Assessment of thermowell vibration fatigue due to vortex-induced vibration (VIV)

In Amenas has a gas processing plant asset located in Algeria that comprises a series of pipework trains. Throughout the plant are a number of thermowells that are subject to changes in process conditions and BP thermowell design requirements.

Some of the thermowell units have welded-on flanges rather than the BP specified alternative of wells machined from single billets. In addition, some thermowells have velocity collars fitted to provide damping rather than alternatives such as probe length shortening or probe diameter tapering. In Amenas are looking to increase the plant throughput by at least 10% and therefore the thermowells need to be assessed for vortex-induced vibration (VIV) and therefore the onset of fatigue failure.

In Amenas is looking to replace any thermowells at risk during their next shut-down in September 2010 and has contracted Jee Ltd to perform assessment and identify those thermowells at risk, subsequently re designing them in preparation for change out.

Jee has updated the In Amenas assessment criteria to come in line with better and more up to date code requirements looking at the complex problem of inline and cross flow forced and resonant vibration cases. This is currently a poorly understood area by many process pipework operators. In Amenas has been advised of some assets that may be at risk and in need of replacement. This will enable In Amenas to avoid any future failures occuring.

Pipework vibration-induced fatigue is an area which Jee has been leading and conducting analysis-based projects for many years.