Interstitially Insulated Coaxial Pipe
Note: This project is a continuation of 2004-2005 Interstitially Insulated Coaxial Pipe
Progress Reports: December 2006 June 2006 December 2005
OBJECTIVE: To further validate that an IICP insulation system incorporating a low thermal conductivity, high strength wire screen mesh between a pipe and an interior liner can be an effective passive thermal insulation solution for deepwater flowlines and risers. Phase II will confirm the low thermal conductance values measured with coupons in Phase I are also attainable for pipes, and demonstrate IICP performance under steady and transient flow conditions. Results will be used to interest industry and contractors in this technology.INTRODUCTION: Phase I demonstrated that a thermal resistance is created at the interface between two materials, in this case a pipe and a liner, due to the surface metrology (roughness) of the contacting surfaces. If the two contacting surfaces are separated by a screen wire or mesh at the pipe and liner interface (Fig.1), the resistance to thermal transport is increased significantly. The screen wire reduces heat transfer by restricting the path available for conduction and forms a stagnant air gap to minimize radiation and convective heat transfer. Heat transfer was further reduced by adding a Mylar film to the exterior of the liner and the interior of the pipe wall. This further reduces the surface contact area between the wire screen mesh and pipe wall, and similarly, reduces the surface contact area between the mesh and liner wall; therefore, increasing the restrictive path for conduction. Moreover, the low thermal conductivity Mylar film adds additional layer of resistance. Such an Interstitially Insulated Coaxial Pipe with Mylar film is illustrated here.
Experiments with coupons (Fig.2) of pipe/mesh/liner materials showed that the thermal conductivity can be reduced up to 50 times lower than the pipe material (Fig.3). Preliminary experimental data showed further enhancement in thermal resistance of appropriately 20% with the Mylar film present. The experimental data show the influence of selected variables (e.g., mesh size and material, contact pressure, air in the interstices, and addition of Mylar film layers) throughout a range of temperatures.
A comparison of the overall thermal conductance has been modeled for a design which incorporates the interstitial wire-screen with and without existing insulation material (e.g., polyolefin foam). The calculated effective thermal conductivities from experimental conductance data compare favorably with insulation technologies presently used for subsea applications.
BENEFITS TO MMS & INDUSTRY: The IICP insulation system is expected to be comparable with other insulation systems presently used for subsea pipeline, flowline, and riser applications, and could prove to be less expensive, easier to install, and more robust than present insulation technologies.DEPLOYMENT OF RESULTS: The results of these experiments are expected to validate the effectiveness of Interstitially Insulated Coaxial Pipe as an insulation system for deepwater pipeline, flowlines, and risers. Results will be disclosed to interested parties (pipe and riser manufacturers, oil and gas companies) to determine interests in potential application of this technology and needs for further testing. It is expected that this technology would be eventually licensed for commercialization.
ANTICIPATED NUMBER OF PHASES: 3
PROJECT PLAN FOR PHASE 2 (2005-2006)
Scope of Work: Laboratory experiments on a small scale prototype IICP will be conducted to validate the IICP concept in the prototype geometry (i.e. pipe versus coupon), and demonstrate its effectiveness as a means to insulate deepwater pipelines, flowlines, and risers. A small prototype IICP (diameter = 6 -12 inches, length = several feet) will be built. The IICP design parameters (wire screen diameter size, mesh number and Mylar film thickness, joint interface pressure) will be based on learnings from the Phase I experiments. A small test loop will be fabricated and will include the IICP section, hot and cold reservoirs to simulate subsea water temperatures (~34 degrees F) and hot oil temperatures (~ 175 degrees F), pumping apparatus, thermal sensors, volumetric flow sensors, and data acquisition instrumentation. The experimental loop arrangement is shown below with the IICP technology (Fig.4). The thermal resistance of the IICP will be determined under conditions representing (1) steady state flow of hot oil through an operating pipeline, and (2) transient conditions following a pipeline shut down to demonstrate the change in thermal resistance of a pipeline with time following the flow stoppage.
A model to estimate the thermal performance of the IICP system for pipeline, flowline, and riser examples under realistic conditions will be developed and calibrated with experimental data. The model will be used to assess the performance of the IICP system in a variety of steady flow and transient shut-down scenarios. Results will be used to determine the needs for further development and optimization of the IICP system and to illustrate ICCP technology to interested parties in the oil and gas industry.
Efforts will be made to engage the oil and gas industry for input and interest in the continued development and testing of IICP technology. Manufacturing methods will also be addressed.
Anticipated Results: The Phase 2 thermal conductivities measured in Phase 2 for the IICP prototype pipe geometry are expected to be similar to the low thermal conductivities measured on coupons in Phase 1. This will confirm the IICP concept as a promising system for insulating subsea pipelines, flowline, and risers. Analytical studies using these results will indicate the potential effectiveness in steady state transient conditions lows, and provide guidance on optimizing the IICP parameters to further enhance thermal performance. Results will be documented in a Final Phase 2 Report, and will be used to encourage industry interest in further supporting the development of this promising technology.
PROJECT PLAN FOR PHASE 3 (2006-2007):
Scope and Plan: Further experiments will be conducted to optimize the thermal insulating properties of the IICP to insulate pipe under a realistic temperatures and conditions. The optimization of the IICP parameters could include the (1) Mylar film thickness; (2) screen wire diameter mesh size, and material; and (3) use of insulation on the pipe exterior to provide additional insulation if needed. Manufacturability would also be investigated through discussions with industry and contractors to determine the impact of manufacturability and installation needs on the IICP parameters.
Phase 3 would also include fabricating a larger scale prototype pipe and testing in a thermal and flow/thermal loop to further confirm the IICP system thermal performance under field conditions and the manufacturability of IICP pipe.
Anticipated Milestones & Results: The effectiveness of the IICP pipe would be demonstrated to the industry, and its use would be licensed to interested parties.
PRINCIPAL INVESTIGATORS AND OTHERS INVOLVED IN THE PROJECT:
PI’s: Egidio (Ed) Marotta, L.S. ‘Skip’ Fletcher
Others: PhD Graduate Student
Date: November, 2006Project Title: Interstitially Insulated Coaxial Pipe
MMS Project: 509 TO Number: 35663
PI: Ed Marotta and Skip Fletcher
COTR: Mik Else
Estimated Completion Date: December, 2006
Project Description:
To demonstrate that an insulation system incorporating a low thermal conductivity screen mesh between a pipe and an interior liner can be an effective passive thermal insulation solution for deepwater flowlines and risers. It has been established that a thermal resistance (due to the metrology of the contacting surfaces) is created at an interface between two materials, in this case a pipe and a liner. If the two contacting surfaces are further separated by a screen wire or mesh at the pipe and liner interface, then a higher thermal interface resistance will result, which will significantly increase the resistance to thermal transport characteristics. The screen wire reduces the heat transfer by restricting the path for conduction and forms a stagnant air gap to minimize convective heat transfer. Heat transfer can be further reduced by adding an insulation layer (screen mesh and interior liner) and minimized by optimizing the total number of layers for actual applications.Progress:
Phase 3 of the investigation involved the construction, assembly, and testing of an initial prototype pipe section as an intermediate stage towards a conventional size pipe for actual applications. The prototype was constructed with cold and hot loops to simulate an actual working environment with hot water as the crude oil and a coolant as the seawater. The prototype section has a 4-inch outer diameter pipe and a 3-inch inner diameter pipe. The pipe section, which is three feet long, was manufactured by Stress Engineering, Houston, TX. The annular space has two layers of stainless steel screen wire mesh separated by a thin aluminum layer that acts as a radiation heat transfer barrier. The inner and outer pipe with wire screen mesh is shown in Figure 1. A schematic of the test apparatus and loop is shown in Figure 2. The loop was designed so as to control the input heat load by using an inlet valve connected to a hot water source with built in temperature control. Hot water and coolant lines were well insulated to minimize heat loss.
Preliminary test results with a relatively large cooling bath indicated that a new design was required to meet the cooling loads. Therefore, a new cooling bath design was fabricated to meet the proper capacity of the coolant bath circulator. The new design is shown in Figure 3. In the new design, a 6-inch inner diameter PVC pipe was used as the coolant bath. It was fully sealed with air cushioned and fiberglass insulation as shown in Figure 4.
Steady State and Transient Test runs have been conducted to investigate the performance characteristic of the insulation technology under the following conditions.
For Steady State:
Temperature of hot water: 50-80°C
Hot water flow rate: 0.05-0.4 GPM
For Transient Conditions:
Hot water temperature for cool down test runs: 50-80°C
Hot water temperature for start up test runs: 77°C
Hot water flow rates for start up test runs: 0.05-0.4 GPMUnder the above operating conditions, the inner and outer surface temperature of the pipe and the hot water and coolant inlet and outlet temperatures were measured via a data acquisition system with 1 Hz sampling rate. Figure 5 shows the temperature distribution for the pipe inner and outer surface from initial to steady state conditions, and also transient cool-down test runs.
For start-up and steady state test runs the hot water temperature was maintained at 70°C with a constant 0.15 GPM flow rate condition. Under these conditions, the pipe test section took appropriately 40 minutes to reach working conditions (i.e., 70oC). Cool-down tests conducted from an initial hot temperature of 78°C to a coolant temperature of 4oC took roughly 18 hours to achieve (cool-down involved no flow rate or quiescent conditions). Further data sets are being collected for various flow rates and boundary conditions for analysis of detail performance characteristics such as thermal conductivity, thermal diffusivity, and thermal conductance for the various combinations tested.
Reports and Publications:
“ Characterization/Modeling of Wire Screen Insulation for Deep-Water Pipe”; Dong (Keun) Kim, Egidio (Ed) Marotta, and Leroy (Skip) Fletcher, Journal of Thermophysics and Heat Transfer, AIAA, Sept. 2006, accepted.
Date: June 2006
Project Title: Interstitially Insulated Coaxial Pipe
MMS Project: 509 TO Number: 35663
PI: Ed Marotta & Skip Fletcher
COTR: Mik Else
Estimated Completion Date: December 2006 (Project term is 6/30/2007)
Project Description:
The focus of this project is demonstrate that an insulation system incorporating a low thermal conductivity screen mesh between a pipe and an interior liner can be an effective passive thermal insulation solution for deepwater pipelines, flowlines and risers. This insulation system, called the Interstitially Insulated Coaxial Pipe, is shown in Figure 1. .In earlier phases of the project, the effectiveness of the insulation system was demonstrated with laboratory tests of coupons. Thermal conductances were measured for coupons of a Stainless Steel wire screen meshes inserted between materials representing a pipe and internal liner. Very low thermal conductances were measured. The addition of a Mylar film to the surfaces representing the interior of the pipe and exterior of the liner show a further reduction in thermal conduction. Wire mesh sizes were and other materials (Inconel, Tungsten, and Titanium) were also tested. Results indicated that this insulation system could be as or more effective as other systems in current use. Potential benefits of this system include lower costs and a more robust and installable insulated pipe.
The focus of this phase is to demonstrate the effectiveness of the IICP system in pipe geometry.
Progress:
A pipe test section that includes an outer pipe and a liner with a stainless steel mesh between the pipe and liner has been fabricated. A sketch of the equipment for testing the pipe configuration is shown in Figure 2. Hot fluid (representing hot oil) flows through the insulated pipe which is surrounded by a cold water environment that represents the seawater near the sea floor. The cold water environment is provided by an ice bath which maintains the water at a constant temperature of 0 degrees C. Hot water (175-180 degrees F) representing hot oil is circulated through the pipe. The pipe section is instrumented to measure temperatures. Figure 3 shows a drawing of the pipe section in the ice bath. The pipe is tilted to keep air from collecting in the upper half of the pipe. Figure 4 shows the actual test apparatus. The equipment has been completed and the data logger has been programmed to analyze the data, so the experiment can now begin.An analytical model of the IICP was developed and programmed in Matlab™. This model will be used to process the data and predict the performance of IICP systems.
Reports & Publications:
1. Dong (Keun) Kim, Carlos Silva, Egidio (Ed) Marotta, and Leroy (Skip) Fletcher, “Characterization of Wire Screen Insulation for Deep Water Pipe Applications”, Proceedings of the 2006 AIAA/ASME Joint Heat Transfer Conference, June, 5-8, 2006, San Francisco, California .
2. Egidio (Ed) Marotta, L.S. Fletcher, “Interstitially Insulated Coaxial Pipe- Phase I Project Report”, Thermal Conduction Laboratory, Department of Mechanical Engineering, Texas A&M University, OTRC Library Number 12/05A160, December, 2005.
Date: December 2005Project Title: Interstitially Insulated Coaxial Pipe
MMS Project: 509 TO Number: 35663
PI: Marotta/Fletcher
COTR: Mik Else
Estimated Completion Date: July, 2005
Project Description:
To demonstrate that an insulation system incorporating a low thermal conductivity screen mesh between a pipe and an interior liner can be an effective passive thermal insulation solution for deepwater flowlines and risers. It has been established that a thermal resistance (due to the metrology of the contacting surfaces) is created at an interface between two materials, in this case a pipe and a liner. If the two contacting surface are further separated by a screen wire or mesh at the pipe and liner interface, then a higher thermal interface resistance will result, which will significantly increase the resistance to thermal transport characteristics. The screen wire reduces the heat transfer by restricting the path for conduction and forms a stagnant air gap to minimize convective heat transfer. Heat transfer can be further reduced by adding a Mylar film to the exterior of the liner and the interior of the pipe. This added layer of polymeric film helps to minimize the contact area between the layer and wire screen mesh, and moreover, helps to lower the effective harmonic thermal conductivity, thus helping to maximize the overall contact resistance from the pipe and liner surface to the wire screen mesh.
Progress:
Phase 1 - The thermal joint resistance for several size wire screens and materials were measured as a function of joint interface pressure and mean interface temperature. All TCC (Thermal Contact Conductance) testing for Stainless Steel, Titanium, and Tungsten wire has been completed and reported. Thermal contact conductance results for Titanium, Tungsten, and Stainless Steel 316 wire-screens indicate that the number of contact points, wire-screen diameter, and material thermal conductivity (Ti and W have approximately 3X higher thermal conductivities than SS 316) have significant influences on the measured conductances. .
Further experiments were conducted for a configuration that consisted of a tubular pipe of known thickness (standard to the pipe-oil industry ~ 19mm) and the integration of the Stainless Steel wire-screen. The experimental data showed two orders of magnitude reduction in thermal contact conductance with integration of the Stainless Steel 316 wire screen with equivalent thickness. This represented a 50X reduction in the pipe thermal conductivity when the Stainless Steel 316 5 mesh wire screen was inserted at the center of the pipe. A further 20% reduction in thermal conductance was realized when a sheet of thin Mylar film was placed at the interface of the wire screen contact points and the solid pipe metal.
Phase 2 - The test set up for the Phase 2 will test this insulation concept in a pipe configuration to confirm the coupon tests completed in Phase 1. The pipe test fixture has been designed and is being fabricated. While the new test setup is being completed, additional coupon tests were completed to test a another wire screen material, Inconel, and a configuration that utilized two Stainless Steel wire screen layers to compare to the previous single layer tests.
Tests have been completed to investigate whether an additional decrease in joint conductance can be obtained by using an Inconel (high strength and low thermal conductivity) wire screen instead of Stainless Steel 316. Tests were completed for configurations which included smooth contacting surfaces; highly roughen contacting surfaces, and the insertion of an Inconel wire screen as shown in the test set shown in Fig. 1. Figure 2 compares the Inconel TCC results with previous results for P110 solid pipe, roughened pipe, and Stainless Steel wire screen mesh. Each set of experimental data shows a reduction in thermal joint conductance as the inserts cut from the pipe wall material are first tested with fairly smooth contacting surfaces (Rrms ? 1.0 um), then tested with a textured contacting surfaces to increase surface roughness, and finally the placement of the Inconel wire screen to form a controlled air gap between the two P110 inserts. In each case there was a reduction in thermal joint conductance by one order of magnitude.
Tests have also been completed to measure the reduction in joint conductance when two Stainless Steel 316 wire screens were integrated into the assembly with a metallic liner separating the two wire screens as shown in Fig.3. Figure 4 shows the experimentally measured results obtained for this set of experimental runs for a range of mean interface pressures and temperatures. The thermal joint conductance for the double Stainless Steel wire screen assembly is lower than that previously determined for the single Stainless Steel screen or the single Stainless Steel wire screen with a Mylar film shown in Figure 2. The average joint conductance (or increase in joint resistance) for the double screen assembly was the reduced by 44.6 % compared to the single wire screen and 21.5% compared to the wire screen/Mylar combination over the entire range of contact pressures. The addition of the Mylar film to a single Stainless Steel screen reduced the average thermal conductance by 28.3% over that of a Stainless Steel wire screen. Overall, the double layered configuration indicates better insulating properties than a single layer with and without a Mylar film.
Reports & Publications:
Report on Phase 1 completed.
