Abstract: A flow assurance system includes an inner pipe disposed within an outer pipe to assure flow through the outer pipe. During installation and relative axial movement with the outer pipe, the inner pipe is nearly neutrally buoyant or fully neutrally buoyant in the fluids of the outer pipe and may extend partially or completely through the outer pipe. The inner pipe may be anchored at one end within the outer pipe. The inner pipe is preferably composite coiled tubing that is installed using a propulsion system. The system may allow fluids to flow through the inner pipe and commingle with the fluids in the outer pipe or may flow fluids through the inner pipe to the exterior of the outer pipe. Hot fluids may pass through the inner pipe to maintain the temperature of the fluids flowing through the outer pipe and chemicals may flow through the inner pipe to condition the fluids in the outer pipe. Tools may be attached to the end of the inner pipe for conducting flow assurance operations within the outer pipe.