JP2005226996A - Pressure test method for pipeline - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of a pressure test for pipelines using an incompressive fluid such as water which can detect deformation or leakage of pipelines with high precision without affecting by the amount of the residual air. <P>SOLUTION: The pressure test method for pipelines is to monitor change in pressure in a pipeline for a predetermined period after applying pressure to the pipeline by injecting an incompressive fluid, and characterized by that the amount of the residual air is obtained and a period for monitoring the pressure change is set according to the amount of the residual air. In addition, the pressure test method for pipelines is also characterized by that the precision of the test obtained during the predetermined monitoring period is evaluated whether it is higher than the required precision or not, and the test result is determined to be accepted or not. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pipeline pressure test method for detecting pipeline deformation and leakage.

  In pipelines that transport petroleum, chemical products, etc., pressure tests are usually conducted as pre-use inspections to confirm that there are no harmful deformations or leaks before construction and use. It is difficult to inspect and check the deformation and leakage of all parts by applying internal pressure to a long structure such as a pipeline, especially when the pipeline is buried. Is possible. Therefore, a pressure test (withstand pressure test) is performed in which pressure is applied to the pipeline and the change in the pressure in the pipeline is measured to check for deformation and leakage. In general, it is said that there is no need for harmful deformation and leakage even when a pressure of 1.5 times the pipeline design pressure is applied in the pressure test.

  When pressure is applied to the pipeline, water is generally used. Since water is an incompressible fluid, the amount used during pressurization is less than when using air, etc., and if it leaks or deforms somewhere, it immediately appears as a pressure drop. This is because even if the pipeline breaks down, there is little influence on the surroundings. When performing a pressure test in the same way with air (or nitrogen, etc.), a large amount of air is required to pressurize the pipeline, and since the pressure propagation is slow, it takes time for the pressure to stabilize and the test time is long. Become. Even if there is a leak, since the ratio of the leak amount to the total air amount is small, it is difficult to reflect in the pressure and the test accuracy is lowered. Furthermore, since the pressurized air stores enormous energy compared to water, there is a problem that if the pipeline is broken, it can be a major disaster.

In such a pipeline pressure test, it is important to be able to confirm the presence or absence of deformation or leakage with high accuracy in a short period of time. A pipeline leak detection method having a leak detection capability higher than that is known (for example, see Patent Document 1). Patent Document 1 discloses a method of adjusting the sensitivity of leakage detection by performing temperature correction when pressure is applied to a pipeline.
JP 2001-27576 A

  However, when a pressure test is performed using water, there is a problem that it is difficult to completely fill the pipeline with water. The pipeline is long and has a height difference depending on the location. Further, since there are bends, ascending and descending, branching, etc., the occurrence of air accumulation is unavoidable, and a certain amount of air remains in the pipeline even after water injection. Residual air that has been compressed and reduced in volume during pressurization expands and suppresses fluctuations in pressure when the volume of water in the pipeline decreases due to leakage, or when the overall volume increases due to plastic deformation of the pipeline. Acts on direction. The effect of suppressing fluctuations in pressure is more pronounced as more air remains, and depending on the amount of remaining air, deformation or leakage cannot be detected within the test time, making accurate pressure tests difficult. is there. Such a problem related to residual air in the pipeline cannot be dealt with by the conventional leakage detection method described above.

  Therefore, the object of the present invention is to solve such problems of the prior art, and in a pressure test of a pipeline using an incompressible fluid such as water, it is possible to accurately deform and leak without being affected by the residual air amount. It is an object of the present invention to provide a pipeline pressure test method capable of detecting the above.

The features of the present invention for solving such problems are as follows.
(1) A pipeline pressure test method for injecting an incompressible fluid to pressurize a pipeline and monitoring pressure fluctuations in the pipeline after the pressurization for a predetermined period. A pressure test method for a pipeline, characterized in that a residual air amount is obtained and a monitoring period of the pressure fluctuation is set according to the residual air amount.
(2) A pipeline pressure test method for injecting an incompressible fluid to pressurize a pipeline and monitoring pressure fluctuations in the pipeline after the pressurization for a predetermined period, A pipeline pressure test method comprising: determining a test result obtained by obtaining a residual air amount and confirming whether or not a test accuracy obtained in a preset monitoring period exceeds a required accuracy, and determining whether or not to accept the test result.
(3) A residual air amount is obtained from a relationship between an injection amount when an incompressible fluid is injected into the pipeline and a pressure in the pipeline, and the pipeline according to (1) or (2) Pressure test method.
(4) The residual air amount is obtained from the relationship between the amount of extraction when the incompressible fluid is extracted from the pipeline and the pressure in the pipeline, and the pipeline according to (1) or (2) Pressure test method.
(5) The pipeline pressure test method according to any one of (1) to (4), wherein the incompressible fluid is water.

  According to the present invention, in a pressure test of a pipeline that uses an incompressible fluid such as water, deformation and leakage can be detected with high accuracy according to the amount of residual air.

  The present invention is a pressure test method for a pipeline in which an incompressible fluid such as water is injected to pressurize the pipeline, and pressure fluctuations in the pipeline after pressurization are monitored for a predetermined period. A residual air amount in the pipeline is obtained, and a monitoring period of the pressure fluctuation is set according to the residual air amount. In addition, by determining the amount of residual air in the pressurized pipeline, confirm whether the test accuracy obtained in the preset monitoring period is greater than the required accuracy, and determine whether to accept the test result. Features.

  By monitoring the pressure fluctuation for a predetermined period, it is determined whether the pipeline is deformed or leaked. The present invention can be applied not only to a newly established pipeline but also to a suspended pipeline, or a structure such as a large or long pressure vessel or conduit other than a pipeline.

  In the pipeline pressure test, it is desirable to inject an incompressible fluid into the pipeline. However, if air remains in the pipeline, the pressure fluctuation is reduced and the test accuracy is lowered. The principle that the pressure fluctuation is reduced according to the amount of air remaining in the pipeline will be described with reference to FIG. FIG. 1 is a graph showing the relationship between the amount of water or air injected into a pipeline and the pressure in the pipeline. If water is 100%, the amount of injection for increasing to a predetermined pressure is small, and due to leakage When water leaks, it can be seen that even a small amount can be detected as a large pressure change. On the other hand, as the air ratio increases, the slope of the graph decreases, and the amount of injection for increasing to a predetermined pressure increases. Even when water leaks due to leakage, the pressure change becomes small, making it difficult to detect. I understand that.

  FIG. 2 shows the relationship between the detection accuracy of leakage, deformation, etc., depending on the amount of residual air in the pipeline, and the holding time after pressurization by water injection. The vertical axis in FIG. 2 is the holding time, and the horizontal axis is the detectable defect size or leaked water amount, which corresponds to the detection accuracy. In general, higher detection accuracy can be obtained by increasing the holding time. This is because even a leak due to a minute defect can be detected because it appears as a large pressure difference over time. Although a short holding time can detect only when there is a large defect, conversely, if the situation does not require high detection accuracy, the holding time can be shortened. Therefore, the graph of FIG. 2 shows a downward trend. If there is a lot of air remaining in the pipeline (the residual air rate in the pipeline is high), the overall detection accuracy deteriorates and the graph shifts to the right. Conversely, if there is little air remaining in the pipeline (the residual air rate in the pipeline is low), the graph shifts to the left. The shape of the graph in FIG. 2 varies depending on the pressure detection accuracy of the measuring instrument.

  Therefore, if the residual air amount in the pipeline is obtained, the residual air rate (residual air rate = residual air amount / pipeline volume) can be obtained, and a graph showing the relationship between the detection accuracy and the holding time (monitoring period) is provided. Confirmed. For example, when the graph is fixed as shown in FIG. 3, the amount of holding time required to satisfy the required detection accuracy is determined, and the pressure fluctuation monitoring period is set. Can do. Alternatively, it is possible to check how much detection accuracy is available in the preset retention time (monitoring period) and whether the detection accuracy satisfies the required accuracy, thereby accepting the test result. Can be determined.

  It is desirable to determine the amount of residual air in the pipeline from the relationship between the injection amount when the incompressible fluid is injected into the pipeline and the pressure in the pipeline.

For example, the amount of residual air in the pipeline is the number of strokes N ′ of the water injection pump required when the pressure is increased from P ₁ to P ₂ when water is used as the incompressible fluid, and the pump discharge amount K. From the theoretically required number of pump strokes N, the following equation (a) can be obtained as the air amount Va under atmospheric pressure using the following equation (pressurization method).

Va = (N′−N) · K · (P ₁ +15) · (P ₂ +15) / 15 / (P ₂ −P ₁ ) (a)
Similarly to the above, when water is drained from the pipeline, it is also possible to obtain the air amount from the pressure drop and the water amount (drainage method).

  As the incompressible fluid, it is desirable to use water because there are few environmental problems, it is relatively inexpensive and easy to procure. In addition to water, oil, alcohols, and the like can be used.

  FIG. 4 is a schematic view of a pipeline in which the pressure test method of the present invention is implemented. Pipeline 1 is made of a welded steel pipe having a diameter of 610.0 mm, has an overall length of about 20 km, and has a maximum height difference of about 60 m. The maximum working pressure of the pipeline was 7 MPa, and when starting to use the pipeline, a pressure test with water was performed at a pressure 1.5 times that of 7 MPa (10.5 MPa).

  The residual air amount calculated from the measurement of the pressurized water amount at the time of pressurization was about 33 liters by the pressurization method, and the residual air content was 0.001% or less. Accordingly, the residual air rate is sufficiently small, and as shown in FIG. 5, the minimum defect size that can be detected with a preset holding time of 20 minutes is the minimum defect size that needs to be detected. It was confirmed that the detection accuracy was sufficiently small.

  For very long pipelines, pressure tests could be performed with high accuracy.

The graph which shows the relationship between the injection amount of water or air into a pipeline and the pressure in the pipeline. The graph which shows the relationship between the detection accuracy with respect to the residual air rate of a pipeline, and holding time. The graph which shows the relationship between detection accuracy when a residual air amount is decided, and holding time. Schematic of the pipeline. 3 is a graph showing the relationship between detection accuracy and holding time in Example 1.

Explanation of symbols

  1 Pipeline

Claims (5)

  A pipeline pressure test method for injecting an incompressible fluid to pressurize a pipeline and monitoring pressure fluctuations in the pipeline after the pressurization for a predetermined period, wherein the residual air in the pressurized pipeline A pipeline pressure test method characterized in that an amount is obtained and a monitoring period of the pressure fluctuation is set according to the residual air amount.   A pipeline pressure test method for injecting an incompressible fluid to pressurize a pipeline and monitoring pressure fluctuations in the pipeline after the pressurization for a predetermined period, wherein the residual air in the pressurized pipeline A pipeline pressure test method characterized in that a quantity is obtained, a test accuracy obtained in a preset monitoring period is confirmed to be equal to or higher than a required accuracy, and acceptance / rejection of a test result is determined.   3. The pipeline pressure test method according to claim 1, wherein the residual air amount is obtained from a relationship between an injection amount when incompressible fluid is injected into the pipeline and a pressure in the pipeline. .   3. The pipeline pressure test method according to claim 1, wherein the residual air amount is obtained from a relationship between a drawing amount when the incompressible fluid is drawn from the pipeline and a pressure in the pipeline. .   The pipeline pressure test method according to any one of claims 1 to 4, wherein the incompressible fluid is water.

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