Copper Pipe Corrosion
Copper and Copper Alloys Introduction
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 thik 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
nonoxidizing 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 turbolent 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 ethytene 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 indeftitely. 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:
INTERAGENCY COPPER PIPE CORROSION PROJECT - This project was initiated in response to complaints of black water occurring in some customer's home in florida.
CAUSES OF COPPER CORROSION IN PLUMBING SYSTEMS - This review is intended for anyone with an interest in the design or the installation of water supply systems using copper pipes or hot water cylinders. It is relevant to plumbers, water industry staff, architests and property owner.
Copper Pinhole Leaks - A Technical note from Toolbase on the mechanisms and prevention of Copper corrosion and Copper pipe leaks
Task Force to Study Pinhole Leaks in Copper Plumbing -
The Task Force to Study Pinhole Leaks in Copper Plumbing was established under the auspices of Senate Bill 54, 2003, in order to help Marylanders understand the pinhole leak phenomenon, and thus deal with its consequences. Pinhole leaks pose problems for several reasons:
• They may cause water damage to plaster and sheetrock walls, electrical systems, flooring, ceilings or furniture; • Undetected water leakage may result in mold growth; • Repairing or replacing copper pipe, because of limited access, is generally costly; • Water damage claims may result in homeowners’ insurance premiums being raised, or non-renewal of policies.
Possible causes to the pinhole leak problem are offered in this report, although it is widely believed that there is no one cause; and there is no one solution. Rather, it is generally held that a number of circumstances may contribute to the problem, and a variety of remedies may be available for consideration
Corrosion Control In Drinking Water Systems
COPPER PIPING CORROSION: A PROBLEM FOR SAN FRANCISCO BAY
CORROSION OF ALUMINUM-FIN, COPPER-TUBE HEAT EXCHANGE COILS
What Is Most Important When Designing And Installing Copper Piping Systems?
Pitting Corrosion of Copper in High-pH and Low-Alkalinity Waters
How to Prevent Corrosion of Copper Tube in Underground or Buried Applications?
Useful website on Copper:
Copper Development Association - North America
Copper Development Association - UK
Copper Corrosion Resistance Data:
Copper-Key: a freely accessible web-site with a computer based reference database ontaining technical information on the most widely used copper alloys