A driver hauls propane in an MC 331 cargo tank under 3,500 gallons capacity, built of non-quenched-and-tempered (NQT) steel, in dedicated propane service. Under 49 CFR 180.407, what is the periodic pressure retest interval for this tank?

49 CFR 180.407(c)

This extended interval reflects the strong safety record of this specific tank design and service combination. Recognizing the exception prevents a driver or inspector from mistakenly treating a compliant, in-service propane tanker as overdue for retest.