Vol.12, No2, 2012, pp.117–123
UDC 620.1:621.643.031

This paper consists on studying root causes of seawater pipeline network failures. The pipe network is installed on the Miskar offshore of the British Gas Tunisia. It provides cold seawater for heat exchangers of gas pipework. The Engineering department cannot ignore these failures since the closure of this network will cause production shutdown. One of identified root causes is the flow induced vibration that provokes excessive vibrations. A numerical simulation is done to ascertain flow turbulence in critical areas. This simulation, based on the CAESAR II pipe stress analysis, proves that maximum of turbulence intensity and velocity are located at welded areas and at points with excessive vibrations. It is noted that the higher the diameter the more likely failure to occur. By calculating stress components in critical areas and points, as tees and elbows, one can estimate the theoretical lifetime of crack appearance in structural supports. Three methods are applied here to estimate the fatigue life of the elbow support: ANSYS Inc software, ASME tables and Wöhler curves for stainless steel material. This lifetime is compared with theoretical lifetime expected by the office who had studied and constructed this compression module.

Keywords: crack, vibration, fatigue, failure, numerical solution, Whöler curve