Compact Coupling for a Confined Space
STRAUB solution saves major tunneling expense
Environmentally friendly, sustainable and renewable, hydropower ranks as one of the most likely sources of electricity in our future. The Klösterle Power Station in Eastern Austria uses a 1,063-foot (324 m) elevation difference between the two communities of Stuben and Danöfen to move water to a power plant that produces more than 60 gigawatt hours of power annually for the region. The water moves downhill through a cast iron pipeline that passes through a narrow tunnel.
Continuous shifts in the bedrock along the pipeline required flexible pipe connections in the original design. This movement increasingly resulted in axial misalignment, angular deflection and changes in axial length at the pipe joints. Powerplant operator Vorarlberger Kraftwerke commissioned local consultants to measure the movements and design a solution to the shifting bedrock that threatened the pipeline.
Confined Space in the Tunnel
The engineers proposed components that included flanged compensators and dual-gasket couplings to manage the shifts in the pipes. However, the installation zone was more than 656 feet (200m) along a very narrow passageway in the tunnel. Two workers would have to manually walk the components into the tunnel. The weight of each component could therefore not exceed 110 pounds (50kg).
The couplings, however, were heavy products that could not be dismantled. It appeared that the tunnel would have to be enlarged and the pipelines moved. Because of the extensive pricetag and the long timeline for widening the tunnel, Vorarlberger Kraftwerke sought a better solution and contacted STRAUB.
The STRAUB technical team developed a prototype coupling featuring welded-on lugs. In addition, STRAUB tested the installation of the pipe coupling in a confined space similar to the tunnel. The STRAUB-Open-Flex 4H pipe coupling met the installation criteria and also passed a pressure test. The 65.7-inch (1,670mm) coupling can accommodate changes in length up to 7.9 inches (200mm), can compensate for up to 0.6 inches (15mm) of expansion and contraction, and can be dismantled into two halves.
Since the weight of the individual components is under 110 pounds (50kg), the components could be easily be moved into the tunnel by two workers. STRAUB’s two-piece housing meant the coupling could be installed without needing to move the pipes or expand the tunnel.
Demonstration and Installation
STRAUB technicians installed the first STRAUB Open-Flex coupling and providing continuing support during the project. Three workers installed the couplings – one on each side of the pipe and a third on top of it. All three pipes in the critical area were supported between the spigot and bell sockets and then cut twice, producing a gap between the pipe ends of approximately 1.18 inches (30mm). The cut surfaces were sealed with corrosion protection.
Next, a 7.9-inch-wide (200mm) steel strip insert was placed around the pipe and the sealing sleeve placed on top of it. Then, workers placed the two halves of the casing over the sleeve from the top and bottom, and tightened the coupling with a torque wrench. All six pipe couplings were installed within one day, allowing the pressure tests on the installed couplings to be carried out without delay.
To monitor movements of the pipe in the future, workers marked the exact position of the couplings by tracing around the perimeter of the pipe. By continually monitoring the markings, engineers can determine when movement within the coupling has reached
By continually monitoring the markings, engineers can determine when the movement within the coupling has reached 0.6 inches (15mm). At that point, the locking bolts are unscrewed and the sealing sleeve adjusted to protect the integrity of the connection.
This simple, elegant STRAUB solution saved the project owner and contractor extensive time and money, and helped to keep the water flowing at the Klösterle Power Station.