Underground pit stop

The day Dimítrius Almeida sets off for work feels a little like the day of the World Cup final. The team has been preparing for this final for months, spare parts and tools are ready at hand, contingency plans have been written, and all the substitute players are in position.

The Voith Hydro project manager and the teams in Cubatão and at the Voith Hydro production hall in São Paulo have rehearsed the process dozens of times. The moment the employee of the local water authority Empresa Metropolitana de Águas e Energia (EMAE) confirms to the team that the pressure in the pressure pipe is zero at 720 meters above sea level, the clock starts ticking.

From this point on, Voith Hydro’s service experts have just 45 hours to replace one of the six spherical valves at the Henry Borden underground hydropower plant. The reason for the rush is a unique geological phenomenon: the pressure of the surrounding groundwater acts on the downpipe installed in the mountain. Without the counterpressure of the water flowing through the pipe, there’s a risk that the pipe’s carbon coating will be damaged and the pipe will bulge. Calculations have shown that this effect will occur after roughly 45 hours.

Now it’s getting tense: The team has prepared everything for the new spherical valve. The clock is ticking.

The HyService team only has 45 hours to replace the spherical valve. The disassembly of the old device marks the halfway point.

Luckily, the team already has quite a bit of experience dealing with this challenging task. This is because it’s now the third of a total of six spherical valves that are being replaced and refurbished as part of the maintenance project. Each spherical valve weighs 60 tons and has a diameter of 1.2 meters. The spherical valve currently up for maintenance is being replaced with one that has already been refurbished.

But what sounds simple in theory poses a number of challenges in practice and under time pressure. Although the system has a modular design and all of the spherical valves are basically identical, there are still differences between the old and new units depending on the level of wear and their operational history. These differences will be eliminated during the refurbishment process at the Voith workshop in São Paulo, 120 kilometers (km) away.

Not all of the components can be completely prefabricated, however. In some cases, the exact condition only becomes visible during disassembly. In this case, the corresponding spare part must be refurbished at the factory within the specified time frame and then quickly delivered to the plant. Replacing the downstream adjusting ring, which ensures the spherical valve’s seal and stability, plays a key. As soon as the old adjusting ring is removed, it is measured and its mechanical condition meticulously documented. This report is then immediately sent to the Voith production team in São Paulo.

The critical phase has been reached: Everything is waiting for the downstream adjustment ring, which is delivered “just in time” by truck from São Paulo after the final finishing touches have been made.

Transportation from the Voith plant went smoothly and the new downstream adjusting ring arrived on time. Everything fits – thanks to the precise coordination between the workshop and the plant.

A blank of the adjusting ring, which is already waiting there, is then precisely prepared so that it corresponds exactly to the component in Cubatão. Once the part is finished, it is loaded onto a truck and sent on its way to the plant – a trip that takes roughly three hours. Once there, the installation team immediately begins installing it.

In order to achieve all of this within the 45-hour time frame, months of preparation are necessary. Similar to a surgical procedure, every step of the process and every position of the employees, components, and tools is precisely defined. In this context, it must be noted that working in this confined space underground isn’t without its hazards. That’s why the work is only carried out under the strictest safety precautions.

“The pressure during a project like this is comparable to a pit stop in a Formula 1 race,” says Project Manager Dimítrius Almeida, who is on site at the Henry Borden plant almost continuously. “There really is zero room for error.” The Team has already successfully mastered this complex task twice with the first refurbished valve taking 37.5 hours to replace and the second only 36 hours. “But something unforeseen can always happen that sets us back a long way, and you have to be prepared for that.”

Like the previous two times, the team once again succeeds – all of the connections, valves, and the adjusting ring are correctly installed after nearly 39 hours. A final check of the system, then the time has come: the EMAE employee opens the downpipe’s water inlet and the water once again flows at full speed towards the refurbished spherical valve.