instead dropping down beams for horizontal reinforce welding. (2nd welding)

if more sliding interlocking spots were made for the walls.  in the surface area of the walls,

(not just the ends)

then, light objects that holds the beam of metal can be descended down following those tracks, and when it reaches the destination (which would be after the first layer of welds are complete)

can push the beam of metal from the outer surface, (if it is connected to a mechanically protruding slide. nothing complicated) and just pushed to contact the first weld,

then the welding machine can traverse between the first wall and the light object holding the metal beam (the gap between) following the wall's tracks, and weld the beam as extra reinforcement.... for the horizontal.

 

but i doubt that there is no water pressure deep enough, strong enough to tear open a metal weld.

and welding depth can be fairly deep as well.