A welding method, to reduce tension due to pipe stretching, for a downhole double-walled insulated pipe is disclosed. The pipe comprises an inner tube, an outer tube, steel spacer rings and insulated material fitted filling the annular space. Special welding links the ends of inner and outer tubes, forming a flexible metallic joint, achieved through the use of filler metal with specific chemical composition during the welding process. The inner tube is heated and extended before the tube welding is performed. The welded joint is strong enough to keep the inner tube in place when it cools down, creating a tension inwards in the tube. This way, when steam flows through the tubing during the operation, the heat stretches the inner tube until the tension direction is outwards, then the tension now becomes about half of the normal tension applied to the tube welded joint with the usual welding process.

A pipe-in-pipe bulkhead assembly has inner and outer rings spaced in concentric relation to define a thermally-isolating gap in the annulus between them. Interlocking formations project into the annulus from each of the rings, presenting confronting faces where they overlap radially. The gap extends between the longitudinally-spaced faces. A thermally-insulating spacer is interposed between the faces in the gap to carry axial mechanical loads between the inner and outer rings. Heating elements outside the inner ring extend longitudinally beyond the gap between the faces and along a longitudinal passageway that passes through or beside an interlocking formation of the inner ring. The spacer may be positioned before or after the outer ring is placed, for example as a discrete element or as an injected mass. An additional sealing mass may also be positioned in the annulus, for example by injection, to promote a gas-tight seal.

A pipe-in-pipe assembly with thermally-insulating spacers positioned in an annulus to act radially between inner and outer pipes is disclosed. The spacers have at least one circumferentially-extending array of circumferentially-spaced ribs that define longitudinally-extending passageways in gaps between neighbouring ribs of the array. Cables including heating elements extend longitudinally along the annulus outside the inner pipe. The cables extend longitudinally along the passageways. At least one insulation layer disposed radially outboard of the cables has insulating elements disposed in the gaps between the ribs and/or an insulating layer extending around the inner pipe, positioned radially outboard of the ribs and bridging the gaps. Bands encircle and retain components of the insulation layer. Insulation may also be disposed on the inner pipe between first and second arrays of ribs, those arrays being spaced longitudinally from each other.

Methods and devices related to multi-layer tubular conduit are disclosed. The method of making the multi-layer tubular conduit includes providing a hermetically sealed metal tube, inserting a thermoplastic conduit within the tube, and surrounding the exterior of the tube with an overjacket. The multi-layer tubular conduit device includes three layers: a layer of thermaplastic conduit, a layer of hermetically sealed metal tube, and a layer of overjacket. The three layers are arranged coaxially such that they share a common central axis. The method of use includes installing a multi-layer tubular conduit device in a public or non-public environment. The multi-layer tubular conduit offers mechanical protection from harsh and/or hostile environments while still offering the flexibility of traditional conduit.

Methods and devices related to multi-layer tubular conduit are disclosed. The method of making the multi-layer tubular conduit includes providing a hermetically sealed metal tube, inserting a thermoplastic conduit within the tube, and surrounding the exterior of the tube with an overjacket. The multi-layer tubular conduit device includes three layers: a layer of thermaplastic conduit, a layer of hermetically sealed metal tube, and a layer of overjacket. The three layers are arranged coaxially such that they share a common central axis. The method of use includes installing a multi-layer tubular conduit device in a public or non-public environment. The multi-layer tubular conduit offers mechanical protection from harsh and/or hostile environments while still offering the flexibility of traditional conduit.

A method of sealing an annulus between inner and outer pipe sections of a pipe-in-pipe system includes positioning a sealing mass in the annulus in contact with the inner and outer pipe sections. Deforming the sealing mass occurs, for example by shearing and compression, by effecting relative longitudinal movement between the inner and outer pipe sections. Fixing the inner and outer pipe sections against reverse relative longitudinal movement to maintain deformation of the sealing mass is then performed. The inner pipe section and a displaced outer pipe section may be fixed by welding them to respective pipes of an adjoining pipe-in-pipe structure. Opposed ramp surfaces, each being similarly inclined relative to the longitudinal direction, extend into the annulus from respective ones of the pipe sections such that the sealing mass may be compressed between the ramp surfaces.

A method of sealing an annulus between inner and outer pipe sections of a pipe-in-pipe system includes positioning a sealing mass in the annulus in contact with the inner and outer pipe sections. Deforming the sealing mass occurs, for example by shearing and compression, by effecting relative longitudinal movement between the inner and outer pipe sections. Fixing the inner and outer pipe sections against reverse relative longitudinal movement to maintain deformation of the sealing mass is then performed. The inner pipe section and a displaced outer pipe section may be fixed by welding them to respective pipes of an adjoining pipe-in-pipe structure. Opposed ramp surfaces, each being similarly inclined relative to the longitudinal direction, extend into the annulus from respective ones of the pipe sections such that the sealing mass may be compressed between the ramp surfaces.

An anti-slip and self-centering device for an inner tube inside an outer tube of a unit length element for an undersea fluid transport pipe, the device having a ring (4) made of elastomer material sandwiched between two annular metal plates (6, 8) having an inside diameter that corresponds substantially to the diameter of the inner tube and an outside diameter that corresponds substantially to the diameter of the outer tube, the device further having a clamp (10, 12) for clamping the plates together to compress the ring.

An anti-slip and self-centering device for an inner tube inside an outer tube of a unit length element for an undersea fluid transport pipe, the device having a ring (4) made of elastomer material sandwiched between two annular metal plates (6, 8) having an inside diameter that corresponds substantially to the diameter of the inner tube and an outside diameter that corresponds substantially to the diameter of the outer tube, the device further having a clamp (10, 12) for clamping the plates together to compress the ring.

A method of sealing an annulus of an electrically trace-heated pipe-in-pipe structure including introducing a flowable filler material to mould a sealing mass in situ is disclosed. The sealing mass closes a restriction at which the annulus is narrowed radially and embeds at least one heating element that extends generally longitudinally through the restriction. The structure includes an inner ring spaced within an outer ring to define the annulus between the rings. The annulus is narrowed radially by one or more projections that extend radially into the annulus from at least one of the rings toward the other of said rings. The restriction may include multiple bores, each of which may contain a sealing mass around a respective heating element in the bore.