External and Internal Corrosion and Its Control of Natural Gas Pipelines
Date
2019-12
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Abstract
Natural gas pipelines suffer from both external and internal corrosion during their service life, which may result in dramatic consequences. In this research, external corrosion of X52 pipeline steel under direct current (DC) interference was investigated in a simulated soil solution. Corrosion acceleration by DC was quantitatively determined as a function of DC current density. DC was found to shift the cathodic protection (CP) potential to positive and negative directions in the anodic and cathodic zones, respectively, on the pipelines, resulting in either corrosion enhancement or hydrogen evolution at the zones. The effect of DC on properties and performance of fusion bonded epoxy (FBE) coating applied on pipelines was studied. The presence of DC interference facilitates water permeation into the coating due to the altered molecular structure and decreased the coating resistance for corrosion protection. Furthermore, corrosion of X52 pipeline steel under dynamic DC interference was investigated. Dynamic DC further accelerates the steel corrosion compared to static DC at specific DC current densities. It is believed that the alternating current (AC) component included in the pulse DC contributes to the corrosion reaction. With increase in the DC pulse frequency, corrosion rate of the steel decreases. The wave form of the dynamic DC does not obviously affect the steel corrosion. Internal corrosion of X52 pipeline steel was investigated in CO2-containing thin layers of solution, simulating the actual corrosive environment generated in the interior of natural gas pipelines. A mechanistic model was developed to explain the internal corrosion of wet gas pipelines. With the decrease of the solution layer thickness, the corrosion rate of the steel reduces. An elevated temperature accelerates the corrosion reaction kinetics, and generates a compact and homogeneous FeCO3 film at the same time. The presence of acetic acid increases the steel corrosion, while the methanol reduces corrosion rate of the steel. For external corrosion control, a micro/nanostructured ZnO-alkylamine composite coating was developed by electrodeposition and anodization to possess multiple functions. The optimal coating film is superhydrophobic, with the water contact angle up to 158o. The coating possesses a good corrosion resistance and excellent self-cleaning performance and a strong anti-adhesion to pseudomonas aeruginosa bacteria. For internal corrosion control, the inhibition performance of imidazoline (IM) and sodium dodecylbenzenesulphonate (SDBS) inhibitors and their synergism on corrosion of X52 steel in CO2-saturated chloride solutions was investigated. The synergistic effect of the two inhibitors enhances the corrosion inhibition performance, compared to the inhibitors acting independently. The adsorption of both inhibitors on the steel is chemisorption, following the Temkin adsorption isotherm.
Description
Keywords
Pipeline steel, Corrosion, Direct current interference, Pipeline coatings, Corrosion inhibitors
Citation
Qian, S. (2019). External and Internal Corrosion and Its Control of Natural Gas Pipelines (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.