Section 154.440 - 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 [SIGMA]B/2.66 or [SIGMA]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 ([SIGMA]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