COPPER CORROSION


49.6 µm


1.07 mm 720 µm


2 mm Figure 2. Pits in a pipe (collected from an Australian hospital).


parameters, e.g. AS5369 table 7.2/7.3/7.4 compliance, or acceptable Ryznar/ Langelier/Puckorius indices, or compliance to the Australian Drinking Water Guidelines (2024).5 For the purposes of this article, we shall look at water quality as parameters that may influence the corrosivity of water, particularly those that may affect the internal protective layers of copper pipe work. Figure 2 images were taken from a scanning electron microscope looking at pipes from a hospital in Australia. This facility was experiencing pin holing and pipe degradation induced by: l Low flow zones. l Particulate damage (possible microbial under deposit) to oxide protective layer.


l Infrequent flow accelerating pitting corrosion.


The facility was looking to implement flow regularity to 0.8-1.5 ms–1


.


In addition, the facility was looking to implement filtration to decrease the amount of fine sedimentary material entering the pipe work and facility.


Types of corrosion Water interacts with the metal pipework in multiple ways. The interaction of corrosion is defined as ‘the phenomena and processes whereby the metal surface undergoes loss caused by chemical or electrochemical action from the surrounding medium’. The process is propagated by means of driving mechanisms. These mechanisms or corrosion types are presented in Figure 4: One of the more commonly discussed mechanisms is microbiologically induced corrosion (MIC). The mechanisms of MIC corrosion damage include: l Cathodic depolarisation: Bacteria absorbs the hydrogen formed at the cathode into their metabolism thereby activating the galvanic cell.


l Attack of biproducts of metabolism: IFHE DIGEST 2026


Water interacts with the metal pipework in multiple ways


Bacterial metabolism produces aggressive substances, for example sulphides, sulphuric acid, nitric acid, or organic acids which attack metal.


l Formation of electrochemical cells: These form underneath deposits as differences arise in aeration, salt concentration, pH, and so on. This is the most prevalent form of MIC.


CETEC use a modelling package to facilitate these calculations. The software is particularly useful in assessing variability in corrosivity with temperature, pH, and other parameters.


Factors affecting the corrosivity of water Mineral constituents of water (anions, cations, suspended matter, soluble matter), temperature, velocity, and microbial activity may all affect the corrosivity of water. Corrosivity may be predicted using these indices: l Langelier: Calculated from pH,


Conductivity, Calcium (Ca), Bicarbonate (HCO3 Temperature (T7


), Carbonate (CO3 of corrosivity or scale formation.


l Ryznar: Calculated from pH, conductivity, Calcium, Bicarbonate, carbonate, temperature.8


l Puckorius: similar to Ryznar but accounts more for the buffering capacity of water (uses the equilibrium pH rather than single reading).


l Larson-Skold: Uses chlorides, sulphate, bi carbonate, and carbonate. Index particularly used for mild steel and the impact of chlorides and sulphate contributing species on corrosivity.9


The indices used have limitations as with any index calculation. The calculation cannot factor in all contributing issues. They may, however, be useful as indicators or predictors of possible issues. The presence of organic materials such


as organic acids, complexing agents, ligands, and other reactive molecules may induce corrosion. Such materials may be present in natural waters such as river waters and recovered waters including recycled municipal water. The presence of bacteria, which is


evident in most water systems, presents the risk of microbiologically induced corrosion. The addition of sanitising agents including chlorine, chloramine, and chlorine dioxide is aimed at providing a residual disinfectant to promote biological control. Due to the reactivity of such species, the residual disinfectant diminishes with time. This is why flushing of lines becomes significant to: l Replenish the chlorine levels to reduce risk of biological growth


l Move through dead or dying microbiological material


l Move through any depositing biomatter and suspended matter


Figure 3. Scanning electron microscopy of sedimentary deposited material from copper line in an Australian healthcare facility.


Measurement of corrosion Corrosion coupons and electronic corrosion measurement methods may be useful in measuring corrosion in systems.


49 ), ) – used for prediction


1 mm


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