Purging a pipe involves inducing an inert gas into the pipe to remove reactive atmospheric gases from the welding area. An inert gas atmosphere eliminates oxidation from forming on the backside of the weld. Oxidation forming on the backside or inside of the weld increases friction around the weld joint and causes structural weakness if the oxidation leads to porosity. Use the same type of inert gas for both welding and purging which increases the stability of the weld.
Cover one end of the pipe with masking tape. Cut a small "X" in the center of the masking tape covering the end of the pipe with a utility knife.
Thread a gas regulator onto a bottle of inert gas. Tighten the regulator with an adjustable wrench.
Slide the hose coming from the gas regulator into the open end of the pipe.
Cover the open end of the pipe with masking tape, securing the hose inside of the pipe.
Purge the pipe. Turn the valve onto of the gas bottle counterclockwise to start gas flowing into the pipe. Allow the pipe to fill with gas for one to five minutes depending on pipe diameter. Cover the cut "X" with masking tape to hold the inert gas in the pipe.
Allow the inert gas to continue to flow as you weld the pipe seam.
