Contact corrosion

Contact corrosion refers to corrosion phenomena that can occur when one metal is in permanent direct "contact" with another metal. When non-recommended materials are combined, separating layers or similar measures are therefore advised. The standards listed below provide an overview of the recommended and non-recommended combinations.

Even though direct contact is minimised when sealing elements are used, this should be taken into account when selecting the materials in the direction of flow.

The steel/stainless steel combination has long been established state of the art and has been used
for decades without complaints or claims.

- Metalwork 2.1 (1) and 3.1 (2) The risk of possible contact corrosion must be taken into account. Table I.1 shows the possible combinations. Separations or protective coatings can be used to prevent it.

- Metalwork 2.1 (1) The risk of possible corrosion in the direction of water flow must be taken into account. Table I.1 shows the possible combinations.

The so-called flow rule per DIN 1988-7 applies to drinking water installations that are permanently exposed to water and states "that, in the direction of flow of the medium, more noble metals must always be used. In particular, care must be taken to ensure that no steel or galvanised steel pipes are installed downstream of copper pipes in the direction of flow (enamelled hot water tanks!). Copper pipes downstream of galvanised pipes, by contrast, generally do not pose a problem." (Source)

- Galvanised steel (GSt) can be installed downstream of Al, Pb, Zn, S.S without any problem, but not downstream of copper (Cu).

- Stainless steel (S.S) can be installed downstream of all the metals listed.