Section 54.15-5 - Protective devices (modifies UG-125)(a) All pressure vessels must be provided with protective devices. The protective devices must be in accordance with the requirements of UG-125 through UG-136 of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1 ) except as modified in this subpart.(b) An unfired steam boiler evaporator or heat exchanger (see § 54.01-10 ) must be equipped with protective devices as required by § 54.15-15 .(c) All pressure vessels other than unfired steam boilers must be protected by pressure-relieving devices that will prevent the pressure from rising more than 10 percent above the maximum allowable working pressure, except when the excess pressure is caused by exposure to fire or other unexpected source of heat.(d) Where an additional hazard can be created by exposure of a pressure vessel to fire or other unexpected sources of external heat (for example, vessels used to store liquefied flammable gases), supplemental pressure-relieving devices must be installed to protect against excessive pressure. Such supplemental pressure-relieving devices must be capable of preventing the pressure from rising more than 20 percent above the maximum allowable working pressure of the vessel. The minimum required relief capacities for compressed gas pressure vessels are given under § 54.15-25 . A single pressure-relieving device may be used to satisfy the requirements of this paragraph and paragraph (c) of this section, provided it meets the requirements of both paragraphs.(e) Pressure-relieving devices should be selected on the basis of their intended service. They must be constructed, located, and installed so that they are readily accessible for inspection and repair and so arranged that they cannot be readily rendered inoperative.(f) Where pressure-indicating gages are used, they must be chosen to be compatible with the pressure to be indicated. The size of the visual display, the fineness of graduations, and the orientation of the display will be considered. In no case must the upper range of the gage be less than 1.2 times nor more than 2 times the pressure at which the relieving device is set to function.(g) The Commandant may authorize or require the use of a rupture disk in lieu of a relief or safety valve under certain conditions of pressure vessel use and design. See § 54.15-13 .(h) Vessels that are to operate completely filled with liquid must be equipped with liquid relief valves unless otherwise protected against overpressure.(i) The protective devices required under paragraph (a) of this section must be installed directly on a pressure vessel except when the source of pressure is external to the vessel, and is under such positive control that the pressure in the vessel cannot exceed the maximum allowable working pressure at the operating temperature except as permitted in paragraphs (c) and (d) of this section.(j) Pressure-relieving devices must be constructed of materials suitable for the pressure, temperature, and other conditions of the service intended.(k) The opening through all pipes and fittings between a pressure vessel and its pressure-relieving device must have at least the area of the pressure-relieving device inlet, and in all cases must have sufficient area so as not to unduly restrict the flow to the pressure-relieving device. The opening in the vessel must be designed to provide direct and unobstructed flow between the vessel and its pressure-relieving device.(l) Safety devices need not be provided by the pressure vessel manufacturer. However, overpressure protection must be provided prior to placing the vessel in service.CGFR 68-82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 88-032, 56 FR 35822, July 29, 1991; CGD 95-012, 60 FR 48049, Sept. 18, 1995; USCG-2003-16630, 73 FR 65170 , Oct. 31, 2008