News & Views, Volume 47 | Metallurgical Lab Case Study: Corrosion Fatigue in WaterWall Tubes Increasingly A Safety Concern as Coal Plants Cycle
By: Ben Ruchte
It is well known that conventional coal-fired utility boilers are cycling more today than they ever have. As these units have shifted to more of an ‘on-call’ demand they experience many more cycles (start-ups and shutdowns, and/or significant load swings) making other damage mechanisms such as fatigue or other related mechanisms a concern.
The most recent short-term energy outlook provided by the U.S. Energy Information Administration (EIA) indicates the share of electricity generation from coal will average 25% in 2019 and 23% in 2020, down from 27% in 2018. While the industry shifts towards new construction of flexible operating units, some of the safety issues that have been prevalent in the past are fading from memory. The inherent risks of aging seam-welded failures and waterwall tube cold-side corrosion fatigue failures are a case in point. It is well known that conventional coal-fired utility boilers are cycling more today than they ever have. As these units have shifted to more of an ‘on-call’ demand they experience many more cycles (start-ups and shutdowns, and/or significant load swings) making other damage mechanisms such as fatigue or other related mechanisms a concern. The following case study highlights this point by investigating a cold-side waterwall failure that experienced Corrosion Fatigue. While this failure did not lead to any injuries, it must be stressed that the potential for injuries is significant if the failure occurs on the cold-side of the tubes (towards the furnace wall).