Improving Machinery Reliability 3 Episode 13 docx

514 Improving Machinery Reliability 2,500 E 2,000 8 r FO 7 1,500 u) 0 8 u) 2 1,000 500 3 5 8 10 13 24 Hours of actual operation, in thousands 3 Figure 12-14. Viscosity stability, bowl mill. had recently been reworked and tested. All three bowl mills were fed the same amount of coal during the test period. All three gear oils were the same IS0 320 vis- cosity grade. The average current draws were: Product Amps Petroleum #I 70 Petroleum #2 75 Synthetic hydrocarbon gear oil 68 The lower amp difference shown by the synthetic hydrocarbon is the result of the lower coefficient of friction shown in Table 12-2. In summary, the synthetic hydrocarbon gear oil has solved the original problems and provided additional benefits not anticipated. The switch to synthetic lubricants has clearly improved performance and achieved significant savings in operating costs, as shown in the following tabulation. Table 12-2 Physical Properties of IS0 VG 320 Gear Oil ~~ Petroleum Synthetic hydrocarbon Viscosity index 95 I40 Thermal conductivity, Btukrlftz 0.071 0.085 Coefficient of friction 0.101 0.086 Pour point, "F +5 -45 Lubrication and Reliability 515 The extended drain interval provides savings in three areas: 1. Lubricant consumption cost savings: Petroleum oil cost per gal $4.00 Petroleum oil changes per yr 2 Volume of gear box, gal 300 Petroleum oil cost per yr ($4.00/ga1)(2 changes/yr)(300 gal/unit) = $2,400 Synthetic oil cost per gal $16.00 0.2 Volume of gear box, gal 300 Synthetic oil cost per yr ($16.00/ga1)(0.2 changes/yr)(300 gal/yr) = $960 Annual savings on lubricant cost-$1,440 per unit 2. Reduced maintenance cost savings 2 Maintenance cost per change $500 Petroleum oil maintenance cost per yr Synthetic oil changes per yr Petroleum oil changes per yr (2 changes/yr)($500/change) = $1,000 Synthetic oil changes per yr 0.2 Maintenance cost per change $500 Synthetic oil maintenance cost per yr Annual savings in scheduled maintenance costs-$900 Petroleum oil used per yr, gal 600 Disposal cost per gal $0.50 Cost of disposal $300 Synthetic oil used per yr, gal 60 Disposal cost per gal $0.50 Cost of disposal $30 Annual savings in disposal cost per year-$270 (0.2 changes/yr)($500/change) $100 3. Lubricant disposal costs The reduction in energy consumption also provides significant savings: Average annual power cost using petroleum oil lubricant Average annual power cost using synthetic hydrocarbon lubricant Annual savings in power consumption-$2,067 $33,278 $31,211 The total annual savings for all of the above categories amount to $4,677. In addi- tion, savings in reduced wear and thus fewer repairs are certain to be realized. Vibration Performance Improved With Synthetics Rolling element bearings can experience significant reductions in vibration ampli- tude and, thus, increased life expectancy when lubricated with synthetic oils. The 516 Improving Machinery Reliability higher film strengths of the synthetic oils reduce the severity of impact when the rolling elements of a bearing move across spa11 marks and other discontinuities. In fact, many defective bearings have been “nursed along” by the high-strength bond- ing characteristics of these films. A major gas-transmission company documented the vibration-shock pulse activity of a compressor turbocharger and oil supply pump before and after switching to a syn- thetic oil. After the changeover, a strong, tenacious and slippery oil film reduced vibra- tion severity by “peening over” asperities on the various metal surfaces of bearings. A variety of equipment has been rejuvenated by switching to synthetics: An external washer-filter in a Willamette, Ind., pulp mill had been operating well above 1.5 G for shock pulse activity and 0.2 in./s for vibration. Upon switching to a synthetic oil, the values dropped to 0.75 G for shock pulse activity and 0.15 in./s for vibration. The change occurred immediately and continued for a month A multistage air blower at a fiber spinning plant had its vibration decreased from 0.155 in./s to 0.083 inh by switching oils. Further, the temperature of the bearing dropped by 20°F A IO-hp centrifugal pump had an acceptable vibration of 0.068 in./s, but the bear- ing housing temperature of 175°F was borderline. After changing to a synthetic oil, the vibration dropped to 0.053 in./s, and bearing housing temperature went down to 155°F. Further, the motor amperage was cut from 5.7 Nphase to 4.4 Nphase To obtain such improvements, however, it is important to choose a well-formulat- ed synthetic oil. As typified in Figure 12-15, there are noticeable differences in the operating temperatures of spur gear units, reactor pump bearings and bevel gear enclosures using products from different vendors. Further, while there are many excellent products on the market today, many may not be appropriate for use in process machine applications. For example, high-film- strength oils based on extreme pressure (EP) technology and intended for gear lubrica- tion typically incorporate additives containing sulfur, phosphorus and chlorine. These EP industrial oils cannot be used as bearing lubricants for pumps, air compressors, steam turbines, high-speed gears and similar machinery, since the sulfur, phosphorus and chlorine will cause corrosion at high temperatures and in moist environments. Testing Provides Proof The best indication of which oil-synthetic or mineral-will excel in an applica- tion can be obtained by comparing their specific performance. There are numerous laboratory tests that are good indicators of how well an oil will perform in service. These includes tests for viscosity, pour point, residue, strip corrosion, rust, demulsi- bility and so on. On the other hand, it should be pointed out that these tests are only predictors. Realistic tests under simulated field conditions are better, while the true measure of a lubricant’s performance can only be determined in actual service. For example, in 1992, Kingsbury, Inc., completed the testing of a well-compounded IS0 Grade 32 synthetic lubricant in a thrust-bearing test machine. Lubrication and Reliability 517 5 E 8. E F 4- ~ ~~ - Synthetic oil “A” - Synthetic oil “B” Figure 2. Not all synthetic oils are equal: Here oil B is superior to A Time (days) IIII’II ,,I Figure 12-15. Not all synthetic oils are equal. Here oil B is superior to A. At low speeds and loads, there appeared to be little difference between this lubri- cant and identical premium-grade mineral oils of the same viscosity. However, at high loads and speeds, above 550 psi and 10,000 rpm, Kingsbury found that the syn- thetic oil cut bearing temperature by 15”F, and decreased frictional losses by 10%. Similarly, engineers from SKF and Exxon conducted a series of tests on rolling contact bearings.13 The objective was to compare the properties of a specially formu- lated diester lubricant with those of a premium-grade mineral oil that was in service in an Exxon petrochemical plant. Two synthetic lubricants and two mineral oils of varying viscosities were experi- mentally compared. The test results indicated that the synthetic lubricant, having a viscosity of 32 centistokes (cSt) at a temperature of 100”F, offered long-term surface protection equivalent to that of the base line mineral oil with a viscosity of 68 cSt, without reducing bearing surface life below the theoretically estimated levels. The same good wear protection could not be achieved with a reduced viscosity mineral oil. The use of the lower viscosity synthetic lubricating fluid could provide projected energy savings of $140,000 per year-prorated to 1998 dollars, when the test was conducted. Other companies, too, have been operating successfully with synthetic oils for many years, and are reluctant to publicize their experience so as not to give away a competitive advantage. Suffice it to say that a forward-looking process plant needs to explore the many opportunities for often substantial cost savings that can be achieved by judiciously applying properly formulated synthetic lubricants. Automatic Grease Lubrication as a Reliability Improvement Strategy Experienced maintenance and reliability professionals have seen rapid progress from reactive maintenance through preventive, predictive and “hybrid” approaches toward today’s proactive maintenance methods. Recognizing that there are still some cost reduction measures that could-and should-be implemented, a number of “Best-of-Class” companies are now focusing on maintenance as part of strategy and 518 Improving Machinery Reliability profit potential. This realization has led these companies to fundamentally reassess their lubrication options for both new as well as existing machinery. Lubrication Should Not Be An Afterthought The most advanced, truly bottomline-oriented owners/purchasers of high-speed paper producing machinery are among a growing number of buyers that base their specification and procurement decisions on life cycle cost calculations. These calcu- lations have shown, in the majority of cases, the long-range maintenance and down- time cost avoidance advantage of incorporating automatic oiling or grease feed pro- visions in modern process machines. Best-of-class design contractors and owner companies insist on automatic lubrication to be part of the design specification and permanent plant operating strategy. This new thinking supersedes the old notion that lubrication automation is diffi- cult to cost-justify, or that automatic lubrication provisions can be retrofitted as needed! In a highly cost-competitive environment or at a time when profit margins can vanish because of a single, unplanned outage event, buying equipment with proven lubrication provisions makes eminent sense. Experience shows that procure- ment of suitable automated lubricant delivery units at the inception of a project may well be the only low-risk opportunity that presents itself to buyers who take reliabili- ty seriously. Buying critically important machinery with the thought that upgrading to full automation at a later date will always be an option could be fallacious and may prove to be a costly mistake. Bearing Manufacturers Prefer Automatic Lube Option The disadvantages of manual lubrication have long been recognized by the lead- ing bearing manufacturers. As can be seen from Table 12-3, the service life of rolling element bearings with automatic grease feed provisions ranks well ahead of most other means of lubricant delivery. This is why many European process plants much prefer engineered automatic lube application systems over traditional static oil sumps or manual regreasing. These plants are often especially mindful of the short- comings of single-point automatic lubricators. Although occasionally found in the United States, these spring or gas-pressurized plastic grease containers offer little control over grease quantity and grease homogeneity. Greases under constant pres- sure tend to separate into their respective oil and soap constituents. This is highly undesirable since the virtually all-soap matrix is now likely to enter the bearing with- out oil. A properly engineered grease injection system will provide near-instanta- neous pressure pulses with adjustable rest periods interspersed to suit the require- ments of a specific application. Although static oil sumps are still used in the majority of centrifugal pumps installed in U.S. paper mills, petrochemical facilities, and general process plants, the experience of Scandinavian pump users should prompt a fundamental reassessment and serious questioning of the role of contamination-prone static oil sumps in an era of reduced maintenance manpower availability. Moves away from “sump, occasion- Lubrication and Reliability 519 Table 12-3 Lubrication Methods Ranked by Order of Decreasing Service Life. (Ref. 14) Oil Grease * Rolling Bearing Rolling Bearing Alone Alone ‘2 Circulation with filter, Automatic feed 2 Oil-air % 8 Circulation without B filter* Occasional renewal Occasional replenishment 1 Lubrication for-life B b) automatic oiler Oil-mist M Sump, regular Regular regreasing of renewal cleaned bearing Regular grease replenishment Sump, occasional renewal *By feed cones, bevel wheels, asymmetric rolling bearings. **Condition: Lubricant service life < fatigue life. a1 renewal” to “automatic grease feed” as ranked in Table 12-3 have resulted in relia- bility increases that can no longer be overlooked. This readjusted thinking has paid off handsomely in a number of Finnish and Swedish paper mills by allowing man- power reductions and resulting in plant availability extensions. Comparing Manual and Automatic Grease Lubrication Provisions Three principal disadvantages of manual lubrication are generally cited: e Long relubrication intervals allow dirt and moisture to penetrate the bearing seals. Well over 50% of all bearings experience significantly reduced service life as a result of contamination. a Overlubrication occurring during grease replenishment causes excessive friction and short-term excessive temperatures. These temperature excursions cause oxida- tion of the oil portion of the grease. e Underlubrication occurring as the previously applied lube charge is being depleted at this time and prior to the next regreasing event. In contrast, automated lubrication has significant technical advantages. Time and again, statistics compiled by SKF (Figure 12-16) and other major bearing manufac- turers have shown lubrication-related distress responsible for at least 50%, and per- haps as much as 70% of all bearing failure events worldwide. Thoroughly well-engi- neered automatic lubrication systems, applying either oil or grease, are now 520 Improving Machinery Reliability Other (18.69’0) \ Lubrication (34.4%) Lubrication Related Failures: 54% \ i Installation Errors - . <Contamination (1 9.6%> Figure 12-16. Bearing failures and their causes. (Courtesy of SKF USA, Inc. also TAPPI 7995 Engineering Conference Proceedings.) available to forward-looking, bottomline-oriented user companies. These systems (Figure 12- 17) ensure that: The time elapse between relubrication events is optimized. Accurately predetermined, metered amounts of lubricant enter the bearing “on The integrity of bearing seals is safeguarded. Supervisory instrumentation and associated means of monitoring are available at the point of lubrication for critical bearings. time” and displace contaminants. How Automated Lubrication Works Depending on the type of installation, engineered lubricant injection systems are configured for either grease or liquid oil delivery. Modular in design and easily expandable, they are suitable for machinery with just a few lubrication points, as well as installations covering complete manufacturing or process plants involving thousands of points. Automated grease lubrication systems are designed for the peri- odic lubrication of rolling element bearings, as in the centrifugal pump depicted in Figure 12-18, or for different types of sleeve bearing. Also, automated grease lubri- cation systems are used on guides (shown in the soot blower in Figure 12-19) and on open gears, chains, and coupling devices. Depending on plant and equipment configuration, engineered automatic lubrica- tion systems consist of a single or multi-channel control center (Figure 12-17, Item I), one or more pumping stations (Item 2), appropriate supply lines (Item 3). tubing Lubrication and Reliability 521 Figure 12-17. Single-header, state-of-the-art automatic lubrication system. (Courtesy of Safematic, Muurame, Finland and Alpharetta, GA.) Figure 12-18. Centrifugal pump with automated grease lubrication. (Courtesy of Safe- matic, Muurame, Finland and Alpharetta, GA.) 522 improving Machinery Reliability Figure 12-19. Soot blower assembly fitted with automatic grease lubrication provisions. (Courtesy of Safematic, Muurarne, Finland and Alpharetta, GA.) (4). which links a remote shutoff valve (5) and lubrication dosing modules (6), and also interconnects dosing modules and points to be lubricated. Different sized dosing modules are used to optimally serve bearings of varying configurations and dimen- sions. The dosing modules themselves are individually adjustable to provide an exact amount of lubricant and to thus avoid overlubrication. A pressure sensing switch (Item 7), completes the system. The control center starts up a pump that feeds lubricant from the barrel through the main supply line to the dosing modules. When pressure in the system rises to a preset level, the pressure switch near the end of the line transmits an impulse to the control center, which then stops the pump and depressurizes the pipeline. The con- trol center now begins measuring the new pumping interval. If for some reason the pressure during pumping does not rise to the preset level at the pressure switch, an alarm is activated and the lubrication center will not operate until the problem has been rectified and the alarm subsequently reset. Special multi-channel controllers are available with state-of-the-art automatic lubrication systems. These have the ability to provide lubrication to installations requiring a variety of lube types or consistencies. Even different timing intervals can be controlled from a single multi-channel controller location. These systems have proven their functional and mechanical dependability in operating environments ranging from minus 35°C to plus 150°C. One Finnish manufacturer tests every type of grease supplied by usedclient companies under these temperature extremes and leaves no reliability-related issues open for questioning. Lubrication and Reliability 523 Cost Studies Prove Favorable Economics of Automated Lubrication Systems A Finnish paper mill, Enso Oy, has documented the production increases, labor savings, and downtime reductions shown in Figure 12-20. Downtime hours for a total of 3 1 process units encompassing over 7,500 lubrication points are illustrated in Figure 12-21. Here, the Kaukopaa mill documented the 1 1-year trend from 9,700 hours of downtime in 1985 to approximately 280 hours in 1995. In the same time period, production went from 620,000 tons (1985) to 950,000 tons (1995). Figure 12-22 shows how, from 1990 until 1995, total maintenance expenditures decreased 26%, and maintenance costs per unit of production were reduced by 46%. Needless to say, Enso Oy has realized millions of dollars in extra profits from the timely intro- duction of engineered automatic lube systems. They have included these systems in the mandatory scope of every new project and Enso Oy’s mill standard (“EGO) defining automatic lubrication systems has been adopted as a National Industrial Standard in Finland, a “high-tech” country in every sense of the word. Washers, agitators, pumps, electric motors, soot blowers, barking drums, chippers, screens, presses, conveyors, and other equipment are automatically lubricated at a modern facility. A machine, which without lube automation often experiences five lubrication-related bearing failures per year, is likely to experience none with an engineered grease injection system. This often translates into 30.40 hours of addi- tional machine time and profit gains of $90,000-$180.000 annually. Figure 12-20. Production, lubrication labor and maintenance downtime statistics. (Courtesy of Safematic, Muurame, Finland and Alphareffa, GA.) [...]... Safety and Reliability Through Modern Sealing Technology AT r F ) 541 AT (‘C) 160 88 140 77 128) 66 1 OB 55 80 44 80 33 40 22 20 11 0 2 1 4 3 5 Test Time (hrs) Fhgure 13- 13 Seal face temperature rise: multiport vs single port flush Two minutes of dry running occurred at about 3. 5 hours 1000 800 600 400 5 0 v) c MULTl PORT INJECTION 1 I I 74 PPM AVG 600 400 200 0 Test Time (hrs) Figure 13- 14 Emission... (1.7 -3. 4 bar) above the vapor pressure at bulk fluid temperature? Special flush arrangements are used to provide an adequate vapor pressure margin in the seal chamber  538 Improving Machinery Reliability +Seal Face Temperature rise (AT) +Vapor Pressure Margin 10 bar 80 "C 70 "C 8 bar 60 "C 50 "C 6 bar 40 "C 4 bar 30 "C 20 O C 2 bar 10 O C 0 O C 0 bar 3. 6 38 4 4.2 4.4 4.6 Test Time (hrs) Figure 13- 10... chamber fluid temperature? This margin can be achieved either by raising the seal chamber pressure or lowering the seal 530 Improving Machinery Reliability Figure 13- 2 Arrangement 2-standard process fluid pressure dual seal with buffer fluid pressure lower than Figure 13- 3 Arrangement 3- dual seal with barrier fluid pressure higher than process fluid Inner seal is double balanced to withstand reverse pressure... significant effect on secondary seal p e r f ~ r m a n c e ’ ~ ~ 22, 23 Figure 13- 20 shows face temperature rise above seal 20 3 Figure 13- 19 “Bad” piping practices Providing Safety and Reliability Through Modern Sealing Technology 547 FACE TEMPERATURE RISE 1 - DELTA T (F) H20/ G LY Diesel Kerosene 10 w t oil 30 w t oil Figure 13- 20 Face temperature rise (AT) for different barrier fluids Diesel is... was increased and a final hour run performed on liquid propane Face temperature rise above bulk fluid temperature is shown in Figure 13- 13 The multiport arrangement resulted in cooler and more stable face temperatures After 540 Improving Machinery Reliability Figure 13- 12 Multiport flush the two minutes of dry running, the single port seal required about 20 minutes to return to a stable face temperature... and it performs well in corrosive applications such as HF acid  536 Improving Machinery Reliability More important than the grade (reaction-bonded or sintered) is microstructure quality High grade reaction-bonded S i c contains minimal anomalies such as silicon streaks, unreacted carbon, and contamination with foreign material. 13 Figures 13- 8 shows the microstructure of a “bad” silicon carbide seal ring... During RollingContact Lubrication,” Wear, Volume 12, 1968, pp 33 1 -34 2 9 Bloch, H P and Geitner, F K., Machinery Failure Analysis and Troubleshooting, 3rd Edition, Gulf Publishing Company, Houston, Texas, 1997 10 May, C H., “Separation of Water from Oil by the Principle of Coalescence,” Lubrication Engineering, Volume 19, No 8, 19 63 526 Improving Machinery Reliabiliry 1 1 Allen, J L., “Evaluating a Waste-Oil... Figure 13- 18 The operating point is the intersection of the two curves Poor piping practices can shift the system resistance curve far to the left, resulting in low flow.19 16 HEAD (FEET) 14 PUMPING RING 12 10 8 6 4 RESISTANCE ACTUAL FLOW 2 0 0 1 2 3 4 FLOW (GPM) 5 6 Figure 13- 18 Pumping ring head-flow curve and system resistance curve Actual flow is at curve intersection 546 Improving Machinery Reliability. .. performance is enhanced by: Providing Safety and Reliability Through Modern Sealing Technology /VAPOR CARBON FACE 539 BUBBLES HARD FACE I Figure 13- 11 Hot surfaces may cause boiling Flush must be sufficient to prevent formation of a vapor pocket Use a multiport injection flange with 4 to 8 ports equally spaced circumferentially around the seal Figures 13- 1 and 13- 12 show an annular plenum with multiple ports... faces, is generated by the pressure distribution in the fluid film When the sealed fluid changes from liquid to vapor as it 534 Improving Machinery Reliability moves across the faces, the opening force can be significantly greater than if the fluid remains in the liquid phase.* Figure 13- 6 illustrates typical pressure distributions in the fluid film for three different fluid conditions: all liquid leakage, . the seal 530 Improving Machinery Reliability Figure 13- 2. Arrangement 2-standard dual seal with buffer fluid pressure lower than process fluid pressure. Figure 13- 3. Arrangement 3- dual seal. 514 Improving Machinery Reliability 2,500 E 2,000 8 r FO 7 1,500 u) 0 8 u) 2 1,000 500 3 5 8 10 13 24 Hours of actual operation, in thousands 3 Figure 12-14 Lubrication,” Wear, Volume 12, 1968, pp. 33 1 -34 2. 9. Bloch, H. P. and Geitner, F. K., Machinery Failure Analysis and Troubleshoot- ing, 3rd Edition, Gulf Publishing Company, Houston,