Water heaters This technology is also used to protect
water heaters. The electrons sent by the imposed current anode (composed of
titanium and covered with MMO) prevent the inside of the tank from rusting. In order to be recognized as effective, these anodes must comply with certain standards: A cathodic protection system is considered efficient when its potential reaches or exceeds the limits established by the cathodic protection criteria. The cathode protection criteria used come from the standard NACE SP0388-2007 (formerly RP0388-2001) of the NACE National Association of Corrosion Engineers.
Pipelines ,
West Yorkshire, England Hazardous product
pipelines are routinely protected by a coating supplemented with cathodic protection. An impressed current cathodic protection system (ICCP) for a pipeline consists of a DC power source, often an AC powered transformer rectifier and an anode, or array of anodes buried in the ground (the anode
groundbed). The DC power source would typically have a DC output of up to 50
amperes and 50
volts, but this depends on several factors, such as the size of the pipeline and coating quality. The positive DC output terminal would be connected via
cables to the anode array, while another cable would connect the negative terminal of the rectifier to the pipeline, preferably through junction boxes to allow measurements to be taken. Anodes can be installed in a groundbed consisting of a vertical hole backfilled with conductive
coke (a material that improves the performance and life of the anodes) or laid in a prepared trench, surrounded by conductive coke and backfilled. The choice of groundbed type and size depends on the application, location and soil resistivity. The DC cathodic protection current is then adjusted to the optimum level after conducting various tests including measurements of pipe-to-soil potentials or
electrode potential. When designing the system, and periodically after installation, engineers will conduct a baseline measurement campaign, during which all existing active protection systems in the area will be switched off (or as many as possible) and the
native or
natural pipe-to-electrode potential is recorded. This measurement will provide clues about how the pipeline can be sectioned into electrical systems, how many anodes and rectifiers will be needed and where they should be placed. It is sometimes more economically viable to protect a pipeline using galvanic (sacrificial) anodes. This is often the case on smaller diameter pipelines of limited length. Galvanic anodes rely on the
galvanic series potentials of the metals to drive cathodic protection current from the anode to the structure being protected. Water pipelines of various pipe materials are also provided with cathodic protection where owners determine the cost is reasonable for the expected pipeline
service life extension attributed to the application of cathodic protection.
Ships and boats s. Cathodic protection on
ships is often implemented by galvanic anodes attached to the hull and ICCP for larger vessels. Since ships are regularly removed from the water for inspections and maintenance, it is a simple task to replace the galvanic anodes. Galvanic anodes are generally shaped to reduced drag in the water and fitted flush to the hull to also try to minimize drag. Smaller vessels, with non-metallic hulls, such as
yachts, are equipped with galvanic anodes to protect areas such as
outboard motors. As with all galvanic cathodic protection, this application relies on a solid electrical connection between the anode and the item to be protected. For ICCP on ships, the anodes are usually constructed of a relatively inert material such as
platinized titanium. A DC power supply is provided within the ship and the anodes mounted on the outside of the hull. The anode cables are introduced into the ship via a
compression seal fitting and routed to the DC power source. The negative cable from the power supply is simply attached to the hull to complete the circuit. Ship ICCP anodes are flush-mounted, minimizing the effects of drag on the ship, and located a minimum 5 ft below the light
load line in an area to avoid mechanical damage. The current density required for protection is a function of velocity and considered when selecting the current capacity and location of anode placement on the hull. Some ships may require specialist treatment, for example aluminium hulls with steel fixtures will create an electrochemical cell where the aluminium hull can act as a galvanic anode and corrosion is enhanced. In cases like this, aluminium or zinc galvanic anodes can be used to offset the potential difference between the aluminium hull and the steel fixture. If the steel fixtures are large, several galvanic anodes may be required, or even a small ICCP system.
Marine Marine cathodic protection covers many areas,
jetties,
harbors,
offshore structures. The variety of different types of structure leads to a variety of systems to provide protection. Galvanic anodes are favored, but ICCP can also often be used. Because of the wide variety of structure geometry, composition, and architecture, specialized firms are often required to engineer structure-specific cathodic protection systems. Sometimes marine structures require retroactive modification to be effectively protected
Steel in concrete The application to
concrete reinforcement is slightly different in that the anodes and reference electrodes are usually embedded in the concrete at the time of construction when the concrete is being poured. The usual technique for concrete buildings, bridges and similar structures is to use ICCP, but there are systems available that use the principle of galvanic cathodic protection as well, although in the UK at least, the use of galvanic anodes for atmospherically exposed reinforced concrete structures is considered experimental. For ICCP, the principle is the same as any other ICCP system. However, in a typical atmospherically exposed concrete structure such as a bridge, there will be many more anodes distributed through the structure as opposed to an array of anodes as used on a pipeline. This makes for a more complicated system and usually an automatically controlled DC power source is used, possibly with an option for remote monitoring and operation. For buried or submerged structures, the treatment is similar to that of any other buried or submerged structure. Galvanic systems offer the advantage of being easier to retrofit and do not need any control systems as ICCP does. For pipelines constructed from
pre-stressed concrete cylinder pipe (PCCP), the techniques used for cathodic protection are generally as for steel pipelines except that the applied potential must be limited to prevent damage to the prestressing wire. The steel wire in a PCCP pipeline is stressed to the point that any corrosion of the wire can result in failure. An additional problem is that any excessive hydrogen ions as a result of an excessively negative potential can cause hydrogen embrittlement of the wire, also resulting in failure. The failure of too many wires will result in catastrophic failure of the PCCP. To implement ICCP therefore requires very careful control to ensure satisfactory protection. A simpler option is to use galvanic anodes, which are self-limiting and need no control.
Internal cathodic protection Vessels, pipelines and tanks (including
ballast tanks) which are used to store or transport liquids can also be protected from corrosion on their internal surfaces by the use of cathodic protection. ICCP and galvanic systems can be used. A common application of internal cathodic protection is water storage tanks and
power plant shell and tube heat exchangers.
Galvanized steel Galvanizing generally refers to
hot-dip galvanizing which is a way of coating steel with a layer of metallic zinc or tin. Lead or antimony are often added to the molten zinc bath, and also other metals have been studied. Galvanized coatings are quite durable in most environments because they combine the barrier properties of a
coating with some of the benefits of cathodic protection. If the zinc coating is scratched or otherwise locally damaged and steel is exposed, the surrounding areas of zinc coating form a galvanic cell with the exposed steel and protect it from corrosion. This is a form of localized cathodic protection - the zinc acts as a sacrificial anode. Galvanizing, while using the electrochemical principle of cathodic protection, is not actually cathodic but sacrificial protection. In the case of galvanizing, only areas very close to the zinc are protected. Hence, a larger area of bare steel would only be protected around the edges.
Automobiles Several companies market electronic devices claiming to mitigate corrosion for automobiles and trucks. Corrosion control professionals find they do not work. There is no peer reviewed scientific testing and validation supporting the use of the devices. In 1996 the
FTC ordered David McCready, a person that sold devices claiming to protect cars from corrosion, to pay restitution and banned the names "Rust Buster" and "Rust Evader." Under section 74.01(1) (b) of the
Competition Act Canada, no performance claims about a product or its effectiveness can be done unless it can be proven that they are based on adequate and proper tests. The Competition Bureau Canada proceeded to investigate several companies selling electronic corrosion devices in Canada. Some were forced to withdraw their product from the market as they could not support their claims scientifically. ==Testing==