T3 is the IMDG Code Chapter 6.7 portable tank instruction for Class 3 packing-group III flammables. Min test pressure 2.65 bar, MAWP matched, 6 mm reference-steel shell, bottom outlet allowed, normal pressure-relief valve. Cargo population: distillate fuels (diesel UN 1202, jet fuel UN 1863, kerosene UN 1223), crude petroleum oil at PG III (UN 1267), white spirit / mineral turpentine UN 1300. Class 3 PG III sits at the lower-risk end of flammable liquids: flash points above 23 deg C and below 60 deg C.
What T3 is built for
The IMDG Dangerous Goods List assigns T3 to most distillate fuels and to crude oil at PG III. Higher-flash-point distillates (some heavy fuel oils) sit in non-DG categories and don’t need a T-coded tank at all. Lighter Class 3 cargoes (PG II flammables like methanol UN 1230, ethanol UN 1170) are assigned T6 or T7 and would not ride a T3 build (the substitution rule runs one way). The T3 fleet is largely a feedstock-trade fleet, moving diesel and jet fuel in 20 to 30-tonne lots from refineries to off-spec markets.
Construction and materials
Mechanically T3 is a low-pressure variant of the T11 build: 316L stainless or carbon-steel cylinder, 6 mm reference-steel shell, no insulation by default (distillate fuels do not need temperature control on standard ocean voyages). Top fittings: DN500 manlid, 3 inch top discharge, sample valve. Bottom fittings: 3 inch foot valve, butterfly secondary, flanged outlet with dust cap. The PRV setting at 2.65 bar matches the test pressure.
A meaningful share of the T3 fleet is carbon-steel rather than stainless because the cargo chemistry doesn’t demand stainless, and the shell-material choice cuts new-build cost by USD 3,000 to 5,000 per tank. Some long-distance fleets prefer stainless anyway because the residual cleaning cost between cargoes is lower and the corrosion margin is forgiving.
When T3 is the right choice
T3 is the right tank when the assigned T-code in IMDG DGL Column 13 is T3 and operator economics prefer the lower-pressure build. As with T6, in practice many T3-eligible cargoes ride T11 because the T11 fleet is bigger and the substitution rule allows it. A dedicated diesel or jet-fuel fleet on a captive refinery-to-customer rotation may run T3 because the unit cost is lower and the pressure rating is matched to the cargo.
When T3 is the wrong choice
T3 is the wrong tank for Class 3 PG II (methanol, ethanol, acetone, MEK, toluene): those need T6 or stronger. T3 is also the wrong tank for non-DG food-grade cargo (pick T4 or T11 food-grade) and for Class 8 corrosives (pick T7 or T8 stainless or T7 / T11 lined).