QQ-S-691 Steel Plate, Carbon Silicon, Carbon Molybdenum And Manganese Molybdenum Alloys Hot Rolled, (Marine Boiler Quality) (Use Astm A515, A516, A204, A306)This specification covers steel plates of marine boiler quality, for use at temperatures not over 800degrees F. for carbon steel and 875 degrees F. for the alloy grades for marine boilers and other pressure vessels where fusion welding, flanging or forming is required: for boiler shells, drums, headers, baffles, supporting plates, and similar applications.