These are three cargo tank specifications defined in 49 CFR Part 178, each built for a different category of commodity. DOT 406 (formerly MC 306) tanks carry flammable liquids like gasoline, diesel, jet fuel, and ethanol at 2.65–4 psig MAWP — typically aluminum, elliptical cross-section, multi-compartment. DOT 407 (formerly MC 307) tanks carry mid-pressure chemicals and certain higher-pressure liquids at up to 35–40 psig MAWP — typically stainless or carbon steel, circular cross-section. DOT 412 (formerly MC 312) tanks carry corrosive liquids like sulfuric acid — stainless steel or lined carbon steel construction required. The DOT spec plate on the tank identifies which specification applies and what commodities it can legally carry. Truck Inspection & Maintenance software tracks each tank's specification and test dates per unit.

Under 49 CFR 180.407, six periodic tests are required. External Visual Inspection (V) — walk-around inspection of shell, heads, piping, and mountings. Leakage Test (K) — pressurize to 80% MAWP and verify no leakage for 5 minutes minimum. Pressure Test (P) — hydrostatic or pneumatic test to 1.5 × MAWP. Internal Visual Inspection (I) — confined-space entry to inspect internal shell, baffles, and lining. Thickness Test (T) — ultrasonic wall measurement. Pressure Relief Valve Bench Test — removal and bench testing of PRVs. Each test has its own interval and its own qualified-inspector requirement under § 180.409.

For standard DOT 406 petroleum fuel tankers, the intervals are: annually for External Visual (V) and Leakage Test (K), every 2 years for Thickness Test (T) on unlined tanks carrying liquids that thin the shell, and every 5 years for Internal Visual (I), Pressure Test (P), and Pressure Relief Valve Bench Test. All three 5-year tests typically happen together on the same service visit. A tank with any overdue test may not be filled or transported under § 180.407(a)(1). The test dates are stamped on the tank's spec plate as V-YYMM, K-YYMM, P-YYMM, I-YYMM, and T-YYMM — inspectors check these first at roadside.

49 CFR 180.409 sets minimum qualifications by test type. External Visual, Leakage Test, and Internal Visual can be performed by a Registered Inspector with training, experience, and knowledge of applicable specifications — employer-designated is acceptable if properly qualified. Pressure Test and Thickness Test require a Registered Design Certifying Engineer with registration number appearing on the certificate, and are typically performed at a certified cargo tank facility. Pressure Relief Valve bench tests are performed at a facility with calibrated test equipment by a Registered Inspector. Every test certificate must document the inspector's qualification level and registration number where required. Contact our team to see how the software captures inspector credentials with each test record.

Under 49 CFR 180.407(a)(1), a cargo tank with any overdue test may not be filled and offered for transportation. Consequences are immediate and severe. At the loading rack: the terminal legally cannot load the tank until testing is completed. At roadside: an immediate out-of-service order that keeps the tank from being moved until the overdue test is completed. On a compliance review: an automatic-failure finding that can result in unsatisfactory rating and revocation of hazmat authority. Civil penalties for operating on an overdue tank can reach into five figures per violation, and each shipment on an overdue tank is a separate violation. Track test dates by unit, not by memory or paper spreadsheet.

The differences are commodity type, design pressure, and construction. DOT 406 is the low-pressure standard for flammable liquids — 2.65–4 psig MAWP, typically aluminum, elliptical, no vacuum loading, multi-compartment fuel deliveries. DOT 407 handles mid-pressure liquids and chemicals — up to 35–40 psig MAWP, stainless or carbon steel, circular cross-section, some variants support vacuum loading. DOT 412 is built for corrosive materials — variable MAWP depending on lading, stainless steel or lined carbon steel required, often with full-opening rear head options for aggressive commodities like sulfuric acid. Classification is set at manufacture and cannot be changed in the field. The spec plate is the authoritative source for what a specific tank can legally carry. Try free: sign up here.