Copper Pipe Corrosion
Introduction to Copper Pipe Corrosion
Copper exhibits good resistance to corrosion in urban, marine, and industrial atmospheres. The major factors that control the initial rate of attack on copper are moisture, temperature, and the level of pollution. Soon after exposure of copper to the atmosphere copper oxidize, the bright copper surface takes on a dull tan tarnish. After a few years this tarnish gradually changes to dark brown or black. At a later stage the corrosion products of copper turn green. The corrosion rate of several types of copper in a 20-yr test averaged 1 pm/yr (0.05 mpy) in an industrial atmosphere, 0.8 pm/yr (0.03 mpy) in a marine atmosphere, and 0.5 pm/yr (0.02 mpy) in a rural atmosphere
Copper Pipe Corrosion
Copper has good resistance to corrosion by all types of freshwater. Corrosion rates of Copper Pipe are from 5 to 25 microm/yr (0.2 to o 1 mpy). Corrosion rates for water saturated with air and carbon dioxide are an order of magnitude greater than those for municipal or distilled water. Copper also has good resistance to corrosion in seawater. Because of its outstanding resistance to fouling by marine organisms, it is widely used for sheathing on surfaces exposed to seawater. Copper is sometimes used in seawater piping, but copper pipes are subject to corrosion-erosion where the flow velocity is greater than 0.9 to 1.2 m/s (3 to 4ft/s). These velocities are often attained at changes in copper pipe cross section or flow direction.
Pitting and Crevice Corrosion of Copper Pipe
Although the failure of domestic copper plumbing systems is rare, pitting failure occurs in cold-water lines that conduct aggressive well waters. Aggressive well waters are those contaminated with corrosive compounds. Hot-water pitting is rare and is usually associated with a soft water. Copper is susceptible to crevice corrosion attack.
Galvanic Corrosion of Copper Pipe
Couples of copper and aluminum or copper and steel can lead to severe galvanic corrosion (see also Galvanic Series of Metals in Seawater or Galvanic Corrosion Chart).
The degree of risk in coupling copper to other metals in water, salt solutions, or acids depends upon the effectiveness of the solution as an electrolyte.
Copper Pipe Corrosion in Neutral Solutions
Copper pipe has good resistance to many salt solutions, such as the sulfates and nitrates of sodium and potassium. Typical corrosion rates are 5 micromm/yr (0.2 mpy). It also has reasonably good resistance to the non oxidizing chlorides of sodium and calcium. Corrosion rates may range from 15 to 279 microm/yr (0.6 to 11 mpy). Copper does, however, have poor resistance to oxidising substances, such as ferric and cupric salts, and to ammonium salts. Cyanides are also very corrosive to copper pipe.
Copper Pipe Corrosion in Natural
Waters (Fresh Water and SeaWater)
Copper pipe alloys are widely used for systems that handle freshwater. Certain of the alloys have become associated with particular components, such as heat exchangers, and with particular types of freshwaters, such as river water containing acid mine drainage. Copper alloys are widely employed in systems exposed to seawater. The corrosion rates of copper alloys in seawater vary, they depend on many factors including the composition, i.e., concentration, of the seawater, the temperature, the velocity past the metal surface, and the degree and kind of pollution. The good resistance of copper pipe alloys to corrosion by seawater depends partly upon the inherent cathodic nobility of the metal, but it also depends on the ability to form protective films. High-velocity and turbulent flow conditions can remove these films and permit local and rapid corrosion.
Automotive Radiators Motor vehicle radiators made of copper are often used with an ethylene glycol, i.e., antifreeze, and water solution as the coolant. Although commercial antifreeze and coolant solutions always contain an corrosion inhibitor, these inhibitors do not last indefinitely. Therefore, the solutions should be renewed or fresh inhibitor should be added periodically because copper can be significantly corroded by uninhibited ethylene glycol and water solutions at the usual operating temperatures and low pH.
reference: MATERIAL DETERIORATION PREVENTION AND CONTROL GUIDE OF ARMY MATERIAL, PARTONE, METALS (MlL HDBK-73S (MR)
Useful Documents on Copper Corrosion and Copper Pipe Corrosion:
Copper Tech Corner - developed by the Copper Development Association to provide industry professionals with a targeted selection of white papers and answers to technical questions of interest to plumbers, installers, contractors and engineers
Useful website on Copper:
Copper Corrosion Resistance Data:
Copper-Key: a freely accessible web-site with a computer based reference database containing technical information on the most widely used copper alloys
Corrosion Resistance Database The Copper & Copper Alloy Corrosion Resistance Database is the outgrowth of the Copper Development Association/International Copper Association Copper Select program which is designed to provide users and potential users of coppers and copper alloys with on-line information on the properties, characteristics and uses of coppers and copper alloys