What type of gas must be used to purge the air from a pipe that has an NPS of less than or equal to 2.5" and is over 50' in length?

The use of an inert gas to purge air from a gas pipe that has an NPS of less than or equal to 2.5 inches and is over 50 feet in length is important for safety and regulatory compliance. Inert gases, such as nitrogen, are non-flammable and do not react with other materials. This makes them ideal for displacing air in pipelines, as they can help eliminate the presence of oxygen, which is necessary for combustion.

When purging pipes, especially those that will carry flammable gases like natural gas or propane, it is essential to avoid introducing combustible materials into the line during the purging process. The use of inert gas helps to create a non-combustible atmosphere, reducing the risk of ignition and explosion as the line is prepared for the introduction of the intended gas.

In addition, using compressed air or flammable gases for purging can create dangerous situations, as they can lead to the potential formation of explosive mixtures in the pipeline. Therefore, using inert gas is the correct and safest approach to ensure that the air is effectively removed without risking ignition.