Rigid-pipe non-integral riser
The lines in a non-integral riser can be run and retrieved separately from each other and from the main structural member. A non-integral riser includes a tensioned central structural member which may carry fluids or perform other functions besides providing structural support and guidance to lines. The structural member is fitted with support/guidance devices to locate and laterally guide individual lines.
The two ends of the structural member are fitted with the two halves of a coupling. A section of the structural member including the coupling and guidance devices is called a “joint”; the associated sections of lines are also called joints. The two ends of each line joint are fitted with mechanical/pressure couplings, typically threaded box and pin, independent of the central pipe coupling. Other lines are installed individually after the structural member is installed and tensioned. They are retrieved individually before the structural member is retrieved.
This design has the advantages of simplicity and of permitting the retrieval of a single line (e.g. for repair/replacement) without requiring the shut-in and retrieval of the whole system. It has the disadvantage of being slow to run or retrieve.
Source: API RP 17A, Design and Operation of Subsea Production Systems—General Requirements and Recommendations, Fourth Edition, Reaffirmed 2011. Global Standards