PEX onto galvanised steel
Hi, I'm currently renovating a kitchen and have a length of steel pipe that I wish to cut back and attach PEX too. I can't fully remove the steel pipe as it is buried in the wall. I understand their needs to be some sort of bridge between the steel and PEX pipe because of electrolysis what would be the best bridge? Thanks
Advice from 7 local tradespeople
You need a dielectrix joint or a special brass fitting
Hi, thanks for your question. If the existing steel pipe is staying in the wall, the usual approach is to transition from the steel using a proper threaded fitting, then bridge onto PEX with an approved transition fitting. The key issue is galvanic corrosion, which occurs when dissimilar metals are joined directly; a dielectric fitting is generally the safest option when joining different metallic materials. PEX itself is non-metallic, so the main concern is the transition point between the metal and the PEX. In most renovation work, the best route is to expose enough of the steel pipe to confirm the condition and thread quality, then use the correct adapter before connecting the PEX. Plumbing codes commonly require dielectric protection at dissimilar metal joints.
If you are in Hull or the surrounding area and want it done properly, HJZ Plumbing can inspect the pipe, advise on the best transition method, and carry out the repair to a professional standard. Visit HJZ Plumbing for reliable plumbing help in Hull.
Cut back to sound pipe, re-thread (or use a repair coupling) and fit a galvanised malleable iron threaded adaptor (e.g., GI nipple + female adaptor / union), then go to PEX with a PEX-to-BSP/NPT threaded fitting (or a brass compression-to-PEX adaptor). Use PTFE + paste suitable for potable water.
Big caution: old galvanised often blocks/corrodes internally—if flow is poor or threads crumble, replace as much as you can back to a better section.
I was taught that copper to steel should bridged with a bronze fitting
Kevin
Yes, you are correct — you must not connect PEX directly to steel due to the risk of galvanic (electrolytic) corrosion.
You can use brass connection coupling.
Can use a Pex x mip adaptor
Brass Adapter: Many professionals prefer using a high-quality brass fitting or nipple as the bridge. Brass is a "neutral" alloy that is less reactive with steel than copper is. A 6-inch brass nipple can physically separate the steel from the PEX connection, further reducing corrosion risk
