Method of connecting pipe-in-pipe structures

Details Method of connecting pipe-in-pipe structures Method of connecting pipe-in-pipe structures

1999-11-16

2000-11-07

Ryan, Patrick

Metal fusion bonding

Process

With measuring, testing, indicating, inspecting, or...

F16L 4700

Patent

active

061423599

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a method of connecting together tubular members which have co-extending elongate members therewithin. The invention will be described with reference to its use in connecting together the pipes of a pipeline and tubular structural members such as those typically utilised in the offshore oil and gas industry.
With the growth of the offshore oil and gas industry, it is necessary to install prefabricated pipelines between offshore oil and gas fields and onshore processing facilities and between different offshore locations. These may be for processing purposes or for loading the oil or gas into shuttle tankers from offshore loading buoys.
To meet the need to install pipelines with a high degree of reliability, it is possible to use barges and vessels with several aligned welding, inspection and coating stations that can fabricate a pipeline from a large number of short lengths of coated pipe, typically 12 metres long. The welded joints of the pipeline have then to be inspected and coated before the pipeline is lowered to the sea bed down a long curved stinger or ramp.
A further alternative is to fabricate, at a suitable shore site, a bundled assembly formed of a pipeline or group of pipelines housed within a large diameter outer steel pipeline, known as a carrier pipe. The void space within the carrier pipe and around the pipelines housed within it is sealed to prevent the ingress of water.
A particular trend is to install pipelines which are to operate at high temperatures and/or pressures, which give rise to significant integral forces when the pipeline is prevented from expanding or allowed only partial expansion.
In use, submarine pipelines are often required to maintain certain fluid temperatures, preventing adverse affect such as hydrate formation or wax deposition. Thermal insulation of the pipelines helps to avoid this and is currently achieved by the application to their external surface a suitable insulation material. The materials are presently applied by various processes including extrusion, impingement, wrapping and casting.
For high fluid temperatures and pressures, provision of thermal insulation is achieved by housing the fluid carrying pipeline or flowline, as it is commonly termed, within an outer and additional pipeline. This is known as a "pipe-in-pipe" system. The annulus between the inner flowline and outer pipeline may be filled with thermal insulant having low order thermal conductivity, such as polyurethane foams, mineral wool or ceramic microspheres. Alternatively, the annulus gap may be a vacuum or full of gas.
Also a particular trend is to install pipelines which are to operate at high pressures and high temperatures, where if the pipeline is prevented from expanding or is allowed only limited expansion, would lead to the pipeline experiencing induced strains beyond the elastic limit of the material from which it is made.
To form elongate tubular structural members such as the tethers on Tension Leg Platforms, short lengths of "tube-in-tube" structural members are adjoined end to end by either butt welding, internal or external collars secured by fillet welds or mechanical means such as screwed ends or splined connectors.
Where pipe-in-pipe pipelines or tube-in-tube structural members are constructed, it is necessary to complete the connection together of two inner pipes or two inner structural members prior to connecting together the two outer pipes or two outer structural members. Where the annulus between the inner pipe or tube and the outer pipe or tube contains materials or mechanical apparatus which prevent relative longitudinal movement of the two co-extending pipes or structural members, there is a technical problem faced in closing the gap between the ends of the outer pipes or structural member which is required for access to connect the inner pipes or structural members.
A solution has been proposed in our co-pending patent application GB 9623131.1. This method of joining pipelines utilises an intermediate member which is screwed on a thread rela

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