Partially Cladding Liquid Seal Drum for Flare Gas Recovery System 3

[Hajiwaji]

Dears,

Is it a sound engineering practice to only clad the water containing part of a liquid seal drum in sour service. Won't this create galvanic corrosion in the interface between the cladded portion and the bare CS portion?

Thank you

 

[EdStainless]

If you clad far enough that the exposed CS is always dry then you are fine.
But if the interface ever gets wet you are in trouble.
Most people try this to save money, and as a result cut it too close, and end up regretting it.

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P.E. Metallurgy, consulting work welcomed

 

[Hajiwaji]

I agree with EdStainless. But what if condensation happen on top shell or head of the vessel and slide back to the clad/CS interface? Or is it assumed that the interface is always dry and no crevice corrosion will happen?

 

[SJones]

No. Yes.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Hajiwaji]

SJones,

Is this a reply to the original post or my reply to EdStainless?

Thank you

 

[SJones]

The original post contains two questions to which I replied.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Hajiwaji]

Thank you Dr. SJones, noted.

 

[MortenA]

I think its a bit harsh to say its against good engineering practices to have partially cladded vessels - but the problem with "over optimized" units are that things always change. So what your design considered a "design condition" can be challenged almost the day its brought into operation. And then people might forget some initial assumption and this might cause trouble.

--- Best regards, Morten Andersen

 

[SJones]

@Morten - that’s part of it. The other issues are how precisely is the water (/glycol) level maintained; how corrosive is the gas; what will be the opex of inspecting the unclad portion of the vessel versus the additional cost of full cladding; what is the impact of having the vessel down for a major repair to the damage at the interface, and so on and so forth. Partial cladding invites issues. Partial coating might be considered a step in the right direction, but, again, full coating would be better.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

I see this in high alloy vessels a lot. The bottom in more corrosive so they use a high alloy and the switch to a lower grade (less expensive) for the upper portion.
The people that were conservative and allowed some extra margins are usually fine, the guys that cut it close are always having failures at the junction.

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P.E. Metallurgy, consulting work welcomed

 

[SJones]

@Ed - I’m with you. I’ve come across a couple of vessels with nice knife line attack on the carbon steel at the interface.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[mrfailure]

This is also a generic general problem where application of resistant material ends before it should. My example comes from when I worked on power boilers, where long term overheat ruptures occurred because the designers placed transitions from chrome-moly to stainless steel too far downstream in the flow path. Like this example, cost estimates drove the process though in power boilers the true cost is the lost generation while the boiler is repaired. (Please forgive me if I got too much off topic...)