Method for repairing a damaged pipe laid on deep sea beds

A method for repairing, from a depot ship, a damaged pipe laid on deep sea beds, comprising lowering an apparatus equipped for pipe recovery from a depot ship, guiding it and clamping it on to the pipe to be repaired, cutting the pipe at one end of its damaged piece by the cutting device of said apparatus, inserting and locking the composite sealing and recovery head of said apparatus into that end of the pipe portion which has been freed from the damaged part, freeing said apparatus and recovering it on board the depot ship, emptying the water which fills said pipe portion, raising the end portion of said pipe portion on to the depot ship by a recovery cable hooked to said composite sealing and recovery head, and releasing the raised end of said pipe portion from said composite sealing and recovery head on board the depot ship, and further comprising subsequently welding a compensation pipe piece to said raised end of the pipe portion on the depot ship and welding to the compensation pipe piece a pipe terminal piece comprising an outer knurled surface band, locking to the free end of said pipe terminal piece, on board the depot ship, a discardable quick-release head which covers and protects said outer knurled surface band of the terminal piece, relaying on the sea bed said end of the pipe portion prepared in this manner by means of a discardable cable hooked to said discardable head, releasing said discardable cable from said discardable head, repeating all the aforesaid stages required to free the other portion of the pipe to be repaired from said piece of damaged pipe, recovering and preparing on board the depot ship the end of said other pipe portion and relowering on to the sea bed said end of said other pipe portion also provided with a compensation pipe piece, a pipe terminal piece and a discardable head, then lowering an alignment framework from the depot ship on to the sea bed over the two said prepared pipe pieces by means of two support cables, the alignment framework being provided with mobile gripping clamps, fixed alignment supports for the pipe and a positionable device for determining the free distance between the two pipe portions, aligning the two said prepared pipe portions and keeping them aligned by clamping the two said pipe portions with said mobile gripping clamps of the framework and moving them on to said fixed alignment supports, filling the aligned pipe portions with water, lowering a service frame from the depot ship into a longitudinal slot in said alignment framework and guiding it by means of the two said support cables of said framework, the service frame being provided lowerly with two longitudinally slidable withdrawal and insertion carriages, each of which is provided with gripping clamps, means for releasing a discardable head and means for locking a coupling sleeve, moving the two carriages of said service frame on to the respective discardable heads of the two said aligned portions of the pipe to be repaired and clamping said heads with the gripping clamps of said carriages, releasing said discardable heads from the respective pipe terminal pieces of the two aligned pipe portions by said release means of the two carriages and withdrawing said discardable heads from said pipe terminal pieces by moving said carriages, recovering on board the depot ship said discardable heads thus freed by raising said service frame, positioning against the terminal pieces of the two aligned pipe portions said alignment framework device for determining the free distance between the two said pipe terminal pieces, returning said alignment framework device to its rest position, preparing on the depot ship a central pipe stub of the determined length, and provided at its ends with two quick locking coupling sleeves which can each slide thereon between an annular projection on the end of said stub and an inner shoulder ring at which the sleeve does not project from the stub, said coupling sleeves being also provided with means to provide a hermetic seal between them and, respectively, said central pipe stub and said terminal pieces of the portions of pipe to be repaired, locking said central pipe stub on to said service frame by tightening the gripping clamps of the two carriages of said service frame on to said coupling sleeves held against said inner shoulder rings, relowering said service frame fitted with said central pipe stub from the depot ship into said longitudinal slot in the alignment frame, while at the same time synchronously moving the two service frame carriages so that said central stub becomes centred between the terminal pieces of the two aligned pipe portions, mounting said coupling sleeves of the central pipe stub on to the respective terminal pieces of the two aligned pipe portions by sliding them so far as the respective annular projections on the ends of the central stub by moving the relative service frame carriages, locking said coupling sleeves of the central pipe stub against said outer knurled surface band of the respective terminal pieces of the two aligned pipe portions using said locking means of the respective carriages of said service frame, making the hermetic seal between said coupling sleeves and, respectively, said central pipe stub and said terminal pieces of the two aligned pipe portions by acting on said seal means of said coupling sleeves, releasing said coupling sleeves of the central pipe stub from the gripping clamps of the two carriages of said service frame and raising said service frame on to the depot ship, laying the joined pipe on to the sea bed by lowering said mobile gripping clamps of said alignment framework, releasing the joined pipe from said mobile gripping clamps of the alignment framework, and finally recovering said alignment framework on board the depot ship.