Why Is the Root Pass Weld Started on Top of a Tack

Multiple Choice

Why is the root pass weld started on top of a tack weld?

A) To eliminate the potential lack of fusion
B) To prevent porosity caused by the lack of shielding gas at the instant the weld starts
C) So the arc light will show the root opening and make it easier to get aligned with the root opening as the weld moves off of the tack weld
D) The root pass can be started anywhere it is comfortable for the welder to begin welding.