On Jul 15, 6:38 am, Andy Dingley wrote:
On Jul 14, 10:44 am, Matty F wrote:

Some expert welder will weld the lug on. I suppose he will have to
grind bits off the new piece in order to weld right to the middle.

On the whole, I'd take the whole flange off, and weld on a whole new
flange. This gives you much better options for cleaning up before the
weld.

Cast iron welding is no big deal (manual arc, nickel rod). It's no
harder than brazing and generally gives a better result. The trick for
both is to pre-heat well with a gas torch beforehand, cool slowly
afterwards (bucket of wood ash) and (for welding with a nickel rod)
peen the weld after it's welded and while it's still hot.

Price of nickel rods is a bitch. If you can buy a handful, then fine.
Otherwise a boxful is spendy for a one-off job, so it's usually easier
to go to someone who already owns a box (and probably welds CI all
day, as many welders in the repair trade do).

I'm rather puzzled to see a CI pipe with a CI flange used like this
on the inside of a firebox though. I'm actually surprised it has
passed any inspection for the last hundred years.

Actually the pipe is at the other end of the boiler from the firebox,
so not red hot. But still hot!
The welding will be done by the best experts around, and inspected by
a boiler inspector, as usual.