Investigation of repeated penstock weld ruptures – Case study

Abstract

In the spring of 2016, a weld ruptured in one of four penstocks at our largest hydroelectric facility. The rupture was repaired; however two subsequent weld failures occurred in the same penstock and in the vicinity of the original rupture over the next year and a half. Each of the three weld failures resulted in progressively extensive repairs and lengthy outages between May 2016 and November 2017. Multiple penstock inspections were completed during this time period and ultimately a highly detailed investigation resulted, including destructive and non-destructive testing, interior laser scanning and strain gauge monitoring. It was determined that a combination of factors was attributed to the weld failures including design, construction and operational components. Given these penstocks were subject to the same design, construction and operational elements, there was concern regarding their condition and an in-depth investigation program was developed and implemented to ensure reliable service.