Flange ring groove inlay 2

[RandomAxe]

I am designing a subsea pipeline system that is tying into an existing manifold. We are reusing a tie-in point (wn flange) for a decommissioned field, so the flange we are tying into has been used previously. Reviewing the original design (20yrs old) it appears that the wn flange (on manifold) is a carbon steel flange with no inlay, but the tie-in spool that was connected to it had a carbon steel swivel ring flange with a ring groove inlay. I haven't seen this done before, are there any reasons it would of? I have always worked on the basis that either both require to be inlaid or neither of them. Should this of corroded?
The new pipeline system will all be inlaid, so I'm thinking a pup piece will be required with carbon steel flange at one end and then inlaid at the other.
Its ASME flanges so no face to face contact.
Thanks

 

[SJones]

It usually happens when responsibility for manifold manufacture and pipeline construction falls on different parties/teams. One party/team decides that sealing surfaces require CRA to control corrosion, and the other party/team doesn't, for whatever reason. Externally, it generally isn't an issue, however, the fluid is expected to be corrosive, hence the pipeline is "inlaid" (assumed to mean clad/lined) which could lead to an internal flange face corrosion problem. Of course, that begs the question: why have a CRA clad/lined pipeline tying into a bare carbon steel manifold? Followed by: where will the cladding/lining be terminated?

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.

 

[RandomAxe]

Thanks for the reply. That sounds about right, there's not much in the way of design documentation to confirm.

Sorry I meant the old pipeline system not new, and the old pipeline and spools had ring groove inlaid flanges, its just the manifold pipework that doesn't.

I was planning to use super duplex spools and assumed the wn manifold flange would be ring groove inlaid at least. Assuming existing flange is carbon steel (no inlay) I guess I will have to use a pup/transition piece (no inlay at one end and full face at the other) to connect to super duplex spool.

 

[SJones]

What is the selection driver for a SDSS spool? There will be issues with material quality and cathodic protection, as well as the remaining question: why CRA spools into a carbon steel manifold.

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.

 

[RandomAxe]

Thanks for replying. It is a WI pipeline and we have selected CRA materials. It is a 3rd party manifold and they have advised that the carbon steel pipework has been inspected and they have no integrity concerns.
Would there be a significant corrosion risk from tying a super duplex flange into a carbon steel flange? It is ANSI/ASME flanges so the faces wouldn't be touching. I'd imagine best practice will be a pup/transition piece as mentioned above.

 

[SJones]

Seawater WI, or Produced Water WI? Mixing the materials shouldn't be an issue from an internal corrosion point of view in produced water. For seawater, loss of oxygen removal treatment control could create substantial problems for the carbon steel. Gasket selection would also be problematic. Thus, it does seem to be that a transition piece offers a workaround. The carbon steel flange to mate with the SDSS flange should have the mating surface completely overlaid with alloy 625 and a 625 gasket/ring.

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.

 

[RandomAxe]

Thanks Steve, it is treated seawater but as you say if there are issues with any of the oxygen removal etc on topsides this could cause problems - my concern is we then introduce a 'weak' section in our system given we've gone for CRA materials elsewhere. However the 3rd party system is carbon steel and been in service 20yrs so they must be doing a decent job of keeping the water in spec.
If there was an issue with the oxygen levels and there was a super duplex flange connected to a carbon steel flange would we then likely see galvanic corrosion in and around the ring groove of the carbon steel flange?
We have specified 825 gaskets.
Thanks

 

[SJones]

Oxygen corrosion issues, including galvanic effects at dissimilar metal interfaces, will be dependent upon the magnitude and duration of the excursion events. Hypochlorite overdosing can also be detrimental. The third party might have been on top of their water treatment game, but someone on your project isn't so confident and has plumped for some serious capex in selecting SDSS. 825 won't be very resistant to oxygenated seawater either. See if you can get hold of EEMUA Publication 194 to look at materials recommendations for flanges and gaskets.

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.

 

[RandomAxe]

Thanks, will do.