Dielectric Unions, Siegenthaler pg.103

Cosmo

for the teflon gasketed unions? Thanks in advance

Cas

Riles

Dielectric Unions,Siegenthaler, Pg 103

I am now confused about Dielectric Unions.

I understood that they were needed in an open system when galvanized and copper are connecting.

However, page 103 of Siegenthaler's "Modern Hydronic Heating" states, "In many hydronic systems, iron or steel components such as boilers and circulators are connected using copper tubing. If the copper and steel components are in direct contact with each other and if the system's fluid is slightly corrosive, which is often the case, a process called galvanic corrosion will cause rusting of the steel or iron components. To prevent this from occurring, it is necessary to place an electrically insulated material, called dielectric, between the two dissimilar metals. This can be accomplished with a Dielectric Union."

Although I do think I have ever seen a heating system with dielectric unions.

I know I am misintrepreting something. Please clarify. When, if ever, is there any need for Dielectric Unions?

Unknown

I have been installing boilers

for 16 years and have never use dialectric fittings on a closed hot water system . Matter of fact , Ive never seen any dialectrics on the boilers we rip out . Almost all the boilers are a mix of steel and iron and copper , and unless there was a leak somewhere , and fresh water was filled in the boiler over a long time , theres very little corrosion in the boiler , if any .

Jim Walls_2

Dielectric

The plan & spec work we do always requires a dielectric between disimilar metals. The majority require using dielectric nipples rather than unions. I questioned an engineer on this topic at one site , his explanation was that a brass ftg will break 90% of the corrosion problem , but the dielectric is for that extra 10%

Alan(CaliforniaRadiant)Forbes

The rubber washer

on dielectric unions usually disintegrates when they see 180* boiler water; maybe not right away, but within a few years.

If you're concerned about electrolysis or corrosion, I'd use a red brass nipple.

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Bill Clinton

John is an engineer

but a pretty good guy nonetheless. He's right that even slightly corrosive water will support corrosion where dissimilar metals connect. That's why dielectrics are needed in OPEN systems. In a closed system, any free ions (the source of corrosiveness in my understanding) are quickly used up leaving behind what is sometimes called "dead water" which is non-reactive. At least this is the theory I've been taught and thirty years experience installing boilers plus obsedrving boilers fifty years old and more confirms the practice. Closed systems do not need dielectrics.

Also, Alan is right: the rubber washer in dielectrics can't take high temperature, AND my observation over the years is that the worst corroded part of just about any system is the inside of the dielectric itself.

Bill

Duncan_2

Even on open systems...

I can't tell you how many times, ESPECIALLY on open systems, the dielectric union is rusted shut to pinhole size. I'm referring mostly to domestic water heaters.

They exaggerate the very problem they are supposed to be taking care of. Good in theory, but experience shows them to be the weakest link. Maybe it's the reactivity of the zinc in the union.

As for closed heating systems, as Alan and Bill point out, the rubber gasket hardens and cracks and leaks, and CREATES a problem that otherwise wouldn't exist in a closed system or using a black iron union.

John knows his stuff, I think as much in the real world as in engineering world. Notice he assumes a condition: IF the water is slightly corrosive (ion-bearing). Maybe he's referring to some other kind of dielectric than the garden variety galvanized unions off the plumbing shelf. Sometimes textbook knowledge doesn't correspond to situations in the real world.

Forget dielectrics on heating systems. They create problems, not prevent them.

Jim Walls_2

dielectric

Have seen alot of problems with dielectric unions , but not one with dielectric nipples , have any of you guys had problems with the dielectric nipples? Victaulic #47 ,Anvil #7090 or similar products?

hr

I'm with Duncan

Skip the dielectrics even on DHW water heaters. For whatever reason they seem to attract corossion and accelerate restriction when they do. I rarely see plumbers around here use them. Mostly a copper to mip adapter screwed into the tank. Sometimes a copper unionn above the connection.

hot rod

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Warmfoot

Dielectrics

We install dielectric unions on all of our new boilers. I get them from my local hydronic supplier and he orders them with teflon gaskets instead of rubber. I have installed these for lots of years and have never seen one break down and leak. I am not too concerned about the corrosion factor, but like the idea of having a union on the boiler in case we ever have to replace it. (which we haven't had to do yet - knock on wood). I would rather be safe than sorry.

Ernie Bogue
Master Hydronics LLC
PO Box 779
Keyport, WA 98345
(360) 394-2049

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Warmfoot

Dielectrics

We install dielectric unions on all of our new boilers. I get them from my local hydronic supplier and he orders them with teflon gaskets instead of rubber. I have installed these for lots of years and have never seen one break down and leak. I am not too concerned about the corrosion factor, but like the idea of having a union on the boiler in case we ever have to replace it. (which we haven't had to do yet - knock on wood). I would rather be safe than sorry.

Ernie Bogue
Master Hydronics LLC
PO Box 779
Keyport, WA 98345
(360) 394-2049

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TechinDC

dialectric unions

I have run service repairs - not installs for many years in the DC area. Most boilers are OK without dialectric unions where the black pipe joins the copper. The place where I see the need is if a system has had many repairs or a consistent leak. In these situations, the connections between the copper and black pipe are usually visibly deteriorated - Our company installs dialectric unions every time copper is joined to black pipe. The old timers say it is not necessary because a closed system doesn't bring in oxygen and the water is dead, but what if that system does have a problem? Dialectric unions seem like cheap insurance. P.S. Never had to change out a dialectric union. P.P.S. Runtal service valves are too expensive.

TechinDC

dialectric unions

I have run service repairs - not installs for many years in the DC area. Most boilers are OK without dialectric unions where the black pipe joins the copper. The place where I see the need is if a system has had many repairs or a consistent leak. In these situations, the connections between the copper and black pipe are usually visibly deteriorated - Our company installs dialectric unions every time copper is joined to black pipe. The old timers say it is not necessary because a closed system doesn't bring in oxygen and the water is dead, but what if that system does have a problem? Dialectric unions seem like cheap insurance. P.S. Never had to change out a dialectric union. P.P.S. Runtal service valves are too expensive.

hr

many factors

come into play in galvanic corrosion. For corossion to occur at all two dissimilar metals must be connected in the presence of an electrolyte. Ordinary fresh potable water is a weak electrolyte. Distilled or condensate, extremely weak. Steam will not act as an electrolyte at all!

Water chemistry weighs heavily into the equasion (ph).

Water temperature has a part.

A protective film barrier inside the pipe makes a huge difference.

The relative area effect has a lot to do with the rate of corrosion also. An iron bolt in a copper plate would corrode very rapidly. A copper bolt in an iron plate would have the opposite effect. This is similar to copper in cast iron boiler applications or copper connections to large steel pipe fire sprinkler systems. Extremely low potential for corrosion. Although never zero potential

There is even a "same" metal corrosion. For example if a new piece of copper tube was installed into an old copper system that had years worth of a protective film layer built up inside. The old pipe becomes noble and would accelerate the corrosion of the new piece! Unless the new pipe could too form a protective layer quickly.

All metals except gold and platium corrode. Most engineered metals EXCEPT copper will corrode in plain water with no O2 present.

Information from "Galvanic and Stray Current Corrosion Causes and Prevention" Ohio State University by Professor R. W. Staehle Dept. of Metallurgical Engineering

hot rod

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Riles

Thanks

I appreciate the responses. I continue to be amazed at the depth of some of the replies to all the posts on "The Wall".

"The Wall" needs to have a "Fact Contest".

I always enjoy posting something and seeing who provides more facts to back up their response. Maybe just a head to head "steel cage" match pitting "Hot Rod" vs "PAH".

This could be a good lunch break at "The Gathering".

Thanks.

ScottMP

The Brawl on the Wall !!

Live tonight on pay-for-view !!!

My hats go off to both of these guys for the massive amounts of knowledge they pass on, here on the wall.

Murph said it best, when asked who helped him with the boiler job, " why all of you guys on the wall ".

By the way, I am in the never-used-em, never-had-a-problem camp.

Great info on water quality HR, I never gave water quality much thought before.

Scott

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phil the drill

IT is Duncan & Hot Rod that won!!!

Thank U guys!

phil the drill

sorry, we all won

Dave Yates (PAH)

Huh?!?

Hot Rod vs PAH??? On what subject? We're in agreement now that HR has been converted regarding open systems(G). Peace reigns supreme. I respect the man. Even if we were at odds, which I don't believe we are, HR has always been a man of honor in his rebuttals here on The Wall and backed up his positions with facts or solid reasoning based on his personal beliefs.

I still owe him a shot though - goes back to when we first met. In Siggy's class at RPA in Providence. I was late by a few minutes - what the hell, I'd just bumped into Rich Tretheway in the hall & been indulging in conversation with the guru of This Old House. Arriving in John's class, I suddenly realized I was missing the classroom booklet. Quickly (and as unobtrusively as posible), I slipped from the front row to retrieve my copy. As I reached into the now almost empty box, a very stern voice said "You can't have one - you were late!". Taken aback, I straightened up to find myself face-to-face with HR. The mischevious grin gave away his game & that was the first "Wallie" I was to meet that day.

I will get even(G).

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Mark Eatherton1

Dielectrics are the least of your problems...

or the lack of same. Most of the hard pipe failures I see have more to do with acid (excess flux) corrosion, hydrazulic erosion corrosion (the z was free) due to excess velocity over long periods of time in pipes that were not reamed, and yeast but by no means last, MIC (microbial bacterial induced corrosion). MIC likes stagnant iron systems, like fire protection. I've seen strong bacterial growth in open systems. Thats why I don't do them. That's why you shouldn't either.

Check this out. http://www.caproco.com/Catalogue - LP/Cat Hydro.htm

I have on occasion seen a strange internal "wierd crystaline electromagnetic" fur growing on the inside of a cast iron boiler. Wierdest thing I ever saw. I figure it must have had something to do with electrolysis.

I hooked it up to a bunch of PEX for a snow melt boiler. If it gets used more than twice a year I'd be amazed. The first utility bill with it running for asny length usually put the cabosh on its operation. We have a saying. "If you need to how much it costs to operate, you can't afford it."

I personally think they should be required to install solar on the snowmelt systems and let 'er rip. I betch they could afford it then!! It would be soe easy to do, and the roofs of some of these places is WIDE open for sun. HMmmmm, maybe I'll talk to my client, and the City of Silverthorne, who dicatates this stuff any way.

Geez, all a person would have to do is mount some solar panels on the roof and pipe them as secondary inputs to the 4" pipe I already installed. We could even set some PV's so the parasitic costs to operate the solar system are held to nothing. Zero. Zip. Nada.

Happy Educated Hydronicing !!

ME

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mp1969

Skip but don'tignore !

> Skip the dielectrics even on DHW water heaters.

> For whatever reason they seem to attract

> corossion and accelerate restriction when they

> do. I rarely see plumbers around here use them.

> Mostly a copper to mip adapter screwed into the

> tank. Sometimes a copper unionn above the

> connection.

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This Contractor,

> Click Here to Visit Their Ad in "Find A

> Contractor"_/A_





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mp1969

Hot Rod

The physics behind the the non electric thermocouple are related to this same debate. Certain non similar materials do create millivolts and therefore electricity. This is a given, the problem or question is not whether you need to addresss this but as to how to best address this.
The experts have addressed tank and component failures caused by this known problem by devising various methods to isolate or separate materials. The use of non conductive materials and the often used and not always practical dielectric union is just one device to address this. Good plumbers do use some sort of isolation or non conductive device for longer tank and metallic component protection. When water heaters fail early this is always a consideration.
I disagree with promoting non use and would recommend alternate methods ( ex: the newer nipples that the mfrs. now provide) or pex on electric heaters.)
Closed hydronic systems do not seem to have this problem if they are tight and well maintained. In fact the di-electric union is truly a miss application for heating due to the chemical and heat related affects on their components.

MP1969

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Joe at krahezfoo@aol.com

Dielectric unions

I have seen a lot of hot water boilers and steam boilers in the last 30 years. The most extreme corrosion that I've seen is at the junction point of dissimilar metals. I have seen water feeders totally corroded shut; but I blame that on lack of proper maintenence procedures. Set it and forget it! I agree with Hot Rod, that water chemistry and temperature have a lot to do with the accelerated corrosion. I think a dielectric union or a waterway helps to stem this problem. A waterway is a steel nipple that is coated on the inside with a teflon-like substance. The contractors that don't believe in them have probably not been in business that long to see this problem; or don't recognise the problem when they see it. Do it right the first time!!!!! Your name goes on the job! Pipe tight, make it right! Krahezfoo.

Joe at krahezfoo@aol.com

To Hot Rod from Joe

Looks like you are on the firing line tonight!Hang tough!