Ammonia and stainless steel, corrosion

[AO1958]

Hi there,

hope everything is fine.
Please, I would be grateful if somebody could help me in following topic.

I have red following topic
thread338-273391
but I am afraid it doesn't answer completely my question.

Following is the topic:

Ammonia is not corrosive for stainless steel without presence of water or condensate.
From the same topic I can quote
<<Unless you are at extreme temperature, pressures, and concentrations; any SS will have a near zero corrosion rate>>
(mr. EdStainless )

Should water be present with the ammonia, are there risks of corrosion ?
The presence of water be even in form of water condensate.

the stainless steel I would be interested is AISI 304 or AISI 316

Thanks for your help.

 

[blacksmith37]

Ammonia will SCC crack high strength steel (> 100,000 psi tensile) if it does not contain about 50 ppm water (as I remember that in cludes a safety factor).

 

[AO1958]

Many thanks Mr.blacksmith37

Therefore may I understand that water in NH3 somehow improves stainless steel corrosion resistance ?

Many thanks

 

[MikeMet]

You don't need water to prevent SCC on stainless steel in ammonia. It is typically considered resistant to ammonia stress corrosion cracking.

 

[blacksmith37]

WE had a few large ammonia plants; I don't remember any SS except the reformer furnace tubes/manifolds (HK-40 > HP mod.)

 

[AO1958]

Hello, thanks for all your feedback.

But I am afraid of not getting the point.
If I have a tube in Stainless Steal (AISI 304 or 316) with some water, or water drops, and then I let ammonia passing into the same tube, is the presence of water affecting the corrosion resistance ?
Is it mitigating the corrosive action of ammonia, isn't it ?

Are there any literature references I can refer to ?

many thanks

 

[EdStainless]

A small amount of water gives corrosion resistance in carbon steel.
With SS the water is no issue at all (doesn't help or hurt) unless it has some chlorides in it.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube