Crevice corrosion on seawater exchanger
Crevice corrosion on seawater exchanger
(OP)
Any ideas or experiences of major crevice corrosion combine with minor pitting on the tube sheet face made in 254 SMO, especially on the gasket sitting areas, medium seawater at moderate temp of 40 deg C. could this be due to using gasket material having inconel 625 impregnation within?
further will a duplex and super duplex SS for the tubesheet will help in improving the situation?
further will a duplex and super duplex SS for the tubesheet will help in improving the situation?





RE: Crevice corrosion on seawater exchanger
2. I doubt that galvanic corrosoion played a role. Sound like simple crevice. Thought, what is the gagket material?
I have seen units made from 6%Mo superaustenitics that had C-276 weld overlay in the gasket regions.
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Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Crevice corrosion on seawater exchanger
http://w
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NORSOK M-001
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Crevice corrosion on seawater exchanger
The gasket material is compressed non asbestos fiber wire impregenated with inconel wire.
The PRE number for SMO 254 is higher compared to that of Dupelex, in what way duplex SS are considred better except their tensile strength which is better than SMO.
Is it standard practice to have overlay of another material on gasket region of SMO 254? In this case this problem is common in nature.
You experience with coating the tube sheet wtih epoxy coating such as Belzona etc for the protection against pitting/crevice?
RE: Crevice corrosion on seawater exchanger
That aside, the 254SMO is at the low end of superaustenitic and superduplex alloys. The range isn't huge and I wouldn't expect an alloy only a few points higher to work significantly better.
Overlay is common, but not for gaskets. Gaskets are uncommon in seawater service because of the crevices formed. A welded joint would be more typical.
What is your tube material? Coating with epoxy is common when you are using low alloy tubesheets. It might work here. Just remember that the edges or the coatings are crevices also. At least if they are in a flow area they are a lot less likely to begin pitting than in a stagnant area.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Crevice corrosion on seawater exchanger
RE: Crevice corrosion on seawater exchanger
Yes, you are right, sample prep is everything with coatings. A good coater is work every penney (I know one).
My concern about the flow is that I wouldn't want the edges of the coating to to be in a stagnant corner.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Crevice corrosion on seawater exchanger
Is this exchanger at BPCL?
RE: Crevice corrosion on seawater exchanger
Its in the middle east, Does BPCL use seawater as cooling medium for heat transfer?
RE: Crevice corrosion on seawater exchanger
I am not sure about that. But i have heard of failure (Severe Pitting and Crevice) of 32750 Over lay on Flange faces Especially below the gasket faces, despite the fact that the PQR was tested for G48 tests.
There is one more thing you may want to check, whether the flange is distorted (however slight may it be).
This is because during welding, if the flange got distorted, then while machining the gasket face, there could be regions where material is removed in excess than required (Especially towards the outer edge, where the gaskets are located, if it where confined type). It is very difficult to determine the actual overlay available after machining.
When you bolt the flange and the Tube sheet, if you observe the difference in OD then the above reason could be attributed to failure.