Allowable stress.

(a) The allowable stresses for an independent tank type A must: (1) For tank web frames, stringers, or girders of carbon manganese steel or aluminum alloys, meet σ B /2.66 or σ Y /1.33, whichever is less; and (2) For other materials, be specially approved by the Commandant (CG-ENG). (b) A greater allowable stress than required in paragraph (a)(1) of this section may be specially approved by the Commandant (CG-ENG) if the equivalent stress (σ c ) is calculated from the formula in appendix A of this part. (c) Tank plating must meet the American Bureau of Shipping's deep tank standards, for an internal pressure head that meets § 154.439(a), published in “Rules for Building and Classing Steel Vessels”, 1981. [CGD 74-289, 44 FR 26009, May 3, 1979, as amended by CGD 82-063b, 48 FR 4782, Feb. 3, 1983; CGD 77-069, 52 FR 31630, Aug. 21, 1987]