Previously, the unit we took down for cavitation had a crack in the hub, so following our repairs we had a mechanical engineer come and perform Non-destructive Testing and Magnetic Particle Testing on the weld seams to check for any cracks or thin areas.

One method was to use a machine that would detect and beep/light display where a crack or thin area appeared.

The Magnetic Particle Method uses a dust that will gather in a location where a defect could be.

Following the testing the conclusion was that there was no trace of any deformities or cracks in the hub and we could end our repairs for this unit. We decided to throw a coat of paint on the hub to help prevent any more damage from the water once the unit is started up again.

This spring we ended up only taking down one unit for cavitation due to the excessive amount of water.

We began by craning down all of our material, welders, plasma cutters, job box and lights to the elevation (664) of the generating station. Following the de-watering of the unit, and after several permits and hold cards were in place, the utility crew installed scaffolding inside the penstock. We went in and installed more lighting on the scaffolding, and inspected and mapped out the unit for cavitation. There was no excessive wear on the blades or liner; however, there were a few places that could use a touch up.

We then hauled in our equipment and began the cavitation process. Our work experience student had never done anything like this, so it was definitely something new for him. We first began to gouge out the areas needing to be repaired, and worked our way around the blades. Due to not having excessive repairs to do we did the welding portion with arc welders and stainless steel rods.

Following the welding, we ground down our welds and polished them up to make them good as new.