(a) The low ductility of cast iron and malleable iron should be recognized and the use of these metals where shock loading may occur should be avoided. Cast iron and malleable iron components must not be used at temperatures above 450 °F. Cast iron and malleable iron fittings conforming to the specifications of table 1 to § 56.60-1 may be used at the pressure limits of the applicable standards at temperatures not exceeding 450 °F. Valves of either of these materials may be used if they conform to the standards for class 125 and class 250 flanges and flanged fittings in ASME B16.1 (incorporated by reference; see § 56.01-2).

(b) Cast iron and malleable iron must not be used for valves or fittings in lines carrying flammable or combustible fluids which are directly connected to, or in the proximity of, equipment or other lines having open flame, or any parts operating at temperatures above 500 °F. Cast iron must not be used for hull fittings, or in systems conducting lethal products.

(c) Malleable iron and cast-iron valves and fittings, designed, and marked for Class 300 refrigeration service, may be used for such service up to a pressure limitation of 300 psig. Malleable iron flanges of this class may also be used in sizes 4 inches and smaller (oval and square design).