COPPER CORROSION
Inter granular corrosion
Uniform or general corrosion
Microbially induced corrosion
Crevice corrosion
Galvanic corrosion
Corrosion in reinforced concrete Figure 4. Types of Corrosion.6
These methods also have limitations: l Corrosion coupons provide a measurement of corrosion rate in isolation (corrosion coupons are mounted on an electrically isolated PVC rod, hence, isolated from the cooling system but in contact with the flowing water at a preset velocity), focused on the water quality impacts. They will not typically provide much information for localised corrosion, microbiological corrosion, dissimilar metals, and erosion corrosion.
l Corrosion coupons may be used to assist with pitting assessments, though again, limited to measurement in isolation from the system itself.
l Electronic corrosion measurement is a rapid measurement method, providing a rapid corrosion measurement in the flowing water. The method may be used for prediction of pitting corrosion but has similar limitations to coupons analysis.
l When using copper coupons, the formation of an oxide layer (protective coating that gives copper its protective capability) will not form rapidly, hence, measurements using fresh coupons may see a skewed result when comparing results with existing aged copper surfaces (Fig 5).
Dosing of disinfectants has often been blamed as the cause of pipe damage, particularly pitting. Research10
disinfectant selection type is required. The effects of breakpoint chlorination, interaction with metals, interaction with PEX or other types of plastic pipes, and microbiological control efficacy should all be considered as part of any selection process.
Prevention of damage to copper pipe at installation and commissioning As has been outlined earlier in this paper, copper must develop an oxide or patina layer to protect itself. Without this layer, copper is reactive, and vulnerable to attack from the corrosion mechanisms outlined. The oxide layer forms with time. The
formation of the layer is affected by time, flow, and activity of chemicals. The data presented in Figure 6 demonstrates the process of oxide formation as measured via an electronic corrosion monitor. Research indicates that copper pipes,
when new or just installed, can be protected using strategies of good practice: l Clean the copper surface carefully, using only approved materials,
Forms of corrosion
Environmentally induced corrosion
Pitting corrosion
Me2+ Me1
Me2+ Me2+ Me1 + Me2
Dealloying or selective leaching
Erosion corrosion
Figure 5. Corrosion coupons from a hospital in Australia.
considering the risk present. Such cleaning materials must be removed prior to use.
l Review residual disinfection process – maintaining enHealth guidelines levels of free chlorine of >0.5 ppm at outlet is recommended.11
l Allow the copper oxide to form before exposing the pipes to more aggressive environments.12
Note the consideration
to delay super chlorination for new pipework may be applied, to prevent high concentration chlorine damage to copper, until the oxide layer has formed.
l Ensure the water circulating in the system is of a low corrosive nature,13 free from particulate matter.14
and Filtration
should be selected based on a particle size distribution and thus removal of potentially damaging particulate matter.15
l Verify flow velocity16 not excessive. Values of 0.8-2 ms–1
is consistent and are
applicable but should be verified by the Hydraulic Engineering team. Flushing procedures and frequencies are required to be implemented particularly in areas where water use may be inconsistent.
l Avoid ammoniacal and sulphurous materials in the copper pipes. This may exclude the use of copper pipework particularly with certain types of bore water. Careful analysis of makeup water, and modelling of such may be required.
Copper is reactive, and vulnerable to attack 11.36 10 8 and experience support the
observation that pipework damage is likely near dosing points, even in stainless steel pipes, and will often appear as pitting. Bends and areas where chlorine may accumulate are regularly seen as failure points. However, when chlorine or other
disinfectants are mixed and distributed correctly, within correct parameters, smaller increases in corrosion rate are observed. Careful consideration of
50 6 4 2 0
100 80 60 40 20 0
00:00 hrs 4/8/23 21:00 hrs 7/8/23 18:00 hrs 11/8/23 15:00 hrs 15/8/23 12:00 hrs 19/8/23 09:00 hrs 23/8/23 Figure 6. Measurement of oxide layer deposition on copper surface. IFHE DIGEST 2026 06:00 hrs 27/8/23
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