46 CFR 154.447: Allowable stress.

(a) An independent tank type B designed from bodies of revolution must have allowable stresses 3 determined by the following formulae:

σm≤f

σL≤1.5 f

σb≤1.5 F

σL + σb≤1.5 F

σm + σb≤1.5 F

where:

σm = equivalent primary general membrane stress 4

σL = equivalent primary local membrane stress 4

σb = equivalent primary bending stress 4

f = the lesser of (σB/A) or (σY/B)

F = the lesser of (σB/C) or (σY/D)

A, B, C, and D = stress factors in Table 2.

Table 2—Values for Stress Factors

Nickel steel and carbon manganese steel values Austenitic steel values Aluminum alloy values

Stress factors:

A 4.0 4.0 4.0

B 2.0 1.6 1.5

C 3.0 3.0 3.0

D 1.5 1.5 1.5

(b) An independent tank type B designed from plane surfaces must have allowable stresses specially approved by the Commandant (CG-ENG).