46 CFR 58.20-20: -20 Refrigeration piping.

(a) All piping materials must be suitable for handling the primary refrigerant, brine, or fluid used, and must be of such chemical and physical properties as to remain ductile at the lowest operating temperature.

(b) Piping systems must be designed in accordance with ASME B31.5 (incorporated by reference; see § 58.03-1). Piping used for cargo reliquefaction systems must also comply with the applicable requirements found in low temperature piping, § 56.50-105 of this subchapter.

(c) A relief valve must be fitted on or near the compressor on the gas discharge side between the compressor and the first stop valve with the discharge therefrom led to the suction side. A check valve must be fitted in the atmospheric discharge line if it is led through the side of the vessel below the freeboard deck, or a shutoff valve may be employed if it is locked in the open position.