46 CFR §56.30-20

1. (a)Threaded joints may be used within the limitations specified in subpart 56.15 of this chapter and within other limitations specified in this section.
2. (b)(Modifies 114.1.) All threads on piping components must be taper pipe threads in accordance with the applicable standard listed in table 2 to § 56.60-1. Threads other than taper pipe threads may be used for piping components where tightness of the joint depends on a seal weld or a seating surface other than the threads, and where experience or test has demonstrated that such threads are suitable.
3. (c)Threaded joints may not be used where severe erosion, crevice corrosion, shock, or vibration is expected to occur; or at temperatures over 925 °F. Size limitations are given in table 1 to § 56.30-20(c).
4. (d)No pipe with a wall thickness less than that of standard weight of ASME B36.10M (incorporated by reference; see § 56.01-2) steel pipe may be threaded. For restrictions on the use of pipe in steam service more than 250 psig or water service over 100 psig and 200 °F (93.3 °C), see part 104.1.2(c)(1) of ASME B31.1 (incorporated by reference; see § 56.01-2).