Lloyd’s Register (LR) is warning shipowners that certain ship’s tanks could be subjected to severe microbial attack, causing significant losses in plating thickness.
The potential problem can arise due to stagnant water in grey and black water tanks after periods of reduced operation. Distillate tanks may also be vulnerable if condensation has occurred.
LR cited a tank with occurrences of microbial pitting of 14mm in a 17mm-thick bottom plate as a potential consequence of the issue.
The potential for a microbial attack depends on factors such as temperature, a suitable nutrient supply and coating condition.
The class society advices ship operators to advance class-related tank inspection due dates in their survey schedule for tanks where an issue is suspected. Associated piping systems should also be monitored as far as practicable for possible diminution or leakage.
“When dry-dockings are being planned, it is recommended that shipowners investigate likely tanks to ensure any steelwork repairs can take place in the docking period. As an initial step, testing kits are available to identify contamination in tanks with elevated risk. Further investigation could include laboratory tests.”
Solutions to the problem range from steelwork renewals to chemical treatments. MARPOL requirements should be considered if any chemical treatments are undertaken.
