6.3.1 Wrought 400 series stainless steels shall not be used for pressure retaining components of pressure vessels, heat exchangers or pipework, but are permitted for non-pressure retaining components up to a maximum operating temperature of 750°F (400°C). Cast 400 series stainless steels may be used for rotating machinery casings and pipework and instrument valves. Integral cladding or weld overlay is permitted for all operating temperatures.
6.3.2 Where 400 series stainless steels are to be welded, low carbon types such as Type 410S (UNS S41008) shall be specified. For non-welded components (such as column trays) higher carbon types, such as Type 410 (UNS S41000) are acceptable.
6.3.3 For rotating machinery casings, the more weldable low carbon 13Cr-4Ni grade CA6NM (UNS J91540) shall be specified in preference to the high carbon grade CA15 (UNS J91150). Carbon content of castings shall not