What is the issue regarding the retesting of the impact energy of the main pressure-bearing components in cryogenic vessels?
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When manufacturing low-temperature vessels, impact energy requirements are specified for the main pressure-bearing components (sheets, forgings, pipes) at the time of procurement. Then the question arises: 1. If the drawings do not require retesting of the material, is it necessary to retest the impact energy of the material upon its return to the factory (since it has already been tested in the quality certificate)? 2. For cases where there is a large quantity of sheets, and HG/T20585-2011 specifies requirements for retesting the impact properties of these sheets, although such standards are not usually indicated in the drawings, should enterprises still carry out impact testing in accordance with these requirements? 3. For forgings, Class IV forgings generally require retesting for impact strength; do companies that use a large number of Class III forgings also conduct retests for impact strength (on a batch basis or per individual forging)? 4. For pipes, the amount used is generally small, so companies tend to overlook them; will they still conduct retests on the impact strength, based on whether it is specified in the quality certificate or not, once the pipes return to the factory? How do various companies implement these in actual manufacturing, and what are the material inspection requirements? PS: If retesting for impact strength is required upon returning to the factory, it incurs high costs and prolongs the material inspection process. If no retesting is done, can the steel mill guarantee that the impact strength of this material meets the requirements specified in the purchase order?
For forgings, Class IV forgings generally require retesting for impact strength. Do companies that use a large number of Class III forgings also conduct retests for impact strength (on a batch basis or per individual forging)?
The drawings do not specify any requirements, so it seems that it is up to the manufacturer itself to decide whether to conduct re-inspection or not. If the drawings do not specify it and the manufacturer does not conduct re-testing, the impact value actually achieved will not meet the material standards. Then the material is unqualified!
If the drawing doesn’t require it, then I won’t do it
The material certificate indicates that the material meets the impact requirements, but in reality the material does not meet those standards. What should be done? Should we ask the material supplier to take it back?
Well, I won’t do any of it. The product is finished, but the test samples fail; I suspect the problem lies with the material. When the material is retested, it still fails. What should I do? Should I ask the sheet metal manufacturer to refund the money?
There’s always a culprit behind every wrong deed, so it’s necessary to talk to the material manufacturers about this
1. For raw materials, it’s essential to use manufacturers who are reputable and reliable, as well as qualified suppliers. 2. If the quality data on the original warranty certificates for the materials is satisfactory, but the finished products fail tests after being manufactured, then it’s necessary to turn to the manufacturer for help. 3. In our factory, for each batch of gas cylinder raw materials that arrive, we conduct retests on their mechanical properties; this process takes several days. Additionally, welding test plates are required after welding, and it’s not feasible to wait several days while my workstation remains idle just because of these tests. As mentioned earlier, having qualified suppliers is very important. 4. As you said, since the drawings don’t specify any requirements, it’s not impossible to conduct re-inspections upon returning; the company can cover those costs. If the products fail the re-inspections across multiple batches, then it will be necessary to switch to another supplier.
That’s true; having suppliers who meet the standards and provide quality assurance is a prerequisite.