Influence of Microhardness and Inclusion on Stress Oriented Hydrogen Induced Cracking of Line Pipe Steels

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概要

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• The influence of microstructure and inclusion on the susceptibility to stress oriented hydrogen induced cracking, SOHIC, or type I sulfide stress cracking, SSC, was investigated for two kinds of line pipe steels which have the different susceptibility to SOHIC. The steel plates, produced by accelerated cooling after controlled rolling, were heated to three temperatures of 1100, 900 and 750°C to vary their microstructures. For the four microstructures including the as cooled one, the susceptibility to SOHIC was evaluated by the SSC test specified in NACE TM0177-90 method A in addition to an SSC test using a large scale plate. The cracking susceptibility depends on the minimum microhardness rather than maximum hardness in the specimens with yield strength of API X65 or less. The local region with minimum microhardness, having lower yield strength, is deduced to become a preferential site for the hydrogen induced blister cracking, HIBC, and also to provide plastic zones through which the existing blisters are prone to link to each other, leading to the cracking through thickness. As a consequence, the decrease in the local hardness is concluded to enhance cracking susceptibility. Non-metallic inclusions were identified as the crack initiation site. The critical dispersion distance of inclusions, within which a second blister can be induced in the plastic zone formed around the first blister, is estimated based upon calculation of the stress around the blister. The observed results of crack propagation and arrest were both well interpreted in terms of the estimated critical distance.

• 社団法人 日本鉄鋼協会の論文
• 1996-03-15

著者

• TAKAHASHI Akihiko

  Yawata R & D Laboratory, Nippon Steel Corporation

• OGAWA Hiroyuki

  Steel Research Laboratories, Nippon Steel Corporation

• Ogawa Hiroyuki

  Steel Research Laboratories Nippon Steel Corporation

関連論文

• Comparison between Full Scale Tests and Small Scale Tests in Evaluating the Cracking Susceptibility of Line Pipe in Sour Environment
• Influence of Softened Heat-affected Zone on Stress Oriented Hydrogen Induced Cracking of a High Strength Line Pipe Steel
• Influence of Microhardness and Inclusion on Stress Oriented Hydrogen Induced Cracking of Line Pipe Steels
• Improvement of Yield Strength-Transition Temperature Balance by Microstructural Refinement
• Microstructural Refinement by Cu Addition and Its Effect on Strengthening and Toughening of Sour Service Line Pipe Steels
• Thermo-mechanical Control Process as a Tool to Grain-refine the Low Manganese Containing Steel for Sour Service Line Pipe

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