For operating platform connectors, pipe support pre-wel […]
For operating platform connectors, pipe support pre-welding parts, heat preservation support pre-welding parts, ear pads, nameplate brackets, grounding plates and other accessories, due to design or manufacturing omissions or temporary additions, they have been shipped to the site after welding Heat treatment of PWHT equipment requires welding. However, in people’s impression, "PWHT equipment must not be hot again" is a red line that cannot be stepped on, nor is welding, nor is it not welding, which makes it difficult for all parties. Can the equipment after PWHT be soldered? Do I need to heat treatment after welding?
For equipment that has undergone post-weld heat treatment PWHT, if re-welded, residual stress will be generated in the welding area; and if heat treatment is performed after this "re-welding", the probability of reheating cracks will increase for some materials. Therefore, whether the equipment after PWHT is re-welded should be subjected to secondary heat treatment, which should be determined according to the specific situation, and the two harms shall be the lesser.
It can be stated as follows: After re-welding, it is necessary to perform heat treatment again, which is called "no re-welding after heat treatment". If there is no need to perform heat treatment after re-welding, it can also be called "re-welding after heat treatment".
In fact, 7.4.3 and 7.4.4 of GB/T 150.4-2011 have provisions on this, and the provisions are as follows:
If any welding repairs are performed on the following vessels after the post-weld heat treatment, the repaired parts should be re-heated:
a) Containers containing extremely or highly hazardous media;
b) Cr-Mo steel container;
c) Cryogenic container;
d) The drawings indicate vessels with stress corrosion.
The welding repair after heat treatment shall be approved by the user. Except for vessels requiring post-weld heat treatment, if repair is performed after heat treatment, when the repair thickness is less than 1/3 of the steel thickness and not greater than 13mm, no post-weld heat treatment is required. During rework welding, preheat and control the thickness of each weld layer not to be greater than 3mm, and a tempered weld bead should be used.