Investigation Into the Formation Mechanisms of Soluble Copper Ions in Oil: Reconsidering the Impact of Corrosive Sulfides and Acids

Soluble copper ions in oil pose a significant filtration challenge, potentially exceeding the threat from suspended copper particulates. However, past research has predominantly focused on the impact of metal particles on insulating oil performance, largely overlooking soluble copper ion formation mechanisms and their adverse effects on insulating oil degradation. This manuscript presents an experimental investigation into the formation mechanism of soluble copper ions in oil considering the influence of corrosive sulfide (notably DBDS) and acids (oleic acid and formic acid). Our findings reveal that oleic acid can react with copper to form copper oleate, which has a high solubility and excellent diffusibility in oil. DBDS and formic acid corrosion products exhibit low oil solubility, precipitating as particles or growing on the surfaces. A synergy between DBDS and acids was observed in the copper corrosion process, as evidenced by the sulfur content change in the corrosion products. The simultaneous addition of both acids peaks surface sulfides proportion, but formic acid surprisingly impedes soluble copper formation. This article contributes to a better understanding of the formation mechanisms of soluble copper in the corrosion process within oil, as well as identifying the decisive factors influencing the generation of soluble copper.