Waterslide Steel 2

[enginerding]

I am working on a job where an existing wood platform with steel supports for a water slide (appx 32' tall) has severe corrosion of all the steel members used to support and connect the wood. The steel beams and columns are experiencing large amounts of section loss. The pool operator says it is from the chlorinated water that drips off the bodies of the people waiting, but also because when someone sits in the slide at the top the water jets will shoot the water at their back and it will reflect back and pour down over the platform.

The slide design is set, and we will have this problem with large amounts of chlorinated (or maybe it's bromine?) water pouring down the steel and wood. They will be replacing much of the platform and stairs. What is the best way to protect this steel and the steel fasteners in wood? Is galvanizing enough? Stainless steel or galvanized fasteners? Do we just have them prime and paint on regular intervals? Any suggestions?

 

[stanweld]

In terms of the supports, why not replace with fiber reinforced plastics?

what materials are the fastners currently made?

 

[enginerding]

I have no experience either with designing or working with fiber reinforced plastics. It would seem to me that they would be much more flexible than steel - thus requiring somewhat different geometry than I already have set.

The fasteners now are steel. I can't tell if they were galvanized or not. Most of the rusted fasteners are lag screws.

 

[CoryPad]

You have several options, with varying cost/performance ratios.

Painted carbon steel is an option, although you will find that corrosion will still occur.

Galvanized carbon steel for the structural members and the fasteners is another easy and relatively inexpensive option, but will still exhibit corrosion over time.

The standard stainless steels are susceptible to chloride ion corrosion, so you need non-standard ones like duplex or superaustenitic grades to provide long-term service. These are available for sheet and fasteners, not at regular suppliers, rather for those that supply to the marine vessel/offshore oil/etc. industries.

Lastly, you could use titanium alloys, which are essentially immune to chloride ion corrosion, but are extremely costly.

 

[cloa]

The solution will be chlorine 1%-2% water with chloramines and chlorides at close to neutral water which is considerably worse than chloride laden water.
Seeing

http://87.230.33.128/_files/stainless_steel/Successful_Stainless_Swimming_Pool_Design.pdf

you would be worried about stress corrosion for the structural members if you used basic stainless steels

 

[cloa]

Wood particularly glued laminated timber as per this article but would design reconsideration as per this article

http://87.230.33.128/_files/stainless_steel/Successful_Stainless_Swimming_Pool_Design.pdf

 

[cloa]

Painted steel (zinc embedded)

http://www.altexcoatings.co.nz/uploads/Wet_n_Wild_ Kamikaze_Slide1.pdf

 

[bimr]

cloa,

Great reference, you deserve a star for that. Swimming pools do not "have the solution will be chlorine 1%-2% water with chloramines and chlorides at close to neutral water which is considerably worse than chloride laden water". The chlorine concentration is typically 1-3 mg/l in a pool and 3-5 mg/l in a spa. Chloramine is probably slightly higher and is formed from the reaction of ammonia (from human waste) and the chlorine.

Chloramine is the cause of burning eyes in pools and is also the cause of the corrosion. As stated in the article, chloramines deposit and accumulate. This deposition will be much higher than the concentration in the pool water.

The recommended materials from the article are the highly alloyed stainless steels 317LMn, 904L, and six-percent-molybdenum (Mo) super-austentic stainless steels along with duplex and super-duplex stainless steels such as 2205 and 2507.

 

[strider6]

have a look also at these publications:

A corrosion protection guide For steelwork in indoor swimming pool buildig

http://resource.npl.co.uk/docs/scie...guides/pdf/indoor_swimming_pool_buildings.pdf

Category: Swimming Pools

http://www.bssa.org.uk/topics.php?sub_category=99

http://www.bssa.org.uk/cms/File/Baddoo Swimming Pools (3p).pdf

http://www.euro-inox.org/pdf/case/pools/Swimmingpools_EN.pdf

S


Corrosion Prevention & Corrosion Control

 

[cloa]

All I add is if this structure can be made free draining and some regular maintenance washing by operators, you can probably get away with lower grades of stainless or even painted steel since it wouldn't as a strenuous environment as a indoor pool. Indoor pools easily get a mist of corrosive water, the structure of anoutdoor water slide only has water splashed on to it.

 

[moltenmetal]

Is the wood ACQ treated? If it is, that is likely a root cause of corrosion of the fasteners and the steel in direct contact with the wood.

ACQ wood is a known and aggressive corrodent toward steel. Singly hot-dip galvanized components (nails, screws etc.) are eaten for lunch...

Direct imbedded fasteners like lag screws are going to need to be a decent grade of stainless steel (ie 316). You're not going to be making lag screws out of AL6XN or 904L, guys! There are coated fasteners that are rated by their manufacturers for ACQ wood service, but stainless fasteners should be more durable.

For the structural steel itself, a properly engineered adn applied coating system is going to be more cost effective than making the whole thing out of an alloy. Stay away from closed sections like HSS which might get wet from the inside and corrode outward. A zinc-rich undercoat would be a good idea, followed by a durable crosslinked topcoat (ie. a 2-part epoxy or polyurethane etc.). There are plenty of coating system options which will work if they are properly applied and maintained.

 

[enginerding]

Honestly I had no idea that the new pressure treatment was so corrosive to fasteners. The structure was originally built in '85, so the original wood would not be ACQ. I do not know if they replaced any wood recently. It is good to note that better corrosion protected fasteners will be required.

A star for you for bringing my attention to something I wouldn't have thought of otherwise!

Everyone else, thank you so much for all your help as well.

 

[EdStainless]

I have seen some larger structures recently built of pressure treated wood. In most cases they have chosen to use fasteners that are double galvanized and then epoxy coated. They do not screw into the wood, they use only bolts and through holes.
Using fiberglass where ever possible for braces and such would help you out a lot.

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Plymouth Tube

 

[fdac]

A photo would be worth 1000 words. The main issues though, sound like the wet chlorinated conditions and possibly the treated timber.

If the steel section loss is not excessive, you could refurbish by cleaning up and applying a suitable coating system.

Replacing with stainless will be very expensive. I think the suggestion of the highly alloyed duplex grades is overkill for a water slide. This is not continuous immersion in sea water so 316 would probably be sufficient.

My suggestion is you need a suitable protective coating system for your steelwork. Exactly what that is depends on the required lifetime, maintenance procedures, aesthetics, application conditions, etc.