Slug flows generate variable loads that excite pipelines, inducing oscillatory displacements and tensions of significant magnitude, raising concerns about the physical integrity of the pipe’s structure. The present paper presents a simulation model to compute non-uniform slugs, to provide a tool for the analysis of the dynamic behavior of horizontal pipelines in subsea petroleum production systems. This model was tested for a straight, horizontal, free span hanging pipeline supported at both ends. The development of the present methodology was based on a previous model of regular slugs. The present model takes into account the expansion of the gas bubble length along the pipeline, generated by the negative streamwise pressure gradient between the pipeline’s entrance and exit, resulting in a longitudinal sequence of non-uniform slugs. The model’s algorithm used to calculate the mass distribution in the slug flow is implemented in a subroutine of a pre-existent software, commonly known to simulate the mechanical behavior of pipelines under dynamic loads. The dynamic responses of a pipeline excited by non-uniform slugs – vertical displacement, bending moment and bending stress – were analyzed as a function of the gas expansion global rate, and were compared to the dynamic responses induced by a regular slug flow. It is concluded that the non-uniform slug distribution imposes a more complex excitation on the pipe, while the perfect regular slug flow induces an excitation with a single well-determined frequency. The difference between irregular and regular flows depends on the magnitude of the pressure gradient acting along the pipeline’s length.

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