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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 immediately informed.

The heating instructions may contain any, or all, of the following:

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:
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)




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Pre-cleaning /washing of cargo tanks

Risk & hazards of chemical contamination onboard

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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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