Metal finishing Q&As since 1989

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316SS Tubing Contamination Problem

I have several coils of 1/8 OD, .020 wall 316SS tubing which were contaminated during a solution anneal process. The culprit was a plastic tie similar to that used for tying garbage bags being left on one of the coils. The result is a dark grey coating, probably carbon, on the tubing. I would like to remove this contamination from the inside of the tubing (the outside is not as important). Can I safely circulate some solution through the tubing to remove the contamination and if so what do you recommend? The coil lengths are 50 ft but would be cut to 10 ft in production.

Robert Doty

2006

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2006

If the color is from the plastic tie, it is no longer PVC, but some oxide of it or a thin layer of carbon.
For starters, cut 5' off of each end and look at both cut ends. I seriously doubt if the contamination could have gotten that far back. If it did, cut another 5" off and look again.
Cleaning operations will probably cost more than replacing the tubing.
If it is basically a carbon smut, then a solvent like carbon disulfide might work. Try it in two inch pieces.
If it is still slightly plastic, soaking in THF, tetrahydorfuran might work.
You might be able to re-anneal it and turn it to a purer carbon You might be able to flow oxygen thru it at a high temp and literally burn it out.
Chromic and sulfuric acid mixtures in high concentrations might remove it, but the waste disposal cost is totally unreal.
Can you mechanically take it out?

James Watts
Navarre, Florida