A B8M hole-bearing bolt (or stud) for ship valves is a critical fastener made from AISI 316 stainless steel that complies with the ASTM A193 B8M standard. The integrated hole is typically used for a safety mechanism, ensuring secure connections in corrosive marine environments.
Material Properties (ASTM A193 B8M)
The B8M designation indicates the use of Type 316 stainless steel, which offers enhanced corrosion resistance compared to other grades like B8 (Type 304) due to the addition of molybdenum.
Corrosion Resistance: Superior resistance to chlorides, pitting, and general corrosion makes it ideal for marine and offshore applications.
Composition: It contains 16-18% chromium, 10-14% nickel, and 2-3% molybdenum.
Strength Classes: B8M comes in two classes:
Class 1: Solution-annealed condition with a minimum tensile strength of 515 MPa (75 ksi).
Class 2: Solution-annealed and strain-hardened for higher strength, with a minimum tensile strength of 860 MPa (125 ksi).
Design and Function
The "hole-bearing" feature is an essential safety requirement for critical applications like ship valves.
Safety Locking: The hole is typically cross-drilled near the end of the bolt or stud to accommodate a split pin or safety wire. This prevents the accompanying nut (often an ASTM A194 Grade 8M nut) from loosening due to vibration or operational stress, which is vital for maintaining pressure integrity in valve assemblies.
Reliability: This design ensures a robust and reliable bolted joint, which is a key requirement in high-pressure and high-temperature services in the petroleum and chemical construction industries where B8M is widely used.