46 CFR §54.01-15

1. (a)The following classifications are exempt from shop inspection and plan approval requirements of this part:
   1. (1)Vessels containing water at a pressure not greater than 689 kPa (100 psig), and at a temperature not above 93 °C (200 °F) including those containing air, the compression of which serves only as a cushion. Air-charging lines may be permanently attached if the air pressure does not exceed 103 kPa (15 psig).
   2. (2)
      1. (i)Hot water supply storage tanks heated by steam or any other indirect means when none of the following limitations is exceeded:
         1. (A)A heat input of 58 kW (200,000 Btu per hour);
         2. (B)A water temperature of 93 °C (200 °F);
         3. (C)A nominal water-containing capacity of 454 liters (120 gallons); or
         4. (D)A pressure of 689 kPa (100 psig).
      2. (ii)The exemption of any tank under this paragraph (a)(2) requires that it must be fitted with a safety relief valve of at least 1-inch diameter, set to relieve below the maximum allowable working pressure of the tank.
   3. (3)
      1. (i)Vessels having an internal operating pressure not exceeding 103 kPa (15 psig) with no limitation on size.
      2. (ii)Cargo tanks of pressure vessel configuration are not included in the exemption in paragraph (a)(3)(i) of this section.
   4. (4)Class I, II, and III pressure vessels that meet the requirements of § 54.01-5(c)(3) and (4).
   5. (5)Condensers and heat exchangers, regardless of size, when the design is such that the liquid phase is not greater than 689 kPa (100 psig) and 200 °F (93 °C) and the vapor phase is not greater than 103 kPa (15 psig) provided that the Officer in Charge, Marine Inspection is satisfied that system overpressure conditions are addressed by the owner or operator.
2. (b)For fluid conditioner fittings see § 56.15-1 of this subchapter.