In situ studies with CUI and corrosion under coating is rare, especially for full scale tests in marine harsh environment. A333 low temperature carbon steel is selected for its versatile use in cold environments. This material is not widely studied in marine environment. Therefore, corrosion type, products, and morphology were reported for thirty-six model pipelines (insulated, uninsulated, coated and uncoated) placed at Argentia, NL. Corrosion products were identified using x-ray diffraction (XRD). The detection and semi-quantification of elements on pipe surfaces was performed using energy disruptive spectroscopy (EDS) which was coupled to a scanning electron microscope (SEM). SEM images confirmed the formation of characteristic morphological structures such as sandy crystal (lepidocrocite), cotton ball (goethite), and small grain (akaganeite) structures. The main phase present on insulated, as well as coated pipes was goethite (α-FeOOH) and SEM images confirm that, generally, the surface oxide appeared more compact than pipes with uninsulated or uncoated surfaces. For uncoated pipes with insulation, lepidocrocite (g-FeOOH), magnetite (Fe304), and goethite (α-FeOOH) were present in differing amounts. Akaganeite (α-FeOOH) was found on most samples regardless of surface protection, likely due to chloride presence from ocean spray. Chromium is used in stainless steel for protection but can form carbides with depleted chromium at nearby grain boundaries thus leading to intergranular corrosion, and this was observed in situ. Other findings related to surface morphologies and corrosion types are discussed. This work presents an understanding of corrosion products formed on A333 low temperature steel pipelines in marine harsh environments for different surface protections.

Corrosion Products and Surface Morphology for Coated, Uncoated, and Insulated A333 Steel Pipelines in Marine Harsh Environment

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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