The floating production system for the Callao Field consists of a processing and storage tanker yoke-moored to a centenary buoy in 300 ft of water. There are four flexible risers connecting tree sea floor pipeline end manifold to the surface buoy. These flexible risers are deployed in a steep "s" configuration and are subjected to well pressure.

In connection with the final design of the riser system, a series of model tank tests were conducted specifically to verify the-performance of the risers. These tests were designed to cover the conditions of different wind, wave and current directions. The test results show that the combined tanker, buoy and flexible riser dynamics in three dimensional space must be included in the design evaluation. Some of the critical motions and loading of the flexible risers and the associated fixtures could not be revealed by the conventional design evaluations.

The observed dynamic behavior of the riser system was further confirmed by analysis. Remedial methods were developed to correct the uncovered problems. Additional confirmation model tests were conducted prior to arriving at a final design.

The engineering experience presented in this paper will help future designers of flexible risers to choose the appropriate set of design criteria. It also pointed out the importance of carefully examining the consequences of the combined dynamic behavior of the buoys and flexible risers in 3-dimensions in different conditions of wind, wave and current directions.


In the summer of 1981, a Floating Production, Storage and Offloading Facility (FPSO) was installed in 300 ft (100 m) of water on Amoco's Cadlao Field in the Philippines. The system consists of a 127,000 DWT tanker attached by a yoke to a centenary Single Point Mooring buoy (SPM). Flexible risers connect the surface buoy to the Pipeline End Manifolds (PLEM) on the sea floor immediately beneath the buoy. The PLEMs are connected by flow lines to remote subsea wellheads.

This paper describes the design evolution of the flexible risers and the related system components. The technical experience gained from this particular design has valuable lessons for the design of similar type of flexible riser systems.

System Description

In this system, crude processing and storage is performed aboard the converted tanker. Crude flows from the satellite wells to two PLEM?s through one mile long 6" steel flow lines. Each PLEM is mounted on a subsea permanent guide base. In the Callao system, two pairs of 6" (152 mm) I .D., 3000 psi (20 MPa) working pressure, H2S service (Colfax) flexible hoses carry live crude from the seafloor to the surface buoy. Each riser pair (Figure If is supported at mid-depth by an underwater buoy to form a steep "S" configuration. Separation between risers in each pair is approximately 14 ft (4 m). This system is installed in an area where tropical typhoons produce severe environmental conditions in which wind, waves, and current have different directions.

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