Historically, utility companies have used commercial divers to inspect and maintain the underwater areas of their facilities. Hydroelectric dams, fossil and nuclear power plants all require routine underwater inspections. Forebays, cooling water intakes, gates, draft tubes, and trash screens are just some of the many areas that require inspecting.

The arrival of ROVs (remotely operated vehicles) has allowed much of the inspection work to be carried out without the use of divers. Often, limited underwater visibility makes it difficult for a diver or video camera to “see” the structure that is being inspected. This can lead to an inconsistent survey and a misinterpretation of collected data.

Glenn Underwater Services has solved this problem with use of multibeam imaging sonar systems deployed with their ROVs. The multibeam sonar can see what the human eye and video systems are not able to see. In simple terms, the sonar uses an echo emitted from a source. This sound wave travels until it reaches an object and then bounces off, reflecting back to the source. As the echo is received, it creates a digital sonar image. The sonar image reveals size, shape, distance, and depth to a digital display.

The multibeam sonar uses multiple echoes to create a 120-degree field with a range of over 300 feet. Glenn’s skilled ROV pilots use a high-tech computer system to monitor and record the images produced by the sonar. As conditions vary, the pilots use sophisticated software to filter an enhance the images. This aids in increased capability for target acquisition and general navigation. Underwater objects that might take days to locate can often be found in minutes.

The multibeam sonar is capable of rendering precise details of an underwater structure in any condition. An example of this is when draft tubes are inspected at a hydroelectric dam. Constructed of concrete and/or steel these structures vary greatly from one dam to the next. ROV’s equipped with the sonar enter the draft tube creating a virtual and digital map of the structure. The high resolution, sonar images record every fastener, seam, and any anomalies with accurate detail. Not only is the survey more accurate than with a diver, it takes less time and is more detailed.

ROVs with multibeam sonar have now made it possible to perform timely, efficient, and accurate inspections of underwater structures, usually with minimal to no downtime to the structure.

Glenn Underwater recently performed an inspection to a cooling water forebay and water intake at a CT Plant using an ROV equipped with the multibeam sonar. If a diver had been deployed, it would have required a shutdown of the cooling water intake pumps with extensive lockout/tag-out preparations before commencing the dive.

Due to the production schedule, this was not an option. Another factor was the extremely poor visibility stopping an accurate dive inspection.Glenn Underwater Services mobilized an ROV team to the site and within several hours had provided the client with a detailed sonar inspection of the forebay and the intake structure. Glenn’s skilled ROV pilot was able to maneuver the ROV right up to the trash screen with the intake pumps running, something that would be possible with a diver. The inspection was able to give the client a detailed view of debris present, integrity of the intake structure, and silt levels in the forebay.

Another advantage of the ROV systems equipped with multi-beam sonar is their ability to be placed into restrictive, hard to access areas that would be more dangerous for divers. However, ROVs with multibeam sonar can not replace all diving work at power generating facilities, they can be used to lessen diver exposure, to increase safety, and to increase the accuracy of inspections.

For more information about our ROV and multibeam sonar, please contact us at Glenn Underwater Services.