i'm looking for opinions on task-line gasket 1

[keller529]

a greybeard i work with is telling me to research the taskline gasket as he's never seen one fail by blowout. does anyone have any experience? we switched most of our plant over to cut eptfe sheet w/ fillers. this was before my time.

fyi taskline gasket is molded ptfe but has a perforated steel core embedded inside. individually hand-made as i understand, so i suppose they're rather expensive? what alternatives exist, just trying to glean on others' experience with it. thank you

 

[LittleInch]

Flange class?, contents, design pressure, temperature, flange material a have an impact on gasket choice, not to mention cost and whether the flange gets made and broken in a regular basis.

PTFE can creep a bit I think.

A link to the vendor would be good.

 

[keller529]

Flange class?, contents, design pressure, temperature, flange material a have an impact on gasket choice, not to mention cost and whether the flange gets made and broken in a regular basis.

PTFE can creep a bit I think.

A link to the vendor would be good.

150# stainless flanges at around 100 psi. used in pulp and paper processing

 

[A8yssUK]

I wish I read your thread here before replying to your other one and told you what you knew already... I regret nothing!

The metal core here really only aids blow out from over pressures and 100 psi is frankly nothing.. so a blow out is really only going to occur with loss of load so creep resistance is what you need more and your using ePTFEs's already so the metal core is basically doing very little. I've seen sheet PTFEs used without metal supports well past 100 bar in industry (but above 40 bar is generally recommended to use metal supports). Blow out testing (ASTM HoBT lab tests ) I have done myself on decent ePTFE and filled PTFE sheet gasket materials exceed 200 bar and the gasket stress loss needs to be over 90% before a major leak occurs.

If you are seeing blow outs then perhaps rather look into used bolt up procedures and see if you can increase the starting installation torques to utilize the gasket/flange/bolt materials better; generally a higher initial torque would then require the system to creep more to lose enough load to become an issue. Also a retorque after a heat up and cooldown procedure does wonders. [But don't hot torque!!]

Extra bonus points can come from disc spring washers / Bellevue washers which are awesome, but require some careful selection and utilisation.

 

[keller529]

I wish I read your thread here before replying to your other one and told you what you knew already... I regret nothing!

The metal core here really only aids blow out from over pressures and 100 psi is frankly nothing.. so a blow out is really only going to occur with loss of load so creep resistance is what you need more and your using ePTFEs's already so the metal core is basically doing very little. I've seen sheet PTFEs used without metal supports well past 100 bar in industry (but above 40 bar is generally recommended to use metal supports). Blow out testing (ASTM HoBT lab tests ) I have done myself on decent ePTFE and filled PTFE sheet gasket materials exceed 200 bar and the gasket stress loss needs to be over 90% before a major leak occurs.

If you are seeing blow outs then perhaps rather look into used bolt up procedures and see if you can increase the starting installation torques to utilize the gasket/flange/bolt materials better; generally a higher initial torque would then require the system to creep more to lose enough load to become an issue. Also a retorque after a heat up and cooldown procedure does wonders. [But don't hot torque!!]

Extra bonus points can come from disc spring washers / Bellevue washers which are awesome, but require some careful selection and utilisation.

Thanks for your insightful response. these gaskets were invented before eptfe was even a thing so perhaps there are better alternatives to them now. however i understand that eptfe is a very porous material under a microscope compared to virgin ptfe which is more dense. do you know how that would affect sealability? i know there are filled eptfe compounds that probably resolve some of those drawbacks - but at the expense of what? chemical compatiibility? thanks in advance. i feel like i need a eptfe sheet 101 class lol

 

[A8yssUK]

ePTFE is porous when uncompressed, apply several tonnes of force in a flange and it is no longer porous so gets to the same density as virgin PTFE, yet has more strength from the now much more structured material. The compression of ePTFE is no way linear, they compress very easily and become dense very quickly. If for some reason you cannot put enough force into the material (plastic flanges, glass lined steel), gaskets exist with pre-compressed dense sections to act as permeation barriers (Gore Universal Pipe Gasket and/or other PTFE envelope types) or add stress peaks/ridges to gain more densification in certain spots ("stress saver" types)

Now the following analogy isn't 100% accurate but is close enough, any material/polymer scientists please look away for a minute

Imagine you are doing a tensile test on a steel bar, pull it until it breaks say at 1500kg of force. During this test it stretches 60%.
Now get another bar twice as big, stretch it 50%. (lets say it takes roughly 2500kg of force to do) Cut out a smaller bar from the stretched deformed section the same dimensions as the first bar. i.e. half the size
Now this third expanded bar with the same dimensions of the first bar and the same material just prestressed, do a tensile test on it... what will you see ?
It basically won't change dimension until you give more than 1250kg of force on it, it will still break at around 1500kg but with only a ~10% deformation.

Now ePTFE is the same(ish) principle, the "fibres" of the PTFE have been prestressed so require more force to now stretch them. Now we can prestress/expand them in different dimensions, x,y or even z. In good ePTFE gasket sheets they are prestressed in both the x and y direction but not the z (z being compression direction). So they are easy to deform in the z direction and hard to deform in the x-y direction. Now, if you deform the z direction so much that you reach a density were to deform it any more in this direction you must also change the x-y dimensions (we call this the ultimate density) it becomes much harder to deform the material. So for a sheet gasket material you want to be able to get quickly down to this ultimate density during installation load then during service when the heat comes in you want it to deform the gasket in the z-direction as little as possible. The pre-stressed "fibres" now hinder the ability to deform in the x-y direction preventing z-direction deformation too. This is how we add creep resistance.

Other sheet PTFEs do it differently by adding fillers which basically increases the friction inside the material which hinders the x-y deformation...guess which way works better

If you want more details on ePTFE gaskets.. head to www.gore.com/sealants or https://teadit.com/us/categoria/eptfe-products/ both make good ePTFE products. Beware of bad ePTFE's

Disclaimer, as I've said before on this forum I work for Gore.