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Copper corrosion by-product release in long-term stagnation experiments
Till H Merkel1, Hans-Jürgen Gross, Wolfgang Werner
1Heinrich-Sontheimer-Laboratory, DVGW-Water Technology Center Karlsruhe, Germany. merkel@tzw.de
Water Research
|May 9, 2002
Summary
Long-term water stagnation in copper pipes leads to complex copper release and refixation, not simple solubility. Corrosion scales, primarily malachite, form but do not prevent pipe corrosion.
Area of Science:
- Materials Science
- Environmental Science
- Electrochemistry
Background:
- Copper piping is common in water distribution systems.
- Stagnant water conditions can lead to metal corrosion and water quality issues.
- Understanding copper corrosion by-product release is crucial for water safety.
Purpose of the Study:
- To investigate the effects of long-term water stagnation on copper corrosion.
- To analyze copper by-product release and corrosion rates in stagnant water.
- To characterize the corrosion scales formed on copper pipes.
Main Methods:
- Pipe-rig experiments simulating stagnant water conditions (DIN 50931, Part 1).
- Analysis of water phase for copper concentration.
- Surface analysis of corrosion scales using techniques like X-ray diffraction (implied).
Main Results:
- Copper concentration did not follow simple solubility curves; release and refixation processes were observed.
- Oxygen consumption followed first-order kinetics.
- Corrosion scales comprised cuprite (Cu2O) and malachite (CuCO3 x Cu(OH)2).
- Malachite crystals formed during stagnation, acting as a copper sink but not providing protection.
Conclusions:
- Copper release during stagnation is a dynamic process involving both dissolution and precipitation.
- The presence of malachite, while sequestering copper, does not inhibit the overall corrosion process.
- Measured copper levels after extended stagnation correlated with malachite solubility, indicating its role in controlling dissolved copper.