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In some industrial processes, such as in power plants, damages causedby corrosion represent a tremendous cost factor. For example, steam generators, used in virtually any industry are subject to the damaging and thereby costly effects of corrosion.
The term corrosion describes what everyone knows when his car shows rust or electric contactsdo not function anymore, because they are corroded. Objects made of steel often remain fully intact, while the body of an old car will eventually collapse completely, because the metal under the paint has turned into a brown, powdery material. According to the German Industry Standard DIN 50900 part I, corrosion describes the reaction of metal toits environment, resulting in measurable changes in the material, which may change the characteristics of a metallic object or the completesystem it is part of, thereby degrading its function. In most cases itis an electrochemical reaction that leads to corrosion, but it mightalso be the result of a chemical or metal physical reaction. This definition already indicates that corrosion means far more than simply rust.
In some industrial processes, such as in power plants, damages caused by corrosion represent a tremendous cost factor. For example, steam generators are used in virtually any industry. Just about anymanufacturing plant at least operates one generator of this type. Yet, all steam generators are subject to the damaging and thereby costlyeffects of corrosion. It is estimated, that corrosion causes annual costs of more than 210 Billion Euro. This includes areas, such as publicutility companies (36.5 Billion Euros), as well as the paper and cellulose industry (4.6 Billion Euros).
Steam made from pure water
Industrial plants generate electricity for their own use. Public power plants produce electricity for public use. Both use power generators of differing dimensions. However, all of them need the same type of pure water which is made from raw water that is passed through a number of filter and demineralization stages.
This continuous flow of purified water is fed into the steam generator which produces thesteam that drives the turbine used to generate electricity. Part of the steam is used to preheat the pure water before it enters the steamgenerator. After passing through the generator, the steam turns into condensate, which is then collected and fed back into the cycle together with newly purified water. The overall construction of such a powerplant depends on the thermodynamic characteristics typical of the respective plant. Energy generation requires high investments into technology. This means, maintenance of the system is of vital importance in order to keep profitability, safety and life cycle at a high level.
Pure water has corrosive effects when it gets in contact with thesteam generator and the condensing system. In addition, leaks may result in chemicals entering the system, thereby increasing the corrosiveeffect. For example, a leaking condenser might lead to untreated cooling water mixing with the purified water. Leaking seals at the turbines and pumps might allow oxygen to enter into the feeding water and increase its aggressive potential. In order to prevent such risks, special corrosion inhibitors are usually added to the feeding water.
In order to protect the capital investment of the power plant, effective chemical-physical treatment of the feeding water is absolutely necessary, especially during maintenance work at the boiler and condensing systems.
Poor quality of the water fed into the boiler may lead to severe problems, such as tindering, pitting or corrosion of thecomponents inside the boiler and condensing systems. The danger of corrosion can be limited by means of adding special chemical additives to the purified feeding water. Most plant operators measure the water quality by means of conductivity sensors and/or pH probes. However, while such measurements are suitable to sufficiently analyse the water quality, they provide no information as to the condition of the piping of the condensing systems.
Practical solution
Using the 4…20 mA real-time signal of the CorrTran MV transmitter, plant operatorsare able to compare historical corrosion data with up-to-date measurements. In this way, they can determine instantly whether the water quality has changed, whether there are changes in the chemical setup of the water or whether the corrosion inhibitors perform correctly. All these conditions have an effect on the corrosion of the piping and can bedetected and monitored efficiently. Following the principles of proactive maintenance, the plant operator is able to prepare and schedule the exchange of components affected by corrosion before the effect of corrosion leads to costly damage. The transmitter assists the operatorin monitoring both general and local corrosion. Especially local corrosion can lead to severe damage if it is not detected at an early stage. This type of corrosion is able to actually puncture a pipe within ashort time. Yet, it can be counteracted effectively if corrective measures are taken before it is too late.
The standard probes usedby CorrTran MV for corrosion detection, consist of three electrodes. One of them induces a low-power signal, while the others measure the resulting potential and current. In order to gain precise measuring results, these electrodes need to be made of the same material as the piping or container to be monitored. The electrodes are placed immediatelywithin the flow of the corrosive media and are induced with a weak signal. Within a few minutes, this signal is monitored and analyzed by the transmitter in order to gain an exact impression of the rate of corrosion. As a result, service technicians are provided with the necessary information to schedule repair and service work according to the actual need, putting them into a position to react before corrosion hasgone too far and degrades the ongoing process. In this way, the transmitter not only contributes to saving time and costs. It also is the basis for proactive maintenance and makes corrosion monitoring part of the daily routine.
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