Restoring aging penstocks

Many steel penstocks of hydroelectric projects built in the early 1900s are showing signs of aging. Engineers and project owners are finding new ways to keep these crucial plant components working into the next century. The issues and methods for rehabilitating existing penstocks differ from the challenges of ddesigning new water conduits. To rehabilitate an existing penstock, one must understand the original design. The original layout and esign of an existing penstock reflects the construction materials, methods, and economics of the time it was built. To efficiently and successfully rehabilitate an existing penstock, planners must understand the limitations of the original design, construction, and material. Hydroelectric project owners can take one of two approaches to penstock rehabilitation: repair or replacement. The repair option includes weld repair and patching of the existing shell or relining the inside of the pipe. Frequently, both repair and replacement are combined to form the optimal solution for a particular penstock. Kleinschmidt Associates, Inc. of Pittsfield, Maine, recently used both the repair and replacement approaches on three penstock rehabilitation projects. These examples demonstrate how different site conditions, design parameters, and owner interests led to various rehabilitation strategies. This article focuses on small (less than 10 MW),more » low- or medium-head plants with steel penstocks.« less