Control of Pitting Corrosion of Copper Tubes in Potable Waters
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report No UWRAA 64
This research has found that a major factor in the corrosion of copper is the nature of the surface oxide which forms during exposure to water. The film is a semiconductor which may have p-type or n-type conductivity. New copper tubes generally have thin p-type films which under most circumstances perform well and protect the surface against corrosion. However, under certain conditions this film changes to an n-type film which promotes corrosion. Copper tubes which are performing satisfactorily have a p-type cuprous oxide film, whereas tubes which are corroding have an n-type cuprous oxide film.
The change from p-type behaviour occurs when the corrosion potential of exposed copper shifts significantly in the positive direction. However, the significant factors which determine this change remain to be determined.
Substantial p-type oxide films may be formed in a number of ways, by:
- controlling the corrosion potential at less than -50 mV vs SCE
- thermal oxidation using the patented UCZ (Sanco) process
- exposure to a dilute solution of hydrogen peroxide
- With further development, the latter two processes could be used fort he production of highly corrosion-resistant copper tube. The peroxide treatment may also be used in conjunction with an appropriate chemical cleaning procedure for the passivation of new and corroded installations.
Bicarbonate dosing of water, as practiced by the Hunter Water Corporation, lowers the corrosion rate of copper and assists in the formation of an adherent cuprous oxide film. A thermochemical method for determining optimum dosing levels has been proposed. The effectiveness of bicarbonate dosing may be monitored using potentiostatic current-time measurements which could be automated.
Chlorination of water causes the formation of potentially deleterious n-type films. Additional studies of the effects of the different forms of disinfection are warranted.
Photo potential and corrosion rate measurements have been found useful in this investigation and these have potential for use in the in situ monitoring of copper corrosion.
Utafiti wa Pitting Corrosion ya Matofali ya Shaba katika Maji ya Kunywa (UCCR) ni utafiti wa utafiti wa maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji ya maji. Utafiti wa URAA 64 umeonyesha kuwa sababu kuu ya kutu ya shaba ni asili ya oksidi ya uso ambayo huundwa wakati wa kuambukizwa kwa maji. Filamu ni semiconductor ambayo inaweza kuwa na aina ya p au aina ya n conductivity. Mabomba mapya ya shaba kwa ujumla yana filamu nyembamba za aina ya p ambazo chini ya hali nyingi hufanya vizuri na kulinda uso dhidi ya kutu. Hata hivyo, chini ya hali fulani filamu hii hubadilika kuwa filamu ya aina ya n ambayo huendeleza kutu. Mabomba ya shaba ambayo ni kufanya satisfactorily kuwa na p-aina shaba oksidi filamu, wakati mabomba ambayo ni corroding kuwa na n-aina shaba oksidi filamu. Mabadiliko kutoka tabia ya aina ya p hutokea wakati uwezo wa kutu wa shaba iliyofunuliwa hubadilika kwa kiasi kikubwa katika mwelekeo chanya. Hata hivyo, mambo muhimu ambayo huamua mabadiliko haya bado yanapaswa kuamuliwa. P-type oxide filamu inaweza kuundwa kwa njia kadhaa, kwa: kudhibiti uwezo wa kutu chini ya -50 mV vs SCE - oxidation joto kutumia patented UCZ (Sanco) mchakato - exposure kwa suluhisho dilute ya peroxide hidrojeni - Pamoja na maendeleo zaidi, taratibu mbili za mwisho inaweza kutumika kwa ajili ya uzalishaji wa corrosion-upinzani sana shaba bomba. Matibabu ya peroxide pia inaweza kutumika pamoja na utaratibu sahihi wa kusafisha kemikali kwa passivation ya mitambo mpya na corroded. Bicarbonate dosing ya maji, kama inavyofanywa na Hunter Water Corporation, hupunguza kiwango cha kutu ya shaba na husaidia katika malezi ya filamu ya oxide ya shaba. Mbinu ya thermochemical kwa ajili ya kuamua viwango bora dosing imependekezwa. Ufanisi wa bicarbonate dosing inaweza kufuatiliwa kwa kutumia potentiostatic sasa-wakati vipimo ambayo inaweza kuwa automatiska. Chlorination ya maji husababisha malezi ya filamu uwezekano wa kuharibu n-aina. Uchunguzi wa ziada wa athari za aina tofauti za disinfection zinahakikishwa. Picha uwezo na kiwango cha kutu vipimo wamekuwa kupatikana muhimu katika uchunguzi huu na hizi kuwa na uwezo wa matumizi katika in situ ufuatiliaji wa kutu shaba.