Insulated welded joint for pipe-in-pipe systems

A method of joining a first pipe-in-pipe segment to a second pipe-in-pipe segment, each pipe-in-pipe segment having an outer pipe enclosing an inner pipe that extends beyond the outer pipe, and each pipe-in-pipe segment having insulation material in an annular space between the outer pipe and the inner pipe for use in a geothermal energy production plant, comprising:

• forming a weld joint between respective ends of the inner pipes of the first and second pipe-in-pipe segments;
• covering the weld joint with joint insulation material;
• welding first and second half-pipe sleeves together via longitudinal welds to form a sleeve segment above the weld joint;
• and
• welding the sleeve segment to respective rings on the first and second pipe-in-pipe segments such that (a) the welds at the rings connect the outer pipes of the first and second pipe-in-pipe segments via the sleeve, and (b) the welds at the rings connect the outer pipes of the first and second pipe-in-pipe segments to the respective inner pipes of the first and second pipe-in-pipe segments via the rings to so allow for transfer of bending and straightening forces from the outer to the inner pipe.

A geothermal energy production plant, comprising:

• a casing in a geological formation, wherein the casing encloses a pipe-in-pipe system comprising a plurality of serially joined pipe-in-pipe segments, each having an outer pipe enclosing an inner pipe, and each pipe-in-pipe segment having insulation material in an annular space between the outer pipe and the inner pipe;
• wherein the pipe-in-pipe segments are coupled to each other such that
• (1) respective ends of the inner pipes are welded to each other;
• (2) respective ends of the outer pipes are welded to respective rings on the inner pipes of the pipe segments;
• (3) a sleeve segment is placed between and welded to the rings of the pipe-in-pipe segments and further welded to the respective ends of the outer pipes to thereby form a continuous outer pipe enclosing the weld connecting the inner pipes and to allow for transfer of bending and straightening forces from the outer to the inner pipe;
• and
• wherein the casing and the pipe-in-pipe system are fluidly coupled to each other and a heat exchanger to form a closed loop working fluid circuit for heat recovery and power generation.