Protector Seals For Gearboxes
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Bearing Housing Protector Seals for Gearboxes In extreme environments, dual-face, magnetic bearinghousing seals will keep contamination out
Stationary elastomer
Outer body
Outer body elastomer
Shroud
Magnet
Circlip
Chris Rehmann and Alan Roddis Aesseal
L
ubricant contamination in gearbox bearing housings can substantially reduce gear life. In critical applications, dual-face, magnetic bearing-protector seals will keep contamination out (Figure 1). Dual-face, magnetic bearing protectors are preferred in many difficult applications, such as wet cooling tower gearboxes, while advanced rotating labyrinth seals are more universally applicable. Both users and gearbox manufacturers should consider peripheral shaft speed, shaft movement and lubrication method. However, all things considered, fully sealing a gearbox by retrofitting advanced bearing protector seals is highly cost-effective. Because many gearboxes operate in environments that are heavily polluted, traditional lip seals or labyrinth seals should not be considered. In these environments, even closeclearance, non-contacting rotating labyrinth seals, shown in Figure 2, may not be ideal. Rotating labyrinth seals have an open gap that allows communication between the housinginternal and external environments. Unless ambient air is excluded, the oil cleanliness condition in these gearboxes may be unacceptable. Therefore, bearing housings with closed vents and face-type seals employing mechanical seal principles and advanced metallurgy are best able to keep the lubricant “clean,” as defined by bearing manufacturers. 44
Stationary seal face assembly
Stationary elastomer
Rotary seal face
Rotary elastomer
Stationary seal face assembly
Figure 1. After many repairs to oil-flooded gear speed reducers, engineers at a U.S. power plant retrofitted the application with magnetic, dual-face bearing-protector seals
Limit contaminant ingress
Whenever a gap exists between the rotating shaft and the surrounding stationary housing components, the housings will breathe, as illustrated in Figure 3. Gearbox manufacturers apply lip seals for bearing protection and oil containment, though they are subject to wear and, unless replaced on a time-based preventive maintenance schedule, will allow contaminants to enter because of the pressure difference between gearbox interior space and the ambient atmosphere. Thus, there is serious risk of water vapor entry and moisture condensation, resulting in corrosion and lip wear, as shown in Figure 4. In particular, note the wear groove in the shaft, caused by lip seal contact. The limitations of lip seals for longerterm contamination control prompted the American Petroleum Institute (API) and many equipment users to seek out superior preventive measures. Alternative sealing devices include the rotating non-contacting labyrinth bearing housing seals shown in Figure 2, and the rotating contacting dual-face magnetic seal of Figure 1. Collectively, these styles are called bearing isolators or bearing protector seals.
Chemical Engineering www.che.com December 2008
Avoid contaminated lube oil
Various factory tests, cost justifications, and a thorough review of field experience have established the viability and effectiveness of cartridge-type, dualface, magnetic bearing protectors. Magnetic sealing has had decades of use in the aerospace industry. Today, the bearings or component housings of pumps, mixers, small turbines, fans, blowers, star feeders, conveyor lines, rotary drum filters and other machines are among the hundreds of shaft-driven and bearing-supported equipment types that have been effectively sealed with dual-face magnetic seals. In particular, many gear speed reducers (Figures 5 and 6) have benefited substantially from the virtual elimination of lube oil contamination. Cost justifications and data on the projected gear life extension are readily available.
Construction features
Few environments are harsher than those that exist in cooling-tower-fan services (Figure 6), where moisture exclusion is very important. In equipment with facetype bearing housing seals, the lubricant is totally contained and the atmosphere is effectively excluded. Therefore, in state-of-the-art gearbox designs, both
Shaft not rotating
Shaft rotating Atmosphere
Atmosphere Stator housing o-ring
Micro lift gap Face shield Energizer
Static seal Rotary
Shut off device
Stator housing
Inboard rotor o-ring
Outboard rotor o-ring
Figure 2. Modern rotating labyrinth bearing-housing seals run a close second to dual-face magnetic bearing-housing seals for gearboxes
Air is expelled
Air is ingested
Figure 3. As air in the gearbox warms up, it expands and is expelled (left). As air in the gearbox cools down, it contracts and surrounding ambient air is ingested (right). The shut-off device shown in Figure 2 allows warm air to escape during operation, but prevents cool, moist air from entering while not in operation
input and output shafts are often sealed with dual-face magnetic seals. The rotary portion of the seal is usually fastened to the shaft by an O-ring that performs both clamping and sealing functions. Figure 1 illustrates this configuration of the dual-face design. Care must be taken to allow some oil to reach the faces of these bearing protector seals in both horizontal and vertical shafts. In shaft systems operating above certain peripheral speeds, the seal manufacturer must be contacted for further guidance. Instead of using springs to hold the faces together, the stationary component of a modern dual-face, magnetic bearing housing seal is fitted with a series of small, nickel-plated samarium-cobalt magnets. The two stationary faces are axially movable and are made of highly wear-resistant, low-friction antimony carbon. These faces are encased in a suitable grade of stainless steel that is attracted by the strong stationary rod magnets. A tungsten-carbide rotary is attached to the shaft. Although single-face, aero-
space magnetic seals date back to the late 1940s, modern dual-face magnetic seals represent a more recent development, with many having been fully operational since 2002.
Properties and limitations
The type of dual-face magnetic seal shown in Figure 1 has had its electrostatic and electromagnetic properties tested to ensure safe operation in hazardous areas and potentially explosive atmospheres. These seals are often used in hazardous areas where a large number of Group II, Category 2 equipment is required. The temperature classification is dependent on the specific application. In typical moderate-speed gearboxes with shaft speeds achieving 1,800 rpm, the application options for dual-face, magnetic bearing-housing seals are almost limitless. These seals are also used on many pump configurations, including horizontal and vertical pumps, rotary lobe, progressive cavity and gear pumps. Gear speed reducers and a wide variety of different machines found
in pulp and paper mills, corn milling equipment, different pillow blocks and rotary valves have also been successfully sealed with these dual-face cartridge magnetic seals. The seal assembly incorporates neither clips nor set screws. Its dimensional envelope fits many locations where lip seals were originally installed. In gearboxes with marginal lubrication (a light oil splash) on the inner face of a dual-face, magnetic bearinghousing seal, and dry-running conditions on the outer face, shaft speeds of 3,600 rpm or peripheral shaft velocities of 20 m/s, whichever is reached first, are allowed. Assuming a 4.25-in. dia. shaft, it would have to rotate at over 3,600 rpm to reach 20 m/s. Thus, for this shaft diameter, there is a “safety cushion” with gear speed reducers operating at only 1,800 rpm. At 18°C ambient temperature, the resulting face temperature would stay considerably below the often applied and generally desired rule-of-thumb limit of 85°C. In order to safeguard against misapplication, manufacturers recommend against dry running above certain shaft diameters and peripheral speeds. As a matter of general policy, continuous monitoring and other appropriate inspection and examination methods are advocated to ensure correct equipment oil levels. Fortunately, the bearing housings of properly designed gearboxes and pumps will always incorporate lube application methods that generate an oil fog. This fog creates adequate bearing lubrication while also providing a thin coating of oil at the active seal faces. Only the complete loss of oil or operation at excessive peripheral speeds would cause an unacceptable temperature increase at one or both of the seal faces. Used within their design parameters, dual-face magnetic seals embodying the features illustrated in Figure 1 are unsurpassed in keeping oil in, and contamination out of gearboxes and bearing housings. Nevertheless, modern rotating labyrinth seals are feasible and highly cost-effective in many applications, including in virtually all gearboxes. The seal incorporates O-rings that never contact sharp edges, whereas
Chemical Engineering www.che.com December 2008
45
Feature Report
Figure 4. A damaged shaft has bearing corrosion and lip-seal-related wear
Lubrication Systems Co.
Figure 5. A gearbox with dual-face, magnetic-bearing-housing seal fitted in a bearing housing end cap
earlier generation rotating labyrinth seals often contained dynamic O-rings in contact with the edge of a groove. During slow-roll operation or with axial movement of opposing components, in these “old-style” bearing isolator seals, the O-ring quickly becomes unserviceable.
Cooling-tower-fan drive gears
Cooling-tower- fan gearboxes are exposed to one of the most adverse saturated-water-vapor environments encountered in the CPI (chemical process industries), as they are typically enveloped in a dense fog that contains a mix of water treatment chemicals. Unless properly protected, the chemically loaded vapors will enter the gearboxes through casing vents and shaft protrusions. Once inside, the water vapors may cause further damage by interacting with the lube oil additives. In one instance, the contaminating mixture caused severe rust formation on gears as well as bearing distress in eight gearboxes at a facility in the U.S. Lip seal life did not exceed six months. With restricted access to cooling-tower internals, implementing time-based preventive maintenance measures seemed too expensive. To gain access, the cooling tower shrouds had to be opened, and special cranes were brought to the site for lifting duty. Temporary scaffolding is needed for some fan cell configurations, and in some locations, safety and health regulations require the wearing of cumbersome breathing apparatuses. 46
Figure 6. Cooling tower gearboxes operate under the most severe conditions
This explains why gear-internal replacements often cost around $80,000, compared to gearbox repairs of $30,000 when equipment rental, labor and overhead costs are considered. In most instances, replacing lip seals with dual-face magnetic seals extends oil replacement intervals from every six months to 24 months. Based on feedback regarding cooling towers in petrochemical plant locations where moisture intrusion has been eliminated, cooling-tower gearbox failures at this facility should be a thing of the past. In the example listed above, the benefits of conversion and upgrading to dual-face magnetic seals were assessed and payback periods were found to range from three to five weeks.
Simple payback calculation
Life-cycle component cost comparisons consider the total lifetime cost to purchase, install, operate and maintain equipment against the total lifetime cost of equipment without magnetic bearing housing seals. The comparison
Chemical Engineering www.che.com December 2008
includes associated downtime, plus certain imputed values of fewer failure events. Reliability-focused plants include the avoided cost of plant fires occasionally brought on by catastrophic bearing failures, and the implicit value of utilizing workforce members that previously spent time on remedial tasks and are now free to proactively work on preventive tasks. Suppose a plant had a dozen coolingtower-fan gearboxes with an average MTBF (mean time between failures) of six years, and that the average repair is costing the plant $46,400. Although this cost includes burden, overhead, field and shop labor, replacement parts and more, it represents a rather low estimate for cooling tower cells that require crane rentals, dismantling of enclosures, safety-mandated lockout-tagout work, and the cost of marshalling and supervising a work crew. Suppose the gearboxes are not fully sealed, and there is clear evidence of lubricant contamination. As-
Where the Know-how is
sume that sets of magnetic seals cost $740 and installation labor amounts to $2,000 per gearbox. It would be fair to anticipate that, together with plugging the vent and switching to a superior synthetic lubricant formulation, this upgrade holds the promise of extending gearbox MTBF to 12 years, a figure often reached by best-of-class plants. The facility would avoid gearbox repairs valued at $46,400, and over a six-year period, would realize a payback of $46,400/$2,740 — a benefit-to-cost ratio of 17 to 1. ■ Edited by Kate Torzewski
References 1. Bloch, Heinz P., “Practical Lubrication for Industrial Facilities,” The Fairmont Press, Lilburn, Ga., p. 479, 2000. 2. Bloch, Heinz P. and Budris, A., “Pump User’s Handbook: Life Extension,” The Fairmont Press, Lilburn, Ga., pp. 232-239, 2006. 3. Bloch, Heinz P. and Geitner, F., “Machinery Failure Analysis and Troubleshooting,” 3rd Ed., Gulf Publishing Co., Houston, Tex., 1997. 4. Eschmann, Hasbargen and Weigand, “Ball and Roller Bearings,” John Wiley & Sons, New York, N.Y., p. 183, 1995. 5. “Industrial Product Guide,” Royal Purple, Ltd., Porter, Tex., 2002. 6. SKF USA, Inc., Catalog 4000US, p. 40, 1991.
Authors Chris Rehmann is general manager of Aesseal’s Component Seal and Bearing Protection Divisions in North America (Aesseal, Inc., 355 Dunavant Dr., Rockford, TN 37853; Tel: 865-531-0192; Email: chris. [email protected]). Rehmann holds a B.S. degree in Electrical Engineering from the University of Notre Dame. He worked for Schlumberger, an oilfield engineering firm, for 15 years, holding positions in field engineering, technical sales, and management in the U.S., Middle East, and AsiaPacific. Chris joined Aesseal in 2002, moving his family from Saudi Arabia to Knoxville, Tennessee. He has taught several courses and authored a number of technical papers dealing with bearing protection on pumps, electric motors, oil mist, and gear boxes. Alan Roddis is the engineering director of Aesseal plc. (Mill Close, Rotherham, U.K. S60 1BZ; Email: alanr@ Aesseal.co.uk) He is a graduate mechanical engineer (honors degree) and has been responsible for the design of modern sealing devices used in pumps, mixers, compressors, steam turbines, gear speed reducers and dozens of other machine categories used by hydrocarbon processing, power generation, pharmaceutical, mining, food processing, paper, and many other industries in dozens of countries. Roddis holds several U.K. and international patents on advanced sealing products and related mechanical devices. In his position at Aesseal, he continues to spearhead the design and development efforts at this manufacturer of advanced technology sealing products.
COALESCERS
Coalescers for separation of aqueous phase from extraction solvent & for separation of extraction solvent from waste water As a worldwide supplier of HIGH-QUALITY SEPARATION PLANTS we stand for: • Outstanding process technology & cost-saving solutions • Long standing technology experience with over 700 units installed worldwide • Customized all-in solutions supplied by one partner • Own Research & Development Department & pilot plants For additional information please contact: FRANKEN FILTERTECHNIK KG, Germany Phone: +49 (0) 2233 974 40-0, e-mail: [email protected], web: www.frankenfilter.com
Circle 26 on p. 62 or go to adlinks.che.com/7379-26
CIOs. CTOs. CHIEF ENGINEERS. O&M, CAPITAL ASSET AND PROJECT MANAGERS
Discover the Most Innovative Ideas, Practices and Technologies at the World’s Leading Plant Asset Lifecycle Management Event. 5)"//6"-
February 23-25, 2009 Hilton Americas–HOUSTON, TX Sponsoring Organization:
NEW Downto wn Venue for 2009 !
Offical Publications:
REGISTER by December 31st
to get the best rates at www.daratechplant.com or call Jill Dean at 832-242-1969, ext. 316 SPONSORS/EXHIBITORS
%4r"S5S"r"DF$BE4PGUXBSF-UEr"VUPEFTL *ODr"7&7"(SPVQQMDr#FOUMFZ4ZTUFNT *ODr#MVF$JFMP&$.4PMVUJPOTr$BENBUJDr$BE4DISPFSr$"9QFSUT(NCIr$&"r$IFNJDBM &OHJOFFSJOHr$MPVEJT-JNJUFEr$0"%& *ODr$4" *ODr%BTTBVMU4ZTUÊNFTr&$&%FTJHOr '"30r(PPHMFr(4/5FDIOPMPHJFT--$r*/07Y4PMVUJPOTr-FJDB(FPTZTUFNTr*OUFSHSBQIr *OOPUFDr0DUBHBr1*1m1SPDFTT*OEVTUSZ1SBDUJDFTr108&3r4LJSF *ODr4ZOFSHJT4PGUXBSFr 5PUBM$"%4ZTUFNTr5SJNCMFr73$POUFYUr; '6, Image courtesy of COADE, Inc.
Chemical Engineering www.che.com December 2008
47
Bearing Housing Protector Seals for Gearboxes In extreme environments, dual-face, magnetic bearinghousing seals will keep contamination out
Stationary elastomer
Outer body
Outer body elastomer
Shroud
Magnet
Circlip
Chris Rehmann and Alan Roddis Aesseal
L
ubricant contamination in gearbox bearing housings can substantially reduce gear life. In critical applications, dual-face, magnetic bearing-protector seals will keep contamination out (Figure 1). Dual-face, magnetic bearing protectors are preferred in many difficult applications, such as wet cooling tower gearboxes, while advanced rotating labyrinth seals are more universally applicable. Both users and gearbox manufacturers should consider peripheral shaft speed, shaft movement and lubrication method. However, all things considered, fully sealing a gearbox by retrofitting advanced bearing protector seals is highly cost-effective. Because many gearboxes operate in environments that are heavily polluted, traditional lip seals or labyrinth seals should not be considered. In these environments, even closeclearance, non-contacting rotating labyrinth seals, shown in Figure 2, may not be ideal. Rotating labyrinth seals have an open gap that allows communication between the housinginternal and external environments. Unless ambient air is excluded, the oil cleanliness condition in these gearboxes may be unacceptable. Therefore, bearing housings with closed vents and face-type seals employing mechanical seal principles and advanced metallurgy are best able to keep the lubricant “clean,” as defined by bearing manufacturers. 44
Stationary seal face assembly
Stationary elastomer
Rotary seal face
Rotary elastomer
Stationary seal face assembly
Figure 1. After many repairs to oil-flooded gear speed reducers, engineers at a U.S. power plant retrofitted the application with magnetic, dual-face bearing-protector seals
Limit contaminant ingress
Whenever a gap exists between the rotating shaft and the surrounding stationary housing components, the housings will breathe, as illustrated in Figure 3. Gearbox manufacturers apply lip seals for bearing protection and oil containment, though they are subject to wear and, unless replaced on a time-based preventive maintenance schedule, will allow contaminants to enter because of the pressure difference between gearbox interior space and the ambient atmosphere. Thus, there is serious risk of water vapor entry and moisture condensation, resulting in corrosion and lip wear, as shown in Figure 4. In particular, note the wear groove in the shaft, caused by lip seal contact. The limitations of lip seals for longerterm contamination control prompted the American Petroleum Institute (API) and many equipment users to seek out superior preventive measures. Alternative sealing devices include the rotating non-contacting labyrinth bearing housing seals shown in Figure 2, and the rotating contacting dual-face magnetic seal of Figure 1. Collectively, these styles are called bearing isolators or bearing protector seals.
Chemical Engineering www.che.com December 2008
Avoid contaminated lube oil
Various factory tests, cost justifications, and a thorough review of field experience have established the viability and effectiveness of cartridge-type, dualface, magnetic bearing protectors. Magnetic sealing has had decades of use in the aerospace industry. Today, the bearings or component housings of pumps, mixers, small turbines, fans, blowers, star feeders, conveyor lines, rotary drum filters and other machines are among the hundreds of shaft-driven and bearing-supported equipment types that have been effectively sealed with dual-face magnetic seals. In particular, many gear speed reducers (Figures 5 and 6) have benefited substantially from the virtual elimination of lube oil contamination. Cost justifications and data on the projected gear life extension are readily available.
Construction features
Few environments are harsher than those that exist in cooling-tower-fan services (Figure 6), where moisture exclusion is very important. In equipment with facetype bearing housing seals, the lubricant is totally contained and the atmosphere is effectively excluded. Therefore, in state-of-the-art gearbox designs, both
Shaft not rotating
Shaft rotating Atmosphere
Atmosphere Stator housing o-ring
Micro lift gap Face shield Energizer
Static seal Rotary
Shut off device
Stator housing
Inboard rotor o-ring
Outboard rotor o-ring
Figure 2. Modern rotating labyrinth bearing-housing seals run a close second to dual-face magnetic bearing-housing seals for gearboxes
Air is expelled
Air is ingested
Figure 3. As air in the gearbox warms up, it expands and is expelled (left). As air in the gearbox cools down, it contracts and surrounding ambient air is ingested (right). The shut-off device shown in Figure 2 allows warm air to escape during operation, but prevents cool, moist air from entering while not in operation
input and output shafts are often sealed with dual-face magnetic seals. The rotary portion of the seal is usually fastened to the shaft by an O-ring that performs both clamping and sealing functions. Figure 1 illustrates this configuration of the dual-face design. Care must be taken to allow some oil to reach the faces of these bearing protector seals in both horizontal and vertical shafts. In shaft systems operating above certain peripheral speeds, the seal manufacturer must be contacted for further guidance. Instead of using springs to hold the faces together, the stationary component of a modern dual-face, magnetic bearing housing seal is fitted with a series of small, nickel-plated samarium-cobalt magnets. The two stationary faces are axially movable and are made of highly wear-resistant, low-friction antimony carbon. These faces are encased in a suitable grade of stainless steel that is attracted by the strong stationary rod magnets. A tungsten-carbide rotary is attached to the shaft. Although single-face, aero-
space magnetic seals date back to the late 1940s, modern dual-face magnetic seals represent a more recent development, with many having been fully operational since 2002.
Properties and limitations
The type of dual-face magnetic seal shown in Figure 1 has had its electrostatic and electromagnetic properties tested to ensure safe operation in hazardous areas and potentially explosive atmospheres. These seals are often used in hazardous areas where a large number of Group II, Category 2 equipment is required. The temperature classification is dependent on the specific application. In typical moderate-speed gearboxes with shaft speeds achieving 1,800 rpm, the application options for dual-face, magnetic bearing-housing seals are almost limitless. These seals are also used on many pump configurations, including horizontal and vertical pumps, rotary lobe, progressive cavity and gear pumps. Gear speed reducers and a wide variety of different machines found
in pulp and paper mills, corn milling equipment, different pillow blocks and rotary valves have also been successfully sealed with these dual-face cartridge magnetic seals. The seal assembly incorporates neither clips nor set screws. Its dimensional envelope fits many locations where lip seals were originally installed. In gearboxes with marginal lubrication (a light oil splash) on the inner face of a dual-face, magnetic bearinghousing seal, and dry-running conditions on the outer face, shaft speeds of 3,600 rpm or peripheral shaft velocities of 20 m/s, whichever is reached first, are allowed. Assuming a 4.25-in. dia. shaft, it would have to rotate at over 3,600 rpm to reach 20 m/s. Thus, for this shaft diameter, there is a “safety cushion” with gear speed reducers operating at only 1,800 rpm. At 18°C ambient temperature, the resulting face temperature would stay considerably below the often applied and generally desired rule-of-thumb limit of 85°C. In order to safeguard against misapplication, manufacturers recommend against dry running above certain shaft diameters and peripheral speeds. As a matter of general policy, continuous monitoring and other appropriate inspection and examination methods are advocated to ensure correct equipment oil levels. Fortunately, the bearing housings of properly designed gearboxes and pumps will always incorporate lube application methods that generate an oil fog. This fog creates adequate bearing lubrication while also providing a thin coating of oil at the active seal faces. Only the complete loss of oil or operation at excessive peripheral speeds would cause an unacceptable temperature increase at one or both of the seal faces. Used within their design parameters, dual-face magnetic seals embodying the features illustrated in Figure 1 are unsurpassed in keeping oil in, and contamination out of gearboxes and bearing housings. Nevertheless, modern rotating labyrinth seals are feasible and highly cost-effective in many applications, including in virtually all gearboxes. The seal incorporates O-rings that never contact sharp edges, whereas
Chemical Engineering www.che.com December 2008
45
Feature Report
Figure 4. A damaged shaft has bearing corrosion and lip-seal-related wear
Lubrication Systems Co.
Figure 5. A gearbox with dual-face, magnetic-bearing-housing seal fitted in a bearing housing end cap
earlier generation rotating labyrinth seals often contained dynamic O-rings in contact with the edge of a groove. During slow-roll operation or with axial movement of opposing components, in these “old-style” bearing isolator seals, the O-ring quickly becomes unserviceable.
Cooling-tower-fan drive gears
Cooling-tower- fan gearboxes are exposed to one of the most adverse saturated-water-vapor environments encountered in the CPI (chemical process industries), as they are typically enveloped in a dense fog that contains a mix of water treatment chemicals. Unless properly protected, the chemically loaded vapors will enter the gearboxes through casing vents and shaft protrusions. Once inside, the water vapors may cause further damage by interacting with the lube oil additives. In one instance, the contaminating mixture caused severe rust formation on gears as well as bearing distress in eight gearboxes at a facility in the U.S. Lip seal life did not exceed six months. With restricted access to cooling-tower internals, implementing time-based preventive maintenance measures seemed too expensive. To gain access, the cooling tower shrouds had to be opened, and special cranes were brought to the site for lifting duty. Temporary scaffolding is needed for some fan cell configurations, and in some locations, safety and health regulations require the wearing of cumbersome breathing apparatuses. 46
Figure 6. Cooling tower gearboxes operate under the most severe conditions
This explains why gear-internal replacements often cost around $80,000, compared to gearbox repairs of $30,000 when equipment rental, labor and overhead costs are considered. In most instances, replacing lip seals with dual-face magnetic seals extends oil replacement intervals from every six months to 24 months. Based on feedback regarding cooling towers in petrochemical plant locations where moisture intrusion has been eliminated, cooling-tower gearbox failures at this facility should be a thing of the past. In the example listed above, the benefits of conversion and upgrading to dual-face magnetic seals were assessed and payback periods were found to range from three to five weeks.
Simple payback calculation
Life-cycle component cost comparisons consider the total lifetime cost to purchase, install, operate and maintain equipment against the total lifetime cost of equipment without magnetic bearing housing seals. The comparison
Chemical Engineering www.che.com December 2008
includes associated downtime, plus certain imputed values of fewer failure events. Reliability-focused plants include the avoided cost of plant fires occasionally brought on by catastrophic bearing failures, and the implicit value of utilizing workforce members that previously spent time on remedial tasks and are now free to proactively work on preventive tasks. Suppose a plant had a dozen coolingtower-fan gearboxes with an average MTBF (mean time between failures) of six years, and that the average repair is costing the plant $46,400. Although this cost includes burden, overhead, field and shop labor, replacement parts and more, it represents a rather low estimate for cooling tower cells that require crane rentals, dismantling of enclosures, safety-mandated lockout-tagout work, and the cost of marshalling and supervising a work crew. Suppose the gearboxes are not fully sealed, and there is clear evidence of lubricant contamination. As-
Where the Know-how is
sume that sets of magnetic seals cost $740 and installation labor amounts to $2,000 per gearbox. It would be fair to anticipate that, together with plugging the vent and switching to a superior synthetic lubricant formulation, this upgrade holds the promise of extending gearbox MTBF to 12 years, a figure often reached by best-of-class plants. The facility would avoid gearbox repairs valued at $46,400, and over a six-year period, would realize a payback of $46,400/$2,740 — a benefit-to-cost ratio of 17 to 1. ■ Edited by Kate Torzewski
References 1. Bloch, Heinz P., “Practical Lubrication for Industrial Facilities,” The Fairmont Press, Lilburn, Ga., p. 479, 2000. 2. Bloch, Heinz P. and Budris, A., “Pump User’s Handbook: Life Extension,” The Fairmont Press, Lilburn, Ga., pp. 232-239, 2006. 3. Bloch, Heinz P. and Geitner, F., “Machinery Failure Analysis and Troubleshooting,” 3rd Ed., Gulf Publishing Co., Houston, Tex., 1997. 4. Eschmann, Hasbargen and Weigand, “Ball and Roller Bearings,” John Wiley & Sons, New York, N.Y., p. 183, 1995. 5. “Industrial Product Guide,” Royal Purple, Ltd., Porter, Tex., 2002. 6. SKF USA, Inc., Catalog 4000US, p. 40, 1991.
Authors Chris Rehmann is general manager of Aesseal’s Component Seal and Bearing Protection Divisions in North America (Aesseal, Inc., 355 Dunavant Dr., Rockford, TN 37853; Tel: 865-531-0192; Email: chris. [email protected]). Rehmann holds a B.S. degree in Electrical Engineering from the University of Notre Dame. He worked for Schlumberger, an oilfield engineering firm, for 15 years, holding positions in field engineering, technical sales, and management in the U.S., Middle East, and AsiaPacific. Chris joined Aesseal in 2002, moving his family from Saudi Arabia to Knoxville, Tennessee. He has taught several courses and authored a number of technical papers dealing with bearing protection on pumps, electric motors, oil mist, and gear boxes. Alan Roddis is the engineering director of Aesseal plc. (Mill Close, Rotherham, U.K. S60 1BZ; Email: alanr@ Aesseal.co.uk) He is a graduate mechanical engineer (honors degree) and has been responsible for the design of modern sealing devices used in pumps, mixers, compressors, steam turbines, gear speed reducers and dozens of other machine categories used by hydrocarbon processing, power generation, pharmaceutical, mining, food processing, paper, and many other industries in dozens of countries. Roddis holds several U.K. and international patents on advanced sealing products and related mechanical devices. In his position at Aesseal, he continues to spearhead the design and development efforts at this manufacturer of advanced technology sealing products.
COALESCERS
Coalescers for separation of aqueous phase from extraction solvent & for separation of extraction solvent from waste water As a worldwide supplier of HIGH-QUALITY SEPARATION PLANTS we stand for: • Outstanding process technology & cost-saving solutions • Long standing technology experience with over 700 units installed worldwide • Customized all-in solutions supplied by one partner • Own Research & Development Department & pilot plants For additional information please contact: FRANKEN FILTERTECHNIK KG, Germany Phone: +49 (0) 2233 974 40-0, e-mail: [email protected], web: www.frankenfilter.com
Circle 26 on p. 62 or go to adlinks.che.com/7379-26
CIOs. CTOs. CHIEF ENGINEERS. O&M, CAPITAL ASSET AND PROJECT MANAGERS
Discover the Most Innovative Ideas, Practices and Technologies at the World’s Leading Plant Asset Lifecycle Management Event. 5)"//6"-
February 23-25, 2009 Hilton Americas–HOUSTON, TX Sponsoring Organization:
NEW Downto wn Venue for 2009 !
Offical Publications:
REGISTER by December 31st
to get the best rates at www.daratechplant.com or call Jill Dean at 832-242-1969, ext. 316 SPONSORS/EXHIBITORS
%4r"S5S"r"DF$BE4PGUXBSF-UEr"VUPEFTL *ODr"7&7"(SPVQQMDr#FOUMFZ4ZTUFNT *ODr#MVF$JFMP&$.4PMVUJPOTr$BENBUJDr$BE4DISPFSr$"9QFSUT(NCIr$&"r$IFNJDBM &OHJOFFSJOHr$MPVEJT-JNJUFEr$0"%& *ODr$4" *ODr%BTTBVMU4ZTUÊNFTr&$&%FTJHOr '"30r(PPHMFr(4/5FDIOPMPHJFT--$r*/07Y4PMVUJPOTr-FJDB(FPTZTUFNTr*OUFSHSBQIr *OOPUFDr0DUBHBr1*1m1SPDFTT*OEVTUSZ1SBDUJDFTr108&3r4LJSF *ODr4ZOFSHJT4PGUXBSFr 5PUBM$"%4ZTUFNTr5SJNCMFr73$POUFYUr; '6, Image courtesy of COADE, Inc.
Chemical Engineering www.che.com December 2008
47
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