Grain size requirements for materials used in pressure vessels
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The appendices to the standards for forgings used in pressure vessels contain additional requirements regarding the grain size of the material. Under what circumstances should this request be made, and what should be the reasonable level?
This requirement is generally not applicable to materials used in pressure vessels; it seems that the grain size requirement exists only for low-alloy steel (HIC) sheets and forgings used in wet H2S environments, where it should be at least grade 5.
It seems that only high-pressure hydrogen-handling equipment such as hydrogenation reactors have requirements regarding the grain size of forgings; different materials have different requirements for grain size.
Even for forgings with resistance to hydrogen corrosion, there are requirements regarding grain size
The grain size requirements for materials used in pressure vessels are as follows: 1. Steel forgings resistant to hydrogen and nitrogen; 2. Steel forgings resistant to stress corrosion; 3. Steel forgings for low-temperature applications; 4. Steel forgings required to meet grade III or higher. The specific grain size requirements at which level are determined according to the requirements set for each individual case.
The determination of grain size is carried out in accordance with GB/T6394-2002 \"Methods for determining the average grain size of metals\", and the required grade shall be determined by the designer.
I would like to ask what material grain size is ?
I would like to ask under what conditions requirements regarding the grain size of forgings and non-metallic inclusions should be specified, and where can such requirements be found? How should a request be made in a reasonable manner?