Overall heat treatment

Update: 20-12-2021

The overall heat treatment is to eliminate the stress g […]

The overall heat treatment is to eliminate the stress generated by welding, stabilize various geometric dimensions, change the welding metallographic structure, improve the toughness and stress resistance of the metal, and prevent the generation of cracks. Due to the local heating during welding, the change in the metallographic structure of the weld metal causes internal stress. In addition, the weld stress distribution is more complicated, and the metal also generates internal stress. In order to eliminate the residual stress and reduce the local hardening of the metallographic structure near the weld, and to improve the mechanical properties of the weld, the overall heat treatment method is adopted. For example, after the spherical tank is assembled and welded, there are two methods of overall heat treatment: one is the internal combustion method, the other is the electric heating method.

Equipment weld heat treatment

The welding seam heat treatment of the on-site assembly equipment should meet the requirements of the conditions and drawings provided in the product qualification certificate. It is related to GB150-89 "Steel Pressure Vessel" and GB50236-98 "Specification for Construction and Acceptance of Welding Engineering of Field Equipment and Process Pipeline" Regulation.

1. If the vessel and its pressure components meet one of the following conditions, heat treatment shall be carried out. Class A and Class B welds, where the nominal thickness of the base metal meets the following conditions: ⑴The thickness of carbon steel is greater than 34mm. ⑵The thickness of 16MnR is greater than 30mm. The thickness of 15MnVR is greater than 28mm. For welds, the thickness mentioned above shall be considered as thinner; for A and B welds of different types of steel, they shall be determined according to the steel type required for heat treatment.

2. The thickness of cold-formed and medium-temperature formed cylinders meets the following conditions:

⑴ The nominal thickness of carbon steel and 16MnR is not more than or less than 3% of the design inner diameter D;
⑵The nominal thickness of other low-alloy steels shall not be greater than or less than 2.5% of the design inner diameter D.

3. The drawings indicate vessels with stress corrosion.

4. The drawings indicate the containers containing extremely hazardous or highly hazardous media

5. The surface of the container made of austenitic stainless steel and composite steel plate with anti-corrosion requirements should be pickled and passivated.

6. According to the established process regulations, if the vessel needs to undergo hydrogen elimination treatment after welding, if the heat treatment to eliminate the residual stress is carried out immediately after welding, the hydrogen elimination treatment can be exempted.


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