REVIEWOF REMEDIAL TREATMENTS FOR COPPER CORROSION BY-PRODUCT RELEASE (BLUE WATER),PITTING AND CUPROSOLVENCY
ReportNo WSAA 205
· The complex issue of corrosion of copper water pipes has been shown ashaving links to manufacturing processes, modes of installation of copper pipeand water quality. A number of preventative and remedial strategy options havebeen reviewed with respect to cuprosolvency, pitting and blue water corrosion.Apart from cuprosolvency, addressing the problem is difficult due to the poorunderstanding of corrosion mechanisms, and the limited data on, and evaluationof, remedial and preventative treatments. The options identified are largelyexperimental, unproven and cannot be used with total certainty in new cases ofcorrosion.
· Remedial strategies for corrosion problems reported in the literaturebefore 1980, with the exception of ‘type 3’ pitting, are well documented. Inthese cases, the corrosion problems were widespread within the reticulation andremedial strategies focused on systematic implementation across toreticulation. Remedial strategies included:
Pitting in cold, high alkalinity, high ionic strength waters. (i.e. type ‘1’ pitting)
The removal of carbonaceous films formed during tube manufacture (both preventative and remedial treatments);
Pitting in hot water with high sulphate concentrations. (‘type 2’ pitting)
Water chemistry protocols to limit the bicarbonate: sulphate ion ratio to greater than 1:1;
(some aspects thereof)
Modification to plumbing design to eliminate the “seldom used” branches or long horizontal sections of small diameter
· Reliableremedial strategies are described for cuprosolvency and involve systematicimplementation of water chemistry through pH adjustment or corrosion inhibitorusage. The on-going treatment cost of corrosion inhibitors requires continualand specific assessment of inhibitor selection and dosing for water companiesadopting the second option (in a manner similar to other water treatmentchemicals).
· A number ofoutstanding cases of pitting and blue water are known to exist for which themechanisms and remedial treatments are unproven. An improvement in theknowledge of tube surface and water chemistry risk factors for copper corrosionin low alkalinity, low ionic strength waters is reflected in the literatureover the last 5 years. Whilst the detailed mechanism of the corrosion modes isnot completely understood, significant advances include:
¨ Microbiologically influenced corrosionhas been associated with a significant number of the anomalous corrosion cases;
¨ The inability to form a protectivesurface film on copper in the first six months of exposure to potable water isrecognised as a feature of the failure process;
¨ Recognition that the surface morphologyand composition can influence the corrosion behaviour.
· Althoughsignificant progress has been made (in the last five years) with regard to thedevelopment of experimental remedial solutions, limited case history isdocumented focusing on the implementation of appropriate remedial strategies.
· Recent,successful remediation options for pitting and blue water (described in theliterature) have predominantly focused on water treatment parameters, biocidaltreatments or plumbing design. A significant opportunity exists to apply andvalidate these treatments in water supplies at two levels:
¨ In systems experiencing relatively highfailure rates, remedial measures should be targeted at making systematicchanges (such as pipe manufacture practices, water treatment protocols, etc.);
¨ In systems experiencing low butpersistent failure rates (which still exceed consumer expectations), remedialaction implementation should potentially focus on controlling the problem atthe failure location, ie. the consumer’s property.
· Prospectiveremedial options include:
¨ Heat shock and long termchlorine/chloramine residual and/or bicarbonate, as a remedial treatment,including re-chlorination and bicarbonate dosing as a systematic approach ormicro-chlorination units in a ‘failure targeted’ approach;
¨ Surface treatments to prevent blue waterand pitting corrosion in low alkalinity waters containing low or no residualchlorine concentrations as developed by Bremer et al, (systematic and ‘failuretargeted’);
¨ Surface treatments to eliminate thecarbonaceous films formed during manufacture and form a passive, non-poroussurface layer (systematic);
¨ Plumbing design, installation, testingand commissioning practices (systematic).
These treatmentsare expected to have a significant impact on the remediation and prevention ofblue water and pitting corrosion initiation. It is unclear whether thesetreatments will be effective on well developed corrosion pits.
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