How Artec Eva helped retrofit an 87-year-old French hydroelectric plant

Scanning the end of the hydroelectric draft tube with Artec Eva

Deep in the heart of France’s Jura mountain range, engineer Damien Delmont stood inside a long concrete draft tube with his Artec Eva 3D scanner in hand, staring up into the darkness towards the motionless turbine four meters above, where two old valves held back millions of liters of surging water on the other side. It was time to begin.

In the hours ahead, Delmont and his project partner Guillaume Demarche captured every square millimeter of the massive draft tube, using scaffolding to ascend into the upper reaches of the structure beneath the turbine.

The team needed to work fast. Every extra hour that the turbine stayed switched off meant a loss of revenue for the plant, which at full capacity generates more than 10 megawatts of electricity, enough to power 5,000 homes.

Further complicating their work, the plant was operating under a state of emergency, on the verge of evacuation, as the water level of the river had risen up into the flood stage.

After 87 years, time for retrofitting

Built by German engineers almost a century ago, in 1934, as part of reparations from World War I, the hydroelectric facility has been in operation ever since. When it came time to replace the first of two of the plant’s four Francis turbines, the contractor in charge of the project understood the complex nature of the task at hand.

Monitoring the level of the water alongside the hydroelectric plant

In order for the turbine manufacturer to design optimally-functioning units for the facility, they first needed to know the exact dimensions of the huge, irregular-shaped draft tubes, which act like exhaust pipes for the water after it’s channeled through the turbines and sent on to the river below.

If inaccurate measurements were used, at best, the turbines would never generate the specified electrical output, thus not meeting the plant’s performance standards.

At worst, faulty measurements could result in power losses, cavitation, and even excessively high turbine vibration levels, possibly leading to an accident such as the Sayano-Shushenskaya hydroelectric plant disaster of 2009.

The need for accurate documentation

The original blueprints of the draft tubes still exist, but in the nearly nine decades since they were drawn up, it’s certain that their dimensions have changed over time, thus ruling them out for use as dependable engineering documentation.

Beyond the immediate physical damage arising from any failure to meet specifications, the turbine manufacturer and the project contractor would also face severe penalties, including fines, damaged reputations, etc.

Understanding that traditional measurement methods would fall short of accurately documenting the tubes within the project timeframes, the contractor turned to Damien Delmont of 3DLM, a specialist in engineering and 3D scanning for industrial applications, including retrofitting, inspection, and reverse engineering legacy structures and components.

Delmont explained, “If the draft tubes were a simple geometrical shape, they could easily be measured using traditional tools. But they’re not. And that’s why, for us to make millimeter-precise CAD models of these tubes, we chose to 3D scan them.”

In search of the right 3D scanner

Several years back, when Delmont launched his engineering firm, he began looking for a 3D scanner that would meet his stringent needs.

After reaching out to Artec Gold Certified partner Boreal 3D and meeting Demarche, he was soon introduced to the Artec Eva, a handheld professional 3D scanner with submillimeter accuracy, favored among engineers and other specialists worldwide.

The Artec Eva

Delmont continued, “The nature of this project demanded tight deadlines, and with our Eva, in just a few hours, we were able to capture all 12 meters (39.3 feet) of the draft tube so precisely that the CAD model can be used for the analyses and CFD (computational fluid dynamics) simulations needed to build the new turbine.”

“For whatever reason, if we didn’t deliver the results within the stated timeframe, everyone else in the project would’ve been impacted, and it also would’ve affected our chances of taking part in future projects.”

Capturing a supersized object, scan after scan

With the deadline rapidly approaching, considering the magnitude and complexity of the project, Delmont brought in Guillaume Demarche to assist. After careful planning, they arrived at the hydroelectric facility and quickly laid out their strategy for the steps ahead.

To make it faster to align the scans in Artec Studio software during the processing stage, they applied spray paint to the wall of the draft tube, designating ten separate sections for scanning.

Boreal’s Guillaume Demarche scanning the draft tube with Artec Eva

By working in sections like this, they were also better prepared to make an immediate exit from the draft tube in the event of an emergency, the threat of which was always close at hand. As an example of this, while the team was scanning, the water was a mere ten centimeters from spilling over the top of the cofferdam directly behind them.

Safety engineers stood watch atop the dam, monitoring the water level the entire time. If the weather were to change for the worse, even a few kilometers upriver, it could cause the water to rise to dangerous levels. In that case, the team would have had less than one minute to grab all their equipment and escape from the draft tube.

Scanning through darkness and water

A constant reminder of the risk was the water pouring into the draft tube, about ten liters per minute, streaming down through the valves above. Unlike residential valves and faucets, these older valves are designed to let through small amounts of water. To avoid the immediate risk of water damage, the team put together a makeshift wooden table to rest their computers and equipment on.

But the presence of water didn’t get in the way of the scanning, not for a minute. “Even though the floor of the draft tube had as much as 2 cm of water in places, the Eva still scanned these areas perfectly,” said Delmont.

Boreal’s Guillaume Demarche capturing an upper section of the draft tube with Artec Eva

He continued, “I’ve heard that 3D scanners can struggle with even a thin coating of water, but not Eva. To be double sure, I checked these areas with laser telemetry and saw that the Eva measurements were spot on.”

Each section took about half an hour to scan, with the entire tube from end to end captured in about five hours.

“The Eva proved to be an ideal scanner for this kind of work, because it is sufficiently precise and allows us to scan without placing any targets in such a humid, even wet environment that is relatively hostile to technology, in complete darkness, with no electrical outlets present,” said Delmont.

Creating CAD models for retrofitting, inspection, and more

During the scanning, Delmont discovered a 5-10 mm layer of mineral buildup on the walls of the draft tubes, deposited there over the decades by the untold millions of liters of water passing through the tubes.

Such deposits affect the flow characteristics through the tube, and they needed to be accurately documented in the resulting 3D model, otherwise the subsequent CFD simulations wouldn’t reflect the actual flow rates of water.

After the scanning and back at the office, it came time to process the scans into a CAD model. According to Demarche, “There wasn’t much work for us on the scan processing side in Artec Studio, which is how we planned it.”

He went on, “Basically, after some minor clean up, I aligned the ten scanned sections and created a single 3D model encompassing all the surfaces of the entire draft tube.”

Final 3D model of the entire hydroelectric draft tube scanned with Artec Eva

Using Artec Studio’s scan-to-CAD tools for optimal results

Following this step, Delmont used Artec Studio’s scan-to-CAD features to fit the 3D model of the draft tube with CAD primitive shapes. He then exported these shapes as STP files over to SOLIDWORKS, where he used them as references for sketching, drawing, and extruding the CAD model of the draft tube.

Highlighting the importance of scan-to-CAD functionality, Delmont said, “If one stage of the workflow takes too much time, this will reduce our efficiency and raise our costs, which will hurt our chances of staying competitive and winning new projects.”

“By being able to create CAD primitives directly from the scan in Artec Studio, just moments after scanning an object, we’re slashing priceless time off the workflow, while not sacrificing anything in the way of quality.”

Capturing everything perfectly from the first scan

Delmont added, “The Eva makes it possible to capture all the dimensions of an object, even one as massive and non-uniform as a hydroelectric draft tube, the first time. That means there’s no need for a second round of scanning, no need to stop the plant again.”

“Because if you start processing the scans and see that you’re missing some surface data, returning to the plant and stopping the turbines can be very expensive in terms of lost revenue for the client. Fortunately, with Eva, when we walk away from a scanning job, we know that all the data is there, down to the last millimeter.”

After finishing the CAD model well before the deadline, Delmont sent it to the client, who in turn forwarded it to the turbine manufacturer. The model met all the specifications and was immediately used for CFD simulations and other analyses.

CAD model of the draft tube created from Artec Eva scans

Weeks later, the team returned to the hydroelectric plant, scanned the second draft tube, and produced a CAD model of it using their established workflow.

Precise CAD models for retrofitting and beyond

Now that CAD models of both draft tubes are readily available, they can also be used as reference models for inspecting the tubes via 3D scanning, for example in Artec Studio, using the software’s surface distance mapping tool. Any differences between the CAD model and scan will show up in an easy to read color heat map.

Today, dozens of such legacy hydroelectric plants in need of retrofitting exist in France alone, with hundreds if not thousands more to be found in countries around the world.

When it comes to the engineering expertise for these projects, in Delmont’s words, “The ultimate question is this: what kinds of accuracy are truly needed? Because only simple objects require just one level.”

Elaborating, Delmont went on, “Many companies will accept lower accuracy tolerances on small, crucial aspects of a component, while other companies will push for the highest tolerances across an entire component, even on sections that don’t require it.”

“But these approaches are not only flawed, they also cause longer project times, wasted resources, higher costs, and finally, poorer results,” said Delmont.

Taking on complex projects where no original documentation exists

“The greatest challenge is how to achieve ideal levels of accuracy when retrofitting very large objects, such as the draft tubes, with various sections featuring different levels of complexity. And at the same time, to adapt your own way of retro-engineering to each individual project.”

“In every project I’ve undertaken with my Artec Eva,” said Delmont, “it’s proven to be a critical solution for helping bridge the gap where no original drawings or documentation can be found, which is the case in about 70% of the retrofitting projects we’ve encountered.”

He continued, “With Eva, I am creating precise measurements and CAD models of objects only a few centimeters in size to others that are many meters long. I believe this is one of Eva’s greatest strengths, its versatility. The resulting CAD models are essential for everything from retrofitting to inspection, maintenance, and much more.”