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Corrosion and Stress Corrosion Cracking of Carbon Steel in Simulated Fuel Grade Ethanol
Cao, Liu

2012, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.

Carbon steel is susceptible to stress corrosion cracking (SCC) in fuel grade ethanol. Dissolved oxygen and corrosion potential have been identified as the critical factors. The threat of SCC prevents the use of the cost-efficient pipeline system for long distance transport of ethanol. Simulated fuel grade ethanol (SFGE) was used in the laboratory. Due to the high electrical resistivity of SFGE, adding non-complexing supporting electrolyte is considered to be the most practical method for accurate potential control. TBA-TFB was found to be the best suitable supporting electrolyte in deaerated FGE among the salts that were tested.


Carbon steel exhibits passivity and high corrosion potential in aerated SFGE. Deaerated conditions are of interest so that the effects of high potential on SCC susceptibility can be determined separately from other possible effects of dissolved oxygen. In slow strain rate (SSR) tests, cracking was reproduced at applied potential without oxygen in the deaerated SFGE + TBA-TFB, which indicates that the role of oxygen in ethanol SCC might be a simple oxidizing agent. However, the passivation effect of oxygen is also required to prevent lateral corrosion at crack tip. A potential range for ethanol SCC was determined by SSR tests at different potentials. No experimental evidence was found to support the proposed role of oxygen to react with ethanol to form an aggressive oxidation product.


The presence of chloride causes decreasing corrosion potential and enhanced pitting corrosion. The chloride effect on ethanol SCC was investigated both in aerated SFGE at open circuit and deaerated SFGE at applied anodic potentials over a wide range of chloride concentration. A minimum concentration of chloride is required for SCC of carbon steel, but it is not the controlling factor for crack growth. There is no upper limit of chloride concentration for cracking in aerated SFGE, but a window of chloride concentration in deaerated SFGE at applied potential.


The dissolution based SCC mechanism has been identified for carbon steel in ethanol environment. SSR testing with periodic potentiodynamic scans at different stains and strain rates show that the anodic current difference between plastic and elastic region has a peak in the cracking potential range. The notched SSR testing is more sensitive to ethanol SCC susceptibility, and it generates more consistent results of current evolution. A high R-ratio and low cyclic frequency crack growth rate (CGR) test was intended to mimic the actual loading condition of pipelines in service at accurately-controlled fracture mechanics conditions. The measured CGR at applied potentials matches the cracking susceptible potential region.


An oxygen depletion induced dissolution model and the traditional film rupture induced dissolution model were proposed to explain the mechanism of ethanol SCC. A few models based on oxygen diffusion and consumption were considered in an attempt to explain the differences of the two proposed mechanisms. Complete oxygen depletion is less likely to occur at crack tip.

Gerald Frankel, Dr. (Advisor)
Narasi Sridhar, Dr. (Committee Co-Chair)
Rudolph Buchheit, Dr. (Committee Member)
Glenn Daehn, Dr. (Committee Member)
318 p.

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Cao, L. (2012). Corrosion and Stress Corrosion Cracking of Carbon Steel in Simulated Fuel Grade Ethanol. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Cao, Liu. "Corrosion and Stress Corrosion Cracking of Carbon Steel in Simulated Fuel Grade Ethanol." Electronic Thesis or Dissertation. Ohio State University, 2012. OhioLINK Electronic Theses and Dissertations Center. 25 May 2015.

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Cao, Liu "Corrosion and Stress Corrosion Cracking of Carbon Steel in Simulated Fuel Grade Ethanol." Electronic Thesis or Dissertation. Ohio State University, 2012. https://etd.ohiolink.edu/

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