For post-weld heat treatment of pressure vessels, what do I use to inspect it?

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Purpose of post-weld heat treatment: Appropriate heat treatment can improve the mechanical and creep properties of welded joints, relieve residual welding stresses, stabilize the dimensional stability of the structure, soften the hardened areas, improve the microstructure of the heat-affected zone, reduce the hydrogen content in the weld metal, and enhance the corrosion resistance of the welded joints. If the heat treatment is improper or does not meet the desired requirements, it can instead cause damage to the equipment. Characteristics of post-weld heat treatment for pressure equipment: Integrity: Whether it is overall or partial post-weld heat treatment, the focus is on the heat treatment effect of the entire welded component, and the heat treatment process should be planned from a holistic perspective. One-time only: Post-weld heat treatment can usually only be carried out in a single, continuous process. If the treatment is not done properly or does not yield satisfactory results, it is difficult to make corrections, and in some cases the equipment may have to be scrapped. Limitations of post-weld heat treatment evaluation methods: The product welding specimens must use the same materials, welding processes, and heat treatment procedures as the equipment itself, and testing must be conducted to verify their performance. However, due to limitations related to their own size, position, etc., test specimens ultimately cannot represent the overall condition of the equipment. Hardness: Hardness testing is one of the important methods for evaluating the effectiveness of post-weld heat treatment. However, current standards for pressure vessels do not specify acceptable values nor the locations where measurements should be taken. In practice, some engineering companies provide guidelines in their design documents, or follow certain pipeline standards (ASME B31.3), but there is a lack of consistency, and a certain degree of arbitrariness exists. Residual stress measurement: There are many methods for measuring residual stress; however, they have high requirements regarding the testing environment. As industrial products, pressure vessels are subject to poor testing conditions, which can affect the reliability of the test results. Secondly, it can usually only detect residual stresses on the surface and in localized areas; it is unable to measure residual stresses in the thickness direction or throughout the entire device. Problems with heat treatment equipment: Since there are currently no specific standards for post-welding heat treatment furnaces, in practice heating furnaces are often used as such. Some organizations use self-made or quickly assembled furnaces, but the quality of the treatment resulting from this approach cannot be guaranteed. There are also no standards for the burners commonly used in extracorporeal heat treatment, as well as ceramic resistance heaters. The lack of standards leads to a high degree of arbitrariness, making it difficult to ensure consistent results. Other issues to note in practice: 1. It is necessary to ensure an effective heating area in the heat treatment furnace, that is, to guarantee sufficient heating space. 2. Although standards such as GB/T150 specify the width of the homogenization zone for localized post-weld heat treatment, the homogenization zone is different from the heating zone; the width of the heating zone needs to be determined based on experience or testing. 3. The heat treatment specification parameters specified in the standards are only general basic requirements and are not necessarily the optimal parameters; specific parameters should be determined based on experience or testing. In general, post-weld heat treatment is a highly practical task. There are numerous factors influencing its effectiveness, and their relationships are complex; many parameters in the heat treatment process must be determined based on experience. The author also believes that due to inadequate regulation and insufficient attention from various entities, the current GB/T 30583 “Procedures for post-weld heat treatment of pressure equipment” has not been implemented effectively.