The Seven Copper Samurai: A Legend of Plumbing Protection

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

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 (Cu2​O) 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.

Hydrogen-Sulfide-Induced Pitting Attack 

Small amounts of dissolved hydrogen sulfide (H2​S) 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
Cu2​O 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.
H2​S can be removed from water supplies through techniques like aeration, which removes sulfide through scrubbing action and oxidation.

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

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 Cu2​O 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 Cu2​O 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

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 Cu2​O 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

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 Cu2​O 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.