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CN-118009242-B - Pressure determination method for reducing pressure and delivering hydrogen through natural gas pipeline

CN118009242BCN 118009242 BCN118009242 BCN 118009242BCN-118009242-B

Abstract

The invention relates to a pipeline hydrogen transmission technology, and aims to provide a pressure determination method for reducing pressure and transmitting hydrogen of a natural gas pipeline. The method comprises the steps of analyzing crack and defect distribution conditions in a pipeline based on an internal detection result of the pipeline, determining risk coefficients of all cracks or defects, selecting three areas with the largest risk coefficients, intercepting corresponding pipeline sections, performing explosion tests on the intercepted pipeline sections by using hydrogen, sampling at the position, axially and centrally symmetrical to a explosion opening, of the cross section of the pipeline section, testing fracture toughness and fatigue crack expansion rate in an in-situ environment, performing safety evaluation on fatigue life and fracture of pipeline materials based on test results, and taking hydrogen delivery pressure as the maximum operating pressure of a natural gas pipeline in the process of reducing pressure and delivering hydrogen if the two evaluated conclusions meet the regulations of mandatory standards. The invention can rapidly position the most dangerous part of the pipeline after hydrogen loading, and accurately confirm the ultimate bearing capacity of the pipeline while replacing the dangerous pipe section.

Inventors

  • GAO RUIZHE
  • Xing Baihui
  • HUA ZHENGLI
  • CHI SHUANGHE

Assignees

  • 浙江大学

Dates

Publication Date
20260508
Application Date
20240306

Claims (8)

  1. 1. The method for determining the pressure of the depressurization and hydrogen transportation of the natural gas pipeline is characterized by comprising the following steps of: (1) According to the requirements of mandatory standards, the natural gas pipeline to be used for hydrogen transportation is comprehensively internally detected, and the defect distribution condition inside the pipeline is analyzed according to the detection result to determine the risk coefficient F H of all defects, wherein the defects comprise cracks, and the mandatory standards comprise GB/T19624 and GB/T27699; (2) The method comprises the steps of selecting three areas with the largest risk coefficient F H in a natural gas pipeline, intercepting corresponding pipe sections, respectively performing explosion tests on the intercepted pipe sections by using hydrogen as a medium to obtain explosion pressure values, and assuming that the actual operation pressure of the natural gas pipeline is P 1 and the average value of the explosion pressures obtained by the tests is P b , obtaining the maximum hydrogen transmission operation pressure of the natural gas pipeline as P 2 =min{P 1 ,0.85P b ; (3) Sampling at the position which is axially and centrally symmetrical with the explosion port on the cross section of the pipe section, and testing the fracture toughness K IH and the fatigue crack expansion rate in an in-situ environment; (4) And carrying out fatigue life evaluation and fracture safety evaluation on the pipeline material based on the test result, and taking the hydrogen delivery pressure P 2 as the maximum operating pressure of the natural gas pipeline in the pressure reduction and hydrogen delivery process if the conclusion of the two evaluation meets the rule of the mandatory standard.
  2. 2. The method according to claim 1, wherein in the step (1), the risk factor F H of the defect is determined by: According to the actual operating pressure P 1 of the natural gas pipeline and the material performance parameters, calculating the position A of the detected crack on the failure evaluation graph, connecting an origin O with the point A, wherein the intersection point of the connecting line and the failure evaluation graph is B, and the risk coefficient is F H =OA/OB, wherein OA and OB are the connecting line lengths of the two points of the origin O and A, B respectively.
  3. 3. The method of claim 1, wherein in the step (2), at least 1 weld zone is included in the cut-out pipe section, the length of the pipe section is at least 10 times the outer diameter of the pipe section, and the target defect is located at the middle part of the cut-out pipe section.
  4. 4. The method of claim 1, wherein in step (2), the cut pipe sections are subjected to a blasting test in the following manner: (a) Firstly, a high-density polyethylene cylinder is put into the pipe section, two ends of the pipe section are blocked by a welding blind plate, and an air charging port is arranged on the blind plate, wherein the diameter of the polyethylene cylinder is 2-5 mm smaller than the inner diameter of the pipe section, and the length of the polyethylene cylinder is 10-20 mm shorter than the pipe section; (b) Filling hydrogen into the pipe section through the filling opening, pressurizing to 85% of the operating pressure P 1 of the natural gas pipeline, and then maintaining the pressure by more than 24: 24h, wherein the pressure loss during the maintaining is less than 5% of the actual operating pressure P 1 of the natural gas pipeline; (c) The hydrogen pressure in the pipe section is increased at a pressurizing rate lower than 1MPa/h until the pipe section is exploded, whether a burst opening is positioned at the position of a target defect or not is checked, if so, the burst pressure is considered to be effective, if not, the pipe section is required to be intercepted for testing, at least 3 effective burst pressure data are obtained, and the average value is recorded as P b .
  5. 5. The method of claim 1, wherein in step (3), the performing of the test in the in situ environment means: (1) If pure hydrogen is to be transported by the natural gas pipeline later, filling hydrogen in the testing process, wherein the pressure is not lower than the actual operating pressure P 1 of the natural gas pipeline; (2) If the mixed gas of the hydrogen is to be transported by the natural gas pipeline subsequently, the mixed gas of the hydrogen is filled in the testing process, the total pressure of the testing gas is not lower than the actual operating pressure P 1 of the natural gas pipeline, and the volume ratio of the hydrogen in the testing gas is not lower than the hydrogen-loading ratio of the mixed gas to be transported subsequently.
  6. 6. The method of claim 1, wherein the ratio of stress intensity factors in the test of the fatigue crack growth rate of step (3) is not greater than the minimum pressure ratio R min in the actual running record of the pipeline.
  7. 7. The method according to claim 1, wherein in the step (4), if one of the two evaluation results does not meet the rule of the mandatory standard, the hydrogen delivery pressure P 2 is multiplied by 0.85, and then fatigue life evaluation and fracture safety evaluation are performed again, and the operation is repeated until the two evaluation results meet the rule, and the hydrogen delivery pressure at this time is taken as the final use pressure of the natural gas pipeline in the depressurization and hydrogen delivery process.
  8. 8. The method of claim 1, wherein in step (4), the pipeline pressure ratio should be no greater than the minimum pressure ratio R min in the pipeline actual operating record at the time of fatigue life evaluation.

Description

Pressure determination method for reducing pressure and delivering hydrogen through natural gas pipeline Technical Field The invention relates to a pipeline hydrogen delivery technology, in particular to a pressure determination method for reducing pressure and delivering hydrogen through a natural gas pipeline. Background The transportation of hydrogen through pipelines is the most economical way to achieve large-scale, trans-regional, long-term transportation of hydrogen. However, the construction time of the hydrogen pipeline is long, the cost is high, the pipeline conveying of hydrogen energy can be realized in a short time through the hydrogen loading and conveying of the existing natural gas pipeline, the construction cost of the pipeline is greatly reduced, and the existing natural gas pipeline is prevented from being abandoned in the subsequent decarburization process. After the natural gas is loaded with hydrogen, hydrogen molecules are dissociated into hydrogen atoms on the surface of the material and invade the interior of the metal material, and are gathered towards the crack tip under the driving of stress, so that the material is more easily broken. Thus, for defective natural gas pipelines, the incorporation of hydrogen can make the pipeline more susceptible to bursting, seriously jeopardizing the operation of the plant and the safety of personnel and property. It is therefore necessary to determine whether the pipeline can be operated at the original pressure after loading, or to reduce the operating pressure to ensure safe delivery of the gas without replacement of the pipeline. Although there are many data concerning the mechanical properties of metallic materials in a hydrogen environment, it is difficult to accurately describe the failure behavior of a defective pipe in a hydrogen environment by the effect of hydrogen alone on the material. In addition, in the current standard, as in GB 32167-2015, the oil and gas transmission pipeline integrity management specification only mentions that a method for reducing the use pressure can be adopted for pipelines with unacceptable defects, but no method for calculating the upper limit of the use pressure of the existing natural gas pipeline in a hydrogen environment is given. Disclosure of Invention The invention aims to solve the technical problem of overcoming the defects in the prior art and providing a pressure determining method for reducing pressure and delivering hydrogen of a natural gas pipeline. In order to solve the technical problems, the invention adopts the following solutions: the pressure determining method for reducing pressure and delivering hydrogen of the natural gas pipeline comprises the following steps: (1) According to the requirements of mandatory standards, carrying out comprehensive internal detection on a natural gas pipeline to be used for hydrogen transportation, analyzing the crack and defect distribution condition in the pipeline according to the detection result, and determining the risk coefficient F H of all cracks or defects; (2) The method comprises the steps of selecting three areas with the largest risk coefficient F H in a natural gas pipeline, intercepting corresponding pipe sections, respectively performing explosion tests on the intercepted pipe sections by using hydrogen as a medium to obtain explosion pressure values, and assuming that the actual operation pressure of the natural gas pipeline is P 1 and the average value of the explosion pressures obtained by the tests is P b, obtaining the maximum hydrogen transmission operation pressure of the natural gas pipeline as P 2＝min{P1,0.85Pb; (3) Sampling at the position which is axially and centrally symmetrical with the explosion port on the cross section of the pipe section, and testing the fracture toughness K IH and the fatigue crack expansion rate in an in-situ environment; (4) And carrying out safety evaluation on the fatigue life and the fracture of the pipeline material based on the test result, and taking the hydrogen delivery pressure P 2 as the maximum operating pressure of the natural gas pipeline in the depressurization and hydrogen delivery process if the conclusion of the two evaluation meets the rule of the mandatory standard. As a preferred embodiment of the present invention, in the step (1), the risk factor F H of the crack or defect is determined by the following method: According to the actual operating pressure P 1 of the natural gas pipeline and the material performance parameters, calculating the position A of the detected crack on the failure evaluation graph, connecting an origin O with the point A, wherein the intersection point of the connecting line and the failure evaluation graph is B, and the risk coefficient is F H =OA/OB, wherein OA and OB are the connecting line lengths of the two points of the origin O and A, B respectively. In the preferred embodiment of the present invention, in the step (2), the cut pipe section incl