What to check on a Cargo Tank Heating.
A cargo tank heating system does one job: keep the cargo warm enough to flow through the ship's pumps and cargo lines without degrading it. Unlike accommodation or engine room heating, the target is not comfort but viscosity control, and overheating is as much a hazard as underheating because many heated cargoes such as edible oils, tar and bitumen coke, oxidise or lose grade quality above a defined ceiling temperature. The system is a closed loop: a heat source, a network of coils inside the tank, and a return line…
What defines cargo tank heating
A cargo tank heating system does one job: keep the cargo warm enough to flow through the ship's pumps and cargo lines without degrading it. Unlike accommodation or engine room heating, the target is not comfort but viscosity control, and overheating is as much a hazard as underheating because many heated cargoes such as edible oils, tar and bitumen coke, oxidise or lose grade quality above a defined ceiling temperature. The system is a closed loop: a heat source, a network of coils inside the tank, and a return line, with the cargo itself never entering the heating medium.
Main components
Heating coils
Welded steel or stainless steel coils run along the tank bottom and up the sides, sized to the cargo's heat-up curve rather than a flat wattage figure. Coil layout matters more than total coil length: coils bunched too close to suction bells can locally overheat cargo before it clears the tank.
Heat source
Steam from the auxiliary or exhaust gas boiler is the most common medium on product and chemical tankers; thermal oil systems are preferred where a steam leak into cargo would be a contamination risk, since a thermal oil leak is easier to detect and does not condense into the cargo.
Control and monitoring
Automatic temperature control valves throttle steam or oil flow against a tank temperature sensor, with local gauges backing up the remote readout. Condensate return lines and steam traps recover condensate for reuse in the boiler feed system.
Selection and sizing
Sizing is driven by the pour point and pumping viscosity of the cargoes the ship is built to carry, the ambient sea and air temperature on the intended trade, and the required heat-up time between loading and discharge. Coil surface area, not steam pressure alone, sets the achievable heating rate; raising steam pressure without enough coil area risks local hot spots against the tank shell.
Typical faults
| Fault | Cause | Consequence |
|---|---|---|
| Coil leak into cargo | Corrosion or fatigue cracking at coil welds | Cargo contamination, rejected parcel, cargo claim |
| Uneven tank temperature | Coil layout leaves dead zones away from suction | Localised solidification, blocked strum box |
| Slow heat-up | Fouled coil surfaces or failed steam trap | Missed loading or discharge window |
| Cargo scorching | Control valve stuck open or sensor drift | Off-spec cargo, especially edible oils |
What to look for in a supplier
- Coil material and weld procedure qualified for the cargo range and tank coating compatibility
- Documented heat-up curves for representative cargoes, not a single generic figure
- Condensate return design that avoids steam hammer on cold start-up
- Control valve and sensor package suited for remote tank gauging integration
Never open a heating coil to steam on a tank still gas-freeing or under inert gas purge without checking the cargo's flash point margin, because a coil surface running well above cargo temperature is an ignition source most crews forget to consider.