Sulfuric Acid and Stainless Steel Tubing/Swagelok
Sulfuric Acid and Stainless Steel Tubing/Swagelok
(OP)
Does anyone have experience using 316L stainless steel tubing joined with Swagelok fittings in 93% sulfuric acid service? This piping is part of a clean-in-place (CIP) process supporting a continuous microfiltration(CMF)unit and was specified/installed by the manufacturer of the CMF unit. The sulfuric acid will be pumped, via PVDF pneumatic diaphram pump, from a 55-gallon drum and transferred through approximately 40-ft of 0.75-inch OD by 0.120-inch wall thickness SS 316L tubing into the top of a 4,000-gallon CIP tank. Based on the pump size, velocity in the tubing will be less than 6 ft/s. Dosing time will be less than 2 minutes and it is expected that an acid cleaning will be required only once every thirty days. The entire system is indoors with climate control. I am very concerned about the safety of using Swagelok fittings in this application and would greatly appreciate any feedback or opinions. Thanks.





RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
1" schedule 80, seamless carbon steel with welded joints is also suitable for this service if you can keep the acid concentration above 80%. I would be concerned about the tie-in at the injection point though if CS is used. Make sure to dehydrate the line following hydro before you introduce the acid.
You should ask how they intend to tighten the Swagelok fitting, 0.75" by 0.120" wall tubing is pretty stout stuff.
Also, remember that the flowing velocity follows a sine wave profile when diaphragm pumps are used with out pulsation dampners and backpressure valves.
Is the intent to leave the line packed with acid between cleanings?
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
If you want metals, try Chlorimet 2 or 3, Hastelloy B-2, Hastelloy C-276, High Silicon Iron, Zirconium. But expect to pay through the nose for them.
Hope this helps.
saxon
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
With the Swagelok® connections, there is a potential for crevice corrosion or stress corrosion cracking. The ferrules are a stronger but less corrosion-resistant SS grade than 316 (the seal design requires ferrules stronger than the tubing), and the tubing is near its yield stress where the ferrule presses in and seals. I once passivated a batch of Swagelok® SS fittings, and recall that it was necessary to use Type II passivation solution, rather than the Type VI (QQ-P-35C) customary for 304 and 316. Check the ferrules with a magnet and/or contact Swagelok: http://www.swagelok.com/
cub3bead,
Check out the Unlined steel corrosion by sulfuric acid (pretty bad at 80%): http://www.resistoflex.com/sulfuric_graphs.htm#7
I suggest you post this in the Corrosion engineering Forum Forum338, with a link to this thread (Thread164-92940).
Ken
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
Thanks for the useful chart. I did not intend to recommend CS for use at less than 93% but in looking back I see how my response could be read that way. Thanks for catching the poor word selection on my part.
I still would like to see the size of the guy who manages to properly install a Swagelok fitting for 0.75" X .120" wall tubing.
There has to be a better solution to the problem for periodic CIP of the membranes than has been proposed.
PVC and CPVC acid lines tend to get brittle with time and I don't think they are worth the risk.
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
WTP03
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
I am leaning towards replacing the system with teflon lined steel piping. Another alternative I am considering is using threaded teflon piping and fittings. Obviously, the mechanical integrity is less than the lined steel but the piping run is only 40-ft and moderately well protected from being damaged by impact. Either way, I still have to deal with the connection to the pump (maybe teflon lined braided hose). Any thoughts on these ideas would be greatly appreciated. As cub3bead said, "There has to be a better solution...".
Thanks.
RE: Sulfuric Acid and Stainless Steel Tubing/Swagelok
picklegt you are to be congratulated on identifying a serious safety hazard and looking for alternative solutions.