A nonlinear model for prediction of stresses in submarine pipelines during pickup operations

AbstractThis paper presents a nonlinear mathematical model for predicting stresses in a submarine pipeline as it is picked up off the ocean floor by barge davits for purposes such as repairs and tie-ins. Large deflections are assumed and the pipeline is modeled as a series of finite beam segments from the ocean bottom on up. Using an initial-value approach, a pipeline configuration satisfying known boundary conditions is determined by an iterative technique, in which bottom conditions are identified by considering the part of the pipeline resting on the sea bed as a semi-infinite tensioned beam on an elastic foundation. The effects of material nonlinearity are included and both Ramberg-Osgood and Hutchinson formulations are considered. With the pipe model suggested, any given pickup procedure can be analyzed or a reliable procedure can be designed based on given constraints and any desired improvement in the final configuration and/or stress levels may be achieved by a variation of the parameters involved. A practical example is examined to illustrate the applicability of the model in either assessing or developing a pickup procedure