Contact corrosion (galvanic corrosion). DIN 50900, T1 (April 1982) gives this definition: Accelerated corrosion of a metal area due to a corrosive element consisting of a metal/metal or metal/electron-conducting solid pairing with differing free corrosion potentials. The metal area affected by accelerated corrosion acts here as the anode of the corrosive element.

The structural elements of mechanical seals particularly susceptible to this type of corrosion are seal faces and stationary seats consisting in either case of several materials, e. g. face housing with soldered face bodies of tungsten carbide.

Stationary seat, whose basic body of Cr-steel 1.4021 is corroded at the point of transition to the silver brazing

Often the first sign of damage by corrosion is increased leakage; the dismantled mechanical seal looks to be undamaged. Closer examination reveals a warping of the sliding faces and the suspected heavy corrosion is confirmed when the carbide seal face is removed mechanically. In an advanced state of corrosion the carbide seal faces are often cracked in comet fashion from the inside outward, because the strength bond between solder and carrier material no longer exists