Mixed installations: how to associate different materials in the same installation
When you design an installation, it is important to select high-quality materials but not only this. To associate different materials (for example c-steel fittings with stainless steel pipes) can be dangerous and it can jeopardize the lifetime of the installation over time. Why? Let’s discover more about “mixed” installations.
A mixed installation is when, during the implementation of a plant, different materials are put into contact.
The materials can be:
Copper alloy (Bronze and Brass)
To associate two different materials of this list can not be a good choice, because this can generate (electrochemical) galvanic corrosion between them.
Galvanic corrosion is when we put into contact two materials with different electrochemical potential. It is possible to give a specific value of electrochemical potential to each material (this value is calculate in standard condition and it is compared to a reference electrode).
The following diagram orders the materials from the “noblest” one, on the right, to the “less noble” one, on the left, according to the electrochemical potential.
Electrochemical potential (compared to a reference electrode)
Besides, the closer the materials are (without any other element between them), the faster the corrosion develop is.
The presence of corrosion phenomena could be dangerous in drinking water applications. Moreover, by associating materials with different electrochemical potential, it is possible to change their mechanical strength, i.e. to modify their stress resistance.
It is really important to consider carefully the chosen materials for an installation and associate materials with the right electrochemical potential.
The following table shows typical installation conditions, which can generate contact between different metals. When the marker is is green, the direct contact is permitted. When the marker is red, the direct contact is not recommended. When the marker is orange, the direct contact can be considered but only under the written condition.