Heating, high viscosity and solidifying cat X, Y chemical substances
In a modern chemical tanker in order to maintain product quality, to minimise the potential for discoloration, and to facilitate some liquid cargo transport in a safe manner cargo heating is required.
The voyage orders will contain heating information, if heating is required. As a rule the final heating
instructions are given by the Shipper in writing to the Master / Chief Officer in the port of loading.
If those written instructions are not given, the master should request them and issue a Letter of
Protest if they are not received at departure. In the latter case the management office should be
The heating instructions may contain any, or all, of the following:
- Minimum and maximum temperature during the voyage
- Minimum and maximum temperature during discharge
- Maximum temperature of adjacent cargo
- Heating medium (when loading edible oils only steam and / or hot water should be utilised
as the heating medium in coils / heat exchangers. Thermal oil should not be used as a
heating medium for edible oils)
- Maximum temperature of the heating medium
- The maximum possible temperature increase per unit of time: delta T°C/hour
The risk of heating a cargo, which should not be heated, must be eliminated. An ‘unintended heating’
of a cargo can not only influence the quality of the cargo, but can endanger the crew, the vessel and
the environment, e.g. lifetime of an inhibitor can be shortened drastically by unintended heating and
a monomeric cargo such as styrene monomer can polymerise.
In order to prevent unintended heating of cargoes that do not require heating the following
preventive measures should be taken:
- Blank the supply and return of the heating coils
- When heat is supplied to other tanks, check manually the supply and return of the tanks that
do not require heating. Maintain a log of temperatures of tanks being heated along with
surrounding tanks on TNK08.
- Do not stow heated cargo adjacent to cargoes that do not require heating
Beware of hot wash of adjacent besides cargo not requiring heating
Heating required by Marpol Annex II
Category Y, high Viscosity and solidifying cargoes may require prewash, if not heated. These
cargoes do not require a prewash if the following is complied with:
Category Y Cargoes with a melting point less than 15°C.
Discharge temperature should be at least 5°C. above melting point of the product. Example: Benzene
with a melting point of 4.5°C. should be discharged with a temperature of at least 9.5°C. to
avoid the prewash requirements.
Category Y Cargoes with a melting point above 15°C.
Discharge temperature must be at least 10°C. above melting point of the cargo. Example: Phenol,
with a melting point of 40.9°C. should be discharged with a temperature of at least 51°C. in
order to be considered not solidifying.
Category Y Cargoes with Viscosity < 50mpa at discharge temperature
The Master has to obtain the shipping document with above information from shipper when
transporting such cargoes so that the products will be heated accordingly so as to avoid the
prewash obligation if at all possible.
When carrying heated cargoes the following parameters are to be checked regularly:
- Temperature of the cargo at 3 levels
- Inflow temperature of the heating medium (or steam pressure)
- Outflow temperature of the heating medium (or steam pressure)
Recommended temperature monitoring equipments onboard
Practical example of solving tank cleaning problems
Pre-cleaning /washing of cargo tanks
Risk & hazards of chemical contamination onboard
Cargo hoses handling ,connection and use
Checklist for handling dangerous liquid chemicals in bulk
Cargo compatibility and reactivity of various chemical cargo
Poisoning and required first aid treatment onboard
Determining presence of contaminants
in chemical cargo
Chemical tanker safe mooring practice
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