| With the inevitability of development of offshore oil and gas resources exploitation todeep sea, subsea production system becomes a necessary technology, using it to achieve theexploitation and transportation is the main direction. Subsea pipeline is an important part ofsubsea production system. Tie-in is a technology that connects the subsea pipeline of thenewly developed, marginal and satellite oil or gas fields with the built subsea facilities, whichmakes offshore oil and gas exploitation cost-effective. Now, the design and installationtechnology of subsea pipeline connection are fully mastered by foreign offshore oilengineering company, which can not satisfy the domestic demand of self-exploited subsea oiland gas resources. Collet connector is used for end connection of deepwater subsea pipelineand installed by remotely operated tool, which needs to solve the problems of high-pressuresealing and installation. To solve these problems, this paper is to study the whole scheme andsealing and contact characteristics of collet connector system.From the structural composition and working principle required for offshore tie-intechnology, the paper presented the whole scheme of non-integral collet connector system.The system consists of installation tool and collet connector, which realizes the installation ofcollet connector through remotely operated vehicle controlling installation tool. Afterinstalling, installation tool can be retrieved from the seabed for reuse.The paper proposed the whole seal structure of collet connector, adopting connectingstructure with the combination of collet, claw, hub and lens ring, using the axial linearmovement of collet to drive claw to pre-tight hub radially, achieving high-pressure sealingbetween lens ring and hub. The surface of metal lens ring is spherical to work with the conicalsealing surface of hub, automatic self-aligning performance is good, the effective contact areais small, high-pressure sealing function can be realized, which is favorable to decrease theoverall size of collet connector. The conical fitting of collet and claw have mechanicalself-locking function, which increases resistant ability of pressure fluctuation and is favorableto simplify the structure of collet connector. Collet connector completes the installation andunloading through the linear motion of hydraulic cylinder, the operation is reliable and quick.The paper established the mechanical model of collet connector, through analysis ofcontact load between collet, claw, hub and lens ring in preloading and operating condition,proposed the calculation formula of pre-tightening load and assemble load for collet connector,which was based on pipeline design pressure. The strength design formulas of the parts were deduced, established the theoretical basis for engineering application of collet connector.Through contact analysis of sealing structure made of claw, hub and lens ring, contactcharacter and stress distribution law were obtained. The results show that connection structurebased on coordination of hub with claw can get bigger axial pre-tightening load than directaxial pre-tightening connecting structure, and has the characteristic of amplifying axialpre-tightening load. The results show that lens ring has the characteristic of self-tightening,which is related to structural type, geometrical dimension and material of lens ring.Adopting design by analysis theory and maximum deformation energy theory to evaluatehub failure stress, the results show, based on the strength design formula deduced fromcontact load formula established in the paper, the hub structure is safe and reliable, plasticcollapse and local failure will not happen.Through the analysis of critical state of collet connector, the results show sealing state issafe and reliable under50Mpa. It shows the strength design and check formulas are correctand valid, reflects the critical failure state of collet connector.Hydraulic pressure experiment on lens ring with hub achieves the highest sealing state of65MPa. Hydraulic pressure experiment on prototype of collet connector is safe and steady in50Mpa. The above results show the sealing performance of collet connector is safe andreliable, the structure design is reasonable, confirming the correctness and effectiveness ofload calculation and strength design formulas. |
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