High quality steel should be used on alloy steel flange. That is, the material should be followed by the letter A, such as 35CrMoA, 25CrMoVA according to the structure of the different types of bolts can be divided into six-angle head bolts and double-headed bolts (also known as stud) two types, and the two-head bolts are divided into wire and non-tong wire.
Hexagon head bolts for use on alloy flanges: often with flat-weld flanges and Non-metallic gaskets for operating under relatively moderate conditions. Hexagonal head bolts commonly used materials are BL3 or q235b; double-head bolts: often with the long weld neck flange in the operating conditions of a more demanding condition, among them, because the wire-type double head bolt on the no cross-section shape changes, so its bearing capacity is strong.
The relative load-carrying capacity of the alloy steel flange is weaker than that of the wire-type double head bolts. The nut material is often determined according to the bolt material with which it fits, and these combinations are specified in the general standard. In general, the nut material should be slightly lower than the bolt material, and ensure that the nut hardness than the bolt hardness of HB30 around.
