Rust-free stainless steel: The clear number one for use in swimming pools
“What goes together, comes together” is a common German saying. In our case, this refers to the use of rust-free stainless steel in swimming pools. If you look closely around an indoor or outdoor swimming pool, you will quickly notice that rust-free stainless steel can be seen in many places – railings, steps, cladding and showers are just a few examples of how this refined material is used.
Easy to clean and corrosion resistant
But why is so much rust-free stainless steel used in swimming pools? The answer lies in the properties of the material. One major factor is the corrosion resistance. Many fixtures are in constant contact with water and must therefore have special protection against corrosion.
This protection is provided by what is called a passivation layer of chromium oxide. It forms naturally as chromium reacts with the moisture in the air at the surface of the material. If the surface is damaged, the passivation layer heals itself. This special property is what gives rust-free steels their corrosion resistance.
Another reason for the use of rust-free stainless steel in swimming pools is the easy cleaning of the smooth surfaces. Additionally, structures of rust-free stainless steel require relatively little maintenance. At outdoor pools, the material is also appreciated for its resistance to frost.
The right material in the right place
Even though austenitic stainless steels are fundamentally suited for the wet and corrosive environment in swimming pools, it is important to also keep an eye on the chloride level in the pool water. As this can rise in many cases, austentic materials alloyed with molybdenum should be used, such as 1.4404. These materials are resistant up to a chloride ion level of approximately 1,000 mg/l. These values are intended as guidance only since operating conditions (e.g. flows, temperatures) can have a significant impact. Currently, 1.4404 is the standard material used for pool lining.
In thermal, brine and ocean swimming pools, higher salt concentrations and temperatures must be expected. Higher-alloyed stainless steels (e.g 1.4462) must therefore be used here.
Atmospheric corrosion in the swimming pool
In indoor baths, consideration must be given to the high corrosion potential from the buildup of chlorides due to evaporation and drying effects. This can lead to damage from stress corrosion. For load-bearing parts that are not or cannot be regularly cleaned, only the stainless steels 1.4565, 1.4529 and 1.4547 may be used.
The listed tools have nickel contents of above 20% and are additionally alloyed with up to 7% molybdenum. This results in a very high corrosion resistance. The corrosion resistance class according to the type certification must be always be taken into account for load-bearing parts. A concept must also be created for regular inspection and cleaning. And finally: The cleaning concept must reduce deposits of chlorides on the surfaces of the parts to a minimum.