(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.
(f) -(h) [Reserved]
(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.
(j) (1) -(2) [Reserved]
(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.