Steel pipe up to 1 1/2-inches (38.1 mm) industry pipe standard (IPS) shall be ASTM A53-1978 Grade B. Steel Pipe 2-inches (50.8 mm) (IPS) and larger shall be either ASTM A53-1978 Grade B seamless or ASTM A106-1978 Grade B seamless. ASTM Schedule 40 or heavier steel pipe shall be used where fabricated and assembled by the fusion-welded process. If fabricated and assembled by the threading process, ASTM Schedule 80 steel pipe shall be used. Threaded and flanged fittings shall be cast steel.