54815763 Shaft Alignment Manual

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Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

EPRI Project ManagerR. Knipschield

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Shaft Alignment Guide

TR-112449

Final Report, September 1999

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Rota-Tech, Inc.

ORDERING INFORMATION

Requests for copies of this report should be directed to the EPRI Distribution Center, 207 CogginsDrive, P.O. Box 23205, Pleasant Hill, CA 94523, (800) 313-3774.

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc. EPRI. POWERING PROGRESS is a service mark of the Electric PowerResearch Institute, Inc.

Copyright © 1999 Electric Power Research Institute, Inc. All rights reserved.

iii

CITATIONS

This report was prepared by

Rota-Tech, Inc.4104 Cindy LaneDenver, NC 28037

Principal InvestigatorJ. Campbell

Nuclear Maintenance Applications Center (NMAC)1300 W.T. Harris Blvd.Charlotte, NC 28262

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Shaft Alignment Guide, EPRI, Palo Alto, CA: 1999. Report TR-112449.

v

REPORT SUMMARY

Shaft misalignment has long been recognized as a source of problems for machinery, operators,and owners. Experts agree that correct shaft alignment is one of the most important elements inimproving machinery reliability. In an effort to reduce the frequency of machinery misalignmentand improve machinery reliability, this guide provides users with an understanding of theconcept of proper shaft alignment through a discussion of the fundamentals of alignment. Thisguide also provides a limited discussion of machine problems, the impact of misalignment on themachine, and the consequences of misalignment on machine reliability.

BackgroundWithin a nuclear power station, machinery shaft misalignment is responsible for majorexpenditures in the form of labor, machinery parts, and lost generation capacity. In response,large amounts of time and money are continually invested in state-of-the-art alignment systems,equipment, and training. Most of the training, however, focuses on operating the new systemswith little or no training on the principles of proper shaft alignment. Consequently, fundamentalproblems and causes of misalignment continue to be overlooked, misalignment continues tooccur, and machinery reliability is not improved—even after deployment of these costly systems.

ObjectiveTo provide maintenance personnel with a thorough understanding of the fundamentals of propershaft alignment in order to enhance the use of all shaft alignment systems.

ApproachThis guide provides users with a tool to assist in decision making for improvement of reliabilityassociated with rotating machinery, specifically improvements in shaft alignment practices. Thedocument is geared to the “whys” rather than the “hows” of shaft alignment. With the age ofmost nuclear power plants and the training programs in place, the procedure for the actual task ofperforming shaft alignments is well documented. The guide could not be written without somespecifics of certain alignment tasks; however, a blend of technical information has been the goalin the preparation of this document.

ResultsThe resulting guide provides a thorough discussion of the fundamental causes and effects ofmisalignment on machinery and how knowledge of the fundamentals of shaft alignment iscrucial to performing consistent, correct shaft alignment.

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EPRI PerspectiveWithin the power station, shaft misalignment is responsible for major expenditures in the form oflost generation capacity, as well as labor and machinery parts. This guide provides plantmaintenance personnel with fundamental information that will enhance their ability to achieveproper alignment using any shaft alignment system, thus increasing mean time between failures(MTBFs) and improving the reliability of all machinery with each alignment.

TR-112449

KeywordsMaintenanceShaft alignmentReliability

EPRI Licensed Material

vii

ACKNOWLEDGMENTS

EPRI would like to recognize the contributions of the following individuals in the developmentand review of this guide:

William Bramlett Oconee Station/Duke Energy Corp.

Deyton Brunson Brunson Instrument Company

Michael Calistrat Michael Calistrat & Associates

Alistair Campbell Bently Nevada Corp.

Pedro Cassanova Ludeca, Inc.

Galen Evans Ludeca, Inc.

Bob Fulbright McGuire Station/Duke Energy Corp.

Jerry Garner Commanche Peak/Texas Utilities Electric Co.

Frank Hale Catawba Station/Duke Energy Corp.

Charlie Jackson Consultant

Darron Jones Commanche Peak/Texas Utilities Electric Co.

Randy Kerr PECO Energy Co.

Jon Mancuso Kop-Flex Couplings

Richard Massey A-Line Mfg.

Larry Pope Commanche Peak/Texas Utilities Electric Co.

Kyle Russell Duke Engineering & Services

Tony Scheetz Commanche Peak/Texas Utilities Electric Co.

Deiter Seidenthal Ludeca, Inc.

Dale Smith Smith Services

Watson Tomlinson Duke Energy Corp.

Randy VanSurDam Oconee Station/Duke Energy Corp.


ix

PREFACE

Shaft misalignment has long been recognized as a source of problems for machinery, operators,and owners. Within the power station, shaft misalignment is responsible for major expendituresin the form of labor, machinery parts, and lost generation.

Because experts agree that maintaining correct shaft alignment is essential to improvingmachinery reliability, large amounts of time and money are continually invested in state-of-the-art laser alignment systems, equipment, and training. Unfortunately, this solution is much akin tothe golfer who thinks “If only I could afford expensive clubs—they would make my gamebetter,” while completely disregarding the fundamentals.

There is no argument that more accurate alignment results can be obtained through the use ofthese systems; however, the problems that caused the misalignment often continue to beoverlooked, just as they were before the systems were deployed. In light of this, the objective ofthis guide is to provide a thorough explanation of the fundamentals of proper shaft alignment andto give examples of how this knowledge can improve all shaft alignment practices. Becausemisalignment is a function of the behavior of the total machine train and system, this guide alsoincludes a limited discussion of machine problems, the effects of misalignment, and theconsequences of misalignment on machine reliability.

The premise of this guide is that practicing shaft alignment with a thorough understanding of thefundamentals can enhance the effectiveness of all shaft alignment systems, resulting in improvedmachine reliability.


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CONTENTS

1 INTRODUCTION.................................................................................................................. 1-1

2 FUNDAMENTALS OF A PROPER SHAFT ALIGNMENT ................................................... 2-1

Thorough Understanding of the Fundamentals of Shaft Alignment ..................................... 2-2

Complete Analysis of the Machine From the Ground Up .................................................... 2-3

Thorough Understanding of the Behavior of the Machine As Part of the System................ 2-3

Thorough Understanding of the Impact of Misalignment on the Machine............................ 2-3

Proper Sequence of Alignment Analysis............................................................................. 2-4

3 EFFECTS OF MISALIGNMENT .......................................................................................... 3-1

Types of Machines Aligned in Nuclear Stations .................................................................. 3-1

Bearings............................................................................................................................. 3-1

Alignment Tolerances......................................................................................................... 3-6

4 MACHINE FRAME DISTORTION - SOFT FOOT................................................................. 4-1

Soft Foot............................................................................................................................. 4-1

Measuring Soft Foot Index.................................................................................................. 4-2

Distinguishing Types of Soft Foot, Possible Causes, and Proper CorrectionTechniques......................................................................................................................... 4-2

Parallel Air Gap.............................................................................................................. 4-3

Bent Foot or Angled Base.............................................................................................. 4-4

Taper Shims to Remove Soft Foot...................................................................................... 4-5

Baseplate and Foundation Irregularities ............................................................................. 4-6

Deterioration .................................................................................................................. 4-6

Machinery Vibration ....................................................................................................... 4-6

Induced Soft Foot and Nozzle Loads.................................................................................. 4-7

Nozzle Loads ..................................................................................................................... 4-9

Jacking Bolts or Taper Pins.............................................................................................. 4-10

Gaps Without Soft Foot .................................................................................................... 4-12


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5 MACHINERY POSITION CHANGES................................................................................... 5-1

Infrared Thermography....................................................................................................... 5-7

Alignment and Preloads ..................................................................................................... 5-8

6 SHAFT COUPLINGS AND POWER TRANSMISSION........................................................ 6-1

Flexible Couplings .............................................................................................................. 6-1

Restoring Forces and Moments.......................................................................................... 6-5

Misalignment ...................................................................................................................... 6-6

Advantages and Disadvantages of Coupling Types............................................................ 6-9

7 VERTICAL MACHINES ....................................................................................................... 7-1

Vertical Machines with Rigid Couplings .............................................................................. 7-1

Vertical Machine Behavior ............................................................................................. 7-1

Causes of Misalignment ..................................................................................................... 7-2

Alignment Procedure (Steps 1–9) .................................................................................. 7-6

Pump Coupling Procedure (Steps A–G).................................................................... 7-7

Alignment Procedure (continued)................................................................................... 7-8

Conclusions........................................................................................................................ 7-9

8 REFERENCES .................................................................................................................... 8-1


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LIST OF FIGURES

Figure 1-1 Reverse Dial Setup ................................................................................................ 1-2

Figure 1-2 Typical Laser Alignment System ............................................................................ 1-2

Figure 2-1 Colinear Alignment................................................................................................. 2-1

Figure 2-2 Offset Misalignment ............................................................................................... 2-1

Figure 2-3 Angular Misalignment............................................................................................. 2-2

Figure 2-4 Offset and Angularity.............................................................................................. 2-2

Figure 3-1 Ball Bearing (Anti-Friction Bearing) ........................................................................ 3-2

Figure 3-2 Laser Alignment System ........................................................................................ 3-4

Figure 3-3 Two Misaligned Shafts Using a Spacer Coupling ................................................... 3-5

Figure 4-1 Parallel Air Gap...................................................................................................... 4-3

Figure 4-2 Bent Foot or Angled Base ...................................................................................... 4-4

Figure 4-3 Step Shim .............................................................................................................. 4-5

Figure 4-4 Pump Base Degradation Resulting From Transmitted Forces................................ 4-7

Figure 4-5 Examples of Induced Soft Foot .............................................................................. 4-8

Figure 4-6 Pump Outboard Replacement Keys ..................................................................... 4-10

Figure 4-7 Key Adjusting Bolts .............................................................................................. 4-11

Figure 5-1 Alignment of Shaft Centerline Heights.................................................................... 5-2

Figure 5-2 Expansion Chart .................................................................................................... 5-3

Figure 5-3 Acculign Bars Measuring Movement of a Steam Generator Feed Pump................ 5-4

Figure 5-4 Laser Monitoring Movement Between Steam Generator Feed Pump andTurbine ............................................................................................................................ 5-5

Figure 5-5 Dynalign (Dodd Bars) Being Used to Monitor Alignment Changes ......................... 5-5

Figure 5-6 Precision Sight Level Used for Optical Alignment Checks...................................... 5-6

Figure 5-7 Jig Transit Used for Measuring Alignment.............................................................. 5-6

Figure 5-8 Scales Used With Jig Transits and Precision Levels .............................................. 5-7

Figure 5-9 Shaft Orbits Acquired From Eddy Current Probes on a Sleeve BearingMachine........................................................................................................................... 5-8

Figure 6-1 Gear Coupling........................................................................................................ 6-2

Figure 6-2 Grid Coupling ......................................................................................................... 6-3

Figure 6-3 Diaphragm Coupling .............................................................................................. 6-4

Figure 6-4 Flexible Disk Coupling............................................................................................ 6-5

Figure 6-5 Stub Shaft Replacement ........................................................................................ 6-6


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Figure 6-6 Point of Moment..................................................................................................... 6-7

Figure 6-7 Angular Misalignment............................................................................................. 6-7

Figure 6-8 Angular Misalignment and Offset at P2 .................................................................. 6-8

Figure 6-9 Angular Misalignment and Offset at P1 and P2...................................................... 6-8

Figure 7-1 Typical Stuffing Box, Noting Four Points Where Dimensional Runouts andConcentricities Are To Be Measured ............................................................................... 7-2

Figure 7-2 Typical Discharge Head (Motor Stand)................................................................... 7-3

Figure 7-3 Alignment Fixture Aligning Motor to Stuffing Box.................................................... 7-4

Figure 7-4 Adjustable Coupling Spacer and Nut in a Typical Pump Coupling.......................... 7-5

Figure 7-5 Pump Coupling Indicator Positions......................................................................... 7-6


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LIST OF TABLES

Table 3-1 Alignment Tolerances.............................................................................................. 3-6

Table 6-1 Coupling Advantages and Disadvantages............................................................... 6-9

Table 7-1 TIR Measurements From Installing the Pump Coupling........................................... 7-7

Table 7-2 TIR Measurements From Installing the Pump Coupling........................................... 7-8

Table 7-3 TIR Readings From the Vertical Pump Shaft Alignment Procedure ......................... 7-8

Table 7-4 TIR Readings From the Final Pump Shaft Alignment .............................................. 7-9


1-1

1 INTRODUCTION

Simply put, shaft alignment is placing two or more shafts along one axis or centerline. Althoughproper shaft alignment that increases machine reliability is much more complex, this simplisticapproach is how alignment is often performed—with total disregard for the fundamentalproblems and causes of shaft misalignment.

The widespread use of this approach is shown by the increasing use of laser shaft alignmentsystems. Management personnel, acting on input from supervisors, technical personnel, and endusers, often purchase these systems with the erroneous assumption that the laser shaft alignmentsystem will eliminate their misalignment problems. In fact, it seems that anyone who can alignmachines relatively easily or quickly using these systems instead of other methods is nowconsidered to have achieved total proficiency in performing shaft alignment, which greatlyimproves reliability.

In some cases, reliability is improved. This is normal where improper practices were previouslyperformed with methods that have been used for a number of years. An example would besomeone performing alignment using the rim and face method and not accounting for sag in theindicator.

In reality, however, this new-found knowledge gives the user and management the ability toperceive that good alignment has been performed by the fact that the given tolerances are quicklyand sometimes easily reached. The result is that fundamental problems and causes ofmisalignment continue to be overlooked, just as they were before these costly systems weredeployed.

The most widely used methods for aligning machines with accuracy are the laser systems and thereverse dial methods. See the reverse dial method in Figure 1-1 and a typical laser alignmentsystem in Figure 1-2.


Introduction

1-2

Figure 1-1Reverse Dial Setup

Figure 1-2Typical Laser Alignment System


Introduction

1-3

It is easy to understand the widespread use of laser alignment systems for these reasons:

• They are easy to set up.

• They record data accurately (when correct data are input).

• They give fast and accurate alignment corrections.

• They assist in making machinery adjustments to achieve alignment.

But, if the goal of proper shaft alignment is to improve machinery reliability, then the success ofthese systems should be measured by whether the mean time between failures (MTBF) increaseswith each alignment and, if so, by what percentage as compared to before the implementation ofthe system.

Misaligned machines can be divided into two categories:

• Machines with minor alignment problems

• Machines with major alignment problems

Machines with minor alignment problems exhibit satisfactory run time with a long mean timebetween failures. These are the machines that, when checked for shaft alignment deviations fromspecified targets and tolerances, are fairly close to being aligned from the last time they werealigned. These are also the machines that do not show signs of stress, that is, the foundation is insatisfactory condition and has been for some time. Removal of the machine does not revealpiping strain or loads. The bearing temperatures are within range, and vibration typically remainswithin acceptable ranges for long periods of time.

These machines have several advantages. In many cases, the machinery is not far from ambienttemperature. Nozzle loads are small, and soft foot has been corrected if there was a problem. Thefoundation and grouting were installed properly, and periodic lubrication is performed at regularintervals and in a prescribed manner. These machines have a long run time between failures.

The machines with major alignment problems are the ones that, when checked for alignment, arealways far out of specifications when “as found” shaft alignment data are taken. If accuraterecords have been kept, the misalignment is always in the same direction perpendicular to thecenterline of the shaft. The offsets and angularities are always somewhat close to the last datathat were taken, if conditions were the same.

These machines typically operate under high load conditions, at elevated temperatures, and withpiping loads. The foundation reveals signs of deterioration, and the mean time between failures isshort. Most of the time used in alignment is spent to put the machine where the correct positionis thought to be. Great energy and expenses are expended to correct the obvious problems, butthe root cause of misalignment is ignored and the cycle continues. These are the machines thatgenerally have high profits associated with them and the ones that this guide focuses on.


Introduction

1-4

A “failure” is defined as the following:

• “The condition or fact of not achieving the desired end or ends”

• “A cessation of proper functioning or performance”

• “Nonperformance of what is requested or expected”

All of the above definitions can be applied to failure of machinery at a power station. As relatedto shaft alignment, a failure can imply a degradation of any of the components or subcomponentswithin a machine or piece of equipment. These failures can damage or destroy couplings, rotors,mechanical seals, or bearings. With proper shaft alignment, machinery reliability is improved,MTBF is increased, and the cost and quantities of replacement parts are reduced.

The new “buzz word” is mean time between repairs (MTBR), which is essentially a MTBFbecause, if a repair is made, in a sense it is still a failure. Only preventive maintenance can beperformed as a repair without a failure. Most maintenance, other than corrective, now beingemployed at power stations is either predictive maintenance (PDM) or reliability-centeredmaintenance (RCM).

Remember that, in order to have complete and satisfactory alignment, there must also besatisfactory coupling alignment. The couplings joining two or more shafts are a part of the rotorsystems; however, based on coupling manufacturers’ allowable misalignment, satisfactorycoupling alignment does not mean satisfactory shaft alignment.


2-1

2 FUNDAMENTALS OF A PROPER SHAFT ALIGNMENT

Proper shaft alignment is the aligning of two or more shafts to a “colinear position” at operatingconditions, while ensuring that the shafts are operating with a minimum of forces applied to theindividual shafts and across the coupling. See Figure 2-1 for an example of colinear alignment.

Figure 2-1Colinear Alignment

How is shaft misalignment defined? There are three types of misalignment conditions:

• Offset - when two shafts are not coincidental to the same axis or centerline (see Figure 2-2)

• Angularity - when one or two shafts move away or toward the centerline as they approach ordistance themselves from one or more machines (see Figure 2-3)

• A combination of the two (see Figure 2-4)

Figure 2-2Offset Misalignment


Fundamentals of a Proper Shaft Alignment

2-2

Figure 2-3Angular Misalignment

Figure 2-4Offset and Angularity

Very seldom is one type of misalignment (offset or angularity) present without the other. Sincethis is the case, the term “offset” better illustrates misalignment not on the centerlines. Someauthors prefer the term “parallel” misalignment, but this implies that the offsets are alwaysparallel to each other. For the purposes of this document, misalignment not on the centerlines isreferred to as “offset misalignment.”

The essential elements for performing proper shaft alignment include:

• Thorough understanding of the fundamentals of shaft alignment

• Complete analysis of the machine from the ground up

• Thorough understanding of the behavior of the machine as part of the system

• Thorough understanding of the impact of misalignment on the machine

Thorough Understanding of the Fundamentals of Shaft Alignment

Although proper training in the fundamentals of alignment is the first step to achievingsatisfactory results, it is by no means the only step. Additional training should include:

• The basic mathematics involved with alignment

• The concept of “soft foot” and all of its variables

• Proper training on the alignment system being used

• A thorough understanding of thermal growth and machine running positions



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• A basic understanding of coupling behavior for the various designs of couplings used

• An understanding how alignment impacts machines of different designs

Complete Analysis of the Machine From the Ground Up

While analysis in this sense does not necessarily mean the use of vibration analysis or infraredthermography, these and other types of data collection techniques do need to be used to gatherdata to analyze machine problems.

Visual inspection plays a very important part in machine analysis as it relates to shaft alignment.The condition of the baseplate and anchor bolts should be one of the first things inspected whenapproaching a machine for alignment or analyzing a problem machine where misalignment is thesuspected cause of problems. Look closely at the condition of the grout under the base of amachine if this type of base is used.

Look for leaks of water, oil, or other fluids, noting any corrosion to the base that these fluidsmight have caused. If the machine train consists of a drive steam turbine, look for leaks aroundthe gland steam sealing area. If the baseplate and grout are damaged or deteriorating, this willhinder satisfactory alignment and ensure that the alignment will have to be done again soonerthan expected.

If the coupling is a lubricated coupling, look closely for a pattern of lubricant spraying or leakingfrom the coupling. Depending on the type of guard, sometimes machines using a gear-typecoupling can be analyzed for coupling or alignment problems by placing a piece of white cloth orpaper on or under the coupling guard. If a pattern of lubricant is visible, you should suspect acoupling problem or misalignment.

Testing shaft runout is an essential part of pre-alignment checks. With the widespread use oflaser systems, sometimes shaft and coupling/coupling hub runouts are overlooked. The shaftsshould be rotated and all runouts taken before aligning the shafts.

Thorough Understanding of the Behavior of the Machine As Part of theSystem

Look closely at the way piping is routed to and from the machine. Visually inspect the pipingsupport apparatus. Are they adjustable struts, rigid struts, or spring hangers? Getting a feel forthe piping route and what the designer had in mind when calculating piping expansion and thedirection of expansion can be very important. Is the machine being operated as it was intended?

Thorough Understanding of the Impact of Misalignment on the Machine

Stated differently, this also refers to the behavior of the machine. First, determine if the machinedisplays symptoms of misalignment. Has a thorough coupling inspection been performed? Hasthe vibration data taken on the machine told you that alignment is the most probable cause of the



2-4

machine behavior? Most of the time, misalignment will show up at half speed, but it can also beseen at full speed. Additionally, misalignment can be seen in the axial direction.

Vibration is not proportional to misalignment. (For more information, see Alignment andPreloads in Section 5.) Forcing functions acting on a machine with misalignment can improvevibration levels.

Knowing the history of a machine is vitally important. What maintenance was performed duringthe last inspection or rebuild? Was the rotor balanced? Has there been a trend of increasedvibration, or was it a sudden change? Has the machine characteristically been a problem? If so, isthe machine being operated at or near its design limits? Have conditions changed?

Proper Sequence of Alignment Analysis

All of these questions and many more require answers when diagnosing the cause of machineryproblems. A good predictive maintenance program in conjunction with a good root causeanalysis program goes a long way toward resolving alignment and machine problems.

Using the proper sequence in alignment is crucial to ensure that if any problems arise from themachine after alignment that they are not due to misalignment or improper alignment, orassociated with areas that should have been checked during the alignment process.


3-1

3 EFFECTS OF MISALIGNMENT

Most machines used in the nuclear industry, such as turbines, pumps, fans, compressors andother equipment, are similar to those used in other applications or other industries. This sectiondetails how shaft misalignment affects these machines and the consequences of these machinesfailing for any reason, but especially due to misalignment. Special consideration must be given tothe equipment in the nuclear industry due to the circumstances under which it operates.

Types of Machines Aligned in Nuclear Stations

The machines in a nuclear station can be divided into three categories: power productionsystems, safety systems, and support systems. Nuclear power production machines do not differgreatly from their counterparts in other power stations. They include:

• Feedwater pumps

• Booster pumps

• Condensate pumps

• Heater drain pumps

• Drive turbines

• Electric motors

• Steam turbines/generators

• Safety pumps

• Fans

It is obvious why failure in these machines is costly; lost generation capacity is the single largestcause of lost income at a power station.

Misalignment can and does affect the support system of machines. This support system consistsof the components of the machine itself and the structure that supports the machine.

Bearings

Bearing failure or degradation is a factor that impairs reliability. Misalignment places forces onthe bearings that reduce the life of the bearing. This can be noted visually when looking at shaftorbits on sleeve bearing machines. The results of this problem on anti-friction bearing machinestypically require vibration analysis and time for the problem to reveal itself. The loads placed on


Effects of Misalignment

3-2

anti-friction bearings are shown during analysis at some frequency associated with the bearingdesign, such as ball pass frequency or inner race frequency. For this to reveal itself, typicallysome damage has to occur to the bearing. Over time, the damage will continue to escalate to thedetectable point.

Bearing temperature is a good indication that a problem exists. Unfortunately, direct readingtemperature instrumentation is typically not installed on anti-friction bearing machines unlessthey are in a critical application. Even then you are getting only part of the picture because theprobe is usually contacting the outer race, and temperature equalization and heat transfer cangive some misleading information. If the area of concern or damage is directly on thetemperature probe, indications of a problem are easily seen.

Figure 3-1Ball Bearing (Anti-Friction Bearing)

The bearing in Figure 3-1 is typical of the radial bearings installed in a majority of pumps thatuse anti-friction bearings. This bearing and the associated data are for a 6312 bearing.

The amount of clearance in a bearing has a relationship to the amount of misalignment presentand the amount of external preload on the bearing and shaft, which is also impacted as themisalignment adds a bending moment to the shaft. Depending on the amount of shaft deflectionand the position along the shaft where this deflection occurs, the bearing acts accordingly. Usingthe above bearing as an example, if shaft deflection or bowing from misalignment or othersources results in the deflection occurring close to the bearing, the bearing must flex a certainamount with the shaft.

The 6312 bearing above, utilizing a C3 fit, has an internal clearance of 23–43 micrometers (µm),or .0009–.0017 inches. This internal clearance is the total distance through which one bearingring can be moved relative to the other. Dividing this clearance in half gives the radial clearancebetween the ball and the inner or outer race. This not only includes the radial direction ofclearance, but also the axial direction of clearance. This says that if shaft deflection occurs thatcauses the inner race to try to skew within the outer race, then on one side of the bearing, the



3-3

clearance is closed, and diagonally across the bearing, the clearance is closed. This generateshigher temperatures, the ability to lubricate the bearing has been diminished, and wear occurs atan accelerated rate.

Mechanical seals fail for several reasons that can be associated with misalignment. First, thebearings begin to fail, and then the shaft is allowed to move in relation to the stationary seal face.Exactly how this happens depends on the type of misalignment present and the state of thebearings. Nozzle loads typically affect the stationary seal faces and their concentricity andperpendicularity to the shaft centerline. Nozzle loads can affect the bearing housing, causingdeflection of the shaft and the rotating portion of the seal. Trying to discover which sealcomponent is being affected is very difficult. Therefore, when the loads need to be reducedanyway, removing nozzle loads on the machine is very important and is the best method ofsolving the problem without major analysis and time expenditure.

In theory, the hysteresis— the failure of a property to return to its original value once an appliedexternal force is no longer applied—of the seal component, particularly a pusher or multiple-spring rotating face, is evident as it tries to maintain contact with the stationary face at a givenmachine speed. This contact and flatness are of utmost importance. Seals are lapped flat, using ameasurement of light bands. If seals did not need to be flat to seal, then shaft movement wouldbe irrelevant. The shaft could bend, move axially a great amount, move radially a great amount,and the seal still would not leak. But shaft deflection in the range of .00001 of an inch (0.254micron) is far greater than the light band range to which the seal is lapped. Surface speed(surface feet per minute or SFPM) is a factor that, when added to the equation, reduces seal life.This is why smaller shafts at higher speeds can use a seal without leakage better than a machinewith a larger shaft.

Most alignments performed on horizontal machines use some sort of laser system. Figure 3-2below shows a typical laser alignment tool attached to a shaft.



3-4

Figure 3-2Laser Alignment System

Methods of measuring misalignment and correcting it are varied. Shaft alignment technology hasprogressed over the years, and systems are now very sophisticated. This does not imply thatsome of the older methods are inadequate or unacceptable under certain situations.

Some tools commonly used to align shafts are the following:

• Straight edge

• Feeler gage

• Parallel blocks (plain or adjustable)

• Micrometers

• Calipers

• Dial indicators

• Lasers

All of these methods are good, based on the following criteria:

• Tolerances

• Speed of machines



3-5

• Criticality of equipment

• Time involved in completing the job

• The resolution required to achieve satisfactory results

To determine how much time should be spent on shaft alignment in order to achieve satisfactoryresults, the following questions must be answered:

• How important is the machine to the overall operations and profit of the plant?

• Has the machine been performing satisfactorily in the past, and are records available to provethe reliability of the machine?

• Has the machine been thoroughly analyzed to determine what has an effect on misalignment?

• What is the cost of maintenance for the machine?

• Are parts expensive, and is the machine labor intensive?

• Is the machine presently off-line for maintenance?

• Is the repair or alignment on the critical path?

Figure 3-3, showing two misaligned shafts using a spacer coupling, is indicative of the type ofproblems encountered in the field.

Figure 3-3Two Misaligned Shafts Using a Spacer Coupling

NOTE: This diagram is exaggerated for the purposes of illustration.

It is worth noting that the spacer coupling, as shown in Figure 3-3, can have two different anglesat the points of power transmission, as denoted by alpha and beta. The angle theta is the angularmisalignment between shafts; the importance of this cannot be overemphasized. However, the



3-6

coupling angle is just as important because the behavior of the rotors of machines is probablyimpacted more by the coupling angle than by the shaft misalignment angle.

Alignment Tolerances

Much of the discussion about shaft alignment centers on alignment tolerances. What is closeenough to achieve the desired results?

Because of the age of most nuclear power plants, the manufacturer’s literature is sometimessketchy. Depending on the date of publication, the Operations & Maintenance (O&M) manualsprovide alignment targets or tolerances are based on a zero offset and a zero angularityalignment. Many O&M manuals state something similar to the following:

“The machine shall be aligned within .002” on the rim (offset), and .001” on the face(angularity).“

Usually, no information on the length of spacer is included.

The alignment tolerance information in Table 3-1 applies to both vertical and horizontal shafts.These suggested tolerances are the maximum allowable deviations from desired values (targets),whether such values are zero or nonzero. Use them in the absence of in-house specifications ortighter tolerances from the machinery manufacturer. Normally, the columns labeled Excellentapply to all alignment work. The exception is rough machinery designed to vibrate, such as ballmills, shaker screens, hammer mills, and so on. For such machinery, the information in theAcceptable columns can be used.

Table 3-1Alignment Tolerances

Courtesy of Ludeca, Inc.

Tolerances for Shaft AlignmentShort Couplings Spacer

ShaftsExcellent Acceptable Exc. Accpt.Offset Angularity Offset Angularity

RPM mils mils perinch

mils per10"

mils mils perinch

mils per10"

mils perinch

mils perinch

600 5.0 1.0 10.0 9.0 1.5 15.0 1.8 3.0900 3.0 0.7 7.0 6.0 1.0 10.0 1.2 2.0

1200 2.5 0.5 5.0 4.0 0.8 8.0 0.9 1.51800 2.0 0.3 3.0 3.0 0.5 5.0 0.6 1.03600 1.0 0.2 2.0 1.5 0.3 3.0 0.3 0.57200 0.5 0.1 1.0 1.0 0.2 2.0 0.15 0.25


4-1

4 MACHINE FRAME DISTORTION - SOFT FOOT

Machine frame distortion or casing deflection is a topic that deserves considerable discussionand is the most overlooked area during the process of shaft alignment. It is also the area that canpay the highest returns for reliability of machinery when associated with proper shaft alignment.

Frame distortion can be divided into three categories:

• Soft foot

• Baseplate and foundation irregularities

• Induced soft foot and nozzle loads

Soft Foot

Soft foot in the classic sense is the flexing or bending of the frame foot when it is tightened to thebase. Any gap that exists is reduced with this tightening, and forces are applied to the frame orcasing. These forces result in casing deformation and in some interaction between the stationaryand rotating parts of the machine.

In most cases, a complete check for soft foot is not done. The machine to be moved (MTBM) isusually checked, but the stationary machine is seldom checked for soft foot. This, in turn,continues to result in problems with the stationary machine. For example, consider thecomparison of turbine-driven feedwater pumps to motor-driven pumps at the power station.When performing alignment on turbine-driven pumps, typically above 10,000 HP, there is atendency to move the pump. In doing so, it quickly becomes evident just how much soft foot ispresent due to classic soft foot problems or piping-induced soft foot. When aligning motor-driven machines and the motor is the MTBM, the machine is seldom checked for soft foot.Rarely is the machine ever unbolted from the pedestal or base.

This is an area where much progress could be made in improving the reliability of the machines.Instead, often the distortion due to piping-induced soft foot on the driven machine is mistaken forother problems. One such problem is the contact of wear rings in overhung horizontal pumps,such as American National Standards Institute (ANSI) or American Petroleum Institute (API)pumps. Often radial reaction of the rotor and impeller are blamed for this when it might be due todistortion, particularly at higher temperatures.

In comparison, on motor-driven machinery, when the motor is the MTBM, there are seldom anyinfluences present other than the classic soft foot examples. The exception to this is rigidconduit, which imposes forces on the motor, or on larger motors, the water cooling lines, whichcan also induce soft foot due to piping strain.


Machine Frame Distortion - Soft Foot

4-2

Measuring Soft Foot Index

It is common to measure soft foot by mounting an indicator on the machine base so that the stemis on top of the foot, but this method has numerous drawbacks. Depending on how the foot isbent, the indicator can under indicate the soft foot or even read zero when there is significant softfoot. This will leave the machinery installer with the mistaken idea that the bolt and foot areokay, when, in fact, harmful distortion exists in the machine frame.

The indicator can also indicate soft foot that does not move the shaft centerline and, therefore,can be ignored. This is usually the case when the shims and feet are very large compared to thesize and the load area of the bolt. If the load area is correctly supported, the rest of the foot canmove a considerable distance vertically without any distortion passed to the machine frame andbearings. The success of the indicator-on-top-of-the-foot method is highly dependent on machinegeometry. For example, a foot movement of 0.002 inches (0.05 mm) has entirely differentconsequences for machines with only 6 inches (15.24 cm) between the feet than for those with40 inches (101.6 cm) between the feet.

In short, the indicator-on-top-of-the-foot method misses significant soft feet, gives false alarms,is highly affected by machine size, and is, in general, a poor method of measuring machine framedistortion. A much more indicative value can be obtained from measurements taken at the shaft.

Because soft foot really means machine frame distortion, any system that purports to measure itmust some how quantify distortion in the machine frame. One simple, yet effective, way to dothis is to determine if the bearings moved when the hold-down bolts were tightened. If thebearings did not move when the hold-down bolts were tightened, then there was little or nomachine frame distortion and certainly not enough to influence the rotor. On the other hand, ifthe bearings did move due to the hold-down bolts being tightened (or loosened), then the frameis sufficiently distorted to affect the running position and, subsequently, the condition of therotor.

For most, if not all, industrial machines, it is geometrically impossible for a single bolt to distorta machine frame in such a way that both bearings move, resulting in a shaft movement that ispure parallel displacement. Furthermore, if only one bolt is inspected at a time, any motion in thenearest bearing will be largely vertical. In fact, purely horizontal movement of a bearing due totightening a single base bolt is geometrically impossible. To summarize this:

• Machine frame distortion from tightening (or loosening) a single bolt always induces achange in the vertical shaft angle.

• Machine frame distortion can be measured by quantifying change in the vertical shaft angle.

Distinguishing Types of Soft Foot, Possible Causes, and ProperCorrection Techniques

Not all soft feet are the same. They are caused by a variety of conditions, some of which mightnot even be related to the machine itself. However, as a rule, all soft feet are bad and should beeliminated. The method of elimination depends upon the source or cause of the soft foot. There is



4-3

no general purpose, one-kind-cures-all soft foot correction. If your soft foot check indicates asoft foot, fix it. However, be careful to analyze the type and cause of the soft foot before doinganything. Indiscriminate shimming or trial and error will most often makes things worse.

Although a high-resolution laser system can be used for gauging the amount and effect of thesoft feet, it cannot determine the cause nor the corrective action. The soft foot mode of a high-resolution laser system senses shaft deflection caused by soft foot, accurately and reliably. Thesesystems display a soft foot index that is an absolutely reliable indication of machine framedistortion (soft foot). They do not display the correction for the amount of machine framedistortion detected.

There is no device yet made that can measure soft foot at the shaft or on top of the foot andaccurately analyze the necessary correction. Shaft-mounted devices, even the best laser systemswith soft foot functions, are not “gap meters,” nor are they “shim meters.” This is a limitation ofall measuring systems that are mounted anywhere except between the bottom of the foot and thetop of the base. In other words, if you are not measuring in the gap under the foot, you are notmeasuring the gap under the foot.

Cause and corrective action can be determined by using feeler gages, which are essential forremoving soft foot. Proper feeler gage technique for a single foot is to measure the gap under allfour corners of the same foot. From these four readings, an excellent idea of the shape of the gapcan be developed. The maximum allowable soft foot typically is 0.002 inch (50 µm), although areal effort should be made to obtain zeros.

Parallel Air Gap

Condition: This is the mental picture most often associated with the word “soft foot.” It is wherethree feet sit solid and flat, but one foot does not touch (see Figure 4-1). A feeler gage will findan equal gap at all four corners of the foot. Contrary to common assumption, this type of softfoot is quite rare. Note that the foot diagonally opposite will show soft foot, but a smalleramount. It is impossible to have three parallel air gaps on one four-footed machine. Likewise, itis impossible to have two air gap feet side by side. They must be diagonally opposite each other.

Soft Foot

Figure 4-1Parallel Air Gap



4-4

Causes:

• One leg is too short.

• One baseplate mounting pad is not coplanar with the other three.

• Inadequate shims are under one foot.

Correction: Add shims to equal the amount shown on the feeler gage. Do not fall into the oftenunproductive trap of attempting to divide the shims with the diagonally opposite foot. The lasersystem readings of the four feet indicate relative coplanarity of the feet. This, in accordance withthe feeler gage results, will often show that three of the feet are largely coplanar, and the fourthfoot is clearly the one to be shimmed. If the laser system shows two diagonal soft feet with thesame value and the feeler gage gaps are the same across the diagonal, then shim both feet. Withexperience, both diagonally opposed soft feet can sometimes be shimmed according to thecoplanarity of the four feet, but this is not recommended. It is far better to shim one foot and takethe readings again. You will often find that the problem is solved.

Bent Foot or Angled Base

Condition: The bottom of the foot is not coplanar with the base. It has feeler gage readings thatclearly show a slope from one corner of the foot to another. Often, but not always, one corner orone side of the foot is touching the base, and the foot acts as a lever when bolted down (seeFigure 4-2). Because of this, the bent foot usually induces soft foot in the two opposing feet andsometimes in the fourth foot as well. This gives the machine the appearance of having three orfour soft feet, but they will all go away when the bent foot is corrected.

Figure 4-2Bent Foot or Angled Base

Causes:

• Machinery that has been dropped or handled roughly

• Bent or poorly machined baseplates

• Severe angularity misalignment

• Feet that have been welded

• Foundation settling



4-5

Correction: Re-machine the feet, the base, or both; or build a step shim. Step shims are a field-proven method that is both safe and effective. The idea is to build a set of steps that match theslope of the foot (see Figure 4-3).

Figure 4-3Step Shim

The procedure to build a step shim is as follows:

1. Fill any gap that exists under the entire foot so that one corner or edge of the foot is touchingthe shim.

2. Measure the largest remaining gap.

3. Divide this gap by 4, 5, or 6 (the number of steps) to obtain the step thickness.

4. Select 4, 5, or 6 shims of the step thickness and insert them one step at a time. Without liftingthe machine, insert them by hand only until they are snug.

Some adapting of the method is required for feet that are bent diagonally or skewed. Eachvertical shim correction to the foot requires the steps to be rebuilt. Do not expect the steps to fitback in exactly the same way after shimming because vertical angularity corrections affect theslope of the feet. After the final alignment, trim and discard the excess portion of the step shims,as shown in Figure 4-3.

Taper Shims to Remove Soft Foot

A shim fabricated with a taper or compound taper can be used in place of step shims. Bymapping or measuring the gap and angles between the base and the subject foot, a shim can bemachined to remove the taper. This provides the advantage of not having gaps or steps associated



4-6

with the step shimming method. However, there are also disadvantages associated with thismethod. First, if you are trying to keep the number of shims to a minimum, the taper shim addsto the total shim thickness being used and must be accounted for on all feet. A minimum shimthickness of 1/16 inch (1.6 mm) is usually required to fabricate a step shim. Second, the shimtypically requires fabrication from carbon steel in order to be clamped to a magnetic chuck on asurface grinder.

Baseplate and Foundation Irregularities

Baseplate or pedestal condition and the foundation play an integral part in the ability of machinesto remain in an aligned condition. The baseplate to foundation interface, which is typically grout,is an area that deserves scrutiny. Because many problems can occur within baseplates andfoundations that affect the operability of the machine, baseplate conditions play an integral rolein shaft alignment.

Deterioration

The baseplate and foundation might be subject to certain environmental conditions that causethem to become unstable or deteriorate over time. The grout can begin to flake, erode, orcrumble due to the environment to which the foundation is subjected. Deterioration is most oftenfound in chemical plants, but it can occur in almost any situation. Continuous cleaning with largequantities of water can also have an adverse effect on the grout and metal portions of baseplates.Over time, rust and erosion of the grout can weaken the baseplate or foundation. If forces arepresent from piping-induced loads, the baseplate reacts to these forces and can moveaccordingly. Piping-induced or nozzle loads can cause the grout to crack.

Machinery Vibration

The problems associated with vibration are twofold:

• The first problem deals with the vibration caused by shaft misalignment. Vibration does notalways reveal misalignment. Several factors are involved, such as stiffness of the bearingsand the machine support structure. The external and internal preloads imposed on themachine can dampen the vibration.

Soft foot, regardless of the type, can cause vibration. This is easily revealed when a soft footbolt is loosened and the vibration decreases.

• The second problem involving vibration is in the baseplate and supporting structure.Baseplate looseness and grout cracking or dusting is evidence of high nozzle loads or highcycle fatigue. An example of high cycle fatigue would be predominantly high vane passingfrequencies on a centrifugal pump. This high frequency vibration for an extended period oftime begins to fatigue the grout and baseplate. Shaft alignment is hard to maintain or correctwithout going to the root cause of the problem.



4-7

The fatigue can manifest itself in the form of broken parts on the machine or even destructionof the baseplate over time. The grout is usually one of the first areas to show damage(see Figure 4-4), such as dusting or crumbling under vibratory loads.

Figure 4-4Pump Base Degradation Resulting From Transmitted Forces

Induced Soft Foot and Nozzle Loads

For the purpose of this guide, nozzle loads are divided into two categories: induced soft footwhich creates nozzle loads in the vertical direction, and nozzle loads for forces and moments inthe horizontal direction.

Condition: A high-resolution laser alignment system shows soft foot, usually two feet on sameside or same end of machine, and a feeler gage finds a gap, usually parallel or nearly parallel. Asecondary symptom is that the foot does not get better (it becomes worse) or another footbecomes much worse after shimming the gap amount (See Figure 4-5).



4-8

Figure 4-5Examples of Induced Soft Foot

Causes: External forces on the machine. Coupling strain and pipe strain are the two mostcommon. If the coupling is difficult to assemble because of misalignment, expect an induced softfoot until the alignment is improved. Other sources of external forces are:



4-9

• Overhung machines or attachments

• Belt or chain loads

• Gears

• Any overhung or extended shafts

• Hoses

• Flex conduit

• Structural bracing attached to the machine

• Jacking bolts inadvertently left tight

Correction: Remove the source of the force. Note that a high-resolution laser alignment systemmakes a good tool for testing for pipe strain during construction. Attach the laser alignmentsystem and enter soft foot mode before attaching any pipe, but with all base bolts tight. Removeany soft foot from the machine and leave the laser alignment system set up to read one foot (anyfoot). Tighten the bolts on the piping. If the laser alignment system records more than 1.5 mils(37 µm) movement while the flange bolts are being tightened, the piping is straining themachine. As further proof, test again for soft foot while the piping is tight, and compare the datato pre-piped soft foot conditions.

Nozzle Loads

Typically, nozzle loads are on the driven machine, unless the driver is a steam turbine (forcesfrom the piping are transmitted into the pump casing or other type machines and continue on intothe foundation or baseplate). Remembering that for every action there is a reaction, it is easy tosee why the large forces applied through the piping can destroy a baseplate quickly. As thebaseplate gives up some of its strength, the loads imposed on the machine tend to move themachine more freely. The result is misalignment and the possibility of catastrophic failure of allmachines in the train. Large, high-energy pumps, such as feedwater pumps, can use keys to limitmovement of the casing. This does not reduce the stresses in the casing or reduce distortion fromnozzle loads or piping strain. It changes only the location where the forces and stresses enter(and leave) the casing.

The forces and moments in the horizontal aligning direction are a very important area of concernassociated with nozzle loads. These forces tend to move the machine in the horizontal directionin much the same manner as the induced soft foot moves the machine in the vertical direction. Inmost cases, a moment is also associated with these forces.

When trying to align a machine with this problem, moving the machine requires a great deal offorce to bring the machine into alignment. By applying this force against the opposing forces,casing distortion is added to the problem. As temperatures increase in the machine, the machinemay move in a direction that is not anticipated in relation to the hot alignment analysisperformed.



4-10

Over time, these forces manifest themselves in the form of rubs internal to the machine, pedestaland baseplate damage, and grout failure. These horizontal forces and moments are best detectedby loosening all hold-down bolts, removing casing keys if they are present on the subjectmachine, and loosening on all jacking bolts if they have been tightened in an effort to maintainalignment. By observing where the machine moves and the forces required to move the pumpback into position, information can be gained about the forces present.

Large pumps, such as feedwater pumps, often use keys to limit movement of the pump and directthermal growth in a particular direction. The typical design uses a pin on the coupling end of thepump and a rectangular key on the thrust end of the pump. The pin on the coupling end providesfor very limited movement in the horizontal and axial direction. The key on the opposite end ofthe pump allows for thermal growth in the axial direction and limited movement, usually lessthan 5 mils (0.1mm) in the horizontal lateral direction.

When pumps such as these are loosened from the baseplate in an effort to detect lateral forcesand moments about the axis of the nozzles, these keys must be loosened or removed. Manytimes, this requires grinding welds that hold the keys or key blocks in place. Figure 4-6 showsone station’s resolution to achieving horizontal moves and remedying lateral or horizontal forcesand a “twist” in the pump. Figure 4-6 shows the modified key block used with adjustments, to bemade after alignment, and the welded jacking brackets.

Figure 4-6Pump Outboard Replacement Keys

Jacking Bolts or Taper Pins

Machine frame distortion can also be caused by dowel or taper pins used to limit the movementof the machine. Jacking bolts are used occasionally in alignment to limit the movement ofmachines that move around on the base. Care must be taken to ensure that casing distortion is notcaused by these jacking bolts (see Figure 4-7).



4-11

Figure 4-7Key A djusting Bolts

In many instances, the taper pin (or in some cases straight type fitted dowels) is used improperlyto limit the movement of machines. Analysis of the total axial growth of machines should beperformed to determine the fixed end of the machine, and the taper pins should be installed onthat end of the machine. Installing taper pins diagonally from one end of the machine to the otherincreases the probability of casing distortion at elevated temperatures. The manufacturer or areliable consultant should be consulted if there are questions concerning doweling the feet of amachine.



4-12

Gaps Without Soft Foot

Condition: Sometimes, a foot that does not show soft foot by high-resolution laser alignmentsystem readings will have a rather large gap under it when the bolt is loose and no gap when thebolt is tight. Another version of this same phenomenon is that the laser alignment systemindicates a relatively small soft foot, but the feeler gages find a much larger gap.

Causes:

• The base is moving.

• The foot is bending without bending the machine (weak or flimsy feet).

• The base or machine is cracked, loose, or otherwise defective.

Correction: Even given the absence of soft foot in this condition, most people choose to shimthe gap, although it rarely improves the running condition of the machine. The base or machinemust be repaired or rebuilt to eliminate this condition. Note that this condition often has the sideeffect of making vertical alignment corrections very unpredictable or even impossible. If themachine can be aligned (it responds to vertical corrections) and is not loose or broken, then thegap can often be ignored. If the tightening and loosening of the foot’s base bolt does not affectthe shaft centerline (no soft foot reading), then the bearings are not being moved or distorted, sono harm to the rotor, bearings, or coupling occurs.


5-1

5 MACHINERY POSITION CHANGES

The running alignment position of machines is the aligned position of two or more machinesrelative to each other at running conditions, which differs from the cold or shutdown alignedposition. Often, machines are misaligned in a shutdown condition in hopes that the alignmentduring operation (or under “running conditions”) is within the acceptable tolerances for thatmachine. While this is often referred to as “hot alignment,” there are others who define hotalignment as mounting alignment equipment and capturing data immediately after machines aretaken off line. Although this method is probably better than nothing if certain rules are followed,it is not very accurate and is about the same as guessing where the alignment of the machinesshould be.

There are several methods that provide alignment criteria for machines to be misaligned in thecold condition and achieve alignment during operation. These methods are listed below in orderof least to most accurate:

• Guess where the machines should be aligned

• Shut down and perform the alignment

• Use the manufacturer’s recommendations

• Monitor the machines from one condition to the other

The manufacturer of a boiler feedwater pump and the manufacturer of a drive turbine tend togive information based on their respective machines. This information is based on eithermonitored or calculated data, and this data is typical for “thermal growth” considerations of therespective machines. Most often, you will get numbers from the manufacturers that representsome vertical change in the machines relative to ground or to another machine. Some horizontalchange might also be provided.

More often than not, however, the horizontal misalignment targets are far from being what themanufacturer of the machines provides or what can be calculated at the power station.Monitoring alignment changes allows you to determine targets in the horizontal direction.Horizontal types of misalignment are generally due to piping forces (either static or dynamic)that prevent the pump from being aligned where desired or move the pump after startup.

Large pumps present problems in this area. Many large pumps have keys or a combination of pinand key along the bottom of the pump casing. Some pumps even have keys radially projectingfrom the sides of the casing to either limit the twist in the pump casing or, in most cases,deliberately try to make the pump casing “grow” in a particular direction.


Machinery Position Changes

5-2

When targets reveal that a pump must have a given amount of horizontal angularity or horizontaloffset, provisions must be made to modify these keys from their as-built configuration (SeeSection 4).

Figure 5-1 is a graphical representation supplied by one pump manufacturer of the calculatedthermal growth of a motor-driven pump with a gear box.

Figure 5-1Alignment of Shaft Centerline Heights

These alignment targets are calculated based on an expansion chart, as shown in Figure 5-2.



5-3

Figure 5-2Expansion Chart

Typically, the horizontal changes supplied by the manufacturer are not close to what isencountered in the field when the machines in question are acting together with the entiresystem. Although the vertical changes may occasionally be within the range provided by themanufacturer, the horizontal changes seldom are.

The terms “hot alignment” and “thermal growth” do not disclose the complete story of runningposition alignment. The most accurate terminology is “transient alignment monitoring” becauseit best describes what running position alignment is about. You must monitor the alignmentchanges under all conditions to establish an understanding of the behavior of the machines.Capturing alignment changes within all operating parameters gives you an opportunity to explorethese changes.

Machines can be monitored starting with the machine cold (at shutdown) and monitoring thechanges as the machine reaches its operating condition. Monitoring can also be performedstarting with the machine at operating conditions and monitoring to shutdown. Monitoring canalso take place anywhere in between, if certain parameters are to be observed withoutdetermining the full amount of changes of the alignment.

The preferred method is to monitor the machine from operating conditions to shutdown. Thisenables you to analyze and implement the alignment data during shutdown and observe theresults on startup. This saves an additional shutdown to align if the opposite method is used.



5-4

There are two concepts involved in monitoring machine movement and arriving at the alignmenttargets. For the purpose of clarity and convenience, these methods can be referred to as absoluteand relative monitoring.

Absolute monitoring involves the technique of measuring one machine from a fixed referencepoint from the ground, such as a column, wall, or floor. The types of monitoring equipment thatdo this include precision sight levels and jig transits, Acculign bars, and Jackson cold waterstands.

The relative alignment methods monitor the changes in alignment between two or moremachines. The equipment used for relative monitoring includes Dynalign or Dodd Bars,Permalign lasers, and rotating Vernier gages. When absolute measurements are comparedbetween two or more machines, these measurements can also be referred to as relative.

See Figures 5-3 through 5-8 for pictures of various types of monitoring equipment.

Figure 5-3Acculign Bars Measuring Movement of a Steam Generator Feed Pump



5-5

Figure 5-4Laser Monitoring Movement Between Steam Generator Feed Pump and Turbine

Figure 5-5Dynalign (Dodd Bars) Being Used to Monitor Alignment Changes



5-6

Figure 5-6Precision Sight Level Used for Optical Alignment ChecksSource: Brunson Instrument Company

Figure 5-7Jig Transit Used for Measuring Alignment

Source: Brunson Instrument Company



5-7

Figure 5-8Scales Used With Jig Transits and Precision LevelsSource: Brunson Instrument Company

Infrared Thermography

Infrared thermography can play a very important part in analyzing misalignment. Thermographycan detect problems through temperature rises in the couplings or bearings. It cannot distinguishthe amount of misalignment, only the results of misalignment. In many cases, this is just asimportant as measuring the amount of misalignment.

Used together, data from both infrared thermography and transient alignment monitoring systemscan be very informative to the technician, as well as to management personnel who may need tosee more evidence of problems in order to allocate resources necessary to resolve the problems.Past studies involving alignment analysis have determined that some previously held beliefsabout misalignment are not necessarily true, including the following:

• Misalignment is easily detected by high vibration levels.

• Misalignment increases cost of operations due to larger energy consumption.



5-8

Both of these have been used in the past as major selling points for alignment hardwarecompanies.

Alignment and Preloads

A preload is a directional load or force applied to the rotating shaft. Two categories of preloadsare internal and external. Internal preloads deal with forces generated from within the machineand go far beyond the scope of this guide.

Only the external type of preload exists for shaft misalignment. There are other types of externalpreloads that interact with or impact the structure or casing of the machine, including pipingloads (forces and moments) and soft foot. The immediate effect of a preload due to misalignmentis to force the shaft into one sector of a bearing. A strong indication of preloads, both magnitudeand direction, can be determined with the use of proximity probes (x and y) close to the bearing.These preload data are in the form of shaft orbits.

The use of bearing metal thermocouples in conjunction with shaft orbits and infraredthermography can yield excellent results in determining if misalignment exists. This is easilydetected and brought to light in a machine, such as turbine generator train, or a high-energypump, such as a feedwater pump. The vibration might be low on one bearing accompanied by ahigh temperature, while the adjacent bearing will have a higher vibration and lower bearingtemperature.

The amount of preload can be related directly to the amount of misalignment. Spring-typecouplings, such as a diaphragm coupling, exhibit the least amount of preloads on a bearing andits supporting structures, while a rigid-type coupling will impose the most preload.

In Figure 5-9, a circle or ellipse, as shown in the first two orbits, is the norm when nounidirectional loading or preloads are present. As you move across the page, greater preloads areencountered. The last orbit is where the shaft is located in the bottom of the bearing due to alarge amount of misalignment, and the results can show up as twice the shaft speed. An elevationin bearing temperatures can also accompany this scenario. Remember, there are other things thatcan cause increased vibration. Misalignment occurs perpendicular to the shaft orbit and forcesthe orbit to flatten; thus, the sensors perceive this as twice the running speed.

Figure 5-9Shaft Orbits Acquired From Eddy Current Probes on a Sleeve Bearing Machine

A phase difference of 90 degrees between x and y probes should be theoretically true; however,two probes can show a phase difference of 180 degrees. A steady-state preload will cause theshaft to move eccentric to a position within the bearing. This type of orbit is seen most often inmachines with gear-type couplings. These preloads can also unload a bearing, resulting in a



5-9

lower temperature in one bearing and creating an opportunity for an unstable shaft, which mayresult in oil whirl.

These external preloads can also be due to the misalignment itself. Piping strain and soft footpose another problem with casing deformation. You have a choice of where you want theseforces to enter the pump. They can enter through the piping or through the keys and supportingstructures of the pump casing. These forces can also be transmitted into the structure supportingthe pump, such as the base and grout of the machine (see Figure 4-4).

Smaller machines with anti-friction bearings pose special problems with preloads. Detectionmight need to be performed with infrared thermography, as well as vibration analysis, to detectpreloads that have an effect on alignment and reliability of the machines. Machines that use agearbox for speed changes will have preloads associated internally with the machine, which actupon alignment while the machine is in operation.

While piping strain impacts alignment, it also impacts the wear of parts. Piping strain as it relatesto misalignment is often overlooked. This is particularly true in the horizontal direction. Whatappears as a minor amount of piping growth to the piping designer can be a major amount torotating machinery personnel. Piping growth due to heat can have a severe impact on themisalignment of machines. Some of this misalignment can be accounted for with transientalignment monitoring and corrections.

Cold piping strain in the horizontal direction must be accounted for and remedied as stated in theInduced Loads section. Radial and axial pump keys under the casing do not eliminate theseloads; they just enter the casing from another location. The forces against the keys constrain thepump, but they add to the loads on the casing just the same. These keys may require modificationfrom the original installed position.


6-1

6 SHAFT COUPLINGS AND POWER TRANSMISSION

Shaft couplings and power transmission go together with shaft alignment. Shaft alignment isseldom performed without the opportunity at least to look at the flexible shaft coupling thatconnects the machines being aligned. During shaft alignment, machines with lubricatedcouplings are generally inspected or preventive maintenance is performed. Dry-type couplingsalso require inspection for damage such as fatigue or cracking.

This guide does not attempt to discuss all the details of shaft couplings and how they aredesigned, applied, and used. Instead, they are briefly discussed in this section in the areas wherethey play an important role in the process of aligning shafts and in the behavior of machines dueto shaft and coupling misalignment.

Flexible Couplings

A flexible coupling transfers or transmits power from one machine to another and makesaccommodation for some shaft misalignment. There are two types of flexible couplings: oneallows for misalignment by sliding, the other by flexing.

Typical couplings that allow for misalignment through sliding are gear-type couplings andflexible grid-type couplings. The misalignment of two shafts is accommodated during rotation ofthe shafts by the sliding of gear meshes (see Figure 6-1) or, in the case of the grid coupling, thegrid to the grooves in the hubs. The grid coupling also has some bending involved, but this isused for torsional loading.


Shaft Couplings and Power Transmission

6-2

Figure 6-1Gear Coupling

Courtesy of Falk Corp.

Figure 6-2 shows a grid-type coupling.



6-3

Figure 6-2Grid Coupling

Courtesy of Falk Corp

Couplings that allow for misalignment due to bending are flexible diaphragm couplings andflexible disk couplings. The diaphragm coupling can use a single steel diaphragm or aconvoluted diaphragm made up of several layers of thin flexible steel plates. Figure 6-3 shows adiaphragm coupling.



6-4

Figure 6-3Diaphragm Coupling

A multiple disk or disk pack coupling is shown in Figure 6-4.



6-5

Figure 6-4Flexible Disk Coupling

Restoring forces are very important because all couplings resist being misaligned. The couplingtends to try to run in a straight direction, and this imposes preloads on the shaft, trying to forcethe shaft into a particular sector of the bearing.

Restoring Forces and Moments

You should be aware of coupling behavior in misalignment. All couplings resist beingmisaligned and try to operate in a non-misaligned condition (hence the term “restoring forces”).These forces act on the shafts in the form of a moment arm trying to bend the shaft and, in doingso, adding stresses to the shaft. Misalignment under these conditions can fatigue a shaft (and/orcoupling) and eventually result in failure (see Figure 6-5).

Resistance to being misaligned occurs only under conditions where torque is transmitted and notin a standstill condition. When machines are borderline aligned and shafts move into a region orarea of misalignment while torque is being transmitted, coupling lockup can occur on gear-typecouplings.



6-6

Figure 6-5Stub Shaft Replacement

Misalignment

Coupling misalignment differs from shaft misalignment. Coupling alignment or misalignment isthe angle in degrees from the axis of one shaft to the axis of another shaft. The couplingmanufacturer usually provides allowable coupling misalignment in terms of degrees ofmisalignment. If the manufacturer gives a number in thousandths of an inch (0.001=25 µm) foroffset, it is the measurement of the distance between flex planes of the coupling times the tangentof the allowable angle of misalignment.

Taking into consideration the restoring forces of the coupling and the bending moments actingon the shafts, a rule of thumb can be proposed. If the misaligned shafts are graphed on paper withthe proper scaling and a line is extended from the centerline of one shaft to a point of intersectionon the opposing shaft, this is the point where the moment occurs (see Figure 6-6).



6-7

Figure 6-6Point of Moment

Figures 6-7, 6-8, and 6-9 illustrate three types of misalignment. These illustrations can be in theform of vertical or horizontal misalignment. For the purposes of illustration, the angles of shaftmisalignment are constant in all examples. Because couplings are the concern in this section, theangles will be given in degrees and mils per inch (25 µm) (mrad). A shaft coupling spacer of 12inches (30.4 cm) is assumed.

The first example (see Figure 6-7) is of a machine to be moved with only angular misalignmentbetween shafts or across the coupling.

Figure 6-7Angular Misalignment

P1 P2



6-8

In Figure 6-7, the angle of the shaft (MTBM) is 15 mils per foot (375 µm per 30 cm). The angleat the coupling flex plane at P1 is 0. The coupling misalignment at P2 is .072 degrees.

Figure 6-8Angular Misalignment and Offset at P2

Figure 6-8 illustrates an offset at P2 of 15 mils (375 µm) and the same angle (15 mils per foot)(375 µm per 30 cm) or .072 degrees. The misalignment of the coupling will be .072 degrees atP1 and 0 degrees at P2.

Note: The actual offset of the shaft (MTBM) at the appropriate measuring point (P1) will be 0.

Figure 6-9Angular Misalignment and Offset at P1 and P2

P1 P2

P1 P2



6-9

Figure 6-9 shows the same offset and angle to the other side of the shaft. Note how the shaft(MTBM) crosses the centerline of the stationary machine shaft. The misalignment of thecoupling at P1 is the same .072 degrees. The coupling misalignment at P2 is .143 degrees ortwice the coupling misalignment at P1.

Note: The actual shaft misalignment as measured at P1 would be 30 mils (750 µm). With theabove referenced misalignment, a bending moment would be introduced into the shaft (MTBM)at approximately 25 inches (62.5 cm) from P1.

Advantages and Disadvantages of Coupling Types

The advantages and disadvantages of various couplings are shown in Table 6-1.

Table 6-1Coupling Advantages and Disadvantages

Coupling Type Advantages Disadvantages

Gear-type couplings • Transmit more power – have agreater power to weight ratiothan other coupling types.

• Accommodate for axial shaftmovements due to rotormovement by design, or rotormovement due to thermalgrowths.

• Require lubrication - Must be stoppedto lubricated. The exception to this is acontinuous lube coupling that provideslubrication with the use of apressurized oil system. If the oil is keptclean, this can add to the life of a gearcoupling.

• Coupling lock up – This can occurunder certain operating conditions.This phenomenon can limit the travelor movements of shafts in the axialdirection or limit the movement of thecoupling to allow for misalignment.

Disk-type-couplings • Disk pack couplings cantransmit more power per givensize or weight than other typesof non-lubricated couplings.

• Inspection can be performedwhile running.

• Failed disks can be replacedrelatively easily.

• Failure of disks and life is proportionalto misalignment

• Corrosion and fretting

Diaphragm-typecouplings

• Simple design

• No lubrication required

• Will tolerate greater angularmisalignment

• Limited axial travel

• Larger diameter

• Heat generation due to windage

Convoluted diaphragmcouplings

• Smaller than other diaphragm-type couplings

• Can accommodate more axialmovement

• Complicated in design

• Heavier than other diaphragm-typecouplings

Grid-type couplings • Torsionally soft • Accommodate small shaft separation

• Very little damping



6-10

Table 6-1 (continued)Coupling Advantages and Disadvantages

Coupling Type Advantages DisadvantagesElastomeric-typecouplings

• Tire couplings • Impose small radial forces onbearings due to offsetmisalignment

• Centrifugal force• Thrust loads

• Geared rubber • Cost is low• Requires no bolting

• One hub must be moved forinstallation.

• Spider couplings • Transmit large torque • Accommodate little offset


7-1

7 VERTICAL MACHINES

Vertical Machines with Rigid Couplings

Vertical Machine Behavior

Power plant pumps in services such as heater drain and/or condensate pump applications tend topose special problems with shaft alignment. These problems are of consequence in nuclearpower stations due to the use of mechanical seals and the possible premature failure of theseseals. Many of the seal failures are due to improperly aligned shafts in the pumps.

When investigating the root cause of these problems, shaft alignment is typically at the top of thelist. Of major concern, along with the seal failures, is the accelerated wear of the pressurebreakdown device found in most stuffing boxes on this type of pump. This wear may beattributable to problems with shaft misalignment as wear escalates in the pressure breakdownarea due to misalignment, causing a pressure increase in the stuffing box area and subsequentseal failures:

• On the surface where the motor adjoins the discharge head

• On the stuffing box mating surface

• On the base mounting plate

• At the last stage bowl joint and surface

Without all of these surfaces being true, coupling alignment is all that can be performed. Shaftalignment is directly related to the accuracy of these mating surfaces and/or fits. Problems of thisnature might not have been evident in packed pumps, and if leakage did occur, it was not a majorconcern.

Note: The discharge head from many manufacturers is supplied with a rabbet fit or registrationfor the motor to fit precisely onto for proper alignment. In some cases, this fit does not accuratelyalign the motor shaft to the pump shaft, and the fit must be machined to achieve properalignment.

The adjoining stuffing box and related fits must also be true to the discharge head because this isthe area where alignment data will be taken. Figure 7-1 is a diagram of a typical stuffing box,noting areas where runouts and concentricities are to be taken.


Vertical Machines

7-2

1

2

3

4

Figure 7-1Typical Stuffing Box, Noting Four Points Where Dimensional Runouts and ConcentricitiesAre To Be Measured

Causes of Misalignment

Parallelism and angularity of shafts are influenced by the amount that the baseplate andsubsequent motor rotor support system are out of level. This support system includes the thrustbearing and housing, motor frame, and motor stand or discharge head. All of these items play animportant role in misalignment that will eventually manifest itself in component failures, in themechanical seal in particular. True shaft alignment cannot be performed on vertical machineswith rigid coupling without alignment of all components that are stacked and/or suspended fromthe base (floor).

Figure 7-2 shows a typical discharge head, also called a motor stand. The discharge head andbase mounting are the starting points for all misalignment problems experienced in this type ofpump. Some manufacturers require a baseplate that is level within .002 inches per foot (50 µmper 30 cm). For example, if the bolt circle is 48 inches (1.2 m), the possible out-of-level is .008inches (200 µm). This might not sound like much, but using the linear approach of alignment,with a the suspended pump that is 15 feet (3 m) long, then .030 inch (650 µm) deflection is at thebottom of the pump. This can cause a moment on the shaft at one of the line bearings, at themounting, or at the bolted joint interface.


Vertical Machines

7-3

Before accurate alignment can be performed, the discharge head must have all of its surfacesparallel to each other. All fits must be concentric. The four surfaces (shown in Figure 7-2) are:

1. The surface where the motor adjoins the discharge head

2. The stuffing box mating surface

3. The base mounting plate surface

4. The last stage bowl joint and surface

1

2

3

4

Figure 7-2Typical Discharge Head (Motor Stand)

Below is one station’s solution to solving the problems with vertical pump shaft alignment andmaintaining accuracy across the rigid-type coupling. This procedure enhances the ability tomonitor exact shaft alignment.

1. Center the motor shaft in the lower bearing guide. This is accomplished with four shaftsupports that are adjustable and allow for the centering of the shaft in two directions, 90degrees apart, or in the X and Y axis. A maximum of 15 ft-lb (20 Nm) torque is applied toensure that the lower guide bearing is not misplaced or skewed in the bearing fit.

2. Align the motor shaft to the stuffing box bore. For this to be an accurate representationof alignment, the stuffing box face to discharge head runout must be less than .001 inch(25 µm), and the stuffing box bore must be true and perpendicular to the face(see Figure 7-3).


Vertical Machines

7-4

Indicator Bracket

Stuffing box

Pump Shaft

Motor Shaft

Figure 7-3Alignment Fixture Aligning Motor to Stuffing Box

3. Slide the mechanical seal onto the pump shaft. The seal must not be bolted or installed anyfurther at this time until the checks are made and the appropriate lift of the shaft iscompleted.

The coupling spacer (spool piece) fit to the shafts can create errors when coupling the twoshafts together. Excessive clearances in the coupling fit (if registrations or rabbet fits are usedto assist in aligning couplings) and spacers to prevent unnecessary runouts from being addedinto the alignment can be significant problems. Due to the fact that most pumps use anadjustable coupling spacer and nut to facilitate the lift and proper running position of theshaft, clearances in this area can cause an accumulation of errors in tolerances of alignment(see Figure 7-4). Most motor shaft coupling hubs have a fit on the periphery of the couplingface that acts as a registration or rabbet to ensure that the spacer aligns properly with themotor hub. This fit must have a small amount of clearance to accommodate the fit of thespacer.


Vertical Machines

7-5

Driver Half Coupling

Spacer Piece

Adjusting Nut

Pump Half Coupling

Figure 7-4Adjustable Coupling Sp acer and Nut in a Typical Pump Coupling

4. Install the coupling spacer (spool piece) to the motor hub. This is a registration or rabbet fit.

5. Install the pump coupling hub and adjusting nut. The pump coupling hub should be blockedup slightly to prevent the weight of the hub from resting on the mechanical seal.

6. Install five bolts using 200 ft-lb (271 Nm) of torque. This particular application has 10 boltsinstalled and this allows for every other bolt to be in place.

7. Install the dial indicators at points 2, 3, and 4 (see Figure 7-5).


Vertical Machines

7-6

1

2

3

4

5

6

7

Figure 7-5Pump Coupling Indicator Positions

8. Rotate the motor shaft and the spacer, and record total indicator runout (TIR) at the followingdial indicator positions: 0, 90, 180, 270, and 0 degrees.

Vertical pump shaft alignment involves more than indicating the shafts to each other or to areference, such as the stuffing box. A high percentage of seal failures and pump internal wear inthe stuffing box area is directly related to shaft alignment and/or total pump-to-motor alignment.

Several instances have been reported where laser alignment has been performed on this type ofpump. The success of this type of alignment has not been as expected, and it has not gained favorat many utilities. The method for aligning these pumps to motor shafts has involved swinging orsupporting the pump shaft from the motor shaft with two coupling bolts left loose or with a gapbetween the couplings. The face must be measured by some means such as feeler gages oradjustable parallel blocks. If a laser is used, it must be mounted 90 degrees from the two bolts toallow for some flexibility in the coupling in an effort to acquire acceptable readings. The pumpshaft must be checked to determine if the shaft is in the center of the stuffing box. This typicallyleads to errors (out of tolerance) at either the stuffing box or the coupling.

Alignment Procedure (Steps 1–9)

1. Center the motor shaft using two indicators.

2. Leave one indicator on for indicator #1 TIR.


Vertical Machines

7-7

3. Align the motor shaft to the stuffing box.

4. Slide the mechanical seal onto the shaft.

5. Install the pump half coupling hub and adjusting nut.

Pump Coupling Procedure (Steps A–G)

A. Check the pump rotor total lift and center.

B. Install five bolts in the pump hub and torque to 200 ft-lb (271 Nm).

C. Install indicators #6 and #7. (Note: Indicators #2 and #3 can be used here.)

D. Sweep and record the TIR.

Table 7-1TIR Measurements From Installing the Pump Coupling

Degrees 0 90 180 270 0

Indicator #1 0 0 0 0 0




E. If #6 is less than .004 inch (100 µm), complete the coupling installation(all bolts and torque).

F. If the runout is greater than .004 inch (100 µm), rotate the pump hub 180 degrees and torque the bolts.

G. Sweep and record the TIR.


Vertical Machines

7-8

Table 7-2TIR Measurements From Installing the Pump Coupling

Degrees 0 90 180 270 0

Indicator #1 N/A

Indicator #4

Indicator #6

Indicator #7

Alignment Procedure (continued)

6. Install the spacer to the motor hub (rabbet fit).

7. Install five bolts; torque them to 200 ft-lb (271 Nm).

8. Install indicators #2, #3, #4, and #5.

9. Sweep and record the TIR.

Table 7-3TIR Readings From the Vertical Pump Shaft Alignment Procedure

Degrees 0 90 180 270 0

Indicator # 1 0 0 0 0 0




Indicator #5 0 1.5 1 0 0


Vertical Machines

7-9

Table 7-4TIR Readings From the Final Pump Shaft Alignment

Degrees 0 90 180 270 0

Indicator #1 N/A

Indicator #2

Indicator #3

Indicator #4

Indicator #5

Note: If indicator #4 is less than 0.002 inch (50 µm), continue with the pump couplinginstallation. If # 4 is greater than 0.002 inch (50 µm), rotate the coupling spacer 180 degrees,torque the bolts, and sweep again.

Conclusions

Vertical machine alignment must be approached with precision. The life of the pump and motorbearings and the mechanical seal (if used) depend on quality alignment. Very few pumps in theseapplications have vibration monitoring on the pump. Dependence is placed on vibrationmonitoring taking place at the stuffing box or on the motor. The first sign of misalignment istypically mechanical seal leakage.


8-1

8 REFERENCES

American Petroleum Institute: Centrifugal Pumps for General Refinery Services, API Standard61, Sixth Edition, January 1981.

Calistrat, Michael M. Flexible Couplings, Their Design, Selection and Use. Caroline Publishing,1994.

Calistrat, M. M. “Metal Diaphragm Coupling Performance,” presented at the 5th TurbomachinerySymposium, Texas A&M University, College Station, TX. 1976.

Evans, Galen and Pedro Casanova. The Optalign Training Book, “All About Shaft Alignment.”Ludeca Inc., 1990.

Jackson, Charles. The Practical Vibration Primer. Gulf Publishing Co. 1979.

Machinery Diagnostics Seminar Handbook. Bently Nevada Corp. 1989.

Mancuso, J. R. “A New Wrinkle to Diaphragm Couplings.” Zurn Industries, Inc., Erie Pa. ASMEpaper 77-DET-128.

Piotrowski, John. Shaft Alignment Handbook, 2nd Edition. Marcel Decker, Inc., New York, 1995.

Webb, S. G. and M.M. Calistrat, “Flexible Couplings,” presented at Manufacturing ChemistsAssociation Second Symposium on Compressor Train Reliability, Dow Center, Houston, TX(April, 1972).

Wright, John, “Which Shaft Coupling Is Best – Lubricated or Non-Lubricated?” HydrocarbonProcessing, Koppers Company, Inc., Baltimore, MD, April 1975.

54815763 Shaft Alignment Manual

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