347LN temperature limit

[Chumpes]

Dear all
I was given the information that the use of stainless steel 347LN should remain limited to temperatures below 450°C - for corrosion reasons -

Unfortunately, I cannot identify the type of (thermal ?) damage that may be so harmful that it would restrict the use of SS 347LN to temperature below 450°C, whereas other similar stainless steels (ex: 316, 304, 321, 347, ...) could be used at temperature above 450°C.

What's the problem with operating SS 347LN above 450°C ?

Thanks

Regards

 

[EdStainless]

I haven't seen S34751 in many years.
The real question is how was it heat treated?
Was it annealed or stabilized?
If stabilized you should be good to the same temps as 321 or 347.
You will begin forming carbides and nitrides above 450C, but that is what the Nb is for.
The problem is that in service if you are above 450C but below 600-650C you are likely to sensitize.
If your service is above 650C it should stabilize in service.

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P.E. Metallurgy, consulting work welcomed

 

[Chumpes]

hello
I spoke to Sumitomo that developped the SS 347LN and they confirmed that there is no reason why SS 347LN should be limited to low temperature service < 450°C.
It seems our mistake came from a typo 540°C vs. 450°C. indeed, 540°C (or 1000F) is ASME max temperature limit for austenitic SS with less than 0.04% carbon, and SS 347LN has less than 0.04% carbon...
sensitization is usually not a problem when no electrolyte is present.
thanks Ed for your answer.
regards

 

[XL83NL]

sensitization is usually not a problem when no electrolyte is present.

That's my reasoning for most cases as well, e.g. when it comes to material selection in services around 600°C.
The 'default' stainless steels may quite often be suitable, but they only dont meet the carbon content requirement.
Under normal operating conditions, electrolytes arent present. During shutdown, or after, condensation may occur.

Is that the general consensus, anyone to concur or have a different point of view on that?

Huub
- You never get what you expect, you only get what you inspect.

 

[EdStainless]

'Normal' SS grades are often used in hot dry applications (gas to gas exchangers) where they sensitize.
But woe to the people that get sloppy dry gas purging or with wash out.
With good practices you can get away with this easily.
In some alloys (higher Ni & Mo) you can also form other detrimental secondary phases which can significantly lower the toughness of the material.
Thermal shock can then become an issue.

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P.E. Metallurgy, consulting work welcomed

 

[XL83NL]

Sorry I’m not native English so I didn’t quite catch what you meant with

But woe to the people that get sloppy dry gas purging or with wash out.
With good practices you can get away with this easily.

Huub
- You never get what you expect, you only get what you inspect.

 

[EdStainless]

If the tubes do sensitize (as is highly likely) and they ever get wet you can get IGA.
I have seen this happen to units during outage.
Either process water is left standing in them or they get wet during the outage.
Either can cause problems.
It is common to wash with very clean water and then blow the system out with dry air.
A lot of this depends on what kinds of residue or fouling might be on the tubes.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[XL83NL]

Thanks for the explanation Ed

Huub
- You never get what you expect, you only get what you inspect.