Study on the mechanics of a coiled tubing within a marine ‘pipe-in-pipe’ system with a low diameter ratio

ABSTRACT

To better understand the mechanics of coiled tubing working within the risers connected to Floating liquefied natural gas (FLNG), this paper studied a specific marine ‘pipe-in-pipe’ system with a low diameter ratio. The experimental results showed that the axial load on the inner pipe of an unfixed system increased with the increase in injected length. In this case, the ‘force-in’ was always larger than the ‘force-out’. The changing trend of force-in and force-out within the unfixed system was essentially found to be stable after a sinusoidal buckling of the inner pipe. Even though the magnitudes of force-in and force-out did not increase a lot, the injected length increased significantly. Relationship of force-in, as well as force-out, between fixed and unfixed system when the pipe was buckled sinusoidally and helically was found. The results help in working of a coiled tubing within small diameter marine risers.

KEYWORDS:

• Coiled tubing
• floating liquefied natural gas
• low diameter ratio
• marine ‘pipe-in-pipe’ system

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study is supported by National Natural Science Foundation of China [grant number 51709006] and China Postdoctoral Science Foundation [grant number 2017M610733].