This specification covers chromium-molybdenum-tungsten alloy steel plates intended primarily for welded boilers and pressure vessels designed for elevated temperature service. The plates shall be available in three grades, namely Grades 23, 911, and 122, having different alloy contents. The maximum thickness of plates is limited only by the capacity of the composition to meet the specified mechanical requirements. The steel shall be killed and the plates shall undergo heat treatment. In order to determine mechanical properties such as yield strength and elongation, the plates shall be subjected to tension and hardness tests.