Should the studs used for pipe flange connections be hot-dip galvanized or blackened?
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For the double-headed bolts used in pipe flange connections, should they be hot-dip galvanized or blackened? The pressure is not high, below 1 MPa, and PN2.0 flanges are used. I’m used to seeing double-headed bolts that are blackened and painted along with the flanges; it seems strange to see those that are hot-dip galvanized. Are there any standards specifying which one to use? For the above operating conditions, what strength and standard of bolts should be used?
HG20592 European-style flange; the fasteners used are HG20613； The HG20615 American-style flange is used, with HG20634 fasteners being employed. There are also the machinery sector, oil, petrochemicals, national standards, and various other areas.
There are too many standards and too few conditions to make a judgment. It is guessed that bolts made of hot-dip galvanized steel are used to reduce the need for anti-corrosion measures later on, as well as for aesthetic reasons
Check if there are any anti-corrosion requirements; galvanizing provides much better anti-corrosion protection than blackening treatment.
It depends on the specific requirements; in the end, it will have to be painted
It is not only related to temperature and pressure, but also to the medium being transported! Derived from HG/T20613-2009