Material and thickness of material.

(a) The type and thickness of material for DOT 412 specification cargo tanks must conform to § 178.345-2, but in no case may the thickness be less than that determined by the minimum thickness requirements in § 178.320(a). The following Tables I and II identify the “Specified Minimum Thickness” values to be employed in that determination. Table I—Specified Minimum Thickness of Heads (or Bulkheads and Baffles When Used as Tank Reinforcement) Using Mild Steel (MS), High Strength Low Alloy Steel (HSLA), Austenitic Stainless Steel (SS), or Aluminum (AL)—Expressed in Decimals of an Inch After Forming Volume capacity (gallons per inch) 10 or less Over 10 to 14 Over 14 to 18 18 and over Lading density at 60 °F in pounds per gallon 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Over 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Over 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Thickness (inch), steel .100 .129 .157 .187 .129 .157 .187 .250 .157 .250 .250 .157 .250 .312 Thickness (inch), aluminum .144 .187 .227 .270 .187 .227 .270 .360 .227 .360 .360 .227 .360 .450 Table II—Specified Minimum Thickness of Shell Using Mild Steel (MS), High Strength Low Alloy Steel (HSLA), Austenitic Stainless Steel (SS), or Aluminum (AL)—Expressed in Decimals of an Inch After Forming Volume capacity in gallons per inch 10 or less Over 10 to 14 Over 14 to 18 18 and over Lading density at 60 °F in pounds per gallon 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Over 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Over 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs 10 lbs and less Over 10 to 13 lbs Over 13 to 16 lbs Thickness (steel): Distances between heads (and bulkheads baffles and ring stiffeners when used as tank reinforcement): 36 in. or less .100 .129 .157 .187 .100 .129 .157 .187 .100 .129 .157 .129 .157 .187 Over 36 in. to 54 inches .100 .129 .157 .187 .100 .129 .157 .187 .129 .157 .187 .157 .250 .250 Over 54 in. to 60 inches .100 .129 .157 .187 .129 .157 .187 .250 .157 .250 .250 .187 .250 .312 Thickness (aluminum): Distances between heads (and bulkheads baffles and ring stiffeners when used as tank reinforcement): 36 in. or less .144 .187 .227 .270 .144 .187 .227 .270 .144 .187 .227 .187 .227 .270 Over 36 in. to 54 inches .144 .187 .227 .270 .144 .187 .227 .270 .187 .227 .270 .157 .360 .360 Over 54 in. to 60 inches .144 .187 .227 .270 .187 .227 .270 .360 .227 .360 .360 .270 .360 .450 (b) [Reserved] [Amdt. 178-89, 54 FR 25031, June 12, 1989; 54 FR 28750, July 7, 1989, as amended at 55 FR 37065, Sept. 7, 1990; 68 FR 19285, Apr. 18, 2003]