The cooling rate of heat affected zone(HAZ)in the process of electrofusion welding of ferritic steel is the key factor that leads to the change of microstructure and residual stress in the near weld zone.Post-weld heat treatment has a positive effect on reducing residual stress,forming tempered martensite structure and reducing hardness,but for the construction of on-site pipeline system,it increases the cost of pipeline construction.There are great differences in the insulation temperature and exemption thickness of PWHT,the standard specification for pressure equipment and pipelines,GB/T 20801.4-2020 also stipulates the relevant provisions of PWHT.
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