ANALYSES OF WATER-WALL TUBE FAILURE FOR A HIGH-PRESSURE DRUM BOILER

The microstructure,crack mode,morphology of the brittle fracture and scale of the damaged water-wall in a high-pressure drum boiler were studied.The composition of the corrosion product was investigated by using X-ray diffraction,scanning microscopy(SEM) and electric energy spectrum as well as chemical analysis.It is believed that the damage of the tubes was caused by hydrogen damage.The superfluous non-captive hydroxyl in boiler water which greatly concentrated under scales and deposits of the tubes due to the bad blowdown system and condenser leakage was the root cause for the damage.Theoretical analysis and investigation on the boiler actual operation and the cycle chemistry supervision confirmed that the main reason of the waterwall tube failure was caustic corrosion.Some improvement measures were put forward.