(a) The wall thickness, after forming of the inner container shell and 2:1 ellipsoidal heads must be not less than specified in Sec. 179.221-1, or not less than that calculated by the following formula:[GRAPHIC] [TIFF OMITTED] TC13NO91.035 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 Sec. 179.221-1, or not less than that calculated by the following formula:[GRAPHIC] [TIFF OMITTED] TC13NO91.036 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 Sec. 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 Sec. 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]