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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.

Instructions

1

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.

2

Thread a gas regulator onto a bottle of inert gas. Tighten the regulator with an adjustable wrench.

3

Slide the hose coming from the gas regulator into the open end of the pipe.

4

Cover the open end of the pipe with masking tape, securing the hose inside of the pipe.

5

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.

6

Allow the inert gas to continue to flow as you weld the pipe seam.

Welding is the process of heating metal to create a permanent joint between the pieces. The three most common welding techniques are MIG (Metal Inert Gas) welding, arc welding and TIG (Tungsten Inert Gas) welding. Each welding technique uses inert gases to shield the welding flame from contacting reactive gases, thereby creating a cleaner and stronger weld. Arc welding utilizes a solid substance called flux that burns and gives off the inert gas. MIG and TIG welding requires gas to be fed from a compressed air bottle through the welding gun in order to protect the welding flame.

Inert Gases

The most common inert gases used in welding include argon and helium. Because argon is noncorrosive, nontoxic and nonflammable, it serves as an ideal inert shielding gas most frequently used in MIG and TIG welding applications. Helium is more commonly used in arc welding processes because it creates a hotter weld necessary for metals such as copper.

Carbon Dioxide

Carbon dioxide is also used in some welding applications, and even though it is nonflammable and inert under most conditions, it may cause a chemical reaction with some metals while welding. Carbon dioxide is most commonly used as a shielding gas in arc welding.

Welding and Cutting Gas Fuels

In addition to shield gases, welding techniques can also utilize gases as a fuel source for cutting and heating metals. Acetylene, propylene and propane are all flammable gases that are used to fuel welding torches. Additionally, because acetylene gas can be mixed with oxygen to create an oxy-acetylene torch that provides its own fuel and oxygen source, it can be used for underwater welding applications.