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Material Selection for Sodium Hydroxide and Hydrochloric Acid

Material Selection for Sodium Hydroxide and Hydrochloric Acid

Material Selection for Sodium Hydroxide and Hydrochloric Acid

I've been asked to select materials in the bid stage for a chemical processing facility. We do tanks, but typically the material selection for our tanks is one step up the engineering chain.

I've performed some cursory research, and I have some undergraduate-level training in material selection.

The first series of tanks will hold sodium hydroxide (NaOH) at 50% by weight at temperatures to 155C. I have Alloy 400, 600, 200 and 201 on my list for this service based on the research. The Monel and Inconel would have more favorable material properties for tank design.

However, down the line, the slurry goes into a 35% hydrochloric acid (HCl) mix by weight at temperatures under 100C. And then into sulfric acid (H2SO4); not yet sure of the concentration. I didn't find any research indicating the expected corrosion rates or prevalence of SCC, but I did research for exposure to HCl to nickel-based alloys. Looks like chromium bearing grades (i.e. Inconel Alloy 600) is non-resistant to HCl, and Alloy 200 is attacked only in the presence of dissolved oxygen. High Mo materials (Alloy B-2, B-3 and B-4) appear to be purpose-built for HCl, but with limited data for caustic mixes.

Tough to make sense of it all, but any help or references would be appreciated.

Thanks for reading!

RE: Material Selection for Sodium Hydroxide and Hydrochloric Acid

While you are on the right track you really shouldn't touch the material selection.
It is the owner's responsibility, period.
If they pass it off to an engineering firm that is their decision.

The two best sources for such info are the Nickel Institute https://nickelinstitute.org/
And MTI (but much of their material is for members only) https://www.mti-global.org/home
I do have some of their reference materials.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Material Selection for Sodium Hydroxide and Hydrochloric Acid

Thanks for your response EdStainless

I utilized the nickel institute documents and website for my cursory research. I can confirm MTI-global requires a membership to view their documents. If they have anything definitive on caustic/acid cocktail and you're willing to share, please do so.

As far as responsibility for material selection goes, I agree this scope should sit with the owner. They have weighed in (Alloy 200 requested), but has placed responsibility on the engineering service provider. We'll engage someone when or if the project kicks off, but in the interim we'll go with either Alloy 200 or a combination of Alloy 600 and B-2 for this proposal. Whatever's less costly.

RE: Material Selection for Sodium Hydroxide and Hydrochloric Acid

Any caustic/acid cocktail will soon have a baby, after generating a lot of heat.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Material Selection for Sodium Hydroxide and Hydrochloric Acid

One question that needs to be addressed involves purity.
What traces are in these chemicals, any trace metals (Fe or Cu for example)?
Is this an extraction operation? If there is ore involved there will be ton of impurities including Fl.
The Sulfuric is not bad, and neither is the caustic. Very proven solutions for those.
HCl is a real pain, and on mixing the solution will want to heat up, a lot.
How is this being actively cooled?
What will the final pH be?
Then this is mixed with sulfuric?
How much of this can be done with non-metalics?
Considering that 50% caustic boils at 146C the 155C sounds a little out of place.
904L has a good record in this service.
As long as the sulfuric is concentrated (>93%) then Alloy 20 would be the go-to.
For various mixtures, you need a lot more information.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

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