Copper Pipe Corrosion

Copper Pipe Corrosion (Blue Water)

There are several types of copper corrosion which occur in potable water systems. These include general corrosion, pitting corrosion, erosion / corrosion, and microbiologically induced corrosion (MIC). Localised (pitting) corrosion of copper is typically classified into three categories Type I (Cold-water pitting), Type II (Hot-water pitting) and Type III (Soft Water pitting). General and pitting corrosion of copper is often associated with specific water qualities. In general, uniform corrosion of copper occurs when exposed to soft waters of low pH. As a result of general corrosion the affected surface may be covered with a loose powdery scale or have a tarnished copper appearance.

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Type I Pitting

Type I pitting produces deep and narrow pits and is typically the result of exposure to hard, cold, water with pH in the range from 7 to 7.8 and high levels of sulphate to chloride and bicarbonate ratios. Soft waters with elevated pH (above 8.0) are associated with type III pitting. Typical of this attack are wide and shallow pits. Type II pitting has been observed in hot waters with relatively low pH (below 7.2) and high sulphate to bicarbonate ratios. There are several types of copper corrosion which occur in potable water systems. These include general corrosion, pitting corrosion, erosion / corrosion, and micro-biologically induced corrosion (MIC). Localized (pitting) corrosion of copper is typically classified into three categories Type I (Cold-water pitting), Type II (Hot-water pitting) and Type III (Soft Water pitting).

Type II Pitting

General and pitting corrosion of copper is often associated with specific water qualities. In general, uniform corrosion of copper occurs when exposed to soft waters of low pH. As a result of general corrosion the affected surface may be covered with a loose powdery scale or have a tarnished copper appearance. Type I pitting produces deep and narrow pits and is typically the result of exposure to hard, cold, well waters with pH in the range from 7 to 7.8 and high levels of sulfate to chloride and bicarbonate ratios. Soft waters with elevated pH (above 8.0) are associated with type III pitting (3). Typical of this attack are wide and shallow pits. Type II pitting has been observed in hot waters with relatively low pH (below 7.2) and high sulphate to bicarbonate ratios.

Recommendations to prevent Copper Pipe Corrosion

  • Do not allow water to stagnate in the system for a long period after installation. Regular replenish with fresh aerated water to help form protective patinas o layer on the internal surface of the copper pipe.
  • Do not drain down the system after pressure testing. It is impossible to remove all the water and localised attack will occur: metal/water/air.
  • Design and installation to minimise dead-legs in the system. These can lead to stagnant water conditions, which helps the development of pitting corrosion.
  • Only use copper pipe to EN 1057 with the BS kitemark. Copper pipe not to this standard may have carbon film residue on the inside from the extrusion process, which can lead to type I pitting in hard water areas.
  • Do not used galvanised pipe in hot water systems and never use downstream of copper pipe.
  • Design a system so that hot water flows in copper pipework are in the range 0.5-1 m/s.
  • Design a system so that cold water flowrate in copper pipe in hot water is in the range 0.5-2m/s. (Too low a flowrate allows debris to settle out and may lead to under-deposit corrosion. Flow rates above these values may induce erosion corrosion on copper.)
  • For larger systems, if there is a risk of deposits being brought into the system, i.e. from surface upland waters, fit a water filter to the incoming mains.
  • Deburr the cut ends of copper pipe and do not have large changes in section at joints. This is to reduce the risk of turbulent flows downstream of the joint and hence the likelihood of erosion corrosion.
  • Do not use excessive soldering fluxes and wipe any excess from the outside of the pipe after soldering. (Flux residues left after soldering may lead to pinholing of pipework several months later.)
  • Lag pipework, especially hot water pipes, to keep water temperatures in the pipes outside the range 25-50°C for any length of time, otherwise, micro-organisms can flourish which increases the risk of legionella and also may lead to microbial induced pitting corrosion.