1.1 This specification covers Chromium-Molybdenum-Tungsten alloy steel plates intended primarily for welded boilers and pressure vessels designed for elevated temperature service.1.2 Plates are available under this specification in three grades 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 12