Sulphidation Prevention of Chrome/Nickel Alloys 3

[dacf]

I have a corrosion problem concerning 25/10 chromium/nickel alloy furnace tubing in a high sulphur reducing environment at temperatures in excess of 700C. I am looking for information on the kinetics and how to reduce the affects of sulphidation on these alloys. Since the atmoshpere is reducing the formation of protective oxide layers is limited. I know that reducing the nickel content will help in preventing the formation of the low melting compound nickel sulphide, but how do iron sulphide and chromium sulphides play a part? Also, why does the corrosion occur with preference to the grain boundary or primary carbide?

Any comments on this topic or where I can obtain info would be greatly appreciated!

 

[unclesyd]

When I left (retired) I had been involved in a long term test of a similar problem. Unfortunately I left all my information with the current overseer of the project and he seems to have problem sharing my data or any current data with me.

Here a website for Haynes Alloys. I would consider Haynes to be on top the current thinking on Sulphidation resistance materials. The reducing atmosphere aspect will present some problems so make sure in any request for information the conditions are highlighted.

http://www.haynesintl.com/556H3013E/556sr.htm

Her is paper on the Si addition.

http://www.netl.doe.gov/publications/proceedings/03/materials/manuscripts/Dunning_m.pdf

You might want to look at these references

http://www.scientific.net/default.cfm?pg=1&issn=0255-5476&isbn=0-87849-774-9

Here is reference at B&W

http://www.babcock.com/pgg/ps/boilertreatments.htm

 

[metengr]

dacf;
The Department of Energy has numerous technical papers on sulfidation of iron and iron base alloys. The following is an abstract from a DOE paper published in 1983;

Identifier # LBL-16089 Titled" High-temperature corrosion of iron and iron-based alloys in sulfur-containing atmospheres"

ABSTRACT
The corrosion morphology, kinetics, and mechanism of the attack on metals and some iron-based alloys by sulfur-containing atmospheres are studied at 871/sup 0/C.^In the case of pure iron, protrusions with sulfide-rich cores are observed on the scale surface.^This morphology is explained by the fast transport of iron ions through the sulfide-rich streaks.^Models of unbalanced diffusion are proposed to account for the formation of an inner porous layer.^The addition of alloying elements, such as Al and Cr, improves the corrosion resistance by forming a protective Al/sub 2/O/sub 3/ or Cr/sub 2/O/sub 3/ oxide scale.^However, sulfur penetration through the scale and its effect on the spalling resistance of the oxide scale can lead to the onset of a catastrophic corrosion and rapid failure of the alloys.^The transport of sulfur through scales, the thermodynamic conditions for the formation of duplex oxide-sulfide scales and the influence of alloying elements are discussed.^It is concluded that sulfur penetration through both performed and growing Al/sub 2/O/sub 3/ and Cr/sub 2/O/sub 3/ scales resulting in an accelerated attack is inevitable.^Nevertheless, ways of slowing down the attack are recommended.


The following web site will get you to other technical papers under the Department of Energy, where you should be able to inquire about ordering a copy of the report/paper of interest.

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5509728

 

[Metalguy]

If the above refs. don't help you out, the basic problem you have is that Cr helps resist oxidizing conditions, while Ni resists reducing ones. But the S just kills the Ni. Simple, huh? <g>

 

[ibf]

In addition to all the above, "Rolled Alloys`" brochure by James Kelly says:

" Sometimes the distinction (between oxidizing or reducing atmosphere) isn`t obvious.For example, there may be solid deposits on metal in an oxidizing environment. Underneath those deposits, in contact with the metal the actual amount of oxygen available to form a scale may be very small. There, the oxygen partial pressure could be as low as 10-8. If the deposit contains sulphur then, the metal may be heavily attacked under the deposit, regardless of how much oxygen is in the atmosphere above it."

Even if that`s not your case, keep it in mind.

ibf.

 

[SMF1964]

I think your temperature is a little low for the formation of the Nickel-sulfide liquid phase. The cracking starts at the grain boundaries and intermetallics at the surface because of a number of factors; we see this all the time in boiler tubes. We see sulphidation type deposits in nickel overlays, stainless steels and low alloy steels. In cracking, it is a thermal fatigue/corrosion fatigue mechanism.