1117.1 Inside Dimensions 6 Inches or Less. Pressure

vessels having inside dimensions of 6 inches (152 mm) or less shall be: (1) Listed either individually or as part of an assembly by an

approved, nationally recognized testing laboratory, or (2) Marked directly on the vessel or on a nameplate attached

to the vessel with a “U” or “UM” symbol signifying compliance with ASME BPVC Section VIII, or (3) When requested by the Authority Having Jurisdiction,

the manufacturer shall provide documentation to confirm that the vessel meets the design, fabrication, and testing requirements of ASME BPVC Section VIII. Exception: Vessels having an internal or external design pressure of 15 psig (103 kPa) or less.

Pressure vessels having inside dimensions of 6 inches (152 mm) or less shall be protected by either a pressure-relief device or a fusible plug. [ASHRAE 15:9.3.1.1]

1117.1.1 Pressure-Relief Device. Where a pressurerelief device is used to protect a pressure vessel having an inside dimension of 6 inches (152 mm) or less, the ultimate strength of the pressure vessel so protected shall withstand a pressure of not less than 3.0 times the design pressure. [ASHRAE 15:9.3.1.2]

1117.1.2 Fusible Plug. Where a fusible plug is used to protect a pressure vessel having an inside diameter of 6 inches (152 mm) or less, the ultimate strength of the pressure vessel so protected shall withstand a pressure 2.5 times the saturation pressure of the refrigerant used at the temperature stamped on the fusible plug or 2.5 times the critical pressure of the refrigerant used, whichever is less.

[ASHRAE 15:9.3.1.3]