Flowline thermal insulation is essential for deepwater field development when long distance subsea tieback is required. Proper flowline insulation design can prevent hydrate and wax formation during production, as well as provide sufficient time, in the event of an unplanned well shut-in, for resuming production before the product temperature drops below the critical temperatures. Although many insulated flowline configurations, (i.e., insulated pipe-in-pipe and insulated multi-flowline bundle) have been installed, insulation designs are usually based on insulation material technical data obtained at standard conditions. Few publications are available on the effects of insulation material aging, operation temperature, and environmental pressure (in the case of a pressurized annulus of pipe-in-pipe or bundle) on the flowline insulation performance.
In this paper, such effects on the thermal insulation properties of an insulated flowline, in both steady state and cool down conditions, are discussed. Insulation material thermal conductivity test data are presented at various pressures, temperatures, and aging effects (duration between manufacture and test). The test data are applied to typical flowline insulation designs and comparisons made with cases when these effects are neglected. Based on the test and analysis results, recommendations are made for insulated flowline designs.
