Field experience with the construction of large diameter Steel Catenary Risers indeep water

摘要

During spring of 2004 four large diameter SCRs werernconstructed and installed to connect the Mardi GrasrnExport System with floating facilities. The challenge inrnconstructing these first risers was the combination of largernwater depth (max 1450m), pipe diameter (16 " - 24”),rnwall thickness (up to 1.14”), high top tensions, weldingrnrequirements (E-curve) and a high weld area ductilityrnlevel.rnAll four risers were constructed and hung off in onernuninterrupted operation. This implied the passing of arnpoint of no return after which lay down of the riser (inrncase of an emergency) would not be possible withoutrndamaging the riser.rnTo minimize the schedule risk in this critical phase, it isrnessential that the chance of weld rejection was reduced tornan absolute minimum.rnThe welding procedure development and qualification,rndemonstrating consistency in high weld quality andrnrepeatability, proved to be beneficial. Welding andrnconstruction crew training and qualification inrnaccordance with the high project standards werernkey elements in reducing risk and achieving steadyrnreliable production. In particular testing against a widernrange of welding parameters brought maximum flexibilityrnduring the welding operation.rnWith the VIV strakes and a strain monitoring systemrnbeing installed over the complete length of the SCRs therninstallation had to be as efficient as possible. This resultedrnin several adjustments to the designs during thernpreparation phase. In addition a huge SPAR preparationrnprogram had to be undertaken to ensure all the SCR pullinrninstallation aids were in place during SPARrnconstruction and prior to tow out. The SPAR preparationsrnand efficient installation methods were crucial tornminimizethe installation period after the point of nornreturn.