ASTM A516 – Pressure Vessel Plates, Carbon Steel, for Moderate- and Lower-Temperature Service Grade: 55   Chemical Requirements Elements Grade55[380] Carbon,max A,B:     1⁄2 in. [12.5 mm] and under 0.18     Over 1⁄2 in. to 2 in. [12.5 to 50 mm], incl 0.20     Over 2 in. to 4 in. [50 to 100 mm], incl…