46 C.F.R. Subpart 54.15—Pressure-Relief Devices
Title 46 - Shipping
(a) All pressure vessels built in accordance with applicable requirements in Division 1 of section VIII of the ASME Code must be provided with protective devices as indicated in UG–125 through UG–136 except as noted otherwise in this subpart. (b) The markings shall be in accordance with this chapter for devices covered by §54.15–10. [CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 88–032, 56 FR 35822, July 29, 1991] (a) 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 the ASME Code except as modified in this subpart. (b) An unfired steam boiler evaporator or heat exchanger (see §54.01–10) shall be equipped with protective devices as required by §54.15–15. (c) All pressure vessels other than unfired steam boilers shall 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 shall be installed to protect against excessive pressure. Such supplemental pressure-relieving devices shall 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 shall 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 shall 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 shall 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 shall be equipped with liquid relief valves unless otherwise protected against overpressure. (i) The protective devices required under paragraph (a) of this section shall 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 shall 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 shall have at least the area of the pressure-relieving device inlet, and in all cases shall have sufficient area so as not to unduly restrict the flow to the pressure-relieving device. The opening in the vessel shall 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 shall 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] (a) All safety and relief valves for use on pressure vessels or piping systems shall be designed to meet the protection and service requirements for which they are intended and shall 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 shall meet §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 shall meet subpart 162.017 or 162.018 in subchapter Q (Specifications) 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 shall 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 shall be equipped with a drain at the lowest point where liquid can collect (for installation, see UG–134 of section VIII of the ASME Code). (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 shall 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 shall 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 shall be based on actual flow test data and the capacity shall 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 Compressed Gas Association Standard S–1.2.5.2. (2) 110 percent of the valve set pressure for valves rated in accordance with UG–131 of section VIII of the ASME Code. (3) 103 percent of the valve set pressure for steam in accordance with PG–69 of the ASME Code. [CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 81–79, 50 FR 9436, Mar. 8, 1985] (a) Paragraph UG–127 of the ASME Code 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 shall: (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 shall 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 shall 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 shall 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 shall be fitted with a vent to prevent a buildup in pressure. In no case shall the vent be less than 1 (b) Safety valves for use on pressure vessels in which steam or pressure is generated shall 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, shall comply with the requirements of §54.15–13. (c) The relieving capacity of evaporator safety valves required by paragraph (a) of this section shall be at least equal to the capacity of the orifice fitted in the steam supply to the evaporator. The orifice capacity shall 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: W=51.45AP (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: W=105.3A√ P1(P−P1)
where: W=The required orifice capacity, in pounds per hour. A=Cross-sectional area of rounded entrance orifice, in square inches. The orifice shall be installed near the steam inlet or the coils or tubes and where no orifice is employed the area used in the formula shall be that of the inlet connection or manifold. P=Set pressure of steam supply safety valve, in pounds per square inch, absolute. P1=Set pressure of evaporator shell safety valve, in pounds per square inch, absolute. (d) The relieving capacity of safety valves on unfired steam boilers shall 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 shall 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 shall be at the normal operating level and the steam pressure shall be at the normal operating pressure, and while under this test the pressure shall 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, shall 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, shall have a liquid relief valve fitted to protect the shell against excess pressure. (2) The discharge capacity of such relief valves shall 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 shall be not less than that determined by the following formula: Q=29.81KD2√ P1−P2
where: Q=Required relief valve discharge capacity, in gallons per minute, based on relief valve set pressure. P1=Pressure in the tube or coils, in pounds per square inch. P2=Set pressure of the shell relief valve, in pounds per square inch. D=Internal diameter of the largest tube or coil, in inches. K=Coefficient of discharge=0.62. [CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 72–206R, 38 FR 17226, June 29, 1973] (a) Each tank shall 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 (Specifications) of this chapter. Valves conforming to specification subpart 162.017 shall 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 shall be in accordance with §54.15–5. (c) The rate of discharge for heat input of fire must meet the following formula: Q=FGA0.82
where: Q=minimum required rate of discharge in cubic meters (cubic feet) per minute of air at standard conditions 15 °C and 103 kPa (60 °F and 14.7 psia). F=fire exposure factor for the following tank types: F=1.0 for tanks without insulation located on the open deck. F=0.5 for tanks on the open deck having insulation that has approved fire proofing, thermal conductance, and stability under fire exposure. F=0.5 for uninsulated independent tasks installed in holds. F=0/2 for insulated independent tanks in holds or for uninsulated independent tanks in insulated holds. F=0.1 for insulated independent tanks in inerted holds or for uninsulated independent tanks in inerted, insulated holds. F=0.1 for membrane and semi-membrane tanks. G=gas factor of: where: L=latent heat of the material being vaporized at the relieving conditions, in Kcal/kg (Btu per pound). C=constant based on relation of specific heats (k), Table §54.15–25(c) (if k is not known, C=.606(315)). Z=compressibility factor of the gas at the relieving conditions (if not known, Z=1.0). T=temperature in degrees K=(273 + degrees C) (R=(460 + degrees F)) at the relieving conditions (120% of the pressure at which the pressure relief valve is set). M=molecular weight of the product. A=external surface area of the tank in m2 (sq. ft.) for the following tank types: For a tank of a body of revolution shape: A=external surface area. For a tank other than a body of revolution shape: A=external surface area less the projected bottom surface area. For a grouping of pressure vessel tanks having insulation on the vessel's structure: A=external surface area of the hold without the projected bottom area. For a grouping of pressure tanks having insulation on the tank: A=external surface area of the pressure tanks excluding insulation, and without the projected bottom area.1 1 Figure 54.15–25(c) shows a method of determining the side external surface area of a grouping of vertical pressure tanks. (c–1) 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 Commandant (G-MSE). (d) In determining the total safety valve relieving capacity, the arrangement and location of the valves on the tank will be evaluated. The valves shall be placed so that a number of valves sufficient to provide the required relieving capacity shall 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 shall 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 shall 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 shall 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 shall be furnished with the valve attested to by the manufacturer that the test requirements of paragraph (e)(1) of this section have been met. [CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 74–289, 44 FR 26007, May 3, 1979; CGD 82–063b, 48 FR 4781, Feb. 3, 1983; CGD 95–072, 60 FR 50462, Sept. 29, 1995; CGD 96–041, 61 FR 50728, Sept. 27, 1996; USCG–2004–18884, 69 FR 58346, Sept. 30, 2004]
Title 46: Shipping
PART 54—PRESSURE VESSELS
Subpart 54.15—Pressure-Relief Devices
§ 54.15-1 General (modifies UG–125 through UG–136).
§ 54.15-3 Definitions (modifies UA–60).
§ 54.15-5 Protective devices (modifies UG–125).
§ 54.15-10 Safety and relief valves (modifies UG–126).
§ 54.15-13 Rupture disks (modifies UG–127).
§ 54.15-15 Relief devices for unfired steam boilers, evaporators, and heat exchangers (modifies UG–126).
§ 54.15-25 Minimum relief capacities for cargo tanks containing compressed or liquefied gas.
Table 54.15-25(c)_Constant C------------------------------------------------------------------------ k C------------------------------------------------------------------------1.00.......................................... .606 (315)1.02.......................................... .611 (318)1.04.......................................... .615 (320)1.06.......................................... .620 (322)1.08.......................................... .624 (324)1.10.......................................... .628 (327)1.12.......................................... .633 (329)1.14.......................................... .637 (331)1.16.......................................... .641 (333)1.18.......................................... .645 (335)1.20.......................................... .649 (337)1.22.......................................... .652 (339)1.24.......................................... .658 (341)1.26.......................................... .660 (343)1.28.......................................... .664 (345)1.30.......................................... .667 (347)1.32.......................................... .671 (349)1.34.......................................... .674 (351)1.36.......................................... .677 (352)1.38.......................................... .681 (354)1.40.......................................... .685 (356)1.42.......................................... .688 (358)1.44.......................................... .691 (359)1.46.......................................... .695 (361)1.48.......................................... .698 (363)1.50.......................................... .701 (364)1.52.......................................... .704 (366)1.54.......................................... .707 (368)1.56.......................................... .710 (369)1.58.......................................... .713 (371)1.60.......................................... .716 (372)1.62.......................................... .719 (374)1.64.......................................... .722 (376)1.66.......................................... .725 (377)1.68.......................................... .728 (379)1.70.......................................... .731 (380)1.72.......................................... .734 (382)1.74.......................................... .736 (383)1.76.......................................... .739 (384)1.78.......................................... .742 (386)1.80.......................................... .745 (387)1.82.......................................... .747 (388)1.84.......................................... .750 (390)1.86.......................................... .752 (391)1.88.......................................... .755 (392)1.90.......................................... .758 (394)1.92.......................................... .760 (395)1.94.......................................... .763 (397)1.96.......................................... .765 (398)1.98.......................................... .767 (399)2.00.......................................... .770 (400)2.02.......................................... .772 (401)2.20.......................................... .792 (412)------------------------------------------------------------------------
