Heat treatment issues after welding the eight-slot flange connection plates
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Dear teachers, I would like to consult regarding the heat treatment process after welding flange connection plates or handles using the eight-character method. All the eight-character flanges produced by our company are blind flanges; the orifice plates are precision-machined after heat treatment, followed by welding of handles or connection plates. No post-weld heat treatment is performed after welding. Because performing post-weld heat treatment after welding cannot ensure precision and surface condition. The customer asked why no heat treatment is done after welding. Are there any relevant regulatory guidelines that can be used to convince the client?
The main consideration for not performing heat treatment after welding is to ensure the dimensional accuracy and surface quality of the product. Since heat treatment can cause deformation and dimensional changes in materials, this is unacceptable for components that have already undergone precision machining. Furthermore, high-temperature heat treatment may also affect the surface condition of the product, such as surface hardness and finish. Customers can be explained that post-weld heat treatment is chosen based on the welding materials and the final application requirements of the product. .
Thank you for the reply; we have also explained this point. The client requires evidence of standard clauses, such as B31.3, etc.
All European codes for boilers, pressure vessels, and pressure pipelines, as well as the ASME codes for boilers and vessels, specify an exemption thickness of around 35 mm for carbon steel PWHT; however, the exemption thickness specified in the ASME B31.3 and B31.1 codes for pressure pipelines has long been set at 20 mm. However, starting with the 2014 version, the ASME B31 piping code relaxed the restrictions on exempt thicknesses, while still emphasizing the need to comply with preheating temperatures and multi-pass welding. For all carbon steels specified in P No.1-1 to 3, those that meet the requirements for preheating and multi-layer welding can be exempted from post-weld heat treatment. I think this is how it should be interpreted; the thickness requirement for chromium-molybdenum steel needs further discussion.