Corrosion Mechanism of 316L Stainless Steel in a Expansion Joint of Blast Furnace Gas Pipeline in a Power Plant

Severe corrosion phenomenon appeared in an expansion joint of blast furnace gas (BFG) pipeline after booster fan in a power plant. The sediment adhered to the inner wall of the expansion joint was analyzed by ion chromatography. The corrosion site of expansion joint was examined by scanning electron microscope (SEM), and the behavior of electrochemical corrosion of stainless steel electrode was discussed through electrochemical impedance spectroscopy (EIS) and polarization curve. The results reveal that the leaching solution of the sediment is a kind of strong electrolyte solution. Along with the increase of immersion period, the impedance of stainless steel electrode decreases dramatically, the impedance spectroscopy experiences such a procedure that a single capacitive reactance arc gradually develops into the contraction of inductive reactance and then tends to be two capacitive reactance arc, which indicates that pitting corrosion transfers from induction period to evolution period until metastable pitting translates into stable pitting. There exists no passive area in polarization curves of stainless steel and shows the characteristics of active dissolution. In conclusion, the failure of the expansion joint stainless steel shows typical pitting characteristic.