Corrosion of distance piece on SOx scrubber discharge water line

Recently, ClassNK has received several reports for incidents that sea water leakage was detected from distance piece attached to hull on SOx scrubber discharge water line (See Figure 1). 

Until now, the leakages were detected at an early stage and did not cause heavy water ingress into E/R. However, ClassNK has concerns that similar incidents would occur in the future for the other vessels as well and may cause more serious accidents such as a large amount of leakage and water ingress into E/R, thus providing this Technical Information.

Figure 1 SOx scrubber discharge water line Leakages have been detected around welds between "distance piece" and "flange (See Picture 1) or bluff body (See Picture 2)". Having inspected the distance pieces internally, the corrosion occurred/progressed around the welds and caused the leakages finally. In some cases, the progress of corrosion which has not resulted in leakage yet was found around the same welds.

Upon the above incidents, ClassNK would like to recommend the owners and the managers as follows: - To inform the above incidents of the masters of your vessels on which SOx scrubber is installed and instruct them to inspect the discharge water lines especially around the distance pieces externally from E/R with more attentions and frequencies. - To inspect the distance pieces internally when there is an opportunity of arranging a diver for hull cleaning, etc. If a leakage were detected, temporary countermeasure to stop it (e.g. covering the distance piece with cement box) should be taken immediately, and Occasional Survey by the surveyor should be arranged as soon as possible.

Source Class NK Tech Bulettin