Inconel 600 corrosion

[deklerk]

Does anyone know about corrosion problems of inconel alloys in CO/CO2 bearing gas (probable formation of nickel-tetra carbonyl)at temperature below 200°C.

Sincerely
MARCODEMARCO

 

[mcguire]

That should be a slow ground ball for Inconel 600. It is designed for much worse environments.

 

[TVP]

I agree with mcguire. I see no reason why Inconel 600 should be experiencing problems in a low temperature CO/CO[sub]2[/sub] environment. Special Metals has a great deal of technical information on their website. The following link is for Inconel 600:

http://www.specialmetals.com/products/publication/tech_bulletin_600.pdf

 

[deklerk]

First of all thank you for the replies.

I know that Ni is extracted by a water gas containing C0 which at a temperature of about 50°C forms Ni(CO)4 , this complex at temperature above 250°C decompose again to Ni + 4CO. It possible that the same gas in contact with a nickel alloy at the above mentioned temperature extract selectively the nickel? I haven't found any reference about this in corrosion literature, but i think this is a normal process of nickel production.

Sincerely
MARCODEMARCO

 

[kenvlach]

MARCODEMARCO,
You are correct. Nickel can be selectively extracted from alloys at 50-60 C to form nickel carbonyl. The nickel carbonyl is primarily used for producing high purity nickel coatings by the chemical vapor deposition process. I knew about this CVD process because people in composites research use it to coat glass & ceramic fibers for bonding with metals. However, the only other thing that I could remember about nickel carbonyl is that it is poisonous, so I did a search:

A Dictionary of Science, Oxford University Press

http://www.xrefer.com/entry/490574

nickel carbonyl
A colourless volatile liquid, Ni(CO)4; m.p. -25°C; b.p. 43°C. It is formed by direct combination of nickel metal with carbon monoxide at 50-60°C. The reaction is reversed at higher temperatures, and the reactions are the basis of the Mond process for purifying nickel. The nickel in the compound has an oxidation state of zero, and the compound is a typical example of a complex with pi-bonding ligands, in which filled d-orbitals on the nickel overlap with empty p-orbitals on the carbon.

http://www.xrefer.com/entry.jsp?xrefid=490349

Mond process
A method of obtaining pure nickel by heating the impure metal in a stream of carbon monoxide at 50-60°C. Volatile nickel carbonyl (Ni(CO)4) is formed, and this can be decomposed at higher temperatures (180°C) to give pure nickel. The method was invented by the German-British chemist Ludwig Mond (1839-1909).

A Dictionary of Science, Oxford University Press, © Market House Books Ltd 1999

************************************************************

http://www.madsci.org/posts/archives/sep99/936669308.Ch.r.html

Message:

“Nickel was named after Satan because of the difficulty of separating it from copper. Nickel is usually found as a sulfide, although it can also be found as an oxide or a silicide. It is almost always found in combination with copper and other metals such as iron and cobalt.

A lot of the history of extracting nickel can be found on INCO's web site: http:\\

http://www.inco.com

. INCO, which used to be named International Nickel, is the largest producer of nickel. Another useful website is the Nickel Page: http:\\

http://www.nipera.org

.

nickel-tetra carbonyl

The other process for producing high purity nickel is the most unique. Nickel will react with carbon monoxide to form a gaseous nickel compound called nickel carbonyl. The nickel is removed in the vapor phase, leaving behind all of the copper, cobalt, and other metals. The nickel carbonyl is heated to a higher temperature, where it becomes unstable and decomposes into metallic nickel and carbon monoxide. The metallic nickel forms round pellets, and the carbon monoxide is recycled to refine more nickel. Pretty slick, don't you think. The nickel carbonyl can also be used to coat things with nickel, such as graphite fibers. The only problem is that nickel carbonyl is very poisonous, so your process controls and containment have to be very, very good.”

************************************************************

http://www.columbia.edu/itc/chemistry/chem-c140498/problems/chembytes/bytes_ch14.html

“CHEMByte 33: Inexpensive, Catalytic Hydrogenation. Paul Sabatier (1854-1941) spent his professional lifetime studying catalysts, for which he was eventually awarded the Nobel Prize. But it was a failed experiment that he conducted in 1897 at the University of Toulouse that got him started on that line of research. Sabatier was fascinated by the fact that nickel could form a volatile compound named nickel carbonyl on reaction with carbon monoxide:
Ni(s) + CO(g)--> Ni(CO)4(g) Preparation of nickel carbonyl
What so interested him was the extraordinary fact that a metal could form stable compounds that vaporized at relatively low temperatures...”
************************************************************
I present a small portion of the following link because it has many figures which won’t reproduce, but maybe the high-level chemistry and experimental technique (they used IR spectroscopy to follow gas-phase rxs.) will be of some use:

http://www.chemistry.unimelb.edu.au/research/groups/best/group/projects/NiCO.htm

Electrosynthesis and Characterisation of Nickel Carbonyl
and Nickel Carbonyl Hydride Clusters

“…Further reduction leads to formation of [Ni(phen)(CO)2]- and, depending on the nickel concentration, di- and trinuclear nickel complexes (together with nickel tetracarbonyl). Corresponding reactions performed under moderate pressures of CO2 lead to electrocatalytic reduction resulting in the formation of CO leading to the generation of [Ni(phen)(CO)2] and [Ni(CO)4] together with higher nuclearity clusters (Ni5 and Ni6)….”

************************************************************The leaching of Ni from Ni-containing alloys by CO(g) does not appear in the general corrosion literature because these alloys normally have a protective oxide surface. It is more of a laboratory & very specialized industry process.

I will try to interpret all of this for non-chemists (ligand theory in plain talk):

The CO(g) acts as a vapor phase chelating agent for Ni in the ground electronic state (metallic, non-ionized). Surface atoms of Ni (if not protected by an oxide film) are sufficiently energetic to combine with adsorbed CO molecules at the temperature of 50-60 C, and these CO molecules, like lift bags used to raise sunken ships, lift it into the gas phase. The activation energy for formation of Ni(CO)4 is very low because no (covalent or ionic) bonds are broken (or created, either. Competing oxidation reactions to form NiO(s) do not occur at this low temperature because of the high activation energies required to break the O2, H2O & CO2 bonds. These molecules adsorb onto the surface Ni lattice but not dissociate and react.

To complete the picture, nickel carbonyl is a very weakly held together complex that will spontaneously decompose at 180 C because of the increasing vibration of the constituent CO molecules (the entropy increase by having 4 free CO molecules overwhelms the enthalpy of the ligand bonding). This very fortuitously can happen even slightly below this temperature at surfaces to give a metallic nickel coating (the weak complex bumps into something solid and breaks).
Ken V.

 

[mcguire]

The nickel in Inconel 600 will not be liberated by any gaseous phase in question because the stable passive film on the surface, which has no nickel, prevents nickel from association with the gas phase. That is how iron-nickel-chrome alloys are designed.

 

[kenvlach]

That is why I said
"The leaching of Ni from Ni-containing alloys by CO(g) does not appear in the general corrosion literature because these alloys normally have a protective oxide surface. It is more of a laboratory & very specialized industry process."

Probably all commercial alloys of common metals [not gold] come from the mill with an oxide film. The carbonyl formation can only happen if you clean the metal and expose it to CO(g) without heating in air, or if you reduced the surface oxide at some higher temperature and then cooled in a strongly reducing atmosphere.
I have removed surface oxides from both iron and cobalt samples by the latter method. Used a silica glass tube inside a tube furnace, with plug and inlet valve at one end and a stopcock at the other, burning off high-purity H2 as it exited. After cooling, I closed the valves and transferred the whole thing to a glovebox containing high purity 'gettered' argon. In such a manner, one can perform reactions normally prevented by the passive oxide film.

The thin amorphous oxide that forms on an alloy at low/room temperature normally differs in composition from the high temperature, crystalline oxide. The metal ratio of the low temperature oxide is much closer to that of the alloy, whereas the composition of the high temperature oxide is primarily determined by the thermodynamic stabilities of the component oxides and the activities of the metals in the alloy. This is why it is necessary to passivate SS, to increase the Cr/Fe ratio of the low temperature amorphous oxide. Whereas, the oxide that forms at higher temperature is naturally Cr2O3-rich.

 

[deklerk]

I agree with the fact that the superficial passive oxide protect tha bare metal from the CO bearing gas ( even if I think that Ni-Oxyde would be present in the inner layer of the oxide film, but not in the external outer layer, mainly made of Cr2O3).
But if in the process fluid some corrosive species is present, which could weak the stable passive film and expose the bare metal to the atmosphere, it is possible the formation of the above mentioned Ni(CO)4 complex? I think it's unlikely on the base of what you clearly exposed, but it's a possibility. Maybe my problem on INCONEL 600 is caused by the presence in the process fluid of ferric species, coming from adiacent stainless steel (with intergranular corrosion phenomena)components.

Thank you again for the clear and helpful explanations.

SINCERELY

MARCODEMARCO

 

[kenvlach]

Describe your INCONEL 600 problem and the process stream a bit better, please.
Does the Inconel look like it’s becoming porous, like brass when zinc is leached out? You earlier described gas as CO/CO2. Do you have water vapor or liquid with iron and corosion products? Why is SS corroding???

What is temperature or temperature range? Nickel carbonyl formation is unlikely without special cleaning,* but one way to tell is that it vapor transports Ni from 60 C area and deposits nickel coating (like bright nickel plating) in 180+ C area. Do you have this temperature range within the INCONEL sytem in the direction of flow?
*I think ‘cleaning’ by corrosion would leave residue (adsorbed species).

 

[deklerk]

My problem occured on INCONEL 600 thermocouple sheaths in a process fluid water/CO/CO2 at 53 bar and 235° C(in the reactor but i think the temp. less in corresponndence with the corrosion phenomena). The corrosion phenomena are localized on the therm. sheaths near the brazed joint to the 304 s.s. tube holder in proximity of the reactor wall. Also on the tube holder near the brazed joint slight intergran. corrosions have been observed (probably due to the sensitization of the steel). I think that some residual brazing flux (with fluoride or other aggressive species) could inizilize such phenomena in presence of some process fluid condensed. It's possible that the s.s. slight corrosion phenomena could put in such condense some Fe+++ ions and these ions accelerate the corrosion on the INCONEL alloy ?

Thanking you in advance.
Sincerely
MARCODEMARCO

 

[hacksaw]

Marco,

You started out with a gaseous process below 200 Deg C and now you're stating that the actual fluid is process water with CO/CO2 present. Unusual.

In reference to your latest statement, the term "thermocouple sheath" usually refers to the thin walled tube that protects the temperature sensor but that is not incontact with the process. So it is not clear just what you are dealing with interms of an assembly.

Are you certain that "brazing" and not MIG welding is used?

What are the dimensions of your sensor "sheath", how long is it?

Is it supported, if so how and in how many places. What is the velocity, nominal composition and state of the process fluid in contact with your device, and what are the materials of construction of the process containment vessel, etc.

These are all questions that factor into offering legitmate and helpful comments.

 

[kenvlach]

Marco,
hacksaw asked good questions. The situation is different than what mcguire, TVP and I first pictured. It sounds like a galvanic problem of the braze material to the SS shell on one side and the Inconel thermocouple well on the other. No doubt, the velocity of the fluid against the thermocouple well, which I presume is unsupported except for the braze joint, caused stress on the joint.
I would think that any brazing flux is long gone, as many solution cycles have probably occurred. Some remaining questions:
1) what braze alloy was used?
2) what is in the solution besides CO/CO2/H2O?
3) as per hacksaw, what are the dimensions of the TC well and the velocity of the impinging fluid (& fluid density)?
4) Does the braze make seamless, liquid-tight contact with the 2 adjoining surfaces for entire circumference?

 

[EngineerDave]

Do you know of any good sources for Inconel 600 microstructures?

The ASM Handbook doesn't appear to have this particular grade.

Any help would be greatly appreciated.

 

[TVP]

The best I can find is a description of the microstructure from Special Metals:

http://www.specialmetals.com/products/publication/tech_bulletin_600.pdf

and this .pdf:

http://web.umr.edu/~glassres/research/presentations/muratceramic1.pdf

Try scrounging around

http://www.metallography.com

and see if there are any images there, or if anyone else can recommend something. I would imagine that Special Metals would email an image to you if you asked.

 

[EngineerDave]

INCONEL 600 Corrosion

Very interesting, I'm looking at my second failure in a row that involves INCONEL 600 (or at least it is suspected)

The first failure has nothing to do with corrosion, it appears to be some stresses introduced during manufacturing.

The second failure appears to involve INCONEL 600 and a brazing flux material. The flux utilized is primarily boric acid and potassium florides are the secondary ingredient. More details will be posted as I determine them.

I will review the microstructure and report back on this. The temperatures and flux have combined to produce a rapid corrosive failure. Is it reasonable to expect Inconel 600 to survive high temperatures and acidic (note this is not a chloride environment, but boric acid) attack?

First I will verify that it is indeed Inconel 600.

 

[Metalguy]

Alloy 600 handles Cl pretty well-don't know about F. But boric acid shouldn't hurt it by itself, at least up to 600 deg. F. Cold-working is a real problem, especially if followed by welding.