Methods and apparatus for a subsea tie back

Flow protection system comprising an inner tube (70) arranged in an outer tube (50) to ensure flow through the outer tube (50). During installation and relative axial movement relative to outer tubes (50), the inner tubes (70) have an approximate or completely neutral buoyancy in the fluids of the outer tubes (50) and may extend wholly or partially through outer tubes (50). The inner tube (70) may be anchored at one end relative to the outer tube (50). The inner tube (70) is preferably a composite coiled tube which is installed with a propulsion system. The system may allow fluids to flow through the inner tubes (70) and be mixed with fluids in outer tubes (50) or may flow through inner tubes (70) to the outside of outer tubes (50). Hot fluids can be passed through inner tubes (70) to maintain the temperature of fluids flowing in the outer tubes (50) and chemicals can flow through inner tubes (70) to condition the fluids in outer tubes (50). Tools can be attached to the end of inner tubes (70) to perform flow-proofing operations inside outer tubes (50).