The optimal protection against corrosion and deposits is essential for the long-term, error-free and economical operation of steam boilers and power steam turbines, heating and cooling systems (piping, heat exchangers, condensers, tanks, pumps, cooling towers and refrigerators, etc.).
What happens to water and steam systems without protection?
Among the harmful components of the water used are salts of alkaline earth metals which precipitate at higher temperatures on heating surfaces and form an insulating layer. This prevents heat transfer. The insulating effect leads to extra energy consumption and efficiency decrease.
Under the deposited solid layer, causes the boiler pipes to overheat, which in turn causes thermal tension (thermal shock) and damage to the boiler.
In addition, scaling builds up on important components and stops them working efficiently.
The situation is similar in the case of cooling systems. Here, the precipitation and scaling of salts, for example on the lamella of cooling towers, is caused by the water movement, temperature fluctuation and evaporation. This causes the same technical and economical problems as in the case of steam systems.
Corrosion and deposition elements that have been released and circulated in the system cause erosion like sandpaper. High deposition also leads to increased circulation pressure. Both of these phenomena reduce the system’s working lifetime. (production loss, repare costs, need for pre-investment).
Iron and copper components are only resistant to the (cooling) water and vapor’s negative effects if their surface has an optimum thickness of fracture-free oxide layer.
An excessively high pH value promotes the release of this protective layer and leads to copper corrosion. An excessively low pH causes iron corrosion. Therefore, it is especially important to ensure an optimum pH range.
To achieve optimanl anti-corrosion protection, the amount of electrolytes in the water must be kept to lower than ≤ 0,2 µS/cm. The conductivity value caused by the added chemicals adds to this.
Optimally, the dissolved, remaining oxygen content is 0,002 mg/l; generally <0,005 mg/l.
The complexity of the above has shown that, to achieve optimal and economical operation, the correct water treatment method (dosing points, chemicals, etc.) can be chosen by taking into account the quality of the water used, system characteristics, state of system, user behavior (e.g. technology or food industry maybe pharmaceutical industry) as well as general and local codes and regulations such as:
MSZ EN 1074-1:2000 MSZ-09-85.0011:1988 MSZ 14121:1968 MSZ EN 442-1:1998 MSZ-09-85.0021:1989 MSZ-09-96.0721:1985 MSZ-09-96.0722:1985 MSZ-09-96.0723:1985 MSZ-09-96.0731:1985 MSZ-09-96.0732:1985 MSZ-09-96.0734:1988 MSZ-09-96.0735:1988 MSZ 1752:1996 MSZ 4668:1983 MSZ 13834-2:1985 MSZ 14258:1983 MSZ EN 297:1997 MSZ EN 303-1:2004 MSZ EN 303-4:2000 MSZ EN 303-5:2000 MSZ EN 303-6:2000 MSZ EN 625:1998 MSZ EN 12952-1:2002 MSZ EN 12953-1:2002 MSZ EN 13445-1:2004 VGB-Richtlinien für Speisewasser, Kesselwasser usw. Nr. R450L; Technische Regeln für Dampfkessel -TRD- vom Deutschen Dampfkesselausschuß (DDA) und dem Verband der Technischen Überwachungs-Vereine (VdTÜV); TRD611 - Daten für Dampferzeuger der Gruppe IV; Anforderungen an Speisewasser für Grosswasserraumkessel nach EN 12953 Teil 10 (außer Einspritzwasser)
What is corrosion?
Although most people think that corrosion is the process that occurs when oxygen and water meet with metal (aerobic corrosion), a big part of corrosion formation happens by the complete exclusion of oxygen (anaerobic corrosion). Black spots can be found on iron pipes corroded this way, iron(II)sulphide. If we remove the black iron(II)sulphide, an anodic recess is exposed which is bare iron.
Sulfate-reducting bacteria are the main cause of biocorrosion. These organisms speed up the corrosion process in the iron pipes, which are covered in water and biological deposits. These environments contain sulfate ions but no oxygen. This reaction is thermodynamically spontaneous, but slow in the absence of bacteria. The reaction on the cathode side is caused in two steps by the sulfate-reducing bacteria – sulfate reduction and further reduction of sulfur produced. On the anode side, a half-cell reaction occurs.
Biocorrosion could also be caused by a group of microorganisms living under other anaerobic conditions. These cover their energy needs by oxidising hydrogen with carbon dioxide. As a result, methane and water are formed. Such a significant number of methane producing bacteria live in oxygen-free environments (for example, under technical slugde deposits in tanks or at the bottom of slow flow pipes). If they do not find hydrogen in the area, they take elemental iron as food, so the required electrons are extracted from the iron.
We recommend the article on corrosion, published with our cooperation, on the Hungarian Wikipedia page, which you can find by clicking the following link: Wikipédia - Korrózió.
