Views: 80 Author: Site Editor Publish Time: 2024-12-20 Origin: Site
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.
What is the ASTM standard for stud bolts?
ASTM A193/A193M
Standard specification for Alloy-Steel and stainless Steel Bolting for High temperature or High Pressure Service and Other Special Purpose Applications.This specification covers alloy steel and stainless steel bolting material for pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications. Ferritic steels shall be properly heat treated as best suits the high temperature characteristics of each grade. Immediately after rolling or forging, the bolting material shall be allowed to cool to a temperature below the cooling transformation range. The chemical composition requirements for each alloy are presented in details. The steel shall not contain an unspecified element for ordered grade to the extent that the steel conforms to the requirements of another grade for which that element is a specified element. The tensile property and hardness property requirements are discussed, the tensile property requirement is highlighted by a full size fasteners, wedge tensile testing.
ASTM A320/A320M
Standard specification for Alloy-Steel and stainless Steel Bolting for Low-Temperature Service This specification covers alloy steel bolting materials for pressure vessels, valves, flanges, and fittings for low-temperature service. Each alloy shall conform to the prescribed chemical composition requirements. The material, as represented by the tension specimens, shall conform to the requirements as to tensile properties such as tensile strength, yield strength, elongation, and hardness. The material shall meet the prescribed impact energy absorption requirements and the recommended test temperature. Mechanical tests shall be conducted on the material, namely: impact testing, tension testing, and hardness testing.
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.
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) |
What is the difference between ASTM A320 Grade L7 and A320 Grade L7M?
ASTM A320 possesses several fastener grades manufactured from either alloy or stainless steel and are intended for cold temperature applications. Both Grade L7 and L7M are manufactured from a quenched and tempered alloy steel. While the chemical requirements for both Grades L7 and L7M are identical, there are several differences that separate the two grades.
Grade L7 bolts are significantly higher in strength than Grade L7m bolts. Additionally, it is important to note that a requirement unique to L7M fasteners is that every part needs to undergo a hardness test. The compatible nut for an L7M bolt, ASTM A194 Grade 7M, also requires hardness test of each part. Machining the Grade 7M nuts after heat treating is prohibited.
A320 Grade L7 fasteners require a permanent marking of “L7” on bolt heads and one end of rods, while Grade L7M fasteners are marked “L7M”. Compatible nuts for both grades that have been impact tested are marked with the letter “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.
