According to 49 CFR 180.407, which type of specialized cargo tank is subject to a shorter periodic pressure retest interval than the standard 5-year interval required for most cargo tanks?

49 CFR 180.407(c)

Tanks that carry insulated or temperature-sensitive cargo wear in ways a casual look won't catch, which is exactly why federal rules test them more often than an ordinary gasoline tanker, provided the tank also lacks a manhole or is lined. A carrier running mixed equipment has to track different intervals, and different test types, for different tanks, not apply one blanket schedule.