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Molybdenum and its applications

 

Thanks to Molybdenum Stainless Steel, Swimming Pools Last “Forever”

An article by IMOA’s Technical Director, Dr Nicole Kinsman

Molybdenum containing stainless steels are widely used to line indoor and outdoor swimming pools across Europe. The first stainless steel linings have been installed around 1970 in Austria. Today, there are over 5000 installations in Europe, mainly in Austria, Germany and Switzerland, but also in Belgium, France, Italy, Czech Republic and Slovakia among others.

In the early years the molybdenum-free 1.4301 (Type 304, UNS S30400) stainless steel has been used for outdoor pools and the 2% molybdenum containing 1.4404 (Type 316L, UNS S31603) stainless steel for the harsher conditions in indoor pools. However, for many years now 1.4404 stainless steel is the standard material for indoor and outdoor applications because of its increased corrosion resistance in chloride containing waters. Stainless steel grades with higher molybdenum content are necessary in swimming pools with more aggressive waters, such as hot spring, brine or seawater pools. Stainless steel can be used for new installations and to restore older pools. Both applications are about equally frequent.

Figures 1, 2 and 3 show the installation of a stainless steel lining in an indoor pool in Vienna, Austria. The goal was the rehabilitation and modernization of the pool. The existing basin has been lined with a new stainless steel skin. This successful renovation project showcases the harmonic integration of a modern stainless steel pool into a grand historic structure. The weight of this stainless steel multipurpose pool is about thirteen metric tons. Berndorf Bäderbau in Berndorf, Austria is the industry leader in Europe and has built over 4000 installations. They have an annual consumption of about 2000 metric tons of stainless steel.

 

Figure 1: demolition works

Figure 2: assembly and installation

Figure 3: finished pool

Figures 1 to 3: Rehabilitation of a historic indoor pool in Vienna, Austria.

Stainless steel linings provide many advantages over conventional tile or plastic pools:

Hygiene:

They are more hygienic because they have a smoother, joint-free surface where bacteria and deposits do not attach easily. The smooth surface can also be cleaned easily. Because of their superior hygienic properties, stainless steels are widely used in sanitary applications such as clean rooms, hospitals, dairies and food processing plants as well as pharmaceutical and chemical plants.

Maintenance:

Due to the corrosion and weather resistance of stainless steel the maintenance is minimal. All that is required to maintain the original finish of the stainless steel is wiping or cleaning of the surfaces.

Longevity:

Stainless steel pools do not change their appearance over time. If properly maintained they keep their original finish indefinitely. Stainless steel will remain leakfree as long as the water chemistry is properly maintained. Stainless steel does not need to be retiled or patched. Stainless steel is also extremely resistant to shock and other mechanical influences. It does not crack or erode easily.

Installation:

Stainless steel pools are prefabricated at the company and then fit on the building site. This is much faster than installation of tiles which has to be done mostly on site. Installation of outdoor stainless steel pools can also be carried out in winter when it is difficult to install other lining materials. This is a big advantage in the case of retrofits. The restoration can be carried out during the winter season when public outdoor pools are closed without losing any business. It is also possible to integrate stainless steel, stairs, jets, slides, showers, and other swimming pool equipment directly into the skin without creating discontinuities and sites for potential leaks. The walls can be curved or have any conceivable shape (Figures 4 and 5). A stainless steel pool can either be built by lining the walls and floors of a pre-built basin with stainless steel sheet or it can be built as a freestanding, self supporting structure that does not necessarily require extensive preparation of the site.

Figure 4

Figure 5

Figures 4 and 5:
Outdoor and indoor pool installations with several attractions.

Design changes:

If a pool design has to be changed, for example if the size of the pool has to be increased or decreased or if new installations have to be made, it is easy to cut and weld the stainless steel and blend any changes so they become invisible. It is much more difficult to blend the old with the new with tile and almost impossible with plastic liners.

 

Winterising:

Stainless steel pools do not need any special protective measures. The cost of stainless steel pools is at the high end of the spectrum compared to alternative materials, comparable with high quality tile installations. However, the longevity and the low maintenance cost quickly make up for the higher initial investment. For this reason many communities across Europe have chosen this economical solution.


Pictures courtesy of Berndorf Bäderbau / www.berndorf-baederbau.com