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Bear with me, I'll get to the chemistry soon.

I have a float tank that I want to attach a skimmer to. Unfortunately, the enclosure is weakened by cutting a hole out of the ABS plastic. The weight of the salt water (1.25SG) to somehow causes a bend in the plastic just enough that getting a good seal isn't possible without additional support.

The float tank consists primary of (pardon the units) 800lbs of $\ce{MgSO4}$ Heptahydrate raised to about 96 degrees Fahrenheit. The pH is roughly 7.2.

My concern with supporting the ABS plastic is that the Epsom salt water may corrode the metal, if it somehow isn't protected by a liner. Would I absolutely need to have stainless steel, or could I get by with galvanized (which is much cheaper).

In case it matters, I estimate the volume of water directly pressing on the skimmer opening to be about 9+ gallons (again at 1.25sg).

Thank you for answering non-chemist, Ben

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    $\begingroup$ "pardon the units" No! $\endgroup$ – Georg Mar 12 '15 at 16:10
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I'm a chemist, but this seems more like a question for an engineer. Unfortunately I don't have some references to back up my answer.

If you use galvanized steel you have a protective layer on the outside of the steel. As soon as you handle it for attaching, welding... you destroy/scratch/bruise this top layer and the underlying steel gets in contact with the salt solution which is normally aggressive towards metal. This mostly is right for e.g. chloride salts in a mix with oxygen and I'm not quite sure how corrosive MgSO4 is. Here is a paper about corrosive currents of steel in Saltwater/cement solutions, but that`s not my speciality: http://www.jmst.org/fileup/PDF/pass543.pdf

Stainless steel is more robust, because it's an alloy of steel and chromium. Therefor it's not just covered with a protective layer but saver as a whole. An I guess it's therefor recommended.

(As a side note, some years ago I had a field trip to a big chemistry company with lots and lots of pipelines. We had some time there with the technical stuff in charge of teh pipelines. They explained, that the most annoying pipelines were the ones with salt water, since it was more aggressive towards the pipes than acids, mineral oils, gases etc.)

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  • $\begingroup$ I remember hearing that in some seawater piping applications, brass was the preferred material, not steel, but I couldn't find any good references for this after a quick Googling. $\endgroup$ – Curt F. Mar 12 '15 at 17:09
  • $\begingroup$ You may find it worth your time to acquaint yourself with the concept of streaming potentials. $\endgroup$ – A.K. Dec 8 '16 at 6:09

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