Pack cementation coatings - dew point corrosion

[YungPlantEng]

I am looking to evaluate the potential for pack cementation coatings, specifically aluminizing, of C276 to form nickel-aluminides that might be more resistant to the erosion-corrosion and sulfidation/hot corrosion that a spray nozzle experiences while in service.

This spray nozzle sprays sulfurous water (water with high concentrations of chlorides, sulfates) at ~125 F onto a gas stream coming in around 2400 F. From my side it's difficult to confirm the "dominant" mode of corrosion, if any, between hot corrosion or sulfidation from particulates as opposed to dew point corrosion from start-up/shutdown. Also not sure since direct cooling is taking place if the outer metal temperature is actually closer to the dew point of the various acids that can form or if it's well outside that range. Pressures are a few psig above atmospheric

That's just some background in case anyone has direct experience. My initial question is would aluminizing a high-nickel alloy be pointless due to dew point corrosion from startup/shutdown immediately dissolving it? There's not too much literature on nickel-aluminides but my understanding is it's akin to nickel in corrosion resistance against sulfuric.

Thanks for any help! Here's a picture of the nozzle in case anyone's seen something like that before.

https://files.engineering.com/getfi...-e56e-4dbb-a71b-421625540645&file=nozzle1.jpg

 

[EdStainless]

Have you looked at other materials?
If you want metal you might try Ultimet, a Co based alloy.
But the best bet might be going to ceramics such as SiC (don't use alumina).

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P.E. Metallurgy, consulting work welcomed

 

[YungPlantEng]

We’ve looked into other materials. The corrosion vendor recommended HR-160 but that was based off their prior prediction of it being sulfidation from dendritic formation observed on the microscopy.

B3 Hastelloy was used but experienced sig ifixabtly shorter life. Train of thought was lack of Cr prevented the formation of an oxide layer with any spall resistance.

It feels more and more like the corrosion is high T but it’s impossible to parameterize the very tip of the nozzle.

SiC was tried in the past but failed - no details on it.

 

[EdStainless]

If it was a reaction bonded SiC then the excess Si may have been leached from it causing failure.
You would need a sintered product.
And there is BN, and a few others that are worth consideration.
I think that you are on the right track with the B3 failure.

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P.E. Metallurgy, consulting work welcomed

 

[YungPlantEng]

I neglected to mention there is significant potential for thermal shock at the nozzle tip as gas contacts the liquid at a 2000 F differential.

The SiC is alumina then nitride bonded. We don’t have much faith in the SiC lasting longer as other areas of the tower require yearly replacement. The idea of a coating is popular as there would be ideally less potential for thermal shock throughout the thickness while still allowing a tightly bound material that resists liquid/molten corrosion.

If I had more choice over the coating I would have recommended a CrAlY or something to that effect..

I guess lastly are there any robust welding techniques, however specialized, that might reduce future corrosion in the heat affected zone?

 

[TugboatEng]

Have you considered cooling your nozzle so that it doesn't require such heat resistant materials?

 

[EdStainless]

Reach out to these people, if you want robust coating this is the way to go.

https://www.linde-amt.com/en/coatin...rocesses/thermal-spray/d-gun-coating-services

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P.E. Metallurgy, consulting work welcomed