Oil Condition Monitoring Using Electrical Conductivity

Article extract from Reliable Plant newsletter:
http://www.machinerylubrication.com/Read/29407/oil-condition-monitoring

Electric conductivity is a measure of a fluid’s electrostatic chargeability. It usually is expressed in picosiemens per meter (pS/m). In addition to the type of fluid, conductivity also depends on the concentration of movable charge carriers. For example, pure distilled water is only slightly conductive. However, if the water contains impurities such as salts, acids or bases, then its conductivity increases.

Lubricants are normally only slightly conductive and therefore can work as insulators in transformers or switches. However, oils can also conduct electric current. Their conductivity is dependent on several different factors, including the base oil, additives and polarity.

Oil Conductivity

The more polar a lubricant is, the less refined and more conductive it is. Based on the manufacturing method and level of refining, the American Petroleum Institute (API) has classified base oils into five groups (see Table 1).

The lightly refined, mineral-oil-based base oils of Group I represent the simplest option and previously accounted for the largest proportion of lubricant production. Over the last few years, that proportion has been in steady decline, as the more refined base oils of Groups II, III and IV are increasingly being utilized for modern lubricants. This trend of using more refined base oils and synthetic alternatives is based on the fact that they generally have better characteristics such as higher aging stability. However, while the higher-quality base oils have many advantages, there are concerns over some of their changed properties, which can lead to problems, especially when unfavorable combinations occur. One such consequence is varnish, which can be due to the base oil’s altered dissolving performance with regard to aging and reaction products. Another consideration is component and lubricant damage, which can be caused by electrostatic discharges. The lubricant’s conductivity is an important factor in the charge buildup, and conductivity is dependent on the type of base oil used (see Table 2).

Table 2. Conductivity of oils and synthetic fluids at 23 degrees C (73 degrees F)

Along with the base oil, additives have a significant effect on an oil’s conductivity. The higher the proportion of metal-organic additives, the higher the lubricant’s conductivity. A prime example would be metal-organic additives such as those frequently used in zinc dithiophosphate (ZnDTP). As a proven multi-purpose additive in engine and hydraulic oils, ZnDTP improves wear and corrosion protection while simultaneously functioning as an antioxidant. However, zinc is considered to have dangerous health implications, so ZnDTP should be largely avoided. This means that the oil’s conductivity decreases and the risk of static charging increases.

A lubricant’s conductivity not only is influenced by the base oil and the additive package but also depends on temperature. The higher the temperature, the higher the oil’s conductivity. Unfortunately, there is no linear correlation between the two parameters, as each oil type has its own conductivity/temperature relationship. Furthermore, at a constant temperature, conductivity still changes during operation due to additive reactions, wear metals, reactions with metal surfaces, water and the formation of aging and oxidation products.

Electrostatic Charges

Although monitoring conductivity so far has been unable to achieve much success in the area of sensor technology, it is gaining significance with regard to electrostatic charges and discharges in lubricant and hydraulic systems.

Figure 1. The relationship between lubricant conductivity and temperature

In oil-circulating systems, electrostatic charges generally can occur if there is friction in the flow between the oil and the surfaces surrounding it. The strength of the static charge depends on many different and partly interconnected factors. The energy density, which builds up in the system and leads to subsequent discharges, is contingent on the oil’s conductivity and volume flow. The more oil that flows through a circulation pipe and the lower the oil’s conductivity, the greater the potential for an electrostatic charge.

Oil can be especially electrostatically charged if:

• It is formulated with a base oil from Group II or III.
• It contains no polarizing (zinc-containing) additives.
• The conductivity of the new or old oil is less than 400 pS/m.
• It is fed into pipes that are too small.
• It is moved with too high a flow velocity.
• It produces friction in poorly designed filter elements.
• Pipes and hoses are not grounded.
• The oil level has dropped too low.
• It contains high proportions of undissolved air (bubbles).

Electrostatic Discharges and Possible Consequences

If the level of electric charge in the system becomes too great, an electrostatic discharge (ESD) will occur. In such cases, microsparks or sparking results. Typically, a crackling or clicking sound will be heard near the filter or in the tank. If the charge is high enough, the discharge could be repeated several times in quick succession. Discharges primarily take place in areas with vastly different material combinations. Modern filters with a high proportion of plastic are often affected.

The microsparks caused by a static charge can lead to temperatures approaching 1,000 degrees C. This can be extremely dangerous if the fluids are even slightly flammable. In addition, if hydrocarbon vapors have formed in the tank ventilation area, the system could spontaneously combust. However, when discharge sparks occur within a turbine or hydraulic oil-circulation system, they are normally smothered very quickly by the oil. Nevertheless, these mini-explosions can burn holes in filters or even seriously damage the oil due to increased sludge buildup.

Effects on Turbine and Hydraulic Oils

In recent years, electrostatic charges and discharges have been occurring more frequently in turbine and hydraulic oil systems. Several developments are responsible for this, including:

• Modern hydraulic fluids and turbine oils have become increasingly less conductive because of the global trend to use modern base oils and additives. Previously, turbine oils were based on relatively conductive, lightly refined Group I base oils. Currently, more oxidation-resistant, better refined Group II base oils or even partly synthetic Group III base oils are being used, especially for gas turbine oils. These oils are considerably less conductive. In addition, turbine oils normally contain very few metal-organic additives, which help to prevent the formation of unwanted deposits (varnish).
• New systems feature a more compact design with a considerably smaller tank capacity and a proportionally larger displaced volume.
• Oil purity requirements have increased. This in turn has led to higher filtration rates.
• The filtration intensity and electrostatic charge properties of the oil (resulting from filtration) have increased.
• The oils’ low conductivity, which often is far below 1,000 pS/m in certain conditions, has resulted in an increased tendency for electrostatic charging.

Measuring Conductivity to Prevent Damage

In order to prevent damage from electrostatic discharges, more than just the conductivity of new oil must be identified. The parameter is also important for older lubricants, especially when dealing with larger quantities, if nothing is known about the used oil or a burning smell or soot particles are noticeable. Therefore, some oil analysis laboratories now offer conductivity measurements at different temperatures. The process has been tested for several years and is conducted in accordance with ASTM D2624. It originally was developed for inspecting airplane kerosene to avoid accidents caused by jet fuel charging.

As mentioned previously, oil’s conductivity value is measured in pS/m. If the conductivity is more than 400 pS/m at 68 degrees F (20 degrees C), there is little risk of damage to the oil or the system from electrostatic charges. However, if the value is lower, there is a very real possibility that the phenomenon could occur.

If an oil with an increased ESD risk is being used, grounding the entire system is not a viable option. The voltage inside the system cannot be discharged through a grounding wire. Fortunately, there are several other approaches for prevention.

4 Ways to Prevent Electrostatic Problems

1. Install special stat-free filters instead of conventional filter cartridges. These filters can discharge or even prevent the charge from occurring.
2. Use an oil with a different makeup and higher conductivity value.
3. Choose or modify the system’s material combinations so microspark formation is prevented despite an electrostatic charge.
4. Optimize flow diameter, tank hold times or tank volumes to minimize the charge potential.

Machinery Lubrication (6/2013)

Using ‘Unscheduled’ Oil Analysis for Early Predictive Maintenance

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29398/unscheduled-oil-analysis

Most oil samples are taken based on a fixed schedule. For large, stationary rotating equipment, monthly or bi-monthly samples are common. Proactive maintenance programs depend on regular checks for oil cleanliness, dryness and lubricant quality. However, machines can and do fail for a variety of reasons, and there is a certain randomness to the onset of these failures. Furthermore, the failure development period is equally unpredictable, with some failures taking months to develop, while others are sudden and abrupt.

In the March-April 2013 issue of Machinery Lubrication, I addressed machine criticality analysis as an essential tool to define the Optimum Reference State (ORS) for numerous lubrication and oil analysis activities. The Overall Criticality Matrix (OCM) is constructed from two assessments: the Machine Criticality Factor (MCF) and the Failure Occurrence Factor (FOF). The MCF relates to the consequences of machine failure while the FOF relates to the probability of machine failure. Both the MCF and the FOF are highly influenced by the effectiveness of “early fault detection.” In other words, the effectiveness of early fault detection sharply reduces machine criticality (for details on this, read the article atwww.machinerylubrication.com/Read/29346/machinery-criticality-analysis).

Figure 1. Early Predictive Maintenance P-F Interval Scheme

This is the critical link to the “unscheduled” oil analysis strategy. Its theme is not just predictive maintenance (PdM), but more specifically, early predictive maintenance (EPM). Let’s start by reviewing the widely used P-F interval. A modified version is shown in Figure 1.

The “P” is the point when an abnormal wear condition or fault is first detected. The “F” is the functional or operational end of the failure cycle requiring repair or replacement. Failures with short development periods usually go undetected when tests (e.g., vibration and oil analysis) are performed infrequently (even monthly analysis is viewed as infrequent). Conversely, frequent detection methods not only can report a developing failure but also have the potential to detect that failure early (in the incipient stage). There are specific tactics and tools for doing this well.

Again, the secret to this strategy is the frequency. It enables a much higher percentage of failure detection (saves) events, especially earlier detection. The purposeful benefit is mitigated machine damage and reduced or no unscheduled downtime (longer P-F interval). While PdM concentrates on predicting the end of a machine’s (or lubricant’s) service life, EPM puts critical focus on timing - not just detecting - by detecting early. It seeks a budding problem, not a burgeoning problem.

Detection by Multi-Modal Surveillance

In Noria’s seminars, we use the expression, “You can’t catch a fish unless your hook is in the water.” Likewise, in oil analysis, you can’t catch a fault unless your hook is in the water. There’s an earlier tier to oil analysis called the “detection phase,” which in my view is a huge untapped opportunity in condition-based maintenance. Most scheduled oil analysis programs skip over the detection phase by attempting to catch impending machine failures and only take infrequent snapshots of oil condition.

Figure 2. Combining lab data with surveillance data for a complete picture of machine condition

The detection phase of EPM is continuous failure surveillance across numerous parameters. It integrates skillful and frequent human inspection tactics with other conventional monitoring technologies. A few years ago, I wrote a column on the power of the one-minute daily inspection. This is a critical and often underutilized modality of surveillance and detection.

Fundamentally, the detection phase of EPM is anything and everything that can be done to detect (not analyze) failure in progress. It includes all of the following:

• Daily routine visual inspections of the oil (level, color, opacity, foam, varnish, tank condition, leakage, magnetic plugs, etc.)
• Audible inspections (change in machine sound)
• Temperature inspections (touch, heat guns, gauges, etc.)
• Portable PdM technology inspections (vibration overalls, thermography, acoustics, motor current, etc.)
• Mechanical inspections (shaft movement, seal conditions, open gear wear, etc.)
• Instrument and gauge inspections (flow rates, proximity probes, pressure, bypass indicators, etc.)
• Onsite oil analysis screening tests (crackle, blotter, viscosity, ferrous density, patch, etc.)

Many impending and precipitous failure conditions that were first reported by scheduled oil analysis could have been detected much earlier if better and more frequent inspection methods were in place, such as those in the list above. The economics of early detection are enormously improved as well.

As noted previously, failure detection and failure analysis are different concepts. Once an abnormal condition has been detected, it can be investigated further to determine where it is coming from, the probable cause of the failure, how severe and threatening it is, and the corrective action. This is where oil analysis and other predictive technologies can be very valuable. “Unscheduled” oil samples can then be forwarded to the lab for troubleshooting purposes (diagnostics and prognostics). These include samples from secondary sampling ports to help localize the source of the problem.

In the laboratory, specialized qualitative and quantitative tests can be performed to characterize the nature of the condition. These might include wear particle identification (XRF, SEM-EDX, analytical ferrography and many others). The skills of a triboanalyst and a multi-technology PdM specialist can combine lab data with surveillance data for the most complete picture of the machine’s condition (see Figure 2).

Proactive Maintenance Still Requires Scheduled Oil Analysis

Unscheduled oil analysis is not an alternative to scheduled oil sampling and analysis. Routine oil analysis is still needed for many reasons. The most important is proactive maintenance, which uses oil analysis to monitor and control the presence of failure root causes. These include verification of the lubricant’s physical and chemical properties as well as contamination control. The benefits of a fine-tuned proactive maintenance program are much slower machine wear rates (longer machine service life), fewer overall machine failures and less associated downtime.

When proactive maintenance is combined with EPM, a comprehensive and more efficient condition-based maintenance program results. Early predictive maintenance is about extreme vigilance. It involves the development of more effective inspection skills and a more effective means of inspection (machine modifications). It also requires a culture change and management support for remediation of machines that have not yet failed.

Machinery Lubrication (6/2013)

About the Author

Jim Fitch

Jim Fitch, a founder and CEO of Noria Corporation, has a wealth of experience in lubrication, oil analysis, and machinery failure investigations. He has advised hundreds of companies on developing ... Read More

Inspecting Reciprocating Compressors with Ultrasound

Article extract from ReliablePlant newsletter:
http://www.reliableplant.com/Read/29745/reciprocating-compressors-ultrasound

Anyone who has benefitted from the advancements made in ultrasound testing will agree that this technology is no longer just for leak testing. It is a complimentary companion technology to vibration analysis, infrared imaging, motor-circuit testing and oil analysis. Some will assert that the foundation of any predictive maintenance program should be based on ultrasound first due partly to its versatility, low cost and easy implementation.

Nowadays, meeting reliability professionals who still believe in archaic methods for detection of machine faults is rare. That's why it was surprising to read Dan Wise's technical paper, "Knocking Compressor? All you really need is a screwdriver to find the source of the problem." His message compelled me to climb back on my soapbox and scream, "You need ultrasound!"

Safety should be taken very seriously. Inspector training is as much about safety as it is about procedure, so it's hard for me to look past the obvious hazards that could come from sticking a greasy screwdriver in your ear and then placing the other end against a knocking compressor valve. It is also difficult to ignore the added risk of working in a noisy compressor room without wearing approved safety gear.

Wise's paper suggests that ultrasound is unnecessary because the technology "takes time to learn." Instead, he urges inspectors to develop their skills with a screwdriver "by spending time, each day, paying attention to the sounds of compressors." His advice is conflicting. Are we better to spend time each day learning his "old-school" screwdriver technique, or are we better off to spend our time learning how to use an ultrasound instrument that can do so much more?

Figure 1. Inspecting reciprocating compressor
valves with an ultrasonic data collector

For more than 20 years, ultrasound has been providing early warning signals for mechanical failure. If you can hear compressor valves knocking with a screwdriver, you are too late. However, there is a fundamental difference in philosophy between what ultrasound inspection proposes to accomplish and what is hoped to be achieved with a screwdriver. Ultrasound monitors the condition of that compressor valve from the time it is new until the time it is ready to be replaced, all the while providing feedback about subtle changes in its operational condition. The screwdriver method is used "to find the source of the problem," which suggests the knocking is already perceivable to the human ear and it is only a matter of days, hours or minutes before the compressor will fail. I call this firefighting. It is certainly not condition-based monitoring, and it leaves no room for planning the repair.

The paper warns that "valves can break without warning for a variety of reasons" and goes on to list some common causes for failure. The real reason machine systems fail "without warning" is because no warning system is in place. Using a predictive technology such as ultrasound condition-based monitoring to indicate subtle changes in machines over time allows industry to avoid firefighting catastrophes.

Advanced Valve Testing

A huge benefit of ultrasound is its ability to record dynamic wave files on reciprocating compressors. Using simple time waveform analysis software, it is easy to expand 1/10th or even 1/100th of a second of data to see a valve open, exhaust and close. During that blink of an eye, you can see if there is complete sealing of the valve seat and can even assess the strength of the valve spring. All of this data can be printed in a logical report, which serves as a summary for management to decide if further action is necessary. Because the document becomes a historical archive, the next decision will have a basis of comparison.

Reciprocating compressors contain one or more cylinders that compress gases. A simplified example is shown in Figure 1. Pistons travel up and down within the cylinder. On the downstroke, new gas is drawn into the cylinder through an inlet valve. On the upstroke, gas already trapped in the cylinder is compressed and pushed through an outlet valve to a receiver or tank. In this example, a vacuum pulls the outlet valve closed and the inlet valve open, while pressure does the opposite. In more complex reciprocating compressors, more robust valves operate with springs.

Opportunities for failure are many. Seal integrity around the piston cylinder wall reduces the efficiency of compression. Dirty and worn valves do not seat properly due to corrosion and buildup around the valve head. Internal leakage around the piston and valve head can be detected with ultrasound inspection by recording a dynamic ultrasound signal and analyzing it over time. Early mechanical failures, which can eventually lead to screwdriver-detectable valve-knocking, can be seen this way, too.

In Figure 2, you can see the impact made by the valve when it is seated and the suction of turbulent air flow when the valve is opened. High amplitude signals between the valve impacts can reveal mechanical looseness (early knocking) or internal leakage from piston rings or the valve seat. A comparison of similar valves can be made easily by scaling the Y-axis of the time signal and presenting it in overlay or side-by-side mode.

A documented report that cites the historical evolution of your compressor's health can be an extremely valuable and professional way to present your data. It is a great tool for conveying to maintenance managers that a problem is escalating and that action is required. It will hold much more credibility than walking into your boss's office with grease dripping from your ear and suggesting that a compressor valve sounds like a "bongo drum" and should immediately be removed from service.

There is no substitution for walking the plant floor and visually taking account of the state of affairs. Much can be learned by talking with operators. Operators have the best pulse for machine condition because they work around them every day. For those who are ready to take the next step (implementation of a condition-based monitoring program), getting to know the expectations of operations, management and front-line staff is the best approach. From that point, defining the assets that need the most critical monitoring will be as an important of a step as figuring out which technologies should be used to collect the data.

Documentation is the final piece of the puzzle. Without it, all other initiatives are pointless. Needless to say, modern techniques for collecting data that can be trended and reported are preferred over archaic methods that rely on individual interpretation and old-school tricks.


Figure 2. Dynamic time signal captured on a recip valve head

About the Author

Allan Rienstra

Allan Rienstra is the president of SDT Ultrasound Solutions and co-author of "Hear More: A Guide to Using Ultrasound for Leak Detection and Condition Monitoring." He has spent the past 20 ... Read More

Grease Analysis: Early Warning System for Failures and Proactive Maintenance Tool

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29284/grease-analysis-system

Taking oil samples on a regular basis as part of a maintenance strategy has become state of the art. Oils are tested with regards to their condition, possible contamination and wear. Laboratory results and evaluations by experienced engineers can support the identification of upcoming component failures, prove whether maintenance actions like filtration or dehydration work properly and help establish condition-based oil drain intervals.

It’s a different story when it comes to grease. In the past, continuous trend-based grease monitoring was not a common practice even though the majority of installed bearings are grease lubricated and have a substantial impact on the reliability of the equipment. However, a change in philosophy seems to be occurring with a trend toward more routine grease analysis. This has been driven by technical issues and supported by positive experiences with oil analysis programs.

In addition, there have been many examples from the field where grease analysis has proven to provide important information about grease, including the amount of wear, contamination, consistency, bleeding behavior and condition of the base oil and additives.

Since grease properties often change significantly during operation and that the contamination and wear information is concentrated within a relatively small volume that’s not affected by filtration or diluted by a huge oil reservoir, grease analysis can be a very effective condition-monitoring tool. In many cases, grease analysis was initially performed only after damage or an accident, but trend analyses of grease samples have shown that trouble with grease or bearings can be recognized in advance with a good grease analysis program.

The Proper Sampling Technique

For a valid grease sample, the proper sampling technique is required. It obviously is much more difficult to take a representative grease sample from a bearing than to take an oil sample.

To take a grease sample, use a 
syringe to pull used grease
into the sampling tube.

To take a grease sample, remove the inspection screw on a slew bearing or take off the grease nipple from a rolling-element bearing. Cut the sampling tube in a length that is appropriate to enter the bearing and reach an area for taking a meaningful sample. Mount the clean tube on a syringe and press the opening of the tube onto the corresponding greased area. Use the syringe to pull the used grease into the sampling tube (at least 1 centimeter).

For some applications, it may be necessary to repeat the procedure on different sampling points of the same bearing. Approximately 1 gram of grease is enough for analysis. Be sure to watch for any color changes to avoid taking fresh grease too close to the regreasing point.

For trend analysis, samples should always be taken at the same points. A sample of the fresh grease should also be sent as a reference sample for all future analysis.

Elemental Analysis

Grease samples can be analyzed by optical emission spectroscopy (OES) according to the rotrode principle. Up to 21 elements can be evaluated to obtain information regarding wear, contamination and additives. These include:

• Wear metals (iron, chromium, tin, copper, lead, nickel, aluminum, molybdenum and zinc)
• Contamination elements (silicon, calcium, sodium, potassium and aluminum)
• Additives or thickeners (magnesium, calcium, phosphorous, zinc, barium, silicon, aluminum, molybdenum and boron)

Of special interest for diagnosing a bearing or grease condition is the amount of iron and chromium, which are present as wear particles from the bearing material. Non-ferrous materials like copper, lead and tin indicate corrosive or abrasive wear from the bearing cage. If dust (silicon or calcium) or sea water (sodium, potassium or magnesium) is present, this information can help determine the reason for the presence of wear metals. The amount of metallic soap elements or a comparison of the additive content in fresh and used grease can also reveal whether the recommended grease is in use.

Particle Quantifier

The particle quantifier (PQ) index is specialized for the determination of all magnetic iron particles. An index value between O and 9,999 characterizes iron particles present in the sample independent of the particle size. Because rust particles are non-magnetic, they are not measured.

The PQ index test is based on the principle that iron (and iron wear) is magnetic and can be detected by a magnet. If a grease sample contains magnetic iron wear particles, a magnetic field is disturbed. This change in the magnetic field can be measured.

Remember, the PQ index gives the total content of magnetic wear particles. Contrary to the iron wear information determined by OES, the PQ index provides information about all iron wear particles. Also, when using OES for used grease samples, only particles up to 5 microns can be detected because larger particles are not excited.

Grease Condition by FTIR

Fourier transform infrared (FTIR) spectroscopy identifies the type of base oil and thickener of the used grease. By comparing the unused fresh grease reference to the used grease sample, additive depletion or contamination by another grease type can be determined.

In comparison to FTIR spectroscopy of oil, the measurement and interpretation of a grease spectrum are more complex. The thickener compounds especially can be very dominant within important areas of the spectrum that are normally used for the calculation of the water content or oxidation.

FTIR spectroscopy is based on the principle that the molecules present in a lubricant can absorb infrared light at corresponding wavelengths depending on its typical structure. Changes in the used grease in comparison to the fresh grease reference spectrum are calculated on the typical peaks at predefined wave numbers and interpreted as oxidation, water, etc.

An FTIR spectrum can provide information regarding contamination
and any changes in a grease sample.

A very small grease sample (less than O.1 gram) is applied to an attenuated total reflectance (ATR) cell. In the contact zone, the grease sample will be exposed to infrared light. An infrared spectrum showing the absorbance of the infrared light on the corresponding wave number will be recorded and interpreted.

The infrared spectrum of a sample provides information regarding contamination and any changes in comparison to the reference spectrum. By a spectra subtraction of used grease with reference grease, the FTIR method indicates what kind of unknown grease is in use. In addition, a mixture of different greases in many cases is revealed. The identification of the original grease and the base oil type can be found by searching a library of reference spectra and can support the cause of a failure.

The FTIR method can also show whether synthetic or mineral base oils are used. If a mineral oil is used as the base oil, FTIR can indicate whether the base oil was oxidized because too much time passed without regreasing or because the temperature was too high. If the grease contains extreme pressure (EP) additives with zinc and phosphorus, the degradation of the additives can be seen. The water content in the grease may also be provided.

Water in Used Grease by Karl Fischer Titration

Besides solid contaminants, which can be identified by the OES elements silicon, calcium or aluminum, water is a type of contamination that is often the cause of corrosion. Typically, short regreasing intervals are the result of too much water. Unfortunately, determining the amount of water in grease is not as easy as in an oil sample.

For water determination according to the Karl Fischer method, a small grease quantity (approximately 0.3 grams) is placed into a glass vial and sealed with a septic cap. In a small oven, the sample is heated to approximately 120 degrees C. The steamed-out water is transferred by nitrogen into a titration vessel in which an electrochemical reaction between the water and a Karl Fischer reagent takes place. A titration curve is recorded, and the water content is defined precisely.

Depending on the grease type and application, the water content in the grease should not exceed the recommended values. Too much water in a grease can produce a variety of adverse effects, including corrosion on bearing metals, increased oxidation of the base oil, softening of the grease, and water washout of the grease.

If the result for water content according to the Karl Fischer method is compared to the elemental analysis by OES, it can be determined whether the water in the sample is “hard” or sea water, which contains minerals like sodium or potassium, or if it is soft water like condensate or rain water. If sodium, potassium, calcium and magnesium are found in the used grease but are not in the fresh grease, the presence of “hard” water is the likely reason. Comparing these two methods, Karl Fischer titration and OES, can also indicate whether the water was already present in the fresh grease as part of the production process.

Additional Tests

Besides the previously described methods, which should be the minimum requirement for grease analysis, there are a few other tests that can be performed. The table on the left lists most of these additional tests. Keep in mind that a failure investigation after damage has occurred often requires a more complex analysis, and not every test method is designed to be a routine analysis.

In summary, grease analysis has proven to be a useful tool to evaluate grease and bearing condition. Different situations and influencing factors for wear, contamination and grease condition have shown complex coherences between the grease analysis results and their practical meaning. This leads to the conclusion that observing and interpreting these factors with expert knowledge can enable proactive maintenance strategies to be applied in a reasonable way for grease-lubricated components.

Machinery Lubrication (2/2013)

Sampling is Key to Oil Analysis Accuracy

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29277/sampling-oil-analysis

Oil analysis is perhaps one of the best tools in your arsenal when it comes to determining the health of a machine. The data in the oil not only holds the key to the health of the lubricant but also to that of any wear modes existing in the machines. When you pair this with historical data, you are able to trend these results and better understand what is going on inside the equipment.

Many people regard drawing oil samples as an “as time allows” activity and fail to reap the benefits this technology has to offer. It should be taken seriously and be performed with the utmost care and diligence. It is not enough to simply fill a bottle with oil from the system; you must perform this task properly to accurately trend the data you receive back from the lab.

The first step to accurately track data from your oil samples is to identify the proper location for an oil sample. Samples should be taken from turbulent or “live” zones within the oil system. Pulling a sample from the drain valve is not an accurate representation of the condition of the machine. Wear particles, contaminants and water settle to the bottom of the sump, thus making this sample full of historical data and difficult to trend as you continue to sample from this location.

Oil Sampling Best Practices

Bull’s-eye Data

• Consistent use of documented “best practice” sampling method and “in application”
• Live zone sampling “on the run”
• Upstream of filters, downstream of machine components
• Flushed sampling valves and sampling devices, clean bottles
• Sampled at proper frequency
• Hours on oil recorded and other meaningful inspection and operating details
• Report make-up fluid volume added prior to sampling (if any)
• Samples forwarded immediately to lab

Drop-tube sampling is another method that should be avoided. This involves a vacuum sample pump, a length of tubing and the reservoir of the machine you are testing. With this method, it is challenging to get the tubing into a live zone of the oil and to repeat the exact same test location time after time. This also leads to poor trending of data and skews the accuracy of your sample.

Modifying your equipment to include sample ports is a must if you wish to accurately trend your oil analysis data. Installing a sample port or sample valve provides a location where you can consistently pull a representative sample of the oil in your systems. The sample valve should be located in a turbulent area of oil flow. This can be found after pumps or in elbows where the oil turns and begins to flow violently. You want to sample upstream of any filters to ensure that you aren’t losing any of the valuable data due to filtration.

Some systems may have only one sample port. For instance, if you have a gearbox, you should install a sample port with a stainless-steel tube extension so that the end of the tube (where the sample will be drawn from) is close to the gear teeth and at least 2 inches away from any of the walls of the gearcase. When you sample, you then will use the same port and draw oil from the same place every time. This leads to consistent and trendable data. It also makes spotting any abnormalities in the oil very easy.

71%	of machinerylubrication.com visitors report equipment at their plant has been modified to include oil sample ports or valves

Many systems should have several sample ports. This is where the discussion of primary and secondary sample ports begins. A primary port is a location in the system downstream of the working components where you can get a good representation of the system as a whole with one sample. As you draw samples from this location and trend the results, there may come a time when you begin to see an increase in wear debris. This is where secondary sampling ports come into play. Secondary ports allow you to track where the increased wear is coming from in the system. Generally, secondary ports should be installed after individual components to allow for monitoring of their health.

For example, if you are sampling the return line of a hydraulic system and see an increase in wear debris, you would want to track where that debris is coming from within the system. In a typical hydraulic system, you would need to have a secondary port after the pump and after any cylinders or hydraulic motors in the system. This would allow you to find where the increase in wear is originating.



Using proper sampling techniques is just as important as the sample valves. You must flush your sampling hardware to limit the data disturbance by environmental contamination. Typically, flushing 10 times the dead space of the sample equipment will suffice and ensure that you are getting a good sample. For very dirty environments, keeping the sample bottle in a sealed bag while you draw a sample will help minimize data disturbance by outside sources.

In addition, take a look at the oil sample bottles you are using. Bottle cleanliness makes a difference in the oil’s particle count. If your particle counts are high, consider purchasing sample bottles that are certified “clean” or “super clean” to make certain that the disturbance is not in the bottle. For systems in which the oil samples are extremely critical, perhaps use glass bottles that are certified “ultra clean.”

Oil analysis data has a wealth of benefits for those who utilize it properly. By ensuring that you are sampling properly, this data is more easily trendable and the results can be more easily understood. Of course, tracking historical results is a must for any good oil analysis program. Keep striving for world-class standards and always keep an eye out for what your oil is trying to tell you.

.

Machinery Lubrication (2/2013)

About the Author

Wes Cash

Wes Cash is a senior technical consultant with Noria Corporation, focusing on machinery lubrication and maintenance in support of Noria's Lubrication Program Development (LPD). He holds a ... Read More

Using Sight Glasses and Level Gauges

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29202/using-sight-glasses

When I go to a plant to examine its current lubrication practices, among the first things I look for are sight glasses. These devices provide a wealth of information in the time it takes to walk up to a component and check it. More than just simple additions to a machine to indicate there is enough oil in the sump for proper lubrication, sight glasses offer an opportunity to monitor the oil.

Generally, sight glasses come in two styles. Columnar sight glasses attach to an oil-bathed component, typically at the drain port. They have cylinders made of a transparent material (glass, acrylic, some plastics, etc.) in which oil is free to fluctuate up and down with the change of the oil level within the machine. The second style is known as the “bull’s-eye” sight glass. It also is made of a transparent material but is threaded into a port where the oil level should be maintained during operation.

Each sight glass has its own strengths and weaknesses. Columnar sight glasses are great for reading the oil volume. Since it is piped into the machine at a low oil level, the level in a sight glass can usually be seen even when the oil volume is low. The appropriate oil level must be marked on the sight glass so you can tell if it is correct.

Other Types of Oil Level Indicators

There are other oil level indicators that should be mentioned but that don’t necessarily represent best practice for a lubrication program. Dipsticks have been utilized since someone had the great idea to put a metal rod into a volume of oil to check its depth. These devices are easy to use and can tell you where the oil level sits. They also allow you to perform a blotter test with the oil that comes off them.

The problem with dipsticks is that you have to open the machine component to the outside atmosphere to check the oil volume. This gives airborne particles a direct source for ingression. Not only can airborne particles fall in and contaminate the system but also any dirt or debris that may be on the cap when you remove it to pull out the dipstick.

Level plugs are common for machines that hold a smaller amount of oil. These are threaded plugs that are unthreaded from the machine case when the oil is being refilled. Once the oil begins to drip from the oil plug, it has the proper amount of oil in the sump. These are great for refilling purposes, but once again the machine is open to the atmosphere and at risk for particle ingression when these devices are used.

The same goes for systems in which you must open a hatch or cap to visually check the oil volume. Any time you open machine components to the outside, you have to be aware that you are giving dirt and contaminants a chance to enter them. Devices like these should be avoided whenever possible, and equipment modifications should be made to accept either a columnar or bull’s-eye sight glass.

When plumbing in this device, you must make sure there aren’t any “goosenecks” or traps in the piping that would enable the oil level shown in the sight glass not to be representative of the volume in the sump. There are more hardware requirements with these types of gauges due to the fact that they are externally mounted. They also need to be able to “breathe.” Some manufacturers actually put small breathers on top of their products. If possible, it is best to pipe the top of the sight glass either back to the headspace of the reservoir or to a desiccant breather. This allows the sight glass to “breathe” if necessary without ingressing any contaminants.


Another disadvantage of the columnar sight glass is that it doesn’t clearly show whether there is a foam or air entrainment problem on the inside of the reservoir. Since the oil filling the level gauge is coming from the bottom of the sump, air has a chance to detrain, preventing you from being able to see any indication of foam in the column.

On the other hand, a bull’s-eye sight glass sits directly on top of the inside oil level so any foam can be seen more easily. Bull’s-eye sight glasses are great for confirming that the oil level is correct. Since there is no piping or potential to create a trap, whatever level is seen in the bull’s eye is what the oil level actually is.

One drawback to these gauges is that it’s hard to see the true oil color when looking through them. If by chance you have a very clean, unstained sight glass, then you can see the color and be on the lookout for any darkening or changes in turbidity (e.g., from oil/water emulsions).

56%	of lubrication professionals use columnar sight glasses most frequently in their plant, according to a recent poll at machinerylubrication.com

It’s not enough just to put a sight glass on a machine and walk away. These devices should be monitored. They are windows into what is happening with your oil and can give you a first-hand account of any problems that are occurring. Things like water contamination, oxidation and low oil levels can all be diagnosed quickly when these accessories are used properly. Being proactive and properly equipping components with a sight glass can provide peace of mind that both the oil and machines are healthy.

Machinery Lubrication (12/2012)

About the Author

Wes Cash

Wes Cash is a senior technical consultant with Noria Corporation, focusing on machinery lubrication and maintenance in support of Noria's Lubrication Program Development (LPD). He holds a ... Read More

Vibration and Oil Analysis Techniques Reveal Root Cause and Severity

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29123/vibration-oil-analysis

When evaluating mechanical defects in roller elements and gears commonly found in rotating machinery, there are several techniques that can be applied to reveal root cause and severity. One is wear particle analysis using either a filter patch or glass slide. Another technique is a wear particle ferrous-density measurement method often referred to as ferrous index. A third technique is an impact-detecting vibration stress-wave analysis method called PeakVue®.

Each of these techniques independently provides insights as to the nature of a damage-causing mechanism, including abrasion, fatigue, boundary wear or corrosive wear. Root cause and severity information learned from these techniques can then guide operators to call for the best proactive and corrective actions. Uncorrected, these mechanisms will produce significant mechanical deterioration.

Figure 1. Vibration and oil analysis reveal proactive root causes and predictive failures in progress.

Industrial plant maintenance departments typically use walk-around and on-line vibration analysis together with periodic oil analysis to determine condition-based maintenance on rotating machines like pumps, motors, compressors, gearboxes, turbines, fans and rolls. Figure 1 shows how vibration and oil analysis collectively address proactive condition monitoring by finding root causes before damage occurs, as well as by identifying component failures in progress, which might range from incipient to catastrophic.

PeakVue Technology

The PeakVue technology is a highly sensitive and trendable impact-detection method for quantifying defects in roller elements, bearing races and gear teeth. It is a unique stress-wave analysis technique distinguished from demodulation, shock pulse, spike energy and other peak detection methods in that PeakVue detects and holds a scalar maximum peak value from each oversampled plurality of sample values collected during each sample interval.

For example, Figure 2 is a comparison of demodulation with PeakVue in six different measurements of the same vibration signal having a periodic impact. The three plots on the left show how demodulation captures and represents only a small fraction of the total signal, so the portion detected is substantially diminished by the sampling bandwidth (1,000 hertz top, 200 hertz middle and 50 hertz bottom). The three plots on the right reveal how PeakVue captures and consistently represents the same data independent from bandwidth selection.

Figure 2. Demodulation (left) vs. PeakVue (right) showing waveform for bandwidths of 1,000, 200 and 50 hertz respectively (top to bottom).

Ferrous Index for Ferrous Density

Abnormal wear mechanisms of abrasion, fatigue, boundary wear or adhesion along with corrosion are common to rotating machinery such as gearboxes, pumps, motors, compressors, rolls, presses and transmissions. A ferrous-density measurement like ferrous index is an excellent method for detecting abnormal wear in the 5- to 60-micron size range. This is usually the result of abnormal fatigue caused by cyclic loading and boundary wear where lubrication is inadequate.

Emerson, Spectro Form Alliance

Emerson and Spectro Inc. recently announced an alliance to combine technical innovation and expertise to deliver best-in-class oil analysis solutions. By combining Emerson’s oil analysis application for the process industry with Spectro’s extensive oil analysis product line and expertise, users can gain more meaningful and accurate information on the condition of their machinery.

Under the new agreement, Spectro gains rights to a suite of Emerson-developed and patent-protected intellectual property in the field of oil analysis for predictive machine maintenance. Included in this portfolio is Emerson’s AMS Suite oil analysis software module as well as the CSI 5200 Machinery Health Oil Analyzer, which is part of the Trivector minilab package.

Effective Oct. 1, Spectro will become the exclusive worldwide supplier of the Spectro 5200 Minilab product and services offering. The onsite minilab is used to quickly test incoming and in-service lubricants with immediate retest when needed, enabling improved lubricant contamination control with effective root-cause detection and elimination.

This ferrous-density measurement is highly sensitive to wear debris or dust contamination produced by abnormal abrasive wear. It is a measure of wear particles typically containing iron alloy particle debris in sizes as small as 5 microns and extending to at least 60 microns. This size range is frequently produced by abnormal severe sliding (boundary lubrication) wear or fatigue wear.

Figure 3. An ASTM D7416 minilab reports
ferrous index and wear particle analysis.

The ferrous index is defined in ASTM D7416 as a “ferrous-density-type parameter measuring the relative concentration and size of magnetically responsive iron particles greater than 5 microns collected on a dielectric-permittivity sensor.”

Wear Particle Analysis

Wear particle analysis is a direct approach to visualizing damaging causes and effects taking place in lubricated machinery by capturing and viewing particles extracted from lubricating oil. ASTM D7684 is a new “Standard Guide for Microscopic Characterization of Particles from In-Service Lubricants.” It provides excellent recommendations for terminology and techniques, such as filter patch analysis or analytical ferrography, and offers insight as to what is likely happening inside the rotating machine.

This new guide defines rolling contact fatigue wear as being “caused by loaded rolling contact typically between the roller and race in bearings or between gear teeth in the vicinity of the pitch line, typically forming spall-type pitting and releasing rolling contact fatigue particles.” Rolling contact fatigue particles are described as “flat platelets, with a length more or less equal to their width, with smooth surfaces, random, jagged and irregularly shaped circumferences, and a major dimension-to-thickness ratio in the range of approximately 5:1 to 10:1 or more.”

Figure 4. PeakVue data from a bearing pedestal.

Performing Ferrous Density and Wear Particle Analysis Onsite

The onsite minilab shown in Figure 3 can be used to measure wear, contamination and chemistry parameters of lubricant samples, including ferrous index and wear particle analysis. Industrial plant maintenance departments employ onsite analytical tools like this to get immediate feedback with retest capability if needed.

Figure 5. Evidence of boundary
lubrication (sliding wear)
due to inadequate lubrication revealed
by wear particle analysis.

On the following page is an example of PeakVue and oil analysis, including wear particle analysis, combining for effective identification of root cause and severity. PeakVue data from a bearing pedestal is shown in Figure 4, while Figure 5 reveals wear particle analysis results from the same machine. Together, these technologies indicate a problem of inadequate lubrication.

In conclusion, vibration and oil analysis each provide valuable insights into the health of machine components and lubricant systems. The combination of PeakVue, ferrous density and wear particle analysis produce three independent perspectives into the root cause and severity of an anomalous condition. Armed with this information, predictive maintenance technicians are able to accurately recommend appropriate corrective actions in order to improve maintenance and plant reliability.

Machinery Lubrication (10/2012)

Using Oil Analysis and Daily Inspections to Improve Lubrication

Article extract from ReliablePlant newsletter:
http://www.machinerylubrication.com/Read/29122/inspections-improve-lubrication

In large industrial plants where a great number of machines are installed, it is necessary to implement an effective lubrication-management system. This type of system can help ensure that machines are well-lubricated and, if a fault or any abnormal situation is detected, further analysis or a corrective action can be carried out.

To make the system work, a machine database with well-defined lubrication points and scheduled lube routes is required. It is also essential to make good use of the data collected daily by the lubrication crew. If this information is promptly introduced into the database and generates an alarm when the machine is in poor condition, the reliability engineer can fix many potential problems.

The information collected by the
lubrication crew will help the 
reliability engineer focus his
analysis only on the critical
machines and their 
specific problems.

Lubrication routes and preventive maintenance (PM) can be modified automatically by lubrication software based on simple oil analysis and field inspection information provided by the lubrication crew. These tailored routes can improve effectiveness by focusing on critical machines, which are checked more frequently depending on the condition of the lube oil and the lubrication system.

Lubrication Management and Scheduled Lube Routes

Before providing details on tailoring lube routes, let’s define what an effective lubrication-management system is as well as its main objectives. Generally, the purpose of a lubrication-management system is to schedule and plan the lubricating tasks of the machinery in the plant and to properly manage the field information supplied by the lubrication crew. The correct grade of lubricant also should be delivered to the proper lubricating points in the right quantity and on schedule to optimize the human and material resources.

When implementing such a system, several key factors must be taken into account to allow for the effective monitoring of the machines at a reasonable cost. The following tasks should be performed during the design of any lubrication-management system:

Develop a Machine Database

This first step involves recording all the machines to be lubricated in a database, along with their lubricating points and the appropriate lubricant. The database should be flexible enough to adapt to such changes as machine revamps or oil type upgrades. It should also allow for the historical recording of incidents that are documented on the lubrication routes.

A field inspection should provide information on the lube oil system conditions and the mechanical condition of the machine.

Audit Lubricant Types

Once a machine database has been developed, the location of the lubricant service stations and the machines that use those lubricants must be studied in order to optimize the distance travelled by the lubrication crew. At this point, it is also important to standardize the lubricant types to a minimum that meets the machine manufacturer’s requirements.

Create Lubrication Routes

The lubrication specialists or the reliability engineers must create the lube routes. These routes consist of a series of points to be lubricated (divided into geographical areas or into production units) with related tasks to be performed on a detailed schedule.

Design a Template

A template can be designed for use as a lubrication guide when performing field work. The template should include all the relevant information for the lubrication operators such as identification numbers of the machines to be inspected, lubricating points, the lubricant to be used at each point and tasks to be performed. There should also be open fields in the guide table in order to note any observation or anomaly detected.

Establish a Procedure for Work Orders

Lubrication work orders should be generated with a frequency that allows for proper planning of the work and should be delivered with the specific work plan attached. Also, be sure to print and detail the work plan for the personnel who will actually carry out the job to avoid unscheduled work and downtime.

This template was designed for use as a lubrication route guideline.

Determine Who Performs the Lube Routes

It is important to decide which members of the staff will be in charge of lubricating the machinery to avoid delays in the task execution. Keep in mind that in this type of work, any problem will affect all subsequent lubrication routes, which can cause serious damage to machinery.

If all of these steps are followed during the implementation of a lubrication-management system, it will be much easier to achieve the desired result in terms of machine reliability.

The Importance of Reliable Field Data

Once the lubrication plan has been created and the material and human resources required are clear, it is essential to utilize qualified personnel (or contact a qualified lubrication company) to carry out the lubrication tasks. Qualified personnel is needed not only to perform good quality work but also to provide reliable daily information regarding the lube and mechanical condition of the machines inspected during the route.

This is an example of a lube oil alarm panel.

In addition to performing all the work and inspections detailed in the routes, any qualified member of the lubrication crew should be able to:

• Carry out simple corrective maintenance jobs related to the lubricating systems.
• Perform quick visual inspections of the lube oil quality (moisture, particles, color, debris, etc.) and report its status in the lube route guideline table.
• Ask his or her manager or the reliability engineer about further analysis of critical machines that are considered to be in poor condition.
• Report any other observed anomaly that could affect the machine or personal safety.

The information collected about the machine’s condition must be reliable in order to allow for a complete subsequent analysis by the reliability engineer. This is of great importance because any information reported by the lubrication crew will help the engineer focus his analysis only on the critical machines and their specific problems. This will save time and labor, as the field information is first filtered by qualified personnel, which simplifies the job of the reliability engineer.

If special care is taken during the filtering of the field information to register all of the data consistently and with a coherent structure, the task of the reliability staff will be simpler and the historic data will be easier to search.

Using Field Inspections from Lube Routes

Depending on the work experience of the lube staff and the available time intended for the lubricating tasks, the lubrication operator should provide the following information about the machine condition:

• Visual analysis of the lube oil condition (water contamination, debris, oil temperature, color, etc.)
• Lube oil system condition (oil leaks, tank cleanliness and superficial condition, oil filters, oil drains, etc.)
• Mechanical condition of the machine (vibration, noise, bearing temperature, etc.)
• Miscellaneous (information on new machinery installed at the plant, reports of other problems in the plant that affect the lubricated machines, etc.)

Qualified personnel is needed
to provide reliable information
regarding the lube and mechanical
condition of machines inspected during a route.

All of this information should be recorded by the lubrication crew in the report table of the route for the inspected machine. This data should be added to the system database as soon as possible in order to help the engineer promptly solve any problems detected within the machines. Remember, the reliability engineer takes care of the machines, and the faster the information is added to the system, the faster he or she can analyze the machine condition with the most advanced predictive technologies.

By updating your lubrication-route software, you can automatically include in the next planned route every lube point that has been found to be in poor condition. With this automatic process, the lube points that are deficient are revised more frequently until the correcting actions have the desired effect. An alarm system for the machine’s lube condition can also be implemented based on the information collected from the lubrication routes.

From this starting point, there are multiple strategies that can be implemented to optimize the lube-route schedule based on the machine condition and how often anomalies are detected. If an integrated system is employed, other information about the machine status can be used to improve the schedule and inspect the machines that are in poor condition more frequently. The difficulty lies in how to combine all of this data and find useful rules to be incorporated in the software. Any strategy should be in accordance with the general lubrication schedule and should not change planned work orders.

The lubrication frequency of points in poor condition that need to be inspected again will correspond to the maximum number of lube points included in the same processing unit of the plant. For example, let’s say the available lubrication frequencies in one unit will be a multiple of a fixed number of days (15, 30, 45, 60 days, etc.). This method allows the mechanical workshop to manage only the planned work orders. The difference is that the number of lube points will be slightly increased depending on the machine’s oil status.

A visual analysis of the 
lube oil condition in the inspected
machine should be reported by
the lubrication crew.

There are other improvements that can be implemented when tailoring lubrication routes and PMs based on the information collected from field personnel, including:

• The status of the lube point inspected in the last route can be included in the guideline table for the next route. This allows personnel to pay more attention to the most critical points.
• Any valuable information or pending work orders on the machine can be included in the guideline table and taken into account by the lube operator.
• Any automatic alarm or advice intended for taking further action like oil analysis, vibration measurements, etc., will improve the performance of the system.
• Other information based on the machine type and the organization of the reliability and maintenance departments can be utilized.

If an organization has obtained reliable information from the lubrication routes, it is critical to process all of this data in order to optimize the frequency of machine lube inspections. This is especially effective if you have lube points that are in poor condition and require more frequent inspections. Inspecting problematic points more often ensures better control of their status and helps the reliability engineer to take corrective action sooner.

Also, if the industrial plant has a computerized reliability system with predictive, preventive and other related machinery condition information, the combination of this data (such as vibration and oil analysis) will allow for improved system performance, as more complex and effective strategies may be used.

Machinery Lubrication (10/2012)

How Oil Quality Changes During Startup

Equipment manufacturers generally provide guidelines on how oil should be maintained for reliable operation. Because components have little tolerance for contamination or oxidation, frequent oil sampling and monitoring are performed while the equipment is online in order to keep the unit operating without any issues. However, many times little attention is paid to the oil quality when the equipment is shut down for a maintenance outage or on standby. This can eventually affect the unit’s reliability.

For instance, when a steam turbine is down for prolonged periods or for a short three-week maintenance outage, the consequences of not having hot, circulating oil running through the system is usually not considered. In fact, the oil quality when placing a turbine on turning gear or during startup is often not the same as when the unit came offline.

Prolonged exposure to water can
rust a control system.

Typical turbine bearings are designed for fluid-film lubrication. Most fluid-film bearings are intended for hydrodynamic lubrication. This means an oil wedge is formed in a hydrodynamic bearing to develop separation and maintain an oil film between the rotor and bearing. The film thickness is a function of rotor speed, load and oil viscosity. Under fluid-film conditions, an increase in viscosity or speed increases the oil film thickness, while an increase in load or decrease in rotor speed reduces the oil film thickness.

In developing an oil film, the bearing surface geometry and rotor surface are just as important as rotor speed, load and oil viscosity. To establish a stable oil wedge and fluid film between the surfaces, the rotor and bearing profiles must be perpendicular. If either or both surfaces become damaged by large particles being pushed through the bearing, the ability to form an oil wedge is diminished, resulting in a thinner oil film thickness. Reducing the oil film thickness increases the susceptibility of additional damage or producing a rub during coastdown or startup.

The congealed mass shown above is an example of particulate matter and
degraded oil buildup that can accumulate in a turbine control servo.
Left unattended, this condition could eventually cause poor
turbine control response and accelerate equipment wear.

When the turbine rotor is at normal operating conditions, the bearing is in hydrodynamic lubrication conditions. However, when a turbine rotor is on turning gear or beginning to roll at slower speeds, the journal bearing is in boundary lubrication conditions. These conditions are generally indicated by some metallic friction and wear.


Very high coefficients of friction may also be reached. At this point, the oil film thickness between the bearing and the turbine rotor will be at its minimum. The film thickness will increase as either the speed is increased, the lubricant viscosity is increased, the load is decreased or the geometric shapes of the journal and bearing surfaces relative to each other are improved. If the surface becomes rougher (the bearing surface becomes damaged), then the risk of rotor and bearing surface contact increases. This relationship between the surface roughness and the film thickness is important in the consideration of hydrodynamic lubrication of a turbine bearing.














 These images show the buildup of particulate in a turbine oil reservoir that is cleaned periodically. Consider the type of buildup that could occur over the life of the plant.

A major concern with rough surfaces, including gouges or grooves around the journal or along a Babbitt surface, is that they allow high-pressure lube oil to flow away from the thinnest film areas. This permits increased contact and shear forces on the Babbitt than would occur with smooth, concentric and round journals on a smoothly bored Babbitt surface bearing. This is why surfaces that appear to have minimal damage can still cause bearing failure during startup or slow-speed operation before a fully developed hydrodynamic film with a normal film thickness exists.

During a plant startup, when a turbine is on turning gear or at lower speeds, the lubrication system may supply lube oil with slugs of particulate matter to the journal and thrust bearings. This is especially damaging to journal bearings because they carry the applied load forces that force the journals into contact with the bearing surface, thus providing a very thin oil film. This form of lubrication is known as boundary lubrication. Because only a very thin oil film exists between the journal and bearing surface, and many of the particles in the oil are larger than this oil film thickness, the bearing surface can be scored as particulate becomes imbedded in the surface of the Babbitt. In some cases, the particulate can score the journal, requiring it to be remachined and/or honed.

Water Contamination

Water contamination in a lubricating or control system is particularly undesirable because it tends to form an emulsion with the oil. Elevated water content in an oil system can also affect lubricity and induce corrosion. When a lubrication or control system is shut down, the normally wetted regions, such as those in the lube oil drain pipes, become exposed to air. Enlarging the surface area of carbon steel that is subject to ambient conditions increases the amount of internal corrosion (rust) a system develops.

While a unit is operating, the amount of water in the lubricating or control system is normally maintained within the manufacturer’s specification by the plant’s oil-conditioning system. These systems often contain some type of demulsifying agent to remove water. Even if the water content is well above normally acceptable standards, the steel surfaces are usually kept wetted with oil, and corrosion (rust) is limited. However, when the turbine is shut down for weeks or months, water will generally separate from the oil in the pipes and components where the oil resides. If water separation occurs, it can corrode the equipment, support microbiological growth and/or affect the functioning of the control system. Additionally, when drained, large portions of the system normally filled with oil become exposed to the environment (air and oxygen). Obviously, the longer the duration a turbine lubrication system remains secured, the more time the equipment has to oxidize.

Particle Contamination

This orifice plug from a boiler feed
pump turbine control has deposits
covering the orifice holes.

Particle contamination not only can cause equipment to wear, but it also clogs lubrication ports, in-line filters and control systems. During operation, the parameters used to monitor oil tend to remain stable, but when the system that is designed to maintain lubrication and keep piping and hardware clear is secured, the rate of oxidation on the exposed surfaces increases. Then, when the unit is returned to service, the newly formed corrosion (rust) on any exposed piping or surfaces often is shaken loose or washed away with the restarted oil flow. Furthermore, where there are pockets in which stagnant oil may have settled, a slug of particulate and coagulating oil can easily form. When the oil flow is restarted, this particulate matter is easily pulled into the lubrication flow streams and circulated throughout the lubrication system.



One substantial area of concern is the control system. Because of the system’s complexity and low-flow velocity within the control piping, the system acts as a collection point for particulate.

Biological Growth

When a lubrication system is secured for prolonged periods of time, biological growth can occur. Low-flow areas can collect a tremendous amount of sludge over the years. With this amount of growth, a sudden change in the lubricating system’s temperature, such as that which occurs when returning the system to service, can result in the biological growth dying off and the remains being pushed through the system.

Biological growth, particulate and separated lubricant additives have
collected on this pump (above left). The lube oil cooler on the
right has biological growth and adhered lubricant additives.

Cleanliness Codes

Most plants have equipment monitoring programs that define lubricant property limits. These limits are usually established for normal operating conditions. One of the parameters typically monitored is particulate levels. The International Organization for Standardization (ISO) has developed a method (ISO 4406) for quantifying the level of particle contamination. The values gathered in a particle count test identify the number of particles in a given volume of fluid that are above a specific size range, which is generally set at 4 microns, 6 microns and 14 microns. The data is normally presented in a format such as 17/15/13, which provides a numeric range value representing the measured quantity of particles greater than 4 microns, 6 microns and 14 microns, respectively.

Case Studies

In a recent turbine outage, the lubrication system was placed into operation, and the main turbine was placed on turning gear. While the system was operating, an auxiliary filtration skid was connected to the main turbine reservoir to run in parallel with the normal filtration system. The skid had dual 7-micron filters and processed the main turbine reservoir four times per hour. An oil sample recorder pulled samples at 20-minute increments from the center of the turbine oil reservoir and then documented 31 hours of results from the mesh blockage particle counter.

Figure 1. The results from a mesh blockage particle counter revealed that a large amount
of contaminants were released into the lubrication system after 12 hours of operation.

As Figure 1 indicates, after approximately 12 hours in operation, a large slug of contaminants must have released into the system, causing the need to change filters. At that point, a decision was made to reduce the filter size and continue. Once the turbine was rolled, the auxiliary filtration unit was secured. Inspection of the last set of filters revealed a significant collection of particulate captured within the filters.

In another example, a filtration skid with a particle counter was tied into a turbine reservoir during the plant’s startup. This power plant normally only operates during peak summer months in the southern part of the United States, leaving it shut down for at least six months out of the year. The particle counter recorded main turbine reservoir contaminant levels above 4, 6 and 14 microns. Figure 2 illustrates the change in particulate levels from the time the turbine was on turning gear until the unit was synchronized to the power grid.

Figure 2. This graph illustrates the changes in oil particulate during the startup
of a turbine. The dash lines provide the lSO 4406 “alert” level for specific particle sizes.

Notice when the turbine rolled off turning gear and increased its speed to 2,400 revolutions per minute for thermal soaking, a large burst of particulate was released into the lubrication system. This caused all three particle levels to increase above the normal operating limits and remain high for more than two hours. Added filtration was able to bring the particle levels down to acceptable limits, but when the turbine speed was increased to synchronize the generator to the power grid, another spike occurred.

Plants generally do not monitor particle levels as equipment is placed back into service. When a turbine is at normal operating speed, the minimum oil film thickness between the turbine rotor and the bearing surfaces is in the order of 0.002 inches for journal diameters from 8 to 16 inches. The minimum film thickness increases to 0.010 inches for the largest journal bearings with 30-inch diameters. However, when the turbine is on turning gear, this oil film thickness is only a few microns thick at best.

As the speed increases, so does the film thickness between the rotor and bearings. If a large mass of particulate gets into a journal bearing when the film thickness is only microns thick, the particulate matter can scar or damage the journal and/or bearing profile, which in turn affects the fluid dynamics within the bearing. This often leads to overheated bearings and possibly to bearing failure.

To control particulate matter, it is better to use filter element sizes than ISO charts, since ISO charts allow a few large particles, which can lead to journal bearing failure.

Understanding what is occurring provides the best way to identify and assess risk. Once a risk is identified, actions can be taken, consequences evaluated, mitigations and contingencies developed, and an implementation plan pursued.

There are many ways to reduce risks when bringing large equipment back into service. A review of vibration data and other parameters can tell a lot about how the equipment performs when going from cold to normal operating conditions. It also will inform you of what is needed to extend the health of the equipment or increase the operating efficiency.

Connecting a kidney-loop filtration system to a tank or reservoir can help
reduce the risks when bringing equipment back into service.

Perhaps the most versatile and cost-effective method to help reduce the risk to equipment is to have a kidney-loop filtration system available. This type of system can be connected to a tank or reservoir to support bringing the equipment back into service.

The filtration unit should be sized to process the contents of the tank or reservoir several times per hour. In addition, the unit can be equipped with a cooler for summer months when thermal loads on the plant limit equipment operation. Along with filtering and cooling, a kidney-loop system can include a dehydrator, which provides an excellent way to extract water from the oil before placing the equipment on turning gear. This will reduce the amount of water that gets pushed through high-pressure differential regions of the oil film in the journal bearing and reduce the risk or amount of flashing, which causes damage and erosion of Babbitted and non-Babbitted surfaces.

Keep in mind that the expense of an auxiliary filtration skid can be quickly offset by a reduction in maintenance costs. In fact, the cost of replacing a damaged bearing or by keeping plant equipment running during peak summer months could easily justify reducing the risk of repeat failures. For example, a 10-percent power reduction at a nuclear plant during peak summer temperatures would pay for auxiliary filtration systems on most challenged equipment within days.

.

Machinery Lubrication (10/2013)

Best Ways to Prevent Equipment Problems

Article extract from MachineryLubrication newsletter:
http://www.machinerylubrication.com/Read/30560/prevent-equipment-problems

Preventive maintenance methods are often promoted but rarely put into practice. This article will attempt to encourage a paradigm shift in maintenance thinking with prevention driving most of the activities. The main thrust will be on leadership and not 
simply management.


Leadership vs. Management


The classic definition of management is to do things right. The definition of leadership is to do the right things. The difference may be subtle but very important. How often have you witnessed someone planning a repair job to be completed within an allotted timeframe when no one was asking why this repair needed to be made so frequently? 


A manager attempts to get work done on time, while a leader attempts to minimize or eliminate the required work. A manager continually asks for more people, while a leader tries to maximize the effectiveness of his or her staff. A manager tackles problems as they arrive, while a leader asks why continual problems are tolerated.


Prevention Depends 
on Leadership


Without proper leadership, problem prevention is very difficult to achieve. The following case studies illustrate a variety of situations in which preventive techniques were used effectively in a typical mill environment.


A Poorly Designed 
Hydraulic System 


In this mill, steel slabs issuing from a caster started as a long, continuous hot metal strand. A torch cutter sliced off 30-foot slabs from the front end as the strand moved at a slow pace. The slabs were lifted off the table rolls and stacked for delivery to a storage yard by a carrier. The tongs resembled two pairs of giant 10-foot scissors operated by hydraulic cylinders and fed by a hydraulic system mounted near the top of the scissor arms. The system had a vertical tank with a pump mounted beside it. Due to space limitations, the valves, tubing and hoses were located directly over the pump and motor, making for a very congested design. The entire assembly hung from a crane. When an O-ring blew or a valve needed changing, quite a bit of disassembly was required to access the bad part. A lot of time was also wasted with repairs on this equipment due to the design.


The cause of the problem was obvious, and only a redesign would suffice. The supplier of the tongs was contacted and told the system design was inadequate. With “manifolding” technology, much of the pipe, tubing and hoses could be eliminated as well as the congestion in the confined spaces. The supplier agreed to redesign this part of the system, which solved the problem. This case exemplified a unique issue where only prevention of future problems would suffice. Learning to live with the problem was not an option.

Inefficient Purchasing 
of Lubricants


At this particular company, lubricants and hydraulic fluids were purchased by individual departments with no coordination between them. Consequently, the number of brands proliferated, increasing the chances of duplication. Products were procured by brand name, and the purchasing department had no choice but to buy what was requested. Because lubricants were purchased by brand name with no competition, suspicions arose that prices might be excessive. When a problem arose, quality was blamed and another supplier was brought in to solve it.


It was suspected that the company was living with a problem that could be resolved. Because ASTM and other test methods could help determine product quality, a committee was formed to decide how to purchase lubricants based on these tests. A strategy was soon developed. All products would be tested for important parameters to uncover duplicates. Products would be separated by categories such as petroleum hydraulic fluids, fire-resistant hydraulic fluids, general-purpose greases, electric-motor bearing greases, petroleum turbine oils, gear oils, anti-friction bearing oils, petroleum circulating oils and synthetic oils.


Specifications were also written for each lubricant type based on the test results of the higher grades in each category. Every specification was assigned a unique number, and equipment throughout the plant was tagged with the number of the product it was 
to receive.


The specifications were sent out for bids from various suppliers. The lowest bidder was awarded the business for one year. The prices received were markedly lower than the comparable branded products.


After the initial groundwork was completed, the system began to function well. The inventory shrank because so many locations used the same products. Purchasing in bulk became possible due to consolidation, which also resulted in a reduction in drums and costs. Samples of incoming products were taken periodically to ensure quality. Gradually, the overall quality improved. 


The goal of the system was to purchase high-quality products at the least possible cost and to eliminate as many empty drums as possible. Mistakes related to applying the wrong lubricant were also reduced. Once the system was in place, it took very little time to maintain it. 


This was an example of a plant living with a problem that not many thought was a problem. It was only after some penetrating questions were asked that most were convinced that there might be a better way of doing things. How the plant was purchasing lubricants was costing much more than necessary both in dollars and in manpower.


Short Motor Bearing Life


In this hot mill, as the steel strand issues from the last finishing stand, a long series of rolls conveys it at high speed to the coilers. Each roll is individually driven by an electric motor. Water cascades down from sprays to cool the strip as it speeds toward the coilers. Despite elaborate splash guards, it is almost impossible to keep water off the motor shafts. The shaft seals were not adequate to keep water out of the motors, and trying different seal designs did not help. The motor repair shop could barely keep up with all the failures. Finally, a seal company recommended adding flingers on the shaft. These consisted of a rubber device that looked much like a shaft seal but with a hole in the center slightly smaller than the shaft diameter. As a motor was repaired and ready to ship, the repairman would slip a flinger onto the shaft up to the housing. When the motor was installed in this wet environment, any water that migrated toward the seal area would be flung off due to the rotating flinger. In this way, water could not get to the seal. Motor bearing life increased tremendously. In this instance, a serious problem was prevented with a simple device but only after someone asked why this was being tolerated.


Frequent Servo-valve Repairs


As steel mill technology improved, more and more servo valves were being used on the mill’s hydraulic systems to gain precision. Because of dirt sensitivity, systems with servo valves must be filtered to extreme cleanliness. Despite great efforts, servo-valve losses were becoming excessive at the mill. Costs were also high since the repairs could not be done in-house. 


To prevent these failures, a non-bypass duplex filter separated by a three-way valve with an electrical alarm was installed ahead of each valve. The filters had a cleanliness level of 1 to 2 microns. When the alarm sounded, maintenance personnel knew they had only a few minutes to switch the three-way valve to the clean side before a shutdown occurred. A clean filter element was always on standby. The result was that the servo-valve failures virtually ceased.


Once again, a simple design change prevented a serious problem. However, the difference with the servo-valve issue was that production was being affected as well as repair costs.

Excessive Oil Losses


Oil losses were becoming excessive in the mill’s hydraulic and lubrication systems. The millwrights dutifully kept the systems filled and operating but did not report all the oil additions as they were made. When additions were reported, there was no good method for determining the amount. Therefore, it was difficult to establish where the bad leaks were and to schedule repairs. Prevention or reduction of these oil losses was the goal, but they could only be attacked when they occurred.


The decision was made to mount small water meters on the fill lines to each system. These meters had some internal friction, but since the oil was being pumped in as makeup oil, the pressure required was adequate. In cases where the oil flowed by gravity from an upper to a lower floor, low-friction meters were required. Each day, an inspector read the meters to determine if any leaks had gone unreported. If so, action was taken. This was an example of taking preventive action (reading the meters) to prevent further losses. No action could be taken without proper information supplied by the meters.


Rapid Motor Burnouts


The plant’s coke oven doors are approximately 20 feet tall and 4 feet wide. They are made of steel, lined with firebrick and weigh about 1,000 pounds. Each is mounted vertically on each end of the oven and must be lifted off by a huge machine so the red-hot coke can be pushed out. The doors are held in place by two steel arms that are rotated into place behind vertical “buckstays.” In the center of the arms is a hexagonal nut that is 5 inches in diameter. The arms are rotated by a large socket that fits the hexagonal nut and is operated by a motor and gear reducer mounted on the machine. The arms often become wedged behind the buckstays, so an electrician must hold in the overload relays to get the motor to turn. Frequent motor burnouts were attributed to this practice. 


Rather than increase the size of the motors, the decision was made to convert the operation to hydraulic motors due to the inherent overload protection in such a system. Relief-valve adjustment serves this purpose.


Because of the large amount of dirt inherent in the coke plant and the dirt sensitivity of the hydraulic motors, the hydraulic systems were redesigned. This redesign was so successful that no hydraulic motor failures occurred for the first five years. The improved cleanliness also increased pump life. This case was an example of prevention involving a radical design change with which not everyone agreed.


Unchecked Oil Temperatures


At another hot mill in the Pittsburgh area, the challenge was determining the cause of losing several back-up bearings. It seemed to be a case of the oil overheating, but when the coolers were examined, none of the thermometers was working. It also appeared that no one was checking the key system parameters, such as temperature, water content, flow, tank levels and cleanliness. 


When the thermometers were replaced, oil temperatures of 175 degrees F were observed. Evidently, the coolers were having no effect. Once the coolers were replaced, the problem ceased. 


This was a case of not paying attention to signs that can warn of impending problems. Management hastily instituted a form to be completed on each shift that forced someone to watch those important system parameters. 


Misreported Oil Demulsibility 


Oil purchased for the mill’s back-up bearing system needed to be able to drop out water quickly. The purchasing specifications gave a very strict number that had to be obtained from the ASTM D-2711 test. ASTM D-1401 is another test for demulsibility, but it is used for light oils. The heavier oils utilized for these back-up bearings had to be tested with the former test, although it took much longer than the ASTM D-1401 test. 


The mill was experiencing a rise in water levels with samples tested from new loads of oil. Samples taken from in-service oil were having the same problem. Under normal conditions, the water levels should have remained under 5 percent but were now 20 percent. The lab assured the mill that the samples of new oil were within the specification. This situation continued for several months as an investigation was conducted. There were concerns that back-up losses would soon begin rising. 


As luck would have it, the lab shut down, which meant the mill had to find another one. When the next sample was sent to the new lab, the mill immediately received a call that the demulsibility was below specification. The load had been pumped out and replaced with a load from another company. It turned out that the old lab had been using the ASTM D-1401 test because it was quicker than the D-2711 test but did not inform the mill. The oil supplier didn’t even have the equipment to perform the D-2711 test but was relying on its additive supplier to provide the percentage to use. This was a case of having all the needed tools in place but still getting bad information.


Three Phases of Prevention


These case studies encompass preventive actions for three types of situations: an obvious situation, a change of methods situation and an unseen situation. Each of these is described below.


An Obvious Situation


These situations are like the poorly designed hydraulic system or the electric motor bearing issue. The problem is very costly, and the solution is either obvious or requires a design change. The solution will also require time, money and the will to do it. Most agree that solving the problem is worth a try since it is easily seen. These situations are usually designated as “crises.” The alternative is to learn to live with the problem.


A Change of Methods Situation


These situations involve a long-standing way of doing things, such as each department buying lubricants with no attempt at consolidation or not reporting system fluid additions. Although the problems are seen, not everyone envisions a solution or agrees one is needed. Personnel have learned to live with the problem. Basically, the way things are done must be changed.


An “Unseen” Situation


Many times actions can be taken to prevent bad things from happening. These include condition monitoring, regular inspections, close monitoring of system gauges and oil sampling for laboratory tests. Every plant system has parameters that must be checked periodically. These checks consist of people making an assessment of the condition and filing accurate reports. When these people do their jobs correctly, bad things are prevented. 


Short-sighted managers only “see” the people who repair things. Those focused on prevention work in a less dramatic environment. Consequently, when the economy is poor, these jobs often are eliminated. 


Leaders not only must ensure the “seen” is handled efficiently but also that the “unseen” is not neglected. The “unseen” typically requires recognizing the indications of bad things about to happen, which can often be identified in regular inspections by sight, feel, smell or hearing. However, most of the “unseen” must be detected by equipment. This would include temperature, vibration, sound and lab tests. 


The “unseen” also involves a conviction that technology can be used to predict events in order to avoid or plan for them. This conviction is an important leadership attribute. Remember, managers don’t see the “unseen,” but leaders do.

Machinery Lubrication (8/2016)