Industrial fastening in low temperature and high pressure systems might hinge on the accurate specification of materials and mechanical performance criteria. Among the commonly specified grades ASTM standards set the requirements for alloy steel fasteners that are used in critical piping, valves and pressure vessels. When it comes to cryogenic or subzero environments, engineers often choose ASTM A320 L7 Bolts that are made from quenched and tempered chromium molybdenum and thus have a high tensile strength of about 125 ksi and excellent notch toughness. They come in diameters starting from 1/2 inch to more than 4 inches with coarse and fine threads, and are mostly used together with heavy hex nuts that meet ASTM A194 Grade 7 standards. Heat treatment, hardness limits and Charpy V notch impact testing are still standard acceptance criteria for petrochemical and LNG facilities.
People go for austenitic stainless fasteners A2 grade materials according to EN ISO 3506 based on corrosion resistance when used in marine, food processing and architectural assemblies where exposure to chlorides is relatively low. This group comprises, for instance A2-70 Bolts that are produced through cold working of 304 stainless steel to a minimum tensile strength of 700 MPa thereby providing a good balance of strength and ductility as no post heat treatment is necessary. The sizes range in general from M16 to M120 with metric coarse threads and they are mostly used with appropriate A2 nuts to prevent galvanic corrosion. Surface finish, passivation along with thread tolerance classes like 6g also play a big role in ensuring performance. Although these fasteners cannot withstand extremely low temperatures as the alloy steel grades do, they preserve oxidation resistance and are at the same time frequently specified in DIN and ISO based assemblies all over the engineering sectors.
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