(a) Where pressure retaining components having different thicknesses are welded together as is often the case when making branch connections, the preheat and postheat treatment requirements of Table 56.85-10 apply to the thicker of the components being joined. Postweld heat treatment is required for Classes I, I-L, II-L, and systems. It is not required for Class II piping. Refer to § 56.50-105(a)(3) for exceptions in Classes I-L and II-L systems and to paragraph (b) of this section for Class I systems.
(b) All buttwelded joints in Class I piping shall be postweld heated as required by Table 56.85-10. The following exceptions are permitted:
(1) High pressure salt water piping systems used in tank cleaning operations; and,
(2) Gas supply piping of carbon or carbon molybdenum steel used in gas turbines.
(c) All complicated connections including manifolds shall be stress-relieved in a furnace as a whole as required by Table 56.85-10 before being taken aboard ship for installation.
(d) The postheating treatment selected for parts of an assembly must not adversely affect other components. Heating a fabricated assembly as a complete unit is usually desirable; however, the size or shape of the unit or the adverse effect of a desired treatment on one or more components where dissimilar materials are involved may dictate alternative procedures. For example, it may be heated as a section of the assembly before the attachment of others or local circumferential-band heating of welded joints in accordance with 46 CFR 56.85-10, Table 56.85-10 Note (12) and 46 CFR 56.85-15(j)(3).
(e) Postheating treatment of welded joints between dissimilar metals having different postheating requirements must be established in the qualified welding procedure.
(i) For those materials listed under P-1, when the wall thickness of the thicker of the two abutting ends, after their preparation, is less than three-fourths inch, the weld needs no postheating treatment. In all cases, where the nominal wall thickness is three-fourths inch or less, postheating treatment is not required.
(3) In local postheat treatment the entire band must be brought up to uniform specified temperature over the complete circumference of the pipe section, with a gradual diminishing of the temperature outward from the edges of the band.