How to seal 304Stainless NPT threads

[Tropicpine]

TLDR; Need advise on sealing 304Stainless NPT threads. Bare threads do not seal. I have tried PFTE tape (not dependable). I could not get solder to flow into threads. Fitting exposed to beer at high temp for log periods ... do not want to use pipe dope or plumbers putty.


When piecing my system together I tried to eliminate anything that could not be simply dismantled, sanitized and reassembled. My choices for a pump that met the above criteria and was rated to operate at 212°F+ was very limited. The pump I could find has NPT threaded ports to which I have fitted 1.5" tri clamp adaptors. My somewhat limited experience with NPT fittings is that they work pretty well with softer metals that will deform to fit under compression (ex. brass, copper, aluminum) but significantly less well harder metals like 304 stainless. My pump and its tri-clamp adaptors are a prime example. The most exasperating task on my brew prep day is applying freshe pfte tape (which has to be removed for post brew cleaning) assembling the system, testing for leaks (which usually occur at the NPT joints on the pump) (all other fitting are 15" tri-clamp), cussing, having to dismantle the system, removing the pfte tape, applying new pfte tape, reassembling, testing and praying.
On my last brew prep day I set aside my asperations of brewing and attempted to solder the NPT fittings with no success.

As these joints are exposed to the hot wert throughout brew day I do not consider plumbers putty or pipe dope acceptable methods.

What would you advise to seal the NPT joints permanently & sanitaryly .

My next guess is to have the joints sanitaryly welded & polished.

 

[MaxStout]

I'm curious as to why PTFE tape doesn't seal. Do the threads have burrs or spalling? What kind of PTFE tape are you using? The thin stuff from the hardware store doesn't do a good job of filling voids. A few turns of good, thick tape might do the trick.

 

[Bobby_M]

First, PTFE tape is the solution for sealing NPT threads. If you can't get it to seal you're not achieving a reasonable thickness so either wrap it more times or use a much thicker tape. Also make sure you're wrapping in the correct direction.

You do not need to break threads down after every brew day if it's on the hot side of the brewing operation. Just pump hot PBW solution through the wort paths for a while and rinse with hot water.

Threading on TC adapters does not make the system any more sanitary. It doesn't remove the nook and crannies and even when NPT threads are meshed together, there are several threads left exposed to the liquid path. Even if you got the silver solder to work, you'd be left with those threads and no way to easily take it apart.

There are some cases where you have minimal threaded connections in an otherwise fully sanitary/TC system where you can permanently convert the threads to TC, but it does get expensive to do it right.

See the fillet weld here... the liquid never touches the threads..

 

[Broken Crow]

TLDR; Need advise on sealing 304Stainless NPT threads. Bare threads do not seal. I have tried PFTE tape (not dependable). I could not get solder to flow into threads. Fitting exposed to beer at high temp for log periods ... do not want to use pipe dope or plumbers putty.


When piecing my system together I tried to eliminate anything that could not be simply dismantled, sanitized and reassembled. My choices for a pump that met the above criteria and was rated to operate at 212°F+ was very limited. The pump I could find has NPT threaded ports to which I have fitted 1.5" tri clamp adaptors. My somewhat limited experience with NPT fittings is that they work pretty well with softer metals that will deform to fit under compression (ex. brass, copper, aluminum) but significantly less well harder metals like 304 stainless. My pump and its tri-clamp adaptors are a prime example. The most exasperating task on my brew prep day is applying freshe pfte tape (which has to be removed for post brew cleaning) assembling the system, testing for leaks (which usually occur at the NPT joints on the pump) (all other fitting are 15" tri-clamp), cussing, having to dismantle the system, removing the pfte tape, applying new pfte tape, reassembling, testing and praying.
On my last brew prep day I set aside my asperations of brewing and attempted to solder the NPT fittings with no success.

As these joints are exposed to the hot wert throughout brew day I do not consider plumbers putty or pipe dope acceptable methods.

What would you advise to seal the NPT joints permanently & sanitaryly .

My next guess is to have the joints sanitaryly welded & polished.

My first thought was to wonder if perhaps your fittings are genuine NPT...not all online dealers are circumspect in their details and too many will pass off BSP as NPT which can be mated, at least in the 1/2" size with a lot of extra teflon tape and torque, but it's not ideal. Since it sounds like this is only your pump threads and you don't name the make of pump, I looked through your older posts and found this:
https://www.homebrewtalk.com/threads/conical-fermenter-also-as-boil-kettle.689845/#post-9201007
Cool! I love unique set-ups! I had actually expected to find the popular MP-15RM, but I can't identify that pump in the picture.
Given you're just going to TC anyway, maybe you could consider replacing the pump for one that has TC fittings from the get-go:
https://www.brewhardware.com/product_p/mark2ss_tc.htm

 

[Tropicpine]

First, PTFE tape is the solution for sealing NPT threads. If you can't get it to seal you're not achieving a reasonable thickness so either wrap it more times or use a much thicker tape. Also make sure you're wrapping in the correct direction.

You do not need to break threads down after every brew day if it's on the hot side of the brewing operation. Just pump hot PBW solution through the wort paths for a while and rinse with hot water.

Threading on TC adapters does not make the system any more sanitary. It doesn't remove the nook and crannies and even when NPT threads are meshed together, there are several threads left exposed to the liquid path. Even if you got the silver solder to work, you'd be left with those threads and no way to easily take it apart.

There are some cases where you have minimal threaded connections in an otherwise fully sanitary/TC system where you can permanently convert the threads to TC, but it does get expensive to do it right.

See the fillet weld here... the liquid never touches the threads..

First, thanks for the reply.

The connections on my pump head are male NPT. Unfortunately the threaded connection on the input side screws flush with the inner surface of the tri-clamp adapter (see attached picture) and the output port protrudes just beyond the inner surface of its tri-clamp adapter. ... If I am sealing the connection with PFTE tape the crevices of the threaded connection are exposed to the process stream. Furthermore, these connections are in contact with the wert until cooldown is complete. ... These threaded connections do need to be broken down, sanitized and resealed between each use.

I would love to have connections like the one you pictured but this pump was the only pump I could find that was rated for sanitary use at or above boiling temp that did not require its own cart.

Also, NPT threading is slightly tapered or conical. ... Once a NPT fitting is sealed if the fitting for any gets any torque that slightly loosens the fitting or the metals on either side of the NPT fitting have a different coefficient of thermal expansion (I would love to have been able to source all my parts from the same manufacturer but I just don't live in that perfect a world) and the fitting undergoes significant thermal changes (like brewing) the fitting can leak. The leaks can be resolved by tightening the fitting but doing so with a hot process column full of sweet, sweet, sticky wert has led to more than more than one fit of cursing.

The other major argument against my ambition is that once brazed/soldered the connection will never again be separable. So long as all surfaces in contact with the wert are sanitizable, this will make me happier.

 

[Tropicpine]

My first thought was to wonder if perhaps your fittings are genuine NPT...not all online dealers are circumspect in their details and too many will pass off BSP as NPT which can be mated, at least in the 1/2" size with a lot of extra teflon tape and torque, but it's not ideal. Since it sounds like this is only your pump threads and you don't name the make of pump, I looked through your older posts and found this:
https://www.homebrewtalk.com/threads/conical-fermenter-also-as-boil-kettle.689845/#post-9201007
Cool! I love unique set-ups! I had actually expected to find the popular MP-15RM, but I can't identify that pump in the picture.
Given you're just going to TC anyway, maybe you could consider replacing the pump for one that has TC fittings from the get-go:
https://www.brewhardware.com/product_p/mark2ss_tc.htm
View attachment 873499

I've seen and fawned over this pump which I was not able to find when I first pieced my system together 5 or 6 years ago. To date I have spent more money than I care to admit to be able to precisely heat water and I and concerned I may be testing my wonderful wife's understanding. I may have to put this on the birthday (not till late in the year)/Christmas list.

FWIW: My current pump is a SeaFlow.

 

[Tropicpine]

I'm curious as to why PTFE tape doesn't seal. Do the threads have burrs or spalling? What kind of PTFE tape are you using? The thin stuff from the hardware store doesn't do a good job of filling voids. A few turns of good, thick tape might do the trick.

From my reply to BobbyM that I was writing as you were replying:

"Also, NPT threading is slightly tapered or conical. ... Once a NPT fitting is sealed if the fitting for any gets any torque that slightly loosens the fitting or the metals on either side of the NPT fitting have a different coefficient of thermal expansion (I would love to have been able to source all my parts from the same manufacturer but I just don't live in that perfect a world) and the fitting undergoes significant thermal changes (like brewing) the fitting can leak. The leaks can be resolved by tightening the fitting but doing so with a hot process column full of sweet, sweet, sticky wert has led to more than more than one fit of cursing"

As for PFTE tape, I hate leaks to the point that the cheesy PFTE that comes in the box with a plumbing fixture gets tossed in the trash. I am using the high temp rated yellow stuff that is even thicker than what I usually use.

 

[Broken Crow]

Looking at the pic just gave me another thought: Since you have such a low-profile TC adapter on there and your MPT fitting comes up flush to the inner TC, you could look around your town for a TIG welder to simply seal it at the inside.
https://duckduckgo.com/?q=tig+welding+stainless+houston&t=ffab&ia=web
Just a thought.

 

[Bassman2003]

Frustrating. I purposefully eliminated all NPT connections that I could in my setup. I think it is the stupidest connection ever made. But that is just my opinion. I use a lot of in-line clamps instead of ball valves for tubing. My pump (Anvil OEM) has the barbs built in, so no extra connectors. I do clean the pump by taking the body apart. So I welded-in solution for your in and out connections would be fine if you need to go with that approach.

 

[Bobby_M]

Furthermore, these connections are in contact with the wert until cooldown is complete. ... These threaded connections do need to be broken down, sanitized and resealed between each use.

If you simply run the boiled, but not yet cooled wort through the whole pump loop and back into the kettle, you will effectively heat sanitize any questionable nooks without having to break the connections down for sanitizing. I ran a kettle with threaded connections for 5 years breaking threaded connections down maybe once a year at most. Heat always does the job better than chemical sanitizers can.

You can have a welder put a bead down in the valley between that threaded face and the adapter that surrounds it and that will make that particular connection more sanitary but there are another hundred spots in any brewing system that will harbor bacteria that only heat can really take care of.

 

[crazyjake19]

Use quality PTFE tape - it will seal. Go to Ace Hardware or a supply house and get some Blue Monster or whatever the purple tape is. Don't use the cheap white garbage tape they give you for free with a Harbor Freight impact wrench. There is a difference.