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353

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July 1, 2007
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Part II: Introduction To Synthetic Lubricants & Their Applications

Part II: Selection

Improved equipment operation and energy savings are two welcome benefits associated with the selection of the correct synthetic for the job.

All synthetics are not alike. Selection should be based on the optimum base stock type for the application. The additive system, which also is very important, imparts unique properties to the finished synthetic lubricant. As a result, there can be major differences in performance for the same synthetic type from different suppliers. Case histories and actual field tests are the best way to select a particular synthetic fluid. There are many applications where mineral oils, because of their cost and performance, are perfectly acceptable. Synthetics are problem solvers to be used in applications where their unique properties are cost-justified under the following conditions:

  • Temperature Extremes—Since synthetics contain no wax they are used at very low temperature conditions. ISO 32 PAO and ISO 32 diesters have pour points > -50 F. They also are effective at temperatures well above 200 F, whereas mineral oils should be limited to a maximum of 200 F and synthetics should be considered at temperatures as low as 180 F.
  • Lower Wear—In general, synthetics provide much higher film strength and lubricity than mineral oils, especially in a high-sliding environment that occurs in worm and hypoid gears.
  • Energy Savings—Some synthetics have low coefficients of friction because of their uniform molecular structure, resulting in significant energy savings in many applications.

0707_formulations_img1Properties & applications of synthetics

Table I illustrates the most common synthetics and their major applications.

Polyalphaolefins (PAO)…
If only one synthetic could be selected in a plant, it would be a PAO. These are the most versatile and most widely used synthetics. They operate over a very wide temperature range, can be produced in a wide viscosity range without changing their basic properties and are compatible with most other lubricant types. Because of their nonpolarity, they have poor additive solubility and cause slight seal shrinkage. Consequently, they must be blended with a polar synthetic such as an ester, which swells seals and gives good additive solubility.

Some of the more common uses for PAOs include:

  • Hot and heavily loaded gear boxes: an EP PAO is used for helical and herringbone gears, while a non-EP ISO 460 is commonly used for worm gears.
  • Rotary screw air compressors: PAOs and polyalkylene glycols (PAGs) are the two most commonly used air compressor oils for extended life service.
  • ISO 68 PAO is used in oil mist lubrication of rolling element pump and motor bearings.
  • PAOs have H1 approval in food plants and are used in a wide range of applications.
  • PAOs are not recommended for high-temperature reciprocating compressors because they can form hard deposits on exhaust valves, thus not allowing them to seat properly.

Diesters…
Diesters are one of the oldest synthetic types—and they are limited in the viscosity ranges produced. The most common ISO VGs are 32, 46, 68, 100 and 150. The viscosity indexes are only high for the ISO 32 while the others are in the 70-100 range, depending on the alcohol and acid used in their manufacture.

The major performance strength for diesters is their excellent solvency minimizing deposit formation. They also have good low-temperature properties and high thermal stability and flash point.

Diesters have a low aniline number and a tendency to swell elastomeric seals. Therefore, resistant seals, such as DuPont Viton, need to be used. Diesters also can hydrolyze in a hot, high-moisture environment—something that
occurs in rotary screw air compressors.

Uses for diesters include:

  • Major application in severe duty reciprocating air and hydrocarbon compressors: diesters’ high thermal stability and excellent solvency will prevent carbon buildup on exhaust valves.
  • The synthetic of choice in air compressors many years ago: diesters are still used, but to a limited extent because of their potential for hydrolyzation. They are blended with mineral oils to form partial synthetics used in air compression and with PAGs for air compression.
  • Diesters are used extensively both in the ISO 68 and 100 viscosity grades for oil mist lubrication of rolling element pump and motor bearings.

Polyol Esters (POE)…
POEs have very high thermal stability allowing them to be used in a very high temperature environment. They also are fire resistant with high flash- and fire-point temperatures. Because they are readily biodegradable, they can be used as hydraulic fluids in environmentally sensitive areas.

The major disadvantage of POEs is their cost. They are 50% more expensive than PAOs, PAGs and diesters. Although they have a tendency to hydrolyze at hightemperature and high-moisture conditions, POEs are more stable than diesters.

Primary uses for POEs include:

  • Aviation and industrial gas turbine applications where the effective operating range is -40 F to 400+ F, with primary viscosity ~27cSt.
  • Extended life fluid for air compressors: rated >12,000 hours and stable at temperatures of 240 F, which is higher than the maximum temperature allowable in a rotary screw air compressor.
  • Fire-resistant hydraulic fluid for underground mining, steel mills and foundries: Factory Mutual approved and MSHA certified; flash point for ISO VG 46 > 510 F and fire point >680 F.
  • Environmentally friendly hydraulic fluids that are readily biodegradable and contain ashless antiwear additives.

Polyalkylene glycols (PAG)…
As discussed in the first article in this series, PAGs are quite versatile. They can be designed to produce a wide variation in water solubility by adjusting the ratio of ethylene and propylene oxide during manufacturing. They have very high viscosity indexes exceeding 250, as well as excellent polarity for metal surfaces that gives them good lubricity. PAGS don’t produce deposits and can be designed to minimize hydrocarbon gas solubility. Their major weakness is compatibility with hydrocarbon lubricants like mineral oils and PAOs. They also shrink many elastomeric seals and attack certain paint types.

Some primary uses for PAGs include:

  • Rotary screw and centrifugal air compressors
  • Enclosed gear boxes in particular worm gears
  • Fire-resistant hydraulic fluids
  • Food grade products ISO VG 150 and higher needing H1 approval
  • Hydrocarbon-flooded rotary screw compressors
  • High-pressure ethylene compressors in HDPE production

Applications
This following list highlights several applications where synthetics provide major cost justifications. Many more applications could have been presented:

  • Air Compressors
    • Rotary Screw
    • Reciprocating
  • Hydrocarbon Compressors
    • Rotary Screw
    • Reciprocating
  • Enclosed Gear Boxes
    • Helical, Herringbone, and Spiral Bevel
    • Worm

Air compression
Rotary screw compressors…

Most of today’s industrial air compressors are rotary screws like that shown in Fig. 1.

0707_formulations_img3In a rotary screw compressor, air is compressed, high temperatures are generated and, along with the moisture that is present, a severe oxidative environment is present for oil. The lubricant in this equipment performs four major functions: cooling, lubricating (bearings, gears and screws), sealing and corrosion prevention. This requires an oxidatively stable lubricant with high VI and good lubricity. Many OEMs have their own fluids—which are mainly synthetics. As shown in Table II, the different lubricants used can be classified based on fluid life.

The expected hours shown in Table II are OEM recommendations on expected life. Depending on the conditions, synthetics may exceed these numbers if the temperature and moisture are lower than normal.

The most common fluids used for air compressors for extended service are ISO VG 46 PAO and PAG/Ester. The esters most commonly used with PAGs are diesters and POEs that swell seals to counteract shrinkage caused by PAG.

POE gives the longest life extension for the fluid and is being used for extendedwarranty applications. Some POEs on the RPVOT test, which is a measure of the oxidative stability of a fluid, give results in excess of 3000 minutes—that’s nearly double the results obtained with PAOs and PAGs. POEs can be used at temperatures up to 240+ F, which is above the shutdown temperature of an air compressor. PAO can handle temperatures up to 220 F and PAGs are lower at 200 F. PAGs have the added advantage of very high viscosity indexes that gives a thicker film at high temperatures which minimizes wear. Furthermore, they don’t form deposits at high temperatures when they oxidize.

Two major cost justification areas for the use of synthetics is in fluid life extension and energy savings. Consider the following case study.

An evaluation was performed on a 300 hp compressor with a 60-gal. sump capacity operating at 180 F. Running mineral oil required change-out every 1000 hours, while a PAO greatly exceeded the OEM recommendation of an 8000-hour change by running 15,000 hours. This resulted in a 67% savings—or more than $1700—in lubricant costs in one year. (Data courtesy of Dr. Ken Hope, Chevron Phillips.)

Energy savings can be significant with air compressors. A number of studies have shown savings between 3-5% with rotary screw compressors. Combining energy savings and longer fluid life, along with less wear and better operation, synthetics make sense for air compression applications.

0707_formulations_img4Reciprocating…
While reciprocating compressors (Fig. 2) are not used much in air compression today, there are still many old compressors working in the industry.

Because of high temperatures, the cylinder region in a reciprocating compressor is the most difficult area to lubricate. One major problem associated with the use of mineral oils for this application is that they form hard deposits when they oxidize and coat the exhaust valves, thus keeping the valves from seating properly. As a result, hot gas is drawn back into the cylinder to be recompressed. This dangerous condition can lead to high heat generation and a possible fire.

The lubricant of choice for reciprocating compressor applications is an ISO 100 or 150 diester with excellent solvency. Fig. 3 shows two actual exhaust valves. The valve on the left had been running for six months on diester. The valve on the right had been running four months on mineral oil. The valve on diester continued to run with no coking, saving over $10,000 in valve replacement costs.

Hydrocarbon compression Rotary screw compressors…
Non-flooded rotary screw compressors running at temperatures below 180 F can use mineral oils without major problems. Users, however, may want to turn to a synthetic like a diester or a PAO for their energy-saving potential. Flooded screw compressors with hydrocarbon gas will quickly lose their viscosity with most mineral oils and synthetics because the gas dissolves in the lubricant, thus lowering the viscosity.

PAGs are the most resistant lubricant to hydrocarbon gas dilution and are recommended for flooded screw compressors. More resistant to dilution than mineral oils, PAGs will, however, be diluted to an extent with hydrocarbon gases, a fact that must be taken into consideration in selecting the initial viscosity to arrive at the correct viscosity at the operating temperature. PAGs have the added advantage of having very high VIs.

0707_formulations_img5Ethylene high-pressure reciprocating compressors…
PAGs are the lubricant of choice for high-pressure ethylene compressors because of their minimal dilution by hydrocarbon gas. The typical viscosity of PAGs used in this application is 270 cSt. The film integrity at a reasonable viscosity is maintained at very high pressures, leading to low lubricant consumption and very low wear rates.

Low-pressure hydrocarbon compressors…
Mineral oils at ISO VG at moderate temperatures have been used successfully. As conditions become more severe, though, synthetics need to be considered. Both PAGs and diesters are good alternatives. PAOs, however, are not recommended because of their tendency to form hard deposits when they oxidize.

Enclosed gearboxes Helical, herringbone and spiral bevel…
Gearboxes experience EHL lubrication through sliding and rolling motion. A key criterion in lubricating gear teeth is to have thick enough film for the high sliding and shock loads. In many cases, EP additives are effective as anti-scuffing agents and are used in many loaded gear reducers. Parallel and right angle shaft gears such as helical, herringbone and spiral bevel are lubricated normally with an ISO VG 220 with EP. Under abnormal conditions, such as high temperatures and high shock loads, an ISO VG PAO with EP is used. Although PAGs can be used, because of their incompatibility problems, PAOs are preferred. Energy savings are more difficult to attain with high-efficiency gears like helicals, herringbones and spiral bevels. Normally, synthetics have shown efficiency improvements of 3% or less. Therefore, the use of synthetics for these gears is not justified by energy savings alone. A better way to justify in these applications is to take into account how dramatically gear performance is improved under difficult load or temperature conditions when synthetics are used.

0707_formulations_img6Worm…
Worm gears (Fig. 4) are highly inefficient. They also are good candidates for synthetics. A worm gear is a right-angle gear with non-intersecting shafts. These units consist of a steel worm and a sacrificial bronze wheel. There is very little rolling motion. Most motion is sliding—which causes the high wear and high heat. Worm gears typically can run 90 F degrees or higher than ambient temperatures. Since EP additives can attack bronze, very few EP gear oils had been used in the past. The only alternative had been to use a compounded high-viscosity mineral gear oil—such as ISO 460—containing animal fat for lubricity to protect the teeth during boundary lubrication. These types of lubricants oxidized quickly at high temperatures and didn’t provide a high level of wear protection.

The two most popular synthetics used in worm applications today are ISO VG 460 PAO and PAG. Each will perform very well. Neither of these synthetics contain EP and they both provide a high film strength and score very high on the FZG test that measures scuffing of gear teeth at different load stages. Mobil SHC 634, which is an ISO 460 PAO with no EP, exceeds 13 stages, the highest level on the test. This results in very low wear rates and energy savings.

Efficiency savings in excess of 7% have been documented. Because of their lower traction coefficient (which is the internal friction in the lubricant) PAGs often provide higher efficiency savings—but PAOs do very well. Temperature drops with a synthetic can be 20-30 F degrees. While PAGs are more common in gearboxes in Europe, more are being used in the United States. A PAG, because of its greater energy efficiency, is a good choice for new gears and can be used on other gears only with the proper flushing procedures. Moreover, PAGs attack some paints. A safer choice to convert a worm gear from mineral to synthetic is to use a PAO.

The following is a case history of the conversion from mineral oil to PAO:

A major can manufacturer used double-enveloping worm gears with an average reduction ratio of 60:1. The company was using a compounded ISO 460 mineral oil. On average, the company was experiencing four gear failures per year, each costing an average of $12,500 to repair. Temperatures typically were 200 F—and in some cases got as high as 215 F. The mineral oil was replaced with an ISO 460 PAO and the failures were eliminated. In fact, to date, 18 months later, there still have been no failures in this equipment. In addition, the average temperature dropped across the worm gears by more than 20 F degrees.

Conclusion
Synthetics are real problem solvers. While they can work well and be cost justified, there are many applications where mineral oils will do just as well. Three applications where synthetics can improve equipment operation and provide major cost savings are air compressors, high-pressure and hot reciprocating compressors and worm gears.

Deciding which synthetic to use is very important. Each candidate will have advantages and disadvantages that need to be considered before a final decision is made.

Keep in mind that the same synthetic type from different manufacturers can give different results. Even though the base stocks may be similar, the additive package may impart different properties from one supplier to another. Make comparisons between the data sheets, but let your final decision rest on field performance. Look at case histories and, if possible, run a carefully controlled plant test where meaningful data can be collected. Even though this will not be possible in some cases, definite equipment improvements can still be observed without rigorous testing and data collection. Be sure to document this data. Since synthetics are more expensive than mineral-based oils, you will want to be very accurate in your cost justifications.

Acknowledgements
The author wishes to thank Tim Taylor of Summit and Dr. Martin Greaves of Dow Chemical for their assistance in the preparation of this article. LMT


Contributing editor Ray Thibault is based in Cypress (Houston), TX. An STLE-Certified Lubrication Specialist and Oil Monitoring Analyst, he conducts extensive training in a number of industries. E-mail: rlthibault@msn.com; or telephone: (281) 257-1526.

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165

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July 1, 2007
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An Independent State Of Mind

ken_bannister

Ken Bannister, Contributing Editor

As this July 4th rolled around, my thoughts drifted back to 1776 and the excitement that must have surrounded America’s independence from British rule. Yet, as the British lamented their loss of the Americas, they too were on the cusp of celebrating a unique revolution of their own—the Industrial Revolution.

Seven years earlier, James Watt had successfully delivered the world’s fi rst viable steam engine capable of powering an entire factory of machines. Improving on the crude design of the original Savery-Newcomen engine used primarily to draw water, Watt’s design converted reciprocating motion into rotary motion. The rotary motion of the driven shaft could now be slaved into driving multiple line shafts simultaneously. Fourteen years later, in 1783, North England inventor James Arkwright was credited as the fi rst industrialist to use a Watt steam engine to power his entire textile mill.

The rotary motion of crank bearings and leatherbelt- driven line shafts introduced a constant need for lubrication. Petroleum-based lubricating oils as we know them today would not be discovered for another 70+ years, requiring the use of animal/ vegetable based lubricants such as olive oil for the rotary bearings and tallow (animal grease derived from cattle and sheep) for the drive belts.

The drawback with animal/vegetable oils is their lack of chemical inertness that results in acid formation after short periods of use, requiring constant cleaning and reapplication of lubricant. This important job became the responsibility of children. Because of their small stature and dexterity, they were able to scurry around quickly on all fours, on severely height-restricted fabricated gantries above the line shafts, applying lubricant as and when required.

Countless youngsters worked 18-20 hours per day in appalling conditions—and many of them were maimed and killed in the lubrication process. These little children, scampering across the gantries in a stooped manner, were said to resemble monkeys, which is how the term “grease monkey” is thought to have originated.

While children no longer take care of the lubrication in our facilties, have times really changed? Today, as I work with companies to implement engineered lubrication management programs, I am constantly amazed by the number of organizations that still treat lubrication as a “necessary evil,” and their lubrication personnel as second-class citizens, referring to them as “grease monkeys,” “grease jockeys” and “oilers.” Many have low expectations for their lubrication personnel, providing little or no training for the job, using the position as preretirement staging positions, etc. Sound familiar?

I submit that it’s time to lead an independent charge of our own to elevate the status of lubrication in the minds of all industrial personnel!

Although we may not be able to strike a unilateral declaration of independence, we all can work toward seriously legitimizing the science of lubrication in the minds of our co-workers. This can be achieved by taking responsibility for reducing machine downtime and reducing energy costs through the use of improved lubricants and lubrication practices. We also need to implement defi ned roles and responsibilities for all lubrication personnel, insist on quality training and accreditation for them and strongly support their being recognized as an integral part of an equipment reliability program/initiative/approach/team.

Are you and your company ready to take on this challenge? Good Luck!

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

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86

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July 1, 2007
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Lubrication Management & Technology News

DECKER TO HEAD TYCO FLOW CONTROL
Patrick Decker has been named president of Tyco Flow Control, a business segment of Tyco International and one of the world’s largest providers of fl ow control products. Decker joined Tyco in May 2003 as the CFO of its Plastics & Adhesives business. In his most recent role with the corporation, he had been serving as CFO for the Tyco Engineered Products and Services (TEPS) segment since January 2005. He also collaborated with Tyco Flow Control’s leadership in the development of the Evolution to Excellence strategic initiative and related imperatives.

MULLER RECEIVES ASHRAE’S DISTINGUISHED SERVICE AWARD
Purafi l’s technical director, Chris Muller, has been honored with the ASHRAE Distinguished Service Award. A 12-year ASHRAE member, Muller serves as a Distinguished Lecturer for the organization and as chair of its Standard Committee 145P, which was charged with the task of engineering the ASHRAE Standard 62.1. He remains thoroughly involved within the organization as a voting member of several committees and as a co-author of the ASHRAE Standard 62.1-2004 User’s Manual.

GE MOVING SOME GAS TURBINE OPS TO HUNGARY
In response to growing international demand, GE Energy has announced the decision to add capacity for its 50-Hertz LM6000 aeroderivative gas turbines to a GE manufacturing facility located in Veresegyhaz, Hungary.

“We are shipping more and more LM6000 units to customers throughout Europe, Asia and the Middle East. By utilizing the Hungary facility, we can provide our international customers with more localized service and support,” said Charles (Chip) Blankenship, general manager of GE Energy’s aeroderivative division. According to Blankenship, this move will free up resources at the company’s Houston, TX, facility to better accommodate increasing demand for the LMS100.

The operations in Hungary, located approximately 20 kilometers outside of Budapest, have been in operation since 2001 supporting the build and repair of the corporation’s heavy-duty gas turbines. Packaging and testing for both the SAC and DLE models of the 50-Hertz LM6000 can now be completed there. GE Energy’s aeroderivative division is the world’s largest service provider for this type of gas turbine technology.

ASSOCIATION NEWS

PUMP SYSTEMS MATTER ANNOUNCES 4 NEW SPONSORS
Pump Systems Matter™ (PSM), a North American educational organization aimed at lowering energy needs by optimizing pump system performance, has announced four new sponsor organizations: Hydro Inc., Engineered Software, Inc., Manitoba Hydro and Xcel Energy. PSM was launched to help assist pump users gain a more competitive business advantage through strategic, broad-based energy management and pump system performance optimization. Its initial development was led by the Hydraulic Institute (HI). Incorporated as a new 501(c) 3 educational organization in 2006, PSM currently is seeking sponsors and board members that can actively contribute to its growth. Membership is open to utilities, market transformation organizations, government agencies, pump users, contractors, consultants, engineering fi rms, trade and professional associations, as well as North American pump manufacturers and suppliers of motors, drives, seals, couplings, bearings, housings, instrumentation and control systems and pump specifi c software. For more information, contact Joananne Bachmann at (973) 267-9700 x 22 or via JBachmann@pumps.org.

NEW EXECUTIVE DIRECTOR NAMED FOR PTDA FOUNDATION
The Power Transmission Distributors Association (PTDA) Foundation has announced the appointment of Phyllis Russell to executive director. In her new role, Russell will be responsible for all aspects of the Foundation’s management. Charged with implementing the Foundation’s missions, goals and objectives, she will oversee fundraising and relationship development in support of the organization’s major workforce development initiative, the Industrial Careers Pathway® (ICP).

SMRP OPENS LOUISVILLE CONFERENCE REGISTRATION
This year’s SMRP Fall Classic conference takes place October 7-10, 2007 in Louisville, KY, and registration is now open. To take advantage of the Early Bird Registration Fee of $825, you’ll need to register by August 26. For more information, visit www.SMRP.org. Remember, to register online, SMRP members must use their membership ID number. Plan now. Don’t miss this opportunity for “Building Your All-Star Team with the SMRP Body of Knowledge.”

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838

6:00 am
July 1, 2007
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Oil Mist Systems In The Plant-Wide Lubrication Of General Purpose Machinery

Plant-wide oil mist systems have been in use in numerous reliability-minded refineries and petrochemical plants since the mid-1960s. The 8th (2000) and subsequent editions of the API-610 Standard for centrifugal pumps also have described advantageous application parameters for oil mist. In the United States, Canada, South America, the Middle East and Pacific Rim countries, oil mist lubrication has matured to the point where major design contractors now are specifying these types of plant-wide systems quite extensively.

0707_equipment_reliability_img2Oil mist is easily controlled & appliedModern plants use oil mist as the lube application of choice. Plant-wide pipe headers distribute the mist to a wide variety of users. Oil mist is easily produced in an oil mist generator console (Fig. 1) and its flow to bearings is not difficult to control. Flow, of course, is a function of orifice (“reclassifier”) size and piping (“header”) pressure. Unless plugged by an unsuitable (e.g., an elevated pour point) lubricant, reclassifiers have a fixed flow area that is selected based on bearing size criteria.

Depending on make and system provider, header pressures range from 20″-35″ (500-890 mm) of H2O. Modern units are provided with controls and instrumentation that will maintain these settings without difficulty. It should be noted, however, that mixing ratios—typically 160,000 to about 200,000 volumes of air per volume of oil—are frequently incorrect on oldstyle mist generators that incorporate gaskets and O-rings in the mixing head, unless these elastomers have been periodically replaced or properly serviced.

Comparing plants with non-optimized mist entry (Fig. 2) to equipment bearing housings with their modern optimized counterparts (Fig. 3), lubricant and air consumption are about 40% less for plants that have implemented the superior mist entry and vent locations of Fig. 3. This has been reported in the cited references and is implied in API-610 8th Edition (2000) and later standards.

Forward-looking plants have used the API method, i.e. Fig. 3, since the mid-1970s. These plants had recognized that mist entering at locations far from the bearings could have difficulty overcoming bearing windage effects. Windage is most often produced by the diagonally-oriented ball cages in angular contact bearings. If such windage were produced by the left row of the thrust bearing in Fig. 2, the mist would take the preferential path straight to the vent exit at the bottom of the bearing housing and insufficient amounts of oil mist would reach the bearing rolling elements.

A larger quantity of oil mist or specially designed “directional” reclassifiers will be needed with certain bearing types unless the API method is used. This latter method will overcome windage, the flow-induced action induced by the skewed cages.

Environmental & health concerns
For decades, environmental and health concerns related to oil mist have been addressed by using oil formulations that are neither toxic nor carcinogenic. Such formulations are available to responsible users. Appropriate lubricants also have been formulated for minimum stray mist emissions. These, too, are readily available to responsible users.

Stray mist emissions can be kept to very low values by installing suitable magnetically-closed dual-face bearing housing seals (Fig. 4, also Ref.1). Unlike old-style labyrinth or other housing seals that allow highly undesirable communication between housing interior and ambient air, face-type devices seal off this contamination route.

Closed oil mist systems also are available—and have been since first being applied in the Swiss textile industry in the late 1950s. Today, closed systems are in use at several U.S. petrochemical plants. They allow an estimated 99% of the lube oil to be recovered and reused. Closed systems emit no oil mist into the environment and are available to environmentally conscious users.

 

 

0707_equipment_reliability_img3

Header temperature & size
Temperature never has been an issue for properly designed systems. Once a mist or aerosol of suitably low particle size has been produced—and particle size is influenced by the temperature constancy of both air and oil in the static mixing head—the oil mist will migrate to all points of application in non-insulated headers at low velocity.

Ambient temperature has little influence on mist quality and effectiveness. Mist temperatures in headers have ranged from well below freezing in North America to over 122 F (50 C) in the Middle East. Regardless of geographic location, conscientiously engineered systems will incorporate both oil and air heaters, since these are needed to maintain constant and optimized air/oil mixing ratios. The heaters must have low-watt density (low power input per square inch of surface area) in order to prevent overheating of the oil. Users that try to save money by omitting heaters or using undersized headers will not be able to realize the greatest life cycle cost benefits from their assets.

Using undersized headers may increase the flow velocity to the point where the small oil globules suspended in the carrier air experience too many collisions. They may thus agglomerate into droplets large enough to fall out of suspension, causing excessively lean mist to arrive at the point to be lubricated.

Wet sump (“purge mist”) vs. dry sump (“pure mist”)
In the wet sump method, a liquid oil level is maintained and the mist fills the housing space above the liquid oil. Wet sump (also called “purge” mist) is essentially “old technology”— and primarily used with sleeve bearing-equipped pumps and blowers(Figs. 5 and 6).

Dry sump oil mist describes the application method whereby no liquid oil level is maintained in the bearing housing. (This principle was illustrated earlier in Figs. 2 and 3.) Pumps lubricated in dry-sump fashion are depicted in Figs. 7 and 8. Here, lubrication is provided entirely by oil mist migrating through the bearing.

The application of dry sump oil mist is advantageous for a number of reasons. Among these, we find lower bearing temperatures, the presence of nothing but uncontaminated oil mist and the exclusion of external contaminants. However, one important, but often overlooked, reason involves oil rings (Fig. 9)—or rather the fact that no oil rings are used with this application method.

0707_equipment_reliability_img4Oil rings often represent outdated 18th century technology as they were developed for slow-speed machinery during the Industrial Revolution. Elimination of oil rings is one of the many keys to improved reliability of virtually any type or style of bearing. Oil rings are known to have journal surface velocity limitations, sometimes as low as 2000 fpm, or 10 m/s. So as not to “run downhill,” which might cause the rings to make frictional contact and slow down, ring-lubricated shaft systems would have to be installed with near-perfect horizontal orientation.

Furthermore, frictional contact often results in abrasive wear and the wear products certainly contaminate the oil. Oil rings will malfunction unless they are machined concentric within close tolerances. They suffer from limitations in allowable depth of immersion and, to operate as intended, need narrowly defined and controlled oil viscosity.

Experience with modern oil mist systems
Actual statistics from a world-scale facility convey an accurate picture of the value of properly applied oil mist technology. This petrochemical plant went on-stream in 1978 with 17 oil mist systems providing dry sump oil mist to virtually every one of the many hundreds of pumps and electric motors in the facility. As stated previously, with the dry sump (“pure”) method per current API recommendation, the oil mist is introduced at a location that guarantees its flow through the bearings and to an appropriate vent location. There are neither oil rings nor any other provisions for the introduction of liquid oil on pumps and motors with rolling element bearings at the plant.

Over a period of 14 years, one qualified contract worker serviced these systems by visiting the plant one day each month. In this 14-year time period, there was only one single malfunction; it involved a defective float switch in one of the 17 systems. The incident caused a string of pumps to operate (and operate without inducing even one bearing failure!) for eight hours. In 1992, the combined availability and reliability of oil mist systems at this U.S. Gulf Coast plant was calculated to be 99.99962%.

Concluding comments 
Being aware of the relative unreliability of conventional lubricant application methods involving oil rings and certain constant level lubricators (Fig. 10), knowledgeable reliability professionals can attest to the utility and overall advantages of properly engineered dry sump oil mist systems. Certainly, the known advantages of properly engineered oil mist systems far outweigh the actual or perceived disadvantages. It is unfortunate that much information to the contrary is either anecdotal or pertains to systems that were not correctly designed, installed, maintained and/or upgraded as new technology became available.

Only dry-sump applications will lubricate, preserve and protect both operating and stand-by rolling element bearings. At all times, only fresh oil will reach the bearings. In many instances, bearing operating temperatures with dry sump oil mist lubrication are 10 or even 20 F degrees (6 or 12 C degrees) lower than with wet sump lubrication.

Industry experience with dry-sump oil mist systems is well documented [Refs. 1, 2 & 3] and its superiority over both conventionally applied liquid oil and wet sump oil mist lube applications has been solidly established.

Regrettably, there are still entire plants that try to get by on wet sump oil mist. Wet sump lubrication makes economic sense on sleeve bearings only. Here, its only function is the exclusion of atmospheric contaminants. It does so by existing at a pressure slightly above that of the surrounding ambient air. Often, the wet sump oil level is expected to be maintained by an externally mounted constant level lubricator. However, due to the slight pressurization, and on bearing housings equipped with traditional open-to-atmosphere constant level lubricators [Ref. 2], the oil level in the bearing housing will now be below the oil level in the lubricator. Keep in mind that fully pressure-balanced constant level lubricators will be more reliable than many other wet sump lubrication alternatives available today.

References:

  1. Bloch, H.P., and Shammim, A.; Oil Mist Lubrication, Practical Applications, 1998, The Fairmont Press, Inc., Lilburn, GA, ISBN 0-88173-256-7
  2. Bloch, H.P., “Case Study in Reliability Implementation,” Hydrocarbon Processing, August, 2002
  3. Bloch, Heinz P. and Alan Budris, Pump User’s Handbook: Life Extension, 2006, The Fairmont Press, Inc., Lilburn, GA, ISBN 0-88173-517-5

Contributing editor Heinz Bloch is the author of 17 comprehensive textbooks and over 340 other publications on machinery reliability and lubrication. He can be contacted directly at: hpbloch@mchsi.com

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Perseverance, Surprises and Unintended Consequences

By the time I joined Rentech in 2000, the three Clark TCV 16 engine/compressors compressing hydrogen and nitrogen at our East Dubuque Ammonia Plant had begun experiencing shortened packing life. Packing life on the 4600 psi 3rd and 4th stages—that historically had reached 18 to 24 months—suddenly fell to just three to six months. Excessive ring wear also was observed.

Maintenance personnel at the plant had noticed that the major brand lubricant we were using on these units looked somewhat different than in the past. When questioned about this, the supplier assured us that no changes had been made. As we continued to pursue the problem, the manufacturer later admitted that the formulation had indeed been changed and the diminished performance we were experiencing was unintended and unexpected. Consequently, we began to look for an alternative lubricant.

The first alternative we selected, an independent brand cylinder lubricant, appeared to work well for about a year. Then we encountered another unintended consequence. The oil carried downstream of the compressor was plugging the chillers in the synthesis loop. At that point, we determined that an oil with a lower flock point (temperature at which wax crystals form) was what we really needed.

We opted to go with Royal Purple’s NGL-NS synthetic lubricant as it had no flock point and no sulfur that could poison the process catalyst. After just three weeks, however, we experienced a packing failure on a synthesis loop compressor cylinder. A repetitive failure occurred just four weeks later. In all, we had six packing failures over a twoto- three-month period. Then, the failures stopped—just as suddenly as they had begun.

Interestingly, only the packings on the recirculation cylinders of compressors C & B were failing. We sent samples of the failed packings, along with foreign material found in them, to Royal Purple for analysis. Because the oil travels downstream of the compressor, the supplier attributed the failures to the NGL-NS cleaning out 37 years of “stuff” that had accumulated in the loop. We were advised to persevere with the clean-up and to expect that the failures would eventually stop. They did. Our packing life increased to two years. Subsequently, we also changed packing materials, increasing our current life to four years with expectations of six years life.

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Each of these engines/compressors has two turbochargers. In summer months, these units would experience pre-ignition problems due to low intake air volume. We would have to reduce the load on the engines in order to operate. At some point in the past, as part of a lubricant consolidation program, our plant had elected to lubricate this equipment with the SAE 40 weight gas engine oils used in the compressors. We were looking for a better bearing lubricant for the turbochargers and elected to try Royal Purple’s Parafilm 68. Again, we found ourselves experiencing unintended consequences.

The first unintended consequence was related to the engines being started with compressed air. The air to the engine is automatically shut-off when the turbocharger speed indicates that the engine is running. After changing lubricants, the engines would not start. We determined that the new bearing lubricants had reduced friction in the turbochargers’ bearings so significantly that they were spinning up just on the compressed air, and that they no longer needed engine exhaust gas to do so. We had to reset the air cut-off parameters in order to start the engines.

The second unintended consequence was that the preignition problems in the compressors completely went away. The engines could now be run fully loaded yearround while still maintaining a slight open position of the waste gate valves.

Identifying more opportunities
We operate a 2500 hp Elliott turbo expander in our Nitric Acid Plant that is one of only four ever made and the last still in operation. It operates at 16,000 rpm. This unit has always experienced problems with short bearing life and high vibrations. We thought this resulted from the equipment’s fabricated case coupled with too much overhung mass on the rotor. At times, the unit would shake the floor grating so violently that it hurt your feet to stand on it. Replacement bearings cost $8000 and would have to be replaced twice a year. The bearing alarms were normallyset based on whatever vibration levels existed after a rebuild. In an effort to reduce vibrations and extend bearing life, we elected to change out the ISO 32 turbine oil to Royal Purple Synfilm 32. We expected to see improvement from this oil change due to the much higher film strength of the Royal Purple lubricant and we were not surprised. Immediately after the oil change bearing vibrations went down from 4 mils to 2.7 mils. Bearing life went from six months to 20 months. Recently we had the rotor balanced, which further reduced the vibrations to 1.2 mils—and is expected to extend bearing life even longer.

Based on these successes, we began to look for even more opportunities to improve machine performance with lubricant upgrades.

Single screw compressor… 
We elected to change the oil on a 400 hp Vilter single screw compressor at our two 20,000-ton ammonia storage tanks. This compressor had a number of operational issues. It continually tripped on high temperatures. Valves failed to operate because of oil deposits gumming up the valves. We had excessive make-up oil due to the oil’s inability to readily separate from ammonia. In this application, we elected to change out the factory oil for Royal Purple Uni-Temp 300 refrigeration oil. Based on assurances from Royal Purple that we would also achieve substantial energy savings, we installed data loggers on the compressor to record volts and amps. All of the operational issues with the compressor disappeared and we documented a 9% reduction in power consumption.

Mycom ammonia compressor… 
Shortly thereafter we changed to Royal Purple oil in the Mycom ammonia compressor serving one of our Nitric Acid Plants. All went well for about a year until we got a water leak in the shell and tube heat exchanger, and unintended consequences recurred. The internals in the compressor rusted and took out the bearings. We also found a black residue in the compressor we believe came from the oil. After a second compressor failure using the new oil, we elected to return to the previous oil as it appeared to have a superior ability to handle wet ammonia.

Rotary screw compressors…
Next we elected to change the oil in our three Sullair rotary screw air compressors to Royal Purple Synfilm. For whatever reason, the larger 400 hp compressor was being lubricated by a major brand multi-purpose mineral oil requiring eight oil changes per year. The two 100 hp compressors were lubricated with a factory synthetic oil with annual oil drains. Being a polyalkaline glycol type oil, the factory oil was incompatible with most other lubricants. Thus, it was necessary for Royal Purple to supply its Royal Flush product to flush the old oil from the compressor before adding new oil. In addition to its price advantages, the new oil has reduced discharge temperatures by 12 F degrees and has extended oil drain intervals via oil analysis to 12,000 hours.

4-stage urea plant compressors… 
In April of 2002, we elected to address issues we were having with our two Clark CMB 4-stage compressors in the urea plant. These units, which compress CO2 to 3000 psi, were experiencing excessive cylinder ring wear, packing sealing problems and plugging of the downstream separators. We elected to change the major brand cylinder lubricant to Royal Purple CAP701W ISO 220. This proved to the solution to each of these issues. So again, we looked for other areas where we could improve the performance and reliability of our equipment with lubricant upgrades.

Steam-driven centrifugal compressor… 
We also looked at a steam-driven 5000 hp Allis Chalmers centrifugal compressor in Ammonia Chiller Service. The speed increaser gear box (4900 rpm input/12,800 rpm output) was in high vibration alarm. The turbine and gearbox share a common lube sump containing 1200 gallons of ISO 32 turbine oil, so we could not drain and replace the oil because shutting the turbine down meant shutting the plant down. We decided to drain the turbine oil to the lowest level we thought was safe and then we added six drums of Synfilm 32 to the existing oil (27 ½%) hoping to get enough film strength into the oil to bring the vibrations down. It worked. Vibrations were reduced from 0.2 IPS to 0.17 IPS (a 15% reduction), which was below the alarm limits. We ran the turbine until our next scheduled turnaround. We drained and replaced the major brand turbine oil with Parafilm 32 and have run the turbine and gear box without incident for the past five years.

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This compressor has a separate oil system for the trapped bushing seal that seals the ammonia into the compressor. Feeling good about our successes, we decided to tackle what we believed was a lubricant related seal problem. The major brand ISO 32 R&O oil we had successfully used for years suddenly became unavailable. We were assured that the supplier’s new offering was equally good, but then some of those unintended consequences reared their ugly heads again. What used to be minor carbon deposits found in the seal at turnaround became significant carbon deposits on the seal—which caused premature seal failure and plant shutdown. We consulted with Royal Purple about a replacement oil and began a new round of unintended consequences.

First we tried Synfilm which didn’t separate well enough from ammonia. To overcome this we changed to Uni-Temp, which we knew separated rapidly from ammonia, but its high solvency began to aggressively clean up deposits from the seal system that were carried to the seals—again causing premature seal failure. Finally, we changed to Royal Purple Barrier Fluid FDA 56, which solved the problem once and for all. That’s because this product does not have the cleaning abilities of the Unitemp. In this case, we felt it simply was better to leave whatever “stuff” was in the system alone.

150 pumps… 
We operate over 150 pumps at the East Dubuque Ammonia plant, all of which had been lubricated by an ATF fluid. A little over a year after changing these pumps over to Synfilm, it occurred to us that we had not experienced a single bearing failure since the move. Even now, we seldom see bearing failures on these pumps—the few problems we do have are usually seal failures.

The road to success
Today our plant is running better than at any time in its 40+ year history. Budget trends are down and equipment availability is up. We are currently at two-year turnaround intervals and feel we could easily go to three. Though it may have started as an accidental journey, we have learned that good lubrication is key to reliability and good lubrication begins with optimum lubricant selection. We also learned that solutions are not always obvious and that patience and perseverance are required in order to stay the course to some solutions.

0707_operationsuccess_img3Sometimes we wound up having to take two steps back before being able to take three forward. We also learned that there is no such thing as a magic bullet—or magic oil. For many applications we see no advantage in using anything but traditional lubricants. For many others, the benefits vastly exceed the cost of premium performing lubricants.

One thing is certain, however. We no longer look at lubricants as an expense. Instead we look at lubricant selection as an opportunity to maximize productivity and profits.

Lance Wilkinson is maintenance superintendent/technical manager with Rentech Energy Midwest, in East Dubuque, IL. He has extensive experience in the Petro-Chemical Industry, including 21 years in engineering, seven years as a craftsman and supervisor and three years as a machinist. Wilkinson holds a BSME from the University of Texas at Austin. E-mail:lwilkinson49@sbcglobal.net

 

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Mineral-Based Lubricant Exchange

Some of the most crucial issues in lubricant management involve getting the right lubricant to the right place at the right time. On many occasions, getting these things “right” is not particularly problematic. What happens, however, when something does go wrong around your operations? Your inventory control may not have been updated, shipments may have been delayed or other unforeseen circumstances may have caused a critical shortage of lubricant(s) at your site. In these situations, substitutions may have to be made—quickly! How, though, do you fi nd a compatible lubricant substitute?

Lubrication Management & Technology’s “Mineral-Based Lubricant Exchange” guide has been compiled to help you in the event that substitutes must be chosen. The chart on the following pages has been designed as an easy-to-use cross-reference of the products of major lubricant formulators, based on the information they provided to our editors.

Keep in mind that the products shown on our chart are general guidelines for comparison purposes only— they do not infer that performance is interchangeable. If you are considering a lubricant substitution for a specifi c application, you MUST consult the respective formulator(s) to ensure proper performance.

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Notes on using the chart
Viscosity is a widely accepted property for comparing lubricants. It is expressed in several ways: ISO, Saybolt, AGMA and Kinematic. Note that the viscosity equivalents of ISO and Saybolt are what we have used in our chart to compare the various products of the listed formulators. (Refer to Figs. 1 and 2 for a comparison of common viscosities and to see the effect of temperature on viscosity.)

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Analyzing the bigger picture
Although following recommended oil-change and greasing schedules is the usual way of doing business in a facility, this alone will not optimize machine performance and minimize downtime. Regular oil analysis—conducted in-house or by a qualified lab—is another powerful tool to use in enhancing reliability and increasing uptime. Remember that accurate and timely oil analysis can alert personnel to impending lubricant deterioration or machine malfunctioning, and allow them to initiate corrective action—well before an actual failure occurs.

Joe Foszcz is a contributing editor to Lubrication Management & Technology. For more information, e-mail him directly: jfoz@atpnetwork.com

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Solution Spotlight: Meeting Specialized Needs Of Air Compressors

Plant operations rely on proper and consistent performance from air compressors—when compressors fail, production can quickly be brought to a halt. Accurate compressor lubricant selection is essential to prevent lubricant-related issues that could cost a plant considerable downtime. The type of lubricant needed can vary greatly depending on the type of compressor or gas being used, while different gas temperatures and discharge pressures may require different qualities in the oil.

“It is critical to match the proper lubricant with its intended application,” says Bill Stein, a product application specialist with Shell Lubricants. “When developing compressor lubricants, consideration must be given to the fluid type and additives used, as well as the intended use of the product.”

To meet the complex needs of today’s air compressors, Shell is now offering next-generation technology in its line of air-compressor oils: Shell Corena AP, Shell Corena AS and Shell Corena S.

Shell Corena AP Oils
These products are intended for the lubrication of industrial reciprocating air compressors, in particular, those up to and above air discharge temperatures of 220 C (428 F) with continuous high delivery pressures. According to the manufacturer, Shell Corena AP incorporates a combination of specially selected synthetic esters and advanced additive technology. As a result, this product works well in the most demanding of conditions, handling continuous high pressures and high temperatures, where traditional mineral oils are not suitable. A low tendency for deposit build-up helps promote continued high compressor performance over long periods. Moreover, the normal valve maintenance period, typically between 250 and 1000 hours of operation using conventional mineral oils, can be extended to 2000, or even 4000 hours.

Shell Corena AS Oils
These advanced synthetic rotary air compressor oils use a specialized additive technology. Shell Corena AS is capable of giving high performance in oil-flooded air compressors of screw or vane design. It provides effective lubrication, even under severe conditions, to oil-flooded single- and two-stage compressors, in particular those operating with output pressures of greater than 20 bar (290 psi) and with air-discharge temperatures greater than 100 C (212 F)— including intermittent operation under these conditions.

The manufacturer also notes that Shell Corena AS can help increase oil drain intervals significantly compared to conventional mineral oils, where allowed by the manufacturer— up to a maximum of 12,000 hours, even when operating at a continuous maximum discharge air temperature in excess of 100 C (212 F).

Shell Corena S Oils
A premium performance mineral oil, Shell Corena S is suitable for the lubrication of rotary sliding vane and screw air compressors, operating with lower discharge temperatures. Based on a blend of high-viscosity index, Group II paraffinic mineral oils and carefully selected additives, the oil provides thermal stability, good water-shedding properties, good seal compatibility, anti-oxidancy, anti-wear and low oil carryover. In field use, Shell Corena S has demonstrated more than 5000 hours of operation.

Shell Lubricants
Houston, TX

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Problem Solvers

Pump-Operated Piston Bins

0707_problemsolvers_img1Assmann’s 400-gallon polyethylene, non-pressure piston bins are ideal for transporting and storing viscous products up to 500,000 centipoise. They function via a pump operated system that both fills and discharges through a 3″ bottom valve. Materials are protected from air, moisture, dirt and other contamination in the bin with the use of a sealed and closed-looped system. The products incorporate a durable design, forklift pockets and reusable containers.

Assmann Corporation 
Garrett, IN

 

Food & Pharma Grease

0707_problemsolvers_img3CRC Industries has added Food Grade White Grease for food and pharmaceutical processing applications to its line of NSF Registered products. According to the manufacturer, this high-purity, high-quality synthetic provides advanced lubrication and durability, while protecting against rust, oxidation and wear. Resistant to water, salt spray and detergent, it’s suitable for use in temperatures ranging from 0 to 450 F.

CRC Industries Inc.
Warminster, PA

 

Metalworking Product Catalog

0707_problemsolvers_img2E&R Industrial offers a new master catalog covering over 100,000 MRO and production metalworking products from more than 500 manufacturers. Product categories include cutting tools, abrasives, precision tools, hand and power tools, lubrication, MRO items, machinery and safety supplies.

E&R Industrial 
Sterling Heights, MI

 

 

 

Lube Storage & Dispensing

0707_problemsolvers_img4LubeRite™ Storage and Dispensing Containers from JustRite protect lube oils, hydraulic oils, gear oils, motor oils and coolants from contamination and spills that can lead to machinery downtime. Fully sealed, these containers are available in pump and pouring applications. Pouring applications come in 2-, 5- or 10- quart drums, while pump applications are available in 5- or 10-quart drums. These durable products feature quick fill ports, flip-switch activated breather vents and color-coded identification systems.

JustRite Mfg. Co. L.L.C. 
Des Plaines, IL

 

Multi-Use Wind Power Lubricant

0707_problemsolvers_img5Klüberplex BEM 41-141 from Klüber has been formulated to reduce the use of multiple greases in wind power stations. It uses one special base oil mixture along with a package of additives to overcome the differing demands of individual bearing lubrication points that are prominent in wind power applications. This new lubricant is suited for use on main bearings, generator bearings and pitch and azimuth bearings, all of which are subjected to high stress conditions. Klüber Lubrication

North America L.P. 
Londonderry, NH

 

 

 

Severe Environment Lubrication

0707_problemsolvers_img6The line of Permatex® brand Anti-Seize Lubricants from ITW Devcon are designed for the harshest industrial environments. The lubricants reduce wrench torque and help protect mated metal parts against corrosion, rusting, galling, friction and seizing. The line includes Permatex Anti-Seize Lubricant, Permatex Copper Anti-Seize Lubricant, Permatex Food Grade Anti-Seize Lubricant and Permatex Nickel Anti-Seize Lubricant. Each lubricant can withstand a wide range of temperatures, up to a maximum of 2400 F in the case of the nickel formula.

ITW Devcon
Danvers, MA

 

Preserving Stored Equipment

0707_problemsolvers_img7Royal Purple’s new VP Preservative Oil helps prevent rust and corrosion in stored equipment such as engines, gearboxes and other closed systems. Protection from this vapor phase preservative formulation lasts up to one year or more, depending upon how well sealed the closed system is and how much temperature- induced “breathing” occurs. Additionally, vapors from the oil form a monomolecular layer on all metal surfaces for further protection. VP Preservative Oil is available in 5-gal. pails and 55-gal. drums.

Royal Purple
Porter, TX

 

Oil Filter Crusher

0707_problemsolvers_img8According to Newstripe, its FilterFlat oil filter crusher reduces the cost of filter disposal by up to 80%. After a simple installation and connection to shop air, the economical product converts used oil filters from EPA hazardous material into recyclable metal and oil. And the process takes only 40 to 60 seconds. With a crushing force of 24,000 pounds, this product can handle filters up to 9″ tall and 6.375″ wide.

Newstripe, Inc. 
Aurora, CO

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