On the Predication of Pipeline As-Laid Embedment Using a Cycle-by-Cycle Approach for Deepwater Application

Abstract

In deep water, pipelines are generally laid directly on the sea bed and a pipeline’s as-laid embedment is a major source of uncertainty influencing the assessment of pipe-soil resistances, pipeline lateral buckling formation as well as lateral buckling response, end expansion and walking behavior. In order to have good control of the uncertainties in pipeline as-laid embedment, pipe laying effects, including static and dynamic pipe-soil vertical contact loads and the likely degree of soil softening due to pipeline oscillation at touch down zone should be reliably predicted. In this paper a new procedure is introduced that uses OrcaFlex [1] to determine pipe laying effects and a cycle-by-cycle approach to predict pipeline as-laid embedment. Validation of the procedure is also presented in this paper by comparing pipeline as-laid embedment results calculated from the procedure with upper and lower bound values developed from field observation data. Very good agreement is obtained. In the study, it is found that pipe-soil vertical contact load amplitude, pipe horizontal oscillation, and duration of the oscillation at touchdown zone are important to soil softening as well as pipeline as-laid embedment. In addition, results calculated from the procedure were also compared with those evaluated from the SAFEBUCK guideline [2]. It was found that results from the SAFEBUCK guideline, in general, underestimates the pipeline as-laid embedment.