Fitting rating for utility piping

A client pipe class for Instrument air service which has threaded fittings of 6000# rating of ASME B16.11. The system has a corrosion allowance of 3 mm. The spec is based on the Shell Piping class for Inst air service. Which specifies 3000# fittings and a CA of 1.27 mm.

The selction of the fitting is based on the matching the bore to the pipe bore. This co-relation is given in B16.11.

The system operating pressure is 11 bar(g).

A 6000# steel fitting seems an over kill, where a Malleable iron fitting would have sufficed for this purpose from the pressure standpoint, considering the service.

ASME B31.3 only disallows use of malleable iron for flammable fluid service. Is there any other reason why a malleable iron fitting cannot be not used for this service.

Sajit Viswan
Piping materials engineer
Technip Abu Dhabi
UAE Received on Fri Feb 09 08:36:00 2007