Material selection for sodium chloride stream

[chicagoeng]

I need to purchase some thermowells and pressure instrument diaphragms for pipe which has a saturated brine solution at 280 degF that is about 25 wt% NaCl? Any concerns with long-term corrosion issues if I use Hastelloy C material? Would titanium be a better choice than Hastelloy C? Where can I find corrosion rate information for NaCl and these materials?

 

[EdStainless]

What else is in the solution? What is the pH?
There are lots of good sources for corrosion data.

Alloys such as C-22, 59, and 686 may be suitable. We will have to check corrosion data.
Regular Grade 2 comercially pure Ti is probably not a good choice.
The pH is very important.

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[TVP]

If the pH is above 3, then one of the titanium grades will be suitable. Crevice corrosion can be a problem for Grade 2 at temperatures above ~ 85 C at lower pH. If there will be any oxidizing species in addition to the NaCl brine, then the passivity of Ti will be extended to lower pH. Grade 12 and Grade 7 have increasing resistance to crevice corrosion relative to Grade 2.

 

[chicagoeng]

The pH is 10.5 to 11.0. Other components in the solution include Ca (~5 ppm), Mg (~1 ppm), SO4 (~500 ppm) and Si (~3000 ppm)

 

[TVP]

At this pH, even grade 2 titanium will perform well without crevice corrosion issues.

 

[EdStainless]

280F, pH >10.5 and 25% NaCl
I have data from 21% NaCl+ 5% CaCl+ 1% MgCl at 224F (boiling) and a pH of 6.8. In crevice testing for 72 hours there was no corrosion on AL-6XN, AL 29-4C or Ti Gr2.

Do you have any concerns about Si scales forming?
Be careful using Ti thermowells in cross flow. They have a lower modulus than Fe or Ni alloys and they will vibrate a lot more.

If it were me, I would go with a Ni-Cr-Mo alloy just for saftey.

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[mcguire]

The lead time on titanium, according to Allegheny, is two years. Similar with other high corrosion resistant alloys.
They are suggesting using alloys like 29-4C and Al6Xn, not as a better alloys, but as a deliverable ones.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

I am not sure that AL-6XN or AL 29-4C offer enough margin in corrosion resistance for me.
The Ni alloys (59, 686, C-22) are available.

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