The process of eliminating hydrocarbon vapours, liquids, or residues from cargo tanks onboard a tanker is known as tank cleaning, one of the marine solutions in Malaysia. One or more of the following causes may need tank cleaning:
- To transport fresh ballast.
- For interior inspections, repairs, or before entering the dry dock, to gas-free tanks.
- To clean the silt out of the tank top plate. This may be necessary if the vessel is transporting fuel oil or other sediment-settling commodities on a regular basis. Although washing between journeys may not be essential if the contents are suitable, many Ship Owners have found it beneficial to water wash a small set of tanks on a rotation basis between voyages to avoid major silt accumulations.
To load freight of a different and incompatible grade. The most typical purpose for tank cleaning is to clean between carrying different types of cargo. Cleaning aboard product tankers may consist of little more than a basic hot or cold saltwater wash in most cargo sequences. Many sorts of chemicals may be dispersed with a simple water wash, and it has been proven to work amongst clean petroleum products like gasoil and kerosene.
However, it should be emphasised that some grade sequences, notably in the petroleum product sector, may not require any washing. As a result, in such transactions, the choice for essential tank cleaning is frequently taken only after information of the next grade to be loaded is known.
The Chief Officer is in charge of the Tank Cleaning, Hydrocarbon Gas (H.C.) Purging, Gas Freeing, and Re-Inerting activities and will monitor them. He must ensure that all operations are carried out in accordance with the most recent edition of the ICS/OCIMF International Safety Guide for Oil Tankers and Terminals (ISGOTT).
Cargo Tank Entry Gas-Freeing
Cargo Tank access is prohibited unless the oxygen level is at least 21% and the hydrocarbon vapour percentage is less than 1% of the Lower Flammable Level (LFL). With regard to permissions, follow the company’s “Procedure for Entry into Enclosed Spaces.” If the preceding cargo included hydrogen sulphide (H2S) or other hazardous substances that might produce dangerous gases (e.g., benzene, toluene, Mercaptans, and so on), the tank should be inspected for such gases. Carrying out “Hot Work” within Tanks in the “Dangerous Area” necessitates extra caution and preparation as outlined in the “Procedures for Hot Work.”
For Cargo Reception, Gas-Freeing or Purging
If the goal of the Gas-Freeing or Purging operations is to keep the next cargo from being contaminated by the previous cargo’s oil hydrocarbon gas, use the gas content specified by the Charterer as a guideline, but continue with the operations described in (2) of Article 1 until the LFL drops to 40% or less.
Precautions for Safety
The Chief Officer must take the following measures in order to carry out the activities. Within pertinent areas of ISGOTT, detailed instructions on preparations and safety procedures are also provided. Make sure that everyone involved in the activity follows the safety measures outlined in this section as well as the “Precautions During Gas-freeing Operations.” To ensure safety, complete the relevant elements of the “Tank Cleaning, Purging, and Gas Freeing Checklist.”