The submarine single-layer insulation pipe with rigid polyurethane as insulation material has been applied to many oil fields in the Bohai Sea and the South China Sea, which has created economic benefits for the development of the CNOOC marginal oil field, but at the same time the technology has also exposed some shortcomings in thermal insulation performance. Wherever it is necessary to conduct a pilot study on the thermal conductivity of rigid polyurethane foams to determine the relevant parameters of the insulation materials under various operating conditions. To this end, CNOOC Energy Development Pipeline Engineering Co., Ltd. has carried out a large number of experimental research work.
1 Test items and standards adopted from the basic properties of polyurethane foam, the effect of closed cell ratio and water absorption on thermal conductivity, the effect of external pressure on closed cell ratio, the effect of closed cell ratio on water absorption, and the different water pressures of different density foams Experimental research was carried out on changes in water absorption rate, and corresponding test data were obtained. The rigid polyurethane foam used in the test was produced in the same process and foaming system. The sample placement time and placement environment are the same.
2006 Determination of apparent density of foam and rubber, compressive strength using GB/T8813-2008/ISO 844:2004 Determination of compressive properties of rigid foam, tensile strength 1986 rigid foam dimensional stability test method, volume water absorption Unless otherwise specified, the C/T114-2000 high-density polyethylene outer protective tube polyurethane foam prefabricated direct buried thermal insulation tube is used. The closed cell ratio is determined by the open cell and closed cell volume percentage of rigid foam of GB/T10799-2008. The thermal conductivity is GB/T 10297-1998 non-metallic solid material thermal conductivity determination hot wire method and SY/T0415-1996 buried steel pipeline rigid polyurethane foam anti-corrosion insulation layer technical standard, heat resistance using SY/T0415-1996 Standard of practice.
2 Basic performance test of rigid polyurethane foam 10 sets of foam samples were tested for compressive strength, tensile strength, water absorption and thermal conductivity of foam at each density (A23A50, closed cell ratio, heat resistance (including Dimensional change rate, strength growth rate, mass change rate), thermal conductivity change rate. Test results are shown in Table 1. Test of the influence of the closed cell ratio of the rigid polyurethane foam on the thermal conductivity 3.1 Test method Sample of the near closed cell ratio setting value Put into the pressurized chamber, gradually increase the air pressure, and measure the closed cell rate of the sample one by one until the sample closer to the closed cell ratio is obtained, and then measure the thermal conductivity of the sample. Repeat the above process to measure other closed cells. Rate the thermal conductivity of the sample at the set point.
3.2 Test results (see) 4 Test of the influence of water absorption rate of rigid polyurethane foam on thermal conductivity 4.1 Test method The change of thermal conductivity is tested under different water absorption conditions. Materials having different water absorption rates of the same density are obtained by pressurization. The sample scale is 100 mm, and each set has at least 10 samples.
Set the water pressure to 0.2 MPa, and the three pieces of density to 40 kg/m3. Table 1 Typical physical properties of different density rigid polyurethane foams Measured density / (kg / m3) compressive strength / MPa tensile strength / MPa volume water absorption / % Closed cell ratio /% heat resistance dimensional change rate /% strength change rate /% mass change rate /% thermal conductivity change rate /% density density 丨OOkg / n closed cell ratio /% circumference I different density foam material closed hole At the same time, the sample of the thermal conductivity failure curve is placed in the test device, the pressure is kept for 24 hours, taken out, the water absorption rate of the sample is measured, and the thermal conductivity is quickly measured; the water pressure is increased to 0.3 MPa, and the density of three pieces is 40 kg/m3. The sample was placed in a test device, held for 24 hours, taken out, and the water absorption rate of the sample was measured. Then, the thermal conductivity was quickly measured. Samples having a density of 60 and 80 kg/m3 were sequentially measured.
4.2 Test results (see) Volume water absorption rate /% circumference 2 Different density foam materials Volume difference of water absorption coefficient Change curve of rigid polyurethane foam pressure (air pressure) on the closed cell rate Test method 3 pieces of parent sample ( The size is 150mmx100mmx100mm), a total of 12 samples are placed in the pressurized chamber together, pressurized by the air compressor. When the pressure gauge shows 500 kPa, the pressure is stopped, the pressure is maintained for 4h, then decompressed, opened, and quickly removed. Foam, according to the requirements of the closed cell rate test standard, 9 samples were prepared for each group (3 pieces), and the closed cell ratio of the sample was measured by a closed cell rate tester; the above process was repeated and pressurized to 1000, respectively. 2000, 3000, 5000, 6000, 7000, 8000 kPa, and measured the closed cell ratio of the foam sample.
5.2 Test results (see) Closed-pore test curve of foams with different densities under different pressures 6 Test of the effect of closed cell ratio of rigid polyurethane foam on water absorption 6.1 Test method Three sets of density of 40, 60, 80 kg/m3 were produced. A sample close to the closed cell rate setting value is placed in the pressurized chamber, and the pressure is gradually increased. The closed cell ratio of the sample is measured successively until a sample closer to the closed cell ratio setting value is obtained, and then the sample is measured. Water absorption rate.
The above procedure was repeated to measure the water absorption values ​​of the other closed cell set point samples.
%/ chisel temple water pressure / MPa different density foam material subjected to different external pressure when the volume of water absorption curve (2> 6.2 test results (see) closed-cell string cyanide-cured foam closed-hole æ´ for water absorption 7 rigid polyurethane Test for the change of water absorption of foam under water pressure 7.1 Test method The change of water absorption rate under test method. The sample size is 150 mm×100 mm, and each group needs at least 27 pieces.
The sample of kg/m3 was placed in the test device, and the pressure was kept for 24 hours. The water absorption rate of the sample was measured. The water pressure was increased to 0.3 MPa. Three samples with a density of 40 kg/m3 were placed in the test device. At 24 h, the sample was taken out, and the water absorption rate of the sample was measured, and the samples were measured to a pressure of 1.0, and the samples were measured at a density of 60, 80, 100, 140, 180, 200 kg/m3.
7.2 Test results (see,) Water pressure / MPa Different density foams subjected to different external pressures, volumetric water absorption rate change curve (Ushe 20 8 test analysis and conclusion of the same density material, with the increase of the closed cell ratio, its thermal conductivity will Gradual reduction; for different density materials, the thermal conductivity of the material increases with the increase of density under the condition that the closed cell ratio is basically the same.
With the increase of water absorption, the thermal conductivity of the same density material will gradually increase. When the water absorption rate is zero, the thermal conductivity increases with the increase of density; when the water absorption, the thermal conductivity is affected. The effects of different densities become less obvious; when the water absorption rate is > 3%, the thermal conductivity is less affected by the density and can be ignored.
For the same density material, when the external pressure is increased, the closed cell ratio is significantly lowered because the foam hole wall is crushed to cause perforation under the action of external pressure.
With the same density of materials, as the closed cell ratio increases, the water absorption rate will gradually decrease. For different density materials, the water absorption of the material decreases with increasing density under the condition that the closed cell ratio is basically the same.
Comprehensive comparison of the test data of each group, it can be seen that at the external pressure <500kPa, the closed cell ratio of all foam materials does not change much, and the water absorption rate does not change much, but since the external pressure of 500 kPa has exceeded the foam density of less than 60kg/m3. Compressive strength, resulting in a density of less than 60kg / m3 foam material deformation is more serious.
It can be seen from the test that regardless of the density of the foam material, the water absorption rate will change (increase) under the external pressure, and this change will lead to a significant increase in the thermal conductivity, so the waterproofing of the foam material is Its performance in insulation is critical.
Technical standard for rigid polyurethane foam anticorrosive insulation layer for geosteel pipe: Polyurethane foam insulation layer density 40~60kg/m3, C/T114-2000 high density polyethylene outer tube polyurethane foam prefabricated direct buried insulation pipe and EN 253 -2009 district heating pipe - a preheating composite pipe system for hot water pipes directly laid underground. A composite pipe system made of steel pipe, polyurethane heat insulation and polyacetyl shell. The density of the polyurethane foam insulation layer is 60kg/m3 or more. The design density of the overseas design company for the submarine single-layer insulation pipe such as PL19-3 is 80~100kg/m3. In the past, the density of the CNOOC submarine pipeline insulation layer was generally designed to be 40~60kg/m3 or 60~80kg/m3. According to the data of this test, the author believes that the density design of CNOOC's previous single-layer insulation pipe insulation layer is low. It is recommended to use foam with a density of 60~80kg/m3 when the water depth is 20m. When the water depth is 20~40m, it is better. Use a foam with a density of 80~100kg/m3. : Zhang Xiaoling (1972-), male, Hebei Wanquan, senior engineer, graduated from Xi'an Jiaotong University in 1994 with a major in chemical engineering. He is currently engaged in marine pipe engineering related technology research.
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