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]