Thickness of plates.

(a) The wall thickness, after forming of the inner container shell and 2:1 ellipsoidal heads must be not less than specified in § 179.221-1, or not less than that calculated by the following formula: Where: d = Inside diameter in inches; E = 0.9 welded joint efficiency; except E = 1.0 for seamless heads; P = Minimum required bursting pressure in psig; S = Minimum tensile strength of plate material in p.s.i. as prescribed in AAR Specifications for Tank Cars, appendix M, Table M1; t = Minimum thickness of plate in inches after forming. (b) The wall thickness after forming of the inner container heads, if flanged and dished, must be not less than specified in § 179.221-1, or not less than that calculated by the following formula: Where: E = 0.9 welded joint efficiency; except E = 1.0 for seamless heads; L = Main inside radius to which head is dished, measured on concave side in inches; P = Minimum required bursting pressure in psig; S = Minimum tensile strength of plate material in psi as prescribed in AAR Specifications for Tank Cars, appendix M, Table M1 (IBR, see § 171.7 of this subchapter); t = Minimum thickness of plate in inches after forming. (c) The wall thickness after forming of the cylindrical section and heads of the outer shell must be not less than seven-sixteenths of an inch. (d) See § 179.220-9 for plate thickness requirements for inner container when divided into compartments. [Amdt. 179-9, 36 FR 21340, Nov. 6, 1971, as amended at 66 FR 45390, Aug. 28, 2001; 68 FR 75762, Dec. 31, 2003]