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Flow assurance is critical in offshore oil and gas production. Thermal insulation is an effective way to reduce heat loss from subsea pipelines and avoid the formation of hydrates or wax deposits that could block the flowlines. This paper presents heat transfer analysis from a subsea flowline with different insulation materials, particularly with nano-enhanced phase change materials (NPCMs) that allow thermal energy storage in the pipeline system. The phase change materials (PCMs) can effectively regulate fluid temperature during production fluctuations or increase the cool-down time during production shutdown. This paper considers a pipe in pipe configuration with different insulation methods; the cool-down times are calculated and compared. The results show that thermal insulation can greatly delay the fluid cool-down process. A significant improvement of cool-down time can be achieved with PCM energy storage under a good conventional insulation layer. Moreover, with nanoparticles in a PCM, the latent energy storage is enhanced thus it takes even longer time for the internal fluid to reach its hydrate formation temperature.