Abstract
The early stage of corrosion formation on X70 pipeline steel under oxyfuel atmosphere was investigated by applying a simulated gas mixture (CO2 containing 6700 ppmv O2, 100 ppmv NO2, 70 ppmv SO2 and 50 ppmv H2O) for 15 h at 278 K and ambient pressure. Short-term tests (6 h) revealed that the corrosion starts as local spots related to grinding marks progressing by time and moisture until a closed layer was formed. Acid droplets (pH 1.5), generated in the gas atmosphere, containing a mixture of H2SO4 and HNO3, were identified as corrosion starters. After 15 h of exposure, corrosion products were mainly X-ray amorphous and only partially crystalline. In-situ energy-dispersive X-ray diffraction (EDXRD) results showed that the crystalline fractions consist primarily of water-bearing iron sulfates. Applying Raman spectroscopy, water-bearing iron nitrates were detected as subordinated phases. Supplementary long-term tests exhibited a significant increase in the crystalline fraction and formation of additional water-bearing iron sulfates. All phases of the corrosion layer were intergrown in a nanocrystalline network. In addition, numerous globular structures have been detected above the corrosion layer, which were identified as hydrated iron sulphate and hematite. As a type of corrosion, shallow pit formation was identified, and the corrosion rate was about 0.1 mma−1. In addition to in-situ EDXRD, SEM/EDS, TEM, Raman spectroscopy and interferometry were used to chemically and microstructurally analyze the corrosion products.
Highlights
Carbon Capture Utilization and Storage (CCUS) is a promising technology for the reduction of CO2 emissions from fossil-fuel-operated power plants, steel and cement mills or refineries
The chemical composition of the investigated X70 specimens, which were sectioned from a real industrial pipeline, was determined using spark emission spectroscopy
The sharpness and high intensity of these lines point at a high crystallinity, and their large number is attributed to numerous electron transfers between different orbitals [34]
Summary
Carbon Capture Utilization and Storage (CCUS) is a promising technology for the reduction of CO2 emissions from fossil-fuel-operated power plants, steel and cement mills or refineries. The early stage of corrosion processes under oxidizing atmospheres at low temperatures (278–288 K), comparable with conditions in subterranean gas pipelines, is currently not well-understood. Ko et al [21,22] performed in-situ synchrotron X-ray diffraction experiments to reveal the effects of microstructure and boundary layer conditions on the formation of CO2 -induced corrosions’ products, mainly siderite FeCO3 and chukanovite Fe2 (OH) CO3. These experiments, were performed at 353K, without impurities such as NO2 and SO2 , which just did not represent underground transport pipeline conditions. The corrosion experiments were performed at an ambient pressure and a temperature of 278 K, representing the pipeline transport conditions
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