Patent Application
20170029961
This disclosure relates generally to systems and methods for preventing corrosion in potable water distribution systems using copper pipes supplied by plastic mains and/or laterals rather than iron pipe.
Construction of water systems using iron piping for mains and distribution laterals is a long- and well-established practice. Copper piping has long been the preferred construction material for domestic and facility potable water distribution systems. This preference was because of copper's:
Copper plumbing systems were connected directly to the iron pipe. Because iron is anodic to copper, the iron piping acted as a sacrificial anode to the copper piping, thus protecting the copper piping from corrosion. However, recently copper is failing due to internal corrosion causing pinhole water leaks and the like. The cause and cure of this corrosion is unknown to others, who assume that the concentration of disinfecting chemicals in potable water are too low to corrode copper.
More recently, plastic has been developed and made readily available in many forms. Plastic has many desirable characteristics, including:
but it lacks many desirable characteristics of copper, such as high pressure and temperature resistance, non-flammability, resistance to punctures, and anti-bacterial and anti-fungal properties, however, on balance for many applications, plastic piping is an acceptable alternative to both iron and copper pipe for potable water systems. However, this change from iron to plastic removed the unintended iron sacrificial anode that protected the copper piping from corrosion by the potable water. The recent occurrence of interior corrosion, causing pinhole leaks in copper piping systems, is the result of this substitution of plastic pipe for the traditionally-used iron pipe.
The interior surface corrosion is caused by the redox reaction between the disinfecting chemicals used to produce the potable water and the copper pipe. Turbulence provides the activation energy need to initiate the reaction and location of the corrosion site.
To produce potable water, particulate free raw water is treated with oxidizing chemicals such as chlorine gas and/or hydrogen peroxide to destroy pathogens harmful to health. These reagents are normally added in stoichiometric excess to provide a reserve for additional purification should the potable water become contaminated during delivery. The concentrations of these purification chemicals remaining in the potable water are not great enough cause a spontaneous redox reaction at room temperature with the inside surface of the copper pipe without the introduction of energy from an outside source such as turbulent fluid flow, sound, mechanical vibration, etc. These chemicals do not cause general corrosion of the pipe interior surface when the water flow is laminar and not turbulent because not enough energy is generated by the laminar fluid flow to satisfy the activation energy needed to initiate the redox reaction. A higher temperature reduces the amount of activation energy required to initiate the redox reaction, possible allowing for a spontaneous corrosion reaction at comparable potentials.
When water flow is turbulent the corrosion becomes more random resulting in a rough interior surface. When turbulence is caused by high flow, pipe joints, rough surface, severe directional change as in a 90 degree elbow, solder prills, etc., vortices and eddies form on the down stream side of the irregularities. These vortices create energy and cause bubbles enriched with the purification chemicals. The bubbles accumulate in the stationary eddies where the turbulence-created energy supplies the necessary activation energy to initiate an anodic chemical redox reaction between the disinfectant chemicals and the interior of the copper pipe. This creates a pit in the pipe wall. This mechanism continues until the pipe wall is penetrated producing a pinhole leak. This explains why pipe corrosion tends to be located down flow of surface irregularities.
The localized redox chemical reactions between the copper pipe and the protective disinfectants that cause the pinholes will now be explained. When the necessary reactants are present in sufficient concentration, and the system is at or beyond the reaction's oxidation potential, and enough activation energy is present, a corrosion reaction ensues. When the copper pipe is one of the reactants it is corroded removing some of the metal as a copper ion. The cuprous copper ion reacts with the chloride ion and the nascent oxygen ion present from the purification disinfectant chemicals process to produce cuprous chloride, cuprous oxide, and cuprous oxichloride. These insoluble compounds are carried down-stream from the reaction site where part of the insoluble portion is deposited on the pipe wall creating a blue/green stain of corrosion products on the pipe interior and the remainder is dissolved in the flowing water. Electrons are exchanged between the participating chemical elements in this redox reaction but no external electrical current is generated, as is the case with electrolytic cell reactions involving sacrificial anode and the copper cathode.
The iron pipe acting as a sacrificial anode protecting the exterior surface copper plumbing from corrosion was an untended consequence of using iron pipe. The iron pipe was sacrificial in that it supplied electrons to the cathodic electrolytic reaction, that protected the external surface of the copper plumbing from corrosion.
In the context of controlling the redox reaction causing the internal surface corrosion of the copper plumbing, the iron pipe acting as a “sacrificial” anode did not corrode to provide electrons to the redox reaction, but raised the cathodic potential of the copper, thus causing the redox reaction to be cathodic, and thus preventing the corrosion of the interior surface of the copper pipe. Isolated copper, in the context of its redox reaction with the disinfecting chemicals, is at a potential that causes the redox reaction to be anodic, thus causing the copper to be corroded. The unintended function of the iron pipe acting as anode was to raise the potential of the copper to the cathodic potential of the redox reaction, thus preventing the corrosion of the copper pipe interior, but otherwise it does not participate in the redox reaction. It was a source of potential chemical energy.
The present invention reverses the corrosive action of the redox reaction by increasing the potential of the copper pipe to at least the reduction potential of the redox reaction thereby preventing chemical reaction with the copper. Furthermore, the present invention prevents the redox reaction between copper piping and potable water.
The potential of the redox reaction is raised to the reduction (cathodic) potential by attaching a grounded sacrificial anode, made of a metal less noble than copper, such as iron, zinc or other less noble metal, with an electrical conductor. Alternately the reduction potential can be raised by attaching the negative terminal of a grounded independent direct current power supply to the copper pipe. This prevents the interior corrosion of the copper pipe by the redox chemical reaction between the disinfectant chemicals and the interior of the copper pipe.
Because the sacrificial anode and the copper pipe share a connection through the ground which acts as an electrolyte the sacrificial anode and copper pipe is an electrolytic cell which generates an electrical current that corrodes the anode and prevents corrosion of the copper cathode.
The interior or shielded surfaces of the cathode are not electrolytically protected from corrosion by the cathodic corrosion prevention system because the interior surface is not in direct contact with the electrolyte. In the case of the pinhole development in the pipe due to interior corrosion caused by a redox chemical reaction between solution chemicals and the pipe interior there is no electrical current flow generated between the sacrificial anode and the copper pipe. The purpose of the sacrificial anode is to raise the potential of the copper to or above the cathodic potential of the redox reaction between the potable water and the copper. The sacrificial anode does not provide an electrical current to drive the redox reaction. The pipe potential determines whether the redox reaction is anodic or cathodic. The required energy of reaction is derived from the internal energy of the reacting chemicals. The activation energy required to initiate the reaction is derived from an outside source such as; turbulent fluid flow, heat, vibration, mechanical shock, ultrasound, etc. Once the reaction is initiated it tends to continue until the reactants are consumed.
The present invention comprises electrically attaching a dedicated passive cathodic corrosion prevention system to the potable water copper piping system. The passive cathodic corrosion system comprises a metal or metal alloy sacrificial anode with a standard reduction potential above that of copper. Less noble metals such as iron, zinc, aluminum, magnesium, titanium, and alloys thereof may also be used to protect various components of the plumbing system from corrosion.
As an alternative to a passive cathodic corrosion prevention system an active cathodic corrosion prevention system may be used. The active cathodic corrosion protection system comprises an independent source of DC power, a voltage controller and a non-sacrificial grounding anode. The negative terminal of the voltage controller is connected to the potable water copper piping system. The system is maintained at a voltage at or above the reduction potential of copper. As previously mentioned, in recent times copper piping is failing, due to internal corrosion, causing pinhole water leaks. The cause and cure of this corrosion is unknown to others, who assume that the concentration of disinfecting chemicals in potable water are too low to corrode copper The present invention claims otherwise.
Further, the methods and systems disclosed herein also protect the exterior surfaces from electrolytic corrosion by maintaining the copper surface at or above the reduction potential of elemental copper. These methods and systems also protects the interior surface of the copper pipe by maintaining its interior surface potential of the pipe above the reduction potential above of the redox potential of the chemical reaction between the pipe interior surface and the excess disinfectant chemicals used to prepare and protect the potable water.
Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show illustrations in accordance with example embodiments.
The systems and methods disclosed herein for preventing corrosion of copper piping and the prevention of copper pipe pin holes comprise electrically attaching a dedicated cathodic corrosion protection system to the copper potable water piping system. The passive cathodic protection system may be composed of a sacrificial anode made of a metal or metal alloy, which is less noble than copper. The anode is in contact with the ground and electrically connected to the copper pipe system. The ground acts as an electrolyte forming an electrolytic cell of the sacrificial anode and the exterior surface of the copper pipe, which are in contact with the ground. This allows the transport of ions to the copper surface where they are reduced, thus preventing the dissolution of metallic copper. If copper ions were present in the electrolyte they would be reduced and plated on the pipe as elemental copper. The sacrificial anode maintains the copper piping system at a voltage above the reduction potential of copper in the potable water environment, thus making the redox chemical reaction between the copper pipe and the potable water cathodic, and thus preventing the interior corrosion of the copper piping system.
Alternatively, an active cathode corrosion protection system supplied by an independent electrical energy source may be used. The positive terminal of the active system is connected to ground by a non-sacrificial anode. The negative terminal is connected to the copper piping system. The voltage between the non-sacrificial grounding anode and the copper piping system is maintained at a level at or above the reduction potential of copper. As previously mentioned above, this prevents formation of interior pinhole leaks as well as exterior corrosion of copper. All connections must be electrically conductive.
Water flows through the copper piping system, past solder prill 140, soldered tee 150, and soldered 90 degree elbow 160, creates turbulence at points 170. In past copper piping systems, these turbulent flow points would have provided the activation energy required to initiate a redox reaction between the copper piped and the potable water; however the iron mains and laterals raised the potential of the copper to the level where the Redox reaction became cathodic, so that corrosion did not occur near the turbulent flow points. Note that solder prill 140, soldered tee 150, and soldered 90 degree elbow 160 are exemplary components of the system, and are only used to explain where turbulence and pinholes may occur. Any number of these components, from none to many, may be present in the system.
The present invention adds sacrificial anode 180, which is electrically connected to the copper piping by, e.g., electrical conductor 190 and clamps 200. While electrical conductor 190 and clamps 200 are provided as an example, any means of electrically connecting sacrificial node 180 to the copper piping may be used, and one of ordinary skill in the art will recognize other such connections. At least part of sacrificial anode 180 must be grounded, as indicated by the cross hatches in
The ground medium provides the electrical return leg of the electrolytic circuit. The required size of sacrificial anode 180 depends both on the area and the size of the copper piping system. The required number and location of sacrificial anodes 180 is dependent on the size of the copper piping system, the electrical conductivity of the common ground medium, and the voltage difference between sacrificial anode 180 and the protected copper piping system cathode. Iron metal may be used for a sacrificial anode for more benign conditions, but zinc, aluminum alloy, magnesium, or titanium may be required for more electrically resistant grounding medium and/or larger area piping systems.
Although the invention has been described in terms of particular embodiments, one of ordinary skill in the art, in light of the teachings herein, will be able to generate additional embodiments and modifications without departing from the spirit of, or exceeding the scope of, the claimed invention. This invention is not limited to using the particular elements, materials, or components described herein, and other elements, materials, or components will be equivalent for the purposes of this invention. Accordingly, it is understood that the drawings and the descriptions herein are proffered only to facilitate comprehension of the invention and should not be construed to limit the scope thereof.
