Bolts are used for the flange
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For a 321 pipe, should a 321 flange be used? What material should be used for the bolts? The medium is a general-purpose liquid that is non-corrosive and non-flammable.
It’s best to use chromium-molybdenum steel directly, as it has high strength and good corrosion resistance. If you think this material is too expensive, use ordinary carbon steel and apply some rust preventive oil.
For a pipe with diameter 321, the flanges should naturally be made of the same material; the bolts, on the other hand, are chosen based on the pressure and temperature requirements. 35CrMoA/35# can be chosen; for a higher grade, 40MnP/35CrMoA can be selected
It also depends on the medium toxicity, pipeline design temperature, and pressure rating. If the pressure is not high, 8.8/8 grade carbon steel bolts will suffice. For high pressure ratings, low-alloy steel double-headed studs must be used. You can take a look at hg20613