A New Method for the Protection of Metals Against Pitting, Tuberculation and General Corrosion

This paper presents a new principle in the field of corrosion for the control of tuberculation and pitting of metals in water-side corrosion. It is termed the dianodic method and employs a dual treatment of molecularly-dehydrated phosphates and chromates over selective pH ranges. Its use in relatively low concentrations gives benefits not obtainable with single treatments such as chromate, phosphate, etc. at considerably higher concentrations. Because it is able to eliminate the typical type of pitting and tuberculation that single chromate and single phosphate treatments cause when used in insufficient concentrations it is believed that this method presents a new approach in the field of corrosion. From the experimental evidence it appears that the two anodic treatments, phosphate and chromate, used together under the conditions of the dianodic method are not acting as two separate treatments but as a new single agency for the elimination of pitting and tuberculation. Pit reductions of 80-90% and more are not unusual to expect from this new method. Quantitative pit data are presented on specially-surfaced steel corrosion specimens accompanied by tuberculation data on the threads of pipe nipples. Plant results in recirculating cooling water systems so far indicate complete accord with the experimental data presented.