A Study of Chemical Compatibility between Corrosion Inhibitor and Biocide in Offshore Application

The main threat to the oil and gas pipeline is due to internal corrosion from corrosive acid gases and microbes. The integrity of offshore pipeline is dependent on successful mitigation of carbon dioxide (CO2) corrosion and microbiologically influenced corrosion (MIC) through effective corrosion inhibitor and biocide treatment. Possible reactions between corrosion inhibitor (CI) and biocide can reduce the efficiency and performance of both chemicals. This can lead to inadequate corrosion protection of the pipeline. This research is to study the chemical compatibility between CI and biocide focusing on the performance of the CI. Corrosion simulation was based on 3% NaCl solution saturated with CO2 at 1 bar and 60oC, with fixed biocide concentration of 500ppm and various CI dosages. The compatibility was studied based on comparison between three injection methods and the individual effect of each chemical. Corrosion measurement was performed in three-electrode glass cell testing by using Linear Polarization Resistance (LPR). Surface film morphology was studied with Scanning Electron Microscope (SEM) and crystallinity structure with -ray diffraction (XRD). 25ppm CI reduced corrosion rate from 1.4mm/yr to 0.04mm/yr with 97% efficiency. The presence of biocide reduced the performance from 2.5% to 25% significantly depending on the injection method. Thus, dosage of CI more than 500ppm was required to increase inhibition efficiency. By using SEM, the existence of CI layer has been observed by no detection of general corrosion on the inhibited surface. The XRD patterns of inhibited surface shows the presence of iron peaks only, the peaks due to oxide of iron were found to be absent. In conclusion, biocide was found to affect the performance of CI efficiency.