Effects of hydrazine and pH on the corrosion of copper-alloy materials in AVT environments with oxygen

The impact of pH and hydrazine on release rates of CDA-706 (Cu/Ni:90/10) and CDA-443-ADM (admiralty brass) was studied at typical plant conditions. Data from these tests could be used to approximate the extent of corrosion transport. Tests on CDA-706 were performed at 274 and 3750F. Tests on CDA-443-ADM were conducted at 1930F. The CDA-706 tests indicated that release rates increased with temperature and decreased with pH under the test conditions studied. The CDA-443-ADM tests displayed a parabolic shaped release rate curve with a minimum at about pH 9.05. A comparison between the two oxygen test values revealed that the higher oxygen tests resulted in the higher release rates for both of the feedwater materials. Likewise, test conditions with less than stoichiometric hydrazine values resulted in higher release rates as compared to test points with excess hydrazine. Due to the high release rates form both CDA-706 and CDA-443-ADM, these feedwater materials are not recommended for future use in feedwater heaters when there is concern for corrosion product transport. 25 figures, 10 tables