Corrosion: Definition & Diagnostic Guide
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Corrosion is the gradual chemical or electrochemical degradation of a metal pipe, fitting, or fixture caused by reactions between the metal surface and its environment, including water chemistry, dissolved gases, soil conditions, and contact with dissimilar metals. Corrosion is the primary cause of pipe failure in aging plumbing systems, responsible for pinhole leaks in copper, tuberculation in cast iron, and disintegration of galvanized steel, ultimately reducing pipe lifespan and compromising water quality.
Oxidation, Water Chemistry Factors & Metal Leaching Risks
Corrosion in plumbing occurs through several mechanisms, but all involve the transfer of electrons from the metal (oxidation) to an oxidizing agent in the surrounding environment. In water supply pipes, the water itself serves as the electrolyte that facilitates this electron transfer. Factors that accelerate corrosion include low pH (acidic water), high dissolved oxygen content, elevated chloride or sulfate concentrations, high water temperature, and low alkalinity.
Water chemistry varies by region and utility. Chloramine is less aggressive than free chlorine toward copper but can accelerate dezincification of brass fittings and components. Limestone-derived water hardness provides some natural corrosion protection through calcium carbonate film formation, but this protection varies by utility and neighborhood.
The consequences of corrosion extend beyond pipe failure. Corroding pipes leach metals into the water supply, potentially elevating copper, lead (from solder), iron, and zinc concentrations above aesthetic or health-based thresholds. Blue-green staining on fixtures indicates copper corrosion, while rusty or brown water indicates iron or steel corrosion.
Uniform, Pitting, Galvanic, Erosion & Microbiological Corrosion Types
Uniform corrosion attacks the entire pipe surface at a roughly even rate, gradually thinning the pipe wall. This is the most predictable form and is common in galvanized steel pipe.
Pitting corrosion creates small, localized penetrations through the pipe wall while leaving the surrounding material largely intact. Pitting is the primary failure mode in copper supply pipes and is difficult to predict or detect before a leak occurs.
Galvanic corrosion occurs when two dissimilar metals are in direct contact in the presence of an electrolyte (water). The more anodic metal corrodes preferentially. Common examples include copper pipe connected directly to galvanized steel fittings without a dielectric union.
Erosion corrosion combines chemical attack with mechanical wear from high-velocity water flow. This occurs at elbows, tees, and restrictions where flow velocity and turbulence are highest.
Microbiologically influenced corrosion (MIC) is caused by bacteria colonies that create localized acidic environments on the pipe surface, accelerating metal dissolution. MIC is a documented cause of cast iron sewer pipe failure in warm climates.
Pinhole Leak Repair, Repiping & Water Chemistry Treatment Services
Corrosion assessment and remediation are critical plumbing services for aging homes. Bonded Plumbworks provides pipe repair and repiping services that address corrosion-related failures, from single pinhole leak repairs to full-house repiping when systemic corrosion compromises the entire supply system.
Bonded Plumbworks’ water treatment and filtration services can modify water chemistry to reduce corrosion rates, including pH adjustment, phosphate-based corrosion inhibitors, and water softening to reduce aggressive mineral content. For properties with galvanic corrosion at copper-to-steel transitions, Bonded Plumbworks installs dielectric unions or brass transition fittings to electrically isolate the dissimilar metals.
EPA Lead and Copper Rule, ASTM D2688 & IPC Section 605.23
The EPA Lead and Copper Rule (LCR) requires water utilities to monitor for corrosion byproducts at customer taps and implement corrosion control treatment when lead or copper action levels are exceeded. ASTM D2688 covers corrosion testing methods for metallic piping materials. The State building codes require dielectric protection at dissimilar metal connections per the International Plumbing Code Section 605.22. AWWA C105 covers polyethylene encasement for ductile iron pipe to prevent soil-side corrosion.
Watts Dielectric Unions, Corro-Protec Anodes & Mueller Alloys
Watts manufactures dielectric unions and nipples for galvanic corrosion prevention. Corro-Protec produces powered anode rods for water heater corrosion protection. Mueller Industries manufactures copper tube alloys formulated for corrosion resistance. Rheem equips water heaters with sacrificial magnesium anode rods that corrode preferentially to protect the steel tank.