SMO254 acidic seawater 1

[siretb]

Would SMO254 Alloy (6-6.5%Mo) be usable, at 40°C in acidic seawater, pH 2.3 and in a very reducing environment? (SO23)

so wz have chlorides (seawaterà
SO2 / sulfuuric qsp pH 2.3

what worries me is SO2, creating a reducing environment

 

[EdStainless]

No.
Don't worry about the SO2, it is the pH that will kill you.
For these alloys each 2 pH units below neutral roughly lowers the Cl limits by an order of magnitude.
This alloy will handle natural seawater, 20k ppm Cl and pH 8, and we know that it would still be OK at pH 6.
Then at pH 2 the Cl limit would drop from 20,000 to perhaps 200ppm, or roughly similar to 316 in neutral environment......

At that pH you need either a Ni based alloy (C22/59/686 or go non-metallic (but watch the S02 with resin systems).

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[siretb]

Thank you very much. With resins I am not overly concerned, we have experience resins . SO2
SO2 / sulfites are not good, but that's still OK

 

[siretb]

I am not expert EdStainless, but I still have a question

According to the OUTOKUMPU figure 254SMO looks suitable for pure HCl (1%) at 70°C (0.1mm/year corrosion)
sea water would have about the same chloride concentration.
You said that the acidity would kill me.
So where is the important difference?
Is it because the figure is limited to general corrosion?
Regards
Figure 254.tif uploaded

Bernard

 

[EdStainless]

Look at some of the technical papers on the subject.

http://www.outokumpu.com/en/tools-a...downloads/technical-papers/Pages/default.aspx

There is one interesting point, Outokumpu refers to 254SMO as a 6% Mo alloy, this is it's max Mo.
The other nominal 6% Mo alloys such as AL-6XN, 1925hMo, and 25-6Mo all are likely to be 21-21.5% Cr and 6.3-6.5% Mo. These alloys will have PREN in the range of 44-48, while 254SMO is 40-42.

HCl is easy, this is very different chemically from acidified seawater.
Look at corrosion tables (

http://tools.outokumpu.com/spt/corrosion/corrstart.asp?_ga=1.93539870.2047413770.1412690806)

for HCL + iron chloride, or HCl + sodium chloride, those get you closer.

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