PTFE Tape?

[Clyde_Wanderer]

I have been advised not to use PTFE tape on s/s to s/s through hull fittings, namely on the threaded part of a s/s through hull where it will be screwed into the s/s ball valve. (both parallel threads)
Was adviced to use Sikaflex or similar, but I am worried that the valve would turn in the event of being opened or closed due to length of its handle.
Whereas with ptfe tape the valve can be horsed up tight on the t h.
What does the board think?
C_W

 

[VicMallows]

I'm a bit puzzled? .... because in my experience it's PTFE tape which tends to leave the joint free (in the sense that it can be undone deliberately or otherwise easilly). Sikaflex tends to be particularly immoveable! I personally prefer the modern anaerobic plumbing thread sealants which seem to be a reasonable compromise between the two.

Edit: Thinking a bit more, I guess you may be talking about the handle ending up in the right position, in which case you do really need some friction to create a good mechanical lock, though I've always found enough adjustment possible in the final turn onto the thru-hull.

Vic

 

[VicS]

The valve should be locked onto the skin fitting by using a back nut. Then it cannot turn but it can be positioned precisely how you want it

I'd not think the choice of sealant then matters greatly but you would have to avoid excess tape, if tape is used, preventing the nut tightening solidly onto the valve body.

 

[Clyde_Wanderer]

I'm a bit puzzled? .... because in my experience it's PTFE tape which tends to leave the joint free (in the sense that it can be undone deliberately or otherwise easilly). Sikaflex tends to be particularly immoveable! I personally prefer the modern anaerobic plumbing thread sealants which seem to be a reasonable compromise between the two.

Vic

Vic, because both fittings have parallel threads I would need to rely on the tape or whateever else to create an unmovable joint as the t h fitting wont be screwed to the last in the valve as the valve has to be in a certain position to allow the operating handle to get a full arc.
I know from fitting domestic radiater tails that it is the ptfe or gas tape (applied in a cone form) that locks up the tail.
C_W

 

[Clyde_Wanderer]

The valve should be locked onto the skin fitting by using a back nut. Then it cannot turn but it can be positioned precisely how you want it

I'd not think the choice of sealant then matters greatly but you would have to avoid excess tape, if tape is used, preventing the nut tightening solidly onto the valve body.

Vic, there wont be any backing nuts, as they dont come with the valves and trying to get s/s back nuts would be like trying to find hobby horse s**t, plus I have shortened the t h fittings (due to lack of height between under side of cockpit sole and position on hull where valves are sited) so no space for back nuts.
.
Nothing is easy these days.
C_W

 

[VicMallows]

The valve should be locked onto the skin fitting by using a back nut.

Agree entirely! - but never seen one (or indeed used one myself!). I think getting a spanner in to do any good has something to do with it.

Vic

 

[Alfie168]

Vic, because both fittings have parallel threads I would need to rely on the tape or whateever else to create an unmovable joint as the t h fitting wont be screwed to the last in the valve as the valve has to be in a certain position to allow the operating handle to get a full arc.
I know from fitting domestic radiater tails that it is the ptfe or gas tape (applied in a cone form) that locks up the tail.
C_W

PTFE will not lock up anything! Its got a massively low coefficient of friction so its characteristics are singularly unsuitable as a thread lock. It does provide a sealing cushion. I think you will find that radiator tails are often not parallel but you do see parallels on TRV tail threads, and even though you have to use PTFE on them to seal them they do still move very easily, but its non critical, so allowable within reason. Your application sounds a bit critical to say the least

In your case you might need a spacer to enable you to tighten the nut sufficiently, then use a medium/high strength resin based threadlock to lock the nut, but if you cannot get the nut good and tight you may get the whole fitting moving anyway.

Not sure if others will agree but thats my take on it.

Tim

 

[Clyde_Wanderer]

The reason given to me not to use ptfe was that it can cause crevis corrosion on s/s fittings immersed in salt water, advice from offshore engineer.
My other thought was to; from outside the hull screw up the t h fitting fully into the valve until it is fully home (using whatever sealant) then apply sikaflex to the t h fitting, position the valve where it needs to be and while t h is being held on outside by a helper tighten down t h back nut to hull.
C_W

 

[Kylora]

I needed to have the handle of the seacock for my engine cooling in an exact position so that I had room to swing it - I didn't have a locknut and I wasn't happy when fitted with PTFE tape as the valve rotated.

I had blue thread lock liquid in my toolbox, left over from working on car disc brakes, so used that.

Seems to have done the trick - valve doesn't move and threads don't leak.

Ash

 

[Martin_J]

I wasn't sure.. couldn't remember.. But I have just this minute checked three seacocks that I replaced at the beginning of last season. All three have a locknut wound up to the bottom of them to prevent turn...

I used Jet-Lube V-2 plus and a few windings of a PTFE thread and they've not leaked and should be easy to remove when needed.

... and you're all correct... without the locknut there would be the risk of them turning.

 

[Maine Sail]

Why would you use parallel or straight threads as opposed to tapered threads designed for sealing? Tapered threads are designed to seal and all that's needed is pipe dope or teflon tape.

I have never once heard that teflon tape causes crevice or pitting corrosion but then again I don't and won't generally use SS for seacocks or thru-hulls and much prefer 85-5-5-5 bronze or Marelon.

I would love to hear this guys explanation for this as the seal created by the tape should thus prevent any salt water from getting to that area.

Do you guys across the pond often use parallel threads below water with metal fittings? We use tapered threads over here, NPT you guys use BSPT I believe. Folks often incorrectly mix a thru-hull with straight threads with a ball valve that has tapered threads which is not a good idea..

 

[Clyde_Wanderer]

Why would you use parallel or straight threads as opposed to tapered threads designed for sealing? Tapered threads are designed to seal and all that's needed is pipe dope or teflon tape.

I have never once heard that teflon tape causes crevice or pitting corrosion but then again I don't and won't generally use SS for seacocks or thru-hulls and much prefer 85-5-5-5 bronze or Marelon.

I would love to hear this guys explanation for this as the seal created by the tape should thus prevent any salt water from getting to that area.

Do you guys across the pond often use parallel threads below water with metal fittings? We use tapered threads over here, NPT you guys use BSPT I believe. Folks often incorrectly mix a thru-hull with straight threads with a ball valve that has tapered threads which is not a good idea..

I am using Vetus through hulls, (BSP) and the s/s valves are BSP, not BSPT, its what I was given when purchasing them.
Would the method in my thoughts on my last post be ok if I used sikaflex as a sealant?
C_W

 

[VicS]

Re the crevice corrosion issue.
I'd doubt if a crevice will exist when using tape but the small possibility should be eliminated by using a jointing compound.

The best engineering solution, other that back nuts to lock the valve on, is tapered threads ... but you will have little or no control over the final orientation other than by building up a mass of tape on the thread.
Common plumbing practice is to use a tapered male thread with a parallel female but the aeronautical engineers will have a fit.

 

[Clyde_Wanderer]

Re the crevice corrosion issue.
I'd doubt if a crevice will exist when using tape but the small possibility should be eliminated by using a jointing compound.

The best engineering solution, other that back nuts to lock the valve on, is tapered threads ... but you will have little or no control over the final orientation other than by building up a mass of tape on the thread.
Common plumbing practice is to use a tapered male thread with a parallel female but the aeronautical engineers will have a fit.

Thanks VicS but I wont be flying, besides I will have to make best of what I have now.
So I guess ptfe tape is out, and seeing as I will be using sikaflex on the through hull fittings, my best bet is to use this on through hull to valve threads, and screw through hulls all the way until they bottom out in the valves, then hold valves in ideal position and tighten down through hull backing nuts.
Thanks, C_W

 

[electrosys]

Personally I would always use PTFE (Teflon) tape when screwing together soft (316) stainless steel pipework. The tape keeps the s/s thread surfaces from rubbing directly against each other, a process which frequently causes 'galling' (a break-up of the metal surface). Once galling starts, you can end up with a fitting screwed only halfway-in, and it then becomes impossible to either tighten or loosen the assembly. At which point you're completely stuffed, and the only solution is to then cut the fitting off. You only need to experience galling once to learn that lesson - and yes, I've been there ...

For the same reason, I'd be leery of using any fluid or semi-fluid compound as a thread sealant, which could be displaced during tightening, and allow the thread surfaces to then rub against each other.

This problem does not occur with 304 stainless, only with the softer 316.

 

[VicS]

This problem does not occur with 304 stainless, only with the softer 316.

316 is harder than 304
217 compared with 183 Brinell

 

[Deleted member 36384]

Liquid Sealant and PTFE Tape

... For the same reason, I'd be leery of using any fluid or semi-fluid compound as a thread sealant, which could be displaced during tightening, and allow the thread surfaces to then rub against each other.

Pipe thread sealants have anti galling additives and some have a shear resistance in excess of 10,000 psi i.e. they will not be squeezed out. Chemically inert to many pollutants. They also have sufficient ductility to stay in place and seal as the connection flexes if it is pressure cycled. Even better most will also now provide a locking function which requires quite a bit of torque to break free.

Its amazing what you can get in a tube.

My employer has a procedure for PTFE tape. Wrap from the pipe end with firm pressure to blend the tape into the thread profile, dont stretch the tape, just enough for it to take up the thread profile, overlap by 50% as you wrap, trim end of tape flush with nose of fitting.

 

[Clyde_Wanderer]

Thanks all for your advice.
I have experienced galling with bolts/nuts etc, but this can be part prevented by ensuring the threads are clean and free from burrs etc.
Blg old bts, any particulat tube you would recommend?
Thanks.
C_W

 

[electrosys]

316 is harder than 304
217 compared with 183 Brinell

It's not as simple as that. Both 304 and 316 are supplied annealed and will subsequently work-harden, but obviously only if worked ! Ergo, a knife blade made from 304 will be far harder than a deck cleat cast from 316. If you don't believe me, then give both a smack with a hammer and see which one dents.

304 contains a higher percentage of chromium than 316, and thus tends to be harder, and when used for knives will keep an edge, where 316 will not. Most cutlery is 304.

I also find that 316 fixings - in practice - tend to be softer that 304.
Don't ask me why, I've no idea - you've have thought that the amount of work-hardening would be equal.

 

[Deleted member 36384]

... Blg old bts, any particulat tube you would recommend?
Thanks.
C_W

Heldite Jointing Compound Here and here and here

Hylomar Universal Blue (Note also seals threads) http://www.hylomarsealant.com/_resources/_pdf/Hylomar_Univ_Data.pdf

Loktite Brand of Thread Sealants with Thread Locking Properties here

Jet Lube TFW and TF-25 but they are not locking here

My rigs use a lot of the Loktite brand products successfully on various threaded connections.