Galvinized fittings or black iron

[hokiefan]

I am doing an install of a homebuilt deb design owb, I am wondering about using galvanized fittings on my connections for my pumps and etc.... seems that their is some thought to using black iron. If my water temps are no more than 185 how will the galvanized cause a problem? I plan on using a water treatment when I set it up as well.

Thanks for the input..

Hokiefan

 

[Frozen Canuck]

Dissimilar metal reactions & the corrosion that follows it is something you want to avoid. Plenty of pros here to confirm & guide you on this. Short version metal boiler gets metal pipes etc. Pex will not react so is safe to use.

 

[heaterman]

Stay with black. Galvy can do some weird things in systems containing copper, brass or other non ferrous metals. lot's of boiler rooms around with 60 year old black steel piping in them. Over 100 years if boiler history is on the side of black pipe and fittings. One of the main things with galvanized is the interaction with some boiler chemicals including antifreeze.

 

[ewdudley]

Historically black iron was used for heating systems because it was less expensive than galvanized, and galvanized is not necessary for a sealed system.

Galvanized pipe is incompatible with propylene glycol.

It should be noted however that the idea of zinc coating on galvanized pipes has been shown to interact with keyboards to produce significant concentrations of afraidium in a self-perpetuating reaction series.

Cheers --ewd

 

[RobC]

Here is a link that explains the importance of saying with certain materials.
http://www.engineersedge.com/galvanic_capatability.htm
There have been other posts on this too.
Rob

 

[hokiefan]

Thanks for the input......It's funny how sometimes you just heed to hear it from others to confirm what you already know!

 

[dogwood]

The terms black iron and black steel pipe are often used interchageably as above. Is there any differnence between the two when ordering fittings?

Mike

 

[hokiefan]

Mike, they should be the same type of fittings, it is getting very hard to find any fittings made in the USA and I suspect the differences in names is because of translation issues to good ole english from chinese or wherever!

 

[ewdudley]

The terms black iron and black steel pipe are often used interchageably as above. Is there any differnence between the two when ordering fittings?

Mike

In the context of fittings, as opposed to pipe, 'black iron' normally refers to black cast malleable iron, while 'black steel' is likely to refer to black forged steel fittings.

Forged steel costs maybe twice as much, but is weldable and is rated for on the order of ten times the pressure. For hydronic applications the pressure rating is not an issue, but if you're welding couplings to LP tanks, for instance, you'll want forged steel, which your fabricator will already know.

--ewd

 

[dogwood]

Thanks ewdudley. all things considered, would both types fit the same then? Great tip on the welding. I do have one damaged thread on the 2" bottom drain opening on my storage tank. If I can't get a good watertight joint, the joint for the elbow going there may need to be welded. I'll make sure to get a black steel fitting for that.

Mike

 

[ewdudley]

Thanks ewdudley. all things considered, would both types fit the same then?

AFAIK they should be perfectly interchangeable dimension-wise, although unions can vary slightly according to type, material, and manufacturer. Generally the least expensive black iron offered by any reputable plumbing supply house is what you want for hydronics, except where there is some overriding consideration as in the case of weldablility, for instance.

Great tip on the welding.

Something I wish I had been bright enough recognize without finding out the hard way.

--ewd

 

[dogwood]

Thanks again EW. You might save me a lot of heartburn with that welding tip. I would have never guessed you can't weld malleable iron pipe.

Mike

 

[Gooserider]

Thanks again EW. You might save me a lot of heartburn with that welding tip. I would have never guessed you can't weld malleable iron pipe.

Mike

Far as I know you CAN weld standard schedule 40 steel pipe - I've never done it w/ hydronic applications, but I've made more than a few projects using pipe as a structural member of various sorts, and not had any problems.

What EWD was talking about in terms of not being weldable, is the FITTINGS - elbows, unions, couplers and so forth... Those are made from cast iron as opposed to steel, and definitely don't like being welded...

Gooserider

 

[dogwood]

Gooserider, you're right, should have been clearer in my response. But you got me thinking. I probably have enough room underneath to put a short length of steel pipe into that bottom tank opening, instead of using a street ell, and then go to a malleable elbow. I could weld that short steel length to the tank if it leaks due to the opening's bad thread. Thanks.

Mike