Evaluation of Stress Corrosion Cracking Susceptibility of the API 5L X70 Steel in Corn and Sugar Cane Ethanol Environments

Abstract

The interest in renewable and cleaner fuels has stimulated ethanol production in the last decades. Some of the drivers for that ever increasing production were the Brazilian Alcohol Program, Kyoto Protocol and the replacement in USA of the octane booster MBTE (methyl-tert-buthyl ether) for ethanol. The world’s largest producers of ethanol are The United States of America and Brazil, where the main sources are corn and sugar cane, respectively. Production flow via pipeline is the safest and most cost effective way to connect the producers, usually spread across the country, to the distribution terminals. However, in USA there are evidences that ethanol may have caused stress corrosion cracking (SCC) in pipelines and also in storage tanks. Controversially, in Brazil ethanol has been transported and stored since the 1970’s without any indication of SCC. The aim of this work is to evaluate the susceptibility of the steel API 5L X70 [1] to SCC in different ethanol (corn and sugar cane) using slow strain rate testing (SSRT). These tests were carried out on notched specimens according to NACE TM 0111 [2]. The SSRT results carried out in corn ethanol have shown a considerable reduction of plastic elongation and a mixed fracture micromechanism of quasi-cleavage and intergranular facets clearly indicating a susceptibility of the API 5L X70 steel to SCC. The SSRT also demonstrated that the carbon steel tested here is completely immune to SCC in sugar cane ethanol.

Stress corrosion cracking of microalloyed pipeline steel in biofuels E-10 and E-85

“…However, in the present study, the X-70 steel did not show evidence that indicates the presence of SCC under the employed conditions. These results are consistent with those reported by Breitenbach et al, which suggests that the SCC phenomenon is attributed to the type of ethanol (cane) used in the gasohol blend [4,6]. The lack of susceptibility to SCC can result from the fact that the rate of passivation of the steel in both types of gasohol is too high.…”

“…The results showed behaviours that are consistent with those obtained by Rangel et al [38], who studied the susceptibility to SCC of an API X-80 steel using ethanol as a corrosive medium, concluding that the steel is susceptible to SCC only when FGE has 5% water + 10 mg/L sodium chloride. On the other hand, Breitenbach et al evaluated the susceptibility of an API 5L-X-70 steel to SCC in corn and sugarcane ethanol [6]. They observed that the corn ethanol medium generated SCC, while sugarcane ethanol did not.…”

“…Some researchers have claimed that the use of ethanol induces the development of SCC [2,5,6], while others have reported the absence of this phenomenon in microalloyed steels [4,6,7]. Research conducted in the U.S.A. reported the presence of SCC in carbon steels in contact with corn FGE, which resulted in extensive research conducted in this regard, where most agreed that the main cause of SCC is the interaction between the steel microstructure, oxygen ions and the chloride and other ions present in ethanol [5,6]. On the other hand, Brazil has been transporting and storing cane ethanol since the 1970s without reports of SCC [4,6].…”

“…Some researchers have claimed that the use of ethanol induces the development of SCC [2,5,6], while others have reported the absence of this phenomenon in microalloyed steels [4,6,7]. Research conducted in the U.S.A. reported the presence of SCC in carbon steels in contact with corn FGE, which resulted in extensive research conducted in this regard, where most agreed that the main cause of SCC is the interaction between the steel microstructure, oxygen ions and the chloride and other ions present in ethanol [5, 6]. On the other hand, Brazil has been transporting and storing cane ethanol since the 1970s without reports of SCC [4, 6].…”

Ethanolic Media Effect on the Susceptibility to Stress Corrosion Cracking in an X-70 Microalloyed Steel with Different Aging Treatments

“…There are studies that have demonstrated the presence of the SCC phenomenon in certain microalloyed steel compositions in different bio-ethanol media, which is attributed the susceptibility of the material to the source of bio-ethanol; corn bio-ethanol is considered a factor that increases susceptibility and cane bio-ethanol shows immunity to SCC [32]. Many authors agree that two of the main factors in crack initiation caused by SCC are water and Cl- [14,15].…”