Issues regarding heat treatment test plates for the recovery properties of cold-formed compressed components
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For cold-formed cylinders or heads that meet the requirements of clause 8.1.1 in GB150.4, if heat treatment to restore their properties is necessary, clause 9.2.1 stipulates that a heat treatment specimen of the base material must be prepared. How is this specimen prepared? I heard that some organizations use flat plates for production, but the experts from the certification review team do not approve of this approach. Is it necessary to prepare test plates in the shape of the molded components? What do everyone else do?
How representative is this test specimen?
In my personal view on this issue, if the heat treatment intended to restore the material’s properties is a stress-relief treatment, then the test pieces made from the base material should undergo the same degree of cold deformation; otherwise, it is impossible to determine the effectiveness of the heat treatment； If normalizing or solution treatment is carried out, since normalizing not only eliminates stresses but also refines the microstructure, resulting in better overall properties, the same heat treatment is sufficient as long as the plates are manufactured in the same way.
Agreed! But for the specimens subjected to stress-relief heat treatment, if they are end caps, how are the specimens taken?
This is a practical issue; therefore, when our company encounters such situations, we carry out normalizing or solution treatment, and the inspection authorities have never raised any objections.
“After using the flat plate for production, the experts from the certification review team did not approve it. So what is done in such a case? I think what the experts don’t approve of is not the flat test specimen, but the heat treatment temperature. Cold-formed cylinders or heads that require recovery performance heat treatment are necessarily those with a high degree of deformation and thin walls. Tensile specimens cannot be prepared from the large deformation regions of thin-walled heads or from the simulation specimens. Therefore, the requirement in GB150 for providing base metal test plates subjected to heat treatment for cold-forming recovery performance (recrystallization temperature heat treatment) lacks practicality. The only solutions are to use normalizing after cold forming or hot forming, with flat base material specimens.
That makes sense; we usually try to avoid such cold forming problems as well. But recently we’ve encountered the issue of requiring heat treatment to restore the properties of cold-formed manway sections, and it’s also confusing to prepare base metal recrystallization test plates – we don’t know how to do it.
I guess after the release of GB150-2011, no one was able to carry out heat treatment for recovery properties at the recrystallization temperature. One can only find ways to avoid such heat treatment. 1) Reduce the wall thickness of the tube sections while meeting strength requirements, or employ stepwise cold forming to minimize the degree of deformation and avoid the need for heat treatment to restore properties ； 2) Normalizing treatment after cold forming, using flat base metal specimens, independent of cold forming and recrystallization. In most cases, the second method is used; since the dimensions of the manhole section are not large, a small furnace can be employed for heating.
Thank you so much! This is the only option left.
After the unit adopted flat plates for production, the experts from the certification review team did not approve it. What about the brick manufacturers? Why didn’t they approve it?
Experts say it’s not representative :(