Applicable design code for Slug catcher

[Kudroli]

Dear friends:

I have a situation where slug catcher is subject to the depressurization temperature of -80 Deg C at 6 bar(With ambient temperature considered as -39 Deg C).

Whether some has experience in design of slug catcher at such a low temperatue? What design code and material to be used?

ANSI B 31.8 has limitation of -29 Deg C. COMPANY specifiaction does not allow to force the material to expose to the temperature beyond the code limited temperature.

Simillar situation may be faced by other who worked in North sea region.

Thanks in advance for the advise.

 

[Kudroli]

Further to above query, If I acn apply ISO 13623 code for the design of Slug catcher, could you please advise the suitable carbon steel material that can be subject to -80 Deg C and provide required notch toughness (27 J average/20 J individual with SMYS less than 360 MPa or 40J average/30 J individual with SMYS greater than 360 MPa).

 

[stanweld]

We used ASME VIII, Div 1 for our Slug Catchers.

 

[TVP]

I am not sure that ISO 13623 covers slug catchers. Have you reviewed DNV-OS-F101? It recommends ASME VIII, BS 5500, or equivalent. The following is a link to the older 2000 revision of the DNV standard:

http://ebookdaukhi.googlepages.com/DNVOS-F101.pdf

 

[Kudroli]

Friends:

Can we apply code ASME Section VIII Div 2. I have been told that, we have the thickness advantage with Div 2 compared with Div 1.

Regards

 

[stanweld]

Div 2 can be used as well.

 

[gr2vessels]

You can use the EN 13445 also. And any Pressure Vessel code recognised internationally. However, the selection of that material should be done by an experienced design engineer in low temperature applications, based on a solid blowdown / depressuring study, performed by an experienced process engineering firm. Can you really confirm the depressuring conditions of -80 deg C at 6 barg? At this temperature (and pressure), perhaps some additional corrosion problems would force you into selecting an exotic alloy and the whole project could blow out the costs because of this specification. You cannot use carbon steel material at -80 deg C, normally use austenitic stainless steel, but if you're looking for NACE MR 0175 compliance also, then you might consider Duplex, Super-Duplex or even higher alloys.
cheers,
gr2vessels

 

[Kudroli]

Gas being handled is sweet one (Almost no H2S). Hence application of NACE does not arise. Please note, Company requirement is Finger type slug catcher.

Selection of ASME Section VIII or any other pressure vessel code for slug catcher is complicating the suitable pipe material/code for the piping upstream and down stream of slug catcher.

 

[Kudroli]

gr2vessels:

As per preliminary depressurization study the depressurization temperature is -80 deg C at 6 barg (With 10 degree Process margin on temperature and no margin on prssure)

 

[gr2vessels]

Hi Kudroli,
OK, depressurizing conditions confirmed;- and no NACE compliance required.
Finger type of slug catcher can be of large size where you have to use rolled plate to form the pipe fingers (assuming diameter of 30" or larger) and you'll still be better off designing for minimum thickness as per any pressure vessel code, rather than using a piping code. Can you confirm the finger diameter? By the way, I can't see how would the design of the slug catcher impact the up / downstream piping selection. After all, you are only bolting a separator between the gas piping flanges.
You can use carbon steel impact tested and certified at -80 deg C (check also the SA 333 and SA 671 piping specs), but you should consider also the austenitic stainless steel, if the piping class is 300# or less. Depends on the loads the fingers might be subjected to, rapid depressurization and re-pressuring the cold system, mechanical loads, etc. The higher strength of carbon steel means lighter construction and less costs.
cheers,
gr2vessels

 

[Kudroli]

Hello gr2vessels:

Thanks for your time and advice,

Finger sizes are 48" & design pressure is 150 Bar.

Factory assembling and transportation of Slug catcher may not be feasible due the transportation related problem (Involvement of field welds may be immanent)

For the upstream and down piping related to slug catcher, if we follow piping code, then we may be force to select the SS material (Project specification do not allow to force the material to expose the material beyond the temperature limits imposed by code by means of impact testing or taking the advantage of stress ratios)

Cheers
Kudroli

 

[stanweld]

If NACE doesn't apply, low Nickel alloy steels recommended.