Spiral Wound Gasket filler selection for seawater applications 1

[Henrique Orlandini]

I'm currently working on a seawater piping service and I need to selected the proper gaskets to avoid corrosion due to seawater in contact with super duplex steel.

For seawater, I was told that the "rule of thumb" was to always use PTFE as a filler for spiral wound gaskets, since graphite filler isn't compatible at all with seawater. But reading NACE paper 07262, I can see that PTFE also performs poorly in contact with seawater. So in a situation where the seawater manages to "leak" into the gasket sealing area, I understand that both graphite and PTFE will allow crevice corrosion to eventually happen.

If I follow the recommendation from the same NACE paper on flat gaskets, I should be using Neoprene or FKM for the filler - if those are actually commercially available is something to consider also.

Is my understanding on filler material for seawater correct? Even though we've been using only graphite and PTFE filler for ages and our customers usually accept those, I would not like to see some warranty situation for flange corrosion in seawater services.

 

[TugboatEng]

I was going to make some suggestions but it looks like Flexitallic has a specific solution.

https://flexitallic.com/product/corriculite/

Whatever you do, don't use graphite.

Crevice corrosion is a result of incorrect flange material selection and will not be prevented with gasket selection.

 

[Henrique Orlandini]

Thanks TugboatEng, this solution from Flextallic seems great.

From what I understand, graphite in seawater would create a extremely favorable environment from corrosion.

So in a situation in where the flange material is correctly selected, a PTFE filler gasket would be acceptable, no?

 

[TugboatEng]

Graphite is by far the most noble in the galvanic series and will cause galvanic corrosion it with any material it is couples with. Graphite is excellent for hot, non-conductive fluids. Not so much for anything else.

PTFE is ok, it's non conductive. It's biggest weakness is creep. PTFE on its own can't support the clamp load from the bolts and loses compression over time. Reinforced PTFE is better but can get very expensive.

Stainless steels are also very noble so your metal reinforcement selection is going to be important. You likely want your reinforcement to be slightly more noble than your piping.

 

[Benoit labre]

Evening
Graphite on sea water application is a definite no. It will corrode quickly any type of flange
PTFE causes also corrosion issues. We have seen it on many occasion when used in spiral wound gaskets.
That is why we have developed the corriculite material as Henrique described above
If you need any more elements on this please drop me a line
blabre@flexitallic.eu

Thanks

 

[SJones]

Is it a definite no? @Benoit labre - what about your CGI gaskets that are indicated as keeping the fluid off the sealing element?

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]

Once you address galvanic issues then think about crevice corrosion.
Remember that the tighter the crevice the more severe the conditions.
This is one reason that you see seawater lines in 2205 with flanges that weld overlayed in C276.

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P.E. Metallurgy, consulting work welcomed