46 C.F.R. Subpart C—Pressure Relief Devices and Vacuum Relief Devices for MPTs
Title 46 - Shipping
A pressure relief device for an MPT must be— (a) From a supplier2 2 Accepted suppliers are listed in CG–190, Equipment list. (b) Accepted by the Coast Guard in accordance with the procedures in §50.25–10 of this chapter. [CGD 84–043, 55 FR 37410, Sept. 11, 1990] A spring loaded pressure relief valve must— (a) Be set at a nominal pressure of 125 percent of the maximum allowable working pressure; (b) Have a minimum normal venting capacity that is sufficient to prevent the tank pressure from exceeding 137.5 percent of the maximum allowable working pressure; (c) Close after discharge of a pressure not lower than 115 percent of the maximum allowable working pressure; and (d) If closed, remain closed at any pressure less than 115 percent of the maximum allowable working pressure. If a rupture disc is the only pressure relief device on the tank, the rupture disc must— (a) Rupture at a pressure of 125 percent of the maximum allowable working pressure; and (b) Have a minimum normal venting capacity that is sufficient to prevent the tank pressure from exceeding 137.5 percent of the maximum allowable working pressure. (a) The total emergency venting capacity (Q) of the relief devices of an uninsulated MPT must be in accordance with Table 1 or the following formula based upon the pressure relief device operating at a pressure not to exceed the test pressure:
where: Q=Minimum required rate of discharge in cubic feet per minute of free air at standard conditions (60 °F and 14.7 psia). M=Molecular weight of the product, or 86.7. T=Temperature, degrees Rankine (460° + temperature in degrees F of gas at relieving temperature), or 710° Rankine. A=Total external surface area of the tank compartment in square feet. L=Latent heat of the product being vaporized at relieving conditions in Btu per pound, or 144 Btu per pound. Z=Compressibility factor of the gas at relieving conditions, or 1.0. C=Constant based on relation of specific heats, in accordance with Appendix J of Division 1 of Section VIII of the ASME Code, 1974 edition, or 315. (b) The total emergency venting capacity (Q) of an insulated portable tank may have a reduction if— (1) It is shown to the Coast Guard that the insulation reduces the heat transmission to the tank; (2) The present reduction of the emergency venting capacity (Q) is limited to the percent reduction of the heat transmission to the tank or 50 percent, whichever is less; and (3) The insulation is sheathed. [CGD 73–172, 39 FR 22950, June 25, 1974, as amended by CGD 84–043, 55 FR 37410, Sept. 11, 1990; 55 FR 47477, Nov. 14, 1990] (a) Each MPT that is designed for an external pressure of less than 7.5 psig must have a vacuum relief device. (b) A vacuum relief device for an MPT must— (1) Open at an external pressure of not less than 3 psig; and (2) Have an opening with a cross-section of 0.44 square inch or more. [CGD 84–043, 55 FR 37410, Sept. 11, 1990] A shutoff valve may not be located— (a) Between the tank opening and pressure relief device; or (b) On the discharge side of the pressure relief device. A pressure relief device must be— (a) Accessible for inspection and repair before stowage of the tank; and (b) Attached so that escaping gas does not impinge on the tank or framework. A pressure relief device must be plainly and permanently marked with the— (a) Set pressure rating; (b) Rated flow capacity expressed as cubic feet of standard air (60 °F 14.7 psia) per minute and the pressure at which the flow capacity is determined; (c) Manufacturer's name and identifying number; and (d) Pipe size of inlet.
Title 46: Shipping
PART 64—MARINE PORTABLE TANKS AND CARGO HANDLING SYSTEMS
Subpart C—Pressure Relief Devices and Vacuum Relief Devices for MPTs
§ 64.57 Acceptance of pressure relief devices.
§ 64.59 Spring loaded pressure relief valve.
§ 64.61 Rupture disc.
§ 64.63 Minimum emergency venting capacity.
Table 1_Minimum emergency venting capacity in cubic feet: free air/hour (14.7 lb/in\2\a and 60 °F)------------------------------------------------------------------------ Exposed area Cubic feet free Exposed area Cubic feet free square feet \1\ air per hour square feet \1\ air per hour------------------------------------------------------------------------ 20 27,600 275 237,000 30 38,500 300 256,000 40 48,600 350 289,500 50 58,600 400 322,100 60 67,700 450 355,900 70 77,000 500 391,000 80 85,500 550 417,500 90 94,800 600 450,000 100 104,000 650 479,000 120 121,000 700 512,000 140 136,200 750 540,000 160 152,100 800 569,000 180 168,200 850 597,000 200 184,000 900 621,000 225 199,000 950 656,000 250 219,500 1,000 685,000------------------------------------------------------------------------\1\ Interpolate for intermediate sizes.
§ 64.65 Vacuum relief device.
§ 64.67 Shutoff valve.
§ 64.69 Location of the pressure relief device.
§ 64.71 Marking of pressure relief devices.
