General Corrosion Behavior of Alloy 800 Steam Generator Tube under Different Water Chemistry Conditions

Through high temperature and high pressure circulating water test and electrochemical test, the uniform corrosion rate and surface oxide film characteristics of alloy 800 tube were studied under the conditions of 300 ℃, 10 MPa, deionized water, 2 mg/L DO (dissolved oxygen) and 2.7 mg/L DH (dissolved hydrogen). The results showed that the uniform corrosion rates of alloy 800 under DO and DH conditions were very low, which were 5.6 μm/a and 1.2 μm/a respectively. The oxide films under these two conditions were both composed of two layers. The inner layer of the oxide film was continuous and dense, while the outer layer was mainly composed of granular oxide. In the normal operation environment (DH working condition), alloy 800 presented more stable electrochemical characteristics and obvious passivation zone; while in the oxygen containing environment (DO=2 mg/L), the open circuit potential increased significantly after 96 h, increased from -0.39 V (vs. SHE) to 0.42 V (vs. SHE). No obvious passivation was observed, but the self-corrosion current density was not increased and the impedance value was much higher, indicating that the alloy surface still had relatively stable oxide film structure.