Welding cast-iron heat-exchanger ( boiler body )

24 Aug 2009
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Bad news from a plumber who says that a leaking boiler is a cracked body (heat-exchanger). Crack is underneath where it sits on top of hot-water contaiiner so cannot be seen. Crack due to freezing.

Currently have to refill expansion-chamber (?) two times per day to bring back to one bar .

Is it possible for cast-iron to be welded ? The plumber says he welds steel but not cast-iron.

Are there any additives that can be tried to seal the leak or do you think it is just too big ?
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Not successfully you can't.

If it's a sectional boiler buy a new section,
If your luck is in, the casting can be bronze welded if you have the correct flux......and a bloody big nozzle on the oxy / acet torch!
John :)
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Normally for this situation i.e fixing cast iron, bronze welding would be recommended as its slightly stronger than brazing.
However for your heat exchanger, I reckon there would be success with either.
Both the bronze (copper / zinc alloy) and brass (copper / tin alloy) are applied as spelter rods using an oxy acetylene flame with an excess of acetylene, and so long as there is enough heat and the correct flux (SIF Bronze is an excellent one.... a pink powder mixed with water to a paste) there should be excellent adhesion.
Think of brazing / bronze welding as high strength, high temperature soldering really....there is locallised alloying with the parent cast iron.
John :)
Not successfully you can't.
Actually, cast iron can be welded, but it is a "somewhat specialised" field and needs very specific weld materials (high nickel content alloys) and techniques for it to work. Just going down the crack with a mild steel stick or wire is guaranteed to fail.

More people are likely to have the materials for bronze welding to hand than nickel welding rods. Having said that, I tried bronze welding once and couldn't make it work - though my normal steel welding isn't anything I like to show off :rolleyes:
I know you can weld castiron and have done loads of times, in fact bronze welding was a favorite of mine back in the 60s.

I said not successfully you can't, obviously it depends on a few things and where it actually is split, but generally it's only a short term stop gap.
The correct flux is the key for the bronze weld chaps.....kosher cast arc welding rods are available, but I wouldn't go over 120 amps.
Had a go once, made a right a rse of it :p Fine for man hole covers and the like, but you'd need loads of practice to tackle a boiler.
John :)

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