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Socket Weld and Corrosion Allowance in Wet CO2 Service

Socket Weld and Corrosion Allowance in Wet CO2 Service

Socket Weld and Corrosion Allowance in Wet CO2 Service

Does anyone have experience with using SW for SB pipe in wet CO2 service. I am finalizing specs for a CO2 Capture FEED and am trying to work out whether I should allow SW for SB pipe. Literature online indicates I may need a small corrosion allowance with 316/316LSS for this service (assuming a 30-yr life) so I wonder if crevice corrosion will be an issue with SW joints. On the other hand, this is a CO2 capture plant and there should be no chlorides or H2S and if folks are using SW in sour service (according to another thread here) I think it would be appropriate for this "sweet" service.

Process stream conditions range:
up to 280F
up to 50% H2O (balance CO2)
up to 750 psia

Any recommendations on corrosion allowance would also be welcome. There are many sources that recommend 316 for wet CO2 but little information on corrosion rates or guidance on whether CA is necessary.

RE: Socket Weld and Corrosion Allowance in Wet CO2 Service

Not necessarily directly applicable to your application, but CGA G-6.1 section 8.3 discusses the use of stainless socketweld fittings in "dry" CO2 service. In general if given the choice, and availability of a competent welder that will pass the 5%RT, I would go with BW fittings due to lower SIF / higher flexibility that can withstand the required cycles over 30 years. At a design pressure around 750 I would think unthreaded sch.40 316 pipe with even 1/16" ca would have more than enough pressure rating for you, but you csn calculate that for yourself in b31.3

Not making a decision is a decision in itself

RE: Socket Weld and Corrosion Allowance in Wet CO2 Service

Have you considered the issues with crevice corrosion that socket weld fittings create?

RE: Socket Weld and Corrosion Allowance in Wet CO2 Service

Just because the design is for a Cl free environment there is no telling what upsets may happen.
And given 750psi CO2 if add a little water and Cl you can have crevice corrosion easily.
Try to avoid it, it will save a weak place in the system.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Socket Weld and Corrosion Allowance in Wet CO2 Service

What is SB pipe? I've looked it up and all I find is adverts for a construction company

Ed, did you miss the bit about the fluid being 50% water?

Personally I've never worked out why people use SW fittings. I think they're terrible things and shouldn't be allowed anywhere near a high pressure corrosive fluid. Any minor savings are overridden by failure later on in operation. And most of the time I suspect many are not installed with the gap at the end of the socket you're supposed to have.... No way of really checking once it's welded

Mind you I hate slip on flanges as well...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Socket Weld and Corrosion Allowance in Wet CO2 Service

Thanks for the responses all:
SB = Small Bore, (< 2"). Everything above would be BW regardless as is standard. So we are *almost* exclusively discussing drains and instrument connections here. I say almost because this is just a FEED and it is conceivable additional process connections could be added in a later stage.

Crevice corrosion was the impetus for this post given the interplay between CO2 and H2O (shame on me for not saying so!). I am not sure how chlorides could get in the mix given the water originates from vapor that is condensed as the CO2 is cooled prior to compression and between compression stages but I would be happy for someone with experience to prove me wrong.

I am not opposed to requiring BW for SB pipe, I just saw this post where folks were discussing SW for sour service and wanted to make sure I was not being overconservative by specifying a 1/16" CA and BW for SB:

Based on the literature I was able to find, 316SS is definitely the right choice but these finer details were not available.

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