Alt. for 304/316SS in chlorinous environment

My company utilizes 304 SS and 316 SS for several fabricated items that serve one of our water treatment systems. These materials serve
us well however when the water is chlorinated with either chlorine gas or hypochlorite prior to entering our system we see corrosion of the metal.
What I'm looking for is a material that can be utilized in these environments that can withstand the chlorine vapors that emanate from the water. The material will need should not be exorbitant in cost in relation to 304 or 316 and I will also need a material that is used to produce hardware such as handles, hinges, nuts, bots, etc.
Thank you all for taking the time to read this message and for any input that you may have regarding my questions.
CD
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I was looking for such an alternative year before last for a machine design to be used in food processing, and which is hosed down once daily with chlorine bleach / water. Frankly a metal possibly isn't made that you can AFFORD to use. Nickel plating of sufficient quality and thickness MIGHT work, but plating can flake or be chipped, and as soon as the base metal is exposed it starts to corrode at breakneck speed. Gold plating obviously is pretty much the same. Tapped holes are a problem anyway with plating. In some cases Delrin (or actually acetal copolymer) is a good substitute for 300 series stainless, as it is USDA approved for contact with food and, thus, probably also water in water treatment applications. It absorbs very little moisture and does not warp, twist or swell. Obviously, it's not strong enough for all uses. It is, however, quite machinable (at low tool speeds to keep melting and fusing to a minimum).
You are probably aware, but I'll mention it anyway, with a strong electrolyte like chlorine you have to be particularly sensitive to electrolytic ("Galvanic") coupling. Using stainless fasteners and keeping aluminum well away from stainless are a couple of important rules, of course, but that's only a beginning. Get yourself a Galvanic table and refer to it often. If you can't find one on the Web I'll type one up from a printed reference I have and send it to ya. See my Web site for a valid email address.
Mark 'Sporky' Stapleton Watermark Design, LLC http://www.h2omarkdesign.com
CD wrote:

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Mark:
1) Actually acetal copolymer is Celcon, and Delrin is the homopolymer.
2) Acetal copolymer is a miserable choice for a bleach environment. Technical information from the manufacturer,Ticona, says that:
"Prolonged or continuous exposure of Celcon acetal copolymer in aqueous solutions containing hypochlorite ions should be limited to hypochlorite concentrations typically found in U.S. domestic potable water supplies".
At higher concentrations Celcon has a nasty tendency to environmental stress cracking. Go to your local big box home improvement store and look at the boxes for the toilet ballcocks. You will see a red lettered warning about not using (acetal) in toilet tanks containing high concentrations of chlorine.
Pittsburgh Pete
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Pittsburgh Pete wrote:

Pete, I'm aware that Delrin is the homopolymer. My advice was intended to be an "either/or" recommendation, although that wasn't entirely clear from the way I wrote it. I WASN'T aware the Delrin or the copolymer shouldn't be used in high chlorine concentrations. Actually, in practice I've seen both used with very good results in the application I described where the machinery was washed down once daily with bleach/water (a fairly stiff concentration). Never degraded the least in over more than six months of constant use. But the water treatment system might be a lot different if gaseous chlorine can be found in the environment at times.
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snipped-for-privacy@yahoo.com (CD) wrote in message

If you haven't already done so, go look at the Nickel Institute web site. It is at www.nidi.org. They have lots of useful information about using stainless steels in various environments. For example, you could look at their publication #10087, "Stainless steel for potable water treatment plants (PWTP) - Guidelines". You may need a more expensive higher alloyed steel than 316.
Pittsburgh Pete
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snipped-for-privacy@hotmail.com (Pittsburgh Pete) wrote in message

Try CPVC for your application. In longhand, that is post-chlorinated polyvinyl chloride. The saturation of the polymer chain with chlorine is so high that further chlorination is not likely, it has very good oxidation resistance, is heat stable past 200F., and is fairly cheap with many off the shelf items in mass production already.(especially pipes, elbows and valves)For strength members such as bolts, look at some of the exotic alloys such as Inconel. The cost of these alloys is high, but when amortized over their longer life, they are cost-effective.-Jitney
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Reportedly, high-phosphorus electroless nickel plating can have good corrosion resistance in such environments. You may want to contact the Nickel Institute in Toronto (www.nidi.org) and ask for a consultation with Ron Duncan. He consults on electroless nickel, with the fee paid by the institute.
You might also try posting your question on www.finishing.com, asking if high-phosphorus electroless nickel will work.
If you decide to try electroless nickel, I would research the effect of phosphorus content carefully. My guess is you'll need > 10.5-11% P by weight. Thickness? Base material? Find a good plater, and discuss the application and design/condition of the parts (edge burrs, blind holes, etc.) You might try North American EN (www.northamericanen.com) where they routinely do > 11% P.
See ASTM B 733 for a general spec. on electroless nickel plating. See ASTM B 571, Section 3.1 for a good bend test to check adhesion. The relative phosphorus content can be checked with a technique called ICP-OES. Galbraith Labs (www.galbraith.com) will do this for $60/element. On their sample submission form, ask them to strip the nickel from an aluminum test strip with nitric acid and then report the concentrations of P and Ni in solution, $120 total, ~2 week turn-around.
Good luck!
Grant

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