Case Study: SOx Scrubber Overboard Discharge Incidents

SOx scrubbers are one of the compliance options for ships to meet the IMO global sulphur cap for 2020. But we are still on a learning curve for ship-based applications of this technology.

On one vessel, a hole in the piece of piping between the SOx scrubber overboard valve and the ship’s hull (the spool piece) led to a large quantity of seawater entering the engine room.

With considerable difficulty the crew eventually managed to stop the water ingress and limit the consequences. During the damage survey, the spool piece was found to be severely corroded.

SOx scrubber overboard discharge incidents
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The diffusor necessary to dilute the acidic outflow of the scrubber wash water and ensure compliance with the emission regulations was also found to be heavily corroded.

Even though the spool piece was made to an approved design (steel piping with epoxy coating), the acidic wash water managed to make contact with the steel pipe and react with it. This was probably due to a flaw in the application of the epoxy coating or the coating being damaged during installation. There have been several other instances of overboard piping connected to SOx scrubbers experiencing leaks.

Lessons learned

  • These incidents highlight the need to select both a suitably durable material for scrubber parts and a robust design.
  • Until the industry converges on reliable design(s) and material(s) for the overboard piece, a yearly inspection of the spool piece is recommended.
  • Particular attention should be paid to the bottom part of the pipe closest to the valve flange, since many incidents indicate that this is the area most affected by corrosion.
  • An alternative to yearly inspections is to install a leakage indicator to the spool piece.


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