§ 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:

³ See Appendix B for stress analyses definitions.

σ_m≤f

σ_L≤1.5 f

σ_b≤1.5 F

σ_L + σ_b≤1.5 F

σ_m + σ_b≤1.5 F

where:

σ_m = equivalent primary general membrane stress ⁴

⁴ See Appendix A for equivalent stress.

σ_L = equivalent primary local membrane stress ⁴

σ_b = equivalent primary bending stress ⁴

f = the lesser of (σ_B/A) or (σ_Y/B)

F = the lesser of (σ_B/C) or (σ_Y/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).

[CGD 74-289, 44 FR 26009, May 3, 1979, as amended by CGD 82-063b, 48 FR 4782, Feb. 3, 1983]