Sour and Sweet Corrosion of Carbon Steel: General or Pitting or Localized or All of the Above?

A model has been previously developed to predict internal pitting corrosion of oil and gas pipelines.  This model is based on experiments carried out in the laboratory at high pressure and high temperature under the operating conditions of the oil and gas pipelines. The inputs are of two kinds: construction (pipe diameter, pipe wall thickness, and pipe inclination) and operational (production rates of oil, water, gas, and solid, temperature, total pressure, partial pressures of H₂S and CO₂, concentrations of sulphate, bicarbonate, and chloride).

Additional experiments have been carried out in a high-temperature, high-pressure rotating cylinder electrode (HTHPRCE) apparatus (ASTM G184) to investigate the influence of soilds, temperature, and oils to expand the applicability of the internal pitting corrosion model for conditions found in oil and gas production pipelines in Western Canada.  Each experiment was conducted over a period of 100 hours.  The general corrosion rates (as determined by mass loss measurement), surface layers (as measured by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis), and pitting corrosion profile (as measured by laser surface profilometer) were correlated to understand the influence of solids, temperature, and type of oil on internal pitting corrosion.