46 CFR § 154.451 - Design vapor pressure.

The Po (kPa) of an independent tank type C must be calculated by the following formula:

Po = 196 + AC(ρ) 3/2

where:

A = 1.813 (σm/ΔσA) 2;

σm = design primary membrane stress;

ΔσA = (allowable dynamic membrane stress for double amplitude at probability level Q = 10−8) 53.9 MPa (7821 psi) for ferritic and martensitic steels and 24.5 MPa (3555 psi) for 5083-0 aluminum;

C = a characteristic tank dimension that is the greatest of h, 0.75b, or 0.45 l;

where:

h = the height of the tank or the dimension in the vessel's vertical direction, in meters;

b = the width of the tank or the dimension in the vessel's transverse direction; in meters; and

l = the length of the tank or the dimension in the vessel's longitudinal direction, in meters; and

ρ = the specific gravity of the cargo.