Copper uniform corrosion

Atmospheric exposure, fresh and salt waters, and many types of soil can cause uniform corrosion of copper aHoys. The relative ranking of aHoys for resistance to general corrosion depends strongly on environment and is relatively independent of temper. Atmospheric corrosion, the least damaging of the various forms of corrosion, is generaHy predictable from weight loss data obtained from exposure to various environments (31) (see Corrosion and CORROSION CONTKOL). 

The most common form of corrosion is uniform corrosion, in which the entire metal surface degrades at a near uniform rate (1 3). Often the surface is covered by the corrosion products. The msting of iron (qv) in a humid atmosphere or the tarnishing of copper (qv) or silver alloys in sulfur-containing environments are examples (see also SiLVERAND SILVER ALLOYS). High temperature, or dry, oxidation, is also usually uniform in character. Uniform corrosion, the most visible form of corrosion, is the least insidious because the weight lost by metal dissolution can be monitored and predicted. 

Dissolution of steel or zinc in sulfuric or hydrochloric acid is a typical example of uniform electrochemical attack. Steel and copper alloys are more vulnerable to general corrosion than other alloys. Uniform corrosion often results from atmospheric exposure (polluted industrial environments) exposure in fresh, brackish, and salt waters or exposure in soils and chemicals. The rusting of steel, the green patina on copper, tarnishing silver and white mst on zinc on atmospheric exposure are due to uniform corrosion.14... 

Dezincification. Copper-Zinc alloys containing more than 15% zinc are susceptible to dezincification. In the dezincification of brass, selective removal of zinc leaves a relatively porous and weak layer of copper and copper oxide. Corrosion of a similar nature continues beneath the primary corrosion layer, resulting in gradual replacement of sound brass by weak, porous copper. Uniform dealloying in admiralty brass is shown in Figure 6.25.5,7,53,54... 

Mortar Uniform corrosion localized attack Copper release Perforation of pipe and leakage... 

In addition to ductile iron and PVC, copper and lead are used in pipes, and brass in fixtures and connections. Lead is released because of uniform corrosion. Copper is also released because of uniform corrosion, localized-attack cold water pitting, hot water pitting, MIC, corrosion fatigue, and erosion-corrosion. Lead pipes and lead-tin solder exhibit uniform corrosion. Brass corrosion includes erosion-corrosion, impingement corrosion, dezincification, and SCC. The direct health impacts are because of increased copper, lead, and zinc concentrations in the drinking water. Mechanical problems because of corrosion include leaks from perforated pipes, rupture of pipes, and the loss of water pressure because of blockage of pipes by corrosion products. 

For copper, the critical rate of 28.5 gmd (285 mdd) is much higher than the uniform corrosion rates in aerated water and 3% NaCl (0.4-1.5gmd, 4-15 mdd) hence, the fatigue life of copper is observed to be about the same in air as in fresh and saline waters (Table 8.5). 

In chloride atmospheres galvanic pitting takes place at the pores in copper layers and galvanic tunneling at cut edges on types 409 and 430 stainless steels, whereas in SO t atmospheres uniform corrosion takes place on the copper coating. 

Copper Uniform Pitting Crevice Erosion corrosion Cavitation Galvanic Concentration cell... 

Corrosion of copper shielding conforms to the mechanism of uniform corrosion. It is inherently resistant to differential aeration and only uniform corrosion of exposed areas occurs. 

General guidelines for acceptable uniform corrosion de-p>end upK>n the coupx>n met Jlurgy. Low-carbon steel (mild steel) corrosion rates less than 0.13 mm/y (5 mpy) are considered good, rates between 0.13 to 0.25 mm/y (5 to 10 mpy) are fair, and rates greater than 0.25 mm/y (10 mpy) are pKK>r. Copp>er-base alloys, such as admiralty and 90 10 copper nickel, should have rates under 0.013 mm/y (0.5 mpy). Above this value is considered excessive. General classification of corrosion rates is shown in Table 4. 

This is a type of corrosion in which brass dissolves as an alloy and the copper constituent redeposits from solution onto the surface of the brass as a metal in porous form. The zinc constituent may be deposited in place of an insoluble compound or carried away from the brass as a soluble salt. The corrosion can take place uniformly or be local. Uniform corrosion is more apt to take place in acid environments while local corrosion is more apt to take place in alkaline, neutral, or slightly acid environments. The addition of tin or arsenic will inhibit this form of corrosion. 

Scardina, P., Edwards, M., Bosch, D. J., Loganathan, G. V., Dwyer, S. K. (2007). Non-Uniform Corrosion in Copper Piping - Assessment, Final Project Completion Report to American Water Works Association Research Foundation, Blacksburg, Virginia Virginia Tech. 

Because of the excellent resistance of copper to uniform corrosion by soil and ground water, especially in oxygen-free environments, copper is a candidate material for fabrication of nuclear-waste containers in Canada (Shoesmith et al., 1996). 

The most important condition is that the metal must be in a passive state for pitting to occur. Passive state means the presence of a film on a metal surface. Steel and aluminum have a tendency to become passive, however, metals which become passive by film formation have a high resistance to uniform corrosion. The process of pitting destroys this protective film at certain sites resulting in the loss of passivity and initiation of pits on the metal surface. It may be recalled that passivity is a phenomenon which leads to a loss of chemical reactivity. Metals, such as iron, chromium, nickel, titanium, aluminum and also copper, tend to become passive in certain environments. 

Copper-containing lead alloys undergo less corrosion in sulfuric acid or sulfate solutions than pure lead or other lead alloys. The uniformly dispersed copper particles give rise to local cells in which lead forms the anode and copper forms the cathode. Through this anodic corrosion of the lead, an insoluble film of lead sulfate forms on the surface of the lead, passivating it and preventing further corrosion. The film, if damaged, rapidly reforms. 

Reactions with aqueous solutions. Uniform dissolution or corrosion of metals in acid, alkaline or neutral solutions (e.g. dissolution of zinc in hydrochloric acid or in caustic soda solution general corrosion of zinc in water or during atmospheric exposure). Reactions with non-aqueous solution (e.g. dissolution of copper in a solution of ammonium acetate and bromine in alcohol). 

---