Best Practice

SABP-G-013 8 October 2007

Rotating Equipment Piping Strain Diagnosis
Document Responsibility: Pumps, Seals and Mixers Standards Committee

Saudi Aramco DeskTop Standards

Table of Contents

1 Introduction......................................................... 2
2 References......................................................... 2
3 Definitions........................................................... 3
4 Piping Strain Vibration Symptoms...................... 4
5 Diagnostic Flowchart.......................................... 4

Appendix A – Cold Service Machine Flowchart..... 13

Appendix B – Hot Service Machine Flowchart....... 14
Appendix C – Runout Categories.......................... 15

Previous Issue: New Next Planned Update: TBD

Page 1 of 15
Primary contact: Hussain, Khaleel Ma'Atug on 966-3-8730311

Copyright©Saudi Aramco 2007. All rights reserved.

Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

1 Introduction

1.1 Purpose

In recent years, piping strain has been one of the major causes of premature
failure in rotating machinery. According to a recent literature survey of 2000
industries across the US and Canada 60% of pump failures were attributed to
some form of misalignment which in many cases was caused by piping exerted
strain. This condition is normally a result of improper piping connection that
can lead to severe equipment coupling misalignment. The purpose of this best
practice is to provide Saudi Aramco engineers clear guidelines in diagnosing,
verifying and correcting piping strain condition.

1.2 Scope

The scope of this Best Practice is to provide field engineers with general
diagnostic guidelines to identify and remedy machinery misalignment caused by
piping strain.

1.3 Disclaimer

The use of this Best Practice does not relieve the engineer from his
responsibility or duty to confirm and verify the accuracy of any information
presented herein. The use of this information or material does not guarantee
results that will satisfy any applicable requirements of Saudi Aramco Standards.
CSD assumes no responsibility or liability whatsoever for the misuse of the
information in this document. This Best practice is intended as guidelines and
shall not be considered as replacement for the Mandatory Saudi Aramco
Engineering Requirements. Saudi Aramco® is a registered trademark of the
Saudi Arabian Oil Company. Copyright, Saudi Aramco, 2007.

1.4 Conflicts with Mandatory Standards

In the event of a conflict between this Best Practice and other Mandatory Saudi
Aramco Engineering Requirement, the Mandatory Saudi Aramco Engineering
Requirement shall govern.

2 References

This Best Practice is based on the latest edition of the references below, unless
otherwise noted.

Page 2 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

2.1 Saudi Aramco References

Saudi Aramco Engineering Standards

SAES-G-005 Centrifugal Pumps
SAES-K-402 Centrifugal Compressors
SAES-K-501 Steam Turbines
SAES-L-350 Construction of Plant Piping

2.2 Industry Codes and Standards

American Petroleum Institute

API STD 610 Centrifugal Pumps for Petrochemical and Natural
Gas Industries
API STD 611 General Purpose Steam Turbines
API STD 612 Steam Turbine Application
API STD 617 Axial and Centrifugal Compressors
API RP 686 Recommended Practices for Machinery
Installation and Design

National Electrical Manufacturers Association

NEMA SM 23 Steam Turbines for Mechanical Drive Service

2.3 Other References

Pitorowski, J., Shaft Alignment Handbook, 2nd Edition, Marcel Dekker, 1995

3 Definitions

Piping Strain: Piping strain is a condition caused by excessive forces on equipment

nozzles, which could result in misalignment leading to excessive vibration. Changes in
coupling alignment in excess of 0.002 inches during tigthening of flange bolting
indicate excessive nozzle loads.

Cold Service Machine: Equipment where there are minimal changes in alignment
conditions between shutdown and full operation, i.e., thermal effects are negligible.

Hot Service Machine: Equipment where alignment can change during operation.
Movement of casing and/or casing distortion greater than 0.005 inches measured on the
bearing housing during operating condition shall be considered "Hot Service."

Page 3 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

4 Piping Strain Vibration Symptoms

There are no easy ways to determine if rotating machinery is misaligned due to piping
strain. However, there are vibration symptoms that can indicate the existence of a
piping strain condition. The following are misalignment related vibration symptoms
which could be caused by piping strain. Misalignment can be noted in data collected
from machine casing-mounted seismic transducers (absolute measurement) or from
shaft relative readings taken using proximity probes (relative movement).

The main misalignment symptoms observed from casing vibration readings are:
1. High 1x or 2x running speed frequency component.
2. High axial vibration levels.
3. 180 degrees phase shift across the coupling.

Likewise, the main misalignment symptoms observed from shaft relative readings are:
1. Preloaded orbit on driver and driven units.
2. Shaft centerlines indicating abnormal shaft movements.
3. Probe readings normally sensitive to ambient or operating medium temperature.
4. Bode plot showing different startup and shutdown responses.
5. Vibration levels more sensitive to load changes.

Other possible secondary mechanical effects exhibit the following symptoms:

¾ Premature bearing, seal, shaft, or coupling failure
¾ High bearing housing or oil temperature
¾ Loose foundation bolts
¾ Coupling wear, lock-up or failure
¾ Bent shaft or shaft failure

5 Diagnostic Flowchart

If a sufficient number of the above vibration symptoms are found to be present, the
attached diagnostic flowcharts may be used to investigate the problem. (See Appendix
A and B.) These charts describe a systematic method of identifying a piping strain
condition in rotating machinery. The diagnosis flowchart will cover two cases that are
common to most machines. The first is for machines with cold service fluid and the
other is for machines with hot service fluid.
Note: In cases where both the driver and driven equipment are connected to external piping
such as: a steam turbine driving a pump, the above investigative procedure will first be

Page 4 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

performed on the machine with the most apparent vibration symptoms (e.g., turbine
first). If the source of piping strain is not identified, then apply the same procedure to
the other machine (i.e., in this example, the pump).

5.1 Cold Service Flowchart

This chart may be followed in diagnosing piping strain condition in machines

that operate with cold service fluids, i.e., where minimal alignment changes are
expected when equipment is in operation. This procedure assumes that the
piping strain condition can be measured when the machine is not in operation
and thermal effects are negligible.

Follow the flowchart "OK" path when the checks performed agree and follow
the "NOT OK" path when the checks performed do not agree.

The following is a description of checks required for the relevant decision block
in the flowcharts presented in Appendices A and B:

5.1.1 Review Installation Data

Review machine installation and piping connection procedures and

confirm that they have been applied in accordance with API RP 686
Section 4.8.

5.1.2 Visual Inspection

Perform a visual inspection on the machine and the connected piping

focusing on the following:

¾ Piping Support Condition

Piping supports are utilized to reduce and protect equipment nozzles

from being overloaded. There are different methods of preventing
nozzle overload, controlling pipe movements and protecting
associated rotating equipment: e.g., anchors, restraints, guides and
limit stops.
1. Piping support condition shall be inspected to confirm that all
associated piping is adequately supported and in full contact
with the supports. Visual inspection of shimming condition,
i.e., poor pipe contact and corrosion shall be documented.
2. Anchors, guides, limit stops and clamps shall permit the piping
to expand and contract freely away from anchored or guided
points. These elements shall be in accordance with piping
design and installation practices.

Page 5 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

¾ Spring Support Condition

Spring supports and hangers normally are designed to exert a

supporting force at the point of attachment to the pipe. Make sure
that variable springs are operating within the specified load range.
Physical deterioration of supports, evidence of corrosion, and cracks
shall be noted.

¾ Expansion Joint Condition

Expansion joints and bellows shall be inspected for functionality and

any type of physical damage such as damaged/corroded control
guides. Make sure that piping expansion joints are moving freely to
accept any thermally induced movements. Note expansion joints are
usually designed to allow movement in one direction only, typically
along the axis of the bellows. Radial or rotary (twisting) movement
should not be seen and should be noted if present.

¾ Foundation and Feet Shims Condition

The machine concrete foundation shall be inspected for cracks and

any type of deterioration that could affect its supporting
functionality. In addition, the machine feet shall be inspected for
excessive shimming, corroded shims, reduced bolting integrity and
gaps between the shims and machine feet.

¾ Comparison of Piping Configuration with Similar Machines

A comparison shall be made between the piping configuration of the

subject machine and similar machines in the facility. Any significant
differences in the piping configuration shall be highlighted and
investigated.

¾ Inspect Machine Bearings

In machines where the bearings are accessible and easy to open, the
bearings and seals shall be inspected for any signs of rubs or unusual
wear patterns.

All the findings of the visual inspection shall be recorded and

corrected before proceeding to the next stage of the investigation.

5.1.3 Preliminary Mechanical Checks

After performing visual inspection and necessary corrections,

preliminary mechanical checks, such as external alignment condition,

Page 6 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

shall be performed to ensure that the cold alignment target figures have
been met. The external alignment check shall include the examination,
and full recording/reporting, of the following:

¾ Check Mechanical Runout Condition

Check eccentricity of the outer surface of shaft or components rigidly

attached to the shaft with respect to the shaft centerline of rotation.
Check also coupling face runout to quantify the amount of
perpendicularity to the shaft. Appendix C shows how to check for
the different types of runout problems.

¾ Check Machine Alignment

Use dial indicators or a laser alignment system to confirm that

machine alignment is per manufacturer specifications. Manufacturer
target figures should be met and readings shall be recorded.

¾ Coupling Condition

Inspect the coupling for any type of damage. Disc couplings should
be inspected for excessive flexible element distortion or cracking.
Gear type couplings shall be inspected for lockup in addition to
verifying proper lubrication. Prior to reinstallation of the coupling,
confirm that either:
a) Each coupling bolt is returned to it's original location or
b) Ensure that all bolts are weight-balanced so they can fit in any
location without impacting the balance of the machines.

Use a new set of matched bolts if any of the bolts are damaged or
missing. Check the coupling register locations to ensure compliance
with standard requirements.

¾ Bent Shaft

Check for bent shaft using dial indicator if there is indication, from
proximity probe measurements, of high 1x runout.

¾ Blue Check if Practical

A blue check on the bearing shall be performed when practical, i.e.,

when the shaft can be rotated manually and the bearing is accessible.
The blue check could provide additional information regarding
machine internal alignment condition.

Page 7 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

¾ Bearing Wear Pattern

Bearings shall be inspected for unusual wear patterns which could be

an indication of internal misalignment may have been caused by
piping strain.

¾ Internal Rubs in Accessible Seals

Machine accessible labyrinth or carbon seals or rotating elements

shall be inspected for any signs of rubbing.

5.1.4 Check Piping Strain

In this part of the flow chart the following procedure shall be used to
verify the existence of a piping strain condition. This procedure is an
extended version of the procedure given in API RP 686 Section 4.8.
However, the person performing the piping stain check is urged to refer
to API RP 686 since it is the source document and contains specific
information not provided here.

¾ The basic method of verifying pipe strain consists of unbolting the

piping from the machine flanges while measuring the deflection of
the machine shaft with dial indicators. This is done with the spring
hangers and spring support locked in the cold position. The
indicators could be supported on the base plate or the coupled
equipment coupling hub. The following steps may be followed
during the piping strain check:
1. Take alignment readings before disconnecting the piping.
2. Disconnect the discharge line and record vertical and horizontal
movements at shaft end.
3. Disconnect the suction line and record vertical and horizontal
movements at shaft end.
4. Take alignment readings again to measure the effect of suction
and discharge piping on the alignment condition.
5. Compare alignment with machine original/vendor supplied
verified target figures.
6. Check the flange fit-up on the suction and discharge nozzles
and verify that the bolt hole offsets, flange gap and flange
parallelism is within the requirements of SAES-L-350.
Note: Corrections of any discrepancies may require flange removal
and adjustment.

Page 8 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

The maximum shaft movement in either vertical or horizontal directions

should be 0.002 inches. If the shaft movement is greater than 0.002 inch,
then a piping strain condition exists and needs to be corrected. The
piping flange shall be loosened from the machine and the correction
procedure detailed in the section 5.1.6 below shall be followed.

In addition to checking the piping strain exerted by suction and discharge

piping on the machine, piping strain exerted by any accessory piping,
such as lube oil drain pipes, shall also be considered where it is felt that
its influence could be significant. The maximum shaft displacement due
to combined suction, discharge, and accessory piping should not exceed
0.002 inches.

5.1.5 Soft-foot Check

A soft-foot check shall also be performed to confirm that the machine is

leveled on its base and no casing distortion is caused by the unevenness
of the feet or the base (API RP 686 Section 5.4.4). Soft-foot can be
checked by measuring the feet vertical movement when they are
unbolted one at a time using dial indicators. Any movement greater than
0.002 inch is considered unacceptable and shall be corrected by either
shimming or machining. Shim requirements are outlined in API RP 686
section 5.4.2.

5.1.6 Piping Strain Correction Procedure

¾ Review the piping system design layout.

¾ Inspect all supports. Highlight and correct the supports that are not
active.
¾ Inspect the pipe support foundation. Report and correct settlement in
the support foundation.
¾ Inspect all spring supports. Review the spring support data sheet if
available.
¾ Check the required load (hot load, cold load) on the spring supports.
¾ Inspect all expansion bellows. Report any damage or deformations.
¾ Review the required equipment loads.
¾ Review the piping stress analysis and the loads on the equipment.
¾ If required, conduct updated piping stress analysis.
¾ Make the required piping modification to reduce the load on the
equipment.

Page 9 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

5.1.7 Further Investigation

If the vibration level of the machine remains unacceptable after

following the above diagnostic procedure, then the problem will most
likely be related to the following:

1. Piping Strain Procedure Implementation

The implemented piping strain correction procedure shall be

reviewed to verify that it has been applied as per the correction
procedure described above.

2. Machine Internal Misalignment

Verify machine internal alignment by performing a concentricity

check of the complete machine. Particular attention should be paid
to bearing housing to casing fits and concentricity of bearings and
seals within the casing. It is important to check both halves of a
horizontally split casing and also the fit of the upper and lower half
to each other. Any misalignment may require machining to
correct.

3. Distorted Machine Casing

The machine casing shall be inspected to verify that there is no

distortion which would cause the machine internals to be non-
concentric.

4. Defective Dowels or Bolts

Machine components such as bearing-housings may become

misaligned with the main casing due to defective dowels/bolts.
Any defective dowels or bolts shall be replaced before any restart
attempt.

5.2 Hot Condition Flowchart

For machines in hot service, a procedure similar to that above shall be followed.
However, it is required to measure the machine movement caused by thermal
effects, covering the period from cold, warm-up and the normal operating
condition. In this case, it is assumed that piping strain cannot be measured when
the machine is down, i.e., the thermal effects due to the hot service will
introduce piping strain as the machine reaches thermal equilibrium at operating
condition.

Page 10 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

Note: Flange alignment must still meet the requirements of SAES-L-350 in the cold
condition and must be corrected if required.

- Measure Machine Movement

There are many methods in measuring machine movement and the decision
on which method to use depends on what tools are available and what is
practical in a given situation.

¾ Dial Indicators

Dial indicators can be setup to measure machine absolute movement

referenced to a fixed structure, i.e., scaffolding or machine base. Using
this method of measurement, fluctuations in the readings due to vibration
and errors due to movement of the reference structure must be taken into
consideration.

¾ Proximity Probes

Proximity probes can also be used to measure machine casing absolute

movement over time and the data can be trended using an ADRE system.
To use this method, it is normally required to prepare a custom made
fixture for the probes to ensure a rigid and stable base.

¾ Other Methods

Laser alignment and optical systems can also be used to measure either
machine-to-machine relative movement or machine casing absolute
movement.

Revision Summary
8 October 2007 New Saudi Aramco Best Practice.

Page 11 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

Acknowledgement

CSD acknowledge the following engineers for their support and active participation in
producing this best practice:

1. K. M. Al Hussain, Vibration Specialist

2. I. Redmond, Vibration Specialist

3. S. A. Al Dossary, Vibration Engineer

4. E. W. Brown, Rotating Equipment Consultant

5. N. I. Al Nasri, Piping Specialist

6. E. Perez, Rotating Equipment Specialist

7. J. P. Abutas, Engineering Technician

Page 12 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

Appendix A – Cold Service Machine Flowchart

COLD CONDITION
Misalignment with
Indication of piping strain

Review Installation Procedure

Physical Check and Correction

Visual Inspection NOT OK 1-Soft foot condition
2-Piping support functionality

OK

Preliminary Correct Faulty

NOT OK
Mechanical Checks Mechanical Condition

Run Machine

OK

NOT OK Check Vibration

END OK NOT OK Check Piping Strain

OK END

Correct Piping OK
Check Vibration Run Machine
Strain

Further Investigation
NOT OK
required

Page 13 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

Appendix B – Hot Service Machine Flowchart

HOT CONDITION
Misalignment with
Indication of piping strain

Review Installation Procedure

Physical Check and Correction

OK Visual Inspection NOT OK 1-Soft foot condition
2-Piping support functionality

Correct Faulty
Preliminary
NOT OK Mechanical Run Machine
Mechanical Checks
Condition

Measure Machine
OK NOT OK Check Vibration
Movement

OK
OK

Correct Piping
END OK Check Vibration Run Machine NOT OK Check Piping Strain END
Strain

NOT OK

Further Investigation
OK
required

Page 14 of 15
Document Responsibility: Pumps, Seals and Mixers SABP-G-013
Issue Date: 8 October 2007
Next Planned Update: TBD Rotating Equipment Piping Strain Diagnosis

Appendix C – Runout Categories

Runout problems usually fall into one of these three categories:

6
110 0 10
6 100
90
20
30
40
110 0 10 80
100 20 70 60 50

0 90
80
70 60 50
40
30

110 0 10
100 20
90 30
80 40
70 60 50

Coupling hub
bored off-center

11
7 110 0 10

2 100
110 0 10
20
100
90
80
20

40
30

110 0 10 90 30
70 60 50
100 20 80 40
90 30 70 60 50
80 40
70 60 50

Bent shaft

4
2 100
110 0 10
20
110 0 10 90 30
100 20
40

0 30 80
90 70 60 50
80 40
70 60 50
110 0 10
100 20
90 30
80 40
70 60 50

Coupling hub
“skew” bored

Page 15 of 15