T17 is the IMDG Code Chapter 6.7 portable tank instruction at 10 bar test pressure with 6 mm reference-steel shell explicitly required (rather than diameter-dependent), bottom outlet permitted only for solids, and a normal pressure-relief valve (no frangible disc). T17 occupies a niche between T15 (which allows liquid bottom outlets) and T19 (which prohibits all bottom outlets and requires a frangible disc). Cargo population: high-pressure Class 3, Class 6.1, and Class 8 cargoes whose IMDG DGL profile fits the no-frangible-disc envelope.
What T17 is built for
The IMDG Dangerous Goods List assigns T17 to specific UN entries where the test pressure must be 10 bar (the cargo’s vapour pressure or operational profile demands it), the cargo’s reactivity does not require a frangible disc, and a solids-only bottom outlet is acceptable. T17 is uncommon in commercial trade because most 10 bar test pressure cargoes also need a frangible disc (T18) or no bottom outlet (T19).
Construction and materials
316L stainless cylinder, 6 mm reference-steel shell, with the stricter “explicit 6 mm” requirement vs the diameter-dependent rule that applies to T1 to T8 / T11 / T12 / T15 / T16. The shell construction is identical to a T11 or T15 from a manufacturing standpoint; the difference is the certification and plate stamps. ASME U-stamp typical.
When T17 is the right choice
T17 is the right tank when IMDG DGL Column 13 specifies T17 for the UN entry. The substitution rule of IMDG 4.2.5.2.5 allows T17 cargo to ride T18 / T19 / T20 / T21 / T22.
When T17 is the wrong choice
T17 is the wrong tank for cargoes that fit T15 (where a liquid bottom outlet is allowed) or T18 / T19 (where a frangible disc is required). The fleet inventory is small; most operators consolidate around T18, T19, and T20 for the 10 bar pressure class.