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download din 50979 pdf5. Surface protection
About 4% of the gross national product of a western
industrial nation is destroyed by corrosion.
5.2 Corrosion types
About 25% of this could be avoided by applying existing
Corrosion is the reaction of a metallic material with its
environment that causes a measurable change to the
material and may lead to an impairment of the function
of a component or of a complete system. This reaction is
usually of an electrochemical nature, but in some cases it
may also be of a chemical or metal-physical nature.
Surface corrosion e.g. rust
We can also observe corrosion in our daily lives:
• Rust on vehicles, railings and fences
• Creeping destruction of road structures, bridges, buildings
• Leaks in water pipelines and heating pipes made of
Corrosion is unavoidable – but the damage caused
by corrosion can be avoided through the correct planning
of suitable corrosion protection measures.
The corrosion system of a screw assembly should, under
operating conditions, be at least as corrosion-resistant as
the parts that are to be connected.
The design engineer’s job is to decide on the necessary
corrosion protection measures. Here, the wear reserve of
a corrosion protection system and the ambient conditions
have to be taken into account.
The ways in which corrosion manifests itself can vary
greatly. (See DIN 50900 for corrosion types).
Corrosion rates, reference values in μm per year
CuNi 1.5 Si
5.3 Frequently used types of coatings for fasteners
5.3.1 Non-metallic coatings
Rubbing with oil
Workpieces are immersed in oil
Bright steel parts
Suitable for short-term corrosion
protection e.g. during transport
Workpieces are immersed in acid Parts of weapons
Salt spray test approx. 0.5 h
or alkaline solutions.
Gauges and measuring technology Corrosion protection oil can
Oxide layers with a (brown) black
colour are created through reaction
No layer development
Purpose: formation of a weak
protective layer on the surface
No hydrogen embrittlement
Steel component in metal
phosphate bath or chamber with
metal phosphate solution
5–15 µm layer connected with the