afaik welding that is no different to mild steel, I believe some of the fittings used last summer when i was a pipe fitters mate were black iron, and they were welded onto the steel pipe with nothing unusal.
It's just your normal black iron that you would get at anystore, usally used for natural gas I beleave. I just want to weld all the fittings together because theres going to be water running through it and with it getting hot and cold it may leak so I want to weld it to make sure it will not leak.
A very brief search on the internet suggests that black iron when you buy it these days is just steel with black paint on it. The fittings look like they are cast which would present their own problems with cracking.
I'd not bother welding it at all - use plumbers tape at the screw joints if you are worried about the seal. Otherwise if cast is involved then brazing is the answer.
No, no, no.
The only screwed black pipe fittings you can weld are known as wrought iron, which is virtually mild steel. All other black screwed fittings are cast, some in the natural state of cast iron but mostly malleable iron which is cast then allowed to heat soak as part of the manufacturing process making it malleable, it can be brazed but is not weldable.
Incidently, having water outside the pipe is not a lot different to it being inside, so if the joint is made correctly it will not leak either way within the tube/fittings pressure rating. W/A
Welding pipe fittings are not threaded just weld prepped for welding
i didnt think anyone made cast screwed any more, last summer I can remember cutting half of a 3" barrel nipple off so it could be welded into a flange, I dont think any of the fittings used on that job were not suitable for welding, except the galv of course