The ASTM A517 specification is the Standard Specification for Pressure Vessel Plates, Alloy Steel, High-Strength, Quenched and Tempered material used in the application of fusion welded boilers and pressure vessels. Under this specification, the plate thickness determines the grade selection and the mechanical properties. Plates 2.5" in thickness and under, will have minimum Yield Strength of 100 ksi. Plates over 2.5" in thickness will have a minimum Yield strength of 90 ksi. Typical applications include unfired vessels and tanks.