T8 is the IMDG Code Chapter 6.7 portable tank instruction at 4 bar test pressure with the bottom-outlet prohibited and a normal pressure-relief valve. It sits between T6 / T7 (which allow bottom outlets) and T9 / T10 (which add a frangible-disc relief regime). The “no bottom outlet” rule signals a cargo where a bottom-outlet failure mode under fire conditions or vehicle rollover is unacceptable, but a frangible disc is not yet mandated.
What T8 is built for
The IMDG Dangerous Goods List Column 13 assigns T8 to certain Class 8 PG I corrosives and selected Class 6.1 PG II toxics where the assigned hazard profile justifies eliminating the bottom outlet without escalating to the full T14 frangible-disc regime. In commercial practice T8 is less common than T11 or T14 because most cargoes either fit into T11 (where a bottom outlet is fine) or escalate to T14 (where a frangible disc is mandatory).
Construction and materials
316L stainless cylinder, 6 mm reference-steel shell. Top discharge through a dip-pipe, no foot valve at the bottom. Manlid hinged or bolted, 3 inch top loading flange, 1.5 inch air-inlet ball valve, sample valve, thermometer well. PRV set at 4.4 bar, vacuum-relief at minus 0.21 bar. Two construction routes available: bare 316L for stainless-compatible cargoes, lined carbon-steel for cargoes that attack stainless.
When T8 is the right choice
T8 is the right tank when IMDG DGL Column 13 assigns T8 to the specific UN entry. The substitution rule of IMDG 4.2.5.2.5 lets a T8 cargo also ride T9 through T22, so an operator may book a stronger code if T8 inventory is short. In practice many T8 cargoes ride T11 because the operator has more T11 fleet and the substitution rule (T8 cargo into T11 tank) does not work backwards: a T11 cannot carry a T8 cargo because T11 allows bottom outlets and T8 prohibits them. The booking has to escalate, not substitute down.
Wait. The substitution rule is not simply “stronger code wins” but “stricter parameter wins on every axis”. A T11 has higher test pressure than T8 (6 vs 4 bar) but allows a bottom outlet, which is less strict than T8’s no-BO rule. So a cargo assigned T8 cannot ride T11 because the bottom-outlet axis is not stricter. The cargo can ride T13, T14, T19, T20, T21, T22 (all of which prohibit bottom outlets), or any similarly strict variant. This is the kind of detail that costs an importer a rejected booking; verify the substitution against IMDG 4.2.5.2.5 case by case.
When T8 is the wrong choice
T8 is the wrong tank for any cargo IMDG DGL Column 13 assigns to T9 / T10 (frangible disc required) or to T14 / T20 / T22 (higher hazard). It is also the wrong tank for cargoes that would ride T11 (where a bottom outlet is required for operational reasons or where the operator’s fleet runs T11 by default).
A specific failure mode
A buyer in Brisbane books a Class 8 PG I cargo from Shanghai. The operator confirms a “T8-equivalent” tank, but ships an unlined T11 build. At Sydney the destination port surveyor refuses to release the cargo because the IMDG plate reads T11 and the bottom-outlet rule for T11 (allowed) does not match the cargo’s assigned T8 (no BO). The fix on the next booking: insist on the IMDG plate stamp matching the assigned T-code, not on a verbal substitution claim. Operator language (“T8-equivalent”) is not legally binding; the data plate is.