PIPEWORK VIBRATION
Identification, assessment and management of the risk of pipework vibration induced fatigue failure and loss of containment

Statistics published by the UK’s Health & Safety Executive show that approximately 20% of pipework failures are due to vibration induced fatigue. The resultant loss of containment carries potentially serious safety, environmental and cost implications. Identifying potential areas at risk from vibration induced fatigue is fast becoming a necessity.

Bureau Veritas has worked closely with industry and regulatory authorities to develop a risk assessment methodology that can be applied to combat the problem. For new facilities, these techniques can be used to identify pipework at risk from vibration fatigue during design, allowing appropriate modifications to be implemented. The techniques are equally applicable to operational assets, particularly where debottlenecking is being undertaken. Here, the results of a formal risk assessment, supported by field measurement studies, can often be utilised to eliminate potential fatigue failures completely. For residual areas of identified high risk, they form a rational basis from which to formulate suitable mitigating inspection programmes.

The risk assessment methodology is based on the MTD Guidelines for steady state vibration mechanisms and Offshore Technology Report 2002/028 for transient mechanisms.

We also provide a comprehensive technical capability to investigate and solve pipwork vibration problems:

Investigation

On-site measurement of pipework vibration is only one tool that can be employed. For example,
dynamic strain measurement using bonded or frictional strain gauges can give a direct estimate of fatigue life for main pipework and small bore connections. Dynamic pressure and flow measurements can often help identify process related issues which result in high piping vibration levels. Recent examples include:

• Vibration, stress and dynamic pressure measurements on offshore high pressure gas pipework to determine the cause of a high frequency vibration problem which was leading to fatigue failure. • Investigation of excessive pipework vibration levels and associated fatigue failures on a condensate pumping system with positive displacement pumps. Recommendations were made to address immediate integrity concerns, and subsequent detailed simulation identified modifications required for the long-term integrity of the system.
• Dynamic testing in-situ of thermowells to confirm critical flow velocities for a gas plant undergoing debottlenecking – this included both internal and external dynamic strain measurement.

Simulation and Prediction

In some situations a simulation is required – either at the design stage of a new system or to ‘recreate’ a problem analytically and then explore various modifications. This may involve structural analysis or simulation of the fluid system to identify non-structural modifications such as pulsation dampers, orifice plates, valve timings or changes to the process itself.

What are the key benefits?

Compliance with statutory duty
Improve safety and reliability
Minimise financial liabilities and lost production
Minimise time detracted from core business
Reduced insurance costs