Previous Issue: New Next Planned Update: TBD
Page 1 of 13 For additional information, contact: Saad H. Al-Dossary on 876-0132 or Mishal I. Al-Zughaibi on 876-0173
SABP-L-005
5 September 2009
Piping Vibration Measurements and Assessment
Document Responsibility: Consulting Services Department
Saudi Aramco DeskTop Standards
Table of Contents
1 Scope... 2
2 Conflicts and Deviations... 2
3 References... 2
4 Piping Vibration Introduction... 3
5 Piping Vibration Identification & Measurements.. 4
6 Piping Vibration Assessment... 6
Appendix-I - Vibration Severity Charts... 7
Appendix-II - Walk-Through Check List (Table-3)... 8
Appendix-III - Measurement Guidelines... 9
Appendix-IV - Vibration Measurements Example.... 10
1 Scope
1.1 The scope of this best practice is to establish an effective vibration measurement and assessment procedure for piping systems. This document provides guidance for identifying the measurement locations, recording important piping system information, providing setup details for the vibration instrument and
implementing effective assessment of the vibration severity.
1.2 In addition, this best practice will provide basic awareness of the most common vibration excitation sources and response mechanisms. This best practice is intended to be used by field engineers and vibration technicians.
2 Conflicts and Deviations
2.1 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.
2.2 Disclaimer
This Best Practice is being provided for the general guidance and benefit of Saudi Aramco engineers and operating facilities. The information or material contained here will not release the users from the responsibility of safeguarding and controlling their operations within Saudi Aramco established guidelines such as GI’s and engineering standards.
3 References
This Best Practice is based on the latest edition of the references below, unless otherwise noted.
1) Energy Institute. Guidelines for the Avoidance of Vibration Induced Fatigue
Failure in Process Pipework 2nd Edition, 2008
2) SAER-5659: Guidelines for Setting Acceptable, Alarm and Shutdown Vibration
Limits
3) SAES-L-310 “Design of Plant Piping”
4) MEX-621 “Piping Systems Vibration Course”
5) Wachel, J. & Smith, D. “Vibration Troubleshooting of Existing Piping Systems”.
Engineering Dynamics Incorporated, 1991
6) Wachel, J. & Morton, S. & Atkins, K. “Piping Vibration Analysis”. Engineering
7) ASME OM3 “ Requirements for Preoperational and Initial Start-Up Vibration Testing of Nuclear Power Plant Piping Systems”
4 Piping Vibration Introduction 4.1 Piping Vibration Types
Understanding piping vibration types is fundamental in order to have better approach for conducting reliable vibration measurements, accurate assessment and consequently effective solutions. Vibration in a piping system can be classified based on vibration frequencies and overall levels. Excitation frequency can be either discrete (single) or broad-band (multiple). Discrete frequencies appear in the vibration spectrum as single components, e.g., vane pass frequency emanating from pumps. Broad band vibration appears over a range of frequencies, e.g., pump cavitation. The following chart shows the interaction between vibration types:
Figure 1 – Types of Piping Vibration 4.2 Piping Vibration Sources
Piping system can be excited by many sources, most common sources are:
Mechanical Excitation: for example; due to machinery unbalance.
Pulsation Forces: for example; caused by reciprocating compressors and pumps, centrifugal compressors and pumps, rotating stall, vortex shedding, and vane pass frequency.
Gas Flow Excitation: for example; due to flow through control valves or orifices.
Liquid or 2-phase Flow Excitation: for example; due to cavitation, flashing or hammering.
4.2 Piping Vibration Consequences
Vibration in piping systems causes dynamic stresses, and when stress level is critical, fatigue crack initiation and/or propagation can occur. Fatigue cracking can lead to through thickness fracture and maybe rupture. In addition, piping vibration can result in fretting, which occurs when two surfaces in contact are being worn due to a cyclic relative motion.
5 Piping Vibration Identification & Measurements
When a piping vibration problem has been observed, the assigned engineer should conduct a site walk-through, and then the vibration group should take vibration measurements to evaluate the vibration severity.
5.1 Conduct Walk-Through to Identify and Document Problem Areas
Before conducting vibration measurements, it is important to walk-through the piping system that is suspected of having high vibration, it is recommended to walk down each vibrating pipe from the downstream equipment to the upstream equipment. During the walk through it is important to look for potential
cause(s) of vibration like control valve, rotating equipments, orifice … etc. Also, during the walk-thought, it is important to record information on general observations that can help in identifying the source of the problem, e.g., identifying the high vibration locations.
A comprehensive checklist can be found in Appendix II which should be completed during the walk-through.
5.2 Measurement Guidelines
The following are general measurement guidelines:
o Select suitable measurements locations and operating condition
o Document the measurement locations on a piping Isometric drawing or a sketch.
o Ensure the proper application of vibration transducer. Detailed measurement guidelines are outlined in Appendix-III.
For your reference, a comprehensive piping vibration example is available in Appendix-IV for clarification.
5.3 Vibration Instrument Setup Procedure
Vibration can be defined in terms of displacement, velocity and acceleration. Displacement and velocity are commonly used for piping vibration assessment. The amplitude of these parameters is frequency dependent. The following table shows the type of measurement required for the assessment based on vibration frequency:
Table 1 – Measurement Types
Frequency Range Discrete Broad Band
Low Frequency (< 300 Hz) Displacement and Velocity Velocity
Medium / High Frequency Velocity Velocity
A basic piping system vibration survey will require a (Fast Fourier Transform) FFT vibration analyzer with suitable accelerometer / velometer.
In all cases three sets of measurements are required: 1. Velocity-low frequency range.
2. Velocity-high frequency range. 3. Displacement-low frequency range.
Note: In exceptional cases where impulse or shock type vibration is observed, in
order to capture maximum vibration amplitude, velocity time waveform should also be recorded. The following table shows the instrument setup for the three sets of measurements:
Table 2 – Instrumentation Setup
Required Setting Measurement Parameter Velocity (Low Frequency) Velocity (High Frequency) Displacement (Integrated) Frequency Range 0-500 Hz 0-2000 Hz 0-300 Hz
Low Cutoff Frequency 1 Hz 5 Hz 1 Hz
Number of Lines 800 1600 800
Window Type Hanning Hanning Hanning
Number of Averages 10 10 10
Scale Type Linear Linear Linear
6 Piping Vibration Assessment
o Compare overall velocity measurements with allowable vibration levels stated in Section 5 of SAER-5659.
o For discrete frequencies below 300 Hz:
1. Plot the velocity values in the severity chart shown in Figure 2 of Appendix I. 2. Convert to displacement using the relationship below and plot the displacement
values in the severity chart shown in Figure 3 of Appendix I.
If any of the above vibration levels is above the acceptance criteria, or the frequency is higher than 300 Hz, CSD should be consulted. In such instances, the following
information should be prepared:
a. Piping safety instruction sheet “SIS”
b. Piping Isometric drawing or a sketch showing all measurements c. All supports types and locations
d. The completed walk-through check list (Appendix-II)
e. Summary table of the vibration points along with main frequencies and amplitude levels in velocity and displacement
f. Plots showing discrete-frequency amplitudes on the severity charts. (Appendix-I) g. Frequency spectrum plots for the high vibration locations
h. If available, provide the piping stress analysis electronic records.
Revision Summary
Appendix-I – Vibration Severity Charts
Figure 2 – Displacement Severity Chart
Appendix-II – Walk-Through Check List (Table-3) Gener a l In fo & Hi st o ry
Line Number: ___________________________________ Design Pressure: _________ Design Temperature: _______ Line Function(from, to): ___________________________________________ Service: __________________________ When was the piping vibration first observed? When was the piping system constructed?
Was there any operational change lately? Specify
Observation Description Yes No Comments
Vib ra tio n Ty p
e Can the vibration be seen?
Is the vibration steady or intermittent?
Is there any noise associated with the vibration?
Does the vibration increase at certain operation conditions?
Is there any sign of weeping/leaking on piping branch connections?
De
sig
n
Is there another identical piping layout in the same plant? If Yes, is it vibrating also?
Was there any piping/equipment modification on this system lately? Specify Is the piping system in compliance with SAES-L-310 section 20 “ Vibration consideration” Ro ta tin g Eq
. Is there a rotating equipment near the vibrating system, if yes, then identify the
following:
1. Rotating equipment type ( centrifugal pump, reciprocating pump, centrifugal compressor, reciprocating compressor, steam turbine … etc) 2. The running condition ( pressure, temperature &flow)
3. The vibration levels on the rotating equipment
Va
lv
es
Is the vibration near a control valve? If yes, then monitor the valve’s control behavior (throttling), and see if the vibration is associated with it.
If there is a check valve in the system, check the following: 1. Is the valve creating slamming noise? If Yes,
2. Is the slamming associated with the piping vibration?
S u p p o rts
Is there any flimsy support?
Check supports anchor bolts, stud bolts, U bolts conditions, is there any loose bolt or sheared bolt?
Check support contact; is every support in full contact?
Is there sliding or rubbing signs on the pipe support? If yes then record the movement direction
Is there a spring support/hanger in the system, if yes, then inspect its condition, and check the below:
1. Is the load indicator on the working range? 2. Is the travel stop (lock) removed?
Appendix-III – Measurement Guidelines
The following are detailed measurements guidelines:
o Vibration measurement should be performed at the most severe vibration condition which may require measurement at multiple operation conditions.
o For main line, take vibration measurements at those locations perceived to have the highest vibration amplitude, e.g., mid span, near valves, elbows, change in diameters, expansions and orifices.
o For small bore connections, measurements should be performed at the end flange of the cantilever arrangement.
o Utilize the piping isometric drawing and mark and label the measurements locations. o Take data in the vertical and horizontal directions at each measurement location. Where
necessary, also take measurement in a direction along the pipe axis (axial), e.g., at an elbow.
o Ensure that the pipe surface temperature does not exceed the transducer allowable temperature range.
o It is critical to ensure that the transducer is firmly secured to the piping. Use a magnet where possible, or if necessary use a glue to obtain a secure mounting. Hand-held transducers should never be used for this type of measurement.
o For small bore piping, you may need to use a smaller size transducer (less than 50% of the pipe mass).
Appendix-IV – Vibration Measurements Example
List of Tables and Figures
o Figure 4: Example of identifying the vibration measurement locations on an isometric drawing.
o Table 4: Method of summarizing the data in tabular format.
o Figure 5: A sample of velocity and displacement spectrum of a single point. As shown, the dominant frequency is 4.0 Hz.
o Figure 6: Displacement severity Chart indicating displacement magnitude at 4.0 Hz. o Figure 7: Velocity severity chart indicating velocity magnitudes at 4.0 Hz.
Appendix-IV – Vibration Measurements Example (continued)
Table 4 – Measurement Summary Table
Velocity (in/sec RMS) Displacement (Mils Pk-Pk) Overall Freq = 4.00 Hz Overall Freq = 4.00 Hz Point-1 0.78 0.66 75 61.71
Point-2 0.25 0.18 18 12.53
Point-3 0.20 0.14 20 15.43
Appendix-IV – Vibration Measurements Example (Continued)
Figure 6 – Displacement Severity Chart
Acknowledgment
CSD acknowledges the following engineers for their support and active participation in producing this best practice:
1) Hussain S. Al-Nassir Piping Engineer (HGP) 2) Husain M. Al-Muslim Piping Engineer (CSD) 3) Irvin Redmond Vibration Specialist (CSD) 4) Khaleel M. Al-Hussain Vibration Consultant (CSD) 5) Muhsen S. Al-Sannaa Piping Consultant ( ES) 6) Nadhir I. Al-Nasri Piping Specialist (CSD) 7) Khalid A. Mahmoud Piping Engineer (JRD) 8) Tony G. Dib Piping Consultant (CSD)