When a Drains Vessel on an FPSO stationed in UKCS waters developed a through thickness crack at a weld between the Inlet Nozzle and the Vessel shell, miSolutions were engaged to design and engineer a replacement nozzle to allow the vessel to be returned to service and remain code compliant (ASME VIII Div 1).  On further investigation the cause of the of the weld defect was established as High Cycle Fatigue (HCF) as a result of ship motion accelerations.  This required not only a new nozzle design for the Drains Vessel but also a modification to the Drains Header Pipework to reduce the cyclic loads seen by the Inlet Nozzle.

The pipework modification to reduce the nozzle loadings was achieved by a combination of bellows units, pipework guides and pipework anchors.  These ensured the pipework itself remained with in code (ASME B31.3) while allowing the nozzle design to satisfy both static and fatigue design criteria and gave a fatigue life for the pipework which was acceptable to the client

Due to the modifications required to the pipework supports there was a need to modify some existing and add new support steelwork to accommodate the large thermal loads seen by the Drains Header Pipework.