Copper Tube Corrosion and Domestic water piping. A dramatic retelling of a scientific article addressing identification and mitigation
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The Seven Copper Samurai: A Legend of Plumbing Protection
The Seven Copper Samurai: A Legend of Plumbing Protection
In the hidden copper veins of every home, a silent war rages. Seven fierce warriors — each born from a flaw, a weakness, or an oversight — roam the pipes, ready to attack when least expected. These Seven Copper Samurai represent the greatest enemies to clean, reliable plumbing, forged over decades of water’s relentless march through metal.
Their names are whispered by plumbers like an ancient cautionary tale:
The Flux Ghost
The Sulfur Shadow
The Flow Demon
The Solvent Monk
The Deposit Bandit
The Cold Ronin
The Hot Shogun
Each brings their own weapon of destruction, each a master of copper corrosion in their own terrifying way. Homeowners seldom see these foes coming — until a leak, a burst, or a water stain reveals their silent work.
But there is hope.
For every army of corrosion, there is a champion. The Legendary Repiping Master rises to stand against these seven — trained in the ways of perfect piping practice, armed with knowledge, tools, and the wisdom of the Copper Tube Handbook and ASTM Standard B828. From the walls of the Copper Dojo, the Master stands guard, prepared to banish these corrosion warriors and restore clean, safe water for every household.
This is their story.
Plumbing and code compliance are key to producing lasting quality products.
College Fund Plumbing
Master's of Repiping
No matter which corrosion Ronin is attacking your home's copper piping, College Fund Plumbing is ready to defend your domicile. From sneaky leaks to hidden corrosion, we have the tools, skills, and knowledge to stop the Seven Copper Samurai in their tracks — and restore your plumbing to legendary condition.
Call us today, and let the Repiping Master protect what matters most.
The Flux Ghost
The Flux Ghost
Soldering-Flux-Induced Pitting Attack
Soldering-Flux-Induced Pitting Attack
This type of corrosion often occurs in cold-water lines or infrequently used hot-water lines and is linked to the use of aggressive or excessive soldering flux. The pits are characterized by porous, reddish-brown cuprous oxide (Cu2O) and covered with green copper-corrosion products, typically basic copper carbonate or copper chloride(s). These pits usually appear in narrow bands parallel to the tube's longitudinal axis. It can be confirmed by detecting chlorides and sometimes zinc in pits using energy dispersive spectroscopy (EDS). Mitigation involves adhering to industry standards for materials and practices (ASTM B813 and B828). There are no known methods to mitigate this attack once it starts; systems are typically replaced after multiple leaks.
The Sulfer Shadow
The Sulfer Shadow
Hydrogen-Sulfide-Induced Pitting Attack
Small amounts of dissolved hydrogen sulfide (H2S) in water can cause pitting in metallic materials, even at concentrations as low as 0.020 mg per liter. This type of pitting occurs randomly, with pits containing dark-reddish-brown to nearly black
Cu2O and overlaid with friable green tubercles of copper-corrosion products, often copper sulfate mixed with black copper sulfide(s). Black, porous layers of copper sulfide(s) are associated with this pitting.
H2S can be removed from water supplies through techniques like aeration, which removes sulfide through scrubbing action and oxidation.
The Flow Demon
The Flow Demon
Erosion Corrosion
This accelerated attack is caused by localized high-velocity/turbulent water flow, commonly in circulating domestic hot water (DHW) systems. Affected areas are typically grooved, bright, shiny, and free of residual corrosion products. U-shaped pits often indicate the direction of water flow. It's often associated with soft waters, particularly those with dissolved oxygen and/or carbon dioxide (CO2), and is facilitated by water temperatures above 140 F and flow rates exceeding 4 to 5 fps. Poor workmanship, such as unreamed cut tube ends or dents, is a leading cause. Mitigation strategies include keeping water velocity below 4 to 5 fps, eliminating abrasive suspended solids, and maintaining water temperatures below 130 F. In cold-water lines, erosion corrosion is usually due to high water pressure (over 80 psig) causing velocities above 7 to 8 fps, and/or poor workmanship.
Cavitation: A specific form of erosion corrosion where vapor/gaseous bubbles form at low pressure and collapse at high pressure, creating shock waves that destroy the protective tarnish film on copper. Cavitated copper is distinguished by the absence of corrosion products and the presence of bright, sponge-like, rounded pits.
The Solvent Monk
The Solvent Monk
Cuprosolvency
Cuprosolvency
Also known as "blue/green" water, this is a slow, general corrosion of copper tubes and fittings that can stain plumbing fixtures and raise copper levels in water after periods of no flow. While annoying, it hasn't been known to cause tube or fitting perforations. It occurs when a protective Cu2O film doesn't form, leading to a thin, loosely adherent layer of blue to blue-green copper-corrosion products (e.g., copper hydroxide) during water stagnation. Cuprosolvent water is typically very soft, with a pH less than 7, and low alkalinity, usually due to dissolved CO2. It's often self-correcting when water flow resumes, allowing the formation of a Cu2O film. Persistent cuprosolvency can be mitigated by raising the water's pH to about 8 with chemicals like sodium hydroxide or calcium hydroxide, or by installing neutralizing filters.
The Deposit Bandit
The Deposit Bandit
Concentration-Cell Corrosion
Concentration-Cell Corrosion
In copper domestic water systems, this often refers to oxygen differential corrosion, where deterioration occurs preferentially as pits under deposits where oxygen content is lower. Deposits are almost always suspended solids like iron oxides or silica/sand, often from corroding cast-iron/ductile-iron mains or galvanized-steel service lines. Identifying and eliminating the source of these deposits, such as through water treatment or filtration, can mitigate this corrosion.
The Cold Ronin
Chemistry-Related Cold-Water Pitting
Also called nodular or Type 1 pitting, this is linked to low-pH, high-alkalinity well water and combinations of well and surface supplies. It typically occurs in cold-water lines and is caused by dissolved CO2. Pits contain reddish-brown Cu2O and are covered with green copper-corrosion products, primarily basic copper carbonate. This pitting is random, unlike flux-induced pitting. Waters associated with this pitting typically have a pH of 7.0 to 7.7 and more than 25 mg per liter of dissolved CO2. Reducing dissolved CO2 content, by raising the water's pH to about 8 and reducing CO2 to less than 5 mg per liter (e.g., using caustic soda, lime, or soda ash), is the most viable mitigation.
The Hot Shogun
The Hot Shogun
Chemistry-Related Hot-Water Pitting
Chemistry-Related Hot-Water Pitting
This is associated with domestic hot waters containing small amounts of iron, manganese, and/or aluminum, with pitting initiated at concentrations as low as 0.10 mg/L for iron and aluminum, and 0.03 mg/L for manganese. It is a concern when water is heated above 160 F and black cupric oxide (CuO) is present. Pits contain reddish-brown Cu2O and are covered with green copper-corrosion products, often copper sulfate, containing small amounts of the pit-initiating metal. Reducing manganese and/or iron at treatment plants, mitigating corrosion of hot-water heaters/storage tanks, reducing water temperature to 120-130 F, and adding sodium-silicate/organic-polyphosphate inhibitors can mitigate this. Aluminum-induced pitting can be mitigated by raising pH to 8.5 and reducing aluminum content below 0.1 mg/L, often by adjusting aluminum sulfate coagulation at the treatment plant or by reducing water temperature. Avoiding sacrificial aluminum-alloy anodes in hot-water heaters can also reduce aluminum content.
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