A cargo tank is insulated and has no manhole opening for internal access. Under 49 CFR 180.407, how often must this tank undergo its periodic pressure retest?

49 CFR 180.407(c)

Insulation can hide corrosion that a normal inspection would catch, so DOT compensates with a much shorter retest cycle for tanks that also lack a manhole for internal access. Drivers assigned this tanker type need to recognize the shorter cycle on its test-date marking rather than assuming the standard 5-year schedule.