Optical Alignment, Thermal Growth and Machinery Movement

8/13/2019 Optical Alignment, Thermal Growth and Machinery Movement

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By Stanley R. Bognatz, P.E.Optical Alignment, Thermal Growth & Machinery Movement 75 Laurel Street, Carbondale, PA 18407

Ph. (570) 282 - 4947 email: [email protected]

2007 M&B Engineered Solutions, Inc. 1

Optical Alignment,Optical Alignment,Thermal Growth, &Thermal Growth, &

Machinery MovementMachinery Movement

Presented For:Presented For:The Vibration Institute, February 17The Vibration Institute, February 17 thth , 2007, 2007

By:By:Stanley R. Bognatz, P.E.Stanley R. Bognatz, P.E.

PresidentPresident

2007 M&B Engineered Solutions, Inc. 2Optical Alignment, Thermal Growth& Machinery Movement

IntroductionIntroductionOur customers often seek help achieving precision alignment of theircritical machinery when standard alignment techniques do not providesatisfactory operation.

While helping them achieve the simple goal of good hot alignment,we ve identified many mechanical issues using Optical Alignment( OA ) that were not intuitive to those involved, and were not previouslysolved using vibration analysis or other techniques.

We would like to share some OA background with you, and how weapply OA to optimize shaft alignment and eliminate machineryproblems.


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Basic Shaft AlignmentBasic Shaft Alignment

How do we define the (mis)alignment of two machine shafts?

Parallel misalignment: coupling rim offset between two shaft centerlinesAngular misalignment: coupling face deviation from parallelCombined the usual field condition .

Parallel (Offset) Misalignment

Angular (Face) Misalignment

Combined Misalignment


Alignment FactorsAlignment FactorsHow accurate do we need to be? What factors might you consider?

Long coupling spansShort coupling spans

Flexible CouplingsDisc -pack couplings (for offset)

Geared CouplingsRigid couplings

Low speed (< 1,800 rpm)High speed (=> 1,800 rpm)

Less Critical:More Critical:

What criteria do you have?


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Alignment CriteriaAlignment Criteria

0.2

0.6

0.4

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2 4 6 8 10 12 14 16 18 20 22 24 26 28SPEED (RPM / 1000)

S H A F T D E V I A T I O N ( M I L S / I N C H )

VERY GOOD

ACCEPTABLE

REALIGNMENT REQUIRED

The Alignment Tolerance Chart ties speed, coupling span, and mis alignment inthe horizontal & vertical directions together to assess alignment accuracy.

SHAFT h2 v2

P.T.DEV.=

Shaft deviation iscalculated for each sideof the coupling (h & v)and plotted as afunction of speed todetermine if alignmentis required.

We can see that at3,600 rpm, deviation

much beyond 1 mil/inchshould be realigned.


Alignment AccuracyAlignment AccuracySo, once again: How accurate does our alignment need to be?

To muddy the water just a bit more:

What is the point in setting a cold shaft alignment within 0.002" if adjacen tbearing housings move 10 20 mils (or more!) in different directions due tothermal growth and static deflection?

If we set a perfect cold alignment, with the shafts collinear, it is a sure betthat thermal growth and static deflection will ruin our alignment when themachine is operating.

This is where Optical Alignment will provide significant improve ment in our

operating (hot) alignment accuracy.


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What isWhat is Optical AlignmentOptical Alignment ??

OA - The use of high -precision optical instruments (jig transits, sightlevels, alignment telescopes) and special tooling to measure therelative alignment of machinery.

Applications of OA include:Align bearing & seal boresAlign diaphragmsSet rolls parallelLevel base & sole platesCheck flatnessAlign & level machine casesMeasure thermal growthMeasure static deflection

OA can help us answer thesequestions with high accuracy:

Is it straight?Is it level?Is it plumb?Is it square?


Why Optics?Why Optics?What advantages does optical equipment have for determining Is it Straight,Level, Plumb & Square?

Measurement flexibility horizontal; vertical; axial; bores; casings; split -lines; diaphragms; rolls; baseplates; soleplates; foundations; rolls; etc.Many measurements quicklyReferences (Benchmarks) allow absolute comparison of componentsEasy to setup in multiple locations around any machineEasily portableExcellent repeatability between surveys

Excellent accuracy


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Optical Alignment EquipmentOptical Alignment Equipment

Several essential pieces of gearcomprise a typical OA kit:

Jig transits; alignment telescopesPrecision ScalesScale LevelsInvar KitTripodsTubesCross -slidesMounting Hardware / ToolingBenchmarksTool kit


Brunson 76Brunson 76 --RH Jig TransitRH Jig TransitBrunson 76 -RH Jig Transit key features & functions:

Main Telescope: 30X magnification;focus 2 to Infinity (and beyond)Main scope sweeps horizontal & vertical planesFine -motion tangent screws for adjustmentCross Telescope: 45X magnification; providessights at precise right angles to the main scopeCoincidence Level: precision leveling (1 arc -sec)Optical Micrometer: offset measurements (0.001 )

Extreme Accuracy - bearing runout < 0.000025Calibration can be verified on -site for every job


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Coincidence LevelCoincidence Level

Vertical tangent screw on transit subtly tilts thetelescope to dead -level the line of sight.

When viewed through the turret, both ends ofthe coincidence level bubble are opticallyfolded and brought together, side -by-side,using a 2.5X mirror path.

The human eye is very good at evaluatingcoincident patterns and can detect the tiniestdeviation from level.

The coincidence level system is the key to the jig transit s accuracy.

How sensitive is this system?

We can easily detect 1 arc -sec of tilt1 arc -sec = The width of dime viewed from 1 miles awayIn practical terms, 1 arc -sec = 0.0013 (1.3 mils) at 17 feet


Optical MicrometerOptical MicrometerOptical Mics and Scales provide the means to make measurements .

The mic uses a drumgraduated in 0.001increments to act as avernier when readingscales

For example, aftersighting a scale between17.4 and 17.5 , the micis adjusted to move thereticle to 17.4, and theamount moved is readfrom the drum, 0.040 ,

This gives a reading of17.440


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Optical ScalesOptical ScalesA little bit more sophisticated than theold wooden ruler

Hardened tool steelMatte white surfaceGlare reducing top -coatVarious sizes, 3 , 10 , 20 , 40Graduated in inches and tenthsAccuracy +/ - 0.001Varying tic spacing for differentsight distances

0.004 (closest)0.0100.0250.060 (farthest)


Invar KitsInvar KitsInvar comes in various lengths, and isassembled as needed to mountscales in the desired line -of-sight.

Invar s extremely low coefficient ofthermal expansion makes it perfectfor consistent measurements in anymachinery environment. Comparegrowths of a 5 rod over a 30 F T:

Aluminum: 0.024Steel: 0.017

Invar: 0.001 !!

Tolerance: +/ - 0.0003 per tube, std.Total stack -up error per kit +/ - 0.001


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Tripods, Tubes & CrossTripods, Tubes & Cross --SlidesSlidesStable bases are critical for reliabledata. Quickset s Hercules tripodshave proven rock solid, light weight &portable.

The tripod s elevator lets us adjustscope height, and tubes allow us toreach high locations.

Cross -slides provide lateral move -ment to let us buck -in the instrumentto a desired line -of-sight.


OA ApplicationsOA Applications

Internal alignment ofcrankcase bearings

(bore alignment)

Alignment of gearboxbearings to extruder bore


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Establishing parallel gearboxbearing bores

Setting parallel roll position (&heights) in paper / steel mills



Plumbing columns / surfaces;measuring horizontal deflection

Leveling; checking flatness;measuring vertical deflection


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The measuring of horizontal and verticalmovement forms the basis for determining howmachinery moves from off -line to runningconditions.

By measuring how each bearing in a machinemoves, we can determine exactly how the coldalignment should offset to produce an accuratehot alignment when operating.

This movement is sometimes referred to asOL2R , but most folks lump it into the termThermal Growth .


Thermal GrowthThermal GrowthThermal Growth is often just considered to be the Vertical change in bearing orshaft position due to temperature changes ( T) in the machine casing, bearingsupports, and foundations.

Movement due to T can be easily calculated. For steel, a coefficient ofthermal expansion of {6.8 x 10 -6 in / in / F} is typically used.

For example, a bearing pedestal 30 tall that was 45 hotter when themachine was running would grow by:

(6.8x10 -6) x 30 x 45 = 0.0092 , or 9.2 mils (not too bad )

But, if the T were 150 F, the change would be:(6.8x10 -6) x 30 x 150 = 0.0306 , or 30.6 milshmmm so much for our cold alignment

Do you know of any machines operating 50 or more above ambient?What effect is that T likely having on the alignment?


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Static DeflectionStatic DeflectionThe Thermal Growth on the previous slide only considered vertica l calculations.This is how many machinery OEMs derive their cold alignment offsets. Andwhile it is a good starting point, it is only part of the equati on.

We should also consider the horizontal bearing housing movement. Machinecasings will often show equal horizontal thermal expansion on bo th sides of abearing due to casing symmetry. However, many (most?) machines also exhibitstatic deflection due to the effects of torque transmission.

Other issues such as grout deterioration, pedestal or foundation flexure, andsoft -foot will compound both the horizontal and vertical movements seen whileoperating.

It is easy to see how our good, cold alignment can quickly becomeunacceptable while the machine is operating. This is where Optic al Alignmentcan provide us with the measurements to properly align the machinery.


Case Study #1Case Study #1 A Tale of 2 Boiler Feed PumpsA Tale of 2 Boiler Feed Pumps

Machinery ConfigurationMotor: 3,585 rpm ; 4 ,500 HPCplg: Disc -PackPump: 11 Stage; 2030 gpm; 7520 hd .

Or, One of these things is not like the other .

8

7

Pump

5

6 Motor

1

2

3

4

B M -1 BM -3

B M -2 BM -4

V- A

H- A

V- B

V- C

H- B

Customer Problem:Poor reliability on #1 BFP inboard pump seals(~6 months)

Diagram showing dowel -pin measurement points (1,2,3, etc.),benchmarks (BM - x ), and jig -transit locations used.


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Case Study #1, continuedCase Study #1, continued

Motor #1 Boiler Feed PumpDowel PinFoot Centerline

As -F o u n d H o t

As - F o u n d C o l d

A s - L e f t C o l d

As - Le f t H o t

P u m p H o t P o s i t o n

Pump Cold Position

Vertical Alignment Data

Alignment Study Results #1 BFP Vertical DataThe pump pivoted very nearly about the outboard pedestal, causing the inboardbearing to go upward, likely due to pipe strain, thus loading the bearing & seals. Theinboard bearing moved upward 0.023 , while outboard went down 0.017 . The motormoved upward 0.002 on the outboard bearing, 0.013 inboard. This required themotor to be set nearly 0.060 high on the outboard bearing, and 0.032 on the inboardbearing. Not your typical motor alignment .


Case Study #1, continuedCase Study #1, continuedAlignment Study Results #1 BFP Horizontal DataThe motor outboard bearing moved 0.005 to the right, while the inboard bearingmoved right 0.013 . The pump outboard bearing moved about 0.004 right, while theinboard bearing was essentially steady. This required the motor to be offset to the leftto achieve reasonable horizontal alignment. The motor was found to be bolt -boundand could not be moved to the ideal position.

0.020"20"

Horizontal Alignment Data

As -F o und C o l d As - F o u n d H o t As-Left Hot

As-Lef t Cold

P ump-Hot/ Fu ll Loa d

Pump - Ho t/S tandby


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Case Study #1, continuedCase Study #1, continuedThermal Growth Results #2 BFP Vertical DataThe motor and pump demonstrated much more typical responses, although the pumpwas found to grow more significantly than the pump vendor had an ticipated for thiscenter -hung design. Final vertical motor alignment required removing 0.010 from allfeet, which was performed at a later date.

#2 Boiler Feed PumpMotor

As - Le f t C o l d

A s - F o u

n d H o t

A s - F o u n

d C o l d

As -Le f t Hot

Pump Ho t Pos iton

Pump Cold Position

Foot CenterlineDowel Pin

Vertical Alignment Data

Remove 0.010" from all motor feet

dcp


Case Study #1, continuedCase Study #1, continuedAlignment Study Results #2 BFP Horizontal DataUnlike #1 BFP motor, this motor moved 0.006 to the left at both bearings. The pumpshowed a similar twisting motion as #1 BFP, but was more pronounced. This resultedin the motor needing to be offset 0.025 at the outboard bearing, and 0.016 at theinboard bearing. Once again, not your typical alignment ..

P ump-Hot / Full Load

0.020"

A s - L e f t C

o l d

A s - F o u

n d C o l d

A s - F o u n

d H o t

20"

A s - L e f t

H o t

Horizontal Alignment Data

Move inboard motor feet 0.008-0.010" to right(as viewed looking motor to pump)


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Case Study #1, continuedCase Study #1, continuedConclusionsThe two otherwise identical boiler feed pumps, mounted only a few feet away fromeach other, required significantly different cold alignment offs ets to produce acceptablealignment while operating at full -flow conditions.

The required offsets, especially on #1 BFP, were far outside the values recommendedby both the OEM and a pump repair specialist that was on site.

Following realignment to the required position, and re -adjustment of the inboard bearingseal, the #1 BFP ran without alignment -related seal problems for over 18 months. #2BFP was later realigned and has run very well.


Case Study #2Case Study #2 Large TurbineLarge Turbine --GeneratorGenerator

Machinery ConfigurationTurbine: 3,600 rpmCoupling: Rigid, rabetted -fitGenerator: 75 MW

Rigid couplings & short bearings spans need attention .

Customer Problem:OEM set alignment during outage. High vibrationand seal rubbing experienced during startup.Orbital & shaft centerline data analysis confirmedthe measured misalignment.

Generator

1D

V-BV-A

IP HP

BM-1

V-GBM-4

BM-610D

12

11

V-F

V-C

V-E

V-D

LP

BM-3

BM-59D

7D

8D

5SL

6SL

3D

4DBM-2

2D

V-H


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Case Study #2, continuedCase Study #2, continuedHP to LP Turbine As -Left OEM AlignmentCoupling faces were left open 0.013 (13 mils) on the bottom, placing bearing #1 at0.104 above the coupling, and bearing #2 about 0.010 high to the coupling. Nosignificant offsets were used.


Case Study #2, continuedCase Study #2, continuedLP Turbine to Generator As -Left OEM AlignmentCoupling faces were left approximately fair, with no significant offsets.


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Case Study #2, continuedCase Study #2, continuedAlignemnt Study ResultsWe found 0.065 growth at bearing #1 (turbine front standard), with 0.050 at bearing2. Bearings #3, 4 and 5 showed 0.020 , 0.019 and 0.015 , respectively. The coldcoupling and combined hot alignment data are shown below. Note high bearing metaltemperatures of 190 at bearings #1 & #4.

HP/IP TURBINE GENERATOR

VERTICAL ALIGNMENT DATA

LP TURBINE

As-Left Cold Alignment 4/24/06

D y n a m i c Al i g n m e n t a t 7 5 M W Lo a d

Bearing MetalTemp. = 190

Bearing MetalTemp. = 148 Bearing Metal

Temp. = 161




Case Study #2, continuedCase Study #2, continuedConclusionsTo normalize bearing loadings, we recommended the following shim changes (shown ingreen below):

Bearing #1: no changeBearing #2: + 0.025Bearing #3: +0.010Bearing #4: no changeBearing #5: - 0.025

VERTICAL ALIGNMENT DATA

As-Left Cold Alignment 4/24/06

D y n a m i c Al i g n m e n t a t 7 5 M W Lo a d

P r o p o s e d H o t Al i g n m e n t

Customer has yet to make any changes,and has since had fluid -induced instability atbearings 2 and 3, and mechanical problemsat bearing 1.


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Case Study #3Case Study #3 Process Compressor TrainProcess Compressor Train

Machinery ConfigurationTurbine: MHI; 4,831 rpm; 27,000 HPCouplings: all disc -packLP Cmpr : Elliott 60M81; 4,831 rpmGearbox: MAAGHP Cmpr : Elliott 29M6I; 11,047 rpm

High speed requires high precision .

Customer Problem:High 1X -filtered vibration on LP compressor sincewater induction event. Misalignment & unbalancesuspected.

LP CMPR.

6 0 M 8 I

LP CMPR.

6 0 M 8 I

4,831 RPM

V- C

GB-201VE RT.

1

2

V-B3

TU RB.

4

5

6

4,831 RPM

GB-201HORZ.

E

2

1

4

TU RB.3

H-B

6

5

H- A

HP CMPR2 9 M 6 I

11,047 RPM14

13

7

8 10

VBM-1

9

12

GB

11V-A

16

VBM-215

HP CMPR

2 9 M 6 I11,047 RPM

13

1410

HBM-2

8

79

12

11

GB

HBM-115

16

HBM-4

HBM-3


Case Study #3, continuedCase Study #3, continuedAlignment Study ResultsUsing prior cold shaft -alignment data and measured thermal growth data, the resultsbelow were obtained. While this graph is busy , we can see the hot offsets present ateach side of each coupling. Shaft Deviation values were calculated for each coupling,and are shown on the Misalignment Tolerance Graph on the next sl ide.

As-Left Cold Alignment 2002

D y na mi c Al i gnme nt - M ay 2 0 0 6

U7-201 TURBINEHP CMPR

VERTICAL ALIGNMENT

ELLIOT 60M8I

D y na m i c A l i g n m e n t

- Ma y 2 0 0 6

C7-202C7-201 LP COMPRESSORMHI 8CL-9

ELLIOTT 29M6IN7-201

SPEED INCR.MAAG G-40

As -Le f t Cold Alignmen t 2002

HORIZONTAL ALIGNM


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Case Study #3, continuedCase Study #3, continuedResults

0.2

0.6

0.4

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2 4 6 8 10 12 14 16 18 20 22 24 26 28SPEED (RPM / 1000)

S H A F T D E V I A T I O N ( M I L S / I N C H )

VERY GOOD

ACCEPTABLE

REALIGNMENT REQUIRED

HP CMPR / GBX

TURB / LP CMPR

LP CMPR / GBX 2.48

SHAFT h2 v2

P.T.DEV.=


Case Study #3, continuedCase Study #3, continuedConclusionsSignificant misalignment was found on the LP Compressor to Gearbox coupling, andwas suspected to be a major contributor to LP Compressor vibration.The large horizontal offsets caused a 1X crank -effect across the disc -pack stylecoupling. This contributed to the residual mass unbalance in the rotor, and causedunacceptably high vibration.Significant misalignment was also found on the HP Compressor to Gearbox coupling.

Alignment changes were recommended to the customer, but the site has yet to shutdown the process to allow corrections to me made.


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Case Study #4Case Study #4 Generator & ExciterGenerator & Exciter

Machinery ConfigurationGenerator: 850MW; 1,800 rpmCoupling: large disc -packExciter: 2-bearing; 1,800 rpm

High stiffness coupling sensitive to offsets .

Customer Problem:High 1X -filtered vibration on exciter bearingsprompted alignment & vibration study.

GeneratorV-B

BM-8

BM-3

8

5

6

V-E

V-D

V-A

LP-B

BM-7

7 Exciter

BM-1

BM-2BM-4

1

24

3

H-B

H-A

BM-5

BM-6

V-C


Case Study #4, continuedCase Study #4, continuedAlignment Study ResultsUsing a 0.007 parallel offset alignment, as supplied by the customer, and adding thethermal growth for the generator and exciter bearings, we have the hot alignmentshown below. It was interesting to note nearly equal vertical thermal growth on thegenerator and exciter bearings.

EXCITER(PARTIALLY SHOWN)

COLD

HOT ALIGNMENTHOT ALIGNMENT

GE NERATOR 1,800 RPM

VERTICAL ALIGNMENT DATAGENERATOR (STATIONARY)


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Case Study #4, continuedCase Study #4, continuedShaft Centerline DataProximity probes were used to gather vibration and shaft centerline data from thegenerator and exciter bearings. During startup from zero to 1,800 rpm, the shaft atbearing 8 (exciter -end of generator) moved upward 0.010 and to the right 0.003 .Bearing 9 (drive -end of exciter) moved up 0.003 toward bearing center.


Case Study #4, continuedCase Study #4, continuedShaft Centerline DataData from bearing 10 showed the shaft moving up only about 0.001 5 , and slightly tothe left, about 0.0005 .

Note:For counter -clockwise rotation (viewedfrom generator to exciter), we normallyexpect the shaft to rise and move to theright due to the lubricating oil forming awedge in the lower -left quadrant of thebearing beneath the shaft. As the shaftrotates, this wedge creates direct and

quadrature stiffness components that liftand push the shaft toward the lower -rightbearing quadrant.


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Case Study #4, continuedCase Study #4, continuedAlignment Study ResultsWhen we add the shaft centerline movement within the bearings (due to oil wedgeeffects) to the hot alignment, we arrive at the dynamic vertical alignment conditionsshown below. The rotors appeared to be well aligned, with only a 0.003 offset at thecoupling in the vertical direction.

EXCITER(PARTIALLY SHOWN)

COLD

HOT ALIGNMENTHOT ALIGNMENT

DYNAMIC ALIGNMENTDYNAMIC ALIGNMENT

GE NERATOR 1,800 RPM

VERTICAL ALIGNMENT DATAGENERATOR (STATIONARY)


Case Study #4, continuedCase Study #4, continuedConclusionsThe rotors appeared to be well aligned, with only a 0.003 offset at the coupling in thevertical direction. Horizontally, we did not have thermal data, but cold alignment anddynamic offsets also yielded less than 0.003 total offset.

The customer indicated the large disc -pack coupling was not loosened during the lastalignment check. Due to its size, it will have an impact on the exciter s alignmentreadings, especially any offset readings at bearing 9.

We have recommended a coupling inspection, including runout checks of all hubs, and are -check of the cold alignment with the disc -pack bolts loosened. This will allow anaccurate indication of the exciter shaft alignment. Soft -foots checks of the exciter framewill also be performed to reduce frame foot vibration.


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Thank You Any Questions?

Optical Alignment, Thermal Growth and Machinery Movement

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