Temporary Intrinsics and Presentism

Disclosed is a method for replacing sub-surface gas mains by isolating a section of the main to which service lines are attached, providing an independent gas supply to the isolated section, inserting a smaller diameter main-replacing tube into the isolated main section and providing and independent gas supply to the interior of the tube so that a dual, independent gas supply is provided, one in the annular space between the main and the tube and another within the tube. The service lines are then, one-by-one or in groups as desired, disconnected from communication with the annular space and placed in communication with the interior of the replacement tube without substantial customer service interruption. The operation is repeated for further sections of the main to be replaced.