Rusting Stainless Steel Screws 1

[chicopee]

Which grade of stainless steel which would not rust to Swimming pool water. A brand new set of stainless steel screws fastening the face plate to a skimmer (above ground pool) are rusting after a couple of months of pool operation. The pool water is chlorinated with tablets and occasionally softened.

 

[Ron]

Most screws are 400 series stainless steel. It will corrode in the presence of chlorides.

 

[Metaljon]

You need a minimum of 316L for pools.

 

[blacksmith37]

Many fasteners are 316; with rolled threads they are fairly magnetic, enough that they can be picked up with a magnet. 410,304,316 will all show rust to some degree , in a wet environment with chlorides. If you don't want to wire brush ,or otherwise clean them, you could get Monel fasteners from a marine supply house.

 

[EdStainless]

My hunch is that if you nitric acid washed (20% acid, room temp, overnight) these screws before installing them, and then used a non-steel screw driver they wouldn't rust.
To be safe find hardware in Monel or Al Bronze.

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Plymouth Tube

 

[chicopee]

From observation, the rust is coming out of the center of the screw Phillips heads. I'll wait until the pool is closed for the season before following some of the above suggestions.

 

[ackattack10]

Try Nylon 606 screws if you do not need a high clamp load.

 

[EdStainless]

There is probably traces of iron in the head from forming or installation. That is why I suggested passivation to clean them. And find a brass screwdriver to install with.
You might also want to look for screws with a more open head, such as square drive. They would drain better and be less prone to corrosion.
Though moving away from stainless is the best long term plan.

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Plymouth Tube

 

[Guest102023]

Always remember that the 'stainless' part of 'stainless steel' originated in the marketing department.

 

[cloa]

Actually it was a cutlery manager that coined the stainless part of stainless steel.

 

[KENAT]

Some fields are very careful to call it 'Corrosion Resistant Steel' or CRS, which unfortunately also gets used for 'Cold Rolled Steel'.

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[Kevpoiluk]

Have a look at engineering the passive layer to improve the corrosion resistance of the stainless. It is possible to Engineer the surface to give to required corrosion resistance.

 

[bimr]

Would agree with EdStainless's comments. The screws were probably installed with a steel screwdriver when brass should have been used.

 

[gr2vessels]

Kenat, that is CRA (Corrosion Resistant Alloy), ASME nomenclature.
EdStainless is right, the carbon steel contamination from the screw driver is the culprit. Try the pickling bit too. Use silicon fill under the head to close any gap between the head and the plate. If feasible, cover the screw heads with silicon. Make sure to use 316 screws, not 304 or 400 series.
Cheers,
gr2vessels