T12 is the IMDG Code Chapter 6.7 portable tank instruction at 6 bar test pressure with bottom outlet permitted only for solids and a frangible-disc plus tell-tale-gauge relief regime. T12 sits between T11 (which allows liquid bottom outlets and uses normal PRV) and T14 (which prohibits all bottom outlets and adds the same frangible disc). The cargo population: Class 6.1 PG II toxics and certain Class 8 corrosives where the IMDG profile requires a frangible disc but a solids bottom outlet is acceptable.
What T12 is built for
The IMDG Dangerous Goods List assigns T12 to specific Class 6.1 PG II UN entries where a frangible disc is required but the cargo can ride with a solids bottom outlet (which on liquid service is plugged or designed for non-DG drainage). T12 sees limited commercial use because most Class 6.1 PG II cargoes either fit T11 (no frangible disc) or escalate to T14 (no bottom outlet at all).
Construction and materials
316L stainless cylinder, 6 mm reference-steel shell. ASME U-stamp typical for ocean carriage. Top discharge through a dip-pipe; bottom outlet plugged on liquid service. Frangible disc plus tell-tale gauge mounted in series with the spring-loaded PRV at 4.4 bar.
When T12 is the right choice
T12 is the right tank when IMDG DGL Column 13 specifies T12 for the UN entry. The substitution rule allows T12 cargo to ride T13, T14, T19, T20, T21, T22.
When T12 is the wrong choice
T12 is the wrong tank for any cargo IMDG DGL assigns to T14 (where the no-BO rule is mandatory) or T11 (where no frangible disc is required, the operator fleet is bigger, and the lease rate is lower).