TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMultiphase product transportation from offshore is facing the challenges of deepwater exploration and long-distance tieback. Prior predictions of the multiphase flow behavior, both steady state and transient, are crucial for successful design and operation of offshore facilities. The pressure surge and thermal stresses caused by transient multiphase flow during emergency shut down (ESD) are critical design criteria for pipeline systems.Numerical methods have been developed to simulate the subsea HIPPS/ESD shut down and the ensuing system transient behaviors. These methods are able to predict pressure and temperature response during and after ESD valve closure. The analytic predictions are used in the design of deepwater pipeline and riser systems. This paper demonstrates the use of transient multiphase flow analyses in the design of a deepwater subsea pipeline and riser systems. The pressure and temperature responses, and the pressure and temperature profiles from wellheads to the platform are investigated. The system design criteria are validated. The study improves the understanding of transient process in multiphase flow pipelines, and will benefit the deepwater production system design.