Hydropower Turbine Repair: From Welders to SCOMPI and ABB

A hydropower turbine runner spins in fast water for decades, and tiny vapor bubbles collapsing against its blades slowly eat pits into the steel. For a long time, hydropower turbine repair meant shutting the unit down, draining it and sending welders into the runner to gouge out the damage, fill it with weld and grind the blade back to shape. This post covers how crews did that by hand and how Hydro-Québec put a small robot on a rail inside the runner in 1992. It then looks at why cavitation is in the news again at Hoover Dam this autumn and where ABB welding and grinding robots could fit.

A small Francis turbine runner with cavitation holes and old stainless steel weld repairs. Photo: Duk / Wikimedia Commons (CC BY 2.5)

Gouge, weld and grind: runner repair by hand

The US Bureau of Reclamation's turbine repair manual, revised in April 1989, explains the damage. Flow irregularities create pockets of very low pressure where vapor cavities form. When pressure changes, the cavities collapse, and where that happens next to the metal, the shock tears out bits of the surface. The cycle repeats at a very high frequency, and the damage rate climbs as the surface deteriorates. Without timely repair, the manual warns, cavitation can destroy the surface under attack. It recommends inspecting a new turbine after about 1,500, 4,000 and 8,000 hours of running, then at least every 24,000 hours or four years.

A Francis runner removed from Crystal Dam Powerplant in 1989, now on display at Glen Canyon Dam, Arizona. Photo: Adam Kliczek / Wikimedia Commons (CC BY-SA 3.0)

Welding is, in the manual's words, the most common and most successful repair method. A crew braces the blade, removes damaged metal by grinding or carbon arc gouging, grinds it to bright metal and preheats it. Then it welds no more than 1/8 inch per pass, grinds the blade back to its contour and checks the dimensions. The manual would rather see the same welders and grinders on every outage. It also notes that overhead gas metal arc welding under propeller and Kaplan blades is difficult and that argon can build up in a badly ventilated runner. A 2009 paper from the University of Brasília describes the work as harsh, at around 40°C and 99 percent humidity for tens of hours.

A broken Pelton runner from the Sy-Sima power plant on display in Eidfjord, Norway. A bucket that came off in service was welded back on. Photo: Jkx88 / Wikimedia Commons (CC BY-SA 4.0)

The first step toward automation was a patent. In November 1988 Jean-Luc Fihey, Bruce Hazel and three colleagues at Hydro-Québec and Ontario Hydro filed for a robot that runs on a track shaped to a curved surface, senses the damaged area and generates its own tool paths for gouging, welding and grinding, so the runner can stay in the turbine pit. Hydro-Québec's research institute IREQ first used its SCOMPI robot in 1992 to repair turbine runners. A later Hydro-Québec paper describes a six-axis, 33 kg robot that stands only 18 cm tall on its track and welds cavitation-resistant overlays overhead on Francis runner blades.

Bureau of Reclamation officials at Hoover Dam with an Allis-Chalmers stainless steel turbine runner for Unit N-4, around 1962. Photo: Bureau of Reclamation via Wikimedia Commons (public domain)

Cavitation in the news and robots in the pit

On 26 September 2026 WorldAtlas reported that only five of Hoover Dam's 17 main turbines are newer wide-head units built for low water. The older machines suffer severe cavitation damage once Lake Mead drops below 1,035 feet, so they have to come offline, and Reclamation's updated figures put the dam's capacity at that level near 382 megawatts, against earlier estimates of 1,302. Reclamation installed the five wide-head turbines between 2011 and 2016 to resist cavitation. In May 2026 it released $52 million to replace three more of the old units.

The wide-head turbine for Hoover Dam's unit A-8 hangs from the dam's permanent cableway during delivery, February 2014. Photo: Bureau of Reclamation / Wikimedia Commons (CC BY-SA 2.0)

In October, Hydro Tasmania reported that its Poatina Power Station was back in service after one of its largest planned outages. A robot blasted the old paint off the inside of the 1.8 km penstock before crews sprayed on new coating, and the team replaced the Pelton runner and nozzles on a 60-year-old generating unit, part of a $200 million plan to upgrade all six 60 MW turbines. Back in Quebec, a 2017 engineering.com profile of IREQ described SCOMPI as a portable, rail-based robot that fits the confined space around a runner, so the runner does not have to be pulled out. It weighs 38 kg and reaches 940 mm.

The former Hydro Tasmania town of Poatina at the foot of the Great Western Tiers, the range the power station's penstock runs down. Photo: Peripitus / Wikimedia Commons (CC BY-SA 3.0)

ABB does not make a turbine repair robot, so its fit here is a possibility. ABB lists welding among the jobs for its GoFa cobot and says the GoFa welding package copes with tight spaces and awkward angles, with welds taught by hand through the Easy Teach Device. The smallest GoFa reaches 0.95 m, close to SCOMPI's 940 mm, and can be protected up to IP67. For grinding, Teqram's EasyGrinder at the German steel stockholder Ancofer uses an ABB IRB 6700 that scans each part in 3D and picks its own grinding process, the same scan-then-grind step a runner repair needs. Our post on grinding and deburring robots covers more of that work.

An ABB IRB 6700 grinds a steel part in Teqram's EasyGrinder cell at Ancofer in Germany. Photo: ABB

What runner repair robots still need

The fleets that need this work are old and large. Poatina's first five units date from the 1960s, and Hydro-Québec ran 63 hydroelectric stations in 2017. Repair robots have to be carried through access hatches and set up quickly, and by 2005 IREQ had a smaller MINI-SCOMPI that one person can install. A cobot-sized arm on a temporary rail is one way an ABB robot could join that work. Its paths could be planned offline from a 3D scan of the blade in RobotStudio, which ABB says matches reality up to 99 percent for GoFa programs.

A worker guides the welding torch of an ABB GoFa cobot while teaching a weld. Photo: ABB

At home, all of this shows up as power that stays on. Poatina alone supplies around 10 percent of Tasmania's generating capacity, so every week one of its units spends drained for repairs is output the grid has to find elsewhere. Faster in-place repairs mean shorter outages and fewer runners shipped away for rebuilding. Welding cobots are also reaching small workshops, as our post on cobot welding from job shops to garages shows, and that could widen the pool of people able to run them.

Generators in the main turbine hall of Hoover Dam, 2026. Photo: Alexander Mason / Wikimedia Commons (CC BY 4.0)

Cost is still the first hurdle. In 1995 Hydro-Québec and Ontario Hydro studied using SCOMPI to repair divider plates in the four steam generators at the Gentilly-2 nuclear plant, and a full simulation showed it would work, yet cost and scheduling led them to repair by hand. Heat input is another. The Reclamation manual warns that excessive weld repairs can distort blades, cut efficiency and cause cracking, so a robot has to control its heat as carefully as a good welder does. People stay in the loop as well, because someone has to read the damage, choose the filler alloy and inspect the welds, even when a robot spends the long hours in the hot, humid runner.

Guiding the torch of an ABB GoFa welding cobot to a pipe joint by hand before the robot repeats the weld. Photo: ABB

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