The Pipeline and Hazardous Materials Safety Administration (PHMSA) recently issued a letter of clarification on cargo tank accident damage protection devices. The clarification relates to the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the manufacture of Department of Transportation (DOT) specification cargo tanks.
Specifically, PHMSA addressed suggestions of reconsidering whether accident damage protection devices specified in § 178.345-8 (applicable to DOT406, DOT407, and DOT412 cargo tanks) are considered structural support members as opposed to appurtenances as stated in PHMSA’s guidance issued July 17, 2015, under Reference Number 15-0049.
PHMSA’s previously issued guidance on this issue remains valid. An accident damage protection device meets the definition of an appurtenance as defined in §§ 178.320 and 178.345-1. If required, accident damage protection devices for DOT406, DOT407, and DOT412 cargo tanks must be attached to the cargo tank in accordance with the requirements of § 178.345-8(a)(3).
If accident damage protection is applied directly to the cargo tank wall, the accident damage protection device must have no lading retention or containment function and provide no structural support to the cargo tank.
Accident-induced stresses resulting from the appropriate accident damage protection device requirements in combination with the stresses from the cargo tank operating at the maximum allowable working pressure (MA WP) may not result in a cargo tank wall stress greater than the ultimate strength of the material of construction using a safety factor of 1.3.