Optimal protection against corrosion and deposits is essential for steam boilers and power plant steam turbines, heating and cooling systems (pipes, pipelines, heat exchangers, condensers, tanks, etc.).
To ensure the long-term, faultless, and economical operation of pumps, cooling towers, and refrigeration equipment, etc.
What happens in water and steam systems without protection?
Destructive components of the used water include, among others, the salts of alkali metals, which precipitate on heating surfaces at higher temperatures and form an insulating layer. This inhibits heat transfer. The insulating effect leads to increased energy consumption and reduced efficiency.
Under the deposited solid layer on the surface of boiler pipes, overheating occurs, leading to thermal stress cracks (thermal shock), causing damage to the boiler.
Furthermore, scale deposits on essential components for safe operation can hinder their functionality. The same situation applies to cooling systems. Here, the precipitation and deposition of salts, for example, on the lamellas of cooling towers, are facilitated by water movement, pressure, temperature fluctuations, and evaporation, causing the same technical and economic disadvantages as in the case of steam operations. Detached corrosion and deposition particles circulating in the system cause erosion like sandpaper. Significant deposits also lead to an increase in circulation pressure. Both phenomena result in a significant reduction in the system’s service life (production loss, repair and associated costs, the need for premature investments). Iron and copper components are only resistant to the negative effects of (cooling) water and steam if they have an optimal thickness, crack-free oxide layer on their surface. Excessively high pH promotes the detachment of this protective layer and leads to copper corrosion. Excessively low pH causes iron corrosion. Therefore, it is particularly important to set the optimal pH value range. To achieve optimal corrosion protection, the number of electrolytes in the water should be kept as low as possible, ≤ 0.2 µS/cm. The conductivity value caused by dosed chemicals contributes to this. The dissolved residual free oxygen content should ideally be < 0.002 mg/l; generally <0.005 mg/l. In conclusion: The complexity of the above description highlights that in order to select the correct water treatment method (dosage points, chemicals, etc.) for achieving optimal and economical operation, one must take into account the quality of the used water, the system’s characteristics, condition, the nature of the users (e.g., technology or food industry, or pharmaceuticals), as well as general and local regulations and requirements, 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 the corrosion?
Corrosion is a natural process that occurs when metal reacts with its environment. While many people think of corrosion as the result of the interaction between oxygen and water (aerobic corrosion), a significant portion of corrosion occurs in the absence of oxygen (anaerobic corrosion). In this manner, corroded iron pipes may show black spots of iron(II) sulphide on their surfaces. If the black iron(II) sulphide is removed, an anodic pit is revealed, with bare iron on the surface. Biocorrosion is primarily caused by sulphate-reducing bacteria. These organisms accelerate the corrosion process in iron pipes covered with water and biological deposits. Such environments contain sulphate ions but no oxygen. This reaction occurs spontaneously thermodynamically but very slowly in the absence of bacteria. The reaction is driven by sulphate-reducing bacteria in two steps on the cathode side – sulphate reduction and further reduction of the produced sulphur. On the anode side, a half-cell reaction occurs. Another group of microorganisms that live under anaerobic conditions can also be responsible for biocorrosion. They derive their energy from the oxidation of hydrogen with carbon dioxide. This process produces methane and water. These methane-producing bacteria live in oxygen-free environments (e.g., beneath technical sludge deposits in tanks, at the bottom of slow-flow pipes). If they don’t find hydrogen in the medium, they take in elemental iron as a food source, extracting the necessary electrons from the iron. We recommend checking our collaborative contribution to the Hungarian Wikipedia article on corrosion by clicking on the following link: Wikipédia – Corrosion.