vibration induced pipework failure.pdf
-
Upload
alvin-smith -
Category
Documents
-
view
253 -
download
5
Transcript of vibration induced pipework failure.pdf
-
7/30/2019 vibration induced pipework failure.pdf
1/8
Vibration induced fatigue of process piping systems is an important and fundamental failure
mechanism. Data published by the UKs Health & Safety Executive (HSE) for the offshore industry has
shown that in the UK Sector of the North Sea, fatigue/vibration failures account for 21 % of all
hydrocarbon releases. Although overall statistics are not available for onshore facilities, available data for
individual plants indicates that in Western Europe, between 10 % and 15 % of pipe work failures are
caused by vibration induced fatigue.
Leading industrial consultants AV Technology Ltd (AVT) are already carrying out pipe-work vibration
assessment tests for a number of major UK companies in line with the requirements of the latest updated
guidelines,published by theEnergy Institute in 2008 (ISBN 978 0 85293 453 1). AVT engineers are fully
conversant with the necessary test procedures and all-important analysis and presentation of data.
Understanding vibration induced pipework failure
-
7/30/2019 vibration induced pipework failure.pdf
2/8
2
Understanding vibration induced pipework failure
Vibration induced fatigue of process piping systems is an important and fundamental failure mechanism. Data
published by the UKs Health & Safety Executive (HSE) for the offshore industry has shown that in the UK Sector of the
North Sea, fatigue/vibration failures account for 21 % of all
hydrocarbon releases. Although overall statistics are not available
for onshore facilities, available data for individual plants indicatesthat in Western Europe, between 10 % and 15 % of pipe work
failures are caused by vibration induced fatigue.
The latest guidelines, published by the Energy Institute in 2008
(ISBN 978 0 85293 453 1), are aimed at minimising the risk of
incurring loss of containment from vibration induced fatigue
failures of process plant pipe-work. The document is an enhanced
and expanded version of the former MTD Guidelines (Marine
Technology Directorate) first issued in 1999, which has been a key element in maintaining integrity in the design and
maintenance of process pipe-work within the oil, gas and petro-chemical industries.
Key benefits of following good practice include:
Compliance with statutory duty
Improved safety and reliability
Reduced liabilities from product
leakage
Minimised plant down time
The Energy Institute guidelines are broken down into two main scenarios:
Proactive Assessments, which can be used to routinely assess all pipework (existing or proposed) on a site
to ensure that good practice has been adopted and to try to identify possible areas of concern
Reactive assessments, used to further investigate and assess known vibration issues or to trouble shoot
actual failures. Some of the sections within the guidelines are further divided into the two main categories of
Main Linesand Small Bore Connections (SBC)
AV Technology Ltd are already carrying out pipe-work vibration assessment tests for a number of major UK companies
in line with the updated requirements. Their engineers are fully conversant with the necessary test procedures and all-important analysis and presentation of data.
The Energy Institute guidelines propose very logical phased approaches and include various Technical Modules,
detailing procedural flowcharts and good/bad practice guidelines for each phase. Key phases include:
Qualitative Assessment
Visual Assessment
Basic Vibration Monitoring
Specialist Measurement Techniques
Specialist Predictive Techniques Corrective Actions
-
7/30/2019 vibration induced pipework failure.pdf
3/8
3
The Qualitative Assessment phase is possibly the most difficult to implement and involves various calculations for
assessing the likelihoodof having a vibration induced fatigue
problem on existing or proposed new plant. This assessment
takes into account many relevant factors, including: fluid
energy, flow velocities, process machinery, types of valves,
chances of flashing or cavitation, construction quality andcyclic operation. The assessment includes a calculation process
for scoring likely excitation factors and conditional and
operational factors, which are then combined to predict the
Likelihood of Failure (LOF) for each pipe branch.
The Visual Inspection phase is a quick yet powerful way to
spot many obvious potential areas of concern. It is a fact that
many pipework vibration problems are simply the result of
operators not following recommended good practice. These
include installing effective pipe supports, bracing SBCs
properly, avoiding fretting, repairing poor condition or damaged supports, avoiding poor geometry and allowing for
thermal expansion of tubing, The Energy Institute guidelines give many good quality photographic examples of good
and bad practice.
The Basic Piping Vibration Measurement phase provides a simple method of identifying areas of concern based
solely upon measured values of pipework vibration. This is an area which falls within AVTs mains areas of expertise
and involves experienced engineers visiting
sites with suitable instrumentation to
measure and analyse vibration data. Initial
vibration levels are typically recorded using
a single axis accelerometer connected to a
portable data collector, with required
frequency measurements ranging from 1
Hz up to 300 Hz. The results are presented
as vibration amplitude (in units of RMS
velocity) versus frequency. By comparing
these measurements against vibration
assessment criteria presented in the
guidelines, the vibration is classified into
one of three categories:Acceptable, Concern or Problem.
For further assessment of pipework with vibration levels in the Concern or Problem classifications or for pipework with
higher frequency vibration (> 300 Hz), the guidelines recommend the implementation of further Specialist
Measurement Techniques. These include:
Dynamic Strain Measurement and Fatigue Analysis
Experimental Modal Analysis
Operating Deflection Shape Analysis
Dynamic Pressure (pulsation) Measurement
-
7/30/2019 vibration induced pipework failure.pdf
4/8
4
In addition, Specialist Predictive Techniques can be deployed, including:
Finite Element Analysis,
Computational Fluid Dynamics (CFD)
Pulsation and Surge Analysis.
AVT have years of cumulative expertise in many of theseSpecialist Techniques, specialising in the provision of
expertise and resources to apply sophisticated tools and
analysis methods in order to provide a more detailed
assessment of the dynamics of specific pipelines throughout
their life cycles. A high percentage of the work carried out
by AVTs Special Projects Division is concerned with the on-
site measurements of dynamic strain and vibration data
using multi-channel instrumentation systems, together with
the analysis and assessment of the measured data,
including fatigue life analysis.
The final stage of any pipe work assessment is to recommend Corrective Actions to reduce vibration levels and the
likelihood of future vibration induced fatigue failures. Corrective actions can take many forms, including:
Improving pipe supports,
Implementing more effective SBC bracing,
Modifying process conditions to reduce fluid loadings
Installing pulsation dampeners and viscous dampers.
The design of practical and appropriate corrective actions is important to achieve cost effective yet practical solutions.
Such work is often supported by AVTs in-house FEA capability, which is particularly useful for predicting the effects of
remedial repairs. Mechanical design of supports is performed using AVTs SolidWorks 3-D CAD software.
AVTs Technical Director Neil Parkinson is clear on the role his company can play in pipe work fatigue analysis and as
he explains:
Our strengths in predictive and condition based maintenance, together with those in structural monitoring and
vibration assessment, provide the perfect knowledge base for delivering a comprehensive service for vibration induced
fatigue projects. Vibration in pipe-work can be affected by a number of
direct and indirect factors relating not just to the pipe-work itself, but
also adjacent support structures and buildings. It is therefore vitally
important to provide clients with a comprehensive overview of the
vibration patterns together with constructive improvement
recommendations.
Strain gauging and FEA are powerful tools in the analysis process.
Although these are often perceived as distinct, alternative technologies
for assessing structural integrity, AVT have long recognised the
-
7/30/2019 vibration induced pipework failure.pdf
5/8
5
increased power of combining practical strain gauge work with theoretical Finite Element Analysis (FEA).to give us a
distinct competitive edge.
Whilst FEA models can produce important predictions of stress, displacement and frequency, often actual in-service
loading conditions are unknown and so results can be highly unreliable unless validated using actual in-service data
such as strain measurements.
Conversely, whilst actual strain gauge data can yield vital accurate information about stress amplitudes and fatigue,
they are normally limited to measurements at just a few positions and therefore do not give a complete 3D picture of
the modal behaviour of a structure.
Mulit-axis accelerometers assembly fixed to pipework
-
7/30/2019 vibration induced pipework failure.pdf
6/8
6
Lining provides protection to line from fretting at the
U-bolt.
U-bolt is attached to the connection on a reducer
section and is not lined. It is therefore susceptible to
fretting damage.
Fretting damage to main pipe. There is no resilient
pad between support and pipe. Note also pipe clash
below.
Reinforcement plate on pipe at rest support to resist
fretting damage to pipe.
Fretting damage to pipe caused by pipework
vibrating relative to deck penetration cover
Resilient pad between support and pipe protects
against fretting damage.
Examples of good and bad practice in pipework
-
7/30/2019 vibration induced pipework failure.pdf
7/8
7
Bracing insufficiently stiff; single plane only;
only protecting weld to parent pipe.
Bracing stiffness increased; diagonal brace
protects in two planes; valve now supported.
Temporary fix of mass loading to detune a
structural resonance still in place some time later.
Rope used to support cable tray!
Fretting due to loose cladding and damage
caused by knife edge contact at insulation end
cap (existing cladding has been removed
Images courtesy of the Energy Institute
Examples of good and bad practice in pipework
-
7/30/2019 vibration induced pipework failure.pdf
8/8
8
AV Technology LimitedAVTECH House
Arkle AvenueStanley Green Trading Estate
Handforth, CheshireSK9 3RW
Tel: +44 (0) 161 486 3737Fax: +44 (0)161 486 3747
www.avtechnology.co.uk
AV Technology operates an ISO 9001: 2000 QA system and applies a strict health & safety policy.
AV Technology Ltd is a leading multi-discipled consultancy with over 30 years experience.
Our portfolio includes:
Consultancy:
Condition Monitoring
Facilities & Assets
Maintenance
Noise & Vibration
Structural Integrity
Training
Hydraulic Systems
Products:
Acoustic Emission Sensors
Condition Monitoring Systems
Lubrication & Filtration
Silo Weigh
Structural Monitoring Systems
Vision Systems
Spi-VR vibration recorder
Services:
Condition Monitoring
Lubrication Management
Maintenance Solutions
Noise & Vibration
Strain Gauging
Structural Monitoring
Visual Inspection