A hole in the spool piece, the piece of piping between the SOx scrubber overboard valve and the ship’s hull, caused a large quantity of seawater to enter the engine room of a ship. The crew manage to stop the water ingress, but with a high degree of difficulty, and limited the damage to the engine room.
The survey of the incident indicated severe corrosion of the spool piece, while the diffusor necessary to dilute the acidic outflux of the scrubber wash water and ensure compliance with IMO 2020 was also heavily corroded.
In spite of the fact the the spool piece was made in accordance to an approved design, the acidic wash water contacted the steel pipe and react. According to DNV GL, this was because of a flaw in the application of the epoxy coating or damage to the coating that took place during final installation. Such cases are difficult to spot during installation.
In addition, except for this incident, there have been several other, less dramatic occurrences of leaking SOx scrubber overboard piping. These cases highlight the need to choose a material and a design that are durable and robust.
Taking into consideration the current state of technology, DNV GL suggests that the spool piece should be designed with a Super duplex or equivalent Stainless Steel (SS) with a high Pitting Resistance Equivalent Number (PREN)) bolted liner in a steel outer pipe.
As such a design does not allow for Ultrasonic Thickness Measurements, annual inspections should be carried out by divers or a leakage indicator, if there is one. For the latter, annual inspection by class may be waived.