Dielectric fittings

Greg Singer

Opinions regarding the need for dielectric fittings and where they should be used vary widely, it seems.
Does anyone know of any authoritative publication that clearly outlines the subject. For example, although I cannot recall seeing a cast iron radiator with copper pipe feed utilizing dielectric fittings, an engineer recently said that they should definitely be used in that application.

hr

The CDA is considered an

authority on this subject. Takes some digging but they have pages and pages of research and studies on this topic. Most you have to purchase.

It's a common issue in fire protection piping also where copper connects to the iron fire valves and shotguns.

www.copper.org

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bob young

di=elect. mumbo jumbo

sounds like another know it all engineer without a train.radiators have been installed without dial. fittings for about 150 years. tens of thousands are still going strong. take the advice of practical mechanics. they are not necessary.

Kal Row

TWO THINGS...

1)if there is no freshwater (with oxygen) coming into the system - (ie leak free – thus no fresh electrolyte), then, the dissimilar metals battery, dies real fast, and is, of no concern

2)the most logical place to put it, is near the cast iron boiler, as, we go to copper pipe, right there, problem is, the high temps, and numerous temp swings at that point, cause the plastic components, to disintegrate, (had one die after ½ season) and cause the union to walk itself apart, and let me tell you, the cat wont be amused by the hot shower, “oooops”, – so, "if you must", – use flanges, with bolt sleeves and fiber washers

John Barnes

I always use a brass fitting in between copper and iron.

gasfolk

Greg, try this site

http://www.hghouston.com/coppers/brass78.htm#Galvanic corrosion

The chemical and oil & gas industries are a harsher environment, but the technical material there may be useful as an outline of the subject.

gf

Greg Singer

Joh- re dielectric

OK- see this is part of why I posed the question. We always see brass valves connected to steel pipe and no one questions it... dissimilar metals. Why? Why is that OK? Does a brass valve or fitting as a transition between copper and steel somewhat eliminate the need for a true dielectric fitting?

gerry gill

Greg-

it would depend on the local code..those ares using the international code can use brass as a converter fitting for a steel to copper joint..just like the valves, yes..dielectric unions themselves are a piece of junk..the steel seems like its not even galvanized or something..the steel side will usually rust shut in just a matter of years..i like the brass conversion just for this reason.

hr

All metals corrode

even similar metals. What brass does is bring the two disimilar metals closer together on the Galvanic chart. It gets more involved with the type and ph of the fluid and the relative area effect, etc.

Here is a fairly basic Galvanic chart from some of the CDA material. It shows the common plumbing and hydronic metals. Plenty more alloys in between on more comprehensive tables, but this show the brass interplay.

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gasfolk

hot rod,

Does bringing two disimilar metals closer together on the Galvanic chart reduce corrosion from galvanic action? If you can recommend it, it would be a whole lot simpler to use brass than dielectric unions.

gf

hr

Yes it limits the potential

You need disimilar metals in contact in the presence of an electrolyte. Fresh water is a weak electrolyte.

Generally the copper to iron connection is an accepted practice. Given the choice by a stubborn inspector or.... I would go with brass nipples or brass valves between the two metals.

Dielectric unions have no place, and are a liability, in a hydronic system, IMO.

You have to do what you have to do, make it as pratical as possible and go with the brass. It is much less likely to present a leak or call back.

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tls_9

If

You find that to please an engineer or inspector that won't accept brass try a dielectric nipple by Victaulic or Gruvlok instead of a union. They will hold up much better.

tom

gasfolk

Is that also the

same on open-loops? In past have used dielectric unions or brass nipples on water heaters.

gf

hr

I still hate

dielectric unions, even on DHW tanks. Many copper flex connectors provide the same protection with the brass nut and plastic insert around the tube.

Even plastic lined and capped dielectric nipples are better than DE unions IMO. Inspectors can be sticky about what they will accept. Regardless of how well they DON'T work

Flex connectors were fine in Utah as the AHJ and inspectors like the sesmic movement they could potentialy allow before pipes snapped. Same with gas flex connectors.

Here in Missouri the local AHJ amended our code to not allow gas flex connectors because he felt "too many contractors misused them"!

He was right in a way, numerous times I would see them installed without the flare adapter! If the thread would fit guys would teflon tape the heck out of them and just screw them to the nipple. Or splice two or three together to make a long run.

Too bad as we are on a big fault here. Some day, I hope not in my lifetime, those WHs will shake, rattle, and roll!

Go figure.

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