Investigation of Corrosion Mechanism of Condenser Tube in a Power Plant

摘要

The composition and mechanical properties of the in-service condenser tube were analyzed, and the morphology of the inside surface and the cross-hatch marks were observed. Results exhibit that the composition and mechanical properties of the in-service tube were comparable to the original tube. The cross-hatch marks made an angle of 45 degree with the tube axis, and appeared mostly at the underside of the tube. After the corrosion product was removed, the bottom of the cross-hatch mark was studied which was characterized by corroded along some special crystal plane. Simulation tests of corrosion fatigue show that under a low applied cyclic stress, some corrosion stripes, similar to the cross-hatch marks, appear on the tube surface in a 3.5% NaCl solution. This result indicates that dislocation movement caused by a low cyclic stress induces the benzotriazole coating broken resulting in the corrosion along some special crystal plane.