Two Pipe-fitters weld a seam joining a large coupling.
Two people are welding a seam.
Pipe-fitters implies people.  A seam can be found on a large coupling.
exists e1 e2 s1 x1 x2 x3.(for(e1,e2) & Theme(e2,x3) & Actor(e2,x1) & v_join(e2) & n_coupling(x3) & a_large(s1) & Theme(s1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_weld(e1) & n_seam(x2) & n_pipe-fitter(x1) & card_eq_2(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_weld(e1) & n_seam(x2) & n_people(x1) & card_eq_2(x1))