T75 is the IMDG Code Chapter 6.7.4 portable tank instruction for refrigerated liquefied gases shipped at cryogenic temperatures. Cargo population: liquid nitrogen UN 1977 at minus 196 deg C, liquid oxygen UN 1073 at minus 183, liquid argon UN 1951 at minus 186, refrigerated CO2 UN 2187, LNG UN 1972 at minus 162, refrigerated ethylene UN 1038, liquid hydrogen UN 1966 at minus 253, and the small-volume liquid-helium fleet. T75 is the most expensive and most engineered portable-tank class. A 20 ft LIN build runs USD 90,000 to 140,000 new ex-factory in 2025; a 40 ft LH2 build with active LIN cryo-shield can reach USD 1.2 million.
The capacity range in the spec block above (20,000 to 50,000 L) covers both frame variants on a single page. The 20 ft 1CC frame typically runs 20,000 to 22,000 L (LIN, LOX, LAR, LCO2, ethylene). The 40 ft 1AAA frame typically runs 39,000 to 50,000 L (LNG at 45,500 L, LH2 at 48,400 L). The frame variant is dictated by the cargo: high-volume light-density cryogens (LNG, LH2) require 40 ft to land a commercially viable payload.
What T75 is built for
The cargo list is short and the engineering is unforgiving. LIN, LOX, and LAR are the workhorses of the industrial-gas supply chain. Air Liquide, Linde, Air Products, and Praxair operate fleets that rotate continuously between air-separation plants and customer sites. LCO2 is a bulk-distribution cargo for the food and beverage industry as well as some chemical processes. LNG is the marine-fuel and energy-import cargo. LH2 is the rapidly evolving frontier: Linde Engineering commissioned the first ferry-mounted LH2 system in 2023; rail / locomotive variants are still in design.
Each gas has its own MAWP class, holding-time profile, and initial-fill pressure. LIN at 18 bar MAWP holds about 70 days. LAR at 18 bar holds about 80 days. LOX at 18 bar holds about 100 days. Ethylene at 18 bar holds about 130 days. LNG at 10 bar (24 bar available) holds 60 to 120 days. LH2 at 12.75 bar / 185 psi holds 30 days standard or up to 200 days with an active LIN cryo-shield surrounding the inner vessel.
Construction and materials
A T75 is a double-wall vacuum-insulated pressure vessel. The inner vessel is 304L stainless steel (or 304N for some builds, aluminium 5083 for LH2 service where stainless embrittles). The outer jacket is 304 stainless or carbon steel. The annulus between inner and outer is evacuated and packed with multi-layer perlite or aluminised mylar (super-insulation), a configuration that delivers thermal performance an order of magnitude better than polyurethane foam.
There is no bottom outlet and no manlid. All connections route through the top via a valve cabinet: liquid filling line, vapour return, pressure-build coil for self-pressurising discharge, primary and secondary pressure-relief devices on the vapour line (PRV plus frangible disc), vacuum gauge and gauge ports, sample valves, flame arrester (for flammable cryos like LH2 and ethylene). Cryogenic isolation valves use globe, needle, three-way ball, emergency-stop, and check-valve types in stainless or bronze depending on cargo. Oxygen-compatible PTFE seals are mandatory throughout the LOX build to prevent ignition under pressure shock.
The 40 ft frame (1AAA per ISO 668) is the standard for LNG, LH2, and high-volume light-density cryogens. A 40 ft LNG build typically runs 39,000 to 47,000 L (commonly 45,500 L), tare 12,500 to 13,200 kg, MGW 36,000 kg. A 40 ft LH2 Linde / Chart build runs 48.4 m3 with a 3,040 kg payload at 10% ullage.
When T75 is the right choice
T75 is the only legal route for cryogenic refrigerated gas in the IMDG portable-tank system. The substitution rule of IMDG 4.2.5.2.5 does not apply to T75: a cryogenic cargo cannot ride a non-cryogenic tank. If the assigned T-code in IMDG DGL Column 13 is T75, the equipment must be a T75 build to that exact gas’s MAWP and inner-vessel material specification.
When T75 is the wrong choice
T75 is the wrong tank for non-refrigerated liquefied gases: LPG, ammonia, propane, butane, chlorine, refrigerant gases. Those cargoes ride T50 with a thick-walled non-vacuum carbon-steel pressure vessel. T75 is also the wrong tank for any liquid that can ride T1 through T22: the cryogenic engineering is dead weight when the cargo doesn’t need it, and the lead time and price are 5 to 10 times higher than the corresponding T-coded liquid tank.
A specific failure mode
A buyer in Sydney books LIN from Tianjin in a 20 ft T75 with a holding-time spec of 70 days (the LIN nominal). The ocean leg runs Shanghai-Singapore-Sydney with a port-of-call delay at Singapore. By the time the tank arrives at Botany Bay, total transit is 78 days. Vapour-line PRV has been venting nitrogen for the last week of the voyage. The tank arrives partially empty. Investigation: the operator assigned a tank with a deteriorated vacuum jacket (the perlite multi-layer insulation had a slow leak) that cut effective holding time from 70 days to 50. The fix on the next booking: require the operator to supply the latest vacuum-decay test result with the booking confirmation, and pad transit time by 10 to 15 days for any East-Asia-to-Australia routing.
How to verify a T75 booking
Pre-loading inspection covers the CSC plate (within 30 months), the 5-year hydraulic test plate, the 2.5-year intermediate inspection plate, and the vacuum-decay test record (cryogenic-specific, not a standard ISO-tank check). EN 13530 and MSC Circ.860 govern the testing regime. Surveyors with cryogenic-tank experience: SGS Cryogenic Services, Bureau Veritas Industrial. Operators with deep T75 fleets: Stolt LNGaz, Linde Gas, Air Liquide, Air Products, Praxair, Eurotainer.