Best Practice

SABP-G-007 30 March 2005

Packaged, Integrally Geared Centrifugal Air Compressor
Dynamic Analysis Factory Acceptance Test
Rotating Equipment Standards Committee Members
Al-Odan, N.M., Chairman
Al-Hashim, I.G.
Al-Hotan, K.Z.
Al-Swailim, F.K.
Beckenbach, J.W.
Brown, E.W.
Kawthar Ali, M.H.
Leary, B.
Nguyen, L.V.
Sabri, H.A.
Salamah, M.M.
Samaha, M.E.
Ward, R.P.

Saudi Aramco Best Practice

Table of Contents

1 Introduction.................................................... 2
2 References.................................................... 2
3 General.......................................................... 3
4 Definitions...................................................... 3
5 Vibration Detectors........................................ 4
6 Shop Verification of Unbalanced
Response Analysis .…..................……. 4
7 Tests Procedure............................................ 5
8 FAT Acceptance Criteria............................... 6

Previous Issue: New Next Planned Update: 1 April, 2010

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Primary contact: Khaleel M. Al-Hussain on 873-0311

Copyright©Saudi Aramco 2009. All rights reserved.

Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

1 Introduction

1.1 Purpose

The purpose of this Practice is to establish guidelines in reviewing the dynamic

analysis of packaged, integrally geared centrifugal air compressors during
Factory Acceptance Test (FAT).

1.2 Scope

This Best Practice gives general guidelines for reviewing vibration

instrumentation requirements, test procedure and acceptance limits during the
Factory Acceptance Test and does not include performance test criteria.

1.3 Disclaimer

This Best Practice is being provided for the general guidance and benefit of
Saudi Aramco engineers attending integrally geared centrifugal air compressors
Factory Acceptance Test (FAT). The use of this Best Practice during factory
acceptance test, however, does not relieve the manufacturer from his
responsibility or duty to confirm or to verify the accuracy of any information
presented or from his contractual liability to perform an accurate FAT that
conforms to Mandatory Saudi Aramco Engineering Requirements. The use of
the information or material contained herein will not guarantee that the resulting
product satisfies the applicable requirements of Saudi Aramco Standards. Saudi
Aramco assumes no responsibility or liability whatsoever for any reliance on the
information presented herein or for FAT performed by manufacturer in
accordance with this Best Practice document. Moreover, this Best practice is
intended only to provide guidelines for Saudi Aramco engineers attending the
Factory Acceptance Test and shall not be considered as a replacement for the
Mandatory Saudi Aramco Engineering Requirements. Saudi Aramco® is a
registered trademark of the Saudi Arabian Oil Company. Copyright, Saudi
Aramco, 2004.

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 below referenced standards:

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

2.1 Saudi Aramco References

Saudi Aramco Materials System Specifications

31-SAMSS-006 Packaged, Integrally Geared Centrifugal
Air Compressors (30 July 2003)
34-SAMSS-625 Machinery Protection Systems (30 June 2002)

2.2 Industry Codes and Standards

American Petroleum Institute (API)

API STD 670 Machinery Protection Systems, 4th Edition
API STD 672 Packaged, Integrally Geared Centrifugal
Air Compressors for Petroleum, Chemical and
Gas Services Industries, 3rd Edition

3 General

 This best practice gives general guidelines for the vibration instrumentation
requirements, test procedure and acceptable limits during packaged, integrally
geared centrifugal air compressors factory acceptance test. The attendee should
review the rotordynamic analysis prior the test.

 At least 6 weeks before the first scheduled running test, the vendor shall submit to
the purchaser, for review and comment, detailed procedures for the mechanical
running test and all specified running optional tests, including acceptance criteria for
all monitored parameters. The oil parameters described in API STD 672 paragraph
4.3.4.1.4 shall be included in these test procedures. (API STD 672 / P 4.3.1.2)

 The vendor shall notify the purchaser not less than five working days before the date
the equipment will be ready for testing. If the testing is rescheduled, the vendor shall
notify the purchaser not less than five working days before the new test date (API
STD 672 / P 4.3.1.3). However, it is suggested that the vendor send notification six
weeks prior any witness test.

4 Definitions

Factory Acceptance Test (FAT): A performance/mechnical running test conducted at

the factory to check the integrity of the machine.

Acceptance Vibration Level: This is the vibration level at which a machine can run
indefinitely without inducing vibration related maintenance.

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

Rated operating point: The point at which the vendor compares the tested rated
operating point to certify that the performance is within the tolerances stated in this
standard. (API STD 672 / P 1.4.20)

Rated speed: The speed corresponding to the requirements of the rated operating point.
(API STD 672/ P 1.4.21)

Trip speed (revolutions per minute): The speed at which the independent emergency
overspeed device operates to shut down a variable-speed prime mover. (API STD 672 /
P 1.4.28)

5 Vibration Detectors

Each high-speed rotor and, when specified, the driver bearings, shall be provided with a
vibration-monitoring system consisting of the following: (a) single radially oriented
noncontacting shaft vibration sensing probe, (b) an oscillator-demodulator, and (c) a
readout instrument. For single-impeller rotors, the probe shall be located at the bearing
adjacent to the impeller. The vendor shall include with his proposal a statement listing
whether x and y radial probes can be mounted adjacent to each impeller. The
monitoring instrument shall be mounted in the instrument and control panel. (API STD
672 / P 3.4.4.6.1)

The vibration monitoring system, to the extent that it is required by 31-SAMSS-006

specification, shall be supplied in accordance with 34-SAMSS-625. (31-SAMSS-006 /
P 3.4.4.6.3)

6 Shop Verification of Unbalanced Response Analysis

6.1 Shop verification of unbalanced response analysis shall be performed as part of

the mechanical running test and the results shall be used to verify the analytical
model. The method to conduct the shop verification test is described in API
STD 672 Appendix C section C.3. (API STD 672/P C.3.1).

6.2 The results of the verification test shall be compared with those from the
original analytical model. The vendor shall correct the model if it fails to meet
any of the following criteria (API STD 672/P C.3.2.2):
a) The actual critical speeds shall not deviate from the predicted speeds by
more than ±5%.
b) The predicted amplification factors shall not deviate from the actual test-
stand values by more than ± 20%.
c) The actual response peak amplitudes, including those are critically
damped, shall be within ± 50% of the predicted amplitudes.

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

6.3 When the test data does not meet the requirements of 672 Appendix C section
C.3, additional more stringent testing is required as per API STD 672, paragraph
C.3.4. The purpose of this additional testing is to determine on the test stand
that the machine will operate successfully.

7 Tests Procedure

7.1 Calibration records for flow, pressure, temperature, and vibration-measuring

devices utilized during the test shall be submitted to the purchaser’s
representative for review. If unwitnessed, certified calibration records shall be
included with the test logs and forwarded to the purchaser. (API STD 672 / P
4.3.4.2.3)

7.2 During the combined mechanical and performance test, compressor and contract
driver vibration levels shall be recorded at every performance data point (API
STD 672 / P 4.3.4.3d)

7.3 The combined total electrical and mechanical runout is presented in Table-1 (for
more detail refer to API STD 672 paragraph 2.2.5.1.3):

Table-1: Allowable Total Runout

Probes Location Applicable Standard Allowable Total Runout (TR)

whichever is greater
 TR ≤ 0.25 x maximum allowed pk-pk
API STD 672 vibration amplitude
Radial
(Sec. 2.2.5.1.3)
 TR ≤ 0.25 mils ( 6 micrometers) pk-pk

Note: If the vendor can demonstrate that electrical or mechanical runout is present,
the demonstrated runout may be vectorially subtracted from the vibration
signal measured on the factory test, up to a maximum of 25% of the
allowable vibration level or 6 micrometers (0.25 mil), whichever is greater.
(API STD 672 / P 2.2.7.4.7)

7.4 Electrical and mechanical runout shall be determined and recorded by rolling the
rotor in V-blocks at the journal centerline while measuring runout with a non-
contacting vibration probe and a dial indicator at the centerline of the probe
location and one probe-tip diameter to either side. (API STD 672 / P 2.2.7.4.5)

7.5 The combined mechanical and performance test of the package, including the
lube oil system, bearings, seals and vibration monitoring system, shall be
conducted at rated operating speed for a continuous period of 4 hours. (API STD
672 / P 4.3.4.1)

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

7.6 A minimum of five test points shall be recorded, including surge, rated, and
maximum capacity. (API STD 672 / P 4.3.4.1.2)

8 FAT Acceptance Criteria

During the test, the measured vibration shall not exceed the limits in Table-2. Steps 1 to
3 below specify the FAT vibration values that need to be checked:

1. The peak-to-peak amplitude of unfiltered vibration in any plane, measured on the

shaft adjacent and relative to each radial bearing, at rated speed shall not exceed
the overall limit specified in Table-2. (API STD 672 /P 2.2.7.4.4)

2. While the equipment is operating at rated speed, sweeps shall be made for vibration
amplitudes at frequencies other than synchronous. As a minimum, these sweeps
shall cover a frequency from 0.25 times to 8 times the rated speed of the shaft being
observed. If the amplitude of any discrete, nonsynchronous vibration (other than
running speed) exceeds 20% of the allowable vibration as defined in 2.2.7.4.4, the
purchaser and the vendor shall mutually agree on requirements for any additional
testing and on the equipment’s suitability for shipment. (API STD 672 / P 4.3.4.1.5)

3. At any speed grater than the maximum continuous speed, up to and including the
trip speed of the driver, the vibration should not exceed 150% of the maximum
value recorded at the maximum continuous speed. (API STD 672 /P 2.2.7.4.4)

Table-2: Radial Vibration Limits for Centrifugal Compressor

Location of vibration Compressor Shaft

Measurement (adjacent to bearing)
Item

whichever is less
Overall ( unfiltered)  Au ≤ (7.74X106 /N)0.5 µm pk-pk
0.5
((12000/N) mils pk-pk)
(i) Vibration limits at
rated speed  Au ≤50 µm pk-pk
(2.0 mils pk-pk)
Discrete frequencies 20% of the above allowable overall limit
(other than N) Af ≤0.2 x Au

(ii) Vibration limits at any speed greater than the

rated speed, up to and including the trip
150 % of the recorded value at rated speed
speed

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Document Responsibility: Rotating Equipment SABP-G-007
Issue Date: 30 March 2005 Packaged, Integrally Geared Centrifugal Air Compressor
Next Planned Update: 1 April 2010 Dynamic Analysis Factory Acceptance Test

Where:
Au = unfiltered displacement determined by FFT.
Af = discrete frequencies, non-synchronous, displacement determined by FFT.
N = rotational speed (RPM).

Revision Summary
30 March 2005 New Saudi Aramco Best Practice.

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