Review of Remedial Treatments for Copper Corrosion By-Product Release (Blue Water), Pitting and Cuprosolvency
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report No UWRAA 205
- The complex issue of corrosion of copper water pipes has been shown as having links to manufacturing processes, modes of installation of copper pipe and water quality. A number of preventative and remedial strategy options have been reviewed with respect to cupro-solvency, pitting and blue water corrosion. Apart from cupro-solvency, addressing the problem is difficult due to the poor understanding of corrosion mechanisms, and the limited data on, and evaluation of, remedial and preventative treatments. The options identified are largely experimental, unproven and cannot be used with total certainty in new cases of corrosion.
- Remedial strategies for corrosion problems reported in the literature before 1980, with the exception of ‘type 3’ pitting, are well documented. In these cases, the corrosion problems were widespread within the reticulation and remedial strategies focused on systematic implementation across to reticulation. Remedial strategies included:
- Pitting in cold, high alkalinity, high ionic strength waters. (i.e. type ‘1’ pitting)
- Pitting in hot water with high sulphate concentrations. (‘type 2’ pitting)
- Blue water (some aspects thereof)
- The removal of carbonaceous films formed during tube manufacture (both preventative and remedial treatments);
- Water chemistry protocols to limit the bicarbonate: sulphate ion ratio to greater than 1:1;
- Modification to plumbing design to eliminate the “seldom used” branches or long horizontal sections of small diameter
Reliable remedial strategies are described for cupro-solvency and involve systematic implementation of water chemistry through pH adjustment or corrosion inhibitor usage. The on-going treatment cost of corrosion inhibitors requires continual and specific assessment of inhibitor selection and dosing for water companies adopting the second option (in a manner similar to other water treatment chemicals).
A number of outstanding cases of pitting and blue water are known to exist for which the mechanisms and remedial treatments are unproven. An improvement in the knowledge of tube surface and water chemistry risk factors for copper corrosion in low alkalinity, low ionic strength waters is reflected in the literature over the last 5 years. Whilst the detailed mechanism of the corrosion modes is not completely understood, significant advances include:
- Microbiologically influenced corrosion has been associated with a significant number of the anomalous corrosion cases;
- The inability to form a protective surface film on copper in the first six months of exposure to potable water is recognised as a feature of the failure process;
- Recognition that the surface morphology and composition can influence the corrosion behaviour.
Although significant progress has been made (in the last five years) with regard to the development of experimental remedial solutions, limited case history is documented focusing on the implementation of appropriate remedial strategies.
Recent, successful remediation options for pitting and blue water (described in the literature) have predominantly focused on water treatment parameters, biocidal treatments or plumbing design. A significant opportunity exists to apply and validate these treatments in water supplies at two levels:
In systems experiencing relatively high failure rates, remedial measures should be targeted at making systematic changes (such as pipe manufacture practices, water treatment protocols, etc.);
In systems experiencing low but persistent failure rates (which still exceed consumer expectations), remedial action implementation should potentially focus on controlling the problem at the failure location, i.e.. the consumer’s property.
Prospective remedial options include:
- The maintenance of hot water circuits above 55C;
- Heat shock and long term chlorine/chloramine residual and/or bicarbonate, as a remedial treatment, including re-chlorination and bicarbonate dosing as a systematic approach or micro-chlorination units in a ‘failure targeted’ approach;
- Surface treatments to prevent blue water and pitting corrosion in low alkalinity waters containing low or no residual chlorine concentrations as developed by Bremer et al, (systematic and ‘failure targeted’);
- Surface treatments to eliminate the carbonaceous films formed during manufacture and form a passive, non-porous surface layer (systematic);
- Plumbing design, installation, testing and commissioning practices (systematic).
These treatments are expected to have a significant impact on the remediation and prevention of blue water and pitting corrosion initiation. It is unclear whether these treatments will be effective on well developed corrosion pits.