Corrosion inhibition to mitigate preferential weld corrosion (PWC) was studied experimentally using the metallurgical condition of the welds and the inhibitor concentration as independent variables. The study simulated environmental conditions in a seawater treatment system sparged with natural gas, 2% CO2 and 150 ppm of H2S, as well oxidants due to bacterial or biofouling control methods. The study used Tafel polarization and electrochemical noise tests on multi electrode assemblies fabricated from sections of parent metal, heat affected zone (HAZ) and weld metal. This technique allows testing of each component separately as well as quantifying galvanic coupling effects. In welds susceptible to PWC, adequate corrosion inhibitor concentration is effective in reducing galvanic corrosion, due to the shifts in the relative corrosion potentials. However the effect depends on the inhibitor dosage. Under dosage actually increases the corrosion rate and exacerbates the effect of the galvanic coupling.

Subject
Corrosion rate, Parent metals, Pipelines, Seawater, Base metals, Anodic current, Corrosion inhibitors, Galvanic coupling, Sulfides, Corrosion coupons, Polarization, Galvanic current, Weld metal
Keywords:
PWC, electrochemistry methods, seawater transport
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2014
Association for Materials Protection and Performance (AMPP)
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