T50 is the IMDG Code Chapter 6.7.3 portable tank instruction for non-refrigerated liquefied gases shipped under pressure. The cargo population: LPG, propane, butane, anhydrous ammonia, chlorine, ethylene oxide, vinyl chloride monomer, butadiene, and the refrigerant-gas series R-22 through R-410. MAWP varies by gas and by the tank’s insulation state per the four-column table in IMDG 4.2.5.2.6: bare, sun-shielded, insulated, fully insulated. The lowest MAWPs (around 7 bar) apply to butane and R-134a. The highest (34.4 bar) applies to R-125 pentafluoroethane.
What T50 is built for
The T50 cargo list is fixed and listed with its specific MAWP and filling density in the IMDG T50 master table. A representative sample: anhydrous ammonia UN 1005 (MAWP 22 bar insulated up to 29 bar bare, filling density 0.53 kg/L), LPG UN 1075 (MAWP 23 to 25 bar bare), butane UN 1011 (MAWP 7 bar, filling density 0.51), chlorine UN 1017 (MAWP 22 bar insulated, no bottom outlet, baffled), ethylene oxide UN 1040 (MAWP 10 bar, insulated only, frangible disc, filling density 0.78), vinyl chloride UN 1086 (MAWP 8.1 to 12 bar, filling density 0.81), butadiene UN 1010 (MAWP 7 to 10 bar, filling density 0.55), R-22 UN 1018 (MAWP 19 to 26 bar by insulation), R-125 UN 3220 (MAWP 24.5 to 34.4 bar, the high end of the table).
Each gas has its own combination of MAWP, filling density, bottom-outlet permission, and pressure-relief regime in the IMDG table. Chlorine and ethylene oxide both prohibit bottom outlets, with the cargo discharged from the top through a dip-pipe and an isolation valve cabinet.
Construction and materials
A T50 is a thick-walled carbon-steel pressure vessel mounted on a saddle suspension inside the ISO 1CC frame. The saddle absorbs thermal expansion and shock loading. Shell thickness is dictated by the design pressure: a 22 bar MAWP build typically runs 12 mm carbon steel, a 34.4 bar build runs heavier. ASME VIII Div 2 with the U2-stamp is mandatory for ocean carriage under 49 CFR 178.276. Most fleets carry both the ASME stamp and the GB 18564.1 / GB 150 / TSG R0005 Chinese national codes for builds that ship from Chinese factories.
Top fittings are concentrated in a valve cabinet bolted to the manlid: liquid filling line, vapour line, PRV, frangible disc (where required by the specific UN), liquid level gauge, pressure gauge, sample valve. Chlorine builds add a two-piece manlid with M24 PTFE-gasketed bolts and twin internal surge baffles. The valve cabinet on a chlorine T50 is a sealed compartment with explosion-relief protection.
Tare runs 9,000 to 11,500 kg, considerably heavier than a T11. Payload sits at 24 to 27 tonnes. The 24,300 L typical capacity is dictated by IMDG filling-density caps: at LPG 0.50 kg/L, 24,300 L tops out at about 12 tonnes; at chlorine 1.25 kg/L, 21,670 L tops out at about 27 tonnes which is the typical chlorine equipment.
When T50 is the right choice
T50 is the only legal route for non-refrigerated liquefied gas in the IMDG portable-tank system. The substitution rule of IMDG 4.2.5.2.5 does not apply to T50: a gas cargo cannot be substituted into T11 through T22 even if the test pressures look stronger on paper, because the relief regimes, shell metallurgy, and filling density rules are gas-specific. If the assigned T-code in IMDG DGL Column 13 is T50, the equipment must be a T50 build to that exact gas’s MAWP class.
When T50 is the wrong choice
T50 is the wrong tank for any cargo that ships refrigerated rather than under pressure. Cryogenic gases (LIN, LOX, LAR, LCO2, LNG, LH2, ethylene refrigerated) ride T75, with vacuum-jacketed double-wall construction holding the cargo at minus 162 deg C (LNG) or below. T50 is also the wrong tank for cargoes the IMDG DGL assigns to T11 through T22 (liquids and solids): pressurising a non-gas in a T50 over-engineers tare and under-uses payload.
A specific failure mode
A buyer in Houston books anhydrous ammonia from Tianjin in a T50 with no insulation upgrade, expecting a 22 bar MAWP. The booking confirmation lists “T50 ammonia, MAWP 22 bar”. The cargo loads in winter at minus 5 deg C ambient. By the time the vessel rounds Singapore in tropical heat, mean cargo temperature has risen and the ammonia vapour pressure now sits at 23 bar at 50 deg C ambient. The PRV chatters but does not vent (within tolerance), and the cargo arrives within spec but with the receiver questioning the safety margin. The fix on the next booking: specify “T50 ammonia insulated” or “T50 ammonia sun-shielded” so the MAWP class matches the worst-case ocean transit temperature. The IMDG T50 table publishes the four MAWP columns for exactly this reason. A bare 29 bar build covers the worst case; an insulated 22 bar build with PUR foam holds the cargo cool enough to stay below the lower MAWP.
How to verify a T50 booking
Pre-loading inspection covers the CSC plate (within 30 months), the 5-year hydraulic test plate, the 2.5-year intermediate inspection plate, the EFTCO ECD, the data plate stamps (ASME U2, IMDG, ADR, CSC, TC, AAR 600, UIC, TIR, EN 12972), and the valve-cabinet seal. For chlorine and ethylene oxide builds the PRV setting and the frangible-disc tell-tale are both visually inspected. Operators with deep T50 fleets: Eurotainer (specialty gas + peroxide), Stolt-Nielsen Gas, Suttons (UK gas speciality), Hoyer Gas, the major industrial-gas houses (Air Liquide, Air Products, Linde Gas).