The increasing demand for oil is causing exploration to reach into greater ocean depths. The ocean floor temperature increases the risk of the crude oil cooling to a temperature that could result in flow blockage from paraffin formation. Oil companies could potentially spend millions correcting this problem due to lost production time. In order to mitigate this problem, appropriate insulation is added to the pipe to maintain the oil at its extraction temperature, and thus, help minimize paraffin formation. This project investigates how an interstitially insulated coaxial pipe with a metal wire mesh can provide improved insulation properties with simplified pipe construction and production issues. By increasing the thermal resistance within the sub-sea pipe, the thermal energy leaving the oil and entering the cold sub-sea environment is decreased.
Experiments have been conducted to determine the heat transfer conductance coefficient for this proposed interstitially insulated coaxial pipe technology and the results have been compared to existing insulation techniques. Different interstitial materials have been tested, including Stainless Steel, Titanium, Inconel, and Tungsten. Along with varying the wire material, the mesh number was varied, determining its effect on the overall thermal joint conductance. Moreover, a Mylar film was added to the test matrix as an additional layer of insulation/resistance. It was determined that a 5 mesh stainless steel wire screen with a Mylar film inserted at the interface between the two layers of pipe material provided the best insulation characteristics. The thermal conductance of the air/wire screen composite was experimentally measured as low as 42.0 W/m2-K (7.40 Btu/ft2 hr oF), which translates to an effective thermal conductivity of 0.08 W/m- K (0.05 Btu/ft hr oF), at an interface pressure of 172.3 kPa (25.0 psi). These values compare very favorably with current insulation technologies whose effective thermal conductivity range from 0.12 to 0.15 W/m-K (0.07 to 0.09 Btu/ft hr oF).
Thus, a comparison of the interstitially insulated coaxial pipe with current technologies has shown the interstitially insulated coaxial pipe to be a potential means to reducing paraffin deposit blockage in deep water pipe-lines and risers. Moreover, the results seem to indicate superior insulating characteristics when compared to current available technologies which have far greater manufacturing complexities. The proposed technology also shows promise for liquefied petroleum gas pipeline/transfer line applications.
