When selecting a flange connection with fastener materials stainless steel flange, pipeline operating pressure, operating temperature ought to be considered at the same time, medium type and gasket type and other factors. Gasket type and operating pressure, operating temperature, directly to the fastener material strength requirements are put forward.
For example, the spiral wound gasket seal of low toxic medium pipeline flange connection, although the pipeline operation pressure and temperature is not high, but because of the spiral wound gasket needed to form the initial seal than pressure, and fasteners to bear load is big, therefore, in this case requires fasteners with high strength alloy steel materials.
Alloy steel stud shall adopt high quality steel. The material mark after all should add letters A, such as 35 crmoa, 25 crmova according to different structure, the bolt can be divided into hexagon head bolts and stud (also known as the stud) two kinds, the stud is divided into two kinds of harness and the harness.
Hexagon head bolts: often used with flat welding flange and non-metallic gaskets with milder conditions for operation. Commonly used material is BL3 or hex head bolt is Q235B; Stud: often used with butt welding flange at the operating condition is harsh working conditions, among them, because there is no cross section shape on the harness type stud, so its bearing capacity is strong. Rather than type harness stud is relatively weak bearing capacity. Nut materials often according to and cooperate with bolt material, these combinations have provisions in the general standard.
Under normal circumstances, the nut material should be slightly below the bolt, and ensure the nut hardness is lower than bolt hardness HB30 around.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)