Marine pipe-lay and recovery. VIII. What do you consider before laying offshore pipelines
In the concluding installment of its series on deepwater pipelaying, Engineering Technology Analysts Inc. points out that water depth greatly affects sag-bend stresses, but not as severely as might be expected. Increasing barge tension reduces stresses to a point of diminishing return where a further increase in tension will not decrease the curvature or the combined stresses. Waves and current heavily affect pipeline response. They must be analyzed as acting simultaneously and cannot be added separately to obtain the total effect. Combined waves and current have a greater influence than when the 2 loads are added separately. Further, the direction of waves and current with respect to the barge heading influences the pipeline curvature and hence combined stresses. Stresses can also be reduced by proper positioning of the barge during hang-on mooring conditions or while laying pipe during hostile weather. If abandonment is inevitable, recovery then becomes the immediate problem. Pipe can be successfully recovered by using the same barge tension as in the pipelay operations and by using the recovery cable. In severe weather, barge response may increase and cause considerable dynamic forces. Quasistatic analysis shows that deflections and stresses due to this excessive motion can be accurately determined.
- OSTI ID:
- 6883070
- Journal Information:
- Oil Gas J.; (United States), Vol. 73
- Country of Publication:
- United States
- Language:
- English
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