What is the relationship between bolt material and low temperature and low stress?
Thread Content
Appendix C of GB150 stipulates: \"Bolt materials are generally not designed for low-temperature and low-stress conditions, but the difference between the design temperature of the bolt and that of the shell must be taken into account.\" ”Does it mean that when the housing and similar components are subjected to low-temperature and low-stress conditions, they are not designed according to the standards for low-temperature vessels, but the bolt materials are still designed in accordance with those standards? (This doesn’t seem very reasonable, as the shell is the main pressure-bearing component and isn’t designed for low-temperature use; how can a small bolt be designed for low-temperature use?) ) Or do the bolts not need to be designed for low-temperature containers?
Personally, I believe bolts still need to be designed for low-temperature conditions, which means using materials suitable for such conditions and conducting low-temperature impact tests.
Low temperature and low internal stress do not mean no low temperature; rather, according to relevant standards, it is considered a state of low stress. Therefore, low temperatures should be taken into account for the bolts, but the temperature difference between the housing and the bolts also needs to be considered; this definition is correct.
In my opinion, aside from materials such as austenitic stainless steel, bolt materials are generally different from those used in equipment, and their brittle transition temperature differs from that of the materials used in equipment. So it should not take low temperature and low stress into account. However, there is definitely a difference in operating temperatures between the housing and the bolts. When the equipment can be designed for low-temperature and low-stress conditions, the temperature to which the bolts are exposed may not drop below -20 degrees Celsius; but special cases cannot be ruled out. Therefore, the standards do not specify anything definite, and the approach to be taken depends on the actual circumstances. In other words, the selection of materials for the bolts and the conduct of corresponding impact tests should be based on their design temperatures, without taking into account low-temperature and low-stress conditions.