Wärtsilä and A.P. Moller – Maersk have developed a means for preventing corrosion in exhaust-gas scrubber discharge pipes. The permanent in-pipe solution is designed to solve corrosion problems associated with open-loop scrubber washwater discharge.
The majority of the estimated 5,000 scrubber systems installed across the world fleet are of open-loop configuration. With this system, seawater is used to scrub SOx from the exhaust gas, with the used water then being discharged back to the sea after cleaning.
Under IMO Guidelines, the washwater from exhaust gas cleaning systems, or scrubbers, should have a pH of no less than 6.5. However, in reality the pH of scrubber washwater is typically acidic, prior to being diluted by seawater. This creates the risk of structural corrosion to the discharge pipes.
The risk of scrubber discharge pipe corrosion is particularly high for pipes made of mild steel. In some cases, if the discharge pipes are inadequately protected, severe corrosion can damage the surrounding mild steel hull plates, resulting in water ingress.
The new “pipe-in-pipe” solution allows for the original overboard pipe to remain in situ while a new glass reinforced epoxy (GRE) pipe is inserted into it. No metal cutting or welding is necessary. An SMO stainless steel sleeve is inserted between the new GRE pipe and the existing steel pipe. An adhesive permanently secures the GRE pipe in place. Since this “pipe-in-pipe” solution has a small impact on the internal diameter of the pipe, it is best suited for overboard pipes with a diameter greater than 300 mm.
“This is a long-term solution that can be planned for at any time, even if corrosion has not yet occurred,” says William Winters, managing director of Wärtsilä Underwater Services. “The component pipes can be prepared and stored either on board or at an engineering facility ready for fitting either during a scheduled drydocking or port-call or, if necessary, while afloat and in operation using a cofferdam at a convenient time and location.”
“This in-operation repair offers substantial overall savings to the ship owner and allows the vessel to stay in service,” adds Winters.
“We have noted corrosion incidents occurring on some scrubber equipped vessels and wanted to be proactive in solving the problem,” says Jorn Kahle, Senior Lead Specialist, Maersk. “Additionally, taking a vessel out of service is extremely costly. One of the key driving forces for development of this pipe-in-pipe concept with Wärtsilä Underwater Services is to minimize these disruptions and costs. We are happy to offer this unique cost-efficient service to any vessel with any make of scrubber”.
Installations of the patented solution and licensed know-how will be carried out by Wärtsilä Underwater Services. In most cases, the repair will be completed in less than two days, which can avoid the ship having to go off hire. Considerable time and cost savings compared to alternative repair solutions have already been demonstrated.
The Wärtsilä/Maersk solution is intended for long-term protection. It reduces complications associated with welding work required on pipes and sometimes hull plates, particularly in underwater repair situations.