Grooving corrosion of seam welded oil pipelines

• A poor quality ERW process left un-melted zones close to the pipe inner surface.
• Grooving corrosion is largely accelerated by lack of fusion leading to rapid thinning.
• When radial stress of flow exceeded the hoop strength cracks initiated and propagated.
• Positioning the seam weld line around the 12 O’clock decelerates grooving corrosion.

24” pipeline carrying oil was failed in the form of longitudinal crack at the 6 O’clock position resulting in oil spill. The failed pipe was investigated to reveal the main cause of its failure. The procedure of investigation was built on studying the intact pipe, rupture area, parent material, and intact weld. Results of chemical analysis, mechanical properties, and microstructure of the pipe material were confirmed with the specified standard. Cracks were originated from weld defected sites, initiated by grooving corrosion, propagated by inertia at the normal designed pressure condition, and stopped when stress relief is attained. It is recommended to use high quality ERW pipe, with its seam weld line positioned around the 12 O’clock during installation, to minimize and decelerate grooving corrosion. It is also important to perform regular or routine inspection, on suitable intervals, determined by past experience.