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which do not form a part of the fluid boundary. This includes any weld made to a weld deposited pad or cladding on the fluid boundary as well as the weld deposited pad or cladding beneath the weld itself. This does not include cladding other than cladding beneath the weld nor does it include welds which join clips. nameplates. insulation supports, or other nonstructural members to the fluid boundary. Examples of pressure vessels in this class are all submergence pressure sea water cooled submarine heat exchangers and catapult steam receivers. (2) Class A-1. Class A-1 includes fabrication welds for fired pressure vessels, drums, and headers, in which steam is generated by the application of heat resulting from the combustion of fuel. It includes economizer and superheater headers. Specifically excluded are welds of pressure vessels meeting the classification criteria of classes A-2. A-3. A-4, or A-LT. (3) Class A-2. Class A-2 consists of fabrication welds for unfired pressure vessels with design pressures or design temperatures exceeding 400 lb/in2 or 650°F. respectively, for liquids at 300°F or higher, and for lethal gases and liquids at any temperature or pressure. Class A-2 also includes valves to be installed in class P-1 piping systems. Specifically excluded are welds of pressure vessel's meeting the classification criteria of classes A-3. A-4. or A-LT. (4) Class A-3. Class A-3 consists of fabrication welds for unfired pressure vessels with design pressures and design temperatures not exceeding 400 lb/in2 and 650°F. Specifically excluded are welds of pressure vessels meeting the classification criteria of classes A-4 or A-LT. (5) Class A-4. Class A-4 consists of fabrication welds for unfired pressure vessels with design pressures or design temperatures not exceeding 150 lb/in2 and 450°F. including tanks subject only to the static head or the liquid contained. Specifically excluded are welds for pressure vessels meeting the classification criteria of class A-LT. (6) Class A-LT. Class A-LT consists of fabrication welds for pressure vessels with design pressures greater than 50 lb/in2 and service temperatures of minus 20°F and below. (d) Steam turbines. Class T. Class T steam turbines consist of fabrication welds for steam turbine components or parts (except piping) listed in table XXI. Since steam turbines consist of components subject to service conditions varying from high pressure to vacuum, class T is broken down as follows:
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