9 replies to this topic

[Zauberberg]

Nomi,

This is the information I can give you based on my experience in gas processing, after several years of working in different treatment plants worldwide:

1. For CO2-only acid gases, the absorber vessel is cladded with 316L stainless steel. Regenerator tower is made of CS cladded with 316L as well. These are experience-based rules. CO2 is much more corrosive if there is no H2S.

2. For H2S/CO2 rich gas, Absorber is normally made of Killed Carbon Steel with extra corrosion allowance (no cladding). Regenerator tower is made of CS cladded with 316L.

For production piping system/pipeline, the material selection criteria is very much different for several reasons. Wellheads, manifolds, platform topsides - all are made of solid Alloy 625 or cladded CS with Alloy 625, the pipeline is CS with 3mm corrosion allowance + continuous injection of corrosion inhibitor.

There are several standards available online (e.g. Norsok: http://www.standard..../1176/M-001.pdf) but if you are not confident with yourself and not sure where do you stand at, it's the best option to hire a consultancy or an engineering company to do this work for you.

Best of luck,

[Zauberberg]

Nomi,

I like your statement, and your problem-solving approach. I really hope you wouldn't accept my recommendation as granted - whether do I say "Yes" or "No". It's simply because it is impossible to give you 100% complete answer just based on the information you have provided in your post. And I am not a Material Selection expert.

My reply to your query was based on my previous experiences (existing plants) with observed Absorber/Regenerator material selection for different CO2/H2S ratios and relatively high partial pressures of these components - operating pressure in these units was/is >70 barg. As said, if the feed gas contains both H2S/CO2 normally the Absorber is made of KCS whereas for CO2-only gases I believe that some sort of vessel cladding is required. In both cases, the tower internals were made of SS.

Best regards,

[Propacket]

I would like to refer API Material Seletion Criteria for CO2 partial pressure.

API SPEC 12GDU states, “Carbon dioxide partial pressures in the gas phase below 3 psia typically do not require corrosion control. Between 3 and 30 psia, some form of corrosion control may be required, such as pH control or inhibitor injection. Corrosion resistant metals may also be needed. For carbon dioxide (CO2) partial pressures above 30 psia, design/operational corrosion control measures will be required.”

[Propacket]

Zauberberg,

• You mentioned above that for CO2/H2S rich gases, absorber is made of Killed Carbon Steel with extra corrosion allowance. I am sure you must be talking about an absorber where temperature is not very high. Because corrosion increases with temperature and becomes severe at temperatures near bulge temperature. Therefore , despite the fact that corrosion with CO2/H2S rich gases is not severe compared to that of H2S & CO2 alone, we have to use cladded carbon steel at high temperatures in absorber as well as in flash drum.

• For a gas containing both CO2 and H2S, ratio of CO2 to H2S is very important. If CO2/H2S ratio is very high, cladded carbon steel must be used in absorber regardless of the temperature.

• I agree that regenerator is normally made of cladded carbon steel because of high temperature prevailing in the regenerator but I have some confusion regarding material for regenerator reboiler. Even if amine in the reboiler contains small amount of H2S & CO2 (Lean Loading), potential threat of severe corrosion exists because skin temperature in reboiler may be extremely high than the operating temperature of reboiler particularly with direct fired reboiler. What is your experience about material of reboiler?

Kindly also comment about material for flash drum.

I could not open the link. I think the path was not complete. Can you provide this again?

Thanks

[Zauberberg]

PEngr,

Norsok standard is attached below. As for the materials of construction, here are some additional comments.

CO2-only case: solvent flash drum is CS/cladded with 304L, regenerator overhead receiver made of solid 316L. Reboiler was fired heater made of CS (if I remember well).

H2S/CO2 case: no cladding on the bottom of absorber; solvent flash drum made of CS/cladded with 304L, regenerator as described in my previous post. Reboilers (kettle) made of KCS - both shell and tubes.

Remember - these are design solutions for two existing plants and NOT the detalied guidelines for material selection in Amine Units. I would like us to be 100% alligned with respect to that.

Attached Files

•  NORSOK STANDARD M-001 Materials selection.pdf   499.01KB   160 downloads

[Zauberberg]

Nomi,

To answer that question is beyond my knowledge and competence. I hope we can get a Material Expert involved in this thread so as to help you in getting the full reply.

Best regards,