The ductile fracture arrest capability of gas pipelines is seen as one of the most important factors in the future acceptance of new high strength pipeline steels for high pressure applications. New North-European pipeline project is based on application of X70 pipes designed for high gas pressure of 9,8MPa. To study fracture propagation behavior in cold climate the full scale tests were carried out using longitudinally and spiral welded pipes with different microstructure of base metal. Results of the tests with crack propagation studies in predominately ferrite-pearlite (FP) and acicular ferrite (AF) steels possessing similar Charpy energy are presented. Crack propagation mechanisms in base metal and along spiral weld were studied and are presented with strain distribution along crack.

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