The Study Of Corrosion Behavior Of Pipe Line Steel In Concrete/Soil Environment

Pipe line steel is widely used in transportation pipe of oil and gas, oil and gas well, gas storage well and other underground constructions. The corrosion of pipe line steel in soil may lead to security risks. Concrete is coated onto some special pipe line construction such as gas storage well to prevent corrosion. Serious corrosion will occur on the outer wall of the pipe line when protecting concrete is destroyed for shrinkage or expansion of the pipe line steel.System of study of corrosion in simulated cement accident was established which was divided into five zones, water-saturated soil zone, crack cement zone, soil and cement mixing zone, regularly wet soil zone and intact cement zone. Results show that corrosion occurs in the soil zones while the samples aren't corroded in the cement zones. The corrosion in the water-saturated soil zone is accelerated as the oxygen concentration cell between the two soil zones, leading to the more serious corrosion in the water-saturated soil zone.The corrosion behavior of pipe line steel in typical soil environment was studied including field and lab exposing study. A large amount of corrosion data including physical and chemical properties of nine kinds of soil, corrosion rate of pipe line steel, corrosion image and the composition of the corrosion products was acquired after 1 year exposing experiment. The corrosion behavior of G30 and G27 steel was studied by the exposing experiment in lab. The results show that the corrosion process is controlled by activation in the early stage of the exposure. With the extension of exposure time the corrosion process gets controlled by diffusion.Chloride is an important cause of metal corrosion in concrete environment. System of study on the effect of chloride ion penetration on the early corrosion process of the steel in concrete was designed. Results show that the potential distribution of the wire beam electrode can reflect the position of the chloride ion in concrete. With the chloride ions in concrete continuing to penetrate, the negative moving of the potential of the wire beam electrode was observed.