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What does fastening hardware include? Pressure vessel fasteners mainly refer to bolts, studs, and nuts, which are commonly used in flange connections. There are standards for vessel flange connections and pipe flange connections in flange connections. These two standards specify the form, material, and selection of fasteners. Special grade: Special-grade fasteners are bolts, studs, and nuts made from specialized materials; these materials have specified steel grades, and their chemical composition, mechanical properties, as well as heat treatment requirements must be met. GB150.1~150.4-2011 specifies pressure vessel-grade fasteners for 11 steel grades, such as 35CrMoA, 30GrMoA, 40MnB, etc. Commercial grade: Commercial-grade fasteners differ from specialty-grade fasteners in that their mechanical properties are not determined by the material used to make them; instead, the performance level of these fasteners is indicated by their mechanical properties after they have been manufactured, such as 8.8, 4.8, etc. The performance grade of bolts (including screws, studs, etc.) is composed of two sets of numbers separated by a “.” The first set of numbers represents 1/100 of the bolt’s nominal tensile strength in MPa, while the second set of numbers, including the decimal point, indicates the ratio of the bolt’s nominal yield strength to its nominal tensile strength (referred to as the yield-to-tensile ratio). Such as commercial-grade 8.8 bolts, with a nominal tensile strength of 800 MPa and a yield strength ratio of 0.8. There are 10 performance grades for commercial-grade bolts: 3.6, 4.6, 5.6, 4.8, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9. Commercial-grade bolts made from stainless steels such as 06Cr19Ni10 (0Cr18N19) or 022Cr19Ni10 (00Cr19Ni10) have performance grades of A2-50 and A2-70. The first part, “A2”, is the material classification code; “A” denotes the material group, while the number “2” indicates the range of chemical composition for that type of steel ； In the second part, 50 and 70 indicate the performance grades of the product; these numbers represent one-tenth of the nominal tensile strength (MPa) of the bolt. In pipe flange connections, the performance grades for commercial-grade fasteners are 8.8, A2-50, or A2-70. Nuts with a nominal height of ≥0.8d (with an effective thread length of ≥0.6d, where d is the nominal thread diameter) are designated by the first digit of the performance grade of the bolt that matches them. For example, the performance grade of a nut that matches an 8.8 grade bolt is 8.