Regarding container heat treatment and test plate issues
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Premise: 16MnDR cylinder, low-temperature vessel (design temperature -25°C); cylinder dimensions are 500×30, and the nozzles are produced by drawing. According to the standard requirements, if the deformation rate exceeds 5%, the cylinder must undergo heat treatment to restore its properties. The drawing process for the nozzles damages the material’s original condition, so normalizing heat treatment is required; in addition, post-welding heat treatment is necessary as per the standards. The normal manufacturing sequence should be: cylinder rolling and straightening – heat treatment to restore properties – tube drawing – normalizing heat treatment – vessel welding – overall post-weld heat treatment. The test plates involved include 1 welding test plate, 1 base metal test plate for the heat treatment to restore properties, and 1 base metal test plate for the normalizing heat treatment. Question: Can the performance-restoring heat treatment be combined with the overall post-weld heat treatment, that is, can this step of performance-restoring heat treatment be omitted for the cylinder? Can the base metal test plates subjected to simultaneous recovery and heat treatment be combined with those subjected to normalizing heat treatment in one piece?
I don’t get it: what’s the relationship between shell rolling and nozzle drawing?
It’s due to the manufacturing sequence: first, the cylinder body is made from steel plates, which require rolling and rounding; then the joints are formed by drawing, rather than by creating holes
This post was last edited by zjq1962 on 2022-7-18 at 16:50. Why are product welding test plates needed? As I understand it, only two base material heat treatment test plates are required (one for performing heat treatment to restore the material properties after cylinder rolling and before welding, and another one obtained through normalizing treatment after nozzle drawing). Post-weld heat treatment does not require a test piece of the product. Furthermore, the purposes of heat treatment to restore material properties and post-weld heat treatment are different, so they cannot be combined.
Low-temperature vessels with seam A require welded test plates. Is the purpose of heat treatment for restoring performance due to over-deformation mainly to eliminate the stress resulting from the deformation? The container medium is natural gas (sulfur-free), and the post-weld heat treatment is also intended to eliminate the stresses generated by welding, right? If the main purpose of each is to relieve stress, can they be combined?
This post was last edited by zjq1962 on 2022-7-19 08:25. Low-temperature containers require the creation of product welding test specimens. Heat treatment for restoring material properties is aimed at ensuring the mechanical properties of the material; it serves a different purpose from stress relief, and the heat treatment processes used are generally also different. Since cold working hardening degrades the material properties, heat treatment is required to restore these properties before welding. If the two heat treatment processes are identical, they can be combined; in such cases, it is best to first discuss this with the quality control department.
Our heat treatment specialist eventually combined the two types of heat treatment – the performance-restoring heat treatment and the post-welding heat treatment. His explanation was that the heat treatment processes were essentially identical, which is why they were combined; the test pieces were also combined in the process. Thank you for your reply!
For normalizing, there is no need to consider any heat treatments prior to normalizing, including those intended to restore properties, as normalizing already performs the function of such heat treatment.