What is Groove Corrosion ?
Groove Corrosion is a type of localized corrosion that typically occurs in areas where grooves or indentations form on a metal surface. These grooves or indentations may be caused by manufacturing processes, mechanical damage, or long-term wear. Groove corrosion usually happens in corrosive environments where the metal surface is not uniformly exposed, leading to accelerated corrosion in certain areas.
Common causes of groove corrosion
- Exposure to corrosive liquids: The surface of the groove often accumulates corrosive liquids or impurities, which accelerates corrosion.
- Lack of flow: Liquids flow poorly in the groove, leading to localized concentration and further intensifying the corrosion reaction.
- Stress concentration: Local defects or points of stress concentration on the metal surface can result in stronger corrosion effects.
Case of Grooving Corrosion
In Electric Resistance Welded (ERW) carbon steel and low-alloy steel pipes, exposure to neutral saline water may cause preferential corrosion at the weld seam area, leading to premature leakage. Selective localized corrosion is likely to occur in the weld seam, especially near the fusion line. ERW joints exposed to corrosive environments are more prone to preferential corrosion at the fusion line.
A long-running 24-inch API 5L Grade X-42 oil pipeline in a desert area began experiencing corrosion due to localized electrochemical corrosion cells (small anode/large cathode effects) in these un-melted grooves. The corrosion rapidly spread, leading to excessive thinning of the metal thickness inside the weld seam, reaching a critical value. The steel pipe’s wall thickness fell below the critical thickness required to support operating stresses, leading to ductile failure of the pipeline.
Prevention of Groove Corrosion
Groove corrosion can be prevented by optimizing design, selecting corrosion-resistant materials, improving surface smoothness, minimizing exposure to corrosive environments, and controlling temperature and flow rate.
Specific measures include removing surface defects, choosing corrosion-resistant alloys or coatings, avoiding dead zones and groove-like structures, performing regular inspections and maintenance, ensuring proper drainage to prevent liquid accumulation, and controlling the presence of corrosive substances in the environment.
By implementing these methods, groove corrosion can be reduced, and the lifespan of equipment can be extended.
