Iron fractionation for corrosion products from natural gas pipelines by continuous-flow sequential extraction

The forms and quantities of iron species in corrosion product samples from natural gas pipelines were examined, using a continuous-flow sequential extraction system. Sequential extraction consists of four steps that dissolve water soluble iron (FeSO4), acid soluble iron (FeCO3), reducible iron (Fe-(oxyhydr)oxides) and oxidisable iron (FeS2) fractions, respectively. Selectivity of extracting reagents for particular iron species was evaluated by determination of co-extracted anions, using ion chromatography, and evolved CO2, using indirect flame atomic absorption spectrometer (FAAS). Iron was found predominantly in the reducible fraction (61-99%), indicating that Fe-(oxyhydr)oxides are the major constituents of the corrosion products.