System contents more metals, for example Fe and Cu, Zn or Al
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System is threatened by a galvanic corrosion
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Important damage threatens of colorful metal´s parts and their alloys (cooper, brass) and corrosion of system iron parts too.
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It proves expressive increasing content of dissolved Cu and other colorful metals in system water.
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Treatment by chemicals based on azole is necesarry. Common anti-corrosion chemicals don´t work.
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Regular treatment is necesarry by biocide, ideally by nonoxidizing biocide
| Fe | Al | Zn | Cu influencing metals | |
| Fe | O | B | A | B |
| Al | A | O | A | C |
| Zn | C | B | O | C |
| Cu | A | A | A | O |
|
Influenced metal |
A – influencing adversely |
Galvanic corrosion
It arises by joining two dissimilar metals and their exposure to the corrosive enviroment. Nobler metal (cathode) corrodes slower than it would corrode itself. Less noble metal (anode) on the contrary corrodes faster than it isn´t connect conductively with second. This phenomenon is used in practice for cathodic protection of anode sacrificed. In our case, it is completely undesirable phenomenon
Non-softened water is used
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System is threatened to scale forming.
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Low flow threatens, low efficiency of cooling to the complete destruction of equipment.
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Acidic cleaning can be inevitable, but it is always a significant risk of damage to the iron parts of the system.
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According to the temperature in the system and content of hardness to the supplemental water suffices either regular treatment with the help of dispersant scale, or it is necessary to treat the water by using of cation ion-exchanger
There is a scale in pipe of untreated system. Evidently there are vestiges of corrosion under deposits, that means you can´t rely on anti-corrosion protection using the scale there is rarely corrosion completely without control and opportunity of treatment under its.
Completely softened water or osmotic water is used
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System is threatened by corrosion of iron parts
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It can prove yellowing, turbidity or redness of water system.
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Water can be clear if it is reguraly exchange. After there is a higher danger that risk will be underestimated by service because water looks clearly.
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It is often necessary in connection with other parameters of the supplemental water "cut" to reduce its corrosion.
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Treatment by anti-corrosion chemicals is necesarry
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Nowdayds the most effective chemicals are based on molybdenum and silicates supplemented by azoles for present protection of colorful metals.
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If nitrites are used like a catcher of oxygen, oxidizing biocide can’tusn´t be use together.
Corrosion
Corrosion is spontaneous, gradual excitement of metal or metals by chemical or electrochemical reaction with the environment. It can pass off take in the atmosphere or other gases, in water and other liquids, soils and various chemical substances that are in contact with the material. This excitement can prove differently; from changes in appearance to a complete breakdown of integrity.
Corrosion is caused by electrochemical processes. The main factor of corrosion is atmospheric oxygen, respectively. hydroxide group (OH), followed by anions, which arised from acids (CO32-, Cl-, NO2-, SO42-, etc.) Hydrogen ions of acids are replaced with metal ions to produce the salts.
Biocide treatment isn´t practised regurally
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System is threatened by corrosion of iron parts and grow of biofilm.
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Surface of system proves like a smooth, slimy which are under the water. We can try a bath with reserve water.
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Water can be pure if it is often exchanged. Usually water can be greenish or yellowish to reddish because of corrosion under biofilm´s places.
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Regular biocide treatment is necesarry. If the system wasn´t treat for a long time it would be needful intensive cleaning from corrosion and biological deposits. This cleaning is possible do during operation but with caution.
Unsuitable biocide is used
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In spite of biocide treatment system is full of biofilm and biological deposits
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System water is colored by dissolved iron into yellowish or reddish.
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It´s necessary to check all parameters and put on biocide treatment, which correspond to existing conditions.
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Very effective sodium hypochlorite can be unsuitable in some cases. It affects strong corrosion.
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On the contrary nonoxidative biocides don´t have to be always effective or wrong type of biocide is chosen because of parameters of the water system.
Comparision of water from sort with water from system affects by corrosion due the insufficient biocide treatment.
Biological (organic) pollution is caused especially by bacteria, eventually blue-green algae or algae depends on the type of system.
Because of it is necessary to cultivate and identify which types of microorganisms in a system dominate and by this put on a biocide protection. Generally always effective, sodium hypochlorite can be unsuitable for the system because of its considerable corrosion, especially where isn´t frequent replacement of the water. Amount of chloride ions is carrying into system, and it is really dangerous for iron systems. For service is often confusing that system can be also affected even it is completely closed and only water is supplemented to its. In closed systems there are ideal conditions for biological growth thanks to optimum temperature of water, eventually thanks to present substances, which are food for the organisms so they can reproduce.
System is treated by unsuitable chemicals
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High pressure on low price of treatment leads to hire a firm without sufficient experience eventually a firm without suitable chemicals in its portfolio.
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The most common mistake is treatment by the same chemicals, which are used in opened cooling systems or steam boilers.
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They are not allowed to protect system for a long time against corrosion, which is higher risk of this treatment.
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Water is usually turbid and is colored in yellow and red if it isn´t exchanged regularly.
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System is fauled by scale and other deposits. Supplier often apologizes that treatment of system won´t be better or oxygen treatment is a common part of service.
An extreme example of closed loop treats by unsuitable chemicals. System is affected by galvanic and general corrosion and currently excessive amount of microorganisms was found and they accelerate the process of corrosion.
Watermeter supplemental water is missing of or it is not monitored
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In the system there are the water losses due by leaks or defects which can remain undetected for a long time.
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This leads to increased payment for water or scale formation because of increasing amount of hardness.
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If the water is softened, the system can be threaten by corrosion, which is masked by the fact that water is periodically rotated to losses, which reduces the effective amount of dissolved iron in the system water - water looks clear, even if the system is highly corrosive.
Finding the place, where water is lost can be a hard peanut. Cracked pipes or faulty seals don´t have to be the main problem. Human factor is good to be checked too. An extreme case happened in a factory, where the softened water from the system is used for car wash of employees. Watermeter after installation wasn´t allowed turn off and culprits were quickly discovered.
Nitrites are used like a oxygen scavengers
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Pitting corrosion threatens in system water when we don´t stand required concentration of oxygen scavengers.
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Nitrites are delecious food for microorganisms and unsuitable biocide treatment causes that is not possible to dose them sufficiently and speed of corrosion strongly rises.
Typical picture of pitting corrosion