Welding arcs put out a lot of UV light so a UV filter will have 2 benefits, firstly reducing the effect of UV on film and second protecting the lens from any molten metal spatter. I would also suggest drapeing your camera in a flame retardent cloth as the metal spatter sticks to everything. If you are looking for artistic effects the extra flare and glare a filter will generate if the arc is in the field of view may be a benefit. Some of the best welding photos I've got in the past were when the welder was using manual metal arc welding (stick welding) and the welders body shielded the camera from the arc. It gave a great sillhouette and the sparks from the welding stood out.