Production • Processing • Handling
Understanding vibration
Fig. 1. Many pipework vibration problems are simply the result of operators not following recommended good practice.
Neil Parkinson explains the six phases in understanding, correcting and preventing vibration-induced pipework failure.
Neil Parkinson explica las seis fases para entender, corregir y prevenir los fallos de las tuberías en la vibración inducida.
Neil Parkinson beschreibt die sechs Phasen zum Verstehen, Beheben und Verhindern von schwingungsbedingten Leitungsdefekten.
V
ibration 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 and 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 pipework failures are caused by vibration induced fatigue. Based on the Energy Institute publication ‘Guidelines for the Avoidance of Vibration Induced Fatigure Failure in Process Pipework’, current best practice is aimed at minimising the risk of incurring loss of containment from vibration- induced failures. Te Energy Institute guidelines break
down into two main scenarios – proactive and reactive assessments – and aim to ensure compliance with statutory duty, improve safety and reliability, reduce liability from leakage, and minimise plant downtime. Proactive assessments can be used to routinely evaluate all pipework
on a site, whether existing or planned, to ensure that best practice has been adopted and to identify possible areas of concern. Reactive assessments follow, and are used to further investigate known vibration issues or troubleshoot actual failures within both mainline pipework as well as small bore connections (SBCs). Tere are six key phases to achieving pipework vibration assessments in line with requirements of the guidelines: qualitative assessment; visual assessment; basic vibration monitoring; specialist measurement techniques; specialist predictive techniques; corrective actions. Te qualitative assessment phase is perhaps the most challenging to implement and involves numerous calculations for assessing the likelihood of encountering a vibration-induced fatigue issue – on either an existing or planned plant. Tis assessment takes into account many relevant factors, from fluid energy, flow velocities and cyclic operation to the construction quality of infrastructure including process machinery and types of valves. It also assesses the chance of flashing or cavitation, and includes a calculation process for scoring likely excitation factors – which are combined
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