plating, anodizing, & finishing Q&As since 1989
Contaminated Bright dip
We recently had the coil for our bright dip rupture and dilute/contaminate the bright dip. Is there any way to salvage the dip, or are we going to have to replace it?
We estimate the dip is about 25% water. Any response would be greatly appreciated.Marty C. [last name deleted for privacy by Editor]
- Evanston, WY.
Getting rid of the water is relatively easy-just heat the bath to somewhere in the 200-220 range and allow the water to evaporate until the specific gravity comes within range, presumably somewhere around 20%. The rest of the answer, about whether the bath is salvageable, is not so easy. Assuming you are talking about a steam coil, I have seen boiler treatment chemicals make their way to the steam coils, and it is possible, depending on the treatment chemistry, that the bath is contaminated,depending on the type of treatment chemicals you use and how long the system is in use, and how long the coil leaked, if it did, before the rupture. Organic additives in the treatment chemicals would be oxidized by the nitric at the hot temperatures, forming a tar which would float to the surface. Inorganics could be more of a problem, so an analysis for metals content would be warranted and give you peace of mind. Once the excess water is out, why don't you try to bright dip some scrap parts? That is the ultimate test anyway.
If this happened you would know it by now, but the other danger is what would happen to your steam lines if the bright dip acid got into the boiler and steam system. I've been there (with another acid bath), and it is not fun. Acid in steam lines can wreak havoc with causing leaks or causing sticking solenoids and traps. Even if you haven't yet had these problems, it would be a good idea to flush out the steam system with clean water, possibly with professional help if you don't have someone on hand with boiler/steam system experience.
- Madison Heights, Michigan
I liked Phil's response since most people don't seem to think of anything other than immediate considerations. My suggestion would be to not only to rinse out the steam lines but dump the bright dip bath if you do highly specular type work, this would also depend upon when you think you caught the leak. If it was as it happened and the operator had enough presence of mind to shut off the valves, etc., that might be a mitigating circumstance. I have worked at three companies all of whom performed a large volume of very high quality bright dip work and even if you processed scrap work you would need to process a wide variety of alloy types to know for sure you were ok. Studies have shown what various impurities in minute amounts do to different alloys and it can be a large difference in emmisivity or reflectivity. Specifically dissolved copper or iron in your case, who knows what other inorganics. At the very least I would run some AA, or ICP tests to determine relative levels!Ward Barcafer, CEF
aerospace - Wichita, Kansas
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