ASTM A320 Grade L7 Heavy Hex Bolts

ASTM A320 Grade L7 Heavy Hex Bolts are high-strength alloy steel fasteners specified under ASTM A320/A320M for bolting applications requiring reliable mechanical performance at low temperatures.

Grade L7 is a chromium-molybdenum alloy steel grade that is quenched and tempered and subject to impact toughness requirements for low-temperature service.

Heavy hex head dimensions are commonly specified in accordance with ASME B18.2.1, with inch-series threads generally following ASME B1.1.

These bolts are commonly used with pressure-retaining components such as flanges, valves, fittings, pressure vessels, and piping systems in oil and gas, petrochemical, chemical processing, power generation, and other industrial applications where low-temperature service conditions are a design consideration. They are commonly supplied with ASTM A194 Grade 7 nuts for compatible bolted assemblies.

A key distinction between ASTM A320 Grade L7 and ASTM A193 Grade B7 is their intended service environment. B7 is primarily specified for high-temperature and high-pressure service, whereas L7 is intended for low-temperature service and has impact toughness requirements associated with that application.

Therefore, L7 should not simply be treated as a low-temperature version of B7; the applicable material specification and service conditions determine which grade is appropriate.