Steam boiler piping question

Side outlet boilers like that are much happier -- and have more even interior water levels -- when they have two outlets, one on each side. Also, each one only gets half the steam flow, so the velocities are correspondingly half as much and much less water gets carrier over into the steam flow.

As to the swing joints, they serve to take most of the stress off the boiler as the header piping expands and contracts differently from the boiler (there is an alternate, even fancier arrangement for drop headers in which there are effectively two swing joints on each riser, which takes all of the stress off. It only works, of course, with threaded pipe, since the joints can give a little in rotation (not much -- just enough!). It doesn't work at all with soldered copper, not does it work with welded rather than threaded pipe, since those joints -- though the geometry is the same -- can't rotate even a little. One (of several) reasons to avoid copper for near boiler piping.

Very small side outlet boilers work ok with one riser if the spec is followed because they aren't producing much steam and it doesn't have to travel across too many sections. If the piping size is smaller than the spec or it is a larger boiler, a single riser will work poorly and produce wet steam which will cause water hammer and spitting vents and will corrode the mains which have much more liquid water in them than just condensate.