(a) All pressure vessels must be provided with protective devices as indicated in UG-125 through UG-136 Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) except as noted otherwise in this subpart.

(b) The markings must be in accordance with this chapter for devices covered by § 54.15-10.

Definitions applicable to this subpart are in § 52.01-3 of this subchapter.

(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.

(a) All safety and relief valves for use on pressure vessels or piping systems must be designed to meet the protection and service requirements for which they are intended and must be set to relieve at a pressure which does not exceed the “maximum allowable working pressure” of the pressure vessel or piping system. Relief valves are not required to have huddling chambers for other than steam service. In addition, safety valves used on vessels in which steam is generated must meet the standards in § 52.01-120 of this subchapter except § 52.01-120(a)(9). For steam service below 206 kPa (30 psig), bodies of safety valves may be made of cast iron. Safety relief valves used in liquefied compressed gas service must meet the standards in subpart 162.017 or 162.018 in subchapter Q of this chapter as appropriate.

(b) Pilot-valve control or other indirect operation of safety valves is not permitted unless the design is such that the main unloading valve will open automatically at not over the set pressure and will discharge its full rated capacity if some essential part of the pilot or auxiliary device should fail. All other safety and relief valves shall be of the direct spring-loaded type.

(c) Safety and relief valves for steam or air service must be provided with a substantial lifting device so that the disk can be lifted from its seat when the pressure in the vessel is 75 percent of that at which the valve is set to blow.

(d) Safety and relief valves for service other than steam and air need not be provided with a lifting device although a lifting device is desirable if the vapors are such that their release will not create a hazard.

(e) If the design of a safety or relief valve is such that liquid can collect on the discharge side of the disk, the valve must be equipped with a drain at the lowest point where liquid can collect (for installation, see UG-134 of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1)).

(f) Cast iron may be employed in the construction of relief valves for pressures not exceeding 125 pounds per square inch and temperatures not exceeding 450 °F. Seats or disks of cast iron are prohibited.

(g) The spring in a relief valve in service for pressures up to and including 250 pounds per square inch must not be reset for any pressure more than 10 percent above or 10 percent below that for which the relief valve is marked. For higher pressures, the spring must not be reset for any pressure more than 5 percent above or 5 percent below that for which the relief valve is marked.

(h) The rated relieving capacity of safety and relief valves for use on pressure vessels must be based on actual flow test data and the capacity must be certified by the manufacturer in accordance with one of the following:

(1) 120 percent of the valve set pressure for valves rated in accordance with CGA S-1.2 (incorporated by reference; see § 54.01-1).

(2) 110 percent of the valve set pressure for valves rated in accordance with UG-131 of Section VIII of the ASME BPVC.

(3) 103 percent of the valve set pressure for steam in accordance with PG-69 of Section VIII of the ASME BPVC.

(a) Paragraph UG-127 of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) provides for the use of rupture disks in series with spring loaded safety or relief valves.

(b) For certain pressure vessels containing substances which may render a relief or safety valve inoperative, or where the installation of a valve is considered impractical, the Commandant may authorize or require the use of a rupture disk in parallel with or in lieu of a spring-loaded safety or relief valve. These rupture disks must:

(1) Comply with the general provisions of § 54.15-5 except as noted otherwise in this section;

(2) Have a capacity for discharge such that the volume of release is sufficient to prevent the internal pressure from exceeding 120 percent of the “maximum allowable working pressure” with the pressure vessel exposed to fire conditions (see § 54.15-25); and,

(3) Operate at a pressure level which does not produce fatigue failure of the disk. The normal maximum operating pressure multiplied by 1.3 must not exceed the nominal disk burst pressure. (Notice that this restriction for protection of the rupture disk will usually require operation below the “maximum allowable working pressure” of the pressure vessel and therefore should be considered in design.)

(c) All disks must be oriented so that if rupture occurs, the disk fragments and pressure vessel discharge will be directed away from operating personnel and vital machinery.

(a) An approved safety valve set to relieve at a pressure not exceeding the “maximum allowable working pressure” of the shell must be fitted to all unfired steam boilers and evaporators except for evaporators of the atmospheric type designed for vapor discharge direct to a distiller with no shutoff valve in the discharge line. The distiller connected to atmospheric evaporators must be fitted with a vent to prevent a buildup in pressure. In no case must the vent be less than 1.5 inches in diameter. Evaporators operating between atmospheric pressure and 15 psig, may use a rupture disc as an alternative to the safety valve.

(b) Safety valves for use on pressure vessels in which steam or pressure is generated must comply with the requirements of § 54.15-10. Rupture discs used in lieu of these safety valves, as provided for in paragraph (a) of this section, must comply with the requirements of § 54.15-13.

(c) The relieving capacity of evaporator safety valves required by paragraph (a) of this section must be at least equal to the capacity of the orifice fitted in the steam supply to the evaporator. The orifice capacity must be determined in accordance with the formula in paragraph (c)(1) or (2) of this section as appropriate:

(1) Where the set pressure of the evaporator shell safety valve is 58 percent or less than the setting of the safety valve in the steam supply:

(2) Where the set pressure of the evaporator shell safety valve exceeds 58 percent of the setting of the safety valve on the steam supply:

(d) The relieving capacity of safety valves on unfired steam boilers must not be less than the maximum generating capacity of the unfired steam boiler as certified by the manufacturer.

(e) On new installations and where the orifice size of an existing unfired steam boiler or evaporator is increased, an accumulation test must be made by closing all steam outlet connections except the safety valves for a period of five minutes. When conducting the accumulation test, the water must be at the normal operating level and the steam pressure must be at the normal operating pressure, and while under this test the pressure must not rise more than 6 percent above the safety valve setting.

(f) A heat exchanger with liquid in the shell and the heating medium in the tubes or coils, must be fitted with a liquid relief valve meeting the requirement of § 54.15-5.

(g)(1) A heat exchanger with steam in the shell and liquid in the tubes or coils at a pressure exceeding that in the shell, must have a liquid relief valve fitted to protect the shell against excess pressure.

(2) The discharge capacity of such relief valves must be calculated on the basis of the discharge from one tube using the difference in pressures between that in the shell and that in the tubes and must be not less than that determined by the following formula:

(a) Each tank must be fitted with one or more safety relief valves designed, constructed, and flow tested in accordance with subpart 162.017 or 162.018 in subchapter Q of this chapter. Valves conforming to specification subpart 162.017 must be limited to use on tanks whose maximum allowable working pressure is not in excess of 10 pounds per square inch. With specific approval of the Commandant, such valves may be connected to the vessel in lieu of being directly fitted to the tanks.

(b) The discharge pressure and the maximum overpressure permitted must be in accordance with § 54.15-5.

(c)(1) The rate of discharge for heat input of fire must meet the following formula:

(2) For an independent tank that has a portion of the tank protruding above the open deck, the fire exposure factor must be calculated for the surface area above the deck and the surface area below the deck, and this calculation must be specially approved by the U.S. Coast Guard, Office of Design and Engineering Standards (CG-ENG).

(d) In determining the total safety valve relieving capacity, the arrangement and location of the valves on the tank will be evaluated. The valves must be placed so that a number of valves sufficient to provide the required relieving capacity must always be in communication with the cargo vapor phase. The possible motions which the tank may see in its intended service and attendant changes in cargo liquid level will be considered. Shut off valves must not be installed between the vessel and the safety relief valves. Manifolds for mounting multiple relief valves may be fitted with acceptable interlocking shut off valves so arranged that the required capacity of discharge will be “lined up” at all times.

(e)(1) Each safety relief valve must be tested in the presence of a marine inspector before being placed in service except as noted otherwise in paragraph (e)(2) of this section. The test must satisfactorily show that the valve will start to discharge at the required minimum pressure.

(2) Each safety relief valve fitted with a breaking pin and rupture disk need not be tested in the presence of a marine inspector before being placed in service. In lieu thereof, a certificate must be furnished with the valve attested to by the manufacturer that the test requirements of paragraph (e)(1) of this section have been met.