**1. Introduction**

There is often a great deal of corrosion data on a number of engineered materials. However, much of the available data is clustered in a limited number of environments, full immersion environments in particular. The report of the National Research Council in the United States (US) [1] revealed that the limited number of environments for corrosion research has resulted in inability to create a meaningful national database of corrosion data useful to industry, government and academia. Aside from the issue of full immersion, atmospheric and alternate immersion aqueous environments, there are also completely different environments such as non-aqueous and high-temperature environments. Ethanol is an example of nonaqueous environments for which a better ability to predict its influence on various engineering materials is paramount due to its planned widespread use.

One of the key drivers for the development of biofuels globally is the concern about universal climate change, which is mainly instigated by combustion of fossil fuels. Considerable scientific evidence abounds indicating greenhouse gas (GHG) emissions as the reason for accelerating global warming. Biofuels are not only renewable and viable energy sources but are toxic-free and so more environmentally friendly than conventional petroleum-based fuels [2, 3]. Biofuels are also biodegradable and therefore their inadvertent spillage is of no significant environmental hazard [2–4]. While biodiesel and PPO are appropriate for diesel engines,


#### **Table 1.**

*Parameters of fuel ethanol in comparison with petrol [6].*

fuel ethanol can replace petrol [5–7]. The properties of fuel ethanol are shown in **Table 1** and compared with the properties of fossil petrol.

The anti-knocking property of the fuel is influenced by the octane number while its energy yield is about one third lower than petrol. Ethanol, also known as ethyl alcohol (CH3CH2OH) is a volatile, flammable, colorless liquid obtained from some energy crop that comprises high quantities of sugar or substance that can be converted into sugar like starch or cellulose from grains [6]. In the US the most common source is from corn and grain. In Brazil, it is sourced from sugarcane [8].

However, ethanol can also be produced naturally (fermented) from any carbohydrate source, such as wheat, cane, beet and fruits like grapes and apples [8]. While grain and synthetic alcohols are technically the same (the molecule is identical), there are differences in the amounts of contaminants (butanol, acetone, methanol, organic acids) in each. According to Paul and Kemnitz [9], for ethanol to be used as fuel, water must be removed. If fuel ethanol is vended with zero water content, it would be referred to as anhydrous ethanol. Typically, denatured alcohol holds about 1% water besides additional constituents. Fuel ethanol with <0.5% water is considered "anhydrous ethanol" [8]. Ethanol with higher water content is usually referred to as "hydrated ethanol". Such hydrated ethanol is uncommon in the US but has been used as a fuel in Brazil.

During the past 8 years, a substantial testing effort on the structural integrity of metallic and non-metallic materials in fuel ethanol has been undertaken by various organizations. Though SCC has not been extensive, it has caused several failures in a number of user facilities. Various factors have been associated with ethanol SCC of carbon steels which include: conditions that promote crack initiation and growth, dissolved oxygen concentration levels, chloride concentration, corrosion potential, water content, and the chemical species of the ethanol itself.

There have been a substantial number of notched slow-strain rate (N-SSR) tests conducted with the aim of studying stress corrosion crack initiation (SCCI) and propagation mechanisms in fuel ethanol [10]. It is worth noting that significant concerns currently exist regarding the SCC behavior of pipeline steels as well as terminal facilities used to handle fuel ethanol.
