Is it not allowed to weld gussets on the outer surface of the 12Cr2Mo1 shell?
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One of the equipment units has a casing made of 12Cr2Mo1R material; brackets need to be welded to the outside of this casing. The dimensions of these brackets are 10 * 100 * 200. Is it necessary to use welding shims before welding the brackets? It has been found that in most cases, welding shims are not allowed to be used on the outside of casings made of 12Cr2Mo1R material. What is the reason for this? On the other hand, there is no such restriction regarding the use of welding shims on the outside of casings made of 14Cr1Mo material. What is the reason for that?
This is due to the tendency of cold cracking in Cr-Mo steel; once a backing plate is used, it becomes impossible to conduct inspections.
Do both 2Cr materials and 1Cr materials exhibit a tendency to develop cold cracks? Why can 1Cr materials be used for welding gussets?
Cr-Mo steel is a steel containing both Cr and Mo, not 1Cr or 2Cr. It is a heat-resistant steel, and according to the requirements of welding procedures, post-weld heat treatment and thermal treatment are carried out. Magnetic particle inspection is even required to detect surface cracks.
You mean the scene, right? It should be possible to weld the pad plates in the manufacturing plant. The chromium-molybdenum steel equipment delivered on-site is all heat-treated; it is rather difficult to carry out post-weld heat treatment on-site.
Of course, shims can be installed and heat-treated along with the equipment; Class E welds are subject to flaw detection, and welding of shims is not allowed after heat treatment.
For 2.25Cr1Mo materials in general, the design is based on API934, which stipulates that there should be no fillet welds, and all connections of accessories must be fully penetrated by welding
How can on-site work take root without shims? I believe that equipment manufacturers need to provide shims that are heat-treated along with the equipment.
Compared to 1cr, 2cr material is more sensitive to cracks. When welding gussets, inspections can only be conducted on the surface; internal defects cannot be detected. This makes it easy for cracks to extend unnoticed to the container shell, which poses a high level of risk. Have you encountered situations where gussets were welded to 2cr material shells?
In manufacturing, the design certainly dictates that welding be carried out where it is required. However, from the designer’s perspective and considering safety factors, I would like to know why 12cr2mo1 material generally isn’t welded with a backing plate, and what the specific reasons are for using 14cr1mo with a backing plate
Mm-hmm, yes, I’ll go check the API requirements, but I find that there are many devices made of 12cr2mo1 material these days. For housings that require welded shaft lugs, shims must be used; should this requirement that welded shaft lugs with shims not be permitted be specified in the technical agreement at the time of signing?