Yara Marine Technologies (Oslo, Norway) has successfully delivered overboard pipes to a customer for the first time. According to the company, the choice of design and material is crucial for successful operation, as the environment inside the scrubber is highly corrosive.
The overboard pipes, which release wash water to the sea, are usually manufactured and delivered by shipyards. However, Yara says that several ship owners have experienced the spool pieces to be below the required standard — and thus, not able to handle the acidic environment. With corrosion issues occurring as a consequence, Yara Marine has started receiving requests from clients to deliver these pipes in order to ensure quality from the scrubber to the hull.
In collaboration with one of its tower suppliers and a customer, Yara Marine has designed, developed, and delivered overboard pipes together with process, drain, and exhaust pipes. The former includes diffusors and was welded to the hull of the vessel by the shipyard.
“An important part of this project has been to collaborate with all stakeholders throughout the process to collect as much information as possible for the best execution from design to installation,” says Martin Gustafsson, technical project manager. “From this, we can see that we are well positioned for future deliveries, as we expect to deliver more overboard pipes in the future.”
According to the company, the Yara Marine SOx scrubbers are made with high-grade nickel alloys selected to withstand scrubbing and high temperatures when dry running. Due to high temperatures when dry running the scrubber, pipes need to be fitted between the scrubber tower and the vessel pipe system. During scrubbing, the wash water is transported via the vessel’s pipe system, normally made in glass-reinforced epoxy that works well in corrosive environments.
As such, Yara Marine recommends the pipe spools to be in an equivalent high-quality material to the scrubber tower — such as high-grade stainless steel — in order to withstand the corrosiveness.
The design of the overboard pipes is new and carefully developed to meet the set requirements with a combination of 254SMO and carbon steel (CS) material, Yara explains. The 254SMO is selected for its corrosion resistance and to ease its installation at the shipyard. A CS transition section is welded between the hull and the overboard pipe to further secure a smooth transition between the coated hull and pipe, with a 625 Inconel weld overlay over the CS.
The transition between the coated CS hull and the SMO254 pipe is highly corrosive due to turbulent flow of acidic wash water. To secure full corrosion resistance in the challenging transition between carbon steel and SM0254, the pipe and carbon steel piece was delivered with a multiple layered weld overlay of 625 Inconel.