Stainless Steel Pressure Vessel for Anhydrous Ammonia Service

[Meekali]

Hi, Looking for some guidance/assistance.

I currently need to replace an existing anhydrous ammonia pressure vessel.
I would like to use austenitic stainless steel in lieu of carbon steel as the existing vessel requires replacement due to external atmospheric corrosion.
My problem arises when dealing with Canadian requirements.....
CSA B51 requires that vessels intended for use in anhydrous ammonia service be:
- subject to PWHT
- have head and shell materials produced in accordance with fine grain practice
I don't have any concerns meeting the PWHT requirement however, the fine grain practice is a tough one as I cannot find any suppliers who manufacture fine grain austenitic stainless steels
- I believe the requirement for fine grain is meant to be applied to carbon steel vessels in an attempt to ward off Stress Corrosion Cracking however it does not exempt stainless steels.
Pressure piping in anhydrous ammonia service are exempt from the above requirements and I have installed stainless steel piping systems extensively with no issues.

So,
1. Does anyone know why the CSA requirements exempt pressure piping? or why the additional requirements are added to pressure vessels?
2. Does anyone know of any suppliers of fine grain austenitic stainless steel?

Thanks in advance!

 

[blacksmith37]

The CSA standards are addressing carbon or low alloy steels which may SCC in anhydrous ammonia ( unless it contains about 0.2 % water ).

 

[Don56]

PWHT for stainless steel generally requires solution annealing in the 1900-2100 deg. F. range. This can turn your vessel into a prune or severely distort it.

 

[Meekali]

Blacksmith37 - do you have any CSA reference for that?
Don56 - Thanks!

 

[metengr]

Most anhydrous ammonia tanks are not constructed of stainless steel because carbon and low alloy steel have been proven and are far cheaper in cost. With that said, I would remain with carbon or low alloy steel, PWHT and coat the outside of the vessel to avoid corrosion concerns.

 

[stunner]

Moreover PWHT and Pre Heat is not advisable for Austenitic SS. Kindly check google