The requirement of PWHT for steel pressure vessel

1. Pressure vessels including high pressure vessel, medium pressure reactor and storage tanks, horizontal storage tanks for mixed liquefied petroleum gas, portable pressure vessels should be used in the furnace as a whole heat treatment. Other pressure vessels shall be of integral heat treatment. Large-scale pressure vessel can be segmented heat treatment, the overlapping part of the length of the heat treatment should be not less than 1500mm, the furnace part of the insulation measures should be taken.

2. The repaired circle welding joint, pipe joints and head to connect the welded joints can be used local heat treatment. Local heat treatment of the weld to include the entire weld, the weld width of each side of the base metal is not less than 2 times the thickness of the shell and the shell is not less than the heating width of both the thickness (whichever is greater) of 6 times , Close to the heating part of the shell should take insulation measures to avoid a larger temperature gradient.

3. The post-weld heat treatment shall be carried out after all the welding work has been completed and tested, and before the withstand voltage test

4. Heat treatment equipment (furnace) should be equipped with automatic recording curve of the thermometer, and to ensure that the heating zone between the maximum and minimum temperature of not more than 65 ℃

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