Cargo tank

Cargo tank: A cargo tank is a bulk packaging for liquids or gases that is permanently attached to or part of a truck or trailer, or is loaded and unloaded without being removed from it. Fuel tankers, chemical tankers and propane bobtails all carry cargo tanks. Source

The legal definition

Federal rules define a cargo tank as a bulk packaging that is a tank intended mainly for liquids or gases, with its fittings and closures, permanently attached to a motor vehicle or loaded and unloaded without being removed from it. Source Tanks built to haul hazardous materials follow federal specifications such as DOT 406, 407 and 412 and MC 331 and 338. Source

Tests and inspections

Spec cargo tanks have their own test schedule on top of the annual vehicle inspection: an external visual inspection and leakage test every year and internal visual and pressure tests every five years for most tanks. Source The dates are marked on the tank. Drivers of tank vehicles over the size threshold need the N endorsement. Source

In practice EXAMPLE

A fuel carrier checks the stenciled test dates before taking a gasoline load and sees the leakage test is due next week. It books the test before the due date, because an expired test means the tank can't be filled with hazmat. Meanwhile it loads only as many gallons as the weight limit allows, using the weight limit checker. More on tanks in the tanker truck guide and tank truck equipment.

Last product and cleaning

What a cargo tank carried last decides what it can carry next. Shippers of chemicals and food check the last products and often require a wash with a ticket before loading. Some products can't follow others at all because residue could react or contaminate. Tank carriers keep a record of the last several loads for each tank and plan washes into the route, because a load offer the tank can't accept without a wash is a load that may not pay once the wash cost and detour are added.

Spec plates on the tank show its specification, capacity and test pressures; read them when you take over an unfamiliar trailer, and keep the inspection and test reports where the rules require them.