ASME SA724 Grade C in the standard ASME SA724/SA724M is a kind of carbon steel plates material used to fabric welded multilayer pressure vessels. jwvivian98 (at) yahoo (dot) com Skype jw-vivian (at) hotmail (dot) com SA724 Grade C is also a Quenching + Tempering steel material. ASME SA724 have three types Grade A, Grade B, and grade B .