6 replies to this topic

[ravi.s]

Hello everybody,

Most modern sour water stripper cooling systems (air coolers) are pump around rather than overhead condensers to avoid Ammonium bisulfate deposition. I have gathered data for circulating water air cooler from various refineries stating MOC for tubes for the application are SS 316 as well as Titanium.

Our process licensor has mentioned MOC for tubes as "TITANIUM"; however to minimize the CAPEX we are thinking to change the MOC to SS316.

Can u suggest the reasons for the difference of MOC being used for the same application?

Regards,

[JoeWong]

Hello everybody,

Most modern sour water stripper cooling systems (air coolers) are pump around rather than overhead condensers to avoid Ammonium bisulfate deposition. I have gathered data for circulating water air cooler from various refineries stating MOC for tubes for the application are SS 316 as well as Titanium.

Our process licensor has mentioned MOC for tubes as "TITANIUM"; however to minimize the CAPEX we are thinking to change the MOC to SS316.

Can u suggest the reasons for the difference of MOC being used for the same application?

Regards,

One the component SS316 don't like is chloride. Check present of Chloride and potential of Chloride Stress Corrosion Cracking (CSCC) in SS316.

You have to evaluate INTERNAL and EXTERNAL also.

[Zauberberg]

Besides chloride problem (which should not be an issue in SWS pumparound loop - at least in majority of applications), I can't see any particular reason for using titanium or high expensive alloys. Actually I don't know for any SWS with titanium-made pumparound loop. 316L is quite appropriate; in most instances - depending on pumparound location and stream composition/properties - NACE carbon steel is commonly used. You can easilly check which NACE category P/A loop belongs to.

[JoeWong]

Besides chloride problem (which should not be an issue in SWS pumparound loop - at least in majority of applications), I can't see any particular reason for using titanium or high expensive alloys. Actually I don't know for any SWS with titanium-made pumparound loop. 316L is quite appropriate; in most instances - depending on pumparound location and stream composition/properties - NACE carbon steel is commonly used. You can easilly check which NACE category P/A loop belongs to.

Ravi,
If you consider to use of Carbon Steel, please assess the potential of corrosion.

[mhameran]

I agreed, it is very strange to use titanium for SW pumparound loop. my refinery is currently using SS. Though chloride is a threat for our 316ss but so far we have no issue with the Cl SCC at that 'particular area'.

We do have problem with NH4HS corrosion with wet/dry environment which has make the corrosion more aggrasive in thermosyphon reboiler - but this is totally different scenario.

Hamer,

[iplan]

please check the link http://www.eng-tips....d=105651&page=7 in this regard. The thread informs that for cyanide containing sour water ( from FCC), titanium is required.

thanks

[Zauberberg]

Iplan,

Sour Water Stripper (SWS) you are referring to is exactly the one I have described in my previous post. Made of CS. No serious corrosion issues.

As I see it, material selection is not only the matter of selection of 100% safe (and the most expensive material), but rather selection of the most suitable material under given conditions and with appropriate corrosion management philosophy. It means, for how many hours/days/weeks you can run your plant if corrosion protection system fails, and still without having catastrophic/shutdown failure. In most of cases, you'll see that less exotic (and less expensive) materials can be chosen to "fit the purpose".