Reheater Tube Failure
Reasons for failure of (reheater) tubes
Failure analysis of a reheater tube showed that the failure was caused by overheating and wall thinning. Finite element modeling, dimensional measurements, and microscopic examinations were performed to investigate the root cause of the failure. Wall thinning is due to excessive coal ash corrosion, and overheating, due to scale buildup on the tube were measured, and estimations, the average corrosion and scale growth rates, were made. The combination of excessive scale formation on the inner tube surfaces and wall thinning due to coal ash corrosion on the outer tube surfaces combined to cause the failure of the reheater tube.
Failure Mechanisms / How do you prevent this?
There are many different types of boiler tube failure mechanisms, which can be sorted into six general categories:
Stress rupture (short term overheating, high temperature creep, dissimilar metal welds)
Water side corrosion (caustic corrosion, hydrogen damage, pitting, stress corrosion cracking)
Fire side corrosion (low temperature, waterwall, ash)
Erosion (fly ash, falling slag, soot blower, coal particle)
Fatigue (vibration, thermal expansion)
Lack of quality control (damage during chemical cleaning, poor water chemistry control, material defects, and welding defects)