A 4" diameter gas pipe requires purging with inert gas under what condition?

Purging a 4" diameter gas pipe with inert gas is necessary to remove any potentially explosive gas mixtures, ensuring safety during installation or maintenance. The requirement to purge is influenced by the length of the gas pipeline, as longer pipes tend to have a greater volume of gas that could linger, increasing the risk of an unsafe atmosphere.

A length exceeding 20 feet is the standard threshold in many regulations and best practices. When a gas pipe exceeds this length, there is an increased risk that there may be pockets of gas that have not properly cleared, especially if the area is not adequately ventilated. By requiring purging in this scenario, it ensures that any residual gas is effectively removed before the pipe is pressurized or put into service, allowing for a safer operation.

This requirement can vary across different codes or regulations, but the specification to purge a 4" diameter pipe when it exceeds 20 feet is widely adopted to maximize safety during gas handling.