ASTM A420

Applies to: Wrought carbon and alloy steel buttwelding fittings for cryogenic and low-temperature service; grades WPL6 (−50 °F/−46 °C), WPL3 (−150 °F/−101 °C), WPL8 (−320 °F/−196 °C, 9% Ni); pairs with ASTM A333 low-temperature pipe.

Does NOT cover: Standard carbon steel fittings for ambient/elevated temperature (use ASTM A234); austenitic stainless or non-ferrous cryogenic fittings.

• Charpy V-notch impact testing at the specified minimum design temperature for each grade
• Normalized (WPL6) or quenched-and-tempered (WPL3, WPL8) heat treatment condition
• Marking includes grade, heat number, and test temperature
• Wall thickness and end preparations per ASME B16.9
• Weldability carbon equivalent limit for field joining

ASTM A420 provides wrought pipe fitting material grades for low-temperature service, bridging the gap between standard carbon steel (A234 WPB) and austenitic stainless steels. Engineers select the grade based on the minimum design temperature (MDT) and verify Charpy impact test results at that temperature. Grade WPL6 covers most LNG vaporizer and cold-box piping at −46 °C; WPL8 (9% nickel) handles liquid nitrogen service to −196 °C.

Engineering note: A420 fittings must be supplied in the heat-treated condition matched to the grade — never substitute A234 WPB fittings for low-temperature service, as they have no guaranteed impact toughness below −29 °C.