parameter.
At present, the method of determining the thermal conductivity of foam insulation material is as follows: First, a sample of thermal insulation material is taken on a prefabricated foam insulation pipe, and the sample taken is processed into a test piece of a predetermined size, and then the thermal conductivity of the sample is measured using a rapid thermal conductivity meter. coefficient. The advantage of this test method is that it requires less equipment, and the operation is simple and the test time is short. The disadvantages are: 1 sampling and processing into the test piece will destroy the microstructure of the test surface of the heat-insulating material; 2 the test time is short, so the surface properties of the test piece have a great influence on the test result, and the probe is required to be in close contact with the surface of the test piece during the test. This is difficult to achieve during actual testing, so there is a thermal contact resistance between the probe and the test piece. 3 When making the test specimens, the foamed samples are generally used. On the prefabricated heat insulating tubes, the foaming uniformity and the non-uniform foaming are present at the same time. Therefore, the test results cannot fully reflect the overall thermal insulation of the foam insulation tubes. effect.
The thermal insulation performance of the insulation pipe can be researched, and the thermal conductivity of the insulation layer of the insulation pipe can be obtained without destroying the insulation layer, which overcomes the shortcomings of the sampling test and can provide reliable basic data for the design and operation of the insulation pipe.
2 Test methods and experimental devices The overall thermal insulation performance of thermal insulation pipes can be determined by two methods. One is the steady state method and the other is the transient method. The so-called steady-state method is to arrange the electric heating tube in the center of the heat preservation tube, and to apply a constant current to the electric heating tube. When the heat value of the electric heating tube is equal to the heat dissipated through the outer surface of the tube, the temperature field is stabilized, and the tube temperature is reached. The temperature of the inner wall of the jacket and the jacket will no longer change. Measure the temperature of the inner wall of the steel tube and the jacket and the power of the electric heating tube at this time, and then the thermal conductivity of the insulation layer can be obtained. This method seems simple, in fact there are many technical problems can not be resolved, the first is the thermal insulation of the end of the insulation tube, to ensure that heat is not lost from the end, only the loss from the outer surface of the pipe, to achieve this is quite difficult; The second is to ensure that the ambient temperature is constant, a large-scale constant temperature room needs to be built, and the investment is too large; it is also very difficult to stabilize the temperature field, and it takes a long time. The so-called transient method is the static temperature drop method (or stop temperature drop method), that is to first let the constant temperature liquid in the test tube flow, when the temperature field reaches a stable, stop the flow, and then measure the liquid temperature in the tube and the jacket wall Temperature changes with time, so as to obtain thermal conductivity of the insulation layer. In order to facilitate the test and reduce the cost of the test device, the transient method was finally chosen to study the overall insulation performance of the insulation pipe and water was used as the transmission medium.
2 Test equipment The test equipment is mainly composed of three parts: the test section of the insulation pipe, the data acquisition system and the water circulation system. The test procedure is as shown.
21 Insulation pipe test section Insulation pipe test section The section of the yellow jacket foam insulation pipe section produced by Shengli Oilfield, a company prefabrication factory, is used. The test section is 2m long, and the steel pipe is å59 (6mm spiral welded steel pipe, the average thickness of insulation layer is 33mm. Polyethylene The thickness of the protective layer is 1.5mm. In order to reduce the heat loss at the end, the heat transfer conditions are closer to the actual pipeline, and the two sides are reinforced and insulated with a soft foam.
22 Data Acquisition System The data acquisition system consists of a primary instrument and a secondary instrument. A meter is a thermocouple, and the temperature of each measuring point is collected. The secondary meter is an HP digital multimeter. The meter converts the temperature of each measuring point into a potential difference output in the form of a temperature difference. According to the needs of the test, a total of 13 measurement points are arranged in the entire temperature measurement system, in which the pipe section has 10 measurement points on the inner diameter of the insulation pipe, and the outer wall of the same section insulation layer has 2 measurement points. The end of the pipe section has 1 measurement point.
During the two temperature measurements, the change in Tw is very small. It can be considered as constant. The integrated result of the above equation is to neglect the thermal resistance between the fluid in the pipe and the inner wall of the steel pipe. The thermal resistance R can be expressed as the circulating water system of the 3 circulating water system. It is mainly composed of a circulating water pump, a temperature control device, a heated water heating coil and a constant temperature heating system. Temperature rise temperature control accuracy. Rc around.
Let the time from the start of the stoppage be the thermal conductivity of the tube and jacket layers in the T minute time dT, W/m.; d?d2, d3, d4, which are the inner diameter of the steel pipe, the outer diameter of the steel pipe, the outer diameter of the insulation layer and the jacket layer respectively. The outer diameter, m.d4, becomes a Tw. The temperature Ti and Ti+i of the fluid in the tube at any two time measured according to the test can be adjusted by pressing the calibration time button.
3. On-site application Since 1994, more than 120 instruments have been installed and operated in the production areas of Changqing Oilfield No. 1 Plant, No. 2 Oil Production Plant, No. 3 Oil Production Plant, etc., except for a few equipment such as relays, drain pump motors, and three links. The solenoid valve malfunctioned, causing the instrument to not function properly, and everything else was operating normally. Because the instrument is simple, functional, durable, and simple to maintain, it is welcomed by oil workers.
The DLY-B single well metering automatic instrument was developed based on the actual conditions of Changqing Oilfield. After more than 6 years of on-site application, the instrument is fully applicable to on-site needs.
Unit length quality (1) 2 = n/4 ((d2 495kg°m) Calculate the formula for C, S2, D2, d2, and D3, and substitute it into A. There are three shutdown temperature drop tests, based on measured temperature drop data. The formula (7) can be used to calculate the thermal conductivity of the insulation layer (see Table 1).
Table 1 According to a certain experimental data obtained thermal conductivity of thermal insulation layer No. Shutdown time section average water temperature thermal insulation layer temperature thermal conductivity of thermal insulation layer can be seen from Table 1, thermal insulation layer thermal conductivity is not affected by the temperature, so you can Take the arithmetic average of the test data of each group as the overall thermal conductivity of the insulation layer of the test. After rejecting the data points with excessive error according to the test criteria, the overall thermal conductivity of the insulation layer measured in this test was 0.0508 W/m°C. The thermal conductivity of the insulation layer as measured by the other two tests was 0.0546 W/. The arithmetic mean value of the overall thermal conductivity of the insulation layer obtained from m〃C3 tests is 0.052 W/m°C. 4 Test results Discussion Under the same conditions, using the same method[1], the overall thermal conductivity coefficient of the foam insulation pipe of the just-formed jacket was measured. A value of 0.039 W/mC is approximately 56% higher than the thermal conductivity (0.025 W/m°°C) measured with the rapid thermal conductivity meter at that time. The value is closer to the standard of the Ministry of Petroleum of the People's Republic of China. The maximum allowable thermal conductivity of the insulation layer is specified in the Technical Criteria of Polyurethane Foam Anticorrosion and Thermal Insulation. 0. The value of the thermal conductivity of the foam insulation pipe can be determined.
Foam plastic tube insulation material with the use of time, foam insulation structure will produce shrinkage, thermal conductivity will increase. Tests determined that after the yellow jacket foam insulation pipe was allowed to stand for 6 years, the average thermal conductivity of the entire molded foam increased to 0.052 W/mC, which was about 33% higher than the thermal conductivity coefficient (0.03 W/mC) measured at the factory. Therefore, when studying the thermal insulation performance of the running foam insulation pipe, it can be based on the actual operating life of the pipeline.
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