Local heat treatment issues of repaired longitudinal welds

According to Article 126 of the regulations, when repairing or modifying pressure vessels by welding, patching or replacement methods should generally be used; filling or patch-welding methods should not be employed. The following requirements must be met: The technical requirements for patching or replacing sections of pressure vessels, as well as post-weld heat treatment, shall be determined in accordance with the relevant manufacturing specifications, and construction plans along with appropriate technical requirements shall be formulated. The welding process must be approved by the person in charge of welding techniques. After defects are removed, surface non-destructive testing should generally be carried out to confirm that the defects have been completely eliminated. Non-destructive testing should also be performed after welding is completed to ensure that the repaired areas meet quality standards. The repaired areas where the base material is patched must be smoothed, and the length of the repaired area after defects are removed must meet the required standards. If heat treatment is necessary, it shall be carried out again after patching. For pressure vessels whose main pressure-bearing components have a patching depth greater than 1/2 of the wall thickness, a pressure test shall also be conducted. As can be seen from this rule, local heat treatment may not be required for the longitudinal welds after repair, or it may be specified by the designer； Looking at this issue from another perspective, ring welds require heat treatment because the stress acting on them is perpendicular to the direction of the weld; such stress concentration can have a significant impact on strength. Therefore, local heat treatment is used to eliminate this stress concentration. Longitudinal welds do not face this problem, and in such cases we only need to pay attention to the welding process. This is just my personal opinion – please feel free to correct me. Last edited by vivo1314 on 2009-4-10 13:16.]

As a weld subject to severe stress, if heat treatment is required after repair welding, the entire weld must be heat-treated.

The code allows for local heat treatment of the repaired circumferential welds, but does not specify anything regarding longitudinal welds; since the stress on longitudinal welds is twice that on circumferential welds, the requirements are even more stringent. Therefore, local heat treatment should not be possible; only overall heat treatment is feasible. Additionally, regarding the point about the third floor: the local heat treatment of the circumferential weld must also cover the entire weld seam; therefore, in cases where local heat treatment is not possible, it is more appropriate to consider that the entire equipment needs to be heat-treated.