F Flow assurance is a fundamental aspect in ensuring the continuity, safety, and reliability of hydrocarbon transportation in offshore oil production pipeline systems. flow assurance challenges become increasingly complex in large-diameter and long-distance pipelines transporting waxy crude oil, particularly in mature fields experiencing declining production rates and system performance degradation. these conditions may result in a decrease in fluid temperature below the wax appearance temperature (wat) and pour point, triggering wax deposition, congealing, and ultimately pipeline plugging. this study aims to evaluate flow assurance issues in an offshore oil production pipeline with a diameter of 20 inches and a length of approximately 30 km located off the coast of java, using an integrated thermal–hydraulic simulation approach. the research methodology employs a case study approach combined with quantitative analysis based on simulation. the flow assurance evaluation is conducted by integrating historical operational data, production fluid characteristics, pipeline geometry and existing conditions, as well as marine environmental parameters. thermal and hydraulic modeling is applied to analyze the distribution of temperature, pressure, and flow velocity along the pipeline under normal operating conditions and during shutdown scenarios. simulations are also performed to identify critical zones with potential wax deposition and plugging, as well as to evaluate the effect of flow rate variations on fluid temperature and operating pressure. in addition, sensitivity analysis is carried out to assess the availability of a safe operating window that simultaneously satisfies thermal and hydraulic constraints. the results indicate that the pipeline system operates under unfavorable conditions from a flow assurance perspective. under existing operating conditions, the fluid temperature along the pipeline remains below the wat, causing the crude oil to enter the wax formation region and experience a significant increase in viscosity. the relatively large pipeline diameter compared to the actual flow rate results in low flow velocity and prolonged fluid residence time, which increases heat loss to the marine environment and accelerates wax deposition. sensitivity simulations show that increasing the flow rate can raise the fluid temperature above the wat; however, this condition is accompanied by an increase in outlet pressure exceeding the maximum allowable operating pressure (maop). conversely, operating at mechanically safe pressure levels results in fluid temperatures remaining within the wax region. shutdown simulations demonstrate that the fluid cools rapidly and reaches the pour point within a relatively short period. this condition leads to the formation of wax gel structures and multi-point plugging along the pipeline, making flow recovery (unplugging) extremely difficult and ineffective. the analysis indicates that unplugging failure is influenced by a combination of massive wax deposition, operational pressure limitations, the high wat characteristics of the waxy crude, and degradation of the pipeline’s thermal performance due to long-term operation. this study highlights the importance of thermal–hydraulic simulation-based flow assurance evaluation in offshore oil production pipeline systems, particularly for aging pipelines transporting waxy crude oil.