Development and production of large-diameter line pipe for offshore applications

The continuous analysis of market requirements for large diameter line pipes used in offshore application reveal that overall the requirements are becoming more and more stringent. This development is triggered by the fact that offshore pipelines are installed in deeper water and operated under higher pressures. Therefore the linepipe material has to show higher strength properties with simultaneously increased toughness. In case that the gas to be transported contains certain amount of H2S additional requirements regarding HIC (Hydrogen Induced Cracking) resistance have to be taken into consideration. As installation of offshore line pipes play a significant role within the whole project costs also the pipe geometry has to be improved steadily with tighter tolerances especially for out of roundness and wall thickness in order to facilitate and speed lip pipe laying. Consequently the applied technologies from steel making to pipe production are continuously improved in order to increase the quality level and the productivity by reducing non-quality costs. In this article, the crucial manufacturing steps necessary tofidfil these stringent requirements for offshore line pipes are described. Special attention is paid to the pipe forming, the welding process and its control as they are qfessential importance for the intrinsic pipeline safety This will be supplemented by review of current project examples for different offshore applications plications with specific requirements such as thick wall pipe for North Sea offshore application and production of sour service line pipes.