Corrosion Characterization of Salvaged Subsea Pipeline

The condition of subsea pipeline is monitored by intelligent pigging and FFS analysis is done based on metal loss data. The understanding of the distribution of metal loss in the form of uniform corrosion and deep penetrating pitting is not well understood. The objective of this project is to conduct visual inspection on the salvaged subsea pipeline, investigate the occurrence of corrosion in the pipeline with relation to the operation and inspection data, and analyse the contributing factor of the corrosion corresponding to the location of uniform and localize pitting corrosion. This study started with gathering data on the operation condition and doing visual inspection on the corrosion pipeline. The metallographic preparation was done in order to reveal the microstructure and material composition by using Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX). Corrosion rates of both pitting and general corrosion samples were examined using Linear Polarization method for 48 hours immersion at 50°C, 3% NaCl solution and 1 bar CO2.The visual inspection shows that the actual pipeline condition is parallel with the IP data where it was indicated that the pipelines undergo metal loss and pitting corrosion. The EDX result shows very small difference in elemental composition between pitting and general corrosion sample and it does not affect the corrosion rate between the samples in the long run. Besides that, the difference in corrosion rates of LPR is small where 4.4 mm/yr for pitting corrosion and 4.0 mm/yr for general corrosion, thus can be considered same. This suggests that the inclusions or deposit might be facilitating the pit initiation. However further study can be done to find suitable prevention method in order to reduce corrosion rate and pitting in the pipeline.