Development and production of high strength pipeline steels

In view of the ever-increasing pipeline length and operating pressure, the development of high-strength steels makes a significant contribution to pipeline project cost reduction. In the case of offshore pipelines, the operating pressure is not the most important but rather the ambient water pressure. Therefore, one of the design criteria for offshore pipelines is less the strength but more the collapse behaviour of the pipe. The pipe to be used in offshore pipeline construction should possess not only good materials properties but also good geometry to ensure good collapse strength. As the H2S content of the gas being transported increases, the requirements for HIC resistance of the pipe material increase. When an aqueous phase is present, CO2, H2S and chlorides are extremely corrosive. For applications in such corrosive environments, a pipe made of either all-corrosion resistant material or of a low-alloy steel pipe clad with a high-alloy corrosion resistant material is used. The initial part of the paper discusses the metallurgical principles and the development of large-diameter linepipe steels. In the second part the production results of different orders represent the state-of-the-art of production of longitudinally-welded large-diameter pipe. Projects of high strength line pipe, pipe for deepwater application, HIC resistant and clad pipe applications are presented. The paper concludes with the need of close collaboration between all parties involved to optimize the pipeline projects in terms of quality and costs. (AU)