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Problem
A valued client contacted Subsea Global Solutions needing support to remove and install two new spool pipes for their vessel’s SOx scrubber system during a port call in Singapore or Busan, both of which are home ports of Subsea Global Solutions. The client was unsure which port these repairs would need to be executed in due to the charter’s time-sensitive schedule, so Subsea Global Solutions prefabricated the new scrubber spool pipes and flanges in both locations per the client’s request. It was indicated early on that both of the scrubber overboard pipes were repaired in the preceding 6 months and were now starting to fail again. The previous repair methods included build-up welding in way of the leaking area on the top spool pipe while the bottom spool pipe had a section cropped and replaced with schedule 80 piping compared to the original schedule 60 design piping. During the previous repairs, each spool pipe was recoated with epoxy, but in the end, the acidic outflow of the scrubber discharge was still compromising the spool pipes integrity. After several months, the client’s proactive NDE inspections were showing pipe thinning in several locations.

Solution
The client was in need of a turn-key—class approved—permanent repair. This included a single contractor that would manage the internal technical repair team, commercial diver team, prefabrication of the new spool pieces with flanges, final application of the 5-year warranty POLYFLAKE protective coating to 3000 microns on the new spool pipes, and achieving final class approval for the full repair procedure. Subsea Global Solutions, having years of experience with complex top side and underwater repair projects, took on the task with confidence for all segments of the SOx scrubber repair—internally and externally.

The location of the repair was finally decided for Singapore. The Subsea Global Solutions centralized Technical Repair Department and Subsea Global Solutions Singapore worked closely to manage each facet of the project for the client. The planned repair timeline included 60 hours, with two commercial diver teams and two internal technical teams working around the clock. The commercial diver team began 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. Then, they de-watered the cofferdam and internal piping through the cofferdam valves with a vacuum pump system. After performing the required safety checks to ensure any water was removed from the internal piping, the internal team technical team began removing the existing concrete boxes around each of the flawed scrubber spool pipes to begin the scrubber spool pipe removal process. They started by first breaking down and removing the valves and the first connecting sections of glass fiber reinforced epoxy (GRE) pipes leaving each of the spool pipe stub pieces as the only remaining components. The existing spool pipes were cropped from the hull and each hull penetration  was prepped with the proper joint preparation as per the class-approved welding procedure. The new spool pipes were pre-grit blasted to near white and pre-coated with 3000 microns of POLYFLAKE protective coating while leaving the last 50 mm of the spool pipe that rests in the HAZ near the hull penetration uncoated until the spool pipe installations were completed and allowed to cool down. The new spool pipes were fitted into position and targeted to the existing valve and GRE pipe sections to ensure the previous distance was adhered to and the full penetration welding (CJP) between the pipe section and the hull began. After the repair area cooled down, final non-destructive testing in the form of visual, ultra-sonic shear wave, and magnetic particle inspection of the CJP and PJP welds were performed to the satisfaction of the attending class surveyor. The internal technical team now began applying the final POLYFLAKE coat and performing a high voltage surface test to ensure there were no pinholes found in the coating system. The valves and the GRE pipes were re-connected and the commercial dive team slowly filled the spool pipes with water while keeping in close communication with the internal technical team to ensure any related components were not leaking. Next, the commercial dive team began underwater welding the root pass, which is the most critical step to achieving a permanent repair with class. The root was cleaned and prepared as needed and the underwater welding was performed in accordance with the Class A requirements of AWS D3.6M: Underwater Welding Code without the need for a dry habitat. All underwater welds were 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 installed corrosion protective barriers over all areas where hull coating had to be removed.

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Conclusion
This complex underwater repair was completed to the client's satisfaction in 60 hours. Subsea Global Solutions managed both the underwater and internal portions of this repair to ensure each phase was executed seamlessly in the limited time frame available. Having a centralized Technical Repair Department allows Subsea Global Solutions to ensure both our Clients and Class receive the same familiar experience from Subsea Global Solutions they are used to, regardless of where the project is taking place on the global scale.

​​​​​Our goal is to always deliver unrivaled service. From hull maintenance to complex ship repair, there is only one global resource you can truly rely on; Subsea Global Solutions.

Learn more about Overboard Repairs in this Case Study

Learn more about Underwater Welding and Repairs

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