What material should be used for the supports of Cr-Mo steel containers?

I think the suggestions put forward by the review experts are reasonable; raising requirements artificially can prevent problems caused by the materials. When a skirt is used for chromium-molybdenum steel equipment, the material of the section of the skirt at the connection point should be the same as that of the shell, and its length can be determined through thermal field analysis; it should generally be no less than 500 mm. A butt joint configuration should be employed to avoid problems such as cracks beneath the layer and the inability to detect internal defects. When the container temperature is high and the rigidity of the joints is relatively large, a thermal box structure should also be employed to reduce the thermal stress at the joints caused by excessive temperature gradients.

This question is quite technical; looking forward to experts’ insights

Personally, I think the question regarding review experts is not very reasonable. Assuming for the moment that the expert’s claim that \"there is a significant difference in the heat treatment temperatures for these two materials\" is true, then what he is concerned about is the large difference in properties between Q235B and 15CrMoR; if the same post-weld heat treatment procedure is used, it may prevent one of these materials from achieving the desired results through heat treatment. Therefore, it is necessary to consider the true purpose of post-weld heat treatment. The main goal of this treatment is to reduce the residual stresses in the welded joint. For 15CrMoR, it also helps to prevent the formation of hardened structures at the weld site. To avoid such hardened structures, metallography requires higher heat treatment temperatures and slower cooling rates; however, these temperatures cannot exceed the recrystallization temperature of 15CrMoR, which is around 700°C. Thus, the heat treatment temperature for 15CrMoR must be below 650°C. But what effect does 650°C have on Q235B? Considering the two possible affected aspects: the Q235B base material and the joint, it can be said that the residual stress throughout the joint will certainly be at a relatively moderate level; thus, this has a positive effect on the joint ； Secondly, heat treatment must reach or approach the phase transition temperature in order to affect the properties of the material. The chemical composition of Q235B is similar to that of 20# steel, and its phase transition temperature is at least 730°C; 650°C does not cause any solid-state phase transitions in the Q235B material – it only makes the room-temperature structure (F+P) more uniform, bringing it almost as close to its as-rolled state as possible. In summary, the experts’ concerns are actually unfounded. If his concerns still cannot be dispelled, the weld evaluation results for 15CrMoR and Q235B can actually be used to prove that the performance of such joints is reliable.

This is not a principle-related issue; using Q235B is definitely fine. Our company has produced many products made from Q235B, and the experts are simply suggesting that Q345R would be better

Thank you for clarifying; I actually had doubts about this as well. The experts identified this issue as a corrective action item, but due to their lack of expertise in the field, they did not dare to object

Yes, I also looked at some previous drawings; I’ve worked on many projects involving Cr-Mo steel, and it wasn’t specified that all the supports had to be made of Q345R

It seems that each company has different strict requirements. For tower-type containers, although the skirt is not a stressed component, it is treated as one; therefore, we never use Q235B for the skirt shells – we always use Q345R instead

I think it’s not really a matter of the material for the skirt sleeve. What comes to mind is whether other types of supports, such as saddle supports or lug supports, also require Q345R

Regarding the material requirements for the skirt sleeve: JB/T4710 stipulates that it should be selected based on the requirements for pressure-bearing components. Although NB/T47041 classifies skirt materials into those used for the skirt shell and those used for the transition section in its main text, it still states that selection should be based on pressure-bearing component requirements. GB/T150 imposes numerous restrictions on Q235B; therefore, considering the stress conditions and importance of the skirt, we choose not to use Q235B for the skirt transition section. For the saddles and lugs of Cr-Mo steel equipment, since the stress conditions are less complex than those in the skirts, we use Q235B when the design allows for it at ambient temperatures. In fact, from a purely technical perspective, given that the calculations and welding process evaluations have been completed, it’s fine to use Q235B for the skirt transition section; any structural steel can be used as well.

Brother, you’re mistaken. The transition section should be made of the same material as the main body of the equipment. The Q235B material I’m referring to is the material used for the skirt cylinder, not for the transition section