A polyethylene-coated steel pipe that had been buried for 51 years was examined to evaluate the deterioration behavior of the polyethylene coating in a buried environment. The investigation revealed that various physical properties and the corrosion protection performance of the polyethylene coating had declined over time. It was found that even in a buried environment, polyethylene undergoes oxidative degradation starting from its surface. This oxidative deterioration can be mitigated by incorporating antioxidants into the material. Therefore, with proper oxidation prevention measures applied to polyethylene coatings, effective corrosion protection can potentially be maintained for over 50 years.

This study investigates the corrosion resistance of stainless steel used in oil and gas wells exposed to corrosive gases such as CO₂ and H₂S. It focuses on the enhancement of corrosion resistance by adding molybdenum （Mo） to 13％Cr steel. The research examines how Mo influences the formation of passive films in HS^－ environments. The effects of Mo alloying vary depending on the presence of HS^－, impacting both the inner oxide layer and the outer sulfide layer, which exhibit p-type semiconductor properties.