Corrosion behavior of oil tube steel in simulant solution with hydrogen sulfide and carbon dioxide

Electrochemical measurement techniques, X-ray diffraction and scanning electron microscopy were applied to investigate the corrosion behavior of N80 tube steel in simulant static solution with carbon dioxide (CO2) and hydrogen sulfide (H2S) at a temperature of 100 °C. Sweet corrosion occurred when a very small partial pressure of H2S was added. At this condition, uniform corrosion was found. The added H2S only accelerated the general corrosion rate. Sour corrosion was primary as the partial pressure of H2S increased to 0.010 MPa. The general corrosion rate decreased quickly, but severe pitting was found. The corrosion scale, mainly composed of coarse grains of mackinawite (FeS1−x), was loose and brittle. In sour corrosion, general corrosion rate decreased slowly and pitting became slight with increasing partial pressure of H2S because the primary corrosion product, fine grains of pyrrhotite (FeS1+x), made the scale more compact and continuous.