The Skuld P&I Club refers to a recent case in which the total cargo of 2,600 MT of fertilizer in one of the holds was completely wetted by sea water due to a combination of human error and technical problems with a non-return valve.
Non-return valves have a very simple design and is self-opening / closing depending on which side the pressure is applied, i.e. if water is sucked out the valve will be pressed up by the water and once the suction stops the valve will immediately drop into its place closing any flow into the bilge.
However, in the event the valve is pressed open and remains stuck due to e.g. dirt, then the non-return valve will remain in open position and once the suction stops, the water remaining in the pipe will be allowed to flow back into the hold bilge.
The incident
In this particular case, the Club explains that the hold bilge non-return valve was found to be stuck to its cover and thus no longer being allowed to drop on its seat to prevent water flowing into the bilge.
From interviewing the vessel’s crew, the Club understood that regular inspection of the non-return valve had not been carried out thereby not enabling them to detect any malfunction / “mechanical” failure.
Furthermore, various valves need to be opened manually and hydraulically in order to allow the water to reach up all the way to the improperly functioning non-return valves. The unintentional leaving open / improper closing of the manually and hydraulically operated valves allowed sea water to get into the hold trough the malfunctioning non-return valve.
As result a few days later the cargo in the hold was completely covered with water.
Although a non-return valve has none to limited (depending on type) mechanically operating parts, it is advisable to carry out regular inspection / checking of the non-return valve for proper functioning, i.e. whether it is properly sealing off.Operators are advised to ensure that a proper check-list has been developed and implemented in the vessel’s Safety Management System and that same provide for a regular inspection on non-return valves.
Source & Image Credit: The Skuld P&I Club