Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A320 / ASME SA-320 Grade L7B Stud Bolts (UNS G41370)
AISI 4137 chromium-molybdenum alloy steel · Quench-and-tempered
ASTM A320 Grade L7B is a low-temperature alloy steel bolting grade specified per ASTM A320/A320M-22. Assigned UNS number G41370. Manufactured from AISI 4137 chromium-molybdenum alloy steel and supplied in the quenched-and-tempered condition. The grade is intended for stud bolts, hex bolts, and screws used in pressure vessels, valves, flanges, and fittings exposed to cryogenic or sub-zero process temperatures. Charpy V-notch impact testing is mandatory per the specification. Grade L7B offers a chromium-molybdenum chemistry similar to L7 with adjusted alloy levels. Grade L7B is equivalent to ASME SA-320 Grade L7B in the ASME Boiler and Pressure Vessel Code Section II Part A.
ASTM A320 Grade L7B properties
ASTM A320 Grade L7B chemical composition
| Grade Symbol | Description | C | Mn | P, max | S, max | Si | Cr | Mo | |
|---|---|---|---|---|---|---|---|---|---|
| ASTM A320 L7B | Cr - Mo (AISI 4137) | Range,% | 0.35 - 0.40 | 0.70 - 0.90 | 0.035 | 0.04 | 0.15 - 0.35 | 080 - 110 | 0.15 - 0.25 |
| Product Variation, % Over or Under | 0.02 | 0.03 | 0.005 over | 0.005 over | 0.02 | 0.05 | 0.02 | ||
ASTM A320 Grade L7B mechanical properties
| Class and Grade, Diameter, in. [mm] | Heat Treatment | Minimum Tempering Temperature, °F [°C] | Tensile Strength, min, ksi [MPa] | Yield Strength, min, ksi [MPa] (0.2 % offset) | Elongation in 2 in. or 50 mm, min, % | Reduction of Area, min, % | Hardness, max |
|---|---|---|---|---|---|---|---|
| ASTM A320 L7B 21/2 [65] and underA | quenched and tempered | 1100 [593] | 125[860] | 105[725] | 16 | 50 | 321 HBW or 35 HRC |
ASTM A320/A320M Impact Test Requirements
| Grade | Test Temperature | CVN Specimen Section Size, mm | Min Average Impact Toughness of Three Test Specimens, ft-lbf [J] | Min Impact Value of a Single Specimen of Set of Three, ft-lbf [J] | |
|---|---|---|---|---|---|
| °F | °C | ||||
| ASTM A320 L7B | - 150 | - 101 | 10 × 7.5 | 16 [22] | 12 [16] |
| 10 × 10 | 40 [54] | 30 [41] | |||
What nuts and washers are specified for ASTM A320 Grade L7B?
For low-temperature service consistency, ASTM A320 Grade L7B stud bolts are paired with ASTM A194 Grade 4 or Grade 7 heavy hex nuts and ASTM F436 hardened steel washers. TorqBolt supplies kit-matched A320 L7B + A194 + F436 sets with a single EN 10204 3.1 or 3.2 certificate covering all three components.
NORSOK M-650 qualification & EN 10204 3.1 / 3.2 certificates for A320 Grade L7B
TorqBolt’s ASTM A320 Grade L7B stud bolt production route is qualified to NORSOK M-650 for North Sea oil & gas offshore service. Each manufacturing record links heat number, melt analysis, heat-treatment batch, mechanical test, dimensional inspection, surface treatment, and dispatch. Standard certification is EN 10204 Type 3.1 (manufacturer’s test report); Type 3.2 third-party witnessed by Lloyd’s Register, DNV, BV, ABS, or TUV is available on request. The qualification packet covers ASME SA-320 L7B equivalence, NACE MR0175 / ISO 15156-2 sour-service compliance (where applicable), and PED 2014/68/EC for European pressure-equipment buyers.
Related ASTM A320 grades & companion specifications
- ASTM A320 Grade L7: AISI 4140 / 4142 chromium-molybdenum, the most widely specified A320 alloy steel grade.
- ASTM A320 Grade L7M: same UNS G41400 chemistry, tempered for NACE MR0175 sour-service hardness limits.
- ASTM A320 Grade L43: AISI 4340 Ni-Cr-Mo alloy steel with deep hardenability.
- ASTM A320 Grade B8: AISI 304 austenitic stainless equivalent for corrosive low-temperature service.
- ASTM A320 Grade B8M: AISI 316 molybdenum-bearing stainless for chloride exposure.
- ASME B18.31.2 inch double-end stud bolts: dimensional reference for studs mating ASME B16.5 flanges.
- ASME B18.2.1 hex bolts: dimensional reference for A320 hex bolts.
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