Heavy Wall Linepipe and Welding Solutions for HP/HT Pipelines

With the increasing drive towards high temperature/high pressure wells, particularly in deep water, riser designs are utilising increasingly heavier wall thickness pipe in conventional strength material, up to 50mm wall thickness in 8" and 10" OD X65 linepipe. In deep water, there is a cost preference to utilise steel catenary risers over other riser designs. Such riser designs are challenging existing seamless linepipe manufacturing and girth welding capabilities. Consequently, in order to establish confidence in the practical realisation of such riser designs there is a need to demonstrate: Adequate linepipe material weldability including the achievement of satisfactory HAZ, elevated temperature and sour service properties.Availability of cost effective girth welding solutions for pipeline fabrication. Subsea 7 and Nippon Steel & Sumitomo Metal Corporation (NSSMC) collaborated on a development programme to qualify both linepipe material and welding solutions for the fabrication of pipelines of dimensions 273mm OD in both 35 and 45mm WT SMLS X65 linepipe. The paper will demonstrate the technical feasibility of using heavy wall pipe for demanding riser applications installed subsea by the reel-lay method. The manufacture of seamless pipe in heavy wall thicknesses will be described together with the alloying and thermal treatment concepts involved. Details of the welding solution for pipeline fabrication will be reported together with the details of the scope and results of the qualification programme performed in support of reel-lay pipeline installation.