T15 is the IMDG Code Chapter 6.7 portable tank instruction at 10 bar test pressure with bottom outlet allowed and a normal pressure-relief valve. It is the high-pressure variant of T11 (which sits at 6 bar test). Cargo population: Class 3 PG II flammables with high vapour pressure that exceed the T11 envelope. T15 sees limited commercial use because most cargoes that need the 10 bar test pressure also need a bottom-outlet restriction (T17 solids-only) or a frangible disc (T16 / T18).
What T15 is built for
The IMDG Dangerous Goods List assigns T15 to specific Class 3 cargoes where the cargo’s vapour pressure at 50 deg C exceeds what a T11 4 bar MAWP can handle, but where a bottom outlet is operationally needed and a frangible disc is not mandated. The cargo list is small. Crotonaldehyde stabilised UN 1144 is one example.
Construction and materials
316L stainless cylinder, 6 mm reference-steel shell, the 10 bar test pressure achieved with a heavier flange and PRV stack rather than a thicker shell. Top and bottom fittings as for T11. PRV set at 4 bar (the MAWP) with vacuum-relief at minus 0.21 bar.
When T15 is the right choice
T15 is the right tank when IMDG DGL Column 13 specifies T15 for the UN entry. The substitution rule of IMDG 4.2.5.2.5 lets a T15 cargo also ride T16 through T22. Most operators do not run dedicated T15 fleets, so a booking typically substitutes upward into a T17 or T18 tank that is already on the loading port.
When T15 is the wrong choice
T15 is the wrong tank for any cargo IMDG DGL specifies for the no-BO codes (T16, T18, T19) where the bottom-outlet would create an unacceptable failure mode. T15 is also the wrong tank for cargoes that fit T11 (lower test pressure, identical operational profile), where the lower lease rate makes T11 the obvious choice.