Method and apparatus for assembling and laying underwater pipeline

A method of assembling and laying an undersea pipe from a surface support having a variable inclination laying ramp comprising, sequentially fixing a new pipe section to the end of a pipe portion supported by the laying ramp and which has already been submerged, moving said surface support by a distance corresponding to the length of the new pipe section simultaneously with submersion of the new pipe section, wherein said submerged pipe portion is suspended from said surface support and the tension in said submerged pipe portion is maintained substantially constant irrespective of vertical movements of said surface support relative thereto by providing first damping means between the pipe suspension means and said surface support, and suspending the new pipe section to be connected from said surface support and maintaining the tension in said new section substantially constant by providing second damping means between the suspension means of said new pipe section and said surface support.

Apparatus for assembling and laying an undersea pipe from a floating support, comprising:

• a variable inclination laying ramp on a surface support, means for suspension of a submerged pipe portion from the surface support, said means suspending the pipe at an upper end thereof, means for bringing a new pipe section into alignment with the upper end of the submerged pipe portion for fixing thereto and means for submerging a newly fixed pipe section, wherein said suspension means is connected to said surface support by first damping means permitting movement of said suspension means relative to the support.

A method of assembling and laying an underwater pipe from a floating surface support including the steps of:

• suspending a portion of said pipe which has already been submerged from said surface support at an end to be coupled to a new pipe section, sequentially fixing a new pipe section to said submerged pipe portion at the end to be coupled, submerging said new pipe section, simultaneously moving said surface support by a distance corresponding to the length of said new pipe section, and maintaining the tension in said submerged pipe portion greater than a critical tension at which waves of transverse deformation appear in said pipe portion by compensating for changes in said tension in said submerged pipe portion resulting from vertical movements of said surface support.

Apparatus for assembling and laying an underwater pipe from a floating surface support, comprising:

• means for suspending a submerged pipe portion from said surface support at an end to be coupled, means for bringing a new pipe section into alignment with the end of the submerged pipe portion to be coupled for fixing thereto, means for lowering the new pipe section when fixed to the submerged pipe portion and means for simultaneously displacing said surface support, wherein said suspension means is mounted on said surface support by compensating means causing movement of said suspension means relative to said surface support so as to maintain the tension in the submerged pipe portion substantially constant and greater than a critical tension at which waves of transverse deformation appear in the pipe regardless of vertical movements of the surface support relative to the submerged pipe portion.