Conducting tank entries is a high-risk activity that requires proper planning to ensure it is carried out safely. One aspect of the operation that is easily overlooked, according to David Patterson, Loss Prevention Executive at North P&I Club, is ensuring that manhole covers are properly closed and secured upon completion.
We see from the numerous claims we receive that hold flooding from inadequately secured manhole covers is a too-regular occurrence, particularly those involving ballast tanks.
On container vessels, bulk carriers and general cargo ships, the manhole covers for fuel and ballast tanks are the only barrier that prevents the contents migrating directly from the tank into the cargo space. If they are not sealed and secured properly it is likely to result in hold flooding or, in the case of bunkers – contamination, which leads to cargo damage claims against the shipowner.
Due to this risk of hold flooding, great care needs to be taken to ensure that they are properly secured following each time they are opened.
Avoiding mistaken identification
When preparing a tank entry, check the manhole cover locations on the vessel’s drawings to ensure the correct cover is opened and subsequently closed.
Stencilling the tank ID on the manhole cover and on the adjacent deck helps prevent the wrong manhole cover from being opened. It also ensures that the same cover is fitted to the manhole upon completion.
Preparation is the key
While waiting for tanks to be ventilated, there is a good opportunity to prepare for refitting the covers on completion of the tank entry. If any issues are identified they can be rectified in good time rather than rushing to put the tank back into service after the inspection.
Think about:
- Cleaning the sealing faces on the deck penetration and cover
- Inspecting the gaskets and replacing if necessary – it may be prudent to replace the gaskets for each entry
- Replacing any broken studs, rounded nuts, or missing washers
- Cleaning and greasing threads
Refit the lids
The task of re-fitting manhole lids should be supervised by a responsible officer, who should satisfy themselves that all the lids have been placed back into their correct location, fitted with the correct good quality gaskets and that the securing nuts are suitably tightened.
To avoid any covers being overlooked, a record should be made of all covers that have been removed. This can be used as a checklist during the re-fitting of the covers.
The officer should also remind the crew of the correct bolting technique to ensure the lid is tightened evenly. Failure to do this can result in a leak, even if a new gasket is used and the sealing faces are clean.
Bringing the tank back into service
Additional precautions should be taken the first time the tank is used after being brought back into service. This includes:
- Checking bilge levels and that bilge alarms are operational prior to filling the tank
- Conducting a visual inspection of all the manhole covers on the tank to ensure all covers are creating a correct seal and there are no leaks
Following dry docking or repairs by shore workers, the same checks should be made. Do not rely on others to make these checks.
It is also recommended to carry out regular checks on all manhole covers to identify any early signs of leakage and take preventative action.
Above article has been initially published on North Club’s website and is reproduced here with author’s kind permission.
The views presented hereabove are only those of the author and do not necessarily those of SAFETY4SEA and are for information sharing and discussion purposes only.
