Corrosive Cargo in Holds

Upon survey of all cargo holds after a transport of sulphur cargo, serious corrosion was found. On the inclined plates of the hopper tanks and the lower stool of the transverse bulkhead, extensive damage in shape of groove corrosion was found with depth up to 9mm in places. This incident information refers to a 17,427 GRT Bulk Carrier in 1997.

The main cause of the damage was considered to be damaged coating in combination with sulphur cargo. Sulphur, moisture and oxygen form sulphur acid, which attacks the steel.

The cargo holds were originally painted, but surfaces had been spot-wise damaged by grabs during previous unloading operations. Further, the cargo holds had not been properly cleaned and the paint not properly maintained after previous sulphur cargoes. Thus bare steel was exposed to attack by the corrosive cargo. In addition, the cargo holds had not been adequately ventilated.

Where the hold surface was without paint, a more general but still significant corrosion would have taken place in way of the cargo as indicated in the figure below.

When trading with bulk cargoes that may be corrosive, the following precautions should be taken in order to avoid serious corrosion damage in cargo holds:

The cleaning after discharging should be carried out properly, in particular when previous cargo was sulphur.
Prior to taking corrosive cargoes, the coating in cargo holds should be dealt with as necessary.
The cargo should be kept as dry as possible during loading and transit.
The hatches should be confirmed weathertight and holds adequately ventilated.

Below is given a few examples of cargoes that need special attention in order to avoid problems as mentioned above: