(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.
Table 1 to § 64.63—Minimum Emergency Venting Capacity in Cubic Feet: Free Air/Hour
[14.7 lb/in
2a and 60 °F]
Exposed area
square feet
1
| Cubic feet free air
per hour
| Exposed area
square feet
1
| Cubic feet free 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
|
source: CGD 73-172, 39 FR 22950, June 25, 1974, unless otherwise noted.
cite as: 46 CFR 64.63