Small Bore Dynamics and some Fatigue Related Issues

Small Bore Attachment and Small Bore Branch fatigue analysis is a problem of considerable interest in the Oil and Gas and in the Nuclear Industry. Almost 50% of hazards from hydrocarbon release in petrochemical plants occur as results of fatigue failure of welds of small bore connection or in the vicinity of (heat affected zone).In 2005, Mousseau from the Commissariat à l'Energie Atomique, Paris (CEA) developed a dynamic model for Small Bore Side Branch (SBB). Failure of Small Bore Branches in the nuclear industry constitutes a major hazard and is referred to as small Loss-of-Coolant Accident (SLOCA). In the Oil and Gas Industry, we are not aware of any development of the subject. EI Guidelines, AVIFF, January 2008 do not refer to any dynamic analysis when dealing with small bore dynamics. The analysis shows how it can be extended later to include the effect of flange rotary inertia and connection-header interaction. A list of findings, which help at an early stage of design against vibration induced fatigue failure, are presented. The model developed allows insight to the parameters affecting SBA vibration and shows the resemblance between SBA dynamics and that of a high rise building on elastic foundation.