Abstract
This paper details tasks and results of a major study to characterize impact of selected metallurgical processing and fabrication variables on ethanol stress corrosion cracking (ethanol SCC) of new pipeline steels. One of the primary goals was also to develop a better understanding of conditions that promote (or mitigate) susceptibility to ethanol SCC in fuel grade ethanol (FGE). The study also included activities to support better monitoring and control, and develop data / insights to generate industry-recognized standards and guidelines to reduce occurrence of ethanol SCC. Key findings of this work included the influence of coatings, metallic platings, and galvanic coupling to enhance resistance to ethanol SCC; conversely, the role of residual stresses in pipelines resulting from fabrication and field joining superimposed with stresses from maximum allowable working pressure was also evaluated. Ethanol SCC tests with cyclic SSR following plastic strain (simulating pipe field bending) showed precursors of SSC (i.e. ductility loss). Methods for monitoring dissolved oxygen (DO) in ethanolic solutions were found to be qualitative at best and corrosion monitoring techniques were not adequate for monitoring corrosion and SCC in FGE, underscoring that there is still a need to develop appropriate monitoring techniques for field use in FGE. Supported in part by this program, an industry accepted test method for ethanol SCC was standardized as NACE TM0111 and updated guidelines for mitigation of ethanol SCC of pipelines was developed for inclusion into API 939E.
