Abstract
Ant nest corrosion is one of the local corrosion which occurs in the pipes of air equipments. Because DHP-Cu (Deoxidized High Phosphorous Copper) is generally used as material of those pipes and heat exchangers, ant nest corrosion of DHP-Cu has been mainly studied. According to a few experimental results included in those studies, corrosion rate of DHP-Cu differed from that of OFC (Oxygen Free Copper). In this report, corrosion resistance to ant nest corrosion of two materials was closely investigated. It was found that the corrosion rate of OFC was slower than that of DHP-Cu. The reason for this difference could be explained as follows: electron probe microanalysis on a cross-section of corroded DHP-Cu revealed that P (phosphorus) was oxidized. Since oxidized P, that is, phosphate generates H+(ex. P+4H2O→H2PO4−+6H++5e−), pH in the corroded pore of DHP-Cu easily drops. As is well known, ant nest corrosion evolves around the broken oxide film (cuprous oxide). If pH drops, the dissolution of cuprous oxide will be promoted and then corrosion rate will increase. Based on the mechanism above mentioned, ant nest corrosion rate of OFC is considered to be slower than that of DHP-C because the former's pH is difficult to drop.
