What is meant by corrosion 2

Water treatment to prevent corrosion in pipes where different materials are used, such as stainless steel, carbon steel, copper and aluminum.

Today, “corrosion” no longer just means “rust”, it now means the change in a material. This can happen on metal, but also on plastics. However, the causes of corrosion differ. With metal, the most common effect is galvanic corrosion, which, depending on the combination of metals, can theoretically affect any metal. Plastics, on the other hand, are primarily attacked by UV light.

In the case of drinking or process water, in open or closed ring lines, cooling or hot water processes, the use of metals and plastics can lead to corrosion.

Galvanic corrosion

Two different metals that are connected to each other and are immersed in an electrolyte (saline solution) (including tap water), a chem. Reaction called galvanic corrosion. This promotes corrosion of the less noble metal.

Open water pipe system

An open system means that it is open to the ambient air and therefore exposed to oxygen. The system does not even have to be completely open for this, it is sufficient, for example, that a riser pipe ensures a constant exchange with the ambient air.

Without protection, oxygen and other contaminants can cause microbiological activity. The result is a biofilm that can cause algae, slime build-up or clogging of the pipes in the system. If nothing is done about microbial contamination, metallic pipelines will be attacked.

Lenntech offers a number of methods to prevent corrosion or to remove existing blockages in the system. We can offer UV disinfection, ozone sterilization, biological dispersion or other chemical solutions that are tailored to the system and its use. Our systems can also be built into existing systems and thus offer protection against microorganisms and corrosion.

For example, by adding corrosion inhibitors (e.g. phosphates), the water is freed from existing corrosion layers.

Another protective effect is achieved by increasing the pH value to approx. 9.2- 9.5 (for steel, the protective effect is most effective at pH 9.8).

We recommend that systems that regularly stand still be converted so that a continuous current flows through the system in order to prevent standstill corrosion.

Filters can also be installed in the system to remove the suspended particles, which in turn settle in pores and small gaps, e.g. through weld seams, and lead to corrosion. These filters have been developed to continuously filter CV cooling systems of e.g. building installations and to remove iron particles (iron oxide, magnetite) and silt from the pipes. Here we offer “magnetic bag filters”, a combination of a bag filter and a magnet that ensures that metal particles do not damage the bag of the filter.

Closed piping systems

Corrosion also occurs in closed (ring) pipe systems. Even though the system is kept closed and free of oxygen, corrosion can still occur. This type of corrosion is called “anaerobic corrosion”. Anaerobic microorganisms feed on sulfate ions in the water. The aim is therefore to lower the sulphate content of the water so as not to provide a breeding ground for the bacteria. The easiest way to do this is to set the pH between 7 and 8. At this pH and in the presence of iron ions, a precipitate of iron (II) hydroxide (Fe (OH)2) and ferrous sulphide (FeS) which can be filtered off.

Sampling and advice

Lenntech offers various test methods to check and monitor pH value, conductivity, water hardness, microbial contamination and inhibitor content.

If you are interested in a consultation for your pipe system or in a water analysis in your pipe system, we are at your disposal.

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