Comparison and Evaluation between the Rapid Evaluation Test and the Field Evaluation for Assessing the Pitting Corrosion Resistance of Copper Tubes

Abstract

Residual carbon on the inner surface of copper tubes is one of the causes of Type I” pitting corrosion, however there are few clear methods for its evaluation. In a previous report, it was reported that a test in which copper tubes were filled with a mixture of H₂O₂, BTA and corrosive anions for one hour enabled the pitting corrosion resistance of copper tubes to be evaluated in a short time (rapid evaluation test). In order to evaluate the correlation between the test’s results and behavior in an actual environment, a three–month water flow test was conducted on copper pipes that had been evaluated in a rapid evaluation test. Rapid evaluation tests assessed samples with residual carbon amounts of 1.1 mg/m² as being in the safe range and above 1.9 mg/m² as being in the critical range. The results were in good agreement with previous reports that pitting corrosion is likely to occur when the residual carbon content is above 2 mg/m². No pitting was observed in samples assessed as safe in field tests, while pitting corrosion was observed in some samples assessed as critical. Agreement between the results of the rapid evaluation test and the field test was observed, and it is expected that the method can be effectively applied in actual environments.