Do the bolts and nuts used for connecting pipe flanges have to be made of the same material as the flanges?
Thread Content
Do the bolts and nuts used for connecting pipe flanges have to be made of the same material as the flanges? Stainless steel flanges for pipeline connections—sus304; then must the bolts and nuts used be made of the same material as the flange?
This depends on the design specifications and the design conditions of the process pipelines. For process pipelines that operate under high temperature and pressure, the bolts must possess a certain level of strength to meet the requirements; in such cases, bolts made from special materials may be used. Like in ordinary stainless steel pipes, the flange bolts can be made of stainless steel (grade 8/8.8), or brass bolts can be used; the nuts for the screws can be made of stainless steel while those for the bolts can be made of brass.
Take a look at HG 20613-2009 and HG 20634-2009! There are specifications for fasteners inside.
Not necessarily! It must meet the requirements of design and manufacturing processes! Take a look at HG 20613-2009
It is not necessary; the connecting bolts and nuts for our 304 flanges and 316L flanges are made of ordinary carbon steel. These bolts and nuts do not come into contact with the medium, so they are only exposed to atmospheric corrosion. As long as their strength is sufficient, that’s enough. However, in some situations, there is a concern that highly corrosive materials might leak from the flanges and corrode the bolts, and in such cases, bolts made of the same material as the flanges are used.
There are no standard requirements that mandate consistency; choose based on the usage scenario
Choose according to the design and operating conditions; please read the relevant instructions in HG20613 carefully. Just make sure that stainless steel and carbon steel do not come into direct contact.
It still has to be based on the design requirements!
“The statement that flange bolts can be made of stainless steel (grades 8/8.8) is incorrect; stainless steel bolts do not have such grades. These are standards for carbon steel bolts. Stainless steel bolts are available in several materials, with austenitic types including A1, A2, A4, and performance grades of 50, 70, 80. For SUS304, A2-70 grade stainless steel bolts should be used.
This post was last edited by cmt2098200 on 2009-8-7 20:09. The material selection for bolts and nuts depends on the design temperature; low-alloy materials are the best choice as they possess higher strength compared to carbon and stainless steel. Their low cost is also an advantage. On the other hand, the galvanic effect must also be taken into account to prevent electrochemical corrosion.