Defect type
High · 2–4/5
Galvanic Corrosion from Mixed Metal Pipework
I traced the potable water pipework and found dissimilar metals joined directly - most often copper connected to older galvanised steel with no dielectric break. Reference: AS/NZS 3500.1. In my experience the galvanic cell at the junction accelerates corrosion, narrowing the bore, discolouring the water, and eventually causing pinhole leaks. I see this most on partial re-pipes over an older galvanised system.
Causes
- Partial pipe replacement joining copper to legacy galvanised steel without a dielectric union
- Brass or stainless fittings installed directly onto galvanised risers
- Repairs completed without matching the existing pipework metallurgy
Symptoms to look for
- Rust-coloured or cloudy water on first draw, especially on hot
- Visible rust blooms, scaling or weeping at metal-to-metal junctions
- Reduced flow rate at outlets fed through the corroded section
Remedies
- Cut out the affected junctions and reinstate with a dielectric union or full like-for-like metal
- Plan a staged full re-pipe if the galvanised mains are near end of life
- Test water quality at outlets after rectification to confirm clarity
Critical
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