This paper discusses key effects of the lateral stability on pipeline design and especially on axial creeping under thermal and pressure cyclic loading when connected through catenary risers to large offset floating platforms. A recent industrial study by Tornes [1] has shown that, under repeated heat-up and cool-down of the transported fluid and assumed lateral stability, some high temperature and/or high pressure deepwater flowlines experience some gradual net axial displacement towards the colder outlet ends. The present paper will further demonstrate that the flowlines may have much larger net axial displacement under repeated production shut-downs if they are laterally unstable. Detailed discussions on the phenomenon are given to 1) Flowline layout as functions of curve radius and routing, global slope and detailed seabed profile, 2) Axial and lateral friction forces applied, 3) Submerged weight of the considered flowline, 4) Operating parameters including cyclic pressure and temperature variations, and 5) catenary riser tensions. The paper provides sufficient details and results for the deepwater pipeline ratcheting phenomenon through extensive finite element analyses. The models will mainly cover production flowlines in both elevation profile and plan layout. The results are also compared with theoretical calculations. Some important considerations on deepwater pipeline design are widely described. It is hoped that the discussions presented in this paper will allow operators to address this issue at the earliest stages of the field development and benefit pipeline designers.

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