photo credits: Geppert
photo credits: Geppert
HYDRO
The removed disc and transport vehicle on the way to the Geppert's works facility
photo credits: Geppert
DAMAGED TRUNNIONS Once the old components had arrived at Geppert’s works halls they were subjected to detailed inspections. Geppert’s specialists worked together with the experts from TIWAG to identify damage to parts and comprehensively document their current state. The inspection process also involved 3D measurement scans of the positioning and orientation of the valve discs and trunnions in relation to each other. This revealed corrosion damage in numerous places at the hard chromium plating of the
trunnions. Markus Klotz outlined a further technical obstacle: “Under these circumstances there was no alternative but to remove the trunnions from the valve discs. The thermically pretensioned bolts that had been used to affix the trunnions to the valve discs had to be warmed up with purpose-built heating rods in order to loosen the round locking nuts that had become particularly difficult to move due to the build-up of dirt and corrosion.” Once the trunnions had been dismantled the remaining bolts in the valve disc were removed. The 600-mm chrome-coated trunnions were then machined on the factory’s own turning machine, and all surfaces and materials were checked for cracks. A fortifying tungsten carbide coating was applied to the surfaces where the bearing is in contact. “In contrast to simple chrome-plating, this coating is de signed to cope with stress and wear far longer” Hugo Götsch adds.
Valve disc in a purpose-built mounting during sandblasting
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RESTORATION OF STEEL COMPONENTS The valve discs were subjected to thorough non-destructive testing after the sandblasting process. “All of the relevant cracks and damaged areas were ground down and a special filler applied to key points. Then the anti-corrosive protection layer was renovated in our own sandblasting facility and our paint application chamber. The profile sealing on the edges and surfaces of the valve discs, as well as all sealing elements on the bearing points, were all renovated” stated Markus Klotz. Following the original assembly instructions, the trunnions were mounted to the valve discs with thermically pretensioned bolts. Correct orientation of the trunnions to the valve disc was analysed in 3D again, set and verified. After sandblasting, as with the valve discs, the halves of the housings were also subjected to non-destructive testing – and all significant cracks were ground away. The existing stopDN600 trunnions after the surfaces have been coated with tungsten carbide
photo credits: Geppert
was around 1.50 metres deep. Fortunately, however, the weather was good.” Under these conditions it was still possible to use a mobile crane to load the components onto AWD articulated vehicles that drove down the toboggan run to Kühtai, cleared of snow for this special purpose, and the along the Sellraintal valley to Geppert’s factory in the town of Hall.
Milling on one side of the housing
May 2022
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06.05.2022 14:22:56
