Hydropower

What’s Hot in Underwater Work at Dams and Hydro Plants

Issue 7 and Volume 33.

Photo (above): A Dual-Axis Sonar (DAS) system supplied by ASI Marine is being deployed to investigate the downstream draft tube slab at the 2,300-MW Robert Moses Niagara Hydroelectric Power Station as part of the Federal Energy Regulatory Commission relicensing investigation of this facility.

Elizabeth Ingram is managing editor of Hydro Review.

Given the need to keep hydroelectric projects operating as much as possible, the alternative of using a remotely operated vehicle or diver to perform inspections and repairs opens a realm of opportunities and applications.

The use of divers and remotely operated vehicles (ROV) at hydroelectric facilities and dams can provide a cost-effective alternative to dewatering to perform inspection and/or maintenance work, as well as needed repairs. This is a wide-ranging field with many implications for hydro project owners. But what are the newest technologies and some interesting applications of these technologies? To answer these and other questions, we interviewed five companies that do underwater work at hydroelectric facilities. The sources for this article are:

Mike Langen, vice president, marine construction, engineering and technology with Global Diving & Salvage Inc. The company is based in Seattle, Wash., and provides marine construction and infrastructure support services.

Bob Clarke, manager, remote underwater intervention services for ASI Marine, which offers inspection, repair, marine construction and marine geophysical and hydrographic surveys. Parent company ASI Group is based in St. Catharines, Ontario, Canada.

Darrell Moody, southern regional manager for Underwater Construction Corporation, headquartered in Essex, Ct. The company specializes in providing underwater services to the power generation industry, as well as many others.

Tom Eason, founder of Eason Diving & Marine Contractors Inc. in Charleston, S.C. The company provides inspection, maintenance and repair services to power companies, among others.

Craig Fortenbery, president of Mainstream Commercial Divers. The company works on new construction and performs maintenance and inspection services at existing dams and hydro facilities.

Below is insight from these experts as to the latest applications for underwater work and divers, as well as where they see this segment of the hydro market heading.

Q: What are the biggest challenges faced at dams and hydro facilities that can be overcome using divers and/or ROVs?

Langen: As hydro facilities in the U.S. and Canada age and begin to reach their original design lives, the need for inspection and rehabilitation becomes increasingly important. However, the critical functions of the facilities as well as their revenue-generating capabilities make the decision to take them out of service for any length of time very difficult. The use of divers and ROVs makes it possible to perform these critical inspections and repairs while minimizing the impact on operation of the facility. Advances in technology, skill levels and safety protocols allow work to be performed underwater at dams and hydro plants with the same level of quality as that performed in the dry.

Clarke: The biggest challenge is the ability to inspect what is out of sight. Technologies like ROVs with sonar and lidar can be used to help discover anomalies that may warrant further inspection. Instead of relying on calendar-based maintenance, owners of dams and hydro plants can use ROV inspections to identify if and where maintenance and repair work is required, thus saving the company money by avoiding unneeded work. An example would be cleaning of trashracks and maintenance of reservoirs and head ponds. ROVs and hydrographic surveys can be used to determine whether or not dredging work is required, and companies can budget accordingly, resulting in more efficient budget practices.

Moody: As dams and hydro plants age, we are finding the underwater components, such as gate guides and seal plates, to be deteriorating. The biggest challenge at the plants is the ability to dewater areas reserved for maintenance. Highly trained divers can inspect, repair and replace deteriorated underwater components, restoring them to their original design purpose and functionality.

This remotely operated vehicle is being lowered into the water at a hydroelectric facility to perform an inspection of a failed moveable trashrack screen.

Eason: Hydroelectric plants can only make a profit when they are operational. One challenge faced at all hydro facilities is balancing the cost/benefit of shutting down production while performing inspections, repairs and upgrades. A challenge with this balancing act that can be overcome by using divers is excessive equipment isolation. Performing tasks underwater often requires a much simpler plant configuration than performing the same tasks in a dewatered unit. While a thorough lock out tag out (LOTO) of each unit is required for diver entry, the LOTO process is much more efficient than dewatering. Dewatering is often equipment intensive, labor intensive and inherently hazardous to the employees performing work in the dewatered space. Again, having the option to not dewater and rewater results in much less downtime for the plant.

With new remote technologies becoming more available in the underwater industry, some of these tasks can now easily be performed with diver-less options, such as ROVs, sonar imaging devices, cameras and remote flow sensors. Using this equipment creates a broader safety margin than performing the same tasks with a human diver. This strategy often results in less downtime by shortening and reducing unit outages.

Fortenbery: The biggest challenges that can be overcome by using divers or ROVs are obviously the ability to work in the wet by allowing maintenance and inspection services to occur without having to dewater any portion of the facility and thus affecting costly and time-consuming outages.

Q: What is the newest technology you offer for use in underwater work at dams and hydroelectric projects?

Clarke: For us, this would be new applications of sonar systems, such as our Dual-Axis Sonar (DAS™) system, which provides data used to generate high-resolution three-dimensional models of the owner’s underwater assets and is particularly useful in confined spaces. And our multi-beam sonar allows for coverage of larger areas and provides 3D imaging beneficial for identifying debris blocking intakes and determining reservoir capacities. In addition, our ROSEbudTM ROV is a small remote controlled crawler system that has cleaning capability. Used for dredging out sand and silt in live pump wells, it limits shut down of operations, and it can work in high-current areas where diver safety would be of concern.

Moody: We are using some great technology that allows us to work and communicate more effectively. Some of this new technology can be seen within our coatings work and underwater lighting. The advanced lighting systems we are using prevent light refraction, which produces much sharper photos and videos. We also use a state-of-the-art, proprietary coating system that has been a real game changer for us and our customers. This coating system allows us to apply coatings underwater without the need to dewater and is more forgiving in harsh environments.

Eason: At Eason Diving, and across the entire energy industry, safety on the job site comes first. Recently, Eason Diving has implemented new technologies to help us gather what we call a “pre-dive safe condition assessment.” Similar to a job hazard analysis, a pre-dive safe condition assessment involves using a remote flow meter attached to a small video inspection-class ROV to gather live underwater information prior to a diver entering the water. This assessment is conducted in the forebays of dams that impound water for hydroelectric facilities, where high flows and differential pressures can pose a life-threatening hazard to a diver. Using the ROV allows the dive team to measure flow, depth and temperature and even record video at specific locations. This information can be used to verify safe working conditions and can be used during the pre-dive brief or job hazard analysis to give the diver specific and accurate information on his work environment.

Fortenbery: Specifically, for inspection work and some maintenance work, we offer ROV services that can be very cost-effective, particularly in deep water applications. Additionally, for inspection services, we utilize different types of newer technologies, such as sonar systems.

Langen: The newest technologies are in data collection, particularly the use of sonar to provide high-resolution imagery of underwater areas, structures and objects. This imagery can be used to create accurate 3D models for design, engineering and planning of underwater construction projects. The advancements in underwater video cameras and lighting have greatly improved the transfer of information between diver and topside engineering and support personnel. While not new technology, the use of saturation diving to perform underwater construction on dams and hydro projects is something Global has pioneered. This technique not only allows construction to be performed by divers at depths previously believed to be inaccessible, but also significantly extends productive bottom times (the amount of time a diver can spend on the bottom doing work) and enhances the quality of the work at a wide range of depths.

Q: Please provide details on a new/interesting/unique application for your underwater technology at a dam or hydro facility in North America.

Moody: We recently worked on a unique project at a plant in the southern U.S. Plant personnel were unable to fully seal the primary tailgate due to a faulty seal plate. Inspection revealed that the seal plate could not simply be replaced due to the poor condition of the surrounding area. UCC devised a clever modification that allowed for the installation of the new seal plate and replacement of the accompanying tailgate guide bar. These repairs restored the tailgate to full functionality that would otherwise have been impossible.

Eason: A hydroelectric facility was closing its head gates to dewater the unit for required runner maintenance that had to be performed in the dry. When closing, once the head gates reach the “full closed” position, a limit switch stops the head gate drive motors to prevent damage to the head gate, head gate stems and drive gears. A plant operator questioned whether the stopped position dictated by the limit switch was correct. If the head gate was not fully closed, the force of water flowing through a gap of only a few inches between the bottom of the head gate and the forebay floor would present a deadly hazard to a diver. Eason Diving deployed an ROV with an attached flow meter to see the head gate’s position and to measure water flow before the diver entered the water. In this specific case, the head gates were closed, conditions were verified to be safe, and the diver was able to enter the water and proceed with his tasks. But, it is easy to see how this technology could save a life at another place or time.

Fortenbery: We were recently able to provide emergency services at a hydroelectric facility that had a unit shut down due to failure of a moveable trashrack screen. This involved work in 200 feet of water. We were able to quickly repair the problem in a cost-effective manner by using our ROV for the deeper portion and using divers for the shallow work. This allowed us to perform the work without having to mobilize mixed-gas diving equipment, which would have been more expensive. Also, we were able to initially inspect the condition and determine what equipment would be required by flying our ROV to the site in our company airplane on a weekend.

This dive platform contains a full saturation diving system that was used to facilitate repairs on Unit 4 at the Horse Mesa project.

Langen: In June 2012, a vertical concrete guide vane located in Unit 4 at Horse Mesa Dam failed. Salt River Project (SRP), operator of Horse Mesa Dam, located 65 miles northeast of Phoenix, Ariz., formed a design team to evaluate repair options and design the repairs. As part of the design team, Global Diving & Salvage participated in design workshops, performed a high-resolution sonar survey of the interior of the intake and provided constructability reviews of the repair design. Global then successfully bid on the construction phase and was contracted to provide project management and diving services to make repairs of Units 1 through 4.

The work on Unit 4, in 160 feet of water, and on Units 1 through 3, in 260 feet of water, necessitated the use of saturation divers. Divers removed the remaining sections of the damaged vane as well as a second intact vane, using wire saws and wall saws. A new steel vane system, consisting of two vertical and nine horizontal vanes, was installed in place of the original concrete structures. New trashracks were installed in the intake. The bulkheads for Units 1, 2 and 3 did not seal adequately to the penstock intakes due to deteriorated concrete on the intake opening face. Divers anchored and sealed new stainless steel sealing frames at each intake. Inspection also identified deteriorated concrete in the three sets of gate guide slots on the upstream face, which was repaired using saturation and surface diving.

Clarke: We were contracted by the New York Power Authority to investigate the downstream draft tube slab at the 2,300-MW Robert Moses Niagara Hydroelectric Power Station as part of the Federal Energy Regulatory Commission relicensing investigation. A safe and effective way was needed to inspect the draft tube slab. Review of potential technologies as options for determining scour, undermining and the condition of the draft tube slab and construction joints included side scan sonar, seismic methods, ground-penetrating radar, acoustic Doppler current profiler, fathometer, ROV and other non-destructive inspection techniques and equipment (including divers).

ASI was awarded the contract and our ROSEbud vehicle, along with our DAS and other sonar systems, were used. Services provided included bathymetric chart of downstream slab, plot of slab edge profiles, mosaic created from image scans of entire slab, series of profiles across construction joints to check for slab offsets, identification of debris and identification of features of interest for classification by owner’s engineer. NYPA engineers were then able to use the data provided to assess the downstream area, specifically for concerns regarding undermining and scour.

Q: What do you see coming down the pipeline in terms of the type of underwater work that will need to be performed at dams and hydro plants?

Eason: Aging infrastructure is a problem in many industries. Hydroelectric facilities are no exception. As these plants age, routine inspections and component upgrades will be key to preserving efficiency. As technologies advance, new and better techniques of underwater imaging are “coming down the pipeline.” These technologies can provide detailed large-scale images of submerged structures, giving us efficient and highly accurate inspection data. Diver-operated three-dimensional laser measurement and multibeam sonar are two tools that are still very specialized right now, but over the next few years we expect to see this technology become more user-friendly and more readily available for the hydro industry to use.

Fortenbery: Upcoming issues regarding new Environmental Protection Act regulations will potentially require extensive underwater work at hydroelectric plants. The regulations will affect water intakes in particular, requiring the installation of environmentally friendly types of intakes. This could involve significant modifications to existing hydro plants and dams that will require extensive underwater work by divers.

Langen: Once again, our aging infrastructure will require ongoing inspection and rehabilitation, much of which can and should be performed underwater. Improvements in dam safety, such as installation of upstream control valves, and enhancements to facility operations (fish mitigation, increase in flow capacities, etc.) can be installed safely and cost-effectively using underwater construction methodology. As unmanned intervention becomes increasingly sophisticated, the demand for ROVs and other remote technology to provide survey data, dimensional information and facility surveillance will increase.

Clarke: Inspection of tunnels/penstocks using advanced robotic systems and other infrastructure/assets dictated by insurers. Insurance companies are playing a bigger role in requiring third party condition assessments in order to minimize their exposure to financial risks. Penstocks in particular are generally difficult to access because they are long, confined spaces on steep slopes and, when operational, have large volumes of high-velocity water running through them. Even when isolated to a no-flow condition, their configuration makes them challenging for manned inspection methods. Robotic systems with sensor packages that can access the full interior lining of the penstock will be a significant leap forward for asset management at hydropower facilities. Aging assets need to be inspected more frequently because their life expectancy is being reached and owners with to extend that operating life, knowing that their assets are in good condition.

Moody: We see the need for gate guide repairs as being the most in demand. There is an ongoing need for repair and replacement of other integral plant systems, such as trashracks, valves, trash gates, spillway gates and spillway aprons, as well as for concrete repair.