*Structural Integrity of Materials in Fuel Ethanol Environments DOI: http://dx.doi.org/10.5772/intechopen.86383*

based on crack growth rates determined from N-SSR testing and KISCC values based on a fracture mechanics treatment of the N-SSR test data. In another study [23], the effects of inorganic chloride in ethanolic solutions on the SCC behavior of carbon steels was assessed by varying the inorganic chloride concentrations between 0 and 70 mg/L using additions of sodium chloride (NaCl) to SFGE. The results indicated that both crack density and crack growth rate increased with chloride concentration. Two laboratory testing programs were used to evaluate the SCC behavior of steel in fuel ethanol and butanol [24]. The first part of the program revealed that cracking of API 5L X42 carbon steel compact tension specimens in FGE solutions (client supplied and synthetically prepared) required high K (stress intensity) values to initiate cracks. Highest crack growth rates were observed in SSR tests and in tests conducted in SFGE and under aerated conditions. Fracture mechanics tests and tests involving an actual field sample of FGE resulted in lower crack growth rates.

The second part of the program evaluated ASTM A36 carbon steel for SCC in the reagent grade butanol and anhydrous butanol solutions using SSR testing. The tests showed no evidence of SCC. Likewise, Cao [25] studied the corrosion and stress corrosion cracking of carbon steel in simulated fuel grade ethanol using SSR techniques and accurately controlled fracture mechanics conditions. Goodman and Singh [26] evaluated the influences of chemical composition of ethanol fuel on carbon steel pipelines using SSR testing on carbon steel samples in five FGE environments. SCC was discovered in two of the as-received FGE environments and in FGE environments to which NaCl was added.

Furthermore, substantial information has been gathered from reviews, reports and summaries of studies investigating the compatibility of fuel ethanol with metallic materials. Nevertheless, care must be taken in interpretation of the information [27]. Examples are:


Unfortunately, it is known from field experience that E10 blends can severely corrode aluminum components, leading to catastrophic failure [27, 30]. Also, carbon steel can suffer severe corrosive attack if the fuel contains water [27, 31]. Likewise, brass components in carburetors are known to corrode when exposed to E10. The carburetor manufacturer who reported this, conducted compatibility testing of its products with petrol/ethanol blends and has identified corrosion of metallic components as an issue, requiring replacement of brass components with more resistant, but more expensive, alloys.

Qinetiq reports the Brazilian experience with ethanol blends [27, 32]. According to Stephen [27], in order to make vehicles more durable when employing ethanol blends, various fuel system components require modifications among which are:

a.zinc steel alloy fuel lines changed to cadmium brass;

b.tin and lead coatings (terne plate) of fuel tanks changed to pure tin; and

c. cast iron valve housings changed to iron cobalt alloy (QINETIQ, 2010).

Beavers et al. [33] carried out a recent research that was funded by the Pipeline Research Council, in which methods for prevention of internal SCC in ethanol pipelines were evaluated. The methods assessed include the addition of inhibitors and oxygen scavengers to ethanol and other ways and means of deaeration. On the other hand, Beavers et al. [34] studied the effects of ethanol-gasoline blends, metallurgical variables, inhibitors and dissolved oxygen on the stress-corrosion cracking of carbon steel in ethanol. Slow strain rate (SSR) and fatigue precracked compact tension (CT) tests were employed to characterize the influence of environmental and metallurgical variables on SCC of carbon steel. Metallurgical factors, including steel grade within a range of pipeline grades, welds, and heat-affected zone, do not seem to have a noteworthy effect on the degree or frequency of SCC. In terms of environmental factors, it was observed that SCC of carbon steel does not take place even in a completely aerated state, if the ethanol-gasoline blends contain below approximately 15 vol.% ethanol; susceptibility to SCC and crack growth rate are greater in 50 vol.% ethanol gasoline blend (E-50) than in either lower or higher ethanol concentration blends; oxygen scavenging can be an effective method to inhibit SCC; water content exceeding 4.5 wt.% prevents SCC in ethanol; and fatigue precracked CT tests display comparable inclinations to SCC susceptibility as SSR tests.

Maldonado and Kane [35] studied the stress corrosion cracking of carbon steel in fuel ethanol service and postulated that the hygroscopic nature of ethanol is an important aspect with potential relevance to its corrosivity. Also, ethanol possesses high potential for oxygen solubility; therefore, the availability of oxygen for involvement in the corrosion reaction is anticipated to be largely greater.

The authors in [36] presented an evaluation of fatigue crack propagation in three steels namely; A36, X52 and X70 steels in a SFGE. By using a fracture mechanics approach to determine crack propagation rates, all the three materials were found to be prone to enhanced fatigue damage in fuel-grade ethanol environments. **Figure 5** shows a macroscopic view of the fracture surface of X52 steel after testing in SFGE. A model for determining crack growth rates in ethanol fuel was further proposed by the authors.

A recent study [37] investigated the corrosion of martensitic stainless steel in ethanol-containing gasoline mixture as a function of water, chloride and acetic acid concentrations. The results obtained showed that, water and chloride ions (Cl<sup>−</sup>) are the primary corrosion causing factors in EtOH/gasoline mixtures; critical water

**Figure 5.** *Macroscopic view of X52 fracture surface after testing in SFGE [36].*

content depends on EtOH/gasoline-ratio; pitting corrosion occurred at tremendously low chloride concentrations; increasing chloride concentration enhanced pit propagation, with slight influence on pit densities and higher concentrations of acetic acid lead to a greater attacked area, with negligible impact on the depth of pit propagation.

Another study [38] investigated the influence and role of minor constituents (organic acids, water and chloride) of fuel grade ethanol on corrosion behavior of carbon steel using X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES) and electrochemical experiments. The results showed that iron (II) acetate is generated on oxide film due to its high solubility in FGE environments. Chloride stimulated anodic dissolution at those sites where iron (II) acetate occurred.

Also, in 2016, Rangel et al. [39] carried out a study on the SCC susceptibility of API X-80 pipeline steel in SFGE. Water contents of 0, 1, 5, 10 and 20 vol.% and chloride content of 0, 10 and 32 g/L were investigated. Results have shown that X-80 carbon steel in the as-received condition was susceptible only when 5% water and 10 g/L NaCl were present. Heat treatments suppressed this susceptibility. Conditions that increased the corrosion rate also increased the SCC susceptibility, which, together with metallographic observations and noise in current measurements, indicated that SCC in this environment is caused by a film rupture, dissolution mechanism.

Recently, an investigation on the fracture behavior of micro-alloyed steel and API-5L X65 steel in simulated fuel ethanol environment was carried out [40]. Micro-alloyed steel was found to exhibit better fracture resistance than API-5L X65 steel in air and in solution. API-5L X65 in solution showed faster crack extension than MAS-in solution. It was also observed that Jstr (fracture toughness derived from stretch zone geometry) obtained for the two steels shows a similar trend with Ji (initiation fracture toughness) which is found at the parting of the blunting line on their J-R curves and as a result appropriate for signifying the initiation toughness of the two steels in solution. On the whole, fuel ethanol decreases fracture resistance in X65 and micro-alloyed steels (**Figure 6**).

All of the findings point to the fact that SCC of metals do occur in FGE environment, whether simulated or field FGE due to several factors which have been mentioned. Most of the SCC tests were carried out using SSR techniques to assess the fracture toughness of the materials in fuel ethanol environment.

Ethanol fuels have gradually developed into a remarkable alternate energy source. Ethanol-based biofuel can be used to power engines and run cars, hence it is now the main alternative to automotive fossil fuels. The combination of gasoline

**Figure 6.** *Fracture surface of micro-alloyed steel and API-5L X65 steel after J tests in E20 SFGE [40].*

with ethanol results into the fuel currently called "**Gasohol**" [4]. Despite the documented cases of corrosion and stress-corrosion failures in fuel ethanol, corrosion rates are typically low and recommendations regarding compatible materials are currently in literature [7, 40, 41]. These materials include carbon steels; microalloyed steel; unplated steel; stainless steel; black iron; bronze; polypropylene; Teflon; neoprene rubber; thermoplastic piping; thermoset reinforced fiberglass; nitrile and viton among many others. Hence, ethanol fuel is still the best possible alternative to fossil fuels.

Most of the gasoline sold in the United States contain some percentages of ethanol.
