Influence of S2-Concentration on the Corrosion Resistance of 10# Carbon Steel in Saline Wastewater
GUO Lin1, XU Xiuqing2
1. Xi'an Sunward Aerospace Materials Co., Ltd., Xi'an 710025, China;
2. Tubular Engineering Research Institute of China National Petroleum Corporation, Xi'an 710065, China
Abstract:The corrosion of a refinery heat exchanger, especially a water-phase heat exchanger, is a serious issue. The corrosion perforation and scaling of tubes are the main causes for the heat exchanger failure due to the existence of plenty of S2-, Cl-, Ca2+ and Mg2+ in the corrosion medium. Based on the experience of corrosion of refinery heat exchanger tubes (10# carbon steel) in their operation processes, the corrosion behaviors of 10# carbon steel in saline wastewater with different S2-concentrations are investigated by means of the immersion test and the electrochemical methods. The surface photographs and the compositions of corrosion products are taken and determined by digital camera and X-ray diffraction spectrometer. The experiment results indicate that the uniform corrosion rates of 10# steel decrease gradually with the increase of the S2-concentration in the corrosion medium within the scope of the test. The corrosion degree of 10# carbon steel comes down to a moderate corrosion from a heavy corrosion when the S2-concentration in the medium is higher than 250 mg/L. XRD results show that the main compositions of the corrosion products are Fe3O4, CaCO3 and FeS. Meanwhile, Cl- in the corrosion medium can penetrate the corrosion product to accumulate and produce the pit corrosion on the surface of 10# carbon steel because of the existence of Cl-when the S2-concentration in the medium was less than 100 mg/L. And the pitting corrosion resistance becomes worse with the decrease of the S2-concentration.