Any experiences in sealing for large diameter body flange (>8ft) in a fluoropolymer lined vessel

[ehbadger]

Hi All

I am researching a new design for a separator in acid service (rules out 100% metallic construction) and am looking for some industry experience... Background:
- horizontal tank
- about 8ft diameter, 15ft long
- body flanged at one head (full tank diameter)
- there is a large baffle assembly inside that was installed through the one end
- once pack installed, vessel was brick lined.
- Operating pressure is low, around 10psig. Temperatures range from about 40F to maybe 110F
- process includes strong HCl acid

Basically the brick in the vessel is at end of life and there is debate on the new vessel design.

1. Glass lined steel is a good candidate except for the huge diameter body flange, which would seem to potentially be very difficult to seal, as flatness issues typically arise >3ft diameter. One way around that was a bafflepack design that can be installed in small pieces through a normal manway, but that will mean nearly impossible to inspect as getting it removed each time would be a huge safety risk (very difficult to clean, as the modular design seems to consists of numerous long, flat plates very close to each other) and time sink. Going with this nearly cements the fact we would not be able to inspect the entire vessel in the future. And designing a vessel knowingly that cannot be inspected doesn't feel right to me at all.

2. Plastic lined steel (vacuum bonded PVDF or PFA) is a good candidate as well; however I have no data on sealing a flange that large. I personally feel this is a good option, but would definitely want the ability to open the head, pull the pack, and 100% internally inspect, since plastic welds aren't quite as reliable as say a brick lined system.

3. Brick again, but we have serious issues cleaning it now (sticky materials, brick outgasses, etc...), and would require huge effort if we needed to change or move the baffle pack (unbrick and rebrick an entire head).

So, all that to say, does anyone have some experience/reliability with a large diameter plastic lined flange that they could share? Specifically on how easy/hard to get a good seal. I just don't have anything of comparable size so I can't comfortably make a strong case one way or the other. I've probably forgotten or mucked up some detail so please ask for any clarification on something, if needed. Thanks!

 

[SnTMan]

ehbadger, no direct experience with so large a flange, but I'd say it will be almost entirely a manufacturing problem, rather than a design problem.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[ehbadger]

SnTMan,

Thanks for the reply. I am inclined to agree; with the vacuum bonding I would think the flatness of the steel flanges is the chief factor, whereas with glass the glass itself can have varying thickness, and the heat cycle can warp the flanges and vessel.

 

[Compositepro]

Glass lined reactors with large head flanges are not unusual. A teflon gasket is pretty conformable. I do not think that sealing will be the problem that you think it is. Just talk to vessel manufacturers.

 

[ehbadger]

We have talked to Pfaulder and De Dietrich. We use expanded PTFE gasketing usually (skivved).
How large of flanges have you worked with? We also have experienced issues with spalling at the radius on the larger diameters. I probably should've included that in my first post.. sorry. That was an additional reason we have been steering away from glass (if we didn't have the spalling issues I think we would've already been sold on glass, however issues in on of the European plants with the aforementioned spalling has people on edge with that strategy).

 

[Compositepro]

By spalling, do you mean chipping due to impact damage? You might also consider looking at a fiberglass vessel for your application.

 

[ehbadger]

Spalling being similar to that from impact damage, but we also see it sometimes on the radius of the flanges (higher stressed area) that should not be a result of impacts. I'll see if I can dig up photos later. Will investigate FRP - not sure if lifetime would be acceptable given the high acid concentration though.

 

[ehbadger]

Anyone have experience with FRP (fiberglass) vessel with a flange this size?

 

[MaverickAppliedScien]

We have quite a bit of experience with FRP flanges this size and larger. The flange should not be a major factor, other than the cost. We are currently inspecting a 5' diameter FRP Scrubber being built with body flanges and we have a great deal of history designing and inspecting this large FRP equipment. I would be happy to help more, if you're still interested.

Tom Haber
thaber@mas-mss.com
Maverick Applied Science

 

[A8yssUK]

Hi all I am a sealing engineer specialising in expanded PTFE, bit late to the party sorry, but hopefully I can still be of use.

Large diameter glass lined steel (GLS) not a problem for expanded PTFE (ePTFE) tapes, I've seen even older 2m+ diameter vessel sealed no problems by it, just requires a careful installation. You can layer them up in local sections (known as shimming) to account for flange flatness issues, I'd suggest getting specific training for this its very useful. I've seen applications were 6mm thick ePTFE has been layered up 10 times (60mm of gasket, shimming up roughly a 30mm gap!), I obviously don't recommend that... but 3-4 times in a local area is easily done and quite commonly done with larger flanges (not just for GLS).

I'd send you a link to a good ePTFE tape made just for GLS as its requires less surface stress, but I work for the company that makes it; so I assume that's against the rules.
However if you spoke to De Dietrich they probably recommended the same thing anyway as they do on this webpage....

http://www.dedietrich.com/en/solutions-and-products/distillation/

As for the spalling, is this just on the flange facings or do you mean on the actual ID of the vessel? If near the flanges ensure your using a ePTFE tape that is wide enough to cover the whole flange face and a bit more into the rounded section. A good gasket should conform to the whole flange face, especially if it's rounded like in GLS applications. Some harder filled PTFE materials (and /or envelope gaskets) don't do this quite so well. The idea is to try and prevent a crevice or dead spot being formed in the vessel were local super concentrations can occur which could attack the surfaces.

Hope this helps.

Dan

 

[ehbadger]

No sure what company you work for, but yes, we typically use ePTFE (specifically Gore) tape on GLS. This year we are starting to use the new Series 1000 Tape. Previously we used Series 600. We did get training on the new tape. I do know we've shimmed before, although I've not heard about 10x! I think Gore literature includes reference for up to 3 shim layers.

We always try to get the wishbone shape - "overhanging" gasket on ID and OD to combat suck-in/blow-out. For the spalling, it seems to be more on the radius of the flange internal to the vessel. As I mentioned before, we've had lots of problems with that specifically from our European plant - and they use envelope gaskets. So it is a "lively" discussion when trying to recommend GLS for this project as they have lots of problems with it (whereas here in the USA we've don't see that radius spalling). Trying to convince them to move away from envelope gaskets is like pulling teeth, but we keep at it

Thanks

 

[A8yssUK]

Good to know you are using the good stuff! Series 1000 is rather good (I should know I helped develop it ) Yes, I work for Gore Sealants in Munich, so I maybe a little biased

Now just to make sure I and/or Gore would never recommend doing more than 3-4 shims, the 10x case was crazy... but it worked and from what I understand is still working... but please consult Gores technical department.. blah blah blah..don't sue me...

As for the spalling of the glass surface on the inner diameter of the vessels, I doubt it's a gasket issue unless bits of envelope gasket are falling off or some sort of particulate is forming in the crevice between the gasket and the flange face.. which is then somehow abrading the surfaces..but these are pretty wild guesses. De Dietrich's engineers are in a better position to help you here I think.

If your European colleagues want any help moving away from 20th century old school envelope gaskets to 21st century ePTFE tape, please point them towards us.

Dan

 

[glsinfo]

To solve the problem of inspection, have you looked at continuous lining monitoring? Both GLS companies you mentioned produce them. They are very "sensitive" (aka. a pain to set up) to process conditions, but it sounds like your process is a settler (my assumption) with very little process conditions changes. Use of this device will allow you to go with insertion of the baffling/ internals from a manhole and eliminating a belly flange in a horizontal tank.