46 CFR 56.20-1 - General.
(a) Valves certified in accordance with subpart 50.25 of this subchapter are acceptable for use in piping systems.
(b) Non-welded valves complying with the standards listed in § 56.60-1 of this part may be used within the specified pressure and temperature ratings of those standards, provided the limitations of § 56.07-10(c) of this part are applied. Materials must comply with subpart 56.60 of this part. Welded valves complying with the standards and specifications listed in § 56.60-1 of this part may be used in Class II systems only unless they meet paragraph (c) of this section.
(c) All other valves must meet the following:
(1) All pressure-containing materials must be accepted in accordance with § 56.60-1 of this part.
(2) Valves must be designed so that the maximum allowable working pressure does not exceed one-fourth of the burst pressure or produce a primary stress greater than one-fourth of the ultimate tensile strength of the material for Class II systems and for all Class I, I-L, and II-L systems receiving ship motion dynamic analysis and nondestructive examination. For Class I, I-L, or II-L systems not receiving ship motion dynamic analysis and nondestructive examination under § 56.07-10(c) of this part, the maximum allowable working pressure must not exceed one-fifth of the burst pressure or produce a primary stress greater than one-fifth of the ultimate tensile strength of the material. The maximum allowable working pressure may be determined by -
(i) Calculations comparable to those of ASME B31.1 (incorporated by reference; see 46 CFR 56.01-2) or section VIII of the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2), if the valve shape permits this;
(ii) Subjecting a representative model to a proof test or experimental stress analysis described in paragraph A-22 of section I the ASME Boiler and Pressure Vessel Code (incorporated by reference; see 46 CFR 56.01-2); or
(iii) Other means specifically accepted by the Marine Safety Center.
(3) Valves must be tested in accordance with § 56.97-5 of this part.
(4) If welded, valves must be welded in accordance with subpart 56.70 of this part and part 57 of this chapter or by other processes specifically approved by the Marine Safety Center.
(d) Where liquid trapped in any closed valve can be heated and an uncontrollable rise in pressure can result, means must be provided in the design, installation, and operation of the valve to ensure that the pressure in the valve does not exceed that allowed by this part for the attained temperature. (For example, if a flexible wedge gate valve with the stem installed horizontally is closed, liquid from testing, cleaning, or condensation can be trapped in the bonnet section of the closed valve.) Any resulting penetration of the pressure wall of the valve must meet the requirements of this part and those for threaded and welded auxiliary connections in ASME B16.34 (incorporated by reference; see 46 CFR 56.01-2).