The type and thickness of material for DOT 406 specification cargo tanks must conform to Sec. 178.345-2, but in no case may the thickness be less than that determined by the minimum thickness requirements in Sec. 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 in gallons per inch of length
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Material 14 or less Over 14 to 23 Over 23
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MS HSLA SS AL MS HSLA SS AL MS HSLA SS AL----------------------------------------------------------------------------------------------------------------Thickness...................... .100 .100 .160 .115 .115 .173 .129 .129 .187----------------------------------------------------------------------------------------------------------------
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 \1\------------------------------------------------------------------------
Cargo tank motor vehicle rated capacity
(gallons) MS SS/HSLA AL------------------------------------------------------------------------More than 0 to at least 4,500............ 0.100 0.100 0.151More than 4,500 to at least 8,000........ 0.115 0.100 0.160More than 8,000 to at least 14,000....... 0.129 0.129 0.173More than 14,000......................... 0.143 0.143 0.187------------------------------------------------------------------------\1\ Maximum distance between bulkheads, baffles, or ring stiffeners
shall not exceed 60 inches. [Amdt. 178-89, 54 FR 25028, June 12, 1989, as amended at 55 FR 37064, Sept. 7, 1990; Amdt. 178-105, 59 FR 55176, Nov. 3, 1994; 68 FR 19285, Apr. 18, 2003]