Welding is not allowed after heat treatment

Here is an explanation regarding HaiChuan bean vines: Link to the relevant post: Welding is not allowed after heat treatment: https://bbs.hcbbs.com/thread-1407456-1-1.html (Source: HaiChuan Chemical Industry Forum). As for the equipment used for heat treatment, there are mainly a few types: 1. Containers subject to stress corrosion. Heat treatment is necessary in order to eliminate welding residual stresses, thereby preventing stress corrosion from occurring in the welded joint and its heat-affected zone under corrosive conditions ； 2. Carbon steel and low-alloy steel containers designed to hold media with an extremely high or high degree of toxicity. The standard sets this requirement actually with regard to the hazards posed by media, in order to prevent accidents from occurring ； 3. Equipment whose welded joints reach a certain thickness requires post-weld heat treatment. As is well known, equipment with thick walls either operates under high pressure or has a large volume, or both. Accidents involving such equipment can cause severe damage. The greater the thickness of the weld joint, the more pronounced the welding stresses generated during the welding process; therefore, standards require post-weld heat treatment. So, let’s analyze what kind of drawings will specify that welding is not allowed after heat treatment I believe it should be equipment made of chrome-molybdenum steel, as this material is prone to temper embrittlement, and to prevent delayed cracking in such steel, the equipment made from it must undergo post-weld heat treatment; accordingly, welding must be carried out carefully after the heat treatment is completed. I have also seen drawings with requirements similar to “welding is not allowed after heat treatment.” I noticed that several people asked where this requirement came from, and it was stated that there is no such provision in the standards. It should be understood that standards are technical specifications, not technical manuals; they represent the minimum requirements. In such cases, we shouldn’t stick strictly to those minimum standards – we need to make a judgment regarding the equipment. For example, in the case of equipment made of Q245R, is welding not allowed after heat treatment? Not necessarily; I think it’s allowed as long as the measures are appropriate. What about equipment made of chromium-molybdenum steel? I think it is absolutely not allowed.

It is possible to use tempering weld passes, but manufacturers generally do not do this

It’s not for equipment design; in my opinion, it’s meant to avoid the generation of stress.

I looked around; it can be used as a reference! According to items 2.(15)-(16) of the explanatory notes for NB/T47015-2011 \"Welding Code for Pressure Vessels\", the provisions regarding heat treatment to be carried out on the welded parts after repair can be found in section 4.7 of NB/T47015. However, it needs to be confirmed whether this repair of the welded part is for quality issues that arose after heat treatment or for those that arose before heat treatment; based on the wording, it seems to be for issues that occurred after heat treatment.

Article 7.4.4 in GB150.4 is very clear.

Welding after heat treatment generates residual stresses in the vicinity of the fusion zone, and the intergranular structure becomes unstable, making stress corrosion more likely to occur. Additionally, in the case of austenitic stainless steels, C precipitation takes place