Triggering would be like placing many tacks - instead of moving a distance from the previous tack you only move about 1/8" from the previous tack and lay a new tack overlapping the previous tack. You have to watch the color of the metal so you don't blow through, but do it fast enough so that you are able to get the base metal hot enough to get penetration, so it is not really one continuous movement, rather a series of small movements. Squeeze your trigger for a second or two, move a little bit and do it again. Travel is the same as it would be if you were able to run a bead, but you might have to build up on one or both side(s) of the joint a little before you get enough thickness to actually sustain an arc for more than a second or two. You will probably not get rid of the huge blob on rusty exhaust pipe, but after you have triggered enough filler metal in so that you have some actual metal there, you can run another pass on top of it to smooth it out.