Start with the cargo, not the heating system
Before planning to heat, establish what temperature the cargo needs and why. The aim may be to support handling or discharge, but the target must come from the cargo requirements and the agreed voyage and discharge plan—not from a generic number applied to every tanker cargo. Confirm the cargo’s relevant temperature characteristics, any restrictions supplied for carriage, and the vessel’s own operating limits. If those details do not line up, resolve the difference with the operator and relevant cargo parties before loading rather than leaving the ship to improvise underway.
For crude oil, temperature can also affect the tank’s vapour conditions. IMO guidance explains that the temperature of the liquid phase contributes to saturated vapour pressure; it also cautions that cooling waxy cargoes too much can promote wax precipitation. That makes the temperature decision a balance: heating is not automatically beneficial, and cooling is not automatically harmless. The cargo plan should make the intended temperature range and the operational reason for it explicit, while leaving the vessel’s approved procedures and cargo-specific instructions in control.
Check whether the ship can deliver the plan
A target is useful only if the ship’s heating arrangements can achieve it safely. Before loading a cargo that will need heating during the voyage, inspect and test the heating or cooling system for tightness, as the cited OCIMF guidance advises. Check the relevant system arrangement and confirm that the intended heating medium is suitable for the cargo. The IBC Code text calls for temperature-control systems to use suitable materials and an approved heating or cooling medium, with consideration given to coil or duct surface temperatures so local overheating or overcooling does not create a dangerous reaction.
The same IBC text describes tank-by-tank isolation and manual flow regulation, a means of measuring cargo temperature, and safeguards to keep system pressure above the pressure that cargo could exert on it when the system is not empty. For applicable chemical cargoes, the required type of temperature-measuring arrangement depends on the substance’s gauging requirements. These provisions are a reminder to check the actual vessel arrangement and applicable cargo requirements; they are not a substitute for the ship’s procedures or the system’s design limits.
MEPC.119(52) · OCIMF SIRE 2.0 Question Library, Part 2: Chapters 8 to 12, Version 1.0, January 2022
Agree controls before applying heat
Turn the target into a controlled operating plan: identify which tanks are to be heated, how the system will be controlled, what temperatures will be observed, and who must be contacted if the cargo or system behaves differently from the plan. Set out the relevant limits and escalation route in the ship’s procedures and the ship–shore exchange. The IBC text specifically points to manual flow regulation and temperature measurement; the practical value is that the watch can compare observations with the intended range instead of treating steam supply as an unattended, all-or-nothing operation.
For oil and chemical tankers, the OCIMF guidance warns that high-temperature cargoes can damage a tanker’s structure, coatings, valves, pumps and gaskets. It recommends spreading hot cargo throughout the ship as evenly as possible to dissipate heat and avoid local heat stress. It also advises ensuring tanks and pipelines are free of water before receiving cargo hotter than water’s boiling point. Treat these as cargo-planning prompts: confirm whether they apply to the cargo and vessel, and have the responsible officers verify readiness before loading rather than relying on a general assumption.
OCIMF SIRE 2.0 Question Library, Part 2: Chapters 8 to 12, Version 1.0, January 2022
Make temperature observations useful
Temperature measurement matters only when it informs a decision. Use the vessel’s approved means and procedures, and keep observations associated with the tank, time, operating condition and relevant heating action. A simple record can help the watch see whether the intended range is being maintained, whether a change follows a heating adjustment, and whether an unexpected reading needs investigation. The cited IBC provisions require means to measure cargo temperature; the record-keeping approach here is a practical way to make those measurements useful, not a claim that the cited text mandates a particular log format or interval.
If the cargo temperature drifts from the plan, do not respond by automatically increasing heat. Check the reading and system condition, consider whether the cargo’s properties or tank conditions explain the change, and follow the vessel’s escalation procedure. For crude cargoes, remember the link between liquid temperature, vapour pressure and possible wax precipitation; for other cargoes, use their specific requirements. Close the loop with the relevant shore parties when the agreed target, expected handling needs or safe system limits may no longer be met. The operational goal is controlled, documented heating within the ship’s and cargo’s limits—not simply a hotter cargo.
MEPC.119(52) · OCIMF SIRE 2.0 Question Library, Part 2: Chapters 8 to 12, Version 1.0, January 2022 · MEPC.1/Circ.680