Construction of high-pressure gas pipelines with API X80 grade welded large diameter pipes is progressing for the improvement of transportation efficiency. The issue has been suggested that the benefit of higher strength steel of thinner wall pipe diminishes the strain capacity of line pipes by larger D/T ratio and higher Y/T ratio of higher strength steel pipe in general. Authors reported that API X80 grade 48- inch (1,219mm) diameter line pipe has enough strain capacity against ground displacement by seismic wave propagation and lateral spread by liquefaction in seismic area based on the JGA guide line. However the pipelines are not always straight, but also curved to follow the route. Hot bends are employed to make curved portion. Mechanical properties and pipe dimensions of hot bends are different from straight pipes due to the heat treatment and deformation during bending. The characteristics of X80 hot bend are going to be investigated, and the strain capacity and the strain demand of curved portion in pipeline are evaluated by FEA for the assessment based on SBD concept.
The operating pressure of natural gas transmission pipelines has been increased for transportation efficiency. High strength line pipes have been developed to carry high pressure gas economically and safely by long distance pipelines. High strength line pipes have secured internal pressure containment capacity, which is the most essential requirement to line pipes. However to secure the safety of high pressure gas pipelines constructed by high strength line pipes, the strain capacity of high strength line pipes has been investigated and discussed, as it is assumed that high strength line pipe is inferior to low strength one in deformability (Liessem et al., 2007). We, pipe manufactures, have focused to develop high strength and high toughness steel for pressure containment capacity and the resistance to fracture initiation and propagation.
