Handbook of Shaft Alignment Part 15 pdf

21.1.1.1 Additional Information on Electric Motors Moderate to excessive soft foot conditions have been experienced on virtually every size motor regardless of frame construction design. Uneven air gap problems found occasionally due to improper positioning of end bells or housing distortion due to uncorrected soft foot. Inboard (coupling end) bearings may run hotter due to misalignment conditions. Excessive vibration may be due to improperly bored coupling hubs. Infrared thermography surveys and motor current signature analysis are very helpful in diagnosing problems. 21.1.2 STEAM TURBINES Steam turbines can range in output from 20 to 100,000þ hp with speeds up to 25,000þ rpm and therefore become some of the more interesting equipment for OL2R surveys and consequentially some (Figure 21.4 through Figure 21.6) of the more difficult equipment to maintain and operate properly. Steam pressures can range from 200 to 4000þ psig and temperatures from 4008F to 11008F. Due to the fact that a high-temperature gas is used to propel blades for shaft rotation, extensive frame and casing design considerations concerning FIGURE 21.4 Small steam turbine with upper casing removed. FIGURE 21.5 Small steam turbine. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 670 6.10.2006 12:19am 670 Shaft Alignment Handbook, Third Edition casing and rotor expansion and contraction are taken into account to minimize excessive positional change of the rotor during operation. However, movement of the shaft invariably occurs from OL2R conditions that can range considerably from unit to unit. In addition, rotor expansion must be taken into consideration when selecting a flexible coupling to prevent thrust transfer from one rotor to another, causing premature bearing or coupling failure. On several occasions, the condensing end of the steam turbine has been observed to move downward during operation. The cooler temperatures and the ‘‘vacuum draw down’’ effect of the condenser may actually move the condenser end opposite of what one might expect. Again, since there is such a wide variety of equipment in existence, it is always best to consult with your equipment manufacturer for initial installation, design modification, over- haul, or operational problems with these units. Thank them for their input, but always do your own research. Typical OL2R movement range of steam turbines (horizontally mounted): Vertical movement: –10þ to 25 mils upward (5 to 500 hp); 5 to 40þ mils upward (500þ hp), typically asymmetrical (i.e., inboard and outboard ends do not move up the same amount) Lateral (sideways) movement: 0 to 40þ mils (can be as much or considerably more than the vertical movement) Axial movement: 10 to 100þ mils (5 to 200 hp); 20 to 250þ mils (200þ hp) 21.1.2.1 Additional Information on Steam Turbines Moderate to excessive off-line soft foot conditions have been experienced on virtually every size steam turbine regardless of frame construction design. Frequently, on small- to medium- sized steam turbines, one end of the casing is rigidly bolted to the frame and a ‘‘sway bar’’ or flexible support is mounted at the other end to allow for axial expansion to occur to prevent casing warpage during operation. Sometimes on larger steam turbines, the casing is keyed at the casing centerline and the hold-down bolts are not tightened to lock the casing against the frame support but are kept loose to allow for symmetric lateral and axial casing expansion to occur. The lateral movement that occurs is often directly related to the expansion and contraction of the steam piping connected to the steam turbine casing and proper design and installation of the piping system is imperative to minimize static (off-line) and dynamic (running) nozzle loads. FIGURE 21.6 Large steam turbine. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 671 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 671 Most steam turbines are supported in sliding-type bearings and therefore exhibit a certain amount of axial clearance between the thrust runner and the active–inactive thrust bearings (often referred to as thrust float). When setting the machinery axial positions off-line, seat the thrust runner against the active thrust bearing before measuring and adjusting the shaft-to- shaft distance. Bear in mind that the axial movement amounts mentioned above are for the casing and housing. The shaft may expand more than that and may influence how you should set the off-line shaft end to shaft end distances. 21.1.3 GAS TURBINES Industrial gas and power turbine drivers are used in a wide variety of applications ranging from compression of gases and electrical generation to propulsion systems for ships (Figure 21.7 and Figure 21.8). The Brayton cycle (i.e., a gas turbine) compresses air via a FIGURE 21.7 Gas turbine. FIGURE 21.8 Gas turbine driving an electric generator. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 672 6.10.2006 12:19am 672 Shaft Alignment Handbook, Third Edition centrifugal or axial flow compressor where the compressed air is mixed with fuel (liquid jet fuel or natural gas) and burned. The hot, high-velocity gas then impinges on a series of several stages of curved blade sets (power turbine) that is used to rotate the driven machinery. Frequently, the gas and power turbines, although separate rotors supported in their own bearings, share a common casing and frame. The residual high-velocity gas is then vented through ductwork that sometimes houses a heat exchanger for a closed loop system or for use in heating liquids for other purposes. The gas turbine produces a tremendous amount of forward thrust in reaction to the high- velocity gas escaping out of the tail end of the machine. A considerable amount of heat is generated in the cycle and a twisting or torsional counter reaction occurs in the frame during operation. These factors all contribute to some of the most radical OL2R machinery move- ment in any type of driver used today. Typical OL2R movement range of gas or power turbines: Vertical movement: Intake end—10þ mils downward to 10þ mils upward; exhaust end—5 to 80þ mils upward Lateral (sideways) movement: Intake end—2 to 20þ mils; exhaust end—2 to 60þ mils Axial movement: See additional information 21.1.3.1 Additional Information on Gas Turbines Moderate to excessive off-line soft foot conditions have been experienced on virtually every size gas and power turbine regardless of frame construction design. Movement in the axial direction from OL2R conditions can also be excessive. Forward movement of gas turbines (i.e., toward the intake end) has been observed to translate 180þ mils. Gear- or diaphragm- type couplings have been employed at the output shaft to drive the equipment. If the coupling is a diaphragm-type (or any flexible disk-type) and there is movement toward the intake end, damage could occur to the coupling and the thrust forces can be transmitted to the driven machine. The shaft-to-shaft distance between the power turbine and the driven equipment shaft is usually 40þ in. in an attempt to minimize the effect from large amounts of OL2R movement and to minimize any heat transfer from the exhaust duct work to the driven machine. Bear in mind that the axial movement amounts mentioned above are for the casing and housing. The shaft may expand more than that and may influence how you should set the off-line shaft end to shaft end distances. 21.1.4 INTERNAL COMBUSTION ENGINES Very few field studies have been conducted (or at least published) on how internal combustion engines move from OL2R conditions (Figure 21.9). Diesel engines, for example, are frequently used to drive backup electrical generators, fire pumps, and portable air compressors. In the wastewater treatment industry, biogas engines can be used to drive the air compressors. The crankshaft is typically set very low in the casing and engine mounts can be found below, at, or slightly above the centerline of rotation of the crankshaft. The relatively few studies that have been done have still shown OL2R machinery movement regardless of the casing support mounting location. Flexible coupling design is somewhat critical since variations in torque occur as each piston delivers rotational force at varying intervals. Typical OL2R movement range of internal combustion engines: Vertical movement: 1 to 5 mils upward (5 to 200 hp); 2 to 20þ mils upward (200þ hp), typically symmetrical (i.e., inboard and outboard ends move up the same amount) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 673 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 673 Lateral (sideways) movement: 0 to 4 mils (usually much less than any vertical movement) Axial movement: Unknown 21.1.4.1 Additional Information on Internal Combustion Engines Moderate to excessive off-line soft foot conditions have been experienced on virtually every size internal combustion engine regardless of frame construction design. On medium and large engines, distortion of the engine frame during installation is a concern. To insure that the crankshaft bearings are not distorted, web deflection tests are conducted as shown in Figure 21.11 and Figure 21.12. A web deflection test determines if the distance between the crank webs is changing when the crankshaft is rotated. If the bearings are misaligned due to casing distortion, or there is an excessive amount of shaft misalignment with the coupling engaged, the distance between the crank webs will vary when the crankshaft is rotated. If the gap variation between the web is excessive, shims must be added between the engine and the soleplates to relieve the distortion of the casing. 21.1.5 HORIZONTALLY MOUNTED CENTRIFUGAL PUMPS Without a doubt, one of the most common drive systems in virtually every industry is a motor-driven, horizontally mounted, centrifugal pump (Figure 21.13 through Figure 21.15). There are several hundred designs of centrifugal pumps and it would be difficult to cover every characteristic of each design used in industry. Their purpose is basically to move an incompressible fluid from point A to point B. The temperature of the fluid conveyed has a great effect on the OL2R conditions of the pump. As discussed in Chapter 5, the piping attached to the pump can have a tremendous influence on obtaining and maintaining accurate alignment, so that many people are unwilling to even try to reposition pumps, henceforth declaring them the ‘‘stationary’’ machine when aligning them. Typical OL2R movement range of centrifugal pumps: Vertical movement: 0 to 80þ mils upward typically asymmetrical (i.e., inboard and out- board ends do not move up the same amount) FIGURE 21.9 Sixteen cylinder biogas engine coupled to a gearbox and compressor. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 674 6.10.2006 12:19am 674 Shaft Alignment Handbook, Third Edition 52 60 60 78 78 64 50 50 53 20 32 34 70 76 76 85 89 77 97 107 108 82 92 92 96 100 96 115 121 128 132 132 139 103 105 88 50 3 2 2 10 5 50 20 5 2 2 2 5 5 5 50 20 20 5 5 10 5 50 25 10 3 5 10 2 25 5 2 2 50 25 5 10 2 5 10 20 10 2 2 10 3 North 3 5 5 5 FIGURE 21.10 Soft foot map between engine frame and soleplates on biogas engine shown in Figure 21.9. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 675 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 675 FIGURE 21.11 Inside dial gauge used to measure web deflection. 1 2 3 4 5 –1/4 –1/4 0 +1/4 +1/4 FIGURE 21.12 Web deflection measurements typically taken at five positions. FIGURE 21.13 Single-stage centrifugal pumps with overhung impeller. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 676 6.10.2006 12:19am 676 Shaft Alignment Handbook, Third Edition Lateral (sideways) movement: 0 to 90þ mils (can be much greater than vertical movement and is usually asymmetrical) Axial movement: 0 to 150þ mils, frequently dependent on temperature of process fluid 21.1.5.1 Additional Information on Horizontally Mounted Centrifugal Pumps Moderate to excessive off-line soft foot conditions have been experienced on virtually every centrifugal pump regardless of frame construction design. Maintaining long-term alignment of ANSI- and API-type pumps can be difficult due to the loosely supported inboard (coup- ling) end of the pump case. Failure of mechanical seals can often be attributed to misalign- ment conditions. Excessive leakage on mechanically packed pumps can also be attributed to misalignment conditions. Pumps can experience internal rubs due to rotor distortion caused FIGURE 21.14 Single-stage centrifugal pump with centered impeller. FIGURE 21.15 Multistage centrifugal pump. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 677 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 677 by moderate to excessive misalignment conditions. Bear in mind that the axial movement amounts mentioned above are for the casing and housing. The shaft may expand more than that and may influence how you should set the off-line shaft end to shaft end distances. 21.1.6 VERTICALLY MOUNTED CENTRIFUGAL PUMPS There are several different types of vertical pumps such as well water pumps, in-line pumps, and reactor coolant pumps. In most cases, vertical pumps are driven by C-flanged motors. These motors are bolted to a cylindrical casting that is attached to the pump casing. In some situations, the pump is supported in its own bearings and the motor is flexibly coupled to the pump. In other situations, the pump is rigidly coupled to the motor shaft and the thrust load is supported by a thrust or radial bearing at the top of the motor. The assumption that many people have is that no alignment is required for these types of machines since the motor, connector casting, and pump casing are perfectly machined, rabbeted fits that precisely align the motor shaft to the pump shaft. In most cases, this is not true. Misalignment can and does occur on these types of drives as often as a horizontally mounted drive system (Figure 21.16 through Figure 21.18). Figure 21.19 shows a large vertical pump driven by a 2500-hp motor, which is bolted to the pump casing with 12 bolts. The pump was new and was experiencing excessive vibration where misalignment was suspected as the cause. The coupling connecting the motor shaft to the pump shaft is a rigid coupling. The upper bearing of the motor has a thrust bearing that supports the weight of the armature and the weight of the pump shaft. Upper and lower bronze bushings act as the radial bearings for the pump shaft. These bushings are lubricated by the water that is pumped upward from the impeller at the lower end of the pump shaft. FIGURE 21.16 Small vertical pumps. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 678 6.10.2006 12:19am 678 Shaft Alignment Handbook, Third Edition As mentioned previously, any attempt to align shafts that are connected together with a rigid coupling are futile. The misalignment can be severe and the shafts will elastically bend to accommodate the misalignment condition making it appear that the alignment is acceptable when capturing readings across the engaged rigid coupling. To properly align a unit like this, the coupling must be disengaged. In doing that however, the pump shaft drops down from its own weight and the impeller touches the housing at the bottom. Any attempt to rotate the pump shaft after the coupling has been disengaged can potentially damage the impeller. Since the motor shaft can still be rotated, either the face–rim or double radial alignment methods could be used. In this particular case, the double radial method was used to check the alignment between the two shafts. Before disconnecting the coupling however, runout mea- surements can be taken to determine if the coupling hubs are bored properly (i.e., concentric) and if the motor or pump shafts are permanently bent. Figure 21.20 shows the runout measured on the shafts and the coupling hubs. After the runout measurements were taken, the mechanical seal was removed and the coupling was disengaged. The specified distance between the end of the motor shaft and the end of the pump shaft was 0.250 in. There is an adjustment nut on the top of the pump FIGURE 21.17 Medium-sized vertical pumps. FIGURE 21.18 Large vertical pumps. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 679 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 679 [...]... 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 683 FIGURE 21.24 Alignment readings taken at the top of the pump shaft at the adjustment nut the eccentricity and determine where the actual centerline of rotation of the pump shaft is as shown in Figure 21.26 The top part of the T-bar overlay shows what thickness of shims need to be installed between each of the 12 bolts that... plane designations in Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 682 6.10.2006 12:19am 682 Shaft Alignment Handbook, Third Edition FIGURE 21.22 Wooden wedges were used to keep the pump shaft centered N or th W es t Figure 21.27 and Figure 21.28 The base to the T-bar overlay will represent the centerline of rotation of the motor shaft Since there was runout observed... pump shown in Figure 21.19 Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 681 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 681 FIGURE 21.21 Centering the pump shaft in its upper bushing shaft that can be rotated to obtain the desired shaft- to -shaft distance with the coupling disengaged The pump shaft was then centered in its upper bushing... W Pump shaft E 0.385 in gap S 0.399 in gap FIGURE 21.33 Measured clearances between the pump shaft extension and the hollow motor shaft Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 688 6.10.2006 12:19am 688 Shaft Alignment Handbook, Third Edition 1 mil 1 mil 5 mils 1 mil 2 mils 1 mil FIGURE 21.34 Measured runout at several points along the exposed pump shaft, threaded... added under the inboard end of the motor, the inboard bearing of the fan, and the inboard and outboard foot bolts of the fan housing as shown in Figure 21.50 A similar alignment model can be generated in top view showing the lateral positions of the motor shaft, the fan shaft, and the centerline of the bore of the fan housing to achieve correct lateral alignment Once again, the alignment modeling method... Two-stage reciprocating compressor Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 702 6.10.2006 12:19am 702 Shaft Alignment Handbook, Third Edition FIGURE 21.56 Chiller compressor mentioned above are for the casing or housing The shaft may expand more than that and may influence how you should set the off-line shaft end to shaft end distances 21.1.9 HORIZONTALLY MOUNTED... Figure 21.50 In this case, rather than finding the location of the bore of the fan housing, air gap measurements are taken between the armature and stator at both ends of both machines to determine the centerline of the bore Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 704 6.10.2006 12:19am 704 Shaft Alignment Handbook, Third Edition 0.090 in E W 0.120 in 0.160 in Motor... 21.37 Remove the motor FIGURE 21.38 Measure the eccentricity at the lower end of the pump shaft Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 691 6.10.2006 12:19am Alignment Considerations for Specific Types of Machinery 691 FIGURE 21.39 Measure the eccentricity at the upper end of the pump shaft the measurements as shown in Figure 21.41 and Figure 21.42 Ideally the... for perpendicularity on the flange surface Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 695 6.10.2006 12:19am 695 Alignment Considerations for Specific Types of Machinery Pump mating flange face and rabbeted fit runout Exaggerated apparent position of male rabbet N 0 0 0 Centerline of shaft Apparent centerline of male rabbet 0 Measurements on male rabbet −6.5 W −9.5... adjustment nut to raise the pump shaft a specified amount There are no FIGURE 21.31 Adjusting the jackscrews to correct the offset misalignment Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 687 6.10.2006 12:19am 687 Alignment Considerations for Specific Types of Machinery FIGURE 21.32 Excessively worn upper pump bushing due to excessive lateral misalignment provisions in . lower end of the pump shaft. FIGURE 21.16 Small vertical pumps. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 678 6.10.2006 12:19am 678 Shaft Alignment Handbook, . 21.19. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 680 6.10.2006 12:19am 680 Shaft Alignment Handbook, Third Edition shaft that can be rotated to obtain the desired shaft- to -shaft. jackscrews to correct the offset misalignment. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C021 Final Proof page 686 6.10.2006 12:19am 686 Shaft Alignment Handbook, Third Edition provisions