“Vibration induced fatigue of process piping systems is an important and fundamental failure mechanism. Data published by the UK’s 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.”
AV Technology Ltd carry out pipe-work vibration assessment tests in line with the updated requirements of the latest guidelines, published by the Energy Institute in 2008 (ISBN 978 0 85293 453 1). These are aimed at minimising the risk of incurring loss of containment from vibration induced fatigue failures of process plant pipe-work. Our engineers are fully conversant with the necessary test procedures and all-important analysis and presentation of data.
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 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
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 AVT’s 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
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 these Specialist 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 our ‘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.