Glass FRP in Salt Water

[metalman8357]

Hi All,

I recently conducted testing with 1/8" fiberglass laminates to determine the durability of this material in sea water. We first conducted tensile tests at room temperature on the material as a control, and then immersed some samples in salt water for 1000 hr. We found that the samples in salt water had 50% of the tensile strength and % elongation when compared to the control samples, but had almost the same modulus. So basically the samples maintained the same stiffness, but lost half of their load carrying capacity and became more brittle. Does anyone have an explanation as to how this could have happened? What is the mechanism at play here that is causing a reduction in strength? Is it the resin that is being attacked, or does the saltwater reach the glass and affect the fibers? Any insight would be greatly appreciated.

Thanks,
M

 

[btrueblood]

Both. Glass fiber can corrode in salt water (the rate of attack is tiny compared to say, steel, but it only takes a tiny flaw before a crack will develop and propagate in glass). Also, water can penetrate via osmosis through the resin and form voids near the glass; these voids become quite acidic due to leaching of excess hardener from the resin, resulting in damage to the glass reinforcement and de-bonding betwee the glass and resin matrix. Google "osmosis blisters fiberglass"...

 

[EdStainless]

You didn't just put a piece into the water did you?
The edges will wick water up and cause all sorts of problems.

If you bought a FRP tank or piping it would have a resin rich layer facing the water side.
This layer of pure resin could even be different from the bulk resin. This greatly slows the attack from the water.
There is a lot of FRP in service as seawater piping and tanks. It is a common application.
Contact a pro, like Smiths to get sound advice.

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