The pipe-in-pipe technology has been developed by the authors for one of the Japanese oil refineries in order to apply the new technology in the renovation project of the existing old submarine pipeline with more than 3 km length. In the project the newly designed flexible pipe, similar to flowlines applied in the subsea projects in the world, is installed in the existing 18 inch submarine pipeline with several bends by pulling the head of the flexible pipe. The flexible pipe can be designed against the appropriate tension expected in the installation by the selection of size and number of wires called as tension members. However, the weight of the flexible pipe might be too heavy if the tension members are wrongly designed. In this report the experimental works for the pulling tension of flexible pipes with small-scale and full-scale models are shown first. Then the analytical studies based on a simple beam theory to calculate the pulling tension are presented to simulate the experimental results. Finally, the measured tension in the actual renovation project, which was successfully executed in June 2002 in Japan, and the calculated tension are compared.


Under the severe economic conditions prevailing in Japan and elsewhere, Japanese oil refineries have been curbing capital investments and promoting longer service life of the existing equipment through stepped-up maintenance. For pipelines, importance is being placed on such technologies as inspection, maintenance and renewal, and the inspection technology by means of intelligent pigs and spot renovation using outer sleeves are already in practical use. As for the renewal technology of pipelines, two methods are in use, i.e., the "Insituform" by lining the pipeline from the inside with hardenable resins and the "pipe-in-pipe technology" by inserting new steel pipe into the pipeline.

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