TransAlta owns and operates the Cascade Hydroelectric Development, located within Banff National Park in Alberta, Canada. The facility was originally constructed in 1942 and has since undergone numerous upgrades. Some of the original infrastructure still in use includes a 117 m segment of riveted steel penstock constructed on a 30-degree slope, buried 2.4 m below the surface.

In 2019, Klohn Crippen Berger (KCB) performed an inspection of the penstock as part of normal dam safety operations. During the inspection, KCB observed the progression of generalized corrosion and advanced pitting in the original 1942 penstock segment. Pipe thickness measurements were made, and a transient pressure analysis was performed which found the structural capacity of the penstock steel to be marginal. Remediation was recommended to be completed prior to 2025 for continued operation.

In 2021, TransAlta commissioned KCB to conduct an options assessment for penstock remediation. After an initial evaluation, KCB considered four remediation methods: internal recoating, internal Carbon Fiber Reinforced Polymer (CFRP) strengthening, replacement of the penstock segment, and decommissioning.
Following a detailed assessment, CFRP lining was selected as the preferred solution to extend the penstock’s lifespan. While CFRP is used in other industries, its application in hydroelectric facilities remains relatively uncommon. This method provides both corrosion protection and structural reinforcement when applied to the interior of steel pipes.

Additionally, the steep grade of the Cascade penstock posed constructability challenges. To address this, a stair system with a trolley and hoist was installed inside the penstock, allowing workers to safely apply the CFRP lining. The successful application of CFRP Lining in the Cascade Penstock demonstrates it’s potential solution for gaining municipal and civil infrastructure, setting a precedent for future pipeline and penstock rehabilitation.

Employing high angle rope access methods, ultrasonic thickness measurements were taken at multiple locations inside the penstock to determine the remaining steel thickness. Based on the amount of corrosion observed, the capacity of the steel penstock was assessed according to the allowable stresses defined by the ASME 1943 Boiler and Pressure Vessel Code.

KCB conducted a transient analysis using modelling software to determine the pressures experienced in the penstock during turbine-generator load rejection. The analysis revealed that the penstock was under capacity. To address this issue, KCB evaluated several options to bring the penstock back into compliance.

After careful consideration of quality and cost, KCB determined that the best option was to apply CFRP lining. Subsequently, KCB developed the technical specifications for a request for proposal (RFP) to potential contractors with experience in CFRP application.

One challenge encountered during the preparation of the RFP was the lack of a design standard for CFRP application to steel penstocks. KCB decided to use AWWA Standard C305, a design standard for the use of CFRP to repair prestressed concrete cylinder pipe. This standard was slightly modified and incorporated into the technical specifications. KCB prepared the RFP documents with the approach that the selected specialty contractor would undertake the detailed design of the CFRP repair, with KCB performing quality control on the installation.

Completed in October 2024, the CFRP strengthens the penstock while improving hydraulic efficiency, reducing energy losses during power generation. Using specialized crews and a custom stair system, the upgrade enhances long-term reliability. Now operational, the penstock supplies water to the Francis turbine generator, supporting renewable energy production for Alberta. The upgrade extends the structure’s lifespan and sets a precedent for future hydroelectric facility remediations in Canada.