Corrosion Bchavior of Carbon Steel in High Temperature and High Pressure Formic Acid Enviornment

High temperature and high pressure autoclave was used to simulate the service environment of oil well pipe.The corrosion behavior of 20 steel in different contens of formic acid was investigated through corrosion weight loss testing.The morphology of corrosion scales were characterized by SEM.The results showed that the corrosion rate of carbon steel decreased first and then increased with the increase of the concentration of formic acid.At lower formic acid concentration,the dissolution of Fe and the deposition of Fe,Ca and Mg were restricted,the corrosion was weak.With the increase of formic acid concentration,there was apparent difference of corrosion in different areas.The corrosion degrees of matrix corresponded with the places covered by different deposition layers.The corrosion was weak in the places covered by the deposition of Ca and Mg.Conversely,in the places without enough deposition of Ca and Mg,the environment mediums can pass through the covered layer and contact with the matrix,as a result,the corrosion of matrix was promoted.