Heat tint in oxygen depleted environment

[Ronin609]

Will stainless steels still tint with heat if the atmosphere is oxygen depleted? I'm looking at the inside of a pyrolysis unit. The process operates under nitrogen blanket to avoid auto-ignition of off-gasses.

Thanks

 

[metengr]

No, it will not develop heat tint if there is no oxygen when heat is applied. However, you may see a very light straw color in some areas even with proper shielding from exposure to oxygen (during arc welding) but nothing like heat tint produced in an typical exposure to atmosphere.

http://www.bssa.org.uk/topics.php?article=140

 

[EdStainless]

The tinting will take a longer time to form in low oxygen environments.
And even parts exposed to high temp may only turn a light straw color.

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P.E. Metallurgy, Plymouth Tube

 

[Ronin609]

Thank you very much for that. Definitely means that colour can't be used to help guess a range of temperature exposure.

 

[weldstan]

If you are seeing heat tint, the nitrogen blanket may be to blame. What grade of nitrogen are you using? Commercial, medical, welding? You may well have more oxygen in the blanket than you realize. In any event, oxygen content can e analyzed.

 

[MagBen]

It is very common to see heat tint on A286 strip products, the tint is mainly Ti nitride.
Also very common to see heat tints on 420 grade, mainly Cr2O3.
To avoid Cr2O3, the dew point needs to be lower than -90F at 500C, needs to lower than -40F at 1000C

 

[harolddavy]

Thank you! for the informative post.

 

[EdStainless]

There are 316SS liners in the cooling zones of our bright annealing furnace. They are a light straw color. This is after two years in a -60C DP environment cycling from room temp to 1000F.
So yes, the color tells you nothing in low oxygen environments, unless you find that you have a leak.

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P.E. Metallurgy, Plymouth Tube

 

[Ronin609]

Thanks again for the extra comments everyone. I'm a consultant in this case and I haven't got access to a lot of detailed information, though I know the N2 is generated on site. I've been asked to give some technical advice to an insurer. Heat tint would have been a neat way to provide guidance on part of the claim. If the insurer doesn't want to pay the claim as filed, I might get to visit the plant - in which case I can look at the outside of the process unit which would be in natural air.