What is Erosion Corrosion?
Erosion Corrosion is caused by high water velocities and high levels of turbulence in the pipework. It affects the pipework by preventing the protective corrosion layer from thickening, and in turn causes thinning of the pipe wall, leading to pitting and pinhole leaks. It also affects fittings in the system, especially elbows where the bend of an elbow can erode over time.
What Causes Erosion Corrosion?
High water velocity can cause Erosion Corrosion as it can prevent the protective corrosion layer inside a copper pipe from thickening, leaving internal areas exposed. As the flow pattern inside a system is fairly consistent, damage will always be exerted at specific points. Eventually pitting will occur causing localised turbulence, which will exacerbate the erosion, leading to increased erosion rates and eventually a leak.
Too few bends in piped systems will cause water velocities to increase, leading to damage of the pipework and fittings. High velocities can also cause gas bubbles to temporarily form in the water, which on collapse will cause a small localised water hammer effect.
Poor workmanship also leads to Erosion Corrosion. Tube that isn’t cut square, globules of solder left behind, tube ends not fully secured against pipestops and residual bur will all contribute to Erosion Corrosion over time. The presence of abrasive solids, e.g. sand, in the pipework has also been associated with Erosion Corrosion.
Before leakage, Erosion Corrosion can only be spotted by inspecting the inside of the pipe or fitting. Affected areas are typically bright and shiny as no forms of protective corrosion have been able to form. U-shaped pits will form, dictating the direction of flow.
How Does Erosion Corrosion Affect The Fitting?
High flow velocities will exert pressure on the wall of the fitting, especially in elbows. This will prevent the protective corrosive layer from forming, and instead over time the wall thickness of the fitting will reduce until a leak forms.
When tube is not finished or connected correctly near the fitting, the flow of water can be upset causing localised turbulence. This will itself erode the fitting and pipe, leading to pitting and in turn leaks.
How To Avoid Erosion Corrosion
Good design and good workmanship will avoid the conditions which lead to Erosion Corrosion.
In design, make sure you don’t have too many long stretches of pipe in your system design. It is advised to ensure that water flow velocities do not exceed 2 m/s in cold water and 0.5 m/s in hot water systems.
During installation, make sure to follow our installation instructions carefully. Ensure that the pipe is cut squarely, is free from any defects and debris before insertion and make surely it well secured against the pipestop on forming the connection.
Abrasive particles can be removed through the use of filtration or settling. In steam and compressed air systems, water traps can be used to reduce the effect of water droplets.
Finally, de-aeration and corrosion inhibitors are additional measures that can be taken to reduce the risk of Erosion Corrosion.