Effect of filler metal chemistry on preferential weld corrosion in hydrocarbon and produced water service using the galvanostatic method

The effect of Ni content in weld consumables on the preferential weld corrosion (PWC) of welded pipeline steel for hydrocarbon and produced water service has been investigated using the galvanostatic method as a preliminary assessment tool. The method involves application of a modest anodic current to the weldment over a short period, in this case 62 h. The distribution of material loss and the extent of PWC is then characterised by 3D profiling. Testing was conducted for 0% Ni, 1% Ni and 2% Ni weld fillers in 50 g/L NaCl at 60 °C with 1 bar CO₂. For these sweet environments, the results demonstrate an increased resistance to corrosion of the weld metal and heat affected zone (HAZ) for the Ni-weld filler, compared to the weld metal free of Ni and to the parent steel. However, for all weldments, the fusion zone and HAZ-parent steel interface were more prone to attack than the parent steel, albeit the addition of Ni reduced the extent of corrosion at the fusion zone.