Comparative assessment of the fracture behaviour of micro-alloyed and API-5L X65 steels in simulated fuel grade ethanol environment

In order to fully realize the benefit of pipeline and automotive materials in fuel ethanol applications, a comprehensive understanding of their fracture behaviour is essential. Very few studies have been undertaken on fracture of materials in stress corrosion environments. This paper presents a comparative assessment of the fracture toughness, tearing modulus and widths of stretch zones for API-5L X65 steel and micro-alloyed steel (MAS). The results show that MAS exhibits a better fracture resistance than API-5L X65 steel in air and in solution. API-5L X65 in solution shows a faster crack extension than MAS-in solution. It is found that Jstr (fracture toughness derived from stretch zone geometry) obtained for the two steels exhibits a similar trend with Ji (initiation fracture toughness) which is obtained at the departure of the blunting line on their J-R curves and thus suitable for representing the initiation toughness of the two steels in solution. In general, fuel ethanol reduces fracture resistance in X65 and micro-alloyed steels.