The mechanism of Nb electropolishing was studied. In particular, the effects of acid concentration, stirring, temperature and amount of material removed on the surface finish were investigated using electrochemical polarization measurement, galvanostatic and potentiostatic techniques. A current density plateau in the niobium polarization curves, characteristic of mass transport control, was observed. Fluoride ion was shown to be the transport-limited species. Galvanostatic results deviated from a perfect semi infinite linear diffusion model, indicating the effects of diffusion and temperature gradients.
The emergence of multiphysics modeling tools that span molecular interactions, solid-state physics, and materials microstructure through to thermodynamics, fluid mechanics and electrochemical kinetics provides new opportunities for the construction of predictive modeling tools for corrosion science and engineering. One particular field in which models have been actively developed from the atomistic to macroscopic levels includes the problem of the prediction of performance and the molecular design of chemical corrosion inhibitors. Herein we provide a concise review of these historical and contemporary approaches. Afterwards, a general outline for a multiphysics model is presented for the prediction of corrosion inhibitor efficiency (i.e. % reduction in corrosion rate) as a function of environment, material, inhibitor concentration, and the molecular identity of the inhibitor. Applications to experimental design and analysis, lifetime prediction and inhibitor design are then discussed.
Organic corrosion inhibitors can provide an effective means to extend the life of equipment in aggressive environments, decrease the environmental, economic, health and safety risks associated with corrosion failures and enable the use of low cost steels in place of corrosion resistant alloys. To guide the construction of advanced models for the design and optimization of the chemical composition of organic inhibitors, and to develop predictive tools for inhibitor performance as a function of alloy and environment, a multiphysics model has been constructed following Staehle's principles of "domains and microprocesses". The multiphysics framework provides a way for science-based modelling of the various phenomena that impact inhibitor efficiency, including chemical thermodynamics and speciation, oil/water partitioning, effect of the inhibitor on multiphase flow, surface adsorption and self-assembled monolayer formation, and the effect of the inhibitor on cathodic and anodic reaction pathways. The fundamental tools required to solve the resulting modelling from a first-principles perspective are also described. Quantification of uncertainty is significant to the development of lifetime prediction models, due to their application for risk management. We therefore also discuss how uncertainty analysis can be coupled with the first-principles approach laid out in this paper.
Quantum chemistry is a powerful tool for computing the properties of molecules and their interactions with one another in a variety of environments. In this second paper of a two-part series, the technique is applied in this work to calculate fundamental properties of inhibitor molecules important to the overall corrosion inhibitor performance. The study focuses on the issue of oil/water partitioning as quantified by the partition coefficient (log P) and the important issue of inhibitor speciation according to the acid dissociation constant (pKa). pKa and log P values are then calculated from first-principles for a series of imidazole derivatives and integrated into a model for inhibitor availability as a function of the water cut. Applications to lifetime prediction and inhibitor design are then discussed.
Blending hydrogen in the natural gas transmission and distribution systems is an option for hydrogen transportation. Integrity management of the existing infrastructure requires a risk evaluation for the planned hydrogen introduction and the challenge of hydrogen embrittlement needs to be considered. The aim of the current study was to evaluate the effect of blending different percentages of hydrogen in methane on the fatigue crack growth rate (FCGR) of X70 line pipe steel. Microstructures associated with base metal, weld center line (WCL) and heat affected zone (HAZ) of girth welds, as well as WCL and HAZ of SAWL seam weld were studied using compact tension specimens based on fracture mechanics. Hydrogen concentrations of 1, 5 and 10 mole% blended in methane were studied. The data was compared to baseline Paris curves in 100% methane as well as the BS7910 in-air mean curve for steel to quantify the increase in fatigue crack growth rate relative to inert environments. In addition, the data was also compared to the ASME B31 curve for carbon steel in hydrogen, to understand the degree of conservatism associated with the ASME curves for the concentrations of H2 evaluated. An increase in FCGR relative to methane baseline was observed for all the microstructures at all concentrations of hydrogen. However, the increase in FCGR relative to the in-air values varied with ΔK. Of the microstructures studied, the base metal showed the highest susceptibility to hydrogen embrittlement for all the hydrogen blends, followed by the girth weld – HAZ location. These two microstructures also had higher hardness compared to the other three locations. A crack growth assessment was also performed for circumferential and axial flaws utilizing the FCGR generated data coupled with pressure cycling data obtained from pipeline operations.
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.
customersupport@researchsolutions.com
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.