A cargo tank is insulated. Under 49 CFR 180.407, how often must it receive an internal visual inspection, compared to a non-insulated tank?

49 CFR 180.407(c)

Insulation covers the tank shell, which can hide corrosion that would otherwise be visible, so DOT shortens the internal inspection interval dramatically for insulated tanks. Drivers hauling insulated tankers should expect this annual cycle rather than the standard 5-year schedule.