Regarding bolt grade and selection issues
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Multi-purpose hexagonal head bolts are used in chemical sites, pipelines and equipment. The ones used in our factory are generally 8.8 grade. I would like to know what kind of places different grades of bolts are suitable for, how to select them, and how to match bolts and nuts. There is no similar information on the Internet. Please ask an expert for help. Thank you.
You can take a look at HG/T20614 20635
Correct answer upstairs. See the technical regulations for the selection of steel pipe flanges, gaskets and fasteners.
The grade of nuts is generally lower than that of bolts. For example, if bolts are grade 8.8, nuts will be grade 8, and the grades of nuts are all integer grades.
The bolts are not hex head bolts, they are stud bolts.
There are regulations for fastener selection behind the flange standard. You can see it by flipping through the standard.
Most of the petrochemical industry uses fully threaded studs, because HG20614 stipulates that commercial-grade hexagonal head bolts and equal-length double-headed studs are not suitable for flammable and toxic media.
Check GB50635-2009, which contains detailed bolt and flange selection standard requirements.
I happened to encounter this problem in the past two days during the project. Generally, hexagonal head bolts are not used much on chemical pipelines, and most of them are full-threaded ones. Hexagonal head is used in pressure ≤ PN16, and is non-toxic, non-flammable and non-severe circulation situations ； Stud bolts are used when the pressure is ≤ PN40 and are not toxic, non-flammable or violently circulated. Otherwise, only full-threaded bolts can be used. In addition, please pay a selection table of studs and nuts so that the usage conditions, usage occasions and usage temperatures are clear at a glance!