Nickel alloy 625 is widely used in marine applications due to its excellent corrosion resistance when exposed to highly oxidizing and reducing environments. However, nickel alloy 625 has been found to be susceptible to localized corrosion when crevices with a large aspect ratio (depth/gap) are exposed to seawater. In this study, two different electrochemical techniques were used to evaluate the mechanisms of crevice corrosion in nickel alloy 625: potentiostatic polarization of remote crevice assemblies (RCAs) exposed to ASTM artificial ocean water and potentiodynamic polarization curves in simulated critical crevice solutions (CCSs). From the electrochemical response of the RCAs, i.e. current vs. time curves, it was found that crevice corrosion damage under potentiostatic conditions occurred in three stages: Stage (I) CCS development, stage (II) crevice corrosion under IR control, and stage (III) crevice corrosion under diffusion control. It was also found that the CCS formed near the crevice tip and moved toward the crevice mouth. Once the CCS reached a critical distance from the mouth, presumably IR*, the corrosion rate drastically increased and severe damage occurred. During the RCA experiments, light green deposits around the outside edge of the RCA were found. When the crevices were opened after the test, additional corrosion products were found. For short exposure times, dark green and brown corrosion products were found spread out over the etching damage while at longer exposure times, accumulation of dark brown corrosion products were found closer to the crevice mouth. Energy Dispersive Spectroscopy (EDS) analysis showed that the crevice corrosion products formed inside the crevice were rich in Mo, Nb, and O, suggesting the possible formation of Mo and Nb oxides. The crevice corrosion products outside of the crevice were rich in Ni, Cr, Fe, Mo and O. The behavior of 625 in the CCS was characterized using potentiodynamic polarization in concentrated metal salt solutions prepared by dissolving NiCl2∙6H2O, CrCl3∙6H2O, FeCl2∙4H2O, MoCl3, and NbCl5 salts in deionized water at concentrations ranging from 3 to 5 molal. It was found that Mo and Nb content increased the current density of the active peak. The properties of these simulated CCSs were determined using thermodynamic calculations via the OLI Stream Analyzer software. Specifically, OLI software was used to predict the precipitation products and solution pH at 25°C. The predictions were used to compare the polarization data generated with the traditional simulated CSS using HCl base solutions.
Explores new methods for assessing the threat of AC corrosion on buried pipelines. The results from this project will improve indirect inspection methods for assessing the impact of induced AC currents on pipeline corrosion rates and could be used for national and international standards. To accomplish this goal the project has three thrust areas: laboratory studies, industrial test facility benchmarking, and in-service pipeline validation. Previous work in our lab has shown that the magnitude of interfacial capacitance of the corroding metal is a key parameter in determining the AC corrosion rate. As such we will investigate the interfacial capacitance that develops on pipeline steel as a function of corrosion product build-up (scaling) and soil properties such as, resistivity, mineral content, and pH. In addition, we will conduct exploratory studies to determine the susceptibility of pipeline steel to environmental fracture during exposure to AC. Results from these tests will be benchmarked in experiments conducted in industrial pipeline testing facilities at Mears Integrity and Marathon Petroleum. Finally, we will validate the project by collecting indirect inspection data on an in-service pipeline in a transmission line right-of-way owned by Marathon. These data will be used as input to an AC Risk Algorithm to prioritize direct inspection of the pipeline. If permissible, the section of the pipeline identified as being at the greatest risk will be assessed using direct inspection.
The baccalaureate program in Corrosion Engineering at The University of Akron is the first of its kind in the nation. It was formed in response to Federal Government interest and industry need in the area. The idea was first presented in 2006 and the University welcomed its first freshman class in 2010. The degree is a traditional engineering degree based on a math, science and general education courses that support engineering science and engineering design courses; students take courses from five different engineering programs. At its core are classes and laboratories in corrosion electrochemistry, high temperature oxidation, and corrosion engineering management. In addition, the students are exposed to hands-on experience as a corrosion engineer through the co-op program. This curriculum was developed using input from a number of stakeholders in government, industry and academia that wanted students with knowledge in corrosion basics, materials characterization and corrosion prevention and the ability to diagnose failures, guide maintenance and repair as well as perform risk based assessment. In this presentation we will review the method that lead to the current program as well as feedback from co-op experiences including both student and employer perspectives.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.