The heated / steam-jacketed ISO tank uses internal stainless steam coils or a full external steam jacket to keep cargoes liquid above their melting points. Steam coils 8 to 12 longitudinal stainless 316 lines totalling 6.5 to 13 m2 of heating area, with 1 inch BSP inlet and outlet fittings, are the most common configuration. Full steam jackets (longitudinal channels welded to the outer shell, carrying steam between channels and dished ends) handle viscous cargoes like sulphur and bitumen at higher temperatures. Glycol-jacketed and electric-heated variants serve food-grade and gentle-heating applications respectively.
What heated is built for
Cargoes that solidify above ambient temperature and need heating to remain liquid for discharge. Glacial acetic acid (UN 2789, melting point 16.6 deg C, ships heated above 20 deg C). Phenol molten (UN 2312, melting point 41 deg C, ships at 70 to 90 deg C). Liquid sugar and glucose syrup (heated to prevent crystallisation, typically 50 to 65 deg C). Liquid chocolate at 45 deg C. Molasses at 50 deg C. Fatty alcohols. The bitutainer (UN 3257 elevated-temperature liquid, 140 to 180 deg C) and molten sulphur (135 deg C) ships in dedicated higher-temperature heated builds covered on the bitutainer-direct-flame page.
Construction and materials
Three configurations. Steam coils inside the shell between cylindrical wall and outer jacket: 8 to 12 longitudinal stainless 316 coils of 6.5 to 13 m2 total heating area. The most common configuration; a single source of process steam (typically 5 to 8 bar, 150 to 175 deg C) raises cargo temperature to the operating envelope. Steam-jacketed (full external jacket): longitudinal channels welded to the shell carry steam, useful for sulphur and bitumen at higher operating temperatures. Hot-water or glycol-jacketed (Eltherm, Holvrieka, Klinge, Loebbe): gentler heating, preferred for food-grade compatibility.
Insulation 100 mm polyurethane foam under aluminium or GRP cladding minimises heat loss during transit. The combination of insulation and active heating maintains operating temperature on multi-week ocean voyages with minimal external heat input.
When heated is the right choice
Heated is the right tank for any cargo that solidifies during ocean transit and would not be discharge-able at the destination port without re-heating. The heating system is sized to operating temperature: 80 to 130 deg C envelope for typical T11 builds; 130 to 200 deg C for bitumen / sulphur builds (separate bitutainer page).
When heated is the wrong choice
Heated is the wrong tank for cargoes that don’t need heating (the heating system adds tare and complexity). Cargoes that should not be re-heated under TPxx special provisions in IMDG DGL Column 14 (acrylic acid stabilised UN 2218, methacrylic acid) prohibit re-heating during transit, so the heating system must be plumbed for one-time pre-loading heating only or disabled entirely.
How a heated booking is verified
Pre-loading inspection covers the standard plate stack plus the steam-coil pressure-test certificate (annual or per-cycle hydraulic test of the coil system to verify integrity), the heating-system maintenance log, and the operator’s history showing successful heated service for the specific cargo. Steam supply at the loading port is part of the booking; if the port doesn’t have process steam available the cargo must load at temperature and the tank must hold that temperature through transit using insulation alone.