Aqueous ammonia storage tank

[Trebormech]

I am trying to understand the relative corrosiveness of aqueous ammonia (29%) in a carbon steel pressure vessel. I have found much reading about SCC in welds and HAZ of welds with anhydrous ammonia, but nothing for aqueous ammonia. All this is in an effort to set up and inspection program for the vessel with the correct inspection frequencies for internal, external UT, and visual inspections.

Anything you can offer is very much appreciated.

Thank you.

 

[Metalero]

The text says: Ammonia gas dissolves well in water giving rise to alkaline solution. Ammonia gas and its solutions are corrosion inhibitors of carbon steels.

In some cases, the humidity are used to inhibite the anhydrous ammonia (1 - 2%), ex. during its rasnportation.

 

[Chumpes]

hello
as stated by metalero, aqueous ammonia will not cause SCC of CS welds by itself, but a too alkaline environement (pH above 10 ? cannot remember a limit...) may promote alkaline SCC.
regards

 

[Dhurjati Sen]

Dear Trebormech,

The weld joints of the vessel are stress-relieved, right?

If this vessel is part of an unit, it cannot have an inspection frequency of its own. The inspection has to be carried out during shutdowns only.

Is this the first time the vessel would be inspected?

Try to find out the general corrosion rate by UT and set the inspection frequency accordingly.

However, the vapour phase corrosion could be an issue. Closely inspect the top side of the vessel. You may get pits there.

Regards.



DHURJATI SEN
Kolkata, India

 

[MJCronin]

Tanner has decades of experience with aqueous ammonia storage tanks and materials ...

Note that they recommend Sched 40 or 80 steel pipe ... Stay away from any brass or copper fittings !!

https://www.tannerind.com/sto-aqua-ammonia.html

MJCronin
Sr. Process Engineer

 

[MJCronin]

The typical customer storage for aqueous ammonia tank is a ASME (or other)Code certified, horizontal storage tank designed to a MAWP of 25 psig (some people say 50psig) The tank must have a vacuum relief device

Storage in flat bottomed tanks designed for only atmospheric pressure (API-650)is discouraged.

Capacity is up to you, it depends on the max volume delivered, but three truckloads is a good rule of thumb.

Particular attention should be paid to the fill and vent line sizing and configuration.

Piping, valve components or instrument fittings of brass. copper or galvanized construction is banned and components will not last long.

Pipe gaskets, seals etc must be evaluated for this service ...

https://airgasspecialtyproducts.com...ndix_D_-_Delivery_and_Storage_Information.pdf

MJCronin
Sr. Process Engineer