, capture-efficiency or other factor.” If this is not the case, or if filter upgrades don’t achieve the desired results, offline filtration may be the best option.

Offline filtration systems, commonly referred to as kidney loops, offer several advantages over active filters in the oil-circulation system. Offline filtration is cost-effective because the kidney loop functions independently and is not bound by the flow rate and pressure requirements of the active circulating system. These systems also allow the use of alternative filter media and types such as depth media, electro-static, water-stripping and others that can remove more than just hard particles.

For critical applications where moisture contamination cannot be prevented, water-removal options include vacuum dehydrators, centrifuges, coalescing filters and water-absorbing filters. Vacuum dehydrators in particular are extremely effective at removing water from lube systems to the point that its presence is insignificant. Additionally, most vac systems include high-efficiency mechanical filters to remove particles, which makes them an excellent choice for contamination removal in any application where the cost can be justified.

Condition monitoring

Although most plants use oil analysis in some fashion, Potteiger believes few reap its full benefit. He views effective oil analysis as “the perfect condition-monitoring technology for proactive maintenance” because it can positively identify and quantify the top three root causes of machine failure: particle contamination, moisture contamination and use of the wrong (or degraded) lubricant.

Oil analysis is not difficult, Potteiger says. “Even a novice can easily learn to use viscosity and elemental analysis to verify oil for use in a machine.” Tests such as acid number, FTIR and QSA can be used to determine if the oil is suitable for use or has degraded, while particle counts and moisture concentrations require no deciphering at all. “Good oil analysis,” he continues, “depends on good oil-sampling practices, data analysis and data management, and with the proper education all of these things can be easily achieved.”

Summary

Potteiger sums up precision lubrication as a fundamental component of any good reliability program. Although it can take time to transform an average program into a great one, he reminds end-users that the fundamentals are simple: “Use the right lubricant, in the right amount, at the right frequency, maintain the lubricant’s condition with aggressive contamination control and verify condition with effective oil analysis.”

Jarrod Potteiger, Sr., is Technical Consultant/Manager–Training Services for Des-Case Corp. (descase.com).

61

8:41 pm
December 14, 2014
Print Friendly

The State of the Lubrication Nation

lt1214f1-1

While our in-depth study of lubrication practices in North American industries provides some good news, it also reveals much room for improvement.

Lubrication plays a significant role in the success of any industrial plant or facility that operates moving equipment. With the “wheels of industry” literally relying on lubricant film mere microns in thickness, it is essential to recognize the need for good lubrication practice and implement a quality lubrication-management program.

As noted this month in the “From Our Perspective” column, thanks to studies performed by the Massachusetts Institute of Technology’s (MIT) Dr. Ernest Rabinowicz, we know that up to 70% of all moving equipment failures (loss of bearing surface usefulness) are caused by mechanical wear and corrosion, which can be directly and/or indirectly attributed to ineffective lubrication practices. Both of these practices, we also know, are entirely preventable with Good Lubrication Practices (GLP).

In practical terms, the impact of lubrication is astounding. GLP translates into asset availability, reliability, uptime, throughput, energy savings, carbon footprint reduction and profit. The Rabinowicz law states that “every year, 6% of the Gross Domestic Product (GDP) is lost through mechanical wear.” Applying Rabinowicz’s law to the 2014 estimated third-quarter U.S. GDP of $17.5 trillion, mechanical wear losses could amount to more than $1 trillion this year!

Determining North America’s ‘State of Lubrication’

To benchmark the current state of lubrication in North America, compared to accepted industry lubrication best practices, we created a comprehensive 37-question “State of the Nation’s Lubrication Practices” study and invited Lubrication Technology’s virtual subscribers to respond. To date, we have received 112 complete responses to this detailed survey, all from North America-based lubrication professionals.

lt1214f1-4

As depicted in Fig. 1, all major Industry types are represented, with Manufacturing as the largest sector at 32%. This is followed by the combined Natural Resources sector at 18% and the Automotive sector at 9%. The combined Food and Drug sector make up an additional 9%, with the Facility Management sector next at 8% and residual industries (the Other/Fleet sector) making up the final 24%.

Scorecard

The answers to all 37 questions were tabulated and averaged for all industry type sectors collectively, and for each specific industry sector, and scored out of 100. Table I shows how the nation scored on its lubrication practices.

lt1214f1-3

At an overall score of 43, these North American industry sectors have much room to improve on their lubrication practices. By a significant margin, the Natural Resource sector, with a score of 54%, leads the way. The good news is that both the individual answers and score levels demonstrate that lubrication awareness has been established.

System Review (Fig. 2)

lt1214f1-5

Individual questions in the survey are grouped into six lubrication-management program elements to enable the reader to understand specific areas requiring improvement. These elements are: System Review, Lubrication Personnel, Work Management, Contamination Control, Application Engineering and Safety. The first, System Review, asks if the company has had its lubrication practices professionally audited in the last three years. Professional audits open lubrication methods, processes and procedures to review by an independent resource skilled in developing best-practice lubrication programs so a customized improvement action plan can be developed.

Figure 2 shows that only 21% all sectors had been audited in the last three years. The most-audited sectors seem to be Automotive and Natural Resources, with 30% of both groups having been audited. The least audited is the Other sector, at 11%.

Another System Review component is the professional lubricant-consolidation exercise/program in which all lubricants on site are documented and analyzed to determine their necessity. This exercise is designed to consolidate and minimize the number of required lubricant SKUs, thereby reducing carrying and purchase costs, storage real estate, and the chance of causing lubricant cross-contamination through use of the wrong lubricant. This usually occurs just after or as part of the audit and, in this case, figures came out the same as those who say they were recently audited, with just 21% of all sectors performing a lubricant-consolidation exercise.

Lubrication Personnel (Fig. 3)

lt1214f1-6

Only 28% of all sectors combined use dedicated lubrication personnel, and only 12% of all sectors combined use only professionally certified (by ICML, STLE or ISO) lubrication personnel to administer their programs. Again, the Resources sector leads with 30% of this group using only professionally certified lubrication personnel. The Facilities sector comes in second with 20%. Manufacturing ranks the lowest: Only 1% of this sector’s lubrication personnel are professionally certified.

Certified and dedicated lubrication personnel appear to have made a difference with the Resource sector’s overall results.

Work Management (Fig. 4)

lt1214f1-7

Surprisingly, only 39% of respondents say they report all lubrication-related instances of machine failure or downtime. This may explain why only 42% of lubrication work is formally managed and tracked in a computerized maintenance management system (CMMS) on a work order and, of those, only 28% are specifically typed (designated) as lubrication work orders for reporting purposes.

Lubrication work orders are only effective if the work actually gets scheduled and completed in a timely manner. Only 28% of all respondents say they complete their lubrication work within 48 hours of WO issue and 29% of respondents review their lubrication PMs for task and schedule effectiveness on an annual basis.

Standard Operating Procedures (SOPs), designed to promote work consistency, are in use across all sectors for lubricants. According to the survey, SOPs are used at receiving by 42%; for manual bearing lubrication by 31%; for rotating lubricant stocks by 30%; and are used when taking oil samples for testing purposes by 26%. Again, the Resource sector is the predominant user of SOPs.

Oil analysis is used by 30% of respondents to determine oil-change intervals based on oil condition, and 43% say they perform regular quarterly (or less) cleaning and system checks on their automated lubricant-delivery systems.

Contamination Control (Fig. 5)

lt1214f1-8

Contamination control is arguably one the most critical aspects of lubrication management. Water, dirt and air all play their part in contaminating and destroying a bearing surface area and, unfortunately, much of it is introduced during the maintenance process.

From new, oil is relatively dirty and must be received correctly and filtered prior to use. Only 22% of all sectors have a lubricant cleanliness agreement with their oil suppliers. More than half—53%—say they do NOT reseal their bulk containers once opened to draw lubricant, and only 22% pre-filter their bulk oil prior to use. There are major opportunities for improvement in this area.

The better news is that 51% of all sectors use dedicated transfer equipment to eliminate cross contamination of lubricants, and 55% of all sectors use transfer equipment with closeable lids and spouts. It was great to see that 75% of all sectors store their lubricants in dedicated areas protected from the outside elements, and encouraging to see 61% of respondents always change/clean their filters when an oil change is performed.

Application Engineering (Fig. 6)

lt1214-f19

A crucial part of GLP is documenting all bearing-point locations and types, so their lubricant requirements can be calculated for application purposes and to help avoid over-lubrication of bearing(s).

Although a crucial part of the lubrication program, the process of locating lubrication points and identifying lubrication types is performed by only 36% of respondents. The Manufacturing sector takes the lead here with 57%, and the Automotive and Resource sectors are right behind with 55% and 53%, respectively. Unfortunately, only 45% of respondents say they have schematics or drawings for their lube systems, and only 9% have lubricant requirement sheets for every bearing in the plant.

The ramifications of the above figures are reflected in the 60% of respondents who say they experience grease leakage from bearings on the floor, and the 41% who experience noisy bearings, hallmarks of ineffective lubrication practices.

There appears to still be a lot of manual greasing performed, yet only 41% of respondents use only one grease-gun type in their plant to eliminate the delivery and pressure issues that arise when different grease-gun types are used. Furthermore, only 6% of respondents measure and label their grease-gun output in cc/cu.in to enable engineered delivery to the bearing point, which is stated on only 20% of all greasing work orders.

Safety (Fig. 7)

lt1214f1-9

Almost every survey respondent indicated that his or her company is concerned about workforce safety. For example, 90% say they have easy access to lubricant Material Safety Data Sheets (MSDS). Additionally, 87% of all sectors operate a formal spill program, and 76% operating a formal waste-lubricant program. This is good news for personal safety and the environment!

Follow-up

Many of our study’s respondents are aware of the elements required to achieve a successful best-practice lubrication-management program and reap the benefits such programs offer and deliver. In upcoming issues of Lubrication Technology, we will address these issues in greater depth and discuss how to build on the foundation that many readers may already have in place at their facilities. The goal, regardless of sector, is to move all industries toward GLP.

Contributing Editor Ken Bannister of ENGTECH Industries, Inc., is a Lubrication Management Specialist and author of Lubrication for Industry (Industrial Press), and the 28th Edition Machinery’s Handbook Lubrication section (Industrial Press). He can be reached at 519-469 9173 or kbannister@engtechindustries.com.

1679

7:37 pm
December 1, 2014
Print Friendly

Lubrication Checkup: Grease Delivery Lines

1014lubecheckupBy Dr. Lube, aka Ken Bannister

Symptom:

“Recent fork-lift damage to one of our machines affected several steel grease-delivery lines connected to one of the Trabon automatic-greasing system’s lube blocks. Can I rely on the lube pump to pre-fill the replacement lines?”

Diagnosis:

A typical Trabon centralized grease-lubrication system consists of a pump assembly connected to a number of progressive divider distribution blocks. Each block has one line in and numerous lines out, connected to either a secondary distribution block or direct to the lube points. Each discharge point on a block could be feeding a different size bearing requiring differing amounts of grease. Therefore, the system and blocks must be custom engineered and built prior to assembly on the machine, and all lines filled prior to use. When a charge of grease is pumped into the block, the pistons actuate progressively, one after another, as the lubricant moves through the porting in the block and the correct amount is delivered to each bearing point.

Prescription:

Remember that you are dealing with a hydraulic system. Its lines must be pre-filled prior to startup so that small, apportioned amounts of grease discharged at the block can simultaneously hydraulically push an equal amount of grease at the line end into the bearing. Using the lube pump to fill lines will take a very long time due to the apportioning aspect of the system. In the process, some bearings could fail as a result of lube starvation.

All block discharge points have the ability to be piped into the side of the block (the most common arrangement) or into the front. Both discharge exits are connected, and the unused one will be plugged. Simply undo this plug and screw in a regular grease nipple. Next, undo the corresponding end of the grease line at the bearing point, connect a grease gun and hand-fill the line.

Once grease appears at the bearing-point end, reconnect the line, take out the grease nipple and re-plug the block. Repeat for all delivery lines and you are good to go! MT

Ken Bannister of Engtech Industries, Inc., is a Lubrication Management Specialist and author of Lubrication for Industry (Industrial Press), and the Lubrication section of the 28th Edition Machinery’s Handbook (Industrial Press). For in-house ICML lubrication-certification training, contact him at 519-469-9173 or kbannister@engtechindustries.com.

42

8:25 pm
October 14, 2014
Print Friendly

Lubricant-Health Monitoring: What We Test For

lt1014f2-1

Keeping contamination and wear-particle levels in check is key to healthy lubricants and lubricated equipment.

Lubricant-health monitoring provides the maintenance department an inexpensive predictive method for understanding the condition of a lubricant. Performing a comparative laboratory analysis of a used-oil sample against its identical virgin-oil sample allows the lab to determine what is in the oil that should not be there, i.e. contamination and wear-particle levels and types (see Table I). This change in the oil’s signature allows maintenance to trend what is happening to the lubricant and to determine a suitable course of action well in advance of bearing failure, and to optimize the oil change/service interval.

lt1014f2-2

Also known as oil and wear-particle analysis, lubricant-health monitoring traces its roots to the 1940s when North America’s railroad industry required an effective and inexpensive way to test engine wear in its new electromotive diesel engines. Using similar spectrographic testing methods as the railroads, the U.S. military performed wear-particle analysis testing on its jet and internal-combustion engines throughout the 1950s and ’60s—which led to the first commercial/ industrial laboratory in the early 1960s.

When subjected to adverse temperature, oxygen (air), contamination and combustion gases, oil will eventually degrade and become less effective in service. Degradation is recognized through viscosity change, additive-package loss, particulate increase (contamination) and oxidation. It’s up to maintenance personnel to collect a representative lube sample, package it and send to the laboratory in a timely manner. Upon receipt of the sample, the laboratory performs a series of tests according to how the lubricant was used in service, and sends a report to the maintenance department.

Elemental Spectrometry

The most popular oil-analysis method, Elemental Spectrometry tests for the concentration levels of wear metal, additive metal and contaminant metal particulate. Trending these levels over time against the known metallurgy of the bearing surfaces and acceptable metal levels inherent in the virgin oil will alert the maintainer of any pending problems. Sharp increases in levels will usually indicate rapid bearing failure or cross-contamination from the introduction of solids contaminants or use of different oil.

Two types of spectrometry-testing instruments (spectrometers) are commonly found in today’s labs: atomic and emission. Of the two, Atomic Spectrometry is the most widely used method. (Spectrometry tests can measure wear particles up to seven microns in size.)

In an Atomic Spectrometry test, a diluted sample of oil is atomized in a 2300 C (4172 F) acetylene flame. This causes metal ions to release photon energy as the metal-particulate atoms absorb light at different wavelengths (change color). Performing a computer comparison against known metal-particulate light-wavelengths, the atomic spectrometer is able to determine what metal wear elements and particulate are present and in what quantity.

In an Emission Spectrometry test, a 15,000-volt (or higher) charge is used to excite the particulate, causing any impurities to emit a characteristic radiation signature that the Emission Spectrometer can measure and analyze.

Analytical Ferrography

Ferrographical Analysis is a visual technique used to determine the size and shape of ferrous (iron-based) wear metals in which wear particles are magnetically separated from the oil on an inclined glass slide. This slide, known as a ferrogram, is then viewed under a bi-chromatic microscope to classify the concentration, shape and size of the different particulate. Knowing the metallurgy of the bearings and the shape and size of the particles, the analyst can determine the wear rate, type of wear that has taken place (rubbing, sliding, rolling, cutting, etc.) and how the particles were formed.

Microscopy

In Microscopy, an oil sample is run through a 0.8-micron filter, and captured particulate is examined under a 100x to 200x optical microscope. This method shows all particulate matter found in the oil, including non-metallic impurities. In addition, other methods are used to monitor the overall state of the oil. The most important are tests for Viscosity, Water Content, Total Acid Number (TAN) and Gauging the Particulate Count.

Viscosity

As defined in the ICML Domain of Knowledge Element 4, “What’s in a Lubricant: Mineral Base Oil and Its Characteristics” (see Lubrication Management & Technology, August 2013), Viscosity is the measure of resistance to flow. Industrial oils are typically measured for viscous flow at a temperature of 40 C (104 F) in a device called a viscometer. A specific amount of oil is poured through this open test-tube-styled device and timed against pre-determined timetables for specific Viscosity ratings: The shorter the time, the less viscous (or thinner) the oil is. The greater the time, the more viscous (or thicker) the oil is.

Lower-than-specification Viscosity can mean water dilution of the oil or the addition of less viscous oil. Higher-than-specification viscosity can mean oxidation (sludge) has taken hold or that more viscous oil has been added.   

Water Content

Water in oil promotes rust and corrosion, and in a dissolved state will accelerate oxidation. Moisture can be introduced as contamination through washdown of the equipment or through leakage.

Testing for Water Content is usually performed using a Karl Fischer titration moisture test that vaporizes the sample that is then carried by oxygen-free nitrogen into a reaction vessel-containing methanol. The trapped water is then titrated to an end point with a reagent to determine the amount of water present in parts per million.

Total Acid Number (TAN)

Oils that have had their antioxidants depleted will quickly oxidize and build up corrosive acids harmful to the lubricant and the lubricated parts. Checking for acid build-up can decrease the oil’s level of serviceability, allowing the oil to be changed before it can cause harm. The TAN is measured using a titration method that dilutes the oil sample with an alkaline solution until a neutral endpoint is achieved. Virgin industrial oils usually have lower TAN values around 0.5, whereas automotive engine oils are much higher, at values close to 1.5.

Gauging the
Particulate Count

Based on ISO 4406: 1999 Solid Contamination Code Suitability, a particulate count can be manually performed using an optical microscope to determine the number of particles in a 100ml sample >5 microns in size and the number >15 microns in size. The final count can then be found in the ISO 4406 Particle Count Chart (shown in Table II) to get a two-number ISO cleanliness rating.

lt1014f2-3

Another technique for gauging particulate counts involves an automatic particle counter. This uses a sensor to detect and count particles based on light-absorption principles. In this method, ISO 4406 calls for three sample counts sized at >4 microns, >6 microns and >14 microns.

Example: If the particle count came to 1030 particles >4 microns, 286 particles >6 microns, and 70 particles >14 microns, using the particle count chart’s corresponding values, a 17/15/13 ISO cleanliness rating would indicate an oil with “light contamination.”

Ken Bannister is a certified Maintenance and Lubrication Management Consultant for ENGTECH Industries, Inc. Contact him at 519-469-9173 or kbannister@engtechindustries.com.

35

8:23 pm
October 14, 2014
Print Friendly

Detection Of Cooling-Water Intrusion Into Standby-Power Diesel Engines

LT1014f1-1

This case study discusses pitfalls associated with the condition-monitoring of oil in a generator’s lubrication system.

By Randall Noon, P.E.

Diesel-engine generators, the stalwart mainstays of standby-power systems, offer several advantages: They efficiently provide electrical power, when needed, with the push of a button or automatically, perhaps, when under-voltage conditions in the grid trip their start relays. Also, the handling and storage of diesel fuel presents fewer safety concerns than gasoline or natural gas. And finally, an on-site storage tank full of diesel fuel offers more reassurance in a crisis than pipeline-supplied natural gas, which could be disrupted by an earthquake, flood or other extreme event.

Despite their robust natures and practical attributes, however, diesel-engine generators require certain levels of care and predictive/preventive maintenance—especially units that function in a standby capacity. Discovering in the middle of a power blackout that a site’s critical standby-power system won’t run is a high-stress headache no maintenance department needs. Allowing water to enter undetected and wreck havoc in these units’ lubrication systems is a sure way to induce that type of headache.

Cooling-water intrusion into the lubrication system often results from a faulty gasket around a cylinder head, a cracked cylinder liner, a warped head or uneven bolting of the cylinder head to the engine frame. In any case, water in the engine oil is undesirable. Such intrusion can have a significant impact on the unit’s ability to run: If enough moisture has entered the lubrication system, water carried by the oil may evaporate during the combustion cycle and leave dry spots that allow the piston and cylinder walls to make metal-to-metal contact. This usually results in damage to the cylinder, the liner and the engine. Continued operation of equipment with this condition will damage the unit and can lead to complete engine failure. With that in mind, consider the following example from the real world.

Uncovering the problem

In a routine test run of a standby 5000 KW, 16-cylinder diesel-engine generator unit, water was observed in a lubrication-oil sight glass. Subsequent investigation discovered a jacket-water leak in the 1-left cylinder.

lt1014f1-2

Fig. 1. Leakage observed in 1-left cylinder in situ with bore scope

During troubleshooting, the water jacket was pressurized to 11 psig, and water began running off the piston on the interior of the cylinder liner. The fuel injector was then removed and a bore scope employed to examine the internal area. As shown in Fig. 1, the liner was found to be leaking from a point about one inch below the piston-ring reversal area and filling the top of the piston. Subsequent examination indicated that the liner had cracked.

As with many units, the water jacket had an automatic refill feature. When the coolant level in the engine-water jacket drops, cooling water is automatically replaced in the standpipe by a level-control device. Given this arrangement, if a leak were to occur in the water jacket, any “missing” water would not be noticed. Consequently, attempting to determine when the liner crack started by checking for “missing” coolant was a dead end.

The coolant consisted of demineralized water with an added corrosion inhibitor: sodium nitrite. Since coolant leaking into the lubrication system would also carry with it sodium nitrite in solution, the presence of this corrosion inhibitor in the oil was used as a marker to indicate when cracking in the liner had sufficiently developed to allow coolant intrusion into the oil. The engine oil was regularly tested, and one of the tests looked for sodium content.

lt1014f1-3

A review of oil-analysis reports showed that on the day of the engine test during which water was observed in the sight glass, the sodium content of the oil exceeded 15 parts per million (ppm)—which was the trending alert level. The sodium content of the oil versus time, as reported in oil analyses, was then plotted as shown in Fig. 2. Since the oil was sampled at quarterly intervals, the resulting plot appears choppy. The plot in Fig. 2 is further complicated by the fact that the oil had been changed several times during the period of the plot. Each oil change would, of course, knock the concentration of sodium back to zero. Despite this complication, interpretation of the plot in Fig. 2 suggests that leakage had likely begun two years earlier.

Since the concentration of the sodium nitrate in the jacket-cooling water and the sodium content in the oil were known, it was possible to estimate the amount of water that had crossed into the lubrication system. This was then compared to the amount of water that had layered out in the bottom of the lubrication reservoir and that remaining in solution in the oil.

When these evaluations were done, the estimate of water carryover through the liner crack matched the total amount of water that had both layered out and remained in solution. This finding further corroborated that the origin of the sodium was the jacket water—and not any other source. The use of the sodium concentration data depicted in Fig. 2 also allowed rough estimates of leakage rates when engine operating time and oil replacements were considered.   

While a laboratory report for an oil sample taken prior to the engine-test run had indicated a sodium content of 18 ppm, it also indicated nil for water content. Water content for the previous six summary laboratory reports also indicated nil with respect to water content. These findings begged the question: If water had been leaking into the lubrication oil long before the test run, why didn’t the previous laboratory reports pick it up? Answer: Because the previous reports had indicated “nil” water, the significance of the sodium noted in previous reports was overlooked. To better understand this chain of events, keep in mind that water can be present in lubrication oil in one, two or three forms: 1) in solution; 2) in an emulsion; 3) as free water.

If not otherwise already saturated, oil is able to take a certain amount of water into solution. In this condition, it will look clear and cause minimal problems in lubricated equipment. If, however, oil has taken into solution all the water it can—i.e., when it is saturated—any excess moisture is held in suspension or emulsion. In this condition, it looks cloudy. If more water is added, the oil and water will separate into two layers. Because water is heavier than most lubricating oils, excess water will sink to the bottom. This is “free” water.

To get a sense of the amounts of water associated with these three forms of water, consider the following:

  • A saturation level of a mineral oil might be about 100 ppm, and the amount of water it can hold in emulsified form could be as much as 1000 ppm. Free water occurs when the concentration is greater than 1000 ppm.
  • Similarly, an ester-based hydraulic fluid could have a saturation level of more than 2000 ppm, and also might be able to hold as much as 5000 ppm in emulsified form. Water in excess of 5000 ppm would then form a free water layer under the oil.

lt1014f1-4

The amount of water that can be taken into solution also depends on oil temperature (as shown by the graph in Fig. 3). Oil at a higher temperature generally can take more water into solution than oil at a lower temperature. (The lubrication oil in the referenced diesel-engine generator unit is maintained at a “ready to run” temperature no lower than 104 F and no higher than 185 F.)

In this case, the water content of the lubrication oil was checked using the “Crackle Test.” This procedure involves putting two drops of oil on a hot, flat surface (about 130 C) and documenting any bubbling or “crackling” (the sound a sample sometimes makes during this type of test). The size of the bubbles is then used to indicate the amount of water in the oil. For example:

  • If no change is observed in the two drops of oil on the hot surface, it can be concluded that no free or emulsified water is present.
  • If very small bubbles (about 0.5 mm in diameter) appear, then disappear, the water content can be estimated at 500 to 1000 ppm.
  • If bubbles of about 2 mm appear, move to the center of the hot plate, increase in size to 4 mm, then disappear, the water content can be estimated at 1000 to 2000 ppm.
  • If bubbles of about 2 to 3 mm appear, increase in size to 4 mm and the process repeats with possible violent bubbling and audible cracking (hence, the test’s name), the water content is more than 2000 ppm.
  • The following limitations to the Crackle Test, however, are crucial to the discussion of this case study:
  • The method is approximate and not considered quantitative. It simply provides a rough indication.
  • If the hot-plate temperature is above 130 C, the heat can induce rapid scintillation that may not be detected by the observer.
  • The method provides no information about the amount of water in solution in the oil.

Developing new best practices

Based on the limitations of the Crackle Test and the data in Fig. 3, it became clear to the site’s maintenance department that water content could “hide out” in solution within the oil of a generator’s lubrication system. This situation had gone undetected over time because oil samples were usually taken right after a test run, when the lubrication oil was still hot (higher temperature => more water in solution).

In short, to proactively detect engine-cooling-water intrusion into the lubrication oil system before it affects the readiness of this site’s standby-power equipment, the amount of oil in solution must be monitored along with the amount of sodium detected in the oil.

Furthermore, personnel now understand that before the standby unit’s lubrication oil is changed—or fresh oil is added—samples of the existing oil must be evaluated. This way, any increase in sodium or water in solution can be compared to where it left off the last time.

Randy Noon is a Root Cause Team Leader at Nebraska’s Cooper Nuclear Station. A Registered Professional Engineer, book author and frequent contributor to Maintenance Technology, he has been investigating failures for more than three decades. Contact him at rknoon@nppd.com.

Navigation