Seeping threaded fittings... *stainless/brass plastic*

[Deuce]

Hi all, just joined to try and get a definitive answer on this!

When connecting threaded fittings, metal of plastic, what single application thread seal product works best?

We have tried:

• PTFE + silicone. Virtually always seals but will seep if agitated after cured.

• PTFE with Fernox general purpose thread sealant, still sometimes seeps on larger threads 1" or over, and can also fail if agitated after cured.

And also just silicone on some ABS/PVC threaded fitting, as advised by the manufacturer (PTFE can react apparently).

We have to quite often adjust the layout of the kit we assemble and we need to be able to make and break threaded connections relatively quickly, cleanly and not waste time re-working seals as we currently do sometimes. We use threads up to 2" max.

Cost of solution is really not an issue as it's having way more impact on time than we can afford as it is. We also need to be really confident our kit will not leak/seep at all.

I have been looking at Loctite 5776 (LOCTITE 5776 - Thread Sealant - Loctite) and wondered if anyone here had used it, or similar, or could reccomend another product.

I guess as it's so important we don't get leaks, products used reliably for gas might prove most appropriate?

Many thanks in advance

David

 

[ShaunCorbs]

577 is great but won't work on anything plastic

Sounds like you need loctite 55 or boss white and hemp

 

[Chalked]

As Shaun says . Don't use 577 on plastic! It ONLY works with metal.

 

[Deuce]

Thanks both of you.

How reliable/foolproof is 577 generally? For example silicone smoothed into first few threads is normally extremely reliable, initially. But it's not reliable long term. So we need a high tech product that seals as reliably but also copes better with a little movement over time. Can't use a thread 'lock' product though as we do need to be able to break the connections sometimes..

 

[ShaunCorbs]

Never had a leak and you can disassemble when you need to

 

[Deuce]

Have you used on threads up to 2"? And I assume just the 577, no other products used alongside it?

 

[ShaunCorbs]

Yep and straight medium non tapered pipe

Even done an pita 4" one that was in a floor

Follow the spec tho eg need to clean the cutting oil off before you apply it

 

[Last Plumber]

Hi all, just joined to try and get a definitive answer on this!

When connecting threaded fittings, metal of plastic, what single application thread seal product works best?

We have tried:

• PTFE + silicone. Virtually always seals but will seep if agitated after cured.

• PTFE with Fernox general purpose thread sealant, still sometimes seeps on larger threads 1" or over, and can also fail if agitated after cured.

And also just silicone on some ABS/PVC threaded fitting, as advised by the manufacturer (PTFE can react apparently).

We have to quite often adjust the layout of the kit we assemble and we need to be able to make and break threaded connections relatively quickly, cleanly and not waste time re-working seals as we currently do sometimes. We use threads up to 2" max.

Cost of solution is really not an issue as it's having way more impact on time than we can afford as it is. We also need to be really confident our kit will not leak/seep at all.

I have been looking at Loctite 5776 (LOCTITE 5776 - Thread Sealant - Loctite) and wondered if anyone here had used it, or similar, or could reccomend another product.

I guess as it's so important we don't get leaks, products used reliably for gas might prove most appropriate?

Many thanks in advance

David

I take it this is a threaded joint?
What are you putting together?

 

[Deuce]

Yep and straight medium non tapered pipe

Even done an pita 4" one that was in a floor

Follow the spec tho eg need to clean the cutting oil off before you apply it

That's very reassuring to hear! I'll get it ordered.

Yes we clean the fittings, we use loctite spray cleaner.

Thank you so much for the help

 

[Best]

Don't use actual Boss White on anything plastic. It is oil based and will react with most plastics and destroy it

 

[Deuce]

I take it this is a threaded joint?
What are you putting together?

Yes, threaded fittings. Everything else we don in solvent weld as far as possible.

The equipment itself is mostly pool filters/pumps. Which are normally all done with solvent weld. But we have to make the kit modular, mobile and very tough, so we often go onto stainless/brass fittings. We use composite bulkheads to go from one to the other unless we have no choice but to directly mate metal and plastic threads..

 

[Deuce]

Don't use actual Boss White on anything plastic. It is oil based and will react with most plastics and destroy it

Thanks. As it happens I just ordered Loctite 5331 for the plastic threads. So should be all OK.

 

[ShaunCorbs]

Loctite 55 for metal to plastic threads
Loctite 577 for metal to metal threads

 

[ShaunCorbs]

Thanks. As it happens I just ordered Loctite 5331 for the plastic threads. So should be all OK.

Never tried that myself let us know how you get on

 

[Last Plumber]

Yes, threaded fittings. Everything else we don in solvent weld as far as possible.

The equipment itself is mostly pool filters/pumps. Which are normally all done with solvent weld. But we have to make the kit modular, mobile and very tough, so we often go onto stainless/brass fittings. We use composite bulkheads to go from one to the other unless we have no choice but to directly mate metal and plastic threads..

I see. I was asking just to make sure that they are taper threads and not face joints.
If you've sorted it, then all's well and good.

 

[Deuce]

I see. I was asking just to make sure that they are taper threads and not face joints.
If you've sorted it, then all's well and good.

Most are taper threads, some straight. For straight we normally apply sealant on male and female, rubbing it down right into the threads before assembly. This generally means the sealant isn't just pushed down the female thread. Obviously a lot is... But we don't have to worry about contamination as not potable water. Also anything that is pushed down the thread, will get picked up by filters down the line.

But is there a better way for straight threads?

 

[Last Plumber]

Most are taper threads, some straight. For straight we normally apply sealant on male and female, rubbing it down right into the threads before assembly. This generally means the sealant isn't just pushed down the female thread. Obviously a lot is... But we don't have to worry about contamination as not potable water. Also anything that is pushed down the thread, will get picked up by filters down the line.

But is there a better way for straight threads?

More often than not, yes.
What make/ type of fitting are you using and I'll let you know if there is a better way.

 

[Deuce]

This kinda stuff..

Low Pressure Stainless Steel Fittings - Dual Pumps

Or

Low Pressure Brass Fittings - Dual Pumps

From any number of manufacturers. We often get very short lead times and have to hunt the UK for stock.. But essentially, brass and stainless. Typically 1" - 2".

 

[Last Plumber]

This kinda stuff..

Low Pressure Stainless Steel Fittings - Dual Pumps

Or

Low Pressure Brass Fittings - Dual Pumps

From any number of manufacturers. We often get very short lead times and have to hunt the UK for stock.. But essentially, brass and stainless. Typically 1" - 2".

Most look like taper threads. The ones that aren't sometimes you can get a fibre washer to sit in the female if there is a shoulder inside so that the male will screw right down onto it but that is normally only possible when the male will screw fully in easily, as in parallel threaded or not tapered enough to tighten into the female thread, if that makes any sense at all?

Do you use BES?

 

[Deuce]

Most look like taper threads. The ones that aren't sometimes you can get a fibre washer to sit in the female if there is a shoulder inside so that the male will screw right down onto it but that is normally only possible when the male will screw fully in easily, as in parallel threaded or not tapered enough to tighten into the female thread, if that makes any sense at all?

Do you use BES?

No shoulder in the female sockets usually. Yes even parallel threads often don't go all the way without quite some effort... plus the thread itself isn't often fully cut for the last 10mm of some fittings. With parallel we probably get less leaks though, as we simply got OTT with sealant. which is messy, yet effective.

We do use BES and others. It really depends what we need and lead time to be honest.

 

[Last Plumber]

I tend to use Loctite 55 on metal threads. Never tried it on plastic though.

 

[quality]

Sorry to butt in here but Ive used 577 since it was introduced in the early 90`s is 5776 something new?

 

[Deuce]

Sorry to butt in here but Ive used 577 since it was introduced in the early 90`s is 5776 something new?

It's just a variant within the range, fast curing. Which for us is good.

 

[quality]

I will stick with 577 it ok above 60 degrees but 5776 maybe cheaper

 

[Deuce]

I will stick with 577 it ok above 60 degrees but 5776 maybe cheaper

The only difference I can see is that 577 says it will lock the thread, whereas 5776 says only seal. Price is the same, £20 ish for 50ml (without discount).

As for price, I would pay £300 a tube for something that was always 100% reliable. £500 if it was overseas work

Our work goes into TV & film studios with 400v power cables strewn across the floor, £200k per day downtime costs etc.. threaded fitting are not the most popular subject in our workshop..