View Full Version : "welding" cast iron pipe

05-18-2006, 12:32 PM
I want to make some adjustment feet to go under my Bridgeport mill base to allow me to level it up. I have a design in my head and it involves welding a nut inside a piece of some tubing.

I have had other situations in the past where using a piece of common cast iron pipe would be easy (and cheap) and have been held back by the presumption that it cannot be welded, so thought I would ask about that here. I know there is a lot of experience here and that others may benefit from being able to make use of common materials like this, so thought I would ask here for the benefit of all.

I know cast iron can be welded, but how about welding to steel? If so, what is the right material? I also know that dis-similar metals are most often joined with a brazing/soldering type process, but typical brazing seems so "weak" for a lot of things. Is my presumption that "welding" cast iron pipe to steel is a no-no or does it just take the right materials? I have an AC buzz box, a smallish 220v mig unit, and an Oxy-Acetylene torch as options.


05-18-2006, 01:09 PM
Why not just use the standard "black iron pipe"? It is mild steel pipe that can be welded with normal process. Nothing special about it.

05-18-2006, 01:15 PM
So black iron pipe is not really iron? Maybe my assumptions were wrong about what I really have. I am talking about the stuff used for gas plumbing etc. It welds OK?

Maybe this is a case where you should try something first;)


05-18-2006, 01:34 PM
ironically, "black iron pipe" you buy now is actually caled...

Black Steel Pipe.

It welds ok. well.....like crap actually, I mean dont go build a racecar or heaven forbid an airplane with it, but For non critial applications not subject to repeated cyclic loading you will do fine welding it however you have available..

05-18-2006, 01:40 PM
It welds fine. There's dozens of stock cars here using that for rollcages in the smaller diameters.
Sched pipe...we weld that all the time.

05-18-2006, 01:45 PM
---ok, saturday night sportsman class racecar perhaps,

-but don't build an airplane with it :)

05-18-2006, 01:57 PM
Yeah-- I think the key there is "rollcage" and not frame ;) In my case, the only load will be compression and not much per-pipe at that.

It sounds like the tubing equivalent of rebar in that its actual content may be a bit variable while still meeting the need at hand.

Now that I think of it, there is an obvious difference in the way black pipe cuts as compared to older cast iron sewer pipe I have dealt with...the latter did really seem to be cast iron.

thanks to all for clarifying my bogus assumption....and politely at that!


05-18-2006, 03:17 PM
There is nothing wrong with brazing cast iron to carbon steel. A good quality bronze brazing rod will make a join stronger than the base material. You can also use NiRod which is a nickle based welding rod but brazing is a better choice as the temperature is lower and there is less need to preheat the cast iron.

However since you have black iron pipe it isn't cast at all.

05-18-2006, 05:11 PM
Evan is absolutely right about brazed joints being stronger than the base material being joined as long as the joint design is proper and the clearances are held very tight (i.e.. .001-.005). And as far as strength goes I would trust my life to a rollcage that was built with this material as long as it was properly designed and welded. Better to have a frame bend than a cage! Although strong enough for an airplane Ithink it might be a tad heavy.:D In other words yeah go ahead and use it,stick,mig or oxy acetylene you can't go wrong.

Tin Falcon
05-18-2006, 05:39 PM
You are just worrying to much. The guys are right any of the methods you mentioned should work. I have literaly welded tons of it. Mosly 1 1/4 pipe to 3/8 mild steel plate, also lots of pipe to pipe for industrial railing. and pipe to mild steel ballisters by the hundred. of course we used mostly MIG.

05-18-2006, 08:54 PM
OK, so we now know you really have steel pipe. As the other guys have said, brazing is fine, especially if joining dissimilar materials, as in iron to steel, etc.
Steel pipe...weld it by what ever process you feel comfortable with, unless having to work to some code or specified proceedure. (Hopefully it's not just plumbing or gas piping...)
For roll cages, black pipe might be fine & the cheapest alternative. Did you compare prices with mech. tubing or struct. shapes...? Does bending save on buying any fittings in your application ?
As for aircraft fusalages...IIRC, there is/ was a guy in Alaska who built a plane out of EMT (conduit, think David Cofer special....?) and even sold plans. Photos were a maze of coped joints....

05-19-2006, 09:25 AM
In the past, I've had to stick weld cast iron grates to steel frames.
Using 87% Nickel rod worked just fine.
A little pricey at about a dollar per 3/32" stick (in my area) but the results were worth it.

05-19-2006, 01:11 PM
I've been welding for nearly 40 years, including black iron pipe (std black pipe ) and have never had a problem welding it. I'v even seen it used for builbing columns. For a mill support, not a problem.

05-19-2006, 10:04 PM
I use black pipe all the time for frames and roll cages on go-karts and sprint cars. Now the go-kart frames are as skimpy as skimpy can get and still support me and never had a weld fail yet - there is one right between the rear axle and front axle but it hasn't even begun to crack (if it had i would no longer be tempting fate by riding it). I use 6013 rod on it and always had great results; bead sinks in nice and looks like a TIG weld when your done. I like welding it to be honest. Also cast iron pipe can be welded but its not usually recomended fro structural members. They make alot of seal welds (still holding up to 15,000 psi of steam) around cast iron pipe plugs and valves at the nuclear powerplant with no problems. All of the fittings for the pipe are cast iron but the pipe itself isn't as has already been mentioned.

05-19-2006, 11:37 PM
Ooops, boiler guys jump in here. That would be way beyond even super-critical steam plant. For a nuke station, I doubt it....1500 psi, maybe.
Cast iron fittings & valves...nope, more like forged steel.
Piping welds would be to boiler & pressure vessel code, x-rayed, no doubt.
Even here in BC, pulp mill recovery & power boilers operate at 600-700 psig and superheated steam. Burrard Thermal plant is 1100 psi and some 1000 F (superheated).
One of the first super-critical plants was in New York, I believe the old Philo plant...highest net thermal efficiency for years....
Just had to mention that....

05-20-2006, 10:35 PM
yup you got me - 1500 psi my mistake. For the record some valves and all plugs they use are in fact cast iron. For instance, a week ago they were to replace a valve and weld it in place but had the problem of being unable to isolate the line from any moisture so they cut a hole farther up with the plan of tapping it and putting in a plug - of course the wall was to thin to engage the needed number of threads so they welded on a steel bung with 6010 low hy rod. After threading the bung they mechanically inserted the plug and then welded it with Softweld 55Ni rod. No x-ray tests on those - no feasible way to do an x-ray test on the pipe line.

And for the record, in a pressurized system on say a 1,200 MW reactor, the core requires the cooling sytem (i.e. the pressure vessel and the closed loop that goes to the heat exchanger - as an interesting side note: from the start-up to full power of a reactor, most heat exchangers grow by a length of 9 feet!) to remain at or near 2000 psi - which is why there was considerable research with the use of liquid sodium as a coolant in the late 70's and early 80's. The sodium would remain liquid over a wide range of temperature at relatively low pressure - in most cases hardly above 1 atm. Much easier on all of the components this way.

1100 psi is the average pressure of the moist steam going to the turbines however there are high pressure lines that are used to operate dump valves, gates and other devices.

05-20-2006, 11:49 PM
Check your bolt holes in the base first,most are actually tapped 5/8-18 or 3/4-16 to accept leveling screws.

I did mine up with some pieces of NF althread rod with a nut welded on one end and a ball end on the other.I sliced off some pieces of 3" round bar 3/4" long and used a ball endmill to put a spherical recess in them to accept the ball end of the leveling screws.Once the leve is set a thin jamb nut locks the screws.

Hope that saves you some time.

A.K. Boomer
05-21-2006, 09:35 AM
I know this aint gonna be popular but black pipe is crap, it sould be used for what it was designed for, natural gas line ------ I cannot believe people concider using this stuff for roll bars and even frame material, its extremely weak, its heavy as all getout and as far as weld strength its junk, save your pennies for some chrome molly it will be worth it, cro-mo tubeing with a wall thickness of just .035" is five times+ stronger and one third the weight, I wouldnt modify my grandma's wheelchair with black pipe, save it for stuff like bird feeder posts:eek: but dont build the feeder to high or your gonna have trouble... black pipe is also a seamed tubing and rule #1 never used seamed tubing for structural purposes but more importantly --- especially if its junk... I hate black pipe....

A.K. Boomer
05-21-2006, 12:53 PM
Sorry, was a little to brutal about the black pipe thingy, had a very bitter cup of coffee this morn. and i think it upset my tummy:p