Objective
The analysis of the static and dynamic behaviour of drilling extension tubes in deep water clearly evidences the interest of reducing the weight of the kill and choke lines and that of the booster line by making them in composite materials rather than in steel. Such tubes have been developed by IFP and the AEROSPATIALE (SNIAS) while using the wirewinding technique with fibre glass, kevlar or carbon impregnated in epoxy resin. After study and computation phases that allowed the optimization of the dimensioning of the tubes and to qualify the prototypes for the envisaged application, it seemed preferable to check the in-situ behaviour of the scale 1 tubes, submitted to real tests following their utilisation during offshore drilling operations for a significant period.
The first phase of the project, described above, has allowed the definition and development of a methodology to test on-site the components of the offshore drilling and production systems (peripheral tubes in composite materials) without disturbing other operations (development drilling operations), nor even interfering with them. This "uncoupling" has allowed to simplify considerably the organization of the test and to reduce its cost. This method, the validity of which was later established (phase 3), could be applied in other circumstances and for other components. From this point of view this phase is a success.
The second phase of the project, described above, has allowed to fabricate a small series of 2 x 5 tubes of a length of 15 m in composite materials by means of a preindustrial machine designed, manufactured and developed outside the scope of this project. These tubes were used, either for destructive qualification tests, or for the third phase of the project. The fabrication technique used for the first time at this scale has proved satisfactory and it was possible to demonstrate the implementation aptitude under industrial conditions of composite tubes developed in laboratory by SNIAS and IFP. This phase also represents a success.
The third phase of the project, described above, has allowed the characterization of the behaviour on-site of composite tubes made in the previous phase, used as peripheral lines for a drilling riser. Booster line tubes, the 350 bar service pressure of which only requires a relatively low wall thickness, present an excessive sensitivity versus handling and transport constraints (pinching and shock effect). They need to be redesigned to be adapted to operational service. On the other hand, the kill and choke lines tubes, significantly thicker due to their service pressure of 1050 bar, supported similar tests without showing any failure after the trials. These tubes are now qualified for the envisaged application. However, additional studies would be necessary for their homologation, specially concerning their external protection and the development of control and in-situ rehabilitation processes. Lastly, it will be necessary to significantly reduce production costs of these tubes before they can be proposed for commercialization. This third phase of the project is thus only half a success.
The offshore trial project of composite tubes being used as peripheral lines for the drilling extension tubes under real utilisation conditions has been carried out in three major phases :
2.1 Test preparation
- Definition of the experimental tube specifications according to two types :
Designation Kill & Choke Booster line
Internal diameter 4" - 101,6 mm 4" - 101,6 mm
Service pressure 70 MPa - 10000 psi 35 MPa - 5000 psi
Effective length 15,24 m - 50 ft 15,24 m - 50 ft
- Definition of practical test conditions :
- parallel assembling of each type of tube on the two upper elements of the riser of the semi-submerisble PENTAGONE 84 operating for TOTAL OIL MARINE in the North Sea
- periodical raise at service pressure of the two additional lines thus formed
- holding of assembly during several drilling operations
- return to laboratory for appraisal of tubes.
- Study of tubes dimensioning oftheir integration in the riser elements, of ancillary equipment required to run the tests and to define the procedures.
2.2 Manufacture and testing of tubes and ancillary equipment
- Construction and development of a machine for the fabrication of long tubes (up to 24 m) in composite materials
- fabrication of 5 tubes of each type according to selected definition
- verification of performance obtained by bursting the first tubes of each series.
Designation Kill & Choke Booster line
bursting pressure 176 MPa 81,2 MPa
service/bursting ratio 2,5 2,3
- verification of axial bursting resistance under internal pressure of each type of tube
- fabrication of ancillary equipment and testing of tubes pressurization flexibles
2.3 Tests
- stamping of all tubes at 1,5 times their service pressure
- truck transport of tubes and their integration with other elements of the riser
- transfer on the P84 platform andimplementation during three drilling campaigns held between May and December 1983. Total immersion period of most solicited tube : 133 days, including 22 cycles under pressure service (534 h) - dismounting of tubes and return in January 1984 - Tubes appraisal after tests : bursting of a kill and chokee tube at 133,5 MPa, showing a limited damage of the tube comapred to initial rupture pressure.
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DEM - Demonstration contractsCoordinator
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