Welders work in low light conditions underground.
they are welding pipes
The welders could have been working on anything, not necessarily pipes.
exists e1 s1 s2 s3 x1 x2.(a_underground(s3) & Manner(e1,s3) & in(e1,x2) & n_condition(x2) & a_light(s2) & Theme(s2,x2) & a_low(s1) & Theme(s1,x2) & Actor(e1,x1) & v_work(e1) & n_welder(x1))
exists e1 x1 x2.(n_thing(x1) & Theme(e1,x2) & Actor(e1,x1) & v_weld(e1) & n_pipe(x2))