The main challenge explored in this case study is the root cause analysis of dynamically hazardous movements in the distillate lines to a plant deaerator. Flownex’s simulation optimisation tool was used to determine the preferred two phase flow regime. By using Flownex to identify the cause, it was possible to mitigate a commercial impact on the project, maintain the planned commissioning schedule and improve the existing plant design thereby also removing the safety risk of unwanted dynamic line movements.