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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Cathodic protection | 2/5 | https://en.wikipedia.org/wiki/Cathodic_protection | reference | science, encyclopedia | 2026-05-05T10:46:35.089302+00:00 | kb-cron |
In some cases, impressed current cathodic protection (ICCP) systems are used. These consist of anodes connected to a DC power source, often a transformer-rectifier connected to AC power. In the absence of an AC supply, alternative power sources may be used, such as solar panels, wind power or gas powered thermoelectric generators. Anodes for ICCP systems are available in a variety of shapes and sizes. Common anodes are tubular and solid rod shapes or continuous ribbons of various materials. These include high silicon, cast iron, graphite, mixed metal oxide (MMO), platinum and niobium coated wire and other materials. For pipelines, anodes are arranged in groundbeds either distributed or in a deep vertical hole depending on several design and field condition factors including current distribution requirements. Cathodic protection transformer-rectifier units are often custom manufactured and equipped with a variety of features, including remote monitoring and control, integral current interrupters and various type of electrical enclosures. The output DC negative terminal is connected to the structure to be protected by the cathodic protection system. The rectifier output DC positive cable is connected to the anodes. The AC power cable is connected to the rectifier input terminals. The output of the ICCP system should be optimized to provide enough current to provide protection to the target structure. Some cathodic protection transformer-rectifier units are designed with taps on the transformer windings and jumper terminals to select the voltage output of the ICCP system. Cathodic protection transformer-rectifier units for water tanks and used in other applications are made with solid state circuits to automatically adjust the operating voltage to maintain the optimum current output or structure-to-electrolyte potential. Analog or digital meters are often installed to show the operating voltages (DC and sometimes AC) and current output. For shore structures and other large complex target structures, ICCP systems are often designed with multiple independent zones of anodes with separate cathodic protection transformer-rectifier circuits.
=== Hybrid systems === Hybrid systems use a combination of the aforementioned systems to achieve some of the benefits of both, utilizing the restorative capabilities of ICCP systems but maintaining the reactive, lower cost, and easier-to-maintain nature of a galvanic anode. The system is made up of wired galvanic anodes in arrays typically 400 millimetres (16 in) apart, which are then initially powered for a short period to restore the concrete and to power ionic migration. The power supply is then taken away and the anodes are simply attached to the steel as a galvanic system. More powered phases can be administered if needed. Like galvanic systems, corrosion rate monitoring from polarization tests and half-cell potential mapping can be used to measure corrosion. Polarization is not the goal for the life of the system.
== Applications ==
=== 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 ===
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 ===