Patent FR-2852677-A1 (FR)
Title: Device for heating and thermal insulation of at least one main underwater pipe transporting viscous fluid, in particular for hydrocarbon riser and using phase-changing insulation
Inventor: CHIESA GIOVANNI
IPC: E21B43/12
Filed: 2003-03-18
Abstract: The insulating coating (2) surrounds a cylindrical internal chamber (4) which is coaxial with the external envelope and fills the annular space between the external envelope and the internal chamber. A heating fluid (5) is maintained at temperature (6) and circulated inside the internal chamber so the heating fluid surrounds the main pipe (1a) which is inside the internal chamber : The device includes a coating of a thermally insulating material (2) surrounding the main pipes. This coating is covered with a sealed external protection envelope (3), preferably cylindrical. The internal chamber has at least one internal gas injection line (7) running through it to allow the injection of gas into the main pipe. The gas injection line is connected to the main pipe at one end inside the internal chamber, and preferably the gas injection line extends out of the internal chamber in the form of an external injection line connecting the internal injection line to a floating support. The means of circulating the heating fluid comprise at least one internal supply line extending from the inside of the internal chamber through a first orifice (8) at one end of the internal chamber, and an outlet orifice at the second end of the internal chamber. The gas injection line is coiled in a spiral around the internal heating fluid supply line inside the internal chamber. Each end of the heating fluid supply line is extended by a flexible external line (62, 63) connecting the first and second orifices to a floating support. A pump circulates the heating fluid which is heated by a heater. The device has an end closure (11) at one or both ends, supporting the main pipe(s) and the means of circulation and with the first and second orifices passing through it. The second end closure has a large orifice with a diameter greater than that of the main pipe so the main pipe passes through it and the heating fluid is in contact with the seawater at the lower end of the internal chamber. Alternatively, the orifice is sealed to the main pipe. The main pipe is coated with a second insulating layer at least around this second end, with the heating fluid circulating outside this second layer. This layer is syntactic mousse or other solid insulating material and fills the space between the main pipe and a second coaxial pipe in which the main pipe is inserted. Alternatively, the second insulating layer is a material subject to migration and contained in a flexible or semi-rigid envelope. The material changes phase with a melting point of between 20 and 80[deg]C, greater than that of the environment and less than that at which the fluid in the main pipe suffers a damaging increase in viscosity. The insulating material is an alcane, preferably a paraffin with a hydrocarbon chain of at least 14 atoms, preferably tetracosane C24H50 with a melting point of around 50[deg]C. This can be mixed with a structural or gelling material such as polyurethane, reticulated polypropylene, or polyethylene or silicone. Two intermediate barriers and an number of centralizing and shaping plates are placed in the internal chamber to prevent excessive migration of the insulation.