A pressure relief device for an MPT must be—

(a) From a supplier accepted under chapter I of title 46, Code of Federal Regulations; or

Note 1 to paragraph (a):

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 subchapter.

[CGD 84-043, 55 FR 37410, Sept. 11, 1990, as amended by USCG-2020-0634, 89 FR 50199, June 12, 2024]

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 to § 64.63 or the following formula based upon the pressure relief device operating at a pressure not to exceed the test pressure:

Formula 1 to Paragraph (a) 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 °F of gas at relieving temperature), or 710 °R. 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, equal to 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; USCG-2020-0634, 89 FR 50199, June 12, 2024]

(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.