Abstract: Velocity/flow measuring of purge gas when welding pipe, is accomplished by providing a controllably fixed orifice at the distal end of the pipe being welded. The purge gas passes through a pressure regulator, a flow meter, and a purifier. An isolation/control valve is used to control access to the purge gas. The purge gas then passes through a header connected to the input end of the first pipe. A second pipe is positioned adjacent to the first pipe. A pressure clamp, tape or other sealing means seals the circumferential weld area between the first pipe and the second pipe. A second pressure gauge monitors the gas pressure at the pressure clamp. The purge gas passes through the weld area, to a manifold in fluid communication with a first pressure gauge, a back pressure control means and to a weld purge orifice fitting, having a selected orifice size.