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What would be the best type of steel to specify? Would a heavy galvanization suffice?

Are there specialty paints/coatings available for this particular application? If so, how long do they last?

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  • $\begingroup$ Afaik mainly nickel alloy is used. $\endgroup$ – peterh says reinstate Monica Jan 20 '15 at 18:48
  • $\begingroup$ This is a notoriously difficult problem to solve. Even the big boys (corrugated metal pipe dealers such as Contech and Big R) don't have a one-size-fits-all solution that always works in highly corrosive environments. Bottom line: the determining question regarding structural metal in corrosive applications is "How long do you want it to last?" $\endgroup$ – Rick supports Monica Jan 20 '15 at 23:15
  • $\begingroup$ What is the location within the building where this steel is to be used? A handrail has very different requirements from a steel support beam for the roof. $\endgroup$ – hazzey Jan 21 '15 at 1:29
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Safety issues in a "natatorium" (swimming pool) environment include the following:

1) Chlorine and other high acid gases that can corrode the steel. Both galvanization and paints/coatings can help, until the weather wears the protection away.

2) Water freezing and thawing. Basically, you need to keep water away from the pool at times when in it is likely to expand or contract through freezing and thawing, so that this doesn't happen. Mostly a problem for northern climes.

3) Algae, molds, etc. You need to keep away organic products that will encourage them to grow, and create destructive acids or other compounds.

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Most stainless steels contain nickel around 10%. It is combined normally with chrome and molybdenum.

The main problem, that a natatorium (i.e. swimming pool) is a highly corrosive environment, and most "stainless" steel alloy is a little bit, slowly, corroding here:

enter image description here

Even aluminium gets a greyish-white surface layer.

In the case of constructive materials, the situation is a little bit better. First, because they are mostly in the wall, and the concrete around them partially protects them.

In case of freely available surfaces, plastic or painting is yet used.

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  • $\begingroup$ Stainless steel corrodes. Even in concrete, 304 and 316 will experience severe deep pitting within 5 to 7 years - as we have discovered from long term exposure testing. It's success or failure very much depends upon the surface condition and the grain structure. If surface treatment removes the surface layer, then corrodents will attack at an inter-granular level. $\endgroup$ – AsymLabs Oct 22 '15 at 10:18
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The presence of a swimming pool in a natatorium causes a few unique issues that most buildings do not experience:

  • High humidity levels - Water is everywhere and is frequently sprayed. Most buildings have ventilation systems that keep the humidity low.
  • High chloride content - Chlorine is used for a disinfectant. Chlorine will rapidly cause corrosion on bare steel.

Each of these items individually is bad for steel, but together they can cause serious issues. As this table shows, swimming pools are as harsh an environment as chemical plants and coastal areas.

To mitigate the corrosive nature of the environment, a double protection system is employed. This system consists of:

  • A layer of hot dip galvanizing or zinc rich primer and 2 coats of epoxy
  • A field applied addition layer of epoxy or acrylic urethane

The top layer is essentially a first line of defense. It will need to periodically be replaced. The galvanized or zinc layer is there to provide extra time when the top layers fail.

These types of systems typically use contrasting colors for each coating layer. This way any reduction of protection due to a missing layer is readily visible.

Together this system can protect the steel structure for up to 50 years.

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