Study of Preferential Weld Corrosion in X52 Mild Steel with the Presence of Acetic Acid

Preferential weld corrosion occurs in the hydrocarbon carrying pipelines due to CO2 presence. The weld segments consist of parent metal, HAZ and weld metal that causes corrosion due to potential difference. The corrosion could be mitigated with the formation of protective layer (FeCO3). However, the mitigation has not been effective as the FeCO3 layer formation is disrupted by environmental conditions like the pH and also the presence of weak acids like Acetic Acid (HAc) The purpose of this research is to investigate the presence of HAc and its effect on the corrosion rate of the weld segments. The influence of pH on the FeCO3 formation on the weld segments with and without HAc present is also analyzed. A coupled sample and an un-coupled sample is prepared from the API 5L X52 mild steel weld segment. Test parameters were set to varying pH 4 and 6.6 with and without 1000ppm HAc present. 4 glass cells are set up to measure the intrinsic corrosion rate of the un-coupled sample and 4 glass cells are set up to measure the galvanic corrosion rate of the coupled sample. Linear Polarization Resistance (LPR) was used to measure the intrinsic corrosion rate and the galvanic corrosion rate of the samples.