Mitigating corrosion of deposit-covered carbon steel in solution containing sulfate-reducing bacteria by purging nitrogen

The corrosion behavior of a carbon steel covered by sand deposits in the solution containing sulfate-reducing bacteria(SRB)under nitrogen purging conditions was studied by electrochemical measurements and surface analyses,aiming at clarifying the mitigation effects of nitrogen purging on SRB-involved under-deposit corrosion.The electrochemical results show that the variation trend of polarization resistance with immersion time is unchanged,but the corrosion current density is the lowest in the presence of SRB and deposits under nitrogen purging conditions,as compared to that without purging nitrogen,which are confirmed by the cross-sectional corrosion morphology observation after removing the sand deposits.Moreover,it is found that there are no positive synergistic effects between SRB and deposits on corrosion under nitrogen purging conditions,corresponding to the corrosion mitigation.Such mitigation on corrosion can be attributed to the less amount of SRB-produced H2S exhausted by purging nitrogen,which is supported by X-ray photoelectron spectrometry analyses.Therefore,purging nitrogen to the solution could be a practically effective way to mitigate the corrosion of deposit-covered carbon steels in SRB-containing solutions.

Can the Prior Cathodic Polarisation Treatment Remove the Air-Formed Surface Film and Is It Necessary for the Potentiodynamic Polarisation Test?

This paper clarifies two issues related to the prior cathodic polarisation treatment(PCPT) for the potentiodynamic polarisation test: whether PCPT can(1) remove the air-formed surface film and(2) affect the polarisation test results. X-ray photoelectron spectroscopy analyses of fluoride ion-labelled samples show that PCPT cannot remove the surface film completely due to the low reaction rate. Potentiodynamic polarisation tests demonstrate that PCPT with proper operating parameters,-1.0 V SCE for 5 min with subsequent open circuit potential(OCP) stabilisation in this study, is necessary because it can improve the test reproducibility without affecting the corrosion parameters by unifying the initial surface state. However, PCPT with lower potentials, longer time or no OCP stabilisation has significant effects on the electrochemical corrosion parameters due to the hydrogen absorption under the conditions of this study.