Methods and systems comprising a first and a second powder coating apparatus, with each apparatus comprising a tubular barrel having an axial bore extending longitudinally therethrough, are usable for coating an interior surface of a tubular member. Each coating apparatus comprises a conical member connected with the tubular barrel and at least one gas conduit connected to the tubular barrel for communicating gas into the tubular barrel. The at least one gas conduit contains a gas flow control valve connected thereto for controlling the volumetric flow rate of gas through the at least one gas conduit. Each coating apparatus further comprises at least one container for holding a coating material, an inlet conduit for communicating the coating material into the axial bore of the tubular barrel, and a plurality of gas nozzles connected to the tubular barrel for inducing spiraling gas flow through the axial bore of the tubular barrel.