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Scrubber Overboard Spool Pipe Repairs with 5 Year Warranty

Case Study

Scrubber Overboard Spool Pipe Repairs with 5 Year Warranty

Abstract

Since 1976, Subsea Global Solutions (SGS) 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. SGS’s involvement is focused on precision cutting of the hull penetrations for the sea chest openings and overboard spool pipe installation below the waterline. SGS 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 SGS would only take care of the underwater portion of the work scope, the reality is, SGS actually manages much more for its clients.

The Integrated SGS Solution

Whether your ship(s) need new installation or repair of existing sea chests or spool pipes, SGS will work closely with related parties to manage each facet of the project for you from start to finish. With the collaboration of the SGS centralized Technical Repair department and the SGS 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.

Conclusion

Planning, coordinating, and executing complex underwater repair projects to perfection has always been key to distinguish SGS 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.

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