I am trying to connect black steel pipe to stainless steel pipe and I am wondering what type of dielectric union is appropriate. I have not seen any iron/stainless unions out there and it seems galvanized will lead to corrosion once the coating is removed during threading the parts together. Is an iron/brass dielectric union best for this with a brass to stainless connection directly? Any help is much appreciated
Kevin

What is the application?

Black steel pipe and dielectric unions are two words that seldom come together. Black pipe is for gas and a dielectric union is a plumbing fitting to join to dissimilar metal pipes. What are you putting together.

Thanks for the replies. I'm in the midst of building a micro-brewery. The black pipe will run steam from a low pressure boiler to the stainless steel jacketed tanks. This steam will be uused to boil. The inlets to the tanks are stainless, as are the outlets. I need to connect the black steel pipe to these inlets.

A parallel note: I recently used a copper/galvanized steel dielectric union to bring the city water to my brew piping (stainless). Now I'm not sure if the fact that it is leaking (about a drop every hour or less) is partly to blame, but the galvanized to stainless connection (threaded) is showing signs of rust (red and smells of iron). This is why I don't think galvanized steel is right.

So, are there stainless/malleable iron dielectric unions out there? Galvanized/iron is the closest I've seen.
Thanks for the help!
Kevin

thanks for the replies. I'm in the midst of building a micro-brewery. The black pipe will run steam from a low pressure boiler to the stainless steel jacketed tanks. This steam will be uused to boil. The inlets to the tanks are stainless, as are the outlets. I need to connect the black steel pipe to these inlets.

A parallel note: I recently used a copper/galvanized steel dielectric union to bring the city water to my brew piping (stainless). Now I'm not sure if the fact that it is leaking (about a drop every hour or less) is partly to blame, but the galvanized to stainless connection (threaded) is showing signs of rust (red and smells of iron). This is why I don't think galvanized steel is right.

So, are there stainless/malleable iron dielectric unions out there? galvanized/iron is the closest I've seen.
thanks for the help!
Kevin

If both threads are male, then use a brass ground joint union.

I agree with Geowler. A dielectric union isn't needed here. Install a regular ground joint union. However, if one thread's female use a brass nipple to pick up the union. Regards, Tom

Sure you did!
I don't have to bother with a plumber who is only interested in scams. Hey! You said it on another thread. Not a very high opinion of plumbers.

"The black pipe will run steam " is it really a piece of black pipe which is normally used for gas?

The black pipe is schedule 40, normall used for low pressure gas...

So, I'm still a little confused. I though the idea of a dielectric union was to keep metals like copper (brass) and steel away from each. The advice given says to connect brass to the black steel and the stainless, which seems to be creating more of a potential problem. Does the brass union do something I'm missing? Is it like a sacrificial electrode? What is meant by grounded joint? Is is a standard brass union?

As If I haven't asked enough questions already: Can I buy a stainless union and a black steel union, disassemble them and make my own dielectric union by adding a rubber washer?

Thanks VERY much for everyone's help!
Kevin

Maybe its me who is confused but I have never heard of using black iron pipe for anything other than gas. I would think that the steam will just get the black pipe rusting.

Bob, Back in the 40's my Dad had a Plumbing and Heating shop. For our main steam supplies they used 4 and 6 inch threaded black iron, but I can't ever remember using smaller sized black iron on anything but gas lines. Regards, Tom

I'm still a little confused. I though the idea of a dielectric union was to keep metals like copper (brass) and steel away from each. The advice given says to connect brass to the black steel and the stainless, which seems to be creating more of a potential problem.
Understandable! I'm pretty sure what Growler meant was a galvanized ground joint union. (see image) and as In remember,( it's been a long time), I seam to remember that the boss of the union had some brass that made contact for a better joint. So the two IRON pipes would be joiined by a galvanized IRON union. Regards, Tom

Guess I'm just getting brain dead , see no good reason to run stream into a pipe that will rust when you could use other materials. I think you once told me that it wasn't that long ago when there were no toilet flanges, things keep changing, sometimes even for the better. Its getting more rare to even use black pipe for gas. Must be an age thing.

This is common in the brewing idustry. The low pressure steam boiler output pipe is black steel. Also, here's a description of uses from McMaster Carr (McMaster-Carr (http://www.mcmaster.com)) page 57:
Standard-Wall (Schedule 40) Black Steel Unthreaded Butt-Weld Pipe Fittings

Use with air, water, oil, natural gas, steam
Pipe: Use standard-wall (Schedule 40) black steel unthreaded (see page 58)
Flanges: Use low-pressure black steel unthreaded (see page 58)

So, hopefully it won't just rust the pipe. Any idea why there's a suggestion to add a brass ground joint, when the dielectric union was designed to separate brass from steel? I'm considering proceeding with connecting the black pipe to galvanized components and then the galvanized components to my stainless steel... thanks for the responses
Kevin

YUP kb and speedball... black pipe and steam work fine... no rust... or at least rare. We pipe steam boilers in black pipe all the time... still do to this day. No comment on union fittings.. you guys seem to have that covered. ;)

Any idea why there's a suggestion to add a brass ground joint, when the dielectric union was designed to separate brass from steel?

A dielectric union is designed to separate steel from copper, not from brass.

While brass does contain copper as an amalgam, it is not subject to the same level of electrolysis as pure copper.

Look at it this way -- Red Brass is the principal material used in ball valves, check valves and gate valves for both copper and galvanized steel piping systems.

As for your low pressure steam system, if it isn't piped yet and you're still concerned about electrolysis, then plumb it with type L copper and make the connection at the boiler and brewing equipment with a dielectric union.

Also -- You can buy dielectric unions that are FIP on both sides, if you go this route, connect the galvanized steel side of the union to the Stainless Steel inlet of the equipment and the brass side of the union to the Iron Pipe side.

An aluminum companion flange (http://www.all-flo.com/images/compkit.jpg) is yet another option.

Well guys you taught me something today. Most or my work is repair and installation, never been around a brewery much but know of its products too well. Thanks,
Bob

I assume you realize that a union is not the proper item you need by now.

I suggest you use carbon steel 150 RF threaded flange on one side.

A stainless steel rf threaded flange on the other side.

And a flange insulation kit to go in between to stop electrolosis.

This is you're best solution.

Trust me

Call me for a quote 530-222-0423

Thank you,

Josh Brown.
Northern Industrial Sales / JW Wood Co.

Doesn't really matter... use any die-elctric union.It is basically the insulation in the union that keeps the dis-similar metals apart.The Black steel can be threaded and the Stainless Steel can be soldered to brass easily.No sweat!

Hi Nevellens...

Thanks for posting but please note the dates of the threads you post to as in this case the thread goes back to 2008... ;)

Mark

And this post is from 2013 from an industrial pipe sup.
All preceding answers except the Josh Brown answer are wrong and do not meet standards established for both process piping (brewing) and pressure piping (steam).

A dielectric flange set is the accepted method of mating SS to Cu. Electrolysis is present in a threaded or brazed connection of SS to Cu directly and it is present in a bronze valve. The amount of degeneration in minimal but the point is not to minimize it. The point is to eliminate it.

I am a civil engineer in charge of mechanical design at a large public agency in California. We use black iron (really steel with a light coating) for steam in small diameters. We also use 316 stainless. I don't know what a ground joint union is, but if it is and un-insulated union, it won't work long term to prevent corrosion and leaks when connecting SSTL to steel pipe.

We have not found (so far) steel to stainless insulated unions, so we use flanges and flange insulation kits.

Incidentally, we get better performance with paint linede and coated plain steel pipe than galvanzed pipe (salty environement)

D

Hi BWDavid and welcome to The Plumbing Page at AMHD.com. You're responding to a 5 year old dead thread . Please check the date before you post. Thanks

I am a civil engineer in charge of mechanical design and I don't know what a ground joint union is Very interesting! But we thank you for your input, Tom