The United States Pipeline and Hazardous Materials Safety Administration (“PHMSA”) published a January 14th Interpretive Letter clarifying the Hazardous Materials Regulations (“HMR”) applicable to cargo tanks. See Reference No. 25-0035.
PHMSA was responding to a March 27, 2025, email from Fleener Consulting LLC (“FC”) addressing the required frequency of the external and internal visual inspections of insulated and non-insulated MC 331 cargo tanks.
FC first asked whether if the company is unable to conduct the annual external visual inspection on an insulated MC 331 cargo tank, is it required to conduct an internal visual inspection once a year?
PHMSA responds in the affirmative, stating that each specification cargo tank must be tested and inspected as specified in § 180.407(c) and in accordance with § 180.407(d)(1), where insulation precludes a complete external visual inspection. Further, the cargo tank must also be given an internal visual inspection in accordance with § 180.407(d)(1).
Second, FC asked whether if the company is unable to conduct the annual external visual inspection on a non-insulated MC 331 cargo tank that has a coating, or vinyl wrap applied to the external shell, is it required to conduct an internal visual inspection once a year?
PHMSA responds in the affirmative, stating that if external visual inspection is precluded because any part of the cargo tank wall is externally lined, coated, or designed, to prevent an external visual inspection, those areas of the cargo tank must be visually inspected in accordance with § 180.407(d)(1).
FC lastly posed the question:
… PHMSA has required an internal visual inspection once every 5 years for insulated MC 331 cargo tanks and an internal visual inspection annually for non-insulated MC 331 cargo tanks that have wraps or other external coverings of the tank. If this understanding is still accurate, why are non-insulated MC 331 cargo tanks with a coating or vinyl wrap required to conduct an internal visual inspection every year?
PHMSA responds that Insulated and non-insulated MC 331 cargo tanks are not treated differently with regard to internal visual inspections. It states that In both cases, a complete internal visual inspection is required once every five years as reflected in the table of § 180.407(c). More explanation is provided in the remainder of PHMSA’s response to the question.
A copy of the Interpretive Letter can be found here.
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