Specifications

ASTM A193 B7 stud bolts

A193 Grade B7 is a chromium-molybdenum alloy steel, typically AISI 4140 or 4142, quenched and tempered. For diameters up to 2½ inches it has a minimum tensile strength of 860 MPa (125 ksi) and a minimum yield strength of 720 MPa (105 ksi), with a maximum hardness of 321 HB (35 HRC). Strength requirements reduce for larger diameters, as given in the standard. B7 studs are used with 2H nuts for flanged joints in carbon and alloy steel piping from ambient up to elevated temperatures.

B7M is the same material tempered to a lower maximum hardness of 235 HB (99 HRB), with each stud hardness tested, for sour service where NACE MR0175 / ISO 15156 applies. It is paired with 2HM nuts.

ASTM A194 2H heavy hex nuts

A194 Grade 2H nuts are medium carbon steel, quenched and tempered, with a hardness range of 248 to 327 HB (24 to 35 HRC). They are made in the heavy hex pattern to ASME B18.2.2, which has a larger width across flats than a standard hex nut, to spread load on the flange. Grade 2HM nuts have a lower maximum hardness for sour service, and Grades 4, 7 and 7M are used where a stronger or alloy-steel nut is specified.

ASTM A320 L7 and A307

A320 Grade L7 studs are chromium-molybdenum alloy steel, impact tested at −101 °C, for flanged joints in low-temperature service, such as LNG, ethylene and refrigeration systems; they are paired with A194 Grade 4 or 7 nuts, impact tested where required. ASTM A307 covers carbon steel bolts and studs with a minimum tensile strength of 414 MPa (60 ksi). Grade A is for general use and Grade B is for flanged joints in low-pressure, low-temperature piping such as water and cast iron systems.

Coatings

Plain or black-oxide studs are used indoors and in protected service. Zinc plating gives light corrosion protection, and hot-dip galvanising gives heavier protection for outdoor and coastal use, with nuts tapped oversize to suit the coating. PTFE fluoropolymer coatings, often in blue or green, are used offshore and in chemical plants; they resist corrosion and reduce friction during tightening, which helps achieve the intended bolt load. When ordering coated fasteners, please state the coating type and thickness, as these affect thread fit and torque values.

How we manufacture stud bolts

Stud bolts are made from heat-treated alloy steel bar of certified heat. The bar is cut to length, the threads are rolled or cut, and the ends are chamfered. Heavy hex nuts are hot forged or machined from bar and heat treated to the grade's hardness range. Each lot is tested for hardness and, as the standard requires, tensile and proof load, and fasteners are marked with the grade symbol and manufacturer's identification. Stud lengths for ASME B16.5 flanges are calculated from the flange class, size, facing and gasket, including the allowance for nut thread engagement.

Ordering carbon steel fasteners

Please give the specification and grade for studs and nuts, diameter and thread, length, number of nuts per stud, washers if needed, coating, quantity and any NACE MR0175 / ISO 15156, impact test or inspection requirement. For flange bolting, give the flange size, class and facing and we can calculate the stud length.

Applications and related products

Carbon steel fasteners are used for flanged joints in process, steam, water and gas piping, for pressure vessels, heat exchangers, valves and pumps, and for structural steelwork and equipment foundations. Matching products include carbon steel flanges, carbon steel pipe fittings, carbon steel seamless pipes and carbon steel ERW pipes, together with carbon steel plates and carbon steel round bars. All fastener materials are on the fasteners page, and material guidance on the carbon steel page.