25 May 2005
technologies, nor to describe all types offered; however, the known effectiveness of
these devices will be stated where performance results have been verified.
Electrical Impressed Current Devices. Electrical impressed current
devices are a proven corrosion control technology, known as cathodic protection that is
used to protect lengths of underground outside surfaces of steel piping and mild steel
heat exchanger water boxes. An electrical current is applied to offset the natural
potential difference between an anode and a cathode. This technology does not prevent
scale deposition or microbiological concerns and is mainly used to protect mild steel.
Grounded Wire Devices. Grounded wire devices use a wire to ground a
pipe or structure to prevent corrosion. This device is useful when stray currents
(electrical) are causing corrosion. These devices have been touted as being able to
prevent and remove scale. The principle of operation is uncertain, but it may be based
on the fact that water impurities are charged ions and grounding affects the ions from
forming scale. The scale control properties of this technology have not been
conclusively and unambiguously verified.
Sacrificial Anodes. The use of sacrificial anodes is a proven technology
that uses blocks of metal that corrode (sacrifice) to protect the metal to which they are
attached. A sacrificial anode is more anodic than the metal to which it is attached (see
paragraph 4-5.1). This technology is actually a form of chemical corrosion protection. As
an example, a zinc or magnesium metal sacrificial anode, when attached to a mild steel
surface, becomes the anode in a corrosion reaction. The sacrificial anode is corroded
preferentially while the mild steel is provided some localized corrosion protection. The
action of sacrificial anodes is limited by the distance over which they can be effective;
usually about 0.18 to 0.56 square meters (2 to 6 square feet) around the anode is
protected, depending upon the water quality.
Filters. Filters are a proven non-chemical method for removing SS in
water. The removal of SS (dirt, silt, sand, corrosion products, and microbiological
organisms) serves to minimize both the formation of deposits and the potential for
under-deposit corrosion. Filtration affects biological control by reducing the presence of
macro- and microbiological organisms in water. Removal of SS via filtration can improve
the performance of all chemical control agents. This is comparable to a person washing
a wound before applying a disinfectant. Filters do not address deposition due to scale
nor do they control corrosion.
Magnetic Filters. Magnetic filters are a proven method for removing
magnetic iron oxides from a water stream. The most common application is the use of
magnetic filters to remove iron oxide before the condensate is returned to the boiler in
steam condensate systems. Magnetic filters usually are high capital costs.
Ultraviolet Light Generators
. Ultraviolet light generators are
method for microbiological disinfection of water. However, their effectiveness is limited
to the distance through which the ultraviolet light can penetrate a water stream. This
technology would not be effective for controlling (destroying) sessile bacteria that are