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The flange connections on my exhaust pieces are rusted out and leaking.
One way I've considered addressing this is just cutting out the flanges and welding in a straight pipe to bridge the pieces.
I imagine flanges are just used so the exhaust is not one large pipe - making it easier to transfer parts, replace sections, etc.
But is there any other reason I might want to not bypass the flange system?
You gave the obvious and real reason - about replacing sections...
Often the only way to get an exhaust into place is for it to be in two, three or more parts that are then joined either with flanges or sleeved and clamped.
I have made exhausts and welded in situ, but if they get damaged it can be a pain to repair later - a risk one takes...
Cut the flanges off then use one of these -
Since the flanges have corroded away , why do you think there is enough metal left in the pipes to make it worth welding them? Also modern exhaust systems are 13 % chrome which can easily crack when welded ,depending on filler metal and the two components being joined. But if the whole system is welded ,flanges are not necessary.
Another consideration is, how are you going to get a comprehensive weld all around the new joints in-situ? Most exhausts sit close enough to the underside of the floorpan that it'd be difficult, if not impossible, to get a welding torch in above them, and if you leave even the tiniest gap it'll blow...
