West P&I Club has issued a loss prevention bulletin in which they describe best practices and give guidelines on cargo tank cleaning and preparation onboard tankers. the Club highlights that product and chemical tankers carry a variety of commodities, often necessitating frequent tank cleaning to prevent a cross-subsequent, off-spec claim. Detailed planning of the tank cleaning is crucial, and the ship’s crew must be informed of the schedule. The extent of cleaning required depends on the properties of the previous cargo, the tank coating, the next cargo’s preloading specifications and the shipper’s requirements.
Why is tank cleaning necessary?
Tank cleaning is essential in the following circumstances:
- Preparing for the next cargo
- Dry dock
- Regulatory Compliance: adhering to MARPOL and other IMO Conventions/Codes
- Preventing build-up of residues e.g. in Residue Oil Tank (ROT) / Slop Tanks
- Facilitating gas freeing for tank inspection / mopping / maintenance / repairs
- Complying with the charter party agreement
- In extreme circumstances to prepare for carrying clean ballast
Cargo tank cleaning and tank preparation encompasses various stages, with tank cleaning being the most common. The preparation steps vary depending on the type of vessel and cargoes.
These steps include:
Planning
Effective tank cleaning requires careful planning, considering cargo details, environmental factors, and system components. The plan should address cleaning methods, risks, and safety measures. Regular risk assessments are needed, especially for new or infrequent cargos. Fire and explosion risks are minimized by washing tanks in an inert atmosphere.
Bottom flush
A line and bottom flush is the first cleaning step required for all non- inert tanks as per ISGOTT.
Verifying results
Verification of the tanks’ level of cleanliness is more often required before the charterer’s permission to load the next cargo. This can be done through enclosed space entry for a visual inspection and coating assessment, which may include wall wash testing, or by wash water analysis, eliminating the need for enclosed space entry.
Pre-wash after discharge
Prewash must be carried out for chemical tankers as per MARPOL Annex II.
Decanting and discharging ashore
Slop tanks must be decanted as per the relevant MARPOL Annex. The ROT must be discharged ashore in a timely manner.
There are a number of safety concerns to be considered:
- Entry into enclosed space
- Exposure limits
- Cargo safety data sheets (SDS)
- Static accumulation
- Reactivity
Common tank cleaning problems
Common tank cleaning problems. The most common issues encountered with tank cleaning are failed inspections and cargo contamination due to inadequate tank cleaning, often influenced by tank coatings. When tanks are considered not clean enough by charterers, further cleaning is costly and time-consuming affair.
Key questions to ask in such cases:
- Were the Charterer’s tank cleaning instructions followed effectively?
- Was a third-party tank cleaning expert consulted, such as Milbros or MIRACLE?
- Did the Chief Officer and crew have sufficient experience with these cargoes?
- Did the vessel fail a Wall Wash Test (WWT) or was Wash Water Analysis (WWA) used for verification?
- Was the previous cargo compatible with the tank coating?
- Have previous cargo residues been absorbed into an epoxy coating?
If a vessel fails a tank inspection and the charterer requests additional cleaning, the Club should be contacted to clarify further details before commencing extra cleaning. If the tanks do require further cleaning and the cleaning instructions have been followed accurately, third party expert guidance should be sought.
In cases where the tanks were not cleaned sufficiently and a cargo contamination claim arises, the Club should be contacted and an investigation conducted. Findings from the investigation should be shared across the company’s fleet to raise awareness and reduce the risk of reoccurrence.
If the charterer’s tank cleaning instructions were not followed effectively and the tanks are considered not clean enough, follow additional charterer’s instructions and consult the latest tank cleaning recommendations from expert companies.
Failure in a WWT, does not always indicate inadequate tank cleaning for a vessel to load the next nominated cargo once dilution factors are considered. As this is known to be a subjective test, vessel’s owners can request a repeat test from another surveyor and retain samples for secondary analysis.
WWA can eliminate the need to gas- freeing and tank entry for WWT. This method has been shown to be more effective than WWTs for verification and tank cleaning. Please see out LP Bulletin on Cargo Tank Cleaning Verification Methods.
Incompatible cargoes with tank coatings, such as a high FFA content edible oil with zinc, are hard to clean and will more often require further cleaning.
Aggressive cargoes carried in epoxy-coated tanks will leave cargo residues within the tank coating. Cleaning will not help desorb the residues, periodic ventilation at an elevated temperature is needed. Please see out LP Bulletin on Cargo Tank Coatings for more information.
In summary, if a vessel fails a tank inspection and the charterer requests additional cleaning, P&I should be contacted to clarify further details before commencing extra cleaning. If the tanks do require further cleaning and the cleaning instructions have been followed accurately, third party expert guidance should be sought. In cases where the tanks were not cleaned sufficiently and a cargo contamination claim arises, P&I should be contacted and an investigation conducted. Findings from the investigation should be shared across the company’s fleet to raise awareness and reduce the risk of reoccurrence.
Download the guidelines at: https://bit.ly/4b7cKhy