Causes of corrosion of gathering pipeline in a gas field

The corrosion occurred in the gathering pipeline of a gas field. The causes of pipeline corrosion were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, scanning electron microscopy and energy spectrum analysis, and X-ray diffraction analysis. The results show that the gas transported by the pipeline contained water, CO₂ and H₂S, and liquid accumulation occurred in the low-lying parts of the pipeline. Under the combined action of CO₂ and H₂S gas, serious hydrogen evolution corrosion occurred in the pipeline. Under the action of higher concentration of H₂S, the corrosion products were loose and did not protect the metal matrix. The corrosion process was mainly controlled by H₂S. The high concentration of Cl^- accelerated the dissolution rate of Fe and further promoted the corrosion process. The ions in the aqueous solution could also increase the conductivity and increase the corrosion current density.