1.1 This specification2 covers high-strength quenched and tempered alloy steel plates intended for use in fusion welded boilers and other pressure vessels. 1.2 This specification includes a number of grades as manufactured by different producers, but all having the same mechanical properties and general characteristics. 1.3 The maximum thickness of plates furnished under this specification shall be as follows: Grade Thickness A, B 1.25 in. [32 mm] H, S 2 in. [50 mm] P 4 in. [100 mm] F 2.50 in. [65 mm] E, Q 6 in. [150 mm] 1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system is to be used independently of the other without combining values in any way. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.