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Procedure for Heating, high viscosity and solidifying cat X, Y chemical substances in bulk


Why heating is required ?

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 immediately informed.

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


Unintended heating

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.



Temperature checks

When carrying heated cargoes the following parameters are to be checked regularly:
  1. Temperature of the cargo at 3 levels
  2. Inflow temperature of the heating medium (or steam pressure)
  3. Outflow temperature of the heating medium (or steam pressure)




Related Info:

Recommended temperature monitoring equipments onboard

Practical example of solving tank cleaning problems

Pre-cleaning /washing of cargo tanks











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Chemicaltankerguide.com is merely an informational site about various aspects of chemical tankers safe practice that should be adopted by any prudent mariner. If you are interested in finding out more about chemical tanker guideline please visit IMO official website www.imo.org.



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