Suitability of SS316 / 22Cr Duplex Stainless Steel in Sour Water Stripper Pump-around Loop 1

[balven]

In one of our projects we are designing a Sour Water Stripping Unit with a Sour Water Stripper Column and a pump-around loop (on the top section of Stripper Column) which has a pump, an air cooler and associated piping. The top section of the Stripper Column is specified as clad with SS316L, the pump in the loop is also SS316, while the air cooler and pump-around piping is 22Cr Duplex Stainless Steel (DSS). Process conditions in this pump-around loop are as follows :

Temperature : Top section of Stripper column is maintained at 90 deg. C. The pump takes sour water at 96 deg. C and sends it to the air cooler which cools it down to 60 deg. C before returning the sour water to the Column.

Pressure : 8 bara maximum

Fluid Composition : H2S : 5.1 wt%, NH3 : 8.43 wt%; expected ammonium bisulphide : around 7.5 wt%; chlorides : 10 ppmw; CO2 : 0.02 wt%
No cyanides are expected to be present.

Fluid velocity : 2 m/s maximum

Based on the above process conditions, is it OK to use SS316 / DSS for this pump-around section ? If not, up to what level should the ammonium bisulphide concentration be brought down to (such as by water washing) in order for SS316 / DSS to be suitable for the above temperatures, pressure and fluid velocity ? Any opinions / past experiences / references will be much appreciated.

Thanks
Balvendra Pal

 

[EdStainless]

the ammonium bi-sulphide won't hurt the SS, unless there is oxygen in the system.
You would get some sulfuric acid then.
That is the real key. If there is any 02 then 316 will not stand a chance.
2205 should be OK. It will also have some CSCC resistance.

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

 

[SJones]

Ed,

You might like to take a look at NACE Corrosion 2010, Paper 10349. The OP might be lucky with the temperature and absence of cyanide, but it's not a straightforward materials selection.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.