Corrosion - A discreet enemy

Corrosion galvanique 1- Darspec
In a water network, the danger can come not from the pressure, but from the material itself. Indeed, a material’s number one enemy is often its own nature. Corrosion, known as rust, is a well-known phenomenon. Among the types of corrosion, that of steel is the most apparent 5 .
Rouille - Darspec
Statue Liberté - Darspec
However, steel is not the only material that corrodes, take copper for example. Copper corrosion resembles a greenish layer that forms on the material’s outer surface. It can be seen on the Statue of Liberty. Several other materials can corrode. The difference is that the corroded layer is not always visible 7 .

Why does a material corrode?

Simply put, a pure or freshly processed material is often chemically unstable. To stabilize, it must undergo a chemical change. When a material comes into contact with oxygen or water (highly reactive elements), a chemical reaction occurs on its surface. This reaction is called oxidation. When a material oxidizes, a layer of corrosion forms on its surface 4 .

Galvanic corrosion

Galvanic corrosion is a corrosion phenomenon that occurs when two different metals are in contact with each other and a conductive liquid flows through them. When two materials like copper and steel are joined together and water circulates within them, an electrochemical reaction occurs. This reaction will gradually degrade the material and create an oxide layer on its surface 2 .
Rouille extérieure - Darspec
This corrosion poses several problems. It can weaken the integrity of the pipe connections, leading to leaks and breaks. It can also reduce the available flow rate and network performance as debris breaks off and accumulates inside the system. Furthermore, since this corrosion occurs when metals come into contact with water, the oxidized layer forms inside the pipes, making it difficult to identify. The longer it remains untreated, the thicker this layer will become, exacerbating existing problems 8 .

Danger and solutions

Galvanic corrosion poses several dangers to the drinking water system. For example, when metal dissolves, metallic particles are released and can contaminate the water. Depending on the material of the pipes, this contamination can lead to iron, copper, zinc and sometimes even lead poisoning, particularly in older pipes 1 .
Furthermore, the constant accumulation of debris in the water system can also trap bacteria, release metals and contaminate the water. In some cases, the deposits can become so significant that the surface of the pipes becomes rough. The water flow will slow down locally, promoting bacteria growth and adhesion 1 .
Débris et bactéries - Darspec

Finally, corroded metal can also alter the water’s chemistry: changing the pH, increasing conductivity, or even reducing the disinfectant’s effectiveness. The water becomes less stable and more susceptible to contamination 6 .

The dangers associated with galvanic corrosion are numerous. However, it is possible to prevent its formation. Several solutions are possible, for example: 

- Choosing identical materials (steel on steel or copper on copper) 3,

- Adding a dielectric fitting to prevent the passage of electric current between the metals 3,

- Adding protective coatings (paint, anti-corrosion tape) 3.

Peinture - Darspec
In short, galvanic corrosion is very problematic for drinking water networks. Whether it is the risk of water damage or contamination, the prevention of this phenomenon is essential.

References

1. https://www.canada.ca/fr/sante-canada/services/publications/vie-saine/document-conseils-controle-corrosion-reseaux-distribution-eau-potable/page-4-document-conseils-controle-corrosion-reseaux-distribution-eau-potable.html

2. https://publications.gc.ca/collections/collection_2020/pch/CH57-4-22-2019-fra.pdf

3. https://www.phcppros.com/articles/2867-corrosion-plumbing-piping

4. https://www.camfil.com/fr-ca/infos/electronique-optique/effets-de-la-corrosion?srsltid=AfmBOooAToYhZcIQ-X3D6HVUS_P8NsCakOwmO9fl6TjE_vEAxlbPwZ-u

5. https://www.q8oils.com/fr/travail-des-metaux/la-corrosion-expliquee/

6. https://www.canada.ca/fr/sante-canada/services/publications/vie-saine/document-conseils-controle-corrosion-reseaux-distribution-eau-potable.html

7. https://www.corrosion-doctors.org/Landmarks/Statue.htm

8. https://primis.phmsa.dot.gov/comm/FactSheets/FSInternalCorrosion.htm

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