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ASTM A320 L7 Stud Bolts This is the most common A320 bolt grade. A320 Grade L7 bolts and threaded studs are manufactured from alloy steel with chromium, manganese, and molybdenum. The bolts undergo a heat treating process to reach their required mechanical properties.
During the extraction, transportation and processing of oil and gas, many equipment and pipelines need to operate in harsh environments such as low temperature and high pressure. ASTM A320 grade L7 stud bolts are widely used in the connection of these equipment and pipelines, such as flange connection, valve installation, etc., due to their high strength and good low temperature performance, to ensure the reliability and safety of the connection.
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 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.
Heat Treatment
Bolting materials shall be allowed to cool to room temperature after rolling or forging,Grades L7,L7A,L7B.L7C,L7M, L43, L1, L70,L71, L72, and L73 shall be reheated to above the upper critical temperature and liquid quenched and tempered.Grades B8,B8C,B8M,B8T，B8F，B8P，B8LN，andB8MLN shall receive a carbide solution treatment. Prod- ucts made from such material are described as Class l.
ASTM A320 Grade L7 Stud Bolts Material
ASTM A320 L7 Stud Bolts Equivalent Properties
Material | Grades | Heat Treatment | UNS | DIN | |
ASTM A320 Grade L7 Bolts | Alloy A286 | AISI 4140/4142 | Quenched and tempered | UNS S66286 | 1.7225 |
ASTM A320 Grade L7 Chemical Composition
Typical chemical compositions include carbon, manganese, silicon, phosphorus, sulfur, chromium, molybdenum and other elements. The addition of alloying elements such as chromium and molybdenum helps to improve the strength, hardness and corrosion resistance of bolts.
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 |
L7 grade means that the stud bolt has a higher strength grade. Specifically, its minimum tensile strength is usually around 740MPa, and the minimum yield strength is about 550MPa. This enables it to withstand greater tension and shear forces, and is suitable for occasions that require higher connection strength.
Mechanical Properties of ASTM A320 L7 Stud Bolts
Grade | Size | Tensile ksi, min | Yield, ksi, min | Elong, %, min | RA % min |
L7 | Up to 2-1/2 | 125 | 105 | 16 | 50 |
ASTM A320 Recomended Nuts and Washer
Bolt Grade | Nuts | Washers |
L7 | A194 Grade 4 or 7 | F436 |
ASTM A193 B7 vs A320 L7 Stud Bolts
Heat treated chromium-molybdenum steel recommended for medium high
temperature service. (Liquid quench -50° to 900° F, Air quench -40°to 900°F)
Mainly used in high temperature, high pressure and low temperature shock environment. Commonly used in high temperature and high pressure equipment and pipeline connections in petrochemical, electric power, boiler and other industries.
ASTM A320 Grade L7
ASTM A320 L7 Stud Bolts are intended for low temperature service down to minus 150° F and has a minimum Charpy impact value of 20 ft. lbs. at this temperature. (-50°to 1100° F)
It focuses on applications in low temperature environments, especially suitable for applications with low temperature shock requirements. It is widely used in low temperature refrigeration, LNG industry, low temperature pressure vessels and other fields.
