What is Corrosion Fatigue?
This type of cracking in boiler metal may occur by two different mechanisms. In the first mechanism, cyclic stresses such as are created by rapid heating and cooling are concentrated at points where corrosion has roughened or pitted the metal surface. This is usually associated with improper corrosion prevention. The second type of corrosion fatigue cracking occures in boilers with properly treated water. In these cases corrosion fatigue is probably a misnomer. These cracks often originate where the metal surfaces are covered by a dense protective oxide film and cracking occurs from the action of applied cyclic stresses. Corrosion fatigue cracks are usually thick, blunt and cross the metal grains. They usually start at internal tube surfaces and are most often circumferential on the tube.
