How the City of Toronto Saved Thousands on Pipe Inspections
Pipe crawlers or push cameras have long been seen as a staple in sewer and stormwater pipe inspections. While these vehicles are fast, effective and reliable solutions for most dry or semi-dry environments, inspecting a fully submerged, low-visibility pipeline can be virtually impossible. So, what is the solution?
ROVs for Submerged Pipe Inspections
When underwater environments render traditional CCTV equipment useless, a remote operated vehicle (ROV) equipped with imaging tools like sonar can effectively inspect submerged pipelines, even with zero camera visibility. Rather than draining or entering a confined space, ROVs provide an effective way of quickly and safely entering a pipe.
Adding an imaging sonar to the ROV enables operators to have a better understanding of the tunnel’s condition. The imaging sonar can cut through murky conditions and provide clearer insights on:
Size and Types of Defects
- Cracking & Pitting
- Disjoints and Separation
- Sediment Levels, can hide deformations, reduce flow rates, increase risk of overflows
- Foreign objects (building materials, tree rooting, cross bore pipes or cables)
- Protruding Laterals
“We’ve so far been able to go up a section of pipe that we weren’t able to do without the sonar,” said Arash Farajian, business operations consultant, Toronto Water. “The murkiness and the debris obviously don’t help because even with the lights on you can’t see anything past a couple inches. Sonar is essential really trying to figure out where you’re navigating.”
Submerged Tunnel Case Study – PipeTek
In 2020, Deep Trekker, a Canadian ROV manufacturer worked alongside Pipetek, a pipe inspection contractor, on inspections of submerged tunnels and other structures for Toronto Water.
The goal of this project was to evaluate the condition of a combined sewer and storm tunnel for Toronto Water. PipeTek needed to provide a report of the tunnel and associated pump and intake structures to determine the best next steps for managing the structure. The main challenges which were identified right away would be water visibility, as well as operating in the tight and busy conditions of Toronto, Canada.
“It’s a 100-year-old sewer; it’s the oldest sewer in the city,” explained Bill Shea, director distribution and collection inspects, Toronto Water. “This particular sewer is under lake level, so it’s always submerged so the only way to do inspections in the past was to use a diver. Diving in the sewer is dangerous and we’d prefer not to do that.”
Deep Trekker REVOLUTION ROV
Submerged tunnels with sediment in the bottom proved to be more difficult for pipe crawlers, robots that PipeTek had significantly more experience with at the time. The crawler’s wheels or tracks can stir the sediment, obstructing the camera view, or worse, getting the crawler stuck. Human entry under these circumstances would be far too dangerous. After evaluating the dangers and obstacles, it was clear that a free swimming ROV with an imaging sonar was the right tool for PipeTek.
Since this was a 530-m long, fully submerged tunnel, the REVOLUTION ROV was chosen for the task. The REVOLUTION is a powerful six thruster vehicle made by Canadian manufacturer Deep Trekker. Not only did its power make it an ideal choice for piloting with 530m of tether behind it, but it was able to be delivered via a battery-powered vehicle. Operating on batteries removes the need for a large topside generator, providing a superior compact solution to use on a crowded city location.
Additionally, its 260 rotating camera and sonar head allows operators to ‘sweep’ the sonar for scanning pipe segments at a variety of angles. Alternative ROV solutions operate with a fixed front-facing sonar and require the vehicle to pitch to change sonar angles. In open water, this can be viable, but in a confined space, these movements were impossible to perform.
Blueprint Subsea Oculus M3000d Multibeam Imaging Sonar
The “d” in the M3000d sonar model name means it is a dual-frequency sonar, meaning the operator can switch between the low and high frequencies with the press of a button. The low-frequency mode provides more range and a wider field of view, while the high-frequency mode is best for up-close inspection for precise measurements.
In this inspection, there were multiple passes through the tunnel. Some were at higher speeds with lower frequency to get a quick general idea of the condition and look for large artifacts or obstructions. The slower passes at high frequency and resolution to focus on smaller defects that were identified in the earlier passes.
Summary of Mission
Overall, this survey was a complete success despite having zero visibility for the camera. Using the imaging sonar combined with the flexibility of the 260-degree rotating camera head on the REVOLUTION, PipeTek was able to identify several points of interest for Toronto Water. These included detailed sonar recordings of protruding laterals, pits, cracks, and sediment levels. Not only were these points of interest located and photographed, they also were able to measure these with the sonar tools available.
The use of ROVs for inspection saves money in several ways. The hiring of external teams, such as dive teams, becomes unnecessary with an ROV. Additionally, the time required for conducting inspections is greatly minimized, allowing for work hours to be utilized efficiently. Finally, the ease of inspection
“Part of my job is actually to try to put some numbers on the paper and actually talk about our return on investment,” explained Farajian. “Just with the first generation of this ROV, so I’m talking about the DTG2 that we got, we saved over $15,000 but also like I said in terms of proactive maintenance we also know about problems ahead of time. Now on the REVOLUTION because of the added stability on it, the sonar on it, we’re really looking to save in the hundreds of thousands of dollars. With the advent of this technology, we can now do it much more safely and quite frankly cheaper.”
Riley Kooh is the content marketing manager at Deep Trekker Inc.