Erosion Corrosion: Causes, Effects, and Prevention Tips

Erosion corrosion is a type of wear that occurs in piping systems due to high water velocities and excessive turbulence. It prevents the protective corrosion layer inside pipes from forming or thickening, leading to thinning of the pipe walls, pitting, and eventually pinhole leaks. This type of corrosion commonly affects fittings, particularly at bends, such as elbows, where turbulent flow can accelerate erosion over time.

What Causes Erosion Corrosion?

Erosion corrosion is primarily caused by high water velocities that disrupt the protective oxide layer inside copper pipes, leaving the internal surfaces exposed to further damage. Because flow patterns in a system are relatively consistent, erosion typically occurs at specific points, leading to erosion and pitting. When pits occur, they create localised turbulence that accelerates the erosion. Both eventually cause leaks.

Several factors contribute to erosion corrosion:

• High Water Velocities: Fast-moving water increases the likelihood of corrosion by eroding protective layers. The design or configuration of a system can lead to high velocities, intensifying damage to pipework and fittings. Additionally, high speeds can cause gas bubbles to form and collapse, resulting in localised water hammer effects that damage the pipe walls.

• Poor Workmanship: Incorrect installation practices, such as uneven pipe cuts, residual solder, improperly secured tube ends, and burrs left on pipe edges, can create conditions that promote erosion corrosion. These defects can disturb flow patterns, causing localised turbulence that accelerates wear.

• Abrasive Solids: Particles such as sand in the system can further exacerbate erosion, acting as abrasive agents that wear away the pipe walls.

Before leaks appear, erosion corrosion can only be detected by inspecting the interior of the pipe or fitting. Affected areas often appear bright and shiny, as no protective layer has had a chance to develop, with characteristic U-shaped pits indicating the direction of flow.

How Does Erosion Corrosion Affect The Fitting?

High flow velocities exert constant pressure on fittings, particularly elbows and bends, where turbulent flow is most intense. This pressure prevents the formation of the protective corrosion layer, gradually thinning the fitting’s wall until it leaks.

If pipe ends are not properly finished or secured near fittings, it can create localised turbulence, which contributes to further erosion of both fittings and pipes, leading to pitting and leaks.

How To Avoid Erosion Corrosion

Preventing erosion corrosion relies on good design and workmanship:

• System Design: Avoid excessively long, straight runs of pipe to control water velocities. It is recommended to keep water flow velocities below 2 m/s in cold water systems and 0.5 m/s in hot water systems to minimise erosion risk.

• Proper Installation: Follow installation guidelines. Ensure pipes are cut squarely, free from defects and debris, and properly secured against the pipe stop when forming connections. Attention to detail during installation can greatly reduce the risk of erosion corrosion.

• Filtration and Settling: Remove abrasive particles from the system using filtration or settling methods.

• Additional Measures: Consider using de-aeration and corrosion inhibitors to further reduce the risk of erosion corrosion, especially in systems prone to high flow rates.

By adhering to good design practices and following installation guidance, you can effectively minimise the risk of erosion corrosion, protecting your piping system from premature wear and leaks.