ASTM A320: Bolting Material With High Standards

ASTM A 320 is a specification set by the American Society for Testing Materials, which includes alloy steel bolting materials for low temperature service valves, pressure vessels and fittings. The material used as tension specimens shall be able to abide the requirements according to tensile strength, elongation, hardness and yield strength.

Testing for materials are done such as Charpy impact test, to determine the amount of energy absorption of the material during separation. Tensile testing is also done to determine the strength of the material through tension by uniaxial force. Hardness testing is also completed to establish the durability of the material to cope with the standards. The results from the test are usually used to choose the appropriate material for an application, for quality assurance purposes.

ASTM A320 Is The Bolt For Extreme Temperatures

The ASTM A320 standard family is ideal for steel and stainless steel bolts used in places with extremely low temperatures. These bolts can be used in ship construction and metal piping uncovered and exposed to cold temperatures, like oil pipes. The bars are hot-wrought and may be processed through centre less grinding or by cold drawing. The austenitic stainless steel is processed in annealed in solution or strain hardened to ensure durability.

Standard bolts for this specification cover the following grades: L7M, L7, L43, L1, B8 CL1A, B8 CL1, B8 CL2 and B8M CL2. American Society for Testing Materials A 320 L7 can be designated ASTM A 320 GR L7.

Other Properties Of ASTM A320

Grade L43 is sustained to meet the impact values at -101 degrees Celsius and additional restrictions such as obtaining steel with lower S and P contents are provided. The compositions should not be compromised to ensure the durability for low temperature environments.

Specifications for bolts of this grade have a size ranging from ¼ inch – 2 ½ inches. The minimum yield of ASTM A320 grade L7 bolts is around 105 kg/sq in (ksi). The smallest tensile strength it can have is at around 125 ksi. The minimum hardness is not mentioned for these graded bolts. Electroless nickel plating can be used as a treatment for bolts to deposit a nickel coating and prevent metal corrosion. Bath powder suspension is another technique to manufacture composite coatings.