Last month, an old customer of our company sent us an inquiry for ASTM A320 Grade L7 Stud Bolts. The order’s main item is some large size bolts and nuts. We have made offer for these items specially with a short delivery time because we have known from the customer that the order is in urgent need. The bolts with coating , especially when they are in a small quantity , are normally with a longer delivery time because the coating process are carried in a galvanized bath, there fore it is requested to be carried under certain quantity. This cooperation further consolidates our long-term cooperative relationship with this old customer and lays a solid foundation for cooperation on more subsequent projects.
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What are ASTM A320 Grade L7 Stud Bolts?
ASTM A320 Grade L7 stud bolts This is the most common A320 grade bolt. ASTM A320 L7 bolts and threaded studs are manufactured from chromium, manganese, and molybdenum alloy steel. The bolts undergo heat treatment processes to achieve the required mechanical properties.
In the extraction, transportation, and processing of oil and natural gas, numerous pieces of equipment and pipelines must operate under harsh conditions such as low temperatures and high pressures. ASTM A320 Grade L7 stud bolts are widely used in the connections of such equipment and pipelines—including flange connections and valve installations—due to their high strength and excellent low-temperature performance. This ensures the reliability and safety of these connections.
Stud Bolts Dimension Inspection
Nominal Diameter
Ensure the stud diameter falls within specified tolerances to guarantee smooth nut engagement.
Overall Length
Verify the stud’s total length meets order specifications. Particularly for double-ended studs, dimensional accuracy is critical for achieving proper preload in flange connections.
Thread Length
Ensure the threaded section is sufficiently long to allow the nut to fully engage and achieve the required preload.
Hot-Dip Galvanizing
ASTM A320 Grade L7 stud bolts are typically used in low-temperature applications, but they can undergo hot-dip galvanizing when required for use in corrosive environments. Hot-dip galvanizing forms a zinc alloy layer on the bolt surface, providing excellent corrosion protection. However, the high temperatures involved in the hot-dip galvanizing process may adversely affect the mechanical properties of L7 bolts, particularly their low-temperature toughness. Additionally, the thickness of the galvanized coating impacts thread fit, so extra thread tolerances are typically incorporated during bolt manufacturing to ensure nuts can still be screwed on smoothly after galvanization.
Standard Specification For ASTM A320 L7 Stud Bolts
| ASTM | A320 L7 |
| Standard | ASME B18.2.1, B18.3 |
| Threads Configuration | ASME B1.1 2A/3A Inch Unified Threads and B1.13M 6h Metric Coarse Threads |
| Type | Stud Bolts, Heavy Stud bolt, Tie Bar, Tie Rod, Continuous Threaded Stud Bolts (Fully Threaded Studs without Chamfered Ends), Tap End Stud Bolts, Double End Stud Bolts, Double End Stud Bolts with Reduced Shank, Flange Stud Bolts (Fully Threaded Studs with Chamfered Ends), MS Stud Bolts, Metric Thread Stud Bolt, Rough Forged Stud Bolts, Stud Half Thread Bolts etc. |
| A320 Grade L7 Bolts Neck type | Square, Hex, Oval, Triangular & Knurled etc |
ASTM A320 Grade L7 Chemical Composition
| Element | Composition,%A |
| Chromium MolybdenumD | |
| Carbon,max | 0.38-0.48 |
| Manganese | 0.75-1.00 |
| Phosphorus,max | 0.035 |
| Sulfur,max | 0.040 |
| Silicon | 0.15-0.35 |
| Chromium | 0.80-1.10 |
| Molybdenum | 0.15-0.25 |
Mechanical Properties of ASTM A320 L7 Stud Bolts
ASTM A320 Recomended Nuts and Washer
| Bolt Grade | Nuts | Washers |
| L7 | A194 Grade 4 or 7 | F436 |
ASTM A320 L7 Temperature Range
| Material | Temperature °c ( °f ) | |
| Minumum | Maximum | |
| Carbon Steel | -29 (-20) | 300 (572) |
| B7, L7 | -73 (-100) | 400 (752) |
| B6 | 0 (32) | 500 (932) |
| B8 | -200 (-325) | 575 (1067) |
| B16 | 0 (32) | 520 (968) |
| B17B | -29 (-20) | 650 (1202) |
| INC 718 | 0 (32) | 750 (1382) |
| 660 | -29 (20) | 538 (1000) |
Stress Rupture Requirements of ASTM A320 Grade L7
| bolts Tensile Class | Test Temperature °F [°C] | Stress, min | Time to Rupture, min, h [Note] | Elongation, min, % | |
| ksi | Mpa | ||||
| A, B and C | 1200 [650] | 56 | 385 | 100 | 5 |
| D | 1200 [650] | 40 | 275 | 100 | 5 |
ASTM A320 Standard Scope
ASTM A320 L7 Stud Bolts specification covers alloy steel bolting materials and bolting components for pressure vessels,valves,flanges,and fittings for low-temperature service.See SpecificationA962/A962M for the definition of bolting. The bars shall be hot-wrought and maybe further processed by center less grinding or by cold drawing. Austenitic stainless steel may be solution annealed or annealed and strain-hardened.When strain hardened austenitic stainless steel is ordered, the purchaser should take special care to ensure that Appendix X1 is thoroughly understood.
Characteristics of Stud Bolts
Superior Low-Temperature Toughness: This is Grade L7’s most prominent feature. It undergoes specialized heat treatment (quenching + tempering) to maintain excellent impact resistance and toughness in cryogenic environments, preventing brittle fracture.
High Strength: Exhibits elevated tensile strength and yield strength, enabling it to withstand high-pressure loads.
Alloy Composition: Typically employs chromium-molybdenum alloy steel, providing excellent hardenability and mechanical properties.
Applications:
Cryogenic Service Environments: Widely used in petrochemical, liquefied natural gas (LNG), refrigeration systems, and oil/gas extraction industries.
Critical Joints: Specifically designed for connecting pipes, flanges, valves, pressure vessels, and pumps subjected to cryogenic temperatures.
Common Media: Suitable for environments involving cryogenic media such as ethylene, liquid oxygen, liquid nitrogen, liquefied petroleum gas (LPG), and liquefied natural gas (LNG).
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