The ISO tube module is technically not an ISO portable tank under IMDG Code Chapter 6.7 but rather a bank of high-pressure compressed-gas cylinders mounted in an ISO frame for intermodal handling. The cylinders themselves are built to DOT 3AA / 3AAX or ISO 11120 specifications, certified for service pressures of 200 to 500 bar. Tube modules ship helium, hydrogen, oxygen, nitrogen, and compressed natural gas (CNG) in volumes that are too large for standard cylinder pallets but too small to justify cryogenic liquefaction in T75 equipment. The module is included in this catalogue because the equipment is widely confused with portable tanks at the booking stage.
What ISO tube module is built for
Helium UN 1046 in long-distance transport from a small number of helium-extraction sites to global customers. Compressed hydrogen UN 1049 for industrial and emerging fuel-cell applications. Compressed nitrogen UN 1066 for inerting and process applications. Compressed oxygen UN 1072 for medical and industrial use. CNG (UN 1971) for energy distribution where pipeline access is unavailable. Tube modules also ship compressed gas n.o.s. (UN 1956) for various specialty industrial gases.
Construction and materials
The cylinders are typically 510 mm outer diameter and 9 to 11 m long, banked together (5 to 12 cylinders per module depending on frame size) inside an ISO frame. Cylinder construction: DOT 3AA / 3AAX or ISO 11120 seamless steel cylinders for 200 to 300 bar service, or composite-overwrapped cylinders (Type II / III / IV) for higher service pressures up to 500 bar. The cylinders share a manifold at one end with a single fill / discharge connection per module.
The 40 ft 1AAA frame is the most common configuration; 10 ft and 20 ft variants exist for smaller-volume operations. Tare runs 14,000 to 22,000 kg because the cylinders themselves are heavy steel pressure vessels. Payload (the gas itself) is small in mass terms (200 to 1,500 kg of gas total per module depending on cargo and pressure) but the frame and cylinder mass dominates the booking weight calculation.
When ISO tube module is the right choice
Tube modules are the right equipment for any compressed-gas cargo above the standard cylinder-pallet threshold and below the cryogenic liquefaction economic threshold. Helium specifically rides tube modules globally because the helium-extraction sites are concentrated in a few locations (Texas, Qatar, Algeria, Russia, Tanzania) and global distribution requires intermodal-compatible high-pressure equipment. Hydrogen for hydrogen-fuel-cell applications increasingly rides tube modules as the supply chain develops.
When ISO tube module is the wrong choice
Tube modules are the wrong equipment for liquefied gas (T50) or cryogenic gas (T75) cargoes. The compression-pressure operating mode is not interchangeable with the liquefaction or cryogenic modes; the cylinders, fittings, and safety systems are entirely different. A booking that confuses tube modules with T75 cryogenics fails at the loading port.
How a tube module booking is verified
Pre-loading inspection covers the cylinder-recertification stack (DOT 3AA / 3AAX or ISO 11120 cylinder retest cycle, typically every 5 to 10 years), the manifold-and-valve integrity check, the frame-condition inspection for ISO-compatibility (corner castings, twist-lock locations), and the operator’s history showing the specific gas service. Tube modules are typically operated by industrial-gas majors (Air Liquide, Linde, Air Products, Praxair) on captive contracts; spot-market booking is uncommon.