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Inconel 625 vs ASTM A182 F55

Inconel 625 vs ASTM A182 F55

(OP)
Which alloy of these two has the higher corrosion resistance? Inconel 625 or ASTM A182 F55??
I understand, A182 is supper duplex alloy, meanwhile Inconel 625 is high alloy steel.

RE: Inconel 625 vs ASTM A182 F55

What environment? What temperature?
In almost every case the answer would be 625, but a C type alloy would even be better for most applications.

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

625 is not a high alloy steel. It is a Nickel-Chromium-Molybdenum alloy (nickel base alloy). Agree with Ed above as to corrosion resistance.

RE: Inconel 625 vs ASTM A182 F55

2
Hi Meshry,

The corrosion resistance is relative term, depending on media, operating conditions( pressure, temperature) and many more factors.
Attached are some information on both the alloys extracted from manufacturers data sheets& are worth looking at.
With respect to O&G(Production)environment by an large alloy 625 has better corrosion resistances,due to higher CPT, CCT, PREN values.
However there's is a huge difference in cost between F55 and 625 alloys.
F55 alloys on the other hand are quite versatile, with the reported applications in Offshore O&G, Downstream Applications, e.g. Refining& Petrochemical, chemical environments.
What is the intended service conditions for these alloys? Selection of the best alloy would influenced by many of the factors stated above.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

RE: Inconel 625 vs ASTM A182 F55

Why the environment matters is that the super duplex is not usable above 600F, or below -40 (maybe even not below 0F depending on the application).
It has high strength, great resistance to aqueous corrosion, but can be difficult to weld (and the welds may have inferior properties).
625 has good strength up to 1400F and good toughness down to LN temps, and it welds well.

The cost between a superduplex, 625, and a C alloy (622, 686, 59) is not that great.
So pick carefully, there is no answer that is always correct

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

(OP)
Gents,Thanks for your replies.
Actually my question is related to a mechanical seal installed on a multi stage water injection pump (Aquifer water).
it failed many times and the internal of the mechanical seal found heavily corroded. all the wet parts are ASTM A182F55.
the other pumps in the same facility/same application are equipped with Inconel 625 mechanical seal internals, this seal is working fine. so I am doubting the ASTM A182 F55 is not suitable for our application (corrosive environment).
the discharge pressure of this pump is 290 barg and seal pressure is 100 barg.
TSS is 20 mg/L.

RE: Inconel 625 vs ASTM A182 F55

How hot does the seal run?
You may be up against the critical crevice corrosion temp for the duplex.
We used to only use 622 for seals in high Cl waters (anything no fresh).

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

What type of corrosion are you experiencing? Is it pitting? Do you have chances of oxygen ingress due to some reasons?




RE: Inconel 625 vs ASTM A182 F55

(OP)
Nickypaliwal,
I will try to get some photos for the corroded parts.
Yes Oxygen ingress is possible.

RE: Inconel 625 vs ASTM A182 F55

(OP)
EDstainless,
The working temperature is fluctuating between 72C to 85C.
Nickypaliwal,
could not arrange any photos due to legal issues, however the corrosion is almost a decay and metal loss. not only pitting.
Gents,
is it possible to have galvanic effect between super duplex and inconel625???? I have discovered that pump shaft is inconel625 meanwhile mechanical seal wet material is super duplex!!

Thanks

RE: Inconel 625 vs ASTM A182 F55

I don't see any risk for galvanic issues, the alloys are similar enough in corrosion resistance.
What pH range do you see?
I would move to a Ni alloy, and something better than 625.

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

I agree that chances of galvanic corrosion is negligible. IN general Alloy 625 should be fine for water injection but if O2 ingress is expected more than 30-40ppb then shifting to a copper based alloy should be preferable.

Note that copper based alloys are not good in H2S service so should check before using it.

RE: Inconel 625 vs ASTM A182 F55

Would say for seawater at 80degC, you'd look for a molybdenum content exceeding 6% - Mo content in 25Cr superduplex is only 4% while than in Inconel 625, Mo is 9% or so.

On the other hand, there may be some problem with the seal system heat removal operation, producing high temps on the contact surfaces in the seal.

RE: Inconel 625 vs ASTM A182 F55

@George : I believe that Alloy 625 should perform great in seawater due to high PREN but I am not sure as why the clients I am working have not recommended the same in any of their facility. I believe this may be due to crevice corrosion and MIC issues for Alloy 625 in sea water. 6Mo also has similar issues as highlighted in NORSOK M-001.

I am not very much aware of these materials in sea water service. Can you please advise and share your experience for use of alloy 625 in sea water ? Thanks in advance.

RE: Inconel 625 vs ASTM A182 F55

(OP)
Gents,
there is no sea water. the pumped fluid is aquifer water( with CL content). the seal barrier fluid is potable water.

RE: Inconel 625 vs ASTM A182 F55

(OP)
Can any one spot more light on crevice corrosion?

RE: Inconel 625 vs ASTM A182 F55

Crevice corrosion is the mother of pitting, it is much worse.
In general crevice corrosion will start at temperatures 20-40C lower than pitting.
All of these alloys rely on chrome to form the passive film that protects them (Mo and N make the film stronger and more self repairing).
The tighter the crevice the worse the conditions.
In the crevice you get oxygen depletion, so it is harder for the passive oxide film to be maintained.
You also get the concentration of corrosion products, one of which is hydrogen ions.
The result is dropping pH in the crevice.
In Fe bearing alloys (stainless and some Ni-Fe grades) we do corrosion testing in ferric chloride because it resembles what forms inside an active pit or crevice. The solution is high in Cl, and has a pH <1.
This is what happens in a crevice.

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

Am aware of OpCos using superduplex (with 3-5% Mo or so) for ambient temp seawater, but not at temps exceeding 80degC. Moreover, aquifer water may be higher in chloride content than seawater.

No info provided on seal system configuration. With what little I know, low chloride deoxygenated potable water should work okay for pressurised plan 53 with superduplex materials on the seal, since the aquifer water cannot migrate into the seal chamber.

Where is the 80degC experienced - seal supply or seal return fluid ?

RE: Inconel 625 vs ASTM A182 F55

Two of the four corrosion control options are: 1) change the material; 2) change the environment. Repeated seal failures suggest that one of these options needs to be deployed. The first thing to do would be to establish the specific cause of the seal failure. Unfortunately, this cannot be achieved on an internet forum; it will be achieved by a properly performed failure analysis exercise, probably involving an experienced laboratory facility.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Inconel 625 vs ASTM A182 F55

Gents, Please provide your views on Alloy 625 use in sea water.

RE: Inconel 625 vs ASTM A182 F55

Is corrosion maximized in the F55 at the interface between it and the 625 shaft? If so I suspect a combination of galvanic mismatch and crevice corrosion. In the current environment I would suggest a seal material change much closer to that recommended by Ed. Although it is understood that the 625 seals on similar units are performing well.

RE: Inconel 625 vs ASTM A182 F55

Check pricing on an alloy "C"version (C22, 622, 686, 59), these are Ni-Mo-Cr alloys.
If you don't need strength at elevated temp then 625 offers less corrosion resistance and the pricing should be similar.

You said that you have general corrosion, I hope that this is actually widespread pitting.
If you actually have general corrosion you need to find out what is being used to clean or flush this system.
General corrosion is almost impossible to have in these alloys.

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

@nickypaliwal

If you want an opinion on 625 performance in seawater, it's in plentiful supply in the literature. Here are a couple of examples:

JS Lee, et al, UNS N06625: A Current Review Of The Literature, Materials Performance, September 2006, pp 36-40
F Martin, et al, Crevice Corrosion Of Alloy 625 In Natural Seawater, Corrosion, Vol 59, (6), 2003, pp 498-504
H Alves, et al, NACE Corrosion 2007, Paper 07215

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Inconel 625 vs ASTM A182 F55

(OP)
Georgeverghese,
80C is the temperature of the pumped fluid. this will be the same as the seal chamber pressure at both sides (thanks to balance line).
I have seen the temperature trend for one month back. all the time this pump was running at 83C. I would say based in the other replies. super duplex is not the correct selection for this temperature??

RE: Inconel 625 vs ASTM A182 F55

(OP)
Weldstan,
You are right the corrosion is more at the interface wet parts, however as per your theory the 625 should be the first to go (higher potential) am I right??

RE: Inconel 625 vs ASTM A182 F55

625 would not be the first to go, alloy 55 would be.

RE: Inconel 625 vs ASTM A182 F55

If 83-85degC is the seal supply temp, that is unusually high. The external cooling on this seal system doesnt seem to be working..why ? What does your company rotating machinery engineer have to say about this ? Is the external cooling with a water cooled tube bank in the seal pot or with an external fin fan cooler?

Or perhaps the pumping ring in the pump isnt running as it should - is this a VFD operated pump, with operating speed too low to enable adequate recirculation of the seal fluid with the internal pumping ring ?

RE: Inconel 625 vs ASTM A182 F55

(OP)
Weldstan,
Why is that?? why would alloy 55 go first?

RE: Inconel 625 vs ASTM A182 F55

(OP)
Verghese,
83 is the pumped fluid temperature NOT the barrier fluid temperature.

RE: Inconel 625 vs ASTM A182 F55

Because in your stated conditions, 625 is the more noble material.

RE: Inconel 625 vs ASTM A182 F55

(OP)
Weldstan, Thanks a lot

RE: Inconel 625 vs ASTM A182 F55

The problem with superduplex alloys is that if someone is slightly off in the heat treatment then the two phases will not have matching corrosion resistance. If the anneal temp is too high or low the elements will partition differently between the phases and either the austenite or the ferrite will end up with lower corrosion resistance.
Considering how often I have seen 625 suffer crevice corrosion in high chloride waters strongly suggest a higher performance alloy.

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P.E. Metallurgy, Plymouth Tube

RE: Inconel 625 vs ASTM A182 F55

Thanks Edstainless.... I went through the documents highlighted above and many other articles/papers on internet.. The conclusion that I can make is that Alloy 625 is very resistant in seawater but can not be used for piping and equipment due to crevice corrosion.

RE: Inconel 625 vs ASTM A182 F55

What alloy(s) does the USN use for shipboard piping systems?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: Inconel 625 vs ASTM A182 F55

Ti and Monel 400 mostly, some 70-30 Cu:Ni also.

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P.E. Metallurgy, Plymouth Tube

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