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I just completed laying irrigation piping (black poly) and by and large it seems solid. I do however have issues with the take-offs from my house's hose bibs, where I have metal risers going into the ground to meet the poly underneath. The "risers" at the start of the system at the sides of the house are stainless steel nipples.

But no matter how much I tighten (with a pipe wrench) and use plumber's tape, the NTP threaded connections between stainless steel nipples and brass reducers (hose-bib end) seems to want to leak. This raises the question, is it a known problem when coupling SS and brass? That their NTP threading isn't exact enough of a match to maintain a dry connection?

I used SS nipples because they were half the price of brass. Was that a mistake?

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    Could be poor quality threading on either part, depending where it comes from. Unlikely to be "different NPT" per material. I'd suggest picking up a small tube of pipe dope (paste-type thread sealer) rather than teflon tape - having used both, It's easier to get no leaks with dope than tape.
    – Ecnerwal
    Commented May 8, 2023 at 13:27
  • Thank you Ecnerwal, I'll have to try the dope
    – Paul W
    Commented May 8, 2023 at 13:35
  • Are you sure those fittings are made to go together? There are a wide variety of pipe and tube fittings, and some seem to have the same thread. Photos would help.
    – Harper - Reinstate Monica
    Commented May 8, 2023 at 20:22
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    Photos would help a lot. My experience with 3 or 4 models of SS plumbing fittings (nipples/couplers/adapters), inexpensive and purchased on Amazon, was that at least half leaked at the threads. Bronze may be more likely to give a bit and produce a better seal.
    – Armand
    Commented May 9, 2023 at 17:16
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    The "Known Problem" is using cheap plumbing fittings made "overseas", which may or may not conform to accepted threading standards. The SS pipe nipples I used to buy cost MANY times the price of standard brass nipples.
    – kreemoweet
    Commented Sep 27, 2023 at 3:20

3 Answers 3

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Stainless steel is a harder metal than brass. The pro is that it's hardness makes it more corrosion resistant and durable. The con is that it doesn't give like brass when tightening threads. I found some info on the Boshart and TerryLove blogs. I'm still working on setting up my water system, but saved this picture of stainless steel grade teflon tape. So far I'm thinking people are using a sealant compound and teflon tape and something for anti-seize protection. enter image description here

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I put Teflon tape on the threads then “pipe dope” over that and don’t over tighten.

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Pic would help, but if you are trying to attach NPT to a hose bib the threads are not the same.

Additionally there should be some type of back flow prevention such as an Anti-syphon valve where the irrigation connects to the home water supply. There are NHT and NPT adapters, but to be safe backflow should be added and is mandated in almost all areas of the country.

Have a look at some youtube videos about irrigation systems such as DIY irrigation here.

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  • A hose bib has two sets of threads. One is for the hose, the other most definitely is NPT.
    – Ecnerwal
    Commented May 8, 2023 at 13:32
  • The SS-to-bronze is nipple to reducer, both NPT. These are not yet at the hose bib itself.. I have another NTP-to-crimp/insert above this connection where a hose takes me to the bib.
    – Paul W
    Commented May 8, 2023 at 13:35

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