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http://www.copper.org/tubehdbk/design-data-general.html
QUOTE “Pitting can also be caused or intensified by faulty workmanship which leaves excessive amounts of residual aggressive flux inside the tube after installation. If the joints have been overheated during installation and the excess residual flux has polymerized, the pitting problem can worsen.
Soft acidic waters can cause the annoying problem of green staining of fixtures or “green water.” Raising the pH of such waters to a value of about 7.2 or more usually solves the problem, but a qualified water treatment person should be consulted. A typical treatment for an individual well water supply is to have the water flow through a bed of marble or limestone chips.
Excessive water velocity causes erosion-corrosion or impingement attack in plumbing systems. As explained in the discussion of pressure system sizing to avoid erosion-corrosion (and noise) problems, the water velocity in a plumbing system should not exceed 5 to 8 feet per second-the lower limit applying to smaller tube sizes.
Velocity effects can be aggravated if the water is chemically aggressive due to pH or gas content as outlined above, or if solids (silt) are entrained in the flow. The combination of a velocity that is otherwise acceptable and a water chemistry that is somewhat aggressive can sometimes cause trouble that would not result from either factor by itself.
Erosion corrosion can also be aggravated by faulty workmanship. For example, burrs left at cut tube endscan upset smooth water flow, cause localized turbulence and high flow velocities, resulting in erosion corrosion.
Any metal pipe laid in cinders is subject to attack by the acid generated when sulfur compounds in the cinders combine with water. Under such circumstances, the tube should be isolated from the cinders with an inert moisture barrier, a wrapping of insulating tape, a coating of an asphaltum paint, or with some other approved material. With rare exception, natural soils do not attack copper.
Copper drainage tube rarely corrodes, except when misused or when errors have been made in designing or installing the drainage system. An improper horizontal slope can create a situation where corrosive solutions could lie in the tube and attack it. If hydrogen sulfide gas in large volume is allowed to vent back into the house drainage system, it can attack the tube. “
