Experimental and Analytical Investigation of the Cool-Down Behavior of an Insulated Pipe Assembly Under Subsea Conditions

An experimental investigation was conducted to determine the cool-down behavior of an insulated pipe assembly under subsea conditions, and an analytical model was developed to predict the cool down of the assembly. The insulated pipe assembly consisted of a straight pipe attached to a production tee and a production elbow, and this was coated with 3 in. of thermal insulation. The pipe assembly was tested in a chamber that can simulate subsea conditions (low temperature, high pressure). The analytical model was the solution to a ID transient heat-conduction problem of a three-layer solid cylinder. The analytical model was first verified with the use of available commercial software, and then validated against experimental data. Results showed a root-mean-square deviation (RMSD) of less than 3.8 degrees F between the analytical model and the experimental data at the location with a geometry similar to that for which the analytical model was developed. It was found that the h values calculated from experimental data were significantly smaller than the ones calculated from empirical correlations. However, this variation resulted only in a slight difference in the cool-down temperatures. From the validation of the analytical model, it was concluded that this model can predict cool-down temperatures as a function of time in insulated pipes during shut-in operations.