Effect of Carbon Equivalent on Toughness of Girth Weld HAZ in Oil and Gas Transportation Pipelines
In order to solve the problem of toughness fluctuations in the heat affected zone of high grade pipeline girth welded joints,the microstructure and mechanical properties of the experimental steel were tested using thermal simulation testing machines,metallographic microscopes,scanning electron microscopes,Vickers hardness testers,and Charpy impact testing machines.The changes in microstructure and low temperature toughness of high grade pipeline steel with different carbon equivalents after secondary thermal cycling at different peak temperatures were compared and analyzed.The results show that after secondary thermal cycling,embrittlement zone will appear in the heat affected zone of the girth welded joint,and even if the toughness of the base material is at a high level,its low temperature toughness may also decrease after multiple thermal cycles.By optimizing the design of metallurgical composition,the proportion of low toughness structures can be reduced,thereby improving the low temperature toughness of the weld heat affected zone.The differences in microstructure and morphology of different experimental steels at different temperatures indicate that the coarse granular bainite structure and many large particle M/A components are the fundamental reasons for the decrease in toughness.By studying the impression of microstructure and low temperature toughness of X80 grade pipeline steel under different heat effects,theoretical support is provided for the development and application of high toughness X80 pipeline steel suitable for fully automatic girth welding.
girth weldheat affected zonecarbon equivalentlow temperature toughnessM/A component
国家科技期刊平台
NSTL
万方数据
维普
