Case StudyWhen a large (3.4 meters long) diaphragm coupling was suspected of causing excessive (120 microns p-p) 1X unbalance vibration between a 90+ Megawatt Gas Turbine and a Propane Compressor in an LNG plant, there was not time to ship the coupling back to a distant factory or service center for troubleshooting. Simple field diagnostic techniques were used to discover the problem, which then led to a field correction and repair so that the unit was able to be quickly restarted with minimum downtime

Corcoran, Joseph

Shatri, Quraisy

English

Texas A&M University

Case Study 
 
1 
Solving a Coupling Unbalance Problem in the Field 
 
Author:  Quraisy A. Shatri P.E. 
  Maintenance Superintendent – Machinery and Reliability 
  RasGas Company Limited 
  PO Box 24200, Doha, State of Qatar 
  Tel: (+974) 4492 3209 
  Mobile: (+974) 5583 8706 
  e-mail: qashatri@rasgas.com.qa 
 
Author: Joseph P. (Joe) Corcoran 
  Manager, Global Services and Training 
  Kop-Flex Emerson Industrial Automation 
  7565 Harmans Road 
  Hanover, MD USA 21076 
  Tel: (+1) 410 787 8522 
  Mobile (+1) 443 831 1811 
  e-mail: j.corcoran@emerson.com 
Abstract 
 
2 
When a large (3.4 meters long) diaphragm coupling was 
suspected of causing excessive (120 microns p-p) 1X 
unbalance vibration between a 90+ Megawatt Gas Turbine 
and a Propane Compressor in an LNG plant, there was not 
time to ship the coupling back to a distant factory or 
service center for troubleshooting. Simple field diagnostic 
techniques were used to discover the problem, which then 
led to a field correction and repair so that the unit was able 
to be quickly restarted with minimum downtime. 
Process Background 
 
3 
 In an LNG Plant, After all impurities such as Hg, H2S,H2O 
are removed in upstream units, sweet feed gas enters the gas 
chilling & liquefaction unit. 
 Two major pieces of equipment in this unit are the Scrub 
Column (SC) & the APCI Main Cryogenic Heat Exchanger 
 SC is a distillation column, steam re-boiled, to remove C5+ 
and provide streams for producing refrigerants (C2 and C3). 
 OH gas of the SC goes in to MCHE mid-bundle for 
liquefaction. The medium to cool is MR or Multi Component 
Refrigerant (MCR - C1+C2+C3+N2) 
Process Background 
 
4 
 The MR circuit is cooled (and partially liquefied) by 
Propane. The Propane refrigeration circuit is also tasked to 
cool Feed Gas in the gas chilling section, De-C2 condenser 
and the reinjection stream from the refrigerant preparation 
unit. 
 The two (2) main refrigeration compression circuits – MR & 
Propane – are illustrated in the next page.  
 If either of these 2 strings are down, there’ll be no 
production from the gas chilling & liquefaction unit, and no 
LNG is produced. 
Simplified schematics 
5 
 6 
HM  
Comp 
56 MB  
Comp 
88 M Comp 7 EA Gas Turbine 
Main Refrigeration Compression Strings 
PROPANE 
MR 
#5.5 MSMH-J, 
Diaphragm coupling 
rated power≅ 92MW; 
3,352.8 mm (Nominal 
cold shaft separation) 
HM  
Comp 
56 MB  
Comp 
60 M Comp 7EA Gas Turbine 
RCA 
 The string comprises of 4 coupled rotors: 7EA GT rotor, 88M and 56MB compressor 
rotors – HM rotor   
 Bearings: 3 radial bearings for a single shaft 7EA rotor, 2 radial bearings each of 88M 
and 56MB rotors, and 2 radial bearings of the HM. 
 Only DE radial vibration of the 88M rotor was extremely high – increasing rapidly with 
increasing speed / load; other bearings-vibe readings were normal. 
 Refurbished 7EA rotor and upgraded (new) 88M rotor were installed during the turn-
around. The GT operating data indicated “perfect”; factory dimensional and high-speed 
balance data of the 88M rotor and as-installed records indicated everything was 
acceptable. 
 Strong suspect was load coupling #5.5 MSMH-J  based on possible coupling imbalance 
as seen via 88M DE vibe plots: new spools & adapter but old coupling-hub were 
assembled; wrong pre-stretch gap; and poor run-out. Coupling components individual 
balance records observed to be “perfect”.  
 On attending the unit, installed couplings run-out checks clearly showed the coupling 
straightness was grossly out-of- straightness (0.018”) in mid-span point.  
 Plans to index, change-out of coupling hub was cancelled; previously-installed spacers 
were re-installed after all necessary checks were done and certified acceptable. Run-out 
checks of the installed coupling was then checked and certified acceptable for services.  
 The whole string was started-up, sent in to normal operations satisfactorily.  
High Vibration – Coupling Suspected 
 
8 
High Vibration – Coupling Suspected 
 
9 
Before Disassembling Coupling Installed 
Runout was Checked 
 
10 
-This is Not Normally Done but Can Provide Important 
Information 
-Sometimes Difficult to Turn Over Machines 
-Many Ways to Overcome 
-Jog Motor (If Motor) 
-Use Turning Gear 
-Even Overhead Crane can be Used with Long Strap  
Wound Around Coupling or Shaft 
 
 
   
Run Out Should Typically be No Greater Than  
0.002” TIR at Flange Connections 
 
0.001” TIR at Hub Bodies 
Field Installed Run Out Check of 
Coupling Confirm a Problem 
 
11 
0.45 mm TIR 
0.20 mm 
TIR 
0.23mm 
TIR 
0.15mm 
TIR 
0.05 mm 
TIR 
0.03 mm 
TIR 
0.00 mm 
TIR 
Next, Previously Installed Coupling was 
Checked to Reinstall to Get Train Running 
 
12 
Run Outs O K 
Minor Issue w/ Length 
Capacity of Available 
Balance Machine 
Is the Available Field 
Repair Equipment 
 Acceptable? 
Checked on 
Calibrated Acceptable 
Balance Machine 
Then Dye Penetrant Checks of 
Diaphragms 
 
13 
Important Check On Used Diaphragms After Handling 
No Indications, Cracks, or Unacceptable Scratches 
Install Replacement Coupling Center 
Section 
 o Use Existing Turbine Adapter and 
Compressor Rigid from the First 
Coupling 
o Do a High Spot Check 
o Line Up High Spots of Male and 
Female Pilots 
o Remember that “High Spot” 
Definition is the Spot Furthest from 
the Center of Rotation 
 
 
 
 
 
 
 
This Guarantees the Best Balance Condition  
From a Concentricity to Center of Rotation  
Perspective 
Installed Replacement Coupling Run 
Out Checks 
 
15 
0.15 mm 
TIR 
0.10 mm 
TIR 
0.10 mm 
TIR 
0.05 mm 
TIR 
0.10 mm 
TIR 
0.03 mm 
TIR 
0.00 mm 
TIR 
0.10 mm 
TIR 
No Problem 
Runout Checks are Good and New 
Vibration Plots are Good 
 
16 
Proof: Vibration Plots are Good 
 
17 
Before and After 
Proof: Vibration Plots are Good 
 
18 
Next - Check of Problem Coupling 
 
19 
OK Too !! 
 
What is the 
Problem ?? 
What Could Have Been the Problem? 
20 
-Installed Run Outs at Positions Other Than Spacer  - OK 
-Mounting Flange and Adapter - OK 
-Hub Mounting Surfaces - OK 
-Then we remembered a comment about the difficulty of 
connecting to the Turbine flange  
-Re-look at Coupling/Turbine Mounting Surfaces 
 
Aha !! ; Clear Evidence of a Mounting 
Problem   
 
21 
Connecting Flanges were not Contacting and were out of 
Square Even Though Bolts Were Tightened Properly 
This out of Square caused the Mounted Center Flange High Runout 
Correct Fit-Up  
Recommendations 
 
22 
-Improve Existing Turbine Flange Connection for Ease of Assembly 
-Reduce Width of Guard Pilot 
-Reduce Amount of Interference at Pilot 
 
-Improve Overall Flange Connection Design 
-Use Standard Design Bolting 
 
-Improve Procedure 
-Leave Coupling Adapter in Place 
 
-Handle Diaphragms “Gingerly” 
Lessons Learned 
23 
-If Coupling Balance is Suspected, Check Installed Run-outs 
-If Replacing Non-Match Marked Components, Find “High  
Spots” and Match Them 
-Dye Check or MPI used and/or handled Coupling 
Diaphragms 
-Carefully Handle any Diaphragm  
- Do not lay face down on rough surface 
-Understand Installation Potential Difficulties When 
Designing Coupling  
 
 
   


Solving a Coupling Unbalance Problem in the Field

Texas A&amp;M Repository

Case Study  1 Solving a Coupling Unbalance Problem in the Field  Author:  Quraisy A. Shatri P.E.   Maintenance Superintendent – Machinery and Reliability   RasGas Company Limited   PO Box 24200, Doha, State of Qatar   Tel: (+974) 4492 3209   Mobile: (+974) 5583 8706   e-mail: qashatri@rasgas.com.qa  Author: Joseph P. (Joe) Corcoran   Manager, Global Services and Training   Kop-Flex Emerson Industrial Automation   7565 Harmans Road   Hanover, MD USA 21076   Tel: (+1) 410 787 8522   Mobile (+1) 443 831 1811   e-mail: j.corcoran@emerson.com Abstract  2 When a large (3.4 meters long) diaphragm coupling was suspected of causing excessive (120 microns p-p) 1X unbalance vibration between a 90+ Megawatt Gas Turbine and a Propane Compressor in an LNG plant, there was not time to ship the coupling back to a distant factory or service center for troubleshooting. Simple field diagnostic techniques were used to discover the problem, which then led to a field correction and repair so that the unit was able to be quickly restarted with minimum downtime. Process Background  3  In an LNG Plant, After all impurities such as Hg, H2S,H2O are removed in upstream units, sweet feed gas enters the gas chilling & liquefaction unit.  Two major pieces of equipment in this unit are the Scrub Column (SC) & the APCI Main Cryogenic Heat Exchanger  SC is a distillation column, steam re-boiled, to remove C5+ and provide streams for producing refrigerants (C2 and C3).  OH gas of the SC goes in to MCHE mid-bundle for liquefaction. The medium to cool is MR or Multi Component Refrigerant (MCR - C1+C2+C3+N2) Process Background  4  The MR circuit is cooled (and partially liquefied) by Propane. The Propane refrigeration circuit is also tasked to cool Feed Gas in the gas chilling section, De-C2 condenser and the reinjection stream from the refrigerant preparation unit.  The two (2) main refrigeration compression circuits – MR & Propane – are illustrated in the next page.   If either of these 2 strings are down, there’ll be no production from the gas chilling & liquefaction unit, and no LNG is produced. Simplified schematics 5  6 HM  Comp 56 MB  Comp 88 M Comp 7 EA Gas Turbine Main Refrigeration Compression Strings PROPANE MR #5.5 MSMH-J, Diaphragm coupling rated power≅ 92MW; 3,352.8 mm (Nominal cold shaft separation) HM  Comp 56 MB  Comp 60 M Comp 7EA Gas Turbine RCA  The string comprises of 4 coupled rotors: 7EA GT rotor, 88M and 56MB compressor rotors – HM rotor    Bearings: 3 radial bearings for a single shaft 7EA rotor, 2 radial bearings each of 88M and 56MB rotors, and 2 radial bearings of the HM.  Only DE radial vibration of the 88M rotor was extremely high – increasing rapidly with increasing speed / load; other bearings-vibe readings were normal.  Refurbished 7EA rotor and upgraded (new) 88M rotor were installed during the turn-around. The GT operating data indicated “perfect”; factory dimensional and high-speed balance data of the 88M rotor and as-installed records indicated everything was acceptable.  Strong suspect was load coupling #5.5 MSMH-J  based on possible coupling imbalance as seen via 88M DE vibe plots: new spools & adapter but old coupling-hub were assembled; wrong pre-stretch gap; and poor run-out. Coupling components individual balance records observed to be “perfect”.   On attending the unit, installed couplings run-out checks clearly showed the coupling straightness was grossly out-of- straightness (0.018”) in mid-span point.   Plans to index, change-out of coupling hub was cancelled; previously-installed spacers were re-installed after all necessary checks were done and certified acceptable. Run-out checks of the installed coupling was then checked and certified acceptable for services.   The whole string was started-up, sent in to normal operations satisfactorily.  High Vibration – Coupling Suspected  8 High Vibration – Coupling Suspected  9 Before Disassembling Coupling Installed Runout was Checked  10 -This is Not Normally Done but Can Provide Important Information -Sometimes Difficult to Turn Over Machines -Many Ways to Overcome -Jog Motor (If Motor) -Use Turning Gear -Even Overhead Crane can be Used with Long Strap  Wound Around Coupling or Shaft      Run Out Should Typically be No Greater Than  0.002” TIR at Flange Connections  0.001” TIR at Hub Bodies Field Installed Run Out Check of Coupling Confirm a Problem  11 0.45 mm TIR 0.20 mm TIR 0.23mm TIR 0.15mm TIR 0.05 mm TIR 0.03 mm TIR 0.00 mm TIR Next, Previously Installed Coupling was Checked to Reinstall to Get Train Running  12 Run Outs O K Minor Issue w/ Length Capacity of Available Balance Machine Is the Available Field Repair Equipment  Acceptable? Checked on Calibrated Acceptable Balance Machine Then Dye Penetrant Checks of Diaphragms  13 Important Check On Used Diaphragms After Handling No Indications, Cracks, or Unacceptable Scratches Install Replacement Coupling Center Section  o Use Existing Turbine Adapter and Compressor Rigid from the First Coupling o Do a High Spot Check o Line Up High Spots of Male and Female Pilots o Remember that “High Spot” Definition is the Spot Furthest from the Center of Rotation        This Guarantees the Best Balance Condition  From a Concentricity to Center of Rotation  Perspective Installed Replacement Coupling Run Out Checks  15 0.15 mm TIR 0.10 mm TIR 0.10 mm TIR 0.05 mm TIR 0.10 mm TIR 0.03 mm TIR 0.00 mm TIR 0.10 mm TIR No Problem Runout Checks are Good and New Vibration Plots are Good  16 Proof: Vibration Plots are Good  17 Before and After Proof: Vibration Plots are Good  18 Next - Check of Problem Coupling  19 OK Too !!  What is the Problem ?? What Could Have Been the Problem? 20 -Installed Run Outs at Positions Other Than Spacer  - OK -Mounting Flange and Adapter - OK -Hub Mounting Surfaces - OK -Then we remembered a comment about the difficulty of connecting to the Turbine flange  -Re-look at Coupling/Turbine Mounting Surfaces  Aha !! ; Clear Evidence of a Mounting Problem    21 Connecting Flanges were not Contacting and were out of Square Even Though Bolts Were Tightened Properly This out of Square caused the Mounted Center Flange High Runout Correct Fit-Up  Recommendations  22 -Improve Existing Turbine Flange Connection for Ease of Assembly -Reduce Width of Guard Pilot -Reduce Amount of Interference at Pilot  -Improve Overall Flange Connection Design -Use Standard Design Bolting  -Improve Procedure -Leave Coupling Adapter in Place  -Handle Diaphragms “Gingerly” Lessons Learned 23 -If Coupling Balance is Suspected, Check Installed Run-outs -If Replacing Non-Match Marked Components, Find “High  Spots” and Match Them -Dye Check or MPI used and/or handled Coupling Diaphragms -Carefully Handle any Diaphragm  - Do not lay face down on rough surface -Understand Installation Potential Difficulties When Designing Coupling       

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Solving a Coupling Unbalance Problem in the Field

Abstract

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Texas A&M University

Texas A&M Repository

Solving a Coupling Unbalance Problem in the Field

Abstract

Similar works

Full text

Available Versions

Texas A&M University

Texas A&amp;M Repository

Texas A&M Repository