Material for Helical Cooler tubes

[isoca]

A client has asked us to manufacture a helical type cooler which is submerged in an aqueous solution of 11% sulfuric acid and 25% sodium chloride, at 55 °C. Initially, the client proposed to manufacture the tubes with CP titanium, however I have some doubts about their resistance considering the concentration of sulfuric acid. Another alternative we are considering is alloy 825. Could someone give me some help or advice about it?
Thanks

 

[EdStainless]

From the MTI MS-3
The figure is for straight acid, and this region is 15%-40% at RT up to 1%-10% at 70C.
B: Platinum; Tantalum; Zirconium (no FeCl3 or CuCl3, no chlorine); Alloy B-2 (no FeCl3 or CuCl3, no
chlorine); Silicon Bronze (no air, no chlorine); Silicon Cast Iron (F47083)

The NaCl isn't that big of a deal, but any Fe, Cu, or other ions in solution can be.
On this list when they say 'no', they mean < fractional ppm levels.

Alloys like 825 are likely to see 100mpy, C276 or 625 will be at least 50mpy.
You could look into Ti gr7/16 and see what it will do.


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P.E. Metallurgy

 

[isoca]

Dear Ed,
As usual, thanks for your help.
Unfortunately I don't have the MTI MS-3.
The corrosion values of 100 mpy for the 825 and 50 for the 625 and C-276 are actually much higher than what I was considering based on the literature. Were these values obtained from the MTI or are they based on your own experience?
Thank you very much

 

[EdStainless]

They are out of MS-3 but these are the original references sited:
1. Avesta Sheffield Corrosion Handbook for Stainless Steels (Stockholm, Sweden: Avesta
Sheffield, 1994).
2. D. L. Graver, ed., Corrosion Data Survey–Metals Section, 6th Edition (Houston, TX: NACE
International, 1985), pp.180-181.

The issue is that one table says 10mpy and the next says 40mpy for what looks to be the same conditions. Acid quality (even very minor impurities) and degree of aeration have a big effect. And for most alloys the curves for both acid concentration and temperature are very steep in this region. For some cases 15% HCl at 40C looks fine while 10% acid at 60C is more than 10x the corrosion rate. And then we can start talking about welds.

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P.E. Metallurgy