One of the primary roles of maintenance and reliability professionals is to run their plant profitably at peak capacity while operating safely and efficiently. As plant professionals strive for increases in production, few would put lubrication at the top of their list of ways to increase plant performance. However, failing to identify the optimal lubricant for an application can lead to decreased efficiency, increased maintenance and the most menacing word of all, “downtime.”

There are roughly 26,000 applications for lubricants in the United States, and each application requires specific performance from its lubricant. Base Oil (mineral versus synthetic), viscosity, additive package, oxidation resistance and thermal stability, are just a few of the characteristics that must be considered when choosing a lubricant.

Identifying the correct lubricant can be a daunting task, especially when faced with all of the other dynamics that impact plant performance. Our own maintenance and reliability staff handles these same issues at the Shell Houston Lubricant Plant, which runs 13 production lines for packaging. The plant can process quart and gallon bottles, pails and drums simultaneously. At a rate of 18,000 quarts per hour, each line is integral to our lubricants business. Letting those lines go down for just a single hour can have a significant impact on production, greatly affecting our customers.

No matter how well developed a production plan is, problems will inevitably arise. The best companies are the ones that can prevent minor problems from developing into very expensive ones. Knowing how efficiency affects our business helps us understand yours. As a result, we work hard to align our entire business around delivering growth and quality customer support.

Your success is our success
At Shell, we believe our success comes from helping our customers succeed, so we work closely with them to develop insight into their businesses. We ensure that we have an intimate understanding of their challenges and goals. Once that foundation has been created, our team begins a customer “deep dive” to identify the customer’s particular needs.

Some of our customers have very intense requirements—onsite maintenance, technical service, new technologies, research and development, the whole package. Companies with multiple facilities often have very specific needs and depend upon 24-hour-a-day reliable service. As downtime can potentially lead to lost revenue, it is important for reliability professionals to identify the lubricants that meet the demands of their machinery and help keep them running efficiently.

Regardless of plant size, maintenance and reliability professionals should take advantage of the services lubricants companies can provide. As facilities are pressured to perform more efficiently with fewer resources, it is beneficial to employ experts who can help you make the most informed lubricant decisions. By reviewing plant equipment applications and operating conditions, suppliers can develop customized lubrication programs that help your facilities work more efficiently.

A lubricants company can provide diverse resources that are not always at hand for most maintenance professionals. For instance, fiber optic video inspection can often save plants time and money by inspecting internal components without dismantling the equipment itself. Some suppliers can also do in-depth fluid and equipment analysis to alert them to conditions that lead to premature equipment failure.

Ultimately, selecting the right lubricants and applying them correctly can have a big impact on your plant’s productivity and total operations cost. World-class lubricants companies are capable of delivering value-added services that support maintenance and reliability professionals in their efforts to deliver superior results. Make the most of your lubricants supplier relationship by asking what they can do to help optimize your business. MT

While it’s the easiest vibration parameter to understand, it’s also been the most rarely measured one. That’s all about to change, with loop-powered displacement sensors now offering a simple, continuous way to get the job done.

Clearing up misconceptions
Regrettably, over time there has been a common misconception that measuring displacement using an accelerometer is not possible or leads to erroneous information. In reality, accelerometers have long been used to measure displacement. It is, however, important to understand that displacement measured with an accelerometer is not the same displacement measured with shaft riders or eddy current-style vibration transducers.

Eddy current probes are precisely thru-hole mounted into a mechanical casing and measure two very important shaft parameters.

• First, eddy current probes indicate the location of the shaft relative to the casing. This is crucial in sleeve bearing applications because it tells the operator where the centerline of the shaft is relative to the casing.
• Second, eddy current displacement measurements indicate the amount of 1x rotational vibration. From this measurement, it can be determined if the shaft vibration is within acceptable limits.

If an operator looks at the vibrational spectral content measured with a displacement probe, it is possible to see higher order harmonics of the shaft. These levels, though, are typically very small in amplitude due to the natural inclination of rotating machinery to dampen and attenuate vibration displacement levels at higher frequencies. Other uses of eddy current probes are to monitor shaft eccentricity or, in the case of probes positioned in the axial direction, to monitor case thermal expansion.

While all of these measurements are useful, they are not the same as a casing vibration measurement made with an accelerometer, then doubly integrated electronically to determine the level of machine displacement. Despite eddy current probes being widely used in sleeve bearing applications, a great majority of field machinery employs roller element bearings. Usually it is neither possible nor practical to mount an eddy current probe on this type of machine. Since the shaft is held tightly in place by a roller element bearing, an accelerometer mounted on the case will detect the force exerted on the bearing by the rotating mass.

Deriving benefits
The benefits of using accelerometers to sense machine vibrations through casing measurements are well known. They have been in general practice for generations of equipment.

Typically, accelerometers internally generate an output voltage proportional to g’s, with 100mV/g being the common reference value. After the accelerometer output signal is received by the measurement instrumentation, the acceleration signal is converted to either velocity or displacement. Depending on the preferred measurement parameter chosen by the plant reliability engineer, the velocity and displacement characteristics are trended against time to indicate when the machine condition has changed enough to warrant special attention or preventive maintenance. While this method is effective, it requires a high degree of instrumentation to accomplish the desired goal of averting machine failure.

The measurement instrumentation involved is usually a spectrum analyzer that collects, conditions, manipulates and displays the data. This raw accelerometer data then is frequently transferred to a software database package that offers significant additional analytical capabilities and record keeping. Considerable resources can go in to the measurement instrument, training personnel in its proper use, interpretation of the data and ongoing software updates. Nevertheless, this approach has been successfully implemented in thousands of plants over the last several decades and has saved industry countless dollars in unscheduled downtime and costly repairs on large, critical machinery.

On the other hand, there remains a large amount of unmonitored plant machinery that could benefit from vibration analysis. Unfortunately, the costs associated with using highly trained staff to collect hundreds—perhaps thousands— of data points makes such widespread analysis impractical, especially when the increased demand on personnel to “accomplish more with less” is taken into account.

Loop powered vibration sensors
In recent years, there has been increasing interest in loop powered vibration sensors, which are powered from 24 volt supplies and output a 4-20 mA signal. The advantages of using 4-20 mA vibration sensors are simplicity and cost-effective continuous monitoring. They take the same accelerometer-based vibration signal discussed above, internally process that signal using one of several detection schemes (rms, peak, peak-to-peak, or true peak) and convert it into a 4-20 mA signal that is proportional to either acceleration or velocity. This signal is then routed to a much more common piece of process equipment, such as a PLC or plantwide DCS system.

So, instead of spending tens of thousands of dollars on sophisticated instrumentation, a plant can invest about $300 per data point and obtain continuous real time data on any piece of equipment. That means a facility can now monitor many more pieces of equipment— more cost-effectively than in the past. Considering the investment in capital equipment, this can be a very small price to pay for continuous operating information on a critical pump or fan stationed remotely in the plant. Even a higher priced analytical system does not offer 24/7 protection, and it usually requires human interpretation.

Today’s technology
While all of the loop powered vibration sensors up to this time based the 4-20 mA output signal on acceleration or velocity, measuring displacement with a 4-20 mA sensor is now an option. With no cabling and no instrumentation before it is converted to displacement, the cleanest signal is possible (where cleanest is defined as the least amount of electrical, thermal and cable noise before conversion). As previously mentioned, in traditional walk-around vibration systems, it is standard practice to convert the accelerometer signal to displacement after the signal reaches the measurement instrumentation. The result often seen in this data has been characterized as ‘ski slope,’ where low-frequency signals are lost in the integration process.

When an accelerometer is mounted on the machinery, the processing is performed right at the point of data collection. As a result, it is possible to control the entire measurement and integration process to a much greater degree than was possible before. The acceleration signal coming from the sensing crystal is first conditioned, that is, made readable by subsequent measurement amplifiers. Once amplified to an acceptable level, the signal is passed through a double integrator, which is similar in design to a low pass filter. This AC signal, representative of the machine displacement, is fed into the averaging circuit, converted to the required DC value and passed out of the sensor as a 4-20 mA signal. Now, data screens for process control machinery can be calibrated in mils displacement in the same manner that vibration velocity signals have been recorded with previous generation sensors.

Expanded opportunities
Through simplicity and the low cost of continuous monitoring, direct reading, accelerometer-based 4-20 mA displacement sensors expand the opportunity to use vibration monitoring within a plant. Fans, for example, offer a significant benefit from this technological improvement. When an accelerometer is sensitive to velocity, the overall vibration level can be dominated by blade pass frequency. Vibration readings of a fan and a pump in terms of velocity are shown in Fig. 1.

By utilizing a sensor based on displacement, the high blade pass frequency (relative to 1x vibration) is attenuated in the signal resulting in a monitoring system that is focused on the rotational (balance) component of the system. The vibration readings of a fan and a pump in terms of displacement are shown in Fig. 2.

Loop powered 4-20 mA displacement sensors also can improve pump monitoring, because the pump vane pass frequency can dominate a spectrum. Velocity sensors may be blind to changes in rotational speed vibration—thus, velocity may not be the ideal measurement parameter. Conversely, 4-20 mA sensors mounted on fan pillow blocks or pump housings can output directly to process control points, providing operators with never-before-seen information on their machines.

While measuring displacement is useful in many instances, most reliability engineers and maintenance managers realize that a single measurement focused on a single parameter (acceleration, velocity or displacement) is only a small part of a comprehensive predictive maintenance program. The choice of available sensors for measuring vibration is constantly changing. Advances in technology enable us to increase the measurement range of sensors; the bandwidth, both low-end and high; and ability to resolve low level signals in the presence of high signals like imbalance. The recent acceptance of loop powered 4-20 mA vibration sensors continues to expand the capability of predictive maintenance and real-time monitoring. Displacement-based accelerometers are the latest addition to the arsenal of vibration measurement tools and provide an easy to understand measurement with the capability to unmask hidden problems. MT

Renard Klubnik is an applications engineer with Wilcoxon Research, Inc., based in Germantown, MD. Telephone: (301) 947-7968; e-mail: Wilcoxon.Techasst@meggitt.com

This is the third installment in a series on “Developing & Deploying a Reliability Culture” that began in the January 2008 issue.

Getting an organization to the point where equipment and process reliability makes sense is essential for successful capital-intensive businesses.

Noted reliability expert Paul Barringer, of Barringer & Associates, Inc. reminds me that “The key to success with reliability lies with management and (their) adoption of a failure free environment…to preserve the process (without failure) to keep the money machine operating.” In other words, top management, senior leadership, must lead the charge for developing a true reliability-focused work culture. While this is an absolutely crucial step, it is not always an easy step for this level of management to take.

Not long ago I made my usual statement to a plant leadership group that “Equipment and process reliability is AS IMPORTANT AS quality, workplace safety, and environmental compliance.” You actually could see the management team bow up at that statement. Then team members began talking how important safety really was around their facilities: “It is our TOP priority here. Without a safe workplace we would be out of business.” And they were right.

We have to ask ourselves what happened to get these top level managers to be so insistent on workplace safety. Moreover, we also need to ask WHAT MUST HAPPEN for them to see that while safety is of utmost importance to business success, so are quality, environmental and process reliability (absence of failures). This is not a case of one or the other. It is ALL OF THE ABOVE—quality and safety and environmental and process reliability. In fact there is a natural synergy among these four TOP priorities.

Getting plant operations’ leadership and plant floor work groups to buy-in to equipment and process reliability requires some new education and some paradigm shifting. In many organizations the “we’ve-always-done-it-that-way” mindset prevails UNTIL there is a new no-options set of priorities and accountabilities with consequences. That’s part of what makes safety and environmental so important to businesses—regulatory compliance is not an option. Outside governmental agencies WILL enforce their safety and environmental regulations. Plus, the financial impacts of non-compliance accidents and incidents appear directly on the financial balance sheet as an expense (a loss). From another perspective, safety and environmental compliance become “risks to be managed”—the more critical the risk the more it is managed.

Regulatory or voluntary compliance
Helping plant operations’ leadership and plant floor work groups to buy-in to equipment and process reliability requires that we also understand the earlier voluntary transformations they had to make for the sake of competitive business success. For example, ISO 9000 ushered in internationally recognized certification standards and registration for “quality management systems.” The “Big Three” U.S. automakers then followed up with their own QS 9000 standards that incorporated auto industryspecific quality systems requirements. That was followed by ISO Technical Standard 16949, an international automotive industry quality systems standard. Each of these standards included very specific requirements, criteria, audits and registration procedures that had to be met for continuing registration and as a condition for continuing supplier status.

Similarly, environmental protection has become a progressively more critical business issue over the past few decades. The U.S. government’s Environmental Protection Agency (EPA) developed and promulgated ever-increasing regulations regarding pollution abatement and prevention. EPA’s regulatory process was similar to the U.S. Department of Labor’s previously developed Occupational Safety and Health Act/Administration (OSHA) regulations. Violations of these regulatory guidelines were punishable with fines and even imprisonment for willful neglect. Then, many businesses voluntarily pursued the new ISO 14000 standards for “environmental management” similar to the earlier quality management systems standards of ISO 9000. Likewise, ISO 14000 included very specific environmental performance requirements, criteria, audits and registration procedures that had to be met for continued registration.

Today’s reality
Within ISO 9000, TS 16949 and ISO 14000, there are sub-sections that deal with criteria for “preventive maintenance programs for key process equipment” (TS 16949, clause 7.5.1.4, for example). But, these are small portions of the overall quality and environmental “process reliability” guidelines. While most businesses comply with governmental safety, health and environmental regulatory requirements, there are many businesses that do not pursue the voluntary standards for quality and environmental management. Sure, there are clauses and sections within the government regs that address some aspects of “maintenance” but, what “standards” or “regulatory requirements” exist for equipment and process reliability? Virtually NONE!

When you Google for “Quality audits,” “…certification,” “…checklists” you’ll find millions of sources, including ISO 9000 and TS 16949. Google for “Environmental audits,” “…certification,” “…checklists” and you will find hundreds of thousands hits, including ISO 14000. However, Googling for “Equipment reliability audit,” “…certification,” “…checklists” generates just seven sources, and only for “equipment reliability audits”—nothing like the nationally and internationally recognized safety, quality, or environmental standards. The sad reality? Equipment and process reliability are NOT perceived as important to business as are safety, quality and environmental issues. Yet, doing business with unreliable processes can be very expensive, time-consuming, frustrating and, at times, even disastrous.

Achieving buy-in
What really happened over the years that made quality, safety and environmental so important to companies? Do you suppose it was the public image, employee revolts, customer complaints, regulatory fines and sanctions or business reputation and recognition? Sure, all that had an awful lot to do with it. So did the high costs associated with workplace accidents, environmental incidents, customer complaints and lost market share! Businesses could measure the costs associated with each of these situations. They tracked and trended the occurrences and costs, then did something about the causes. It was almost a no-brainer.

So, what about equipment and process reliability? In the absence of obvious regulatory compliance pressures, we have to focus on the costs associated with unreliable equipment and processes.

The cost of unreliability
Almost 20 years ago, several of us in the Total Productive Maintenance (TPM) and Reliability- Centered Maintenance (RCM) consulting fields started talking about the “cost of failures” and the “cost of unreliable equipment.” We asked, “Do you know, or can you find out what an hour of downtime costs the business?”

If you dig enough, if you ask the right people in production and accounting, you might be able to answer that question. Once you have it, you also have the foundation for a paradigm-shifting business case for improving reliability—more production in less time, higher process efficiencies, better utilizations, higher return on net assets, better on-time deliveries, uninterrupted flows and lower costs. The more compelling the business case for reliable equipment and processes, the more operations leaders and plant floor work groups will understand why RELIABILITY is so important to competitive business success.

Try the following approach. Begin by asking the question “What does an hour of downtime cost the business?” Look at your critical processes first. Take recent incidents of unplanned downtime that stopped a critical process and “dollar-ize it” in terms of lost production, lost revenue, lost profits, late deliveries, expedited processing, etc. Lost time never can be made up. It’s lost forever. Sure, you can work overtime to catch up, but that’s paying double to produce the same amount—a false economy. Think about it this way: What would an hour of downtime cost a NASCAR team? Could the team quantify the impact of such downtime on the business? You bet! Could they ever make it up? No way!

Focused improvement
Focus on the critical processes, the critical few. These processes, for example, can be a chilled water system, a production line, steam system, a complex multi-station machine, a material handling system, a dust collection bag-house or a wastewater treatment system. Next, target the weakest links within those processes. Determine the root causes of the problems and eliminate them. Develop the “reliability business case” for making these critical processes problem-free, one equipment component at a time.

Synergy…
The whole is greater than the sum of the parts. That says it all. Here are the options: We can champion a Safety Program, a Quality program, an Environmental Program and/or a Maintenance & Reliability Program with the appropriate departments taking the lead to fulfill management expectations. Yet, the real sustainable breakthroughs happen when we put them all together with an equal emphasis. That’s synergy!

Workplace safety…
Ron Moore, author of the book Making Common Sense Common Practice, made the statistical observation that workplace injuries increase as equipment breakdowns increase. The opposite occurs, too. The more reliable the plant, the fewer accidents and injuries you can expect. Clearly, there is a direct correlation between accidents and equipment reliability.

Quality and yield…
Many of us also have observed that the more reliable the manufacturing processes, the higher first-pass quality yields, the less waste and rework.

Environmental…
The more reliable the environmental equipment and processes the fewer incidents.

Maintenance…
The reduction of “reactive maintenance” work because of more reliable processes makes more time available for planned, preventive, predictive and proactive maintenance work. What a powerful business model for process reliability— capital-intensive business processes doing what they are supposed to do, first time, every time!

Getting operations’ and plant floor leadership buy-in for reliability is a joint effort, a partnership whether the maintenance group takes the first step or the operations group does. Reliable processes produce revenue. Cost effective reliable processes produce wealth. MT

References

1. Moore, Ron, Making Common Sense Common Practice: Models for Manufacturing Excellence, 2002, Butterworth- Heinemann, Woburn, MA.

When a small reducer fails, in most plants the usual reaction is to replace it without even opening it up to see what happened. But, when a large or critical unit is involved, the inspection and evaluation can be incredibly intimidating.

Where should the inspection start? Is the foundation and grouting important? Are those pits on the teeth something to worry about—or is the gear good for another 10 years? What sort of a contact pattern is acceptable and when is it a warning of problems? Is that oil the correct viscosity? Is it contaminated?

Gear design
In gear design, there is a combination of rolling and sliding motions. At first contact between two teeth, the motion is mostly sliding but as the two pitch circles become closer and closer, more and more rolling occurs. When the pitch circles intersect, and the teeth are on the centerline between the two shafts, the contact is all rolling. Then, as the teeth go out of mesh, there is progressively more and more sliding.

Gear drives and reducer units are designed using some basic rules. The bearings are based on a certain L10 life, while the teeth have to withstand the operating fatigue stresses. These stresses are complex and provisions have to be made for cantilever loading, similar to a beam in bending; Hertzian fatigue loading of the contact surface, similar to a rolling element bearing; plus sliding friction and the lubrication demands of a pair of surfaces that involves both sliding and rolling. This sounds confusing, but evaluation and failure analysis of gear drives and reducers isn’t terribly difficult—if some simple rules are followed.

Starting the inspection
With the unit running, conduct a general inspection of the area around the gears or reducer, including support structure, bolting, foundation block, baseplate and grout. (These elements need to be in good condition so they can help resist forces that distort the housing and cause excessive gear and bearing wear.) Be sure to conduct a detailed vibration analysis and:

For an enclosed reducer…

• Determine if there are significant differences in vibration levels in the reducer housing, the baseplate and the foundation block. There should only be a small percentage of change in vibration as you go from housing to baseplate and then on to the foundation block. A large difference indicates a looseness problem that will increase the operating stresses.
• Listen to the unit with a stethoscope. Are there any unusual or irregular signals or noises that indicate cyclical loading, looseness, or other problems? Gear units are designed around given loads and the peaks of those cyclical variations can be a problem.

For an open gearset…

• Use the stethoscope to listen to the pinion pillow blocks, again searching for any unusual or irregular noises. Then, listen to the bearings while watching the gears rotate, looking for cyclical noise patterns that match the pinion or bull gear rotation, which may be clues to problems.
• Carefully open the guard so you can watch the tooth mesh with a strobe light,and:
  • From a side view, try to understand and measure the eccentricity in the bull gear.
    • Root clearance on a spur gear ideally should be 0.071 X tooth height, but there is always some runout. On large gears, the minimum allowable is generally taken as 0.05 X tooth height.
    • Interference is an invitation to disaster. Too much clearance is always better than interference, but it changes the tooth meshing geometry, increasing the cantilever tooth loads, and the wear rate.
  • From a head-on view, analyze how the contact pattern changes as the bull gear rotates.
  • Using an infrared thermometer, measure the temperature variation both across the teeth and around the gear to get an idea of the loading and misalignment. (For good reliability, the maximum variation should not exceed 10 F.)

At about the same time:

• Look at input power data and calculate both the peak and average power required by the unit. Compare these data to the machine’s design and rating.
• During a heavily loaded period, take housing and lubricant temperatures.
• Take an oil sample and:
  • Calculate if viscosity at that peak operating temperature is acceptable.
  • Compare the wear particle analysis with historical data.

With this data, you’ll have a good start on the overall evaluation and an insight into any impending problems. Now, it’s time for visual inspection and evaluation of the gears.

Understanding unit metallurgy
The first step should be to determine the tooth hardness and understand the metallurgy. Most industrial gears used today in North America and Europe are case hardened (also called surface hardened) to somewhere between HRC 54 and HRC 63, and they should never show measurable wear or pitting. However, large gears, open gears sets and many older reducers will have through hardened teeth with hardness values anywhere from BHN 140 to about BHN 400.

Further confusing the issue is the fact that from the 1960s through the 1980s, some manufacturers supplied larger reducers with case hardened pinions and through hardened gears. Additionally, while most open gears are relatively soft, some manufacturers made their products from medium carbon steel and then flame hardened the teeth to about HRC 36.

If the tooth’s hardness is above HRC 40, treat it as though it were case hardened. If you don’t have a hardness tester, use a fine file and try to cut the top of the teeth. If the file just skids, you know that the teeth are hardened.

The next step is to understand the contact pattern during operation. The ideal is to have a contact pattern completely across each tooth that was uniform all around each gear. This design is based on full contact, but sometimes there are machining or assembly errors and other times there is distortion of the housing. Consequently, tooth stress can increase tremendously (see Fig. 1.)

In addition...

• Less than full contact should be carefully documented.
• Any evidence of contact on the back of the teeth is cause for great concern as it indicates very high peak tooth loads, and the manufacturer or a skilled consultant should evaluate the situation.

Inspecting through hardened gears
A difficult part of your analysis comes when you try to convince people that pitting of a through hardened gear is not only nothing to be overly concerned about, but that it also can be used as a predictive tool.

There have been many articles written about the various forms of through hardened gear wear and pitting. In them, you will see terms like polishing, corrective pitting, destructive pitting and normal dedendum wear. Unfortunately they all mean that the gear is wearing out. From an operational and maintenance viewpoint, what’s most important is determining the rate of wear.

Through hardened gear pitting…
Through hardened gears rarely break teeth. Because of the high local contact stresses, they usually wear and pit. The aforementioned damage classifications refer to the pitting rates. Through hardened gears usually are:

• Designed with huge safety factors with respect to the cantilevered bending stresses.
• Generally made from relatively tough materials.
• Designed so corrective pitting makes up for minor surface irregularities and misalignment. This initial wear removes the areas of hardest contact and slowly redistributes the load over a greater surface area. Then, as the contact becomes better, local stress decreases and the wear rate drops rapidly (see Fig. 2).

Normal dedendum wear is fine pitting seen in the dedendum of teeth. It occurs after millions of load cycles when a minimal oil film and sliding contact put the tooth surface into tension. The result is minor cracking and pitting and slow removal of the dedendum surface.

Destructive pitting, like that shown in Fig. 3, happens when the lubricant is grossly overloaded and large or sharp pits develop. The result is a noisy and rough gear in serious trouble with rapidly increasing damage. If the pits are relatively small and well rounded, they can support the lubrication film and the gear will last a long time. At the other extreme, large irregular pits destroy the lubrication film and sharp, linear pits can cause formidable stress concentrations.

In through hardened gears, corrective pitting and normal dedendum wear result in slow and measurable tooth deterioration—which typically allows for a relatively long and predictable life. Destructive pitting, though, will rapidly grow rougher and noisier and may result in a catastrophic failure. Early in the gear’s life, it may be difficult to determine if the wear is corrective or destructive, but with corrective pitting the wear rate rapidly drops off.

Rolling and peening…

The most common other damage seen on through hardened gears occurs when the teeth are so heavily loaded that plastic deformation occurs. This is commonly called rolling, where metal is rolled or pushed up the active faces of the teeth (see Fig. 4), and peening, where the shape of the tooth is hammered irregularly until it is no longer an involute curve. In both rolling and peening, the tooth form is slowly destroyed and both mechanisms show that either the gear is very heavily loaded or there is poor lubrication.

The amount of allowable wear depends on the possible consequences of a failure. If it is not a critical application, through hardened gears are frequently run until the pitch line thickness is reduced by more than one-third. On the other hand, with a critical mine hoist, the loss may be limited to only 15%.

Through hardened gear predictive monitoring…
One positive point about through hardened gear wear is that the wear can be easily monitored. Using a gear tooth micrometer as a predictive tool and periodically taking measurements at several points across the teeth and around the circumference, the charted wear rate can be used in planning for gear replacement, evaluating lubricants, etc.

Inspecting surface (case) hardened gears
Most of the confusion in evaluating gears occurs because surface (case) hardened gears, unlike through hardened gears, can tolerate almost no surface damage. On a surface hardened gear, even small pits—those that would be ignored on a through hardened unit—can be indications of a looming disaster. Thus, Best Practices demand that the evaluation of surface hardened gears has to be very different from that of through hardened components.

The case on a surface hardened gear is much harder and much stronger than the softer core. These gears are almost always machined to much closer tolerances than through hardened gears—and the hardened surfaces tend not to wear. Consequently, damage to that hard external “shell” frequently is difficult to see, making surface hardened gears and reducers far more difficult to inspect than through hardened ones. Because the hardened case is not very ductile:

• Alignment is much more critical than on through hardened gears.
• Once damage penetrates the hard outer case, it grows rapidly through the weaker core.

Most surface hardened gears have relatively thick cases from carburizing or carbonitriding, but some have very thin nitrided cases.

The internal inspection of surface hardened gears should begin with a VERY careful inspection of the teeth and the contact patterns. The teeth should look like new and show no surface damage other than mild polishing—using a bright light for the close visual inspection of the teeth is strongly recommended. Because of the fine surface finish, determining the contact pattern on surface hardened gear teeth can be difficult at times. That is why you may have to look at them from several angles.

One note of caution: Some folks run carbon paper through a gear set or use bluing to check contact patterns. We have no problem doing this, but there are many times when it is misleading because the dynamic forces on a reducer or gear set in operation cause deflection of the housing or the machine base. In these applications, the static contact check is almost useless and may lead to a false impression as to the contact pattern. There is no substitute for that previously mentioned careful visual inspection.

While broken teeth clearly are the most serious problem, because of the relative weakness of the softer core material, any tooth that has substantial surface deterioration may be at risk of breakage. The following section describes some common forms of tooth damage and the dangers they present.

Pitting and micropitting…
The most common surface damage mechanisms are pitting and micropitting. Gear pitting occurs as the result of a combination of Hertzian fatigue forces and surface tension. Any pits on a surface (case) hardened gear are cause for great concern because they show that the tooth loads are far in excess of the design loads. Pitting also is indicative of either serious overloading or metallurgical problems. In addition, once the strong and hard outer layer is penetrated, the remaining core is much weaker and there is a good chance of tooth breakage in the very near future.

Micropitting, a less severe form of surface fatigue damage, sometimes occurs when there is an inadequate lubricant film. It shows up where the high spots of mating gear surfaces create pressures great enough to cause a series of tiny fatigue spalls that look as though the area had been sandblasted.

If the micropitting occurs in bands—and is uniform and well distributed—it indicates that the gears are heavily loaded and there are some machining errors. This type of micropitting, however, poses no real problem. For example, in the pair of 30-yearold case hardened gears from a 900 hp reducer in Fig. 5, there is no perceptible wear except for the bands of micropitting across the teeth. Although this shows that these gears are heavily loaded, after having run for several billion cycles, the degree of micropitting they reveal is not a cause of concern. However, when micropitting is off to one side of a gear, as shown in Fig. 6, it indicates there is excessive misalignment within the unit and a serious chance of catastrophic failure.

The normal progression of damage in a surface hardened tooth with excessive loads and misalignment is that the micropitting eventually yields to pitting, followed rapidly by tooth fracture. By the same token, if the entire active face of the teeth was covered by micropitting, it would indicate that the teeth are extremely heavily loaded, the lubricant film isn’t adequate and there is a substantial likelihood of pitting and eventual catastrophic failure

Other common surface hardened problems…
Poor tooth contact and the eccentric loading that causes pitting and the resultant tooth fracture are the most frequently seen surface hardened gear problems. Several other tooth damage modes have to be recognized, though.

Rippling (see Fig. 7) occurs when the contact loads are so heavy that there is plastic deformation of the hardened case. Inspection of a rippled tooth surface will show surface variations that look like ripples in water and should be watched carefully.

Case crushing is seen when the load on the case is so heavy that the ductile supporting core plastically deforms, can’t support the case and the case fractures. The typical symptom is a crack horizontally across the tooth, indicating the loads are excessive and the tooth is in danger of breaking.

Metallurgical problems…
There are many metallurgical defects that can cause gear problems—most of which are beyond the scope of a basic article.

One such defect that is within the scope of this article, however, is the appearance of a single large spall or a few large spalls on well separated teeth (see Fig. 8) This is typically the result of manufacturing problems. If these large surface flaws are well separated, they don’t require immediate action. Nevertheless, they should be carefully monitored, with plans for eventual replacement.

Concluding thoughts Now that you understand the condition of your gears and the severity of any damage, think about the fact that there are always multiple contributors to machine deterioration and equipment failures. Go back, review the installation and, with the help of your PdM findings, you can understand those changes that will most efficiently improve your gear and reducer life. MT

After a long career in industry, Neville Sachs joined with Phil Salvaterra in 1986 to form Sachs, Salvaterra & Associates, Inc., a reliability consulting group of engineers and technicians, headquartered in Syracuse, NY. Since then, he has conducted thousands of failure analyses and hundreds of failure analysis classes across North America. A Registered Professional Engineer, Sachs is a member of and active in several engineering societies and a frequent speaker for both regional and national programs. He is the author of Practical Plant Failure Analysis: A Guide to Understanding Machinery Deterioration and Improving Equipment Reliability (CRC Press, 2006), and also has contributed significant sections to two other technical books. Contact him directly at: sachscracks@att.net

Better lubrication practices could prevent the type of bearing damage that leads to costly premature motor failures in countless plants. How are you taking care of these crucial activities in your operations?

Proper lubrication of ball and roller bearings in electric motors is essential to their health. Grease reduces friction and protects the surface finish from rust during long idle periods and in unfavorable environmental conditions. It also transfers heat from the bearing and even helps protect the bearing from dirt and contaminants. Since bearing life—and, by extension, motor life—depends on proper lubrication, it’s important to use the right grease for the application and to re-lubricate bearings at the correct intervals.

The basics
Grease is a “dirt magnet,” so it’s surprising to many that packing it into the cavity around the bearing actually helps keep dirt and other contaminants from getting into this critical component.

On very old motors, lubrication was provided by oil-soaked felt that “wicked” oil to the bearings. Grease serves this function in today’s machines. Consisting of oil suspended in a base material like lithium, calcium or polyurea, it lubricates the bearing continuously while preventing the oil from leaching out. Depending on its composition, different greases may be better suited for one application than another. For example, one may be superior at high or low temperatures, another impervious to water, while still others retain oil better under extreme pressures.

The lesson here is to select the right grease for the application. An electric motor in an Arizona open-pit copper mine where the ambient temperature is 130 F requires different grease than an identical motor in the Arctic Circle.

Of course, it’s sometimes necessary to meet one stringent requirement at the expense of others. In the food process industry, for instance, the most important property of lubricants is that they won’t poison you if they somehow get into the can of beans you’re going to eat for supper.

Compatibility issues
An old professor of Texas history used to say, “Never mix gunpowder and alcohol, ’cause you can’t shoot it, and it tastes terrible!” Although it’s usually okay to combine lithium- and calcium-based greases, mixing lithium- and polyurea-based greases causes the oil to leach out much more quickly than normal, potentially starving the bearing of lubrication. Be sure you know which types of grease your plant uses—and know which ones are compatible with one another.

Table I provides general guidelines for grease compatibility, based on the variances in compatibility of different greases tested by the National Lubricating Grease Institute (NLGI), April 1983. Grease manufacturers often can provide similar charts.

Although compatibility guidelines are helpful, there are enough exceptions to warrant care. Before mixing two greases, check with both manufacturers. If both say it is all right to mix those specific greases, it probably is safe to do so. If either of them says no, don’t risk it (see Fig. 1). Note that in some instances both manufacturers may say it is safe to mix specific greases that are incompatible according to the general guidelines in Table I.

Types of grease in motor bearings
Some motor manufacturers have used polyurea-based grease—which performs well at high temperatures (over 250 F) and high speeds (10,000 rpm or higher)—almost exclusively for more than 30 years. Recently, though, several of them have switched to a second-generation polyurea grease that reportedly has even better properties than the old standby. Because these manufacturers produce tens of thousands of motors weekly, their decision to change grease is significant. Such a move indicates a high confidence level in that grease.

Bearing manufacturers, on the other hand, use various greases, depending on application requirements. As a result, the replacement bearings you buy from your local bearing supplier might not contain grease that is compatible with what you use in your plant. So, be careful.

Lubrication intervals
Ultrasonic listening equipment, vibration analysis and thermography all can help predict bearing failures. But according to some sources, an operator tends to grease a bearing only when it “gets noisy enough that he can hear it” over the ambient sound of surrounding equipment. By that time, the damage has been done. Pumping in a few ounces of grease may mask the noise for a while, but it is too late to save the bearing.

Assuming you have a good predictive maintenance program and want to improve on preventive maintenance, how often should you grease the bearings in an electric motor? If you read the manuals for a dozen different electric motors, you’ll likely find 12 different recommendations.

Some of the factors that determine how often a bearing should be greased are:

• Operating hours
• Operating temperature
• RPM
• Bearing size
• Bearing type (ball or roller)
• Cleanliness of environment
• Vibration levels
• Criticality of operation

One of the best charts for determining lubrication intervals is based on the bearing bore diameter, rpm, yearly operating hours and type (ball, roller, thrust, etc.). Unfortunately, this chart is not very practical. That’s because the person responsible for greasing the bearings usually doesn’t know the bearing sizes of every motor, and some motors have a different bearing size on each end.

Another drawback of this method is that each motor in a plant probably will have a different lubrication schedule—motors could be installed at different times, they could operate a different number of hours/year, their usage could vary with the seasons. It’s easy to see why something that sounds simple (e.g., “Grease the bearing every 4000 operating hours with 1.0 ounces of fresh grease”) may be hard to implement.

Various industries have tried to simplify the task by developing practical guidelines like those in Table II. Each represents a compromise, though, so none of them works for every situation.

One thing that bearings and motor windings have in common is the 10-degree rule. Every 10 C degree increase in temperature cuts their life expectancy in half. If a blanket of grease raises the winding temperature 20 C degrees, the winding will last only one-fourth as long as it should have. With an increase of 50 C degrees, a winding that should last 20 years would have a life expectancy of only about eight months. Unless you really enjoy changing motors in the middle of the night, try not to do anything that increases the motor temperature!

Lubrication procedure
Now we come to the recommended procedure for greasing bearings. Under normal conditions, first remove the grease drain plug and wipe all the dirt and debris off of the grease fitting and the nozzle of the grease gun. With the motor running, pump fresh grease into the bearing while observing the old grease that is being forced out of the grease drain. When the purged grease looks fresh, stop pumping. Run the motor for at least 20 minutes to purge any excess grease and then replace the drain plug.

Caution: Remember that the shaft is rotating. The motor is coupled or belted to something, so there are lots of things to get hung up in. You probably need all your fingers, so work safely.

Some manuals say to “pump 0.8 ounces of grease into the bearing.” That sounds simple enough. Many operators know how many pumps it takes to deliver an ounce of grease, because they actually have checked. But, it is hard to determine if the passage between the grease fitting and the bearing is full of grease or empty. What if that precise 0.8 ounces of grease doesn’t even fill the grease passage?

Ultrasonic equipment affords a more reliable way to know when the grease reaches the bearing. While listening to the bearing, pump in fresh grease until the sound changes for the better. If you pump four tubes of grease into a 5 hp motor and still don’t see any grease coming out of the drain, please stop! Tell the boss what you did, and be prepared for him to yell a little.

If he’s fair, you’ll probably get the task of removing the motor, cleaning out all that excess grease (Fig. 2) and reinstalling the motor.

There are some good, low-tech ways that make it easier to do a good job. One way is to replace the drain plug with a low-pressure (0.5 to 1 psi) pressure relief fitting. That makes removing the drain plug or waiting for the grease to purge unnecessary.

For motors installed in out-of-the-way places, bearing suppliers sell another useful device—a small grease can powered by a watch battery that provides a regulated flow of fresh grease to the bearing (see Fig. 3). Simply screw it onto the pipe in place of the grease fitting. Be sure to write the date on it and replace it annually or semi-annually.

Specialty equipment
All the specialized equipment in use today around the world makes grease selection more complicated. Specialty applications like kilns or ovens may be good places for synthetic grease. Synthetic grease typically can handle 30 C-degree higher temperatures than conventional grease, but it’s not as suitable for high-speed operation. To avoid compatibility problems, be sure to identify all special cases.

Belted applications may require an extreme-pressure (EP) grease. It might be a good idea to identify these motors in some clear way—like painting the end bracket a different color from your other motors. The color won’t match the rest of the motor, but it will make it easier to identify a roller bearing that has a shorter relubrication interval and requires an EP grease. Be sure to tell your service center whether a motor is direct-coupled or belted when sending it out for repair.

End notes
Most premature motor failures result from bearing damage that may have been prevented with good lubrication practices. Choosing the right grease for the application and following the correct lubrication schedules and procedures will assure long, trouble-free motor life with a minimum of unscheduled downtime. It’s also important to avoid mixing incompatible greases and over-greasing. Finally, when sending a motor out for repair, make sure the service center motors knows what grease you use. MT

Chuck Yung is a technical support specialist at the Electrical Apparatus Service Association (EASA), in St. Louis, MO. EASA is an international trade association of more than 2100 firms in 50 countries that sell and service electrical, electronic and mechanical apparatus. Telephone: (314) 993-2220; Web: www.easa.com

This article is the last installment in a four-part series based on a presentation delivered at the 2007 NPRA Reliability & Maintenance Conference in Houston, TX. As in the previous installments, (which ran in the July and September 2007 and February 2008), the authors discuss how to distinguish competent pump repair operations.

In this fourth and concluding part in our series on non-OEM pump repair facilities, we discuss two actual case studies. As you read on, please recall that we coined the acronym “CPRS” to convey the term Competent Pump Repair Shop.

Repair case study #1:
Two IR Type J4x 15 lean amine pumps The first of our two case studies concerns the repair of two IR Type J4 x 15 radially split, double suction, betweenbearing pumps purchased in 1982 for lean amine service. Figs. 1 through 3 provide specifics.

The pumps were to be repaired using new 316 stainless steel casings and heads furnished to a CPRS by the refinery client. The client had bought these parts from the “current” OEM—a successor company to the initial OEM. While one pump was being repaired, the other pump remained in service, operating without a spare. However, the new casings and heads required considerable rework before they could be used. This rework included:

1. Sleeving and re-machining an oversize stuffing box bore;
2. Re-machining the two spiral wound gasket faces;
3. Weld-repairing a sand inclusion on a stuffing box face;
4. Re-facing the stuffing box faces to remove steps caused by the milling operation;
5. Re-machining two stuffing box bores that had been damaged so that the seal gland pilot would not engage.

Based on the location of the bolt holes in the bearing housing mounting flanges, neither cast casing was symmetrical with respect to its shaft centerline. The new casings and covers also were drilled for the bearing housing alignment dowel pins. The casing and head for the second pump were returned to the “current” OEM after a pinhole leak was discovered while air testing the mechanical seals. The second pump was returned to the refinery with the original carbon steel casing and head.

Repair case study #2: Worthington Type 8 UZDL21 multistage ash sluice pump
A Worthington Type 8 UZDL21 two-stage pump from a power plant was received by this CPRS in 2006. It was disassembled and inspected and the names of the personnel involved in this work were recorded in the evaluation. By recording these names, the owner-operator (“client”) of the pump was able to ascertain the experience levels of staff assigned to dismantling and inspection duties. Client representatives were in attendance for the inspection and met with CPRS personnel. A comprehensive Inspection Report & Repair Proposal was generated, submitted and quickly approved by the client. Repairs were started without delay.

The purpose of an Inspection Report and Repair Proposal is to evaluate repair options and/or design changes that may (or may not) be included in the repair plan, but which the examining engineer believes could increase the run time of the pump. The following design changes were implemented in this repair sequence:

1. Wear ring configurations were changed from “saw tooth” to “smooth.”
2. All wear rings were coated with 88-12 tungsten carbide, 0.020” thick.
3. Thrust bearings were changed from MRC 8317 AB to SKF 7317 BEGAM.
4. Oil flinger ring diameters were increased from 7” to 7.50”.
5. An appropriately sized oil drain hole was added in the bearing housing bore at the 6 o’clock position
6. Bolt-in bearing housing oil dams were eliminated.
7. The bearing housing oil level was changed from its previous level to an appropriate new level.

Based on the condition of the ash sluice pump and conversations with the client, the abrasive action of the ash sluice mixture limited the run time of the 316 stainless steel pumps to between 12 and 18 months. Based on the client’s information package, this particular pump had operated for about 18 months and was taken out of service due to a catastrophic thrust bearing failure. In turn, this failure caused rubbing of the 2nd stage impeller back shroud to the casing and the shaft-to-thrust-end cover. The direction of thrust was away from the coupling and opposite to the preferred direction for the SKF/MRC “PumPac 8317 AB” bearing. The wear ring clearances were abnormally large and there was no evidence of oil in the thrust bearing or in its housing. Other damaged components included:

1. Coupling end sleeve nut;
2. Oil slinger rings;
3. Radial bearing; and
4. Cracked first stage impeller shroud.

The most probable and primary cause of the failure was (initially) determined to have been lack of lubrication to the thrust bearings. Nevertheless, the failed radial bearing showed a slight hint that there had, in fact, been oil in its housing. The CPRS examining engineer realized that the pump could not have operated for 18 months without oil in the bearing housings. Hence, lack of oil was judged a maintenance issue that would have to be addressed at the plant.

But, the examining engineer also believed that a thrust bearing failure could have occurred—even if the housings did have the required amount of oil. He knew that Type 8317 AB bearings, as had been installed, are designed to carry axial thrust toward the coupling. Calculations were made indicating that, with normal running clearances, the direction of thrust would be toward the coupling.

From common pump experience, the CPRS reasoned that wear ring clearances become larger with time; the direction of axial thrust then reverses. Further calculations demonstrated that if the pressure on the backside of the second stage impeller is 17-psi lower than on the front shroud, the axial thrust force will be approximately 3000 lbs away from the coupling. A 17-psi reduction in pressure can occur due to excessive leakage across the balance drum wear ring to the first stage impeller suction chamber. To overcome the thrust reversal problem, two recommendations were more closely evaluated by the CPRS:

1. Reducing the wear rate of the rings and bushings; and
2. Increasing the axial thrust capacity of the pump away from the coupling.

Comments on wear rate of rings and bushings…
The informative input from a CPRS explains why a certain course of action is recommended. The report generated during this case study discussed the following items:

1. Flushing One method of reducing the wear rate of the rings and bushings would be to reduce the concentration of abrasive matter forced through the running clearances. Flushing the rings and bushings with clean water would accomplish this. (Slurry pumps used in refineries are often designed with this feature.) This option was briefly discussed but did not seem to be feasible due to the lack of high-pressure clean water at or near these ash sluice pumps. Low-pressure water is available for bearing housing cooling and mechanical seal flushing. If this option were to be pursued, it would be necessary to determine the flow rate and pressure of the water needed so that a booster pump could be selected and the economics of the system could be evaluated.

Another source of flush water that might be investigated would utilize separators to remove fly ash from a small side stream of the pump’s discharge. However, the maintenance cost associated with separator wear might make this option uneconomical.

2. Ring and bushing geometry The CPRS now considered various popular wear ring configurations. The examining CPRS engineer believed that the pump was last repaired with “saw tooth” type rotating rings and smooth stationary rings and bushings. For the same running clearance and differential pressure per length of seal, this style has the lowest leakage rate. The “saw tooth” geometry disrupts the flow causing high turbulence and thus increases the friction coefficient. During the inspection process it was noted that the rotating wear rings for this pump were oriented so that the direction of flow was opposite to normal. This would most likely cause the wear rings to become less efficient— to have higher leakage rates. In an abrasive-laden ash sluice service the saw-tooth wear ring profiles, stationary casing wear rings and balance drum bushings would show wear. The disassembled pump showed this to be the case. The outside diameter of the 300-series stainless steel impeller wear rings had a hard surface coating, but the inside diameters of the 300-series stainless steel case wear rings and balance drum bushing were soft. It was assumed that the stationary wear parts supplied by the client had a hard surface coating but that it had worn away.

This is where experience helps. The CPRS had recently repaired a multistage pump in coke cutting (abrasive) service. In this instance, the stationary wear rings and bushings incorporated “saw tooth” geometry and the rotating rings were smooth. The impeller wear surfaces had been overlayed with Stellite 6 (42 RC) and the stationary wear rings and bushings were made from 440 C material (48/52 RC). When, after three months of service, the pump was shut down due to a sleeve bearing failure caused by insuffi- cient oil, it was discovered that the smooth cylindrical wear surfaces on the impeller had become grooved due to the abrasive coke fines.

Based on these two experiences (and notice how the CPRS uses what it learns), the lead examining engineer believed that the “saw tooth” grooves trap and, therefore, locally increase abrasive particles. This then causes greatly accelerated wear. The trapped abrasive particles can originate from the pumpage and from the worn hard-coated surfaces. High turbulence created by the “saw tooth” geometry also increases the wear rate.

In an effort to reduce the rate of wear on the inside surface of the case wear rings and balance drum bushing, the lead engineer recommended changing to the normal smooth ring configuration traditionally used in pumps. This would reduce the impact angle of the abrasive mixture to zero, eliminate much of the turbulence and reduce the high local concentration of abrasives caused by groove trapping. The plain cylindrical surfaces also would be simpler to coat and, accordingly, have a higher bond strength.

Hard surface coating…
The center stage bushing, impeller, case and balance drum wear rings were to be coated with 0.020” of 88-12 tungsten carbide (88% tungsten carbide, 12% cobalt) using the HVOF process. Having access to a good reference library, the CPRS knew this coating (70-72 RC) had been recommended in the Proceedings of the 9th International Pump Symposium (“Evaluation of Coatings for Abrasive Service”) for slurry services. Running clearances were being increased over API-610 minimum standards to compensate for the reportedly low galling resistance associated with making both the rotating and stationary wear parts from 88-12 tungsten carbide. The design and “as built” running clearances are shown in Table I.

Bearing load capacity issues: thrust direction away from coupling…
When it was received at the CPRS facility, the ash sluice pump was found to be fitted with MRC (SKF) 8317 AB PumPac thrust bearings oriented for axial thrust toward the coupling. With the cracked thrust bearing end cover and worn back shroud of the second stage impeller, it was obvious that the thrust direction had reversed.

History is of interest here. PumPac bearings were developed in the mid 1980s to overcome ball skidding in heavyduty applications where the thrust load is in one direction only [Ref. 1]. Ball skidding becomes a more significant problem as bearing size and operating speed increase. At nDm (rpm “n” times mean diameter “Dm”) values below 250,000, there is little risk of ball skidding. (This ash sluice pump with an operating speed of 1785 rpm and a mean bearing diameter of (85 + 180)/2 or 132.5 mm has an nDm value of 236,513.)

Assuming over the life of the ash sluice pump that the axial thrust load changed direction, a pair of lightly preloaded 40° angular contact bearings would represent a better bearing selection. Nonetheless, to evaluate the improvement in L10 life, calculations were performed for the existing MRC 8317 AB PumPac bearing set and for a more conventionally applied SKF 7317 BEGAM bearing set. PumPac life calculations were performed by one of the bearing manufacturer’s application engineers. His calculations were based on an axial thrust load of +/- 3000 lbs and radial loads of 167 and 250 lbs. They demonstrated that the values used by the CPRS for bearing life estimates were in the right league (see Table II, as follows). Again, in essence, this situation shows what happens when a CPRS facility involves competent suppliers of pump components in cooperative analyses: The pump user benefits.

The calculations assumed clean ISO VG 32 oil operating at approximately 160 F [Ref. 2]. It appeared, with the original design, that the oil lubricating both the radial and thrust bearings was trapped in its own sump with the oil level above the center of the lowermost ball. Consequently, the oil level in the original bearing sump was being controlled by the two ½” diameter radial drain holes shown in Fig. 4. By eliminating the bolted-in dams in each bearing housing, the bearing balls would no longer be submerged in the oil and churning would be reduced. The temperature rise would be less and the bearings would run cooler.

The CPRS opted for a larger diameter flinger (7.50” instead of 7”), which now makes it possible for the outside diameter of the flinger to be submerged in 0.25” of oil. A 3/8” diameter third drain hole was added to the bearing bore at the 6 o’clock position to drain oil from the cavity between the inboard bearing covers and the bearings. The inboard covers were notched at that position to provide an unobstructed opening to the drain holes. Again, these reflect small, but important, experience-based changes with major beneficial impact on uptime of the pump [Ref. 3].

The CPRS calculated hydraulic thrust generation (in the axial direction) based on the following assumptions:

1. The first stage double suction impeller is axially balanced.
2. The back hub of the second stage impeller is essentially the same diameter as the balance drum wear ring, but has neither bushing nor case wear rings.
3. The head vs. capacity curve for each impeller is similar to the United L-10x23 TC proposal curves.
4. The specific gravity of an ash sluice mixture is 1.0.
5. Differential pressure at zero flow is 260 psi, at BEP it is 220 psi.
6. Each stuffing box is at or near suction pressure.
7. The pressure distribution on each impeller shroud is equal and has an average value of 0.75 times the pump differential head.
8. The impeller eye side ring diameter is 11.75”, the shaft diameter is 3.937” and the spacer sleeve diameter is 4.937”. 9. Because suction pressure acts throughout the pump, its effect does not influence the axial thrust and is taken as zero to simplify calculations.

At this point, the CPRS engineer listed his assumptions and submitted detailed calculations. At zero flow and P = 260 psi, the calculations corroborated his assumptions, yielding T = 3604 lbs toward the coupling. Similarly, at BEP and P = 220 psi, the calculations indicated thrust T = 3049 lbs toward the coupling.

While we elected to omit further details, the radial bearing loads were investigated in a similar manner. The message, once again, is that one should select a CPRS that will support its recommendations by readily providing the client with every relevant calculation or evaluation [Refs. 4 through 8].

Furthermore, some pump issues deserve to be tackled just as one would approach a new design. The effects of operation with worn running clearances must be considered; with wide-open clearances, only the anti-friction bearings will carry the radial loads [Ref. 9].

CPRS personnel also know that bearing life is reduced by incorrect bearing-to-shaft fits. Therefore, and in this example, relevant dimensions were recorded. Table III shows the bearing vs. shaft interference fits associated with the ash sluice pump. (Note that “T” stands for “tight.”)

Considering the cracked first stage impeller shroud…
As identified in an Inspection Report and Repair Proposal issued by the CPRS, the outside diameter of the outboard shroud on the first stage double suction impeller was cracked at three locations. Each crack occurred adjacent to a discharge vane tip. These types of cracks are common, especially on impellers that have accrued relatively long run times [Ref. 10]. The CPRS knows this and will not try to sell new impellers where none are needed.

Cracking failures usually result from fatigue associated with pressure pulsations caused by the impeller vanes passing the casing volute tips. The magnitude of these pressure pulsations decreases with the clearance [generally called “B” gap, Ref. 11] between the impeller and volute vane tips. The first stage impeller had a “B” gap that met the API-610 criteria—an important reassurance.

Another, less common, cause of shroud cracking is found on impellers having a natural frequency coincident with a multiple of the operating speed, most frequently the vane passing frequencies. With a 5-vane impeller and two volutes, the pressure pulsations occur at 5 and 10 times running speed of 8900 cpm (148 Hz) and 17,800 cpm (297 Hz). Thus, the natural frequencies of the damaged impeller were measured experimentally using an accelerometer and hammer and the results of this “ring test” cataloged. The lowest natural frequency above running speed was found to be about 658 Hz (22 times running speed).

No conclusive root cause for the cracked shroud was found. The impeller was weld-repaired, re-machined and rebalanced. The shrouds were not thickened as proposed in the original repair scope. The message here: CPRS facilities and their staffs apply scientific principles and analyses every step of the way. (Note: Recent publications, including several “Proceedings of the Texas A&M International Pump Users Symposium,” have shown that new pumps suffering from different resonance phenomena have, on occasion, been delivered and put into service. So, in the case of this ash sluice pump, the testing done by the CPRS was justified, as was deviating from the original repair scope.)

At the conclusion of its work, the CPRS recapitulated and documented the repairs by restating problems and observations, and by again highlighting solutions that were both merely considered and actually implemented. It was a very thorough undertaking, much like this fourpart series, whose purpose, among other things, has been to alert you, the pump user, to the following very important fact:

As denoted by the acronym “CPRS,” a truly Competent Pump Repair Shop, be it OEM or otherwise, will provide considerable value to you and your organization through its experience-driven and highly cooperative efforts. Choose wisely when it comes to entrusting your pumps to others. MT

Regular 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 Jim Steiger is senior aftermarket engineer with HydroAire, Inc., in Chicago, IL. Telephone: (312) 804-3694. Robert Bluse is president of Pump Services Consulting, in Golden, CO. Telephone: (303) 916-5032.

Putting proven technology to work
Engineered with proven planetary and helical gear technology, the new MagnaGear XTR line covers a full range of horsepowers, up to 2000 HP. Designed as a global product, the reducers are offered with parallel shaft or right-angle configurations, a solid or hollow shaft output and will initially offer torque capacities up to 920,000 lb-in. Incorporating a modular design that allows for multiple mounting configurations, they can be used with a variety of soft-start mechanisms.

Developed to meet or exceed AGMA and international standards, heavyduty, cast iron units feature carburized, hardened and precision-ground gearing. Tandem HBNR lip seals are standard for extra protection. All bearings exceed AGMA standards for L10 life. All components are power matched for optimum performance at a lower installed cost.

A complete line of engineered accessories are available for MagnaGear XTR, including internal lift-off style backstops, cooling systems, rigid couplings, torque arms, swing base mounts, tunnel housings and baseplate. MT

Baldor Electric Company
Fort Smith, AR

It’s widely known that investing effectively in crane maintenance can help reduce the risk of safety and environmental incidents, breakdowns, loss of production and premature equipment failure. Unfortunately, what level of investment is “optimal” is not as well known. There are various levels of crane maintenance that dictate what value, benefits and return a company can expect on their investment. The optimal level must not only remediate risk factors but also demonstrate a measurable return on investment.

Cranes represent a substantial investment for a company. Thus, determining the right level of maintenance required to maximize that investment should be a high priority. This is especially important for companies that depend on cranes as a part of their process.

When a crane becomes an integral part of a production process, it is called a “process crane.” Since process cranes are designed for round-the-clock use, they call for maximum reliability. They must be able to answer the most stringent performance requirements, including: automation, highly demanding duty cycles, difficult operating environments, high operating speeds and special control systems. The cost of downtime for a process crane can easily exceed $1 million US per day. Repairing the equipment after it breaks (i.e., corrective maintenance) is simply not enough. The optimal solution is to prevent the breakdown from occurring in the first place.

Optimal maintenance of process cranes can significantly reduce overall operating costs associated with downtime, etc., while boosting productivity. This is considered a proactive maintenance approach. In order to truly develop a proactive maintenance strategy, companies must conduct an in-depth crane reliability survey to gain the insights needed to develop their plans. Systematic and exhaustive surveys of this type will provide the facts needed to develop a smart strategy. In-depth crane reliability surveys also generate the information needed to enhance safety and mitigate issues, improve performance and reliability and extend the service life of a company’s process cranes.

Enhancing safety and mitigating issues
An in-depth crane reliability survey relies on the use of advanced diagnostic tools that penetrate deep into equipment and uncover problems that are undetectable by standard equipment inspections. Addressing those problems in advance prevents injuries from occurring and presents tremendous savings in injury-related costs.

Improving performance and reliability
A crane reliability survey provides a roadmap for improving equipment performance and reliability. Knowing what repairs are needed in advance allows a company to prioritize its maintenance activities and schedule the work so as to maximize productivity and increase uptime over the life cycle of its equipment. This not only helps prevent unnecessary production downtime— it saves money.

Extending equipment service life
A crane reliability survey also can help extend the service life of equipment by providing a guide for preventive maintenance, which, in turn, helps reduce capital investment costs. Knowing when to anticipate repairs allows a company to forecast expenses and put them into its budget for improved cash flow. This will help to avoid the unpleasant surprise of a sudden breakdown and the unexpected expense of the repair or replacement of their crane, which could lead to a loss in production revenue.

Conducting a crane reliability survey
A crane reliability survey is a very sophisticated undertaking. Every crane is different. Therefore, it’s important to study documentation, interview users and conduct in-depth analyses using advanced instruments that detect potential problems other inspections miss. A crane reliability survey should include four key modules: the CORE inspection, structures and working conditions, components and the maintenance assessment.

CORE inspection and analysis…
The aim of the CORE Inspection is to calculate the crane’s Safe Working Period—a time period assessed in which the operating characteristics of the crane (running speeds, acceleration, and deceleration) are suitable to the current use of the crane. During this phase, all crane information should be collected. It is important to become familiar with the crane through a review of all available documentation—reports and notes from past inspections and photographs of the crane and its parts. It also is important to gather information regarding the service history and current condition of the crane.

Next, it is important to conduct interviews to fully understand the usage and performance of the device. Any machine is best known by its primary operators. In some cases, the operator may need to adjust usage behavior and habits in order to extend the service life of the machine. Lastly, a detailed inspection is required. A field inspection should include gathering information on the overall crane condition. The crane should be inspected and the service life analyzed.

Structures and working conditions…
This study provides an overall analysis of the crane’s condition by evaluating the operating environment, the present state of the power supply, the alignment of the crane structure, its associated runways and the steel structures of the equipment. A series of four exhaustive analyses should be performed.

1. An ambient conditions analysis ascertains the operating conditions of the equipment, in which temperature, humidity and dust of operating equipment are analyzed. In addition, it is important to define the corrosive effects of the environment, using both tests and visual inspections.
2. A power supply analysis can detect potential problems related to the supply voltage of a crane. Common problems may include: a too high or too low voltage level, voltage dips, swells or interrupts.
3. It also is essential to conduct a geometric analysis to study the runway where the equipment is located. The condition of the runway strongly influences how well a crane moves on its rails, affecting the usability and lifetime of the traveling machinery units. It’s important to inspect the permitted geometrical tolerances: measuring, visually inspecting the rails and their fixings and comparing them to original installation drawings.
4. During the final stage in this phase, it is crucial to conduct a steel structure analysis to scrutinize each individual part for deficiencies in physical condition and assess structural safety.

Components…
The component analysis is a specific, detailed assessment of the present condition of the crane’s electrical components— all motors, gearboxes, hook block assemblies and the wire rope and its revving component. It is important to evaluate the risks that can lead to production loss due to component failure and explore options to minimize such occurrences.

An electrical component analysis will help to determine the condition of crane electrification. To improve reliability, there are many objects in the electrification that require monitoring. Furthermore, a motor analysis is necessary to determine the current condition of the motors on the crane.

The wire rope is one of the most critical parts of the hoisting machinery. The rope is stressed by tension, compression and bending during lifting cycles. Along with visual inspection, it is imperative to perform an advanced, non-destructive assessment with a rope tester.

Determining the condition of the crane’s hoisting and traveling gear is critical. Gears are normally designed so that the gear surfaces wear clearly and the load-carrying capacity is not lost—assuming that the gear case is maintained correctly. The purpose of the gear analysis is to define the current status of the gear in order to reduce the risk of gear failure.

Based on international standards, the hook and hook block also should be examined. The hook is used during every lift cycle and can be subjected to conditions that will produce mechanical stresses.

Maintenance and reliability…
During this phase, evaluate the overall maintenance of the crane by analyzing the reliability of the crane. The purpose of this analysis is to define the reliability of the crane and identify the most critical components that could cause downtime.

The reliability analysis should include a Life Cycle Assessment (LCA) environmental impact analysis, a spare parts analysis, and a cost analysis. The Life Cycle Assessment (LCA) determines the total environmental impact the crane will produce during its operating lifetime. This analysis includes emissions to air and water.

Spare part availability can cause an increased threat to productivity. The purpose of the spare parts analysis is to determine the parts that are critical and that should be readily available. The analysis also considers the suitable requirements of a storage location and estimates the value of the inventory of spare parts.

Next, evaluate all costs associated with the operation of the crane in a cost analysis. This analysis documents the company losses—time and monetary—as a result of inefficient equipment. Examine maintenance and operation records from a two-year span to determine the duration and frequency of a crane’s downtime and its overall impact on the production line. During this phase, analyze maintenance costs, production and quality losses. Moreover, a complete audit of the current maintenance situation of the company’s material handling equipment is recommended.

A company can perform its own crane reliability surveys or obtain them through outside sources (see Sidebar). Whatever approach you take, the point is to help you determine that “optimal” level of maintenance that will keep your process cranes up and running as scheduled—safely, reliably and cost-effectively. MT

Mike Williams is vice president of Service with Konecranes Americas. Telephone: (937) 525-5560; e-mail: mike.williams@ us.konecranes.com

In 1995, the U.S. National Safety Council published a provocative paper entitled “In Safety, Half Truths Hide the Story.” It stated: “Practically every [safety related] incident is the result of inadequate management action, supervisor and worker training, procedures and work conditions and/or safety rules and policy enforcement.” This reflects the common belief that a safe workplace is most likely one in which management has embraced worker safety as the highest priority.

While worker education and policy enforcement is an absolute requirement to realizing a safe workplace, we cannot dissolve individual accountability when it comes to personal safety. This is apparent when, despite all the safety messages, procedures, meetings, checks, specialized equipment, training, permits, measures and good intent, we still hear about maintenance professionals getting hurt on the job.

A parallel prime non-workplace example can be found with the automobile. Here, the manufacturer has been both legislated and proactive in providing the user with what is arguably the safest environment in the world.

Today’s vehicles are emblazoned with colorcoded safety messages, safety glass, seat belts, front and side air bags, body roll protection, energy-absorbing crumple zones, climate control, traction control, ABS braking systems, warning systems, etc. Yet, we still see an alarming amount of injury and death on the roadways.

Conjectured opinion has placed blame for most automobile accidents on human error caused by distraction. Driver distraction takes many forms, including eating and drinking, primping, listening to loud music, using cell phones, reading and the not-so-obvious distractions such as fatigue, anger, relationship problems and other types of emotional stress, among others.

How often, while driving or performing a task at work, have you found yourself distracted and poorly focused on the task at hand? Unfortunately, stress caused by workloads, relationship problems, poor diets and/or sleep deprivation all can cause distraction and compromise safety. The reality is that we are all partners when it comes to safety. Accordingly, we are responsible for both our own and each other’s safety.

Frame of mind
Safety is a combination of understanding, managed risk, common sense and—above all— frame of mind.

Prehistoric man truly understood the dangers of his environment, as his life very much depended on personal awareness every minute of the day. In today’s world, we are accustomed to “handing over” our safety to others, often ignoring our intuition, and rarely seeking to truly understand the dangers that accompany us every minute. Changing one’s frame of mind begins when we actively seek understanding about the dangers within our working environment.

With management providing the safety tools and training, it is up to us as individuals to make that training personal. Many individuals work in potentially hazardous environments; risk is managed through understanding consequence of failure and being competent in our response to those failures. Thus, making an effort to fully comprehend your work environment and method of manufacturing or process deliverable is crucial to understanding and managing risks you face should a failure occur.

Stay well and aware
Learn to recognize both normal and abnormal equipment behavior. Check out the Material Safety Data Sheets of both production and maintenance materials. Know what you are handling. Being trained in confined space management is futile if you cannot personally recognize a true or marginal confined space within your workplace— without an identification signpost. Knowing how to operate an emergency wash station is wasted, if you don’t know where the emergency wash stations are located.

Managing risk is all about marrying understanding, knowledge and common sense. However, developing and using a common sense approach to managing stressful and dangerous situations can be difficult to achieve when an individual’s frame of mind is distracted and unable to focus. To combat this, more and more companies now recognize that wellness—or an individual’s good mental and physical health—is equally important as a safety-driven workplace culture in providing enhanced employee self-esteem and a clear frame of mind. In turn, this all translates into a much healthier, safer and more productive workforce.

Forward-thinking companies are now providing opportunity for their employees to elevate their personal fitness levels by offering differing workplace programs that include gymnasium sports, field sports, meditation and healthier, lighter fare in their company cafeterias. Mental health programs are rapidly on the rise and manifest themselves in workplace day care programs, personal counseling programs, education completion programs, generalinterest training programs, etc. These types of company-sponsored or sanctioned initiatives are all clearly aimed at cutting down the stress in employees’ daily lives by significantly reducing distractions and growing healthier, safer workplace environments.

Be careful out there
Subscribing to a safer and healthier attitude toward work and life in general is all about developing and maintaining a true connection with your own self. Health and safety truly is a personal issue, connecting each and every one of us as partners. MT

Ken Bannister is lead partner and principal consultant for Engtech Industries, Inc. Telephone: (519) 469-9173; e-mail: kbannister@engtechindustries. com