Question: Are these 2 heat treatments necessary?

Does heat treatment of the A-class materials mentioned earlier remove hydrogen? If that’s the case, come honestly. Dehydrogenation must be carried out within a certain period after welding; it cannot be delayed for too long. If strain relief is what is intended, I think the designer’s approach is unreasonable. Multiple heat treatments of the material do not improve its properties.

It’s impossible to determine just by considering whether heat treatment is necessary or not; designers may have various considerations in mind, such as hydrogen removal from thick plates or stress relief in Co-Mo steel. Since technical requirements exist, it’s clear that this step cannot be omitted. The quality standards for pressure vessels relate to the control of the entire process, and many aspects are not visible to the naked eye, and testing may not be able to detect them completely. Otherwise, why would they be classified as special equipment, with seven different stages involved in their production?

This post was last edited by realben on 2009-11-8 at 22:40. First and foremost, from a standardization perspective, it is necessary to follow the technical requirements strictly. Secondly, is the material used by the poster Cr-Mo steel? Especially 2.25Cr1Mo. There is a tendency for delayed cracks after welding, namely cold cracks. This is usually caused by the hardenability of the material, welding stresses, and the effect of diffused hydrogen. Typically, a dehydrogenation treatment at around 350 degrees for 2 hours is carried out immediately after welding; this applies to each weld seam, meaning that the treatment is performed as many times as there are seams. Or maintain the heat after welding until the heat treatment at around 650 degrees is carried out. If, as the original poster suggested, the intermediate dehydrogenation heat treatment is also omitted without using insulation, it will definitely be detrimental to delaying crack formation

This post was last edited by welding on 2009-11-9 09:11. The material is SA516GR60N, which is equivalent to 16MnDR. It was deemed unnecessary to perform dehydrogenation treatment, as there was no tendency for delayed cracking. Even with a thickness of 82 mm, its weldability is very good.

For 5# welding, based on the information provided by the original poster, it can be determined that only overall stress-relief heat treatment after welding is required; no dehydrogenation heat treatment is necessary for Class A welds after they have been welded.

I think it’s extremely necessary. I’m not sure whether LZ uses the national standards or ASME standards; in any case, for plates manufactured according to ASME standards, if the thickness exceeds 38 mm, post-weld heat treatment (PWHT) as well as final overall heat treatment is required! I’m not in design, so I’m not entirely sure about its specific function! Hehe~

I definitely don’t need to; our factory already has 84 thick towers made of SA516 GR70N, and all that’s required is overall heat treatment after welding

The purposes of the two heat treatments are different; it is necessary to follow the drawings and technical requirements.

The friend upstairs said it well; since the designer requested it to be done this way, there must be a reason for it – otherwise no one would go to the trouble of doing it. If you really don’t understand, you can ask the designer, and then you’ll understand her intention. It can’t be said that heat treatment should be carried out based solely on the thickness. Other conditions also need to be considered, such as the medium, etc. Consider everything comprehensively.

The intended purpose of this design is to eliminate hydrogen. Although SA516 GR70N has decent weldability, delayed cracks can still occur during the actual manufacturing process due to various factors. By adding this heat treatment step, it is possible to more reliably increase the chances of preventing the formation of such delayed crack defects