The issue of the holding time for overall annealing heat treatment of containers
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At present, our unit has 2 pieces of equipment that need to undergo full annealing. One piece has a plate thickness of 12 MM, while the other has a thickness of 20 MM. I followed the recommended heat treatment parameters specified in Table 5 of NB/T47015-2011: for a 12 MM thick plate, the holding time at 620 degrees is 0.5 hours, and for a 20 MM thick plate, it is 1 hour. Now, the workers in the workshop are asking whether it’s possible to keep both pieces under heat treatment for 1 hour each. Since the formula given in the table indicates the minimum holding time, I’m not sure if an extension is allowed; therefore, I’m seeking advice from experienced colleagues on this forum. Is it possible to extend it? If so, where is the standard source?
There’s no problem; the insulation time specified by the standards is the minimum required time, and it’s fine to extend that time. However, it is necessary to consider the relationship between the holding time for welding process qualification and the holding time for heat treatment in terms of equipment time.
Regarding the relationship between the container insulation time and the insulation time for welding procedure qualification, refer to clause 6.1.4 of NB/T47014.
For 12mm, the heat treatment time specified in the process evaluation is sufficient if it is 48 minutes or more
In the welding process qualification you have chosen, it is acceptable if the heat treatment time is longer than 48 minutes:victory:
A long heat treatment time is also not desirable, as it can lead to an increase in grain size; therefore, heat treating them together is not recommended.