repair crack on cast iron piece on heat exchanger

You are correct it is brazing and not welding with bronze.

 

Since the item is still in one piece and doesn't have to bare any structural* loads, I'll think when well prepared, brazing wouldn't be a problem for any metal workshop with acetylene+oxygen equipment, which is fairly common.

* in my view its cracked by thermal loads and stresses, so a slow and even heat up and insulated cooldown of the whole piece will relieve internal stresses, so after a well done and cheap brazing repair job it might be even better than a new one, I believe...

2 of the 5 post #1 pics​

 

Thanks for the detailed photos.
Looks to me like the problem originated with casting flaws, and has progressed from there to crevice corrosion.
The piece has corrosion problems beyond the leak currently under discussion, I would seriously consider replacing the part.

 

I didn't think of that the problem could have started with casting flaws, but seeing the pictures it sounds very plausible, so thanks KapnD for adding that observation and the info . .

But by now all the casting flaws are exposed I think, so it could still be worth to shot blast the piece, and grind out the flaws and cracks, and see what you have then, it still could be well brazeable, which would avoid the casting flaws a new piece can have, and that are prone to be exposed in the next 4 decades or so.

 

A machine shop could make a similar piece from bronze stock. Bore in from the sides at appropriate angles for the inlet/outlet then bore face for cavities. It might not look exactly the same, and pipe stubs would have to be added to accommodate hose barbs, but really not that complicated.
It might even be cheaper than the OEM product, and would certainly be higher quality.

 

That part is not long for this world. Welding/braizing have equal odds of thermal cracking, distorting the casting, and you never know when the next cavity is going to cause it to fail.. JB Weld the crack up and start looking for a new one.