Under what circumstances is post-weld heat treatment required when welding pressure vessels?
Time of issue：
2022-05-16
Under what circumstances should post-weld heat treatment be performed on pressure vessels and pressure components? The purpose and conditions of the heat treatment will now be described.
Under what circumstances should post-weld heat treatment be performed on pressure vessels and pressure components? The purpose and conditions of the heat treatment will now be described.
1. The main purpose of post-weld heat treatment for pressure components of pressure vessels
(1) Eliminate welding residual stress and prevent various welding cracks and stress corrosion cracking.
(2) Eliminate cold work hardening in the process of cold forming, and restore the original performance of the base metal and welded joints.
(3) The mechanical properties of the steel or welded joints are made to meet the requirements through heat treatment. In particular, after hot coiling and hot pressing, the structure or performance of the steel plate in the supply state is destroyed; or electroslag welding (BSW) or vertical welding with large line energy is used to make the grain of the weld coarse, and it is normalized after welding. be eliminated.
2. Conditions of post-weld heat treatment
The national standard GB50 specifies the post-weld heat treatment according to the strength, thickness of the steel, the medium of the container and the degree of cold deformation of the steel.
(1) According to the strength and thickness of the steel, the conditions of post-weld heat treatment are shown in Figure 1.
(2) According to the medium of the container.
① The drawing indicates that the container contains extremely or highly hazardous medium.
② The drawings indicate the containers with stress corrosion, such as liquefied petroleum gas, liquid ammonia, etc.
(3) Deformation amount according to cold forming
①Deformation of carbon steel and 16MnR: δs/Di≥3%.
② deformation of other low alloy steel: . δs/Di≥2.5%.
In addition to the above provisions of GB150 in the "Pressure Vessel Safety Technology Supervision Regulations", for ferritic materials using electroslag welding or vertical welding seams with large welding line energy, normalizing should be used to refine the grains. For containers containing mixed liquefied petroleum gas at room temperature, post-weld heat treatment is also required. Spinning heads shall be stress relieved after spinning, with the exception of spinning heads of austenitic stainless steel.
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