1.1 This specification covers specially heat treated 5 % and 5 ½ % nickel alloy steel plates intended primarily for welded pressure vessels for service at low or cryogenic temperatures. This specification covers specially heat treated 5% and 5 1/2% nickel alloy steel plates intended primarily for welded pressure vessels for service at low or cryogenic temperatures. Plates are classified as Grade A and Grade B. The steel shall be kille