Hydrogen embrittlement at Inconel 718 springs 2

[ballvalve1337]

Hi,

what kind of Belleville spring material can i use at high temperature (550°C / 1000°F) and gaseous hydrogen service.
Was thinking about Inconel 718 as it is suitable for high temperature service. But i am not sure about hydrogen embrittlement could be a problem.

Thanks!

 

[SnTMan]

ballvalve1337, contact these guys. Great applications engineering support.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

EPRI would have publically available reports covering this, since 718 is used for nuclear fasteners (though maybe not in gaseous hydrogen service).

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

 

[ballvalve1337]

Thank you both! Will have a look at SolonMFG

 

[iainuts]

302 and 316 cold worked SS is the go to material for springs where you've got high temperature and pressure.

 

[EdStainless]

iainuts, If you really want H resistance you need an alloy that stays fully austenitic when heavily cold worked. 300 series stainless steels don't meet this criteria. They are also very susceptible to CSCC.
For this application you need a Ni based alloy.
718 may work, but the secondary phases that form when you age harden it do give it some susceptibility to environmental cracking. Perhaps heavily cold worked C276 or 625 would be better options.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[SJones]

https://www.cartech.com/en/product-solutions/cartech-mp35n-alloy/

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[iainuts]

My experience is with valves used in H2 recips up to 400 F with excursions to 450 F and pressure to 14,000 psi. Valves operate at 400 to 800 RPM so stresses are high and cyclic. Stress amplitude is high. Fatigue is an issue.

Needless to say, at 1000 F, 300 series SS will anneal so they'd need to be designed in the annealed state. Maybe not a good answer.

I don't see Inconel 718 as a good option:

https://www.sciencedirect.com/science/article/abs/pii/S0921509396103841

https://www.tms.org/Superalloys/10.7449/1991/Superalloys_1991_635_651.pdf

Perhaps A286 is an option

https://www.sandia.gov/matlsTechRef/chapters/2301TechRef_A286.pdf

 

[btrueblood]

A large variety of parts of the space shuttle main engine (which used hydrogen from cryogenic to middling hot (1000 F or so) temperatures) are were made from Inconel 718, so I would expect NASA archives to be a rich source of data on the subject. From my memory, warm H2 and 718 is a better combination than at room temperature...but it can still embrittle, and you need to design for that condition.

a quick google netted:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720019924.pdf

(see fig. 6)

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790013258.pdf

and many more...

Realize all of that data is now 20+ years old (sigh...) so newer alloys like the Carpenter stuff aren't there.

 

[ballvalve1337]

What I do not understand is: Why NASA used Inconel 718 in the Space Shuttle Main Engine when actually it is not suitable?

 

[btrueblood]

Not suitable in what way? It was used in areas where it was suitable, and it worked.

 

[cap1a79]

Generally, hydrogen embrittlement does not occur at the high temperature. Note that HE occurs when hydrogen is trapped in material but the atomic hydrogen will be diffused at the elevated temperature.

(Quoted from API RP 571, clause 4.5.6.3)

e) The effect is pronounced at temperature from ambient to about 149 C. Effects decrease with increasing temperature.

(Unquoted)
Although HE does not occur at the high temperature, start up or shut-down sequence procedure might be required not to exposed to the hydrogen whose temperature between amb and 149 C.




Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[ballvalve1337]

Thank you all for the information. I think we will give Inconel 718 as spring material a chance... Operating temperature usually is above 300°C and hydrogen occurs only temporarily.
We will see...

 

[WKTaylor]

Anyone here familiar with Inconel X750 for springs in applications like this??

Per ASMH 4105...
Inconel X-750 is a precipitation hardenable nickel chromium
alloy containing aluminum and titanium,
which form the hardening component. Although
much of the effect of precipitation hardening is lost
with increasing temperature over 1300 F, the heat treated
material has useful strength and oxidation
resistance at temperatures up to 1800 F. It also has
excellent properties at subzero temperatures;
consequently, it is useful for cryogenic applications.
The alloy has good formability, weldability and
resistance to corrosion and stress corrosion in most
environments. Aerospace applications include rotor
blades, wheel and bolts for gas turbines; rocket
engine thrust chambers; and hot air ducting systems
and thrust reversers for airframes. It is also used for
large pressure vessels, forming tools, extrusion dies
and heat-treat fixtures. For springs and fasteners,
Inconel X-750 is used from subzero temperatures to
1200 F.

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]
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[MagBen]

718 is susceptible to H2 embrittlement reason being unstable sigma or delta phase that weakens grain boundaries. Higher temperature can relieve HE is because of baking effect (bake off H2), there exists an ASTM spec on that.

Basically ferretic, martensitic and PH grades are quite susceptible to HE, austenitic is the least.

Co based superalloy are ideal in your situation. Co can normally increase stacking fault energy so beneficial to HE. MP35N SJones referred is a Co-based alloy with exceptional resistance to HE, but the application temp cannot go above 750F. Conichrome is another Co-based alloy displaying very good resistance to HE, the other name oif this alloy is Elgiloy, or Phynox alloy designed particularly for springs.