Alloy Steel Fasteners
Giriraj Impex is a manufacturer, stockist, supplier and exporter of alloy steel fasteners – ASTM A193 Grade B7, B7M and B16 stud bolts and hex bolts, ASTM A320 Grade L7, L7M and L43 low-temperature studs, and ASTM A194 Grade 2H, 2HM, 4, 7 and 7M heavy hex nuts. We manufacture alloy steel fasteners in imperial and metric sizes, in plain, black, zinc-plated, galvanised and PTFE-coated finishes, with mill test certificates.
Alloy steel bolting is used for flanged joints in high-temperature, high-pressure and low-temperature piping, pressure vessels, heat exchangers, valves and turbines in refineries, petrochemical plants, power stations and oil and gas facilities.
Specifications
| Standard | Grade | Material | Service |
|---|---|---|---|
| ASTM A193 | B7 | Chromium-molybdenum (4140/4142), quenched and tempered | General high-pressure and elevated-temperature bolting |
| ASTM A193 | B7M | As B7, tempered to 235 HB max | Sour service – NACE MR0175 / ISO 15156 |
| ASTM A193 | B16 | Chromium-molybdenum-vanadium, quenched and tempered | High-temperature service, better creep and relaxation resistance |
| ASTM A320 | L7, L7M | Chromium-molybdenum, impact tested at −101 °C | Low-temperature service |
| ASTM A320 | L43 | Nickel-chromium-molybdenum (4340), impact tested at −101 °C | Low-temperature service, larger diameters |
| ASTM A194 | 2H, 2HM | Medium carbon steel, quenched and tempered | Nuts for B7, B7M and L7 |
| ASTM A194 | 4 | Carbon-molybdenum, quenched and tempered | Nuts for high-temperature and low-temperature service |
| ASTM A194 | 7, 7M | Chromium-molybdenum, quenched and tempered | Nuts for B16, L7 and high-temperature service |
| Item | Details |
|---|---|
| Products | Stud bolts, threaded rods, hex and heavy hex bolts, heavy hex nuts, washers |
| Threads | UNC and 8UN (imperial); ISO metric |
| Dimensions | ASME B18.2.1, B18.2.2; stud lengths to ASME B16.5 / B16.47 |
| Finish | Plain, black oxide, zinc plated, hot-dip galvanised, PTFE (xylan) coated |
| Documents | Mill test certificate (MTC); third-party inspection on request |
Mechanical requirements
| Grade | Tensile strength min, MPa (ksi) | Yield strength min, MPa (ksi) | Hardness max |
|---|---|---|---|
| A193 B7 | 860 (125) | 720 (105) | 321 HB / 35 HRC |
| A193 B7M | 690 (100) | 550 (80) | 235 HB / 99 HRB |
| A193 B16 | 860 (125) | 725 (105) | 321 HB / 35 HRC |
| A320 L7 | 860 (125) | 725 (105) | 321 HB / 35 HRC |
Strength requirements reduce for larger diameters, as given in each standard. A194 2H nuts have a hardness of 248–327 HB; requirements for Grades 4, 7 and 7M are given in ASTM A194. The mill test certificate reports the results for each lot.
High-temperature bolting – B7 and B16
B7 is the standard stud for flanged joints from ambient up to elevated temperatures. At higher temperatures, bolts gradually lose preload through stress relaxation, which can lead to leaking joints. B16, with vanadium added to the chromium-molybdenum steel, keeps its strength and resists relaxation better, so it is specified for high-temperature steam, hydrocracker, reformer and turbine bolting. B16 studs are normally paired with Grade 4 or 7 nuts. For the highest temperatures, A453 Grade 660 or nickel alloy bolting is used.
Low-temperature bolting – L7 and L43
Alloy steels lose toughness at low temperatures, so bolting for cryogenic and low-temperature service must be impact tested. ASTM A320 L7 and L43 studs are Charpy impact tested at −101 °C (−150 °F), and are used in LNG, ethylene, ammonia and refrigeration plants and for cold-climate installations. L43, with nickel added, keeps through-hardening and toughness in larger diameters. L7M is the sour-service version with controlled hardness. Nuts for these studs are A194 Grade 4 or 7, with impact testing where required.
Sour service and coatings
For bolting exposed to hydrogen sulphide, B7M studs with 2HM nuts, and L7M studs with 7M nuts, are supplied to NACE MR0175 / ISO 15156 on request, with every stud hardness tested. Plain and black-oxide bolting is used in protected service; zinc plating, hot-dip galvanising and PTFE fluoropolymer coatings protect against atmospheric and marine corrosion. PTFE coatings also reduce thread friction, so torque values for coated bolting differ from those for plain bolting.
How we manufacture alloy steel fasteners
Stud bolts are made from certified alloy steel bar, quenched and tempered to the required grade. The bar is cut to length, threads are rolled or cut, and ends are chamfered. Nuts are hot forged or machined from bar and heat treated to the grade's hardness range. Each lot is hardness tested and, as the standard requires, tensile, proof-load and impact tested, and every stud and nut is marked with its grade symbol and manufacturer's identification.
Ordering alloy steel fasteners
Please give the specification and grade for studs and nuts, diameter and thread, length, number of nuts per stud, washers, coating, quantity and any impact test, NACE MR0175 / ISO 15156 or inspection requirement. For flange bolting, give the flange size, class and facing and we can calculate stud lengths.
Applications and related products
Alloy steel fasteners are used for flanged joints in high-temperature steam and process piping, high-pressure gas lines, low-temperature LNG and refrigeration systems, pressure vessels, heat exchangers, valves, compressors and turbines. Matching products include alloy steel flanges, alloy steel pipe fittings, alloy steel pipes and tubes, alloy steel plates and alloy steel round bars. All fastener materials are on the fasteners page, and grade guidance on the alloy steel page.
Frequently Asked Questions
Both are quenched and tempered chromium-molybdenum steels. B16 contains vanadium, which gives better strength and resistance to stress relaxation at high temperatures.
A320 L7 stud bolts are impact tested at −101 °C and are used for flanged joints in low-temperature service such as LNG, ethylene and refrigeration plants.
B16 studs are normally used with ASTM A194 Grade 4 or Grade 7 heavy hex nuts for high-temperature service.
L7 is a chromium-molybdenum steel; L43 is a nickel-chromium-molybdenum steel that keeps its hardenability and toughness in larger diameters. Both are impact tested at −101 °C.
Yes. B7M studs with 2HM nuts and L7M studs with 7M nuts are supplied to NACE MR0175 / ISO 15156 on request, with controlled hardness.
Yes. Studs and nuts can be supplied PTFE coated, zinc plated or hot-dip galvanised for corrosion protection.
Request a Quote for Alloy Steel Fasteners
Tell us the product, grade, size, standard, quantity and delivery location, and our sales team will reply with a quotation.