Try the Welder script from scriptspot, it'll create splines at the intersections of two meshes, and either bunches a couple of noise and TS modifiers together for quick'n dirty seams, or extrude a weld shape (though I haven't gotten it to work). I've used the resulting curves exported as geometry to mudbox for some…
in max, select edge loop, under edge sub object mode select the create shape function. it will create a shape(spline) out of your selection. To scatter the models like bardler said you have a few options. you can use the constrain to path, path deform or snapshot tool in max. there might also be scripts for it. also you…
What 3D app are you using? In Maya you can select the edges where you want the welds, and create curves based on those edges. Then model a few weld beads using whatever method you find best, then take that weld mesh and duplicate it along the curve. There is a free script that lets you do this, I forget the name of it…