The issue of the main bolts in equipment of grade M36 and above as primary compression members
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Article 25 of the code stipulates that the main bolts of equipment of size M36 and above serve as the primary compression members. And are the bolts on the connection flange of a container the main bolts of the equipment, and are bolts larger than M36 the main compression members?
This tolerance specification is quite clear: bolts larger than M36, which serve as the main compression elements, fall under the scope of inspection according to these tolerances; otherwise, they can only be treated as compression elements.
"Can the term \"main bolt of the equipment\" be understood as the bolt on the equipment flange? And why aren’t the bolts on the pipe flange used as the main bolts of the equipment?
We consider anything that is M36 to be a pressure-bearing component, whether it is a equipment flange or a pipe flange
The bolts larger than M36 on the connection flanges of the container shall be the main bolts of the equipment.
Bolts on the nozzle flange of the container that are larger than M36 should be considered the main compression members
In my opinion, while standard specifications certainly need to be carefully crafted, it is even more important to understand the essence of those standards. For main bolts in equipment of grade M36 and above, which serve as primary compression elements, their selection should be based on the degree of harm that could result from their failure. Therefore, the loading conditions on pipe flanges are more stringent than those on device flanges that are not subjected to additional bending moments, such as those subjected to pipeline thrust and bending moments; consequently, the requirements for the bolts used in these pipe flanges are even higher. From this perspective, stricter requirements should be imposed on the bolts used in pipe flanges. Therefore, I believe bolts larger than M36 should be the primary compression members.
Whether the bolts used on the takeover flange are the main bolts of the equipment depends on their location of use; generally, even if the bolts are larger than M36, they are treated as compression members only, rather than primary compression members.
Recommendation: Bolts of grade M36 or higher are generally used. The main pressure-bearing components in GB150 are also clearly specified.