Corrosion has emerged as the arch-enemy of the exhaust gas cleaning systems as the uptake of the technology rose with the entrance into force of the IMO 2020 sulphur cap.
Like with any new technology, scrubber maintenance and operation has been a learning curve for ship owners and operators, especially in the context of preventing failures of the technology and reducing downtime.
“Corrosion mainly happens on the overboard pipes, the last piece from GRE piping and connection to shell plating of the hull, especially near the connections and welding seams, and the area on the external hull around the overboard pipe outlet,” Manuel Hof, Sales & Production Executive, NACE Coating Inspector Level 2 at Subsea Industries, said in an interview with Offshore Energy-Green Marine.
“These areas will need to be protected against acid-containing water (highly corrosive sulphuric acid) coming from the exhaust gas cleaning system. Traditional coatings applied inside the overboard pipes and on scrubber outlet areas are in most cases not chemically resistant. In that case, the coating will degrade, the steel will be affected and corrode. This can result in water ingress in the engine room, ballast tanks and cargo holds.”
As explained, the lower the pH value of the discharge water after cleaning, the more acidic the fluid and higher likelihood of corrosion.
“Material selection is also important. That is why scrubbers are made of special materials and most of the piping made of GRE/GRP. The last part of the overboard pipe and area of the hull will be in steel. Protection on those areas is very important, if not vital. To apply the correct coating system is essential and should not be tampered with,” he added.
Hence, coatings for scrubbers have become as equally important as good quality material of scrubber components.
A coating is applied inside the overboard pipes and on the external part of the hull around the overboard pipe outlets.
Subsea Industries produces coating and cleaning systems for various types of vessels and applications, including scrubbers and outlets.
In one of its most recent projects, Subsea Industries had its Ecospeed coating system, which is usually used for underwater hull protection, applied on the outlet of the scrubbers of three bulk carriers in Zhoushan, China.
The company has been applying Ecospeed inside scrubbers on board various types of ships, including container ships and oil tankers, since 2016.
Up till now, the company has carried out around 30 scrubber related applications and expects the same number for the remaining year as demand is increasing significantly.
As explained by the company, the coating can withstand the hazardous pollutants of the exhausts and protect the areas surrounding the outlets, which is of critical importance due to the nature of processes taking place in a scrubber.
“Ecospeed has excellent resistance to acids, alkalis, chlorides, and many solvents because of the well-balanced and unique composition of the coating. That is why Ecospeed is very suitable to protect these areas that are usually prone to corrosion,” Hof said.
“Application of Ecospeed for instance can be done in one day. Practically it will take two days, in most cases. It consists of two layers with an overcoat time between the layers of approximately 3 hours. The first layer of Ecospeed can be applied directly on the prepared surface.
“After a successful application, a warranty of 10 years will be issued. The expected lifetime of the coating is 25 years or even longer. If the scrubber lifetime is estimated at 10 years, then Ecospeed can follow this demand.”
As explained the coating is TBT-free, copper-free and biocide-free solution, posing no threat to the water quality or marine environment.
Commenting on the challenges from the Covid-19 pandemic and estimates on the impact on the coatings market and overall scrubber uptake seeing that many projects are being delayed, Hof expects the demand for coatings to stay the same.
When it comes to its own operations, Hoff said that the pandemic has had no major impact on its activities, as the company’s production, supply, and inspection on-site remained uninterrupted.
“Scrubbers that are scheduled to be installed will still need to be completed. Now we see quite a lot of issues from scrubbers installed last year with corrosion and leakage problems. Protection systems are failing after a few months in service. We have been involved in repairs where it was required to replace overboard pipes of the vessel while still in the water,” he added.