Preventing corrosion & pinhole leaks

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WHAT CAUSES PINHOLES IN COPPER PIPES?

Although no one knows the exact cause of pinhole leaks in every situation, most researchers/experts attribute their occurrence to some form of electrolytic corrosion, which is an electrochemical phenomenon in which a metal reacts with its environment causing it to deteriorate.

“The Washington Suburban Sanitary Commission (WSSC) experts believe that pinhole leaks are not the result of corrosive water but of dissimilar metals interacting and starting a battery of reactions that just consume the pipe. Otherwise, dissolving of the copper would be a widely spread problem.” (Washington Post, July 2000)

Copper pipe, though primarily comprised of copper particles, is not homogeneous and contains multiple other metallic particles including alloying metals (for strengthening the copper) and unintentional impurities. The presence of water (an electrolyte) in a copper pipe causes electric currents to flow naturally between these dissimilar metal particles which, in turn, leads to corrosion.

The cell which triggers this corrosion process has three essential components:
• anode (the metal that is corroding)
• cathode (a second metal in contact with the anode)
• electrolyte (such as water, which provides the corrosive medium)
At the anode, the corroding metal passes into the electrolyte as positively charged ions, releasing electrons which participate in the cathodic reaction. Hence, the corrosion current between the anode and the cathode consists of electrons flowing within the metal and ions flowing within the electrolyte.

The surface of one component of the pipe may act as the anode and the surface of another component (in contact with it) may act as the cathode. Usually, corrosion cells will be smaller and numerous, occurring at different points on the surface of the pipe. Anodes and cathodes may arise from differences in the constituent phases of the metal itself, from variations in surface deposits or coatings on the metal, or from variations in the electrolyte (water).

The ability of metals to resist corrosion is to some extent dependent upon their position in the Galvanic Series. The “nobler” or less reactive metals, tend to act as cathodes and remain intact, while the more reactive metal particles act as anodes and corrode. A more noble metal will not generate a flow of positive ions. The reverse of this is the least noble metal, which will generate an electrical current. The farther two metals are separated from one another in the Galvanic Series, the more powerful is the electric current and corrosion produced by their contact in the presence of an electrolyte.

The illustration below shows a typical corrosion process in a copper pipe. In the presence of water, metals in the interior of a copper pipe (such as Copper (Cu), Aluminum (Al) and Iron (Fe)) interact with one another which naturally causes electric currents to flow between them. This current causes a series of electrochemical reactions, which leads to the creation of “corrosion cells” and ultimately to the dissolution of the materials in the pipe.

In some cases, the copper in the pipe is less noble with respect to the surrounding metals, and acts as the anode and corrodes. In other cases, it is more noble, acts as the cathode and the other metals corrode. Regardless of which metal acts as the anode or cathode, the fact is that the metals in the pipe are reacting, creating corrosion cells and slowly destroying the integrity of the pipe.

 

HOW DOES COPPER KNIGHT STOP THE PINHOLES?

The COPPER KNIGHT device offered by Minuteman Distribution Systems, Inc. uses a well proven method called “Impressed Current Cathodic Protection” (ICCP) to prevent the Anode-Cathode reaction (or Corrosion) that causes the metals in copper water pipes to corrode.

ICCP uses a direct electric current from an external source that is stronger than the naturally occurring currents between the particles. This has the effect of stopping the natural corrosion of metals in their environment by creating an artificial corrosion cell that is more powerful than all the naturally occurring corrosion cells.

As shown in the illustration below, COPPER KNIGHT provides a low voltage (3 volt) current, together with a magnesium rod (which is among the least noble metals), to create a “sacrificial anode”. Due to the externally applied voltage, the magnesium rod has a higher positive potential than the pipe (the cathode) or any other particles that may be imbedded in the pipe. Thus, instead of the pipe materials corroding, the magnesium “sacrificial anode” will corrode (requiring periodic replacement). Once installed, COPPER KNIGHT halts the formation and progression of corrosion cell sites that spawn pin hole leaks.

This same Cathodic Protection method is already widely used to prevent corrosion in various systems, including in every domestic and commercial water heater in the country, underground storage tanks, marine equipment, bridges, etc. COPPER KNIGHT simply applies this same tried-and-true technology in a new way to protect the entire internal surface of copper piping systems.

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