MANUFACTURING CHALLENGES OF HIGH STRENGTH LINE PIPES

摘要

The International Energy Outlook 2006 (IEO2006) projects strong growth for worldwide energy demand over the decades. The use of high strength steels is considered as the best economical option to transport large gas volumes under high pressure from remote areas to the market. When the first steps of this development were undertaken, the grade X100 was widely considered as an advanced X80 with additional 20,000psi yield strength. Subsequent to the extended worldwide research and the herewith related better and broader understanding of the material behaviour itself and the corresponding design requirements, the development steadily progressed until today when several demonstration pipelines mark a further crucial milestone before the first commercial projects. rnThis paper provides an overview of the challenges of line pipe manufacturing for high strength pipelines. As the necessary microstructure for X100 consists of a very fine, fully bainitic microstructure it is essential to understand the formation and the mechanical properties induced by this. Especially the work hardening of the plate and the pipe needs to be investigated, as it determines the final stress-strain behaviour of the pipe eventually coated. High uniformity of the mechanical properties requires tighter production control with smaller tolerances for the production parameters. Compared to X70 the stress-strain curve differs considerably, which challenges especially the cold forming of UOE pipes as the elastic springback is increased. Therefore the forming and expansion process needs accordingly to be modified. The second major challenge during pipemaking is the high performance submerged arc welding process. Overmatching strength properties, high weld seam toughness, limited HAZ softening are the essential keywords in this area. The assessment of the significance of low HAZ toughness is required as low Charpy-V values adjacent to the fusion line are obtained. As crack arrestors seems inevitable to guarantee crack arrest of such a high strength-high pressure, a short review of manufacturing and design of fibre reinforced crack arrestors will be given. Referring to the above technical matters the paper will summarise the actual status of issues which are solved and those where questions still need to be answered.