Corrosion under insulation in-situ testing in marine environment

Hillier, Alan (2023) Corrosion under insulation in-situ testing in marine environment. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Oil and gas pipelines in marine or coastal environments experience significant corrosion when moisture and chloride penetrate surface protections. There is lack of in-situ work studying corrosion under insulation (CUI) and corrosion under coating, especially in marine atmosphere. As well, monitoring and inspection of assets under corrosion attack is a concern, as it can spread insidiously in out of sight areas. Real time monitoring of pipelines and other assets is best to get information quickly, especially in difficult to reach areas. Electrochemical potential noise (EPN) is one proposed method to investigate CUI using simple equipment and should be further investigated in determining quantitative corrosion results. This thesis investigates corrosion and pitting from pipelines which were coated, uncoated, insulated, and not, in a marine harsh environment field experiment. The surface morphology, and mechanisms of corrosion were also studied. Thirty-six A333 low temperature carbon steel pipelines were placed at Argentia, NL, Canada, an extremely corrosive environment (C5) near shoreline. High humidity, winds, and sea-spray are present throughout most of the year. Corrosion rate was assessed using mass loss and optical inspections were used for pit depth. X-ray diffraction and scanning electron microscope were used to determine corrosion products and surface morphology. Corrosion near the ends of the pipe were most severe, perhaps due to crevice corrosion, and ingress of moisture and chloride. Insulated uncoated pipes showed deepest pits, therefore when pipes are insulated, anti-corrosion protective coating should be applied. Corrosion and pitting rates were lowest in insulated and coated pipes. Real time monitoring using EPN was explored, varying electrode size, temperature, and electrolytes. EPN was recorded using Keithly digital multimeter controlled by LabVIEW software. Potential was investigated using time and frequency domain methods to determine its usefulness in monitoring corrosion. In this research the best way to relate potential to mass loss and corrosion type occurred using time-frequency domain power spectral density from raw potential noise generated from electrodes. This in-situ testing enhanced the understanding of corrosion mechanisms and pitting in the environment. Important coating and insulation time to failure was recorded, which provides insights for oil and gas operations regarding inspection, maintenance, and design life. EPN tests proved a simple method and equipment can be used for in-situ corrosion detection, which can help ensure safety and asset integrity.

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