STRESS CORROSION BEHAVIORS OF E690 HIGH-STRENGTH STEEL IN SO2-POLLUTED MARINE ATMOSPHERE

Abstract

With the development of industry, the atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO2, and has been changed to coastal-industrial atmosphere with the coexistence of SO2 and Cl-. The corrosion and stress corrosion cracking (SCC) behavior and mechanism of steel in this environment is different from that in the coastal atmosphere containing only Cl- or the industrial atmosphere containing only SO2. Previous study have indicated that SO2 in the marine atmosphere can greatly promote the stress corrosion cracking of high-strength steel due to acidification of thin electrolyte layer and reproduction of H+ through FeSO4. E690 steel, as a newly-developed high strength steel, is very promising to be widely used in offshore platform in the near future for its excellent performance. However, there is few research about its SCC behavfor in marine atmosphere, especially in SO2-polluted atmosphere. Therefore, it's of great importance to investigate the SCC behavior and mechanism of E690 steel in this environment. In this work, U-bend specimen corrosion test under dry/wet cyclic condition, electrochemical measurements, crack morphology observation and rust layer analysis, were conducted to investigate the effect of SO2 on SCC behavior of E690 steel in simulated SO2-polluted marine atmosphere. The results indicated that E690 steel has a high SCC susceptibility in SO2-polluted marine atmosphere with a combined mechanism of anodic dissolution (AD) and hydrogen embrittlement (HE). SO2 in the atmosphere can facilitate the densification of inner rust layer by promoting the formation of alpha-FeOOH and enrichment of Ni and Cr in the inner rust layer, leading to the concentration of Cl- under the rust layer, which may result in the initiation and propagation of SCC cracks significantly and therefore enhance the SCC susceptibility.