above-ground pool failure

[PSUengineer1]

I have a 10-year old above-ground pool where severe rust is present on the metal pool walls. Current liner is only 2 years old. A portion of the pool wall collapsed. I am attributing the collapse to age-related deterioration of the pool walls (rust), causing the pool wall to collapse at the bolted lap splice connection.

How did water get between the liner and pool wall? Rust is visible on the metal slotted tube that goes over the v-bead coping near the failure point.

My thoughts:

Vinyl liners contract with decreases in temperature, which can result in liner separation from the coping over winter months. Thermal contraction of the liner may have contributed to separation of the liner from the coping. Other factors including direct accidental force to the interface of the liner and coping or excessive movement of the pool wall may have contributed to separation of the liner from the coping. Sufficient evidence is not available to definitively determine what caused the pool liner to separate from the top coping, allowing water to rust the pool.

Please look at attached photos and comment.

Thanks!

 

[MikeHalloran]

Vinyl weld seams are not perfect.
Vinyl and other polymer films are often porous; even the best will have pinholes.
It's possible that the new liner was damaged at installation, or was inherently more porous than the old one. Even if they came from the same source, recent versions may be different.
There may be tricks that the replacement installers did not know or heed; e.g. if the steel was already suprerficially rusted, or just dirty, special precautions might have been necessary to prevent abrasion of the new liner.
The steel may have been painted with chalking paint, which disappears over time. Even the most durable paint has a finite lifetime.

Also see capillarity. If (when) water splashed/flowed over an edge where the vinyl and steel were in nominal contact but not sealed, that water _must_ flow into the gap.

You got ten years of good service. Roll up the remains and take it to the junkyard.




Mike Halloran
Pembroke Pines, FL, USA

 

[Ron]

Condensation.

 

[dhengr]

Just trapped moisture and condensation on the steel every time it cools. The dew point can be high because the water in the pool stays warm, but every night the steel exterior cools and condensation forms on it. Any liner separation just exacerbates this situation by holding more moisture, and recycling it. Moisture vapor could also be migrating up into the system from the ground below.

 

[msquared48]

And the pool was chlorinated...

Mike McCann
MMC Engineering

 

[msquared48]

Evaporation, condensation, chlorine, steel = rust = eventual failure without maintenance or a change.

Might consider switching from Chlorine to either Bromine or an Ozone system to purify the water. Still might have the same problem with Bromine, though. Don't know about that.

Mike McCann
MMC Engineering

 

[IRstuff]

This is why bridges are constantly being repainted.

TTFN
faq731-376

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[PSUengineer1]

What about earth movement being a contributing factor to liner seperation?

 

[charliealphabravo]

That is some pretty serious corrosion considering the timeframe. I would probably check the possible chemical/galvanic interactions. Is the steel in contact with aluminum? How do the pool chemicals interact with the steel? What is the spec on the galvanization? Does the pool shell package come with a sacrificial anode that perhaps was never installed? Is it a salt water pool or a chlorine pool? I'm not convinced yet that just being wet is the problem.

 

[charliealphabravo]

The other think I notice is the presence of a relatively new deck. You might look into the possible chemical reactions between the pressure treated wood and the galvanized pool shell. Some pressure treating methods are not compatible with galvanized steel and can cause significant corrosion.