**2.3 Structural integrity of materials in fuel ethanol environments, previous research and current trends**

Investigation of the corrosion and stress corrosion cracking (SCC) mechanism of steel in fuel ethanol is still in the early stages and several countries are considering increasing biofuel production as an approach to secure future energy supplies and mitigate global warming. When these come to the market, the infrastructure will play a key role in ensuring safe, reliable, and efficient distribution of these fuels to the end users [14]. Pipeline is the most effective transportation method in meeting these requirements. Hence, there is dire need of evaluating and predicting the influence of fuel ethanol on various steel grades which can be used for such pipelines.

A most recent study [18], jointly funded by API and Renewable Fuels Association (RFA), using the slow strain rate test method (SSRT), found that SCC of steel can take place in fuel ethanol meeting the ASTM D4806 standard specification (see **Table 2**). From the study, the inhibitor, Octel DC1-11 was discovered to lower the corrosion rate of steel in ethanol but had no effect on SCC. In addition, the team found that in addition to water, the most important factor that caused SCC in fuel ethanol appeared to be dissolved oxygen. When dissolved oxygen was minimized through nitrogen purging, no SCC occurred in the presence of all other species at their maximum levels. But on introducing oxygen, the reverse occurred. Furthermore, corrosion potential was used to monitor the potential for SCC of steel exposed to ethanol. One short coming of the study was that the results obtained are limited to fuel ethanol of ASTM D4806 standard and the study of the effect of stress level on SCC was left out. Hence, parameters for estimating risk of SCC from known defects in the studied environment were not obtained.

Other studies include those of Beavers et al. [19] and Lou et al. [20]. While [19] examined pitting corrosion in simulated fuel grade ethanol (SFGE) solutions on carbon steel, [20] examined the addition of chemical additives to SFGE to provide scavenging of oxygen in solution or inhibition of SCC in fuel grade ethanol (FGE) using slow strain rate (SSR) techniques. The latter study found a dependence of ethanol SCC on electrochemical potential that was consistent with observations from previous API studies (i.e., increased susceptibility to SCC with increasing corrosion potential). Based on this study, three active techniques of non-chemical deaeration were recognized. Altogether, the three methods reduced the corrosion potential below −100 mV Ag/AgCl EtOH and alleviated SCC.

Also, Beavers and Gui [21] summarized the results of research studies involving factors affecting ethanol SCC of carbon steel as water content, level of aeration, aging during storage, blend ratio with gasoline, steel type and welding. In addition, Gui et al. [22] carried out studies on the influence of ethanol composition on SCC susceptibility of carbon steel by evaluating ethanol SCC in field FGE samples and correlating the results in terms of SCC severity to compositional differences in the FGE samples. Carbon steel was found to be susceptible in all FGE samples conducted in two laboratories but with a varied degree of susceptibility in one FGE sample compared with the others.

Furthermore, Venkatesh et al. [10] evaluated the SCC behavior of pipeline steel in multiple ethanol environments. The program used N-SSR testing and field samples of FGE obtained from Brazilian sources. Severity of cracking was assessed


## **Table 2.**

*Quality specifications of fuel ethanol per ASTM D4806 [16].*
