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Scrubber Overboard Spool Pipe Repairs with Five Year Warranty


Since 1976, Subsea Global Solutions has consistently pioneered new and ship owner-friendly repair and refit solutions for the shipping industry. Today, as part of our expanded service portfolio, we can repair, replace, refit, retrofit, or perform new installations of any type of hull penetrations or internal spool pipes from start to finish, whether it is scrubber related or not, during a vessel’s port operations. For these projects we typically work in conjunction with several Exhaust Gas Cleaning System (EGCS), also known as Sulfur Oxide (SOx) Scrubber, manufacturers to ensure complete alignment between different stakeholders and maximize the benefit for the ship owner.

The installation of complete SOx scrubber systems is entirely possible without taking the vessel out of the water. Subsea Global Solutions' involvement is focused on precision cutting of the hull penetrations for the sea chest openings and overboard spool pipe installation below the waterline. Subsea Global Solutions will also provide class approved wet underwater welding procedures and commercial divers, pre-approved repair procedures, as well as Non-Destructive Examination (NDE) on internal and external welds, and the installation of a 5-year manufacturer warranted coating system (POLYFLAKE) against the acidic outflow of high sulfur discharge water. While you may think Subsea Global Solutions would only take care of the underwater portion of the work scope, the reality is, Subsea Global Solutions actually manages much more for its clients.


EGCS, or scrubber systems, are air pollution control devices used to remove particulates and/or gases from industrial exhaust streams. The term "scrubber" has traditionally referred to such devices using liquid to wash unwanted pollutants from an exhaust gas stream.  New exhaust gas regulations issued by the IMO came into effect on January 1st 2020, capping the amount of Sulphur discharges at 0.5%. Without the use of an EGCS,  vessels would not be able to use heavy fuel oil as their primary fuel as per the IMO 2020 regulations. Some years ago, when the regulation was first published, scrubber systems were known to have a “weak leak” in overboard spool pipes from the acidic discharge water and have caused hundreds of scrubber overboard spool pipes to fail in operation. As a result of that, Subsea Global Solutions receives 2 to 3 inquires each week throughout our 13 offices around the globe requiring us to replace the scrubber spool pipes, due to reduction in wall thickness and leaks that were temporary repaired with cement boxes. The core issue here is the acidic discharge water making contact with the spool pipes bare metal due to a pin hole(s) in the hard coating, which then begins to corrode/erode at a rapid rate. Most coating failures are related to lack of preparation on the inside of the new spool pipe and flange by omitting the grit blasting process altogether or not grit blasting to a surface roughness of Sa 2½ (as per IMO guidelines); with surface profiles between 30-75 µm before the coating is applied.This type of preparation is not typical in a shipyard on a new pipe.  The performance of protective coatings of paint and related products applied to a steel is significantly affected by the state of the steel surface immediately prior to the application of the protective coating. The main factors known to influence this performance are the presence of rust and mil scale and/or the presence of surface contaminants, including salts, dust, oils and greases. If the surfaces, prior to the application of the coating are not prepared as previously mentioned, there is little chance of making any type of coating last the 5 years needed. Since these failures became so common, annual Ultrasonic Thickness Measurements (UTM) and/or visual inspections performed by divers are now required by all the major classification societies on an annual basis. If divers notice that there is a coating deficiency located inside of the scrubber overboard discharge, it must be reported to the vessel owner/manager immediately. If it is determined that a spool pipe has a reduction of wall thickness 20% or more, it would generate a Condition of Class (COC) on the vessel.


For similar repair types, you may choose alternative dive companies, but in that case you will typically get the diving portion of the work scope covered only. This requires the vessel owner/manager to oversee and issue PO’s to various service providers, coordinate the writing and approval of the repair procedure to class, arranging class approved internal welders, planning the final class inspection, arranging NDE inspectors, sourcing and fabrication of class approved materials, arranging the grit blasting and coating of new spool pipes, and coordinating the work boats/launch service. What we are offering instead is the “one stop shop” solution. From the preparation to the execution, Subsea Global Solutions manages the entire work scope to ensure minimum off-hire time to the vessel, if any, and permanent class approval of the final product. When a vessel owner/manager choses Subsea Global Solutions, they get the option to choose the work scope that best fits their needs, including the option for a turn-key solution with a single PO and a class approved permanent repair that has a  5-year coating system warranty. Our track record is exceptional, thanks to an impressive reference list of class approved afloat repairs soon to exceed 800 projects.

The Integrated Solution

Whether your ship(s) need new installation or repair of existing sea chests or spool pipes, Subsea Global Solutions will work closely with related parties to manage each facet of the project for you from start to finish. With the collaboration of the Subsea Global Solutions centralized Technical Repair department and the Subsea Global Solutions local region executing the project, we will manage the class repair/installation procedure, logistics, class approved materials sourcing, spool pipe fabrication and protective coating, NDE, internal technical teams, and external commercial dive teams. We provide a planned repair timeline and assign proper crew levels to our internal technical team and external commercial dive team and grit blast the new spool pipes to Sa 2½; with profiles between 30-75 µm, before we apply the coating as per the IMO Guidelines for Maintenance and Repair of Protective Coatings. The coating we use is built up in layers to fill the void between the flange and valve, which is a common area of wastage on a spool pipe due to the turbulence.  

For a permanent scrubber spool pipe repair work scope, we would begin the underwater operation by templating and fitting cofferdams over each of the damaged scrubber overboard locations maintaining the required distances from the heat-affected zone (HAZ) of the internal weld joints. We would then de-water the cofferdam and internal piping through the cofferdam valves with a vacuum pump system. After performing the required safety checks to ensure water is removed from the internal piping, the internal team technical team would begin removing any existing concrete boxes around each of the flawed scrubber spool pipes so the scrubber spool pipe removal process can begin. This process would start by first breaking down and removing the valve and the first connecting section of glass fiber reinforced epoxy (GRE) pipe leaving the spool pipe stub piece as the only remaining component. The internal technical team would then begin cropping the wasted spool pipe(s) from the hull and preparing the hull penetration with the proper joint preparation as per the class-approved welding procedure.  The new spool pipes would be pre-grit blasted to near white and pre-coated with 1,000 to 1,500 microns of POLYFLAKE protective coating that includes a 5-year warranty. The last 50 mm of the spool pipe that rests in the HAZ near the hull penetration is left uncoated until the spool pipe installation is completed and has cooled down. The new spool pipe(s) will be fitted into position and targeted to the existing valve and GRE pipe sections to ensure the previous distance is adhered to.

Then, we weld the full penetration weld (CJP) between the pipe section and the hull. After the repair area cools down, final non-destructive testing in form of visual, ultra-sonic shear wave, and magnetic particle inspection of the CJP and PJP welds will be performed to the satisfaction of the attending class surveyor. At this phase, the internal technical team would begin applying the final POLYFLAKE coat and performing a high voltage surface test to ensure there are no pinholes in the coating system. Now, the valve and the GRE pipe will be re-connected and the commercial dive team will slowly flood and remove the cofferdams. While the spool pipe is slowly filling with water, the internal technical team will monitor the related components for leaks keeping in close communication with the dive team controlling the water inlet. The next step is the most critical step to achieving a permanent repair with class, the wet underwater welding of the root pass. The root is cleaned and prepared as needed and the underwater welding is performed in accordance with the Class A requirements of AWS D3.6M: Underwater Welding Code without the need for a dry habitat. All wet underwater welds are verified using magnetic particle inspection (MT) while following the class-approved NDE procedure. After successfully completing the final inspection with the attending class surveyor, the dive team would install the corrosion protective barriers over all areas where hull coating had to be removed.


Planning, coordinating, and executing complex underwater repair projects to perfection has always been key to distinguish Subsea Global Solutions from others in the commercial diving industry. Both the underwater and internal portions of repairs of this size and magnitude can be managed through a single point of contact to ensure each phase is executed seamlessly in the time frame available. The unique advantage of having a centralized Technical Repair Department allows us to provide the same familiar experience to which both, our Clients and Class are used to, regardless of where in the world the project would take place.


Randy Harp