Inspecting for Corrosion Fatigue

Power boiler startup and shutdown cycling and proper water chemistry are paramount in extending the life and reliability of the unit. Loss of control of either of these processes can cause cracking of the protective magnetite scale on the inside surface of the boiler tube so that the unprotected surfaces create corrosion initiation sites. Damage to, or failure of, a metal due to corrosion combined with fluctuating fatigue stresses - also know as corrosion fatigue - can then ensue. The bulk of corrosion fatigue failures are usually 'pinhole' in nature, however some have been catastrophic, with injury to personnel. The recent catastrophic failures worldwide have prompted a second look at the inspection tools and methods for mitigating corrosion fatigue.