Stress Corrosion Cracking of API 5lX52 in Ethanolic Environment

The human interest on renewable energy it is due environmental preservation. In substitution of Methyl-therbutyl-ether (MTBE), ethanol it is being used as replacement of the oxidant agent in gasoline, because not only increases the fuel octane number and represents the best option for the increasing demand for fossil fuel observed over the last few years. However, one of the most common failures on mild steel found in ethanolic environments is stress corrosion cracking (SCC) and pitting corrosion. Based on the report of American Petroleum Institute (API), the safer way for transporting the blend is by the existing pipeline.

Thus, the aim of the present study is to investigate the effect of water content (0.5%, 5%, 10% ) in E95 blends on the stress corrosion cracking susceptibility of API 5L X-52 steel. In order to assess the steel mechanical and electrochemical response, slow strain rate tests (SSRT) of 1 X 10-6 s-1, coupled with electrochemical noise measurements (ECN) were carried out. In addition, the material response immersed into the various solutions was analyzed by using linear polarization resistance (LPR) measurements and weight loss measurements. Furthermore, fracture surface observations by scanning electron microscopy (SEM) on samples exposed to the various solutions were done. In general, a ductile behavior was observed. However, secondary cracking was only observed for specimens exposed to solution containing up to 2%V water. ECN gave indication of a likely localized corrosion process occurring at low water concentrations, whereas for water content above 2%V, a uniform corrosion process seems more likely to occur. the LPR results indicated that specimens exposed to water content up to 2%V disclosed the lower corrosion rates. Further, the results of weight loss measurements supported the behavior found.