Low-temperature valve inner leakage detection method based on multi-stage combination

Abstract

The invention provides a low-temperature valve inner leakage detection method based on multi-stage combination. According to the detection method, a first monitoring valve group and a second monitoring valve group are arranged on the upstream and downstream of each low-temperature valve in a process system before commissioning; the method is used for performing inner leakage detection in a water pressure detection stage, a purging and drying stage and a precooling stage on each low-temperature valve in a process system before commissioning, and comprises the following steps: in the water pressure detection stage, acquiring a water dew point difference value delta T in each upstream and downstream detection valve of a first monitoring valve group through a dew point detector to judge the water leakage condition of the low-temperature valves; a purging and drying detection stage: collecting a gas concentration difference value delta C in single upstream and downstream detection valves of the second detection valve group through a gas state detector to judge the gas leakage condition of the low-temperature valve; a pre-cooling detection stage: collecting upstream and downstream natural gas concentration difference delta F of single upstream and downstream detection valves of the second detection valve group through a combustible gas detector to judge the gas leakage condition of the valves; through a portable instrument and multi-index comprehensive analysis, valve quality detection on a construction site can be rapidly and accurately completed, and the problem of reworking after commissioning is effectively avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of valve sealing performance detection, and particularly to a method for detecting internal leakage of cryogenic valves based on multi-stage combination. Background Art

[0002] As an important device in industrial pipeline systems, the sealing performance of valves is directly related to the operation safety and efficiency of the systems. In a cryogenic environment, especially in LNG (liquefied natural gas) gasification stations, liquid nitrogen storage and transportation systems, liquid hydrogen storage and transportation equipment, and other cryogenic refrigeration systems, valves need to have excellent sealing performance to ensure the stable operation of pipeline systems. However, once the problem of internal leakage of valves occurs, it will not only cause energy waste, but may also trigger safety accidents and even lead to unplanned shutdown of the systems.

[0003] In the prior art, the detection of the sealing performance of cryogenic valves mostly relies on the detection platforms under factory experimental conditions. In the ex-factory detection stage, the working condition environment is usually simulated by a cryogenic test platform to detect the sealing performance of valves. However, after the valves are installed on-site and debugged, their sealing performance may change due to the influence of transportation, installation, and on-site working conditions. Due to the lack of an efficient and convenient on-site detection method, it is difficult to detect internal leakage problems during the construction process or before commissioning in a timely manner. Once a failure occurs after commissioning, it usually requires production suspension and returning to the factory for repair, seriously affecting the construction progress and economic benefits.

[0004] The current on-site detection methods for cryogenic valves are usually limited to the testing of a single index (such as pressure decay or leakage rate), and their detection sensitivity and reliability are relatively low. Especially in a complex construction environment, they are easily affected by external interference, resulting in inaccurate detection results. In addition, the prior art does not fully utilize the detection potential of the conventional operations (such as hydrostatic testing, nitrogen purging, and pre-cooling process) before pipeline commissioning, and cannot meet the requirements of multi-index comprehensive detection, resulting in blind spots in the judgment of internal leakage problems.

[0005] Before the commissioning of an LNG gasification station, it is usually necessary to successively carry out technological processes such as hydrostatic testing, nitrogen purging, and cryogenic pre-cooling to meet the requirements of national and industrial standards such as GB / T 《24259-2020 Petroleum and Natural Gas Industry Pipeline Transportation System》, 《GB / T 20801.5-2020 Pressure Pipeline Code Industrial Pipeline Part 5: Inspection and Testing》, and 《Q / SY 08713—2020 Safety Technical Regulations for Trial Commissioning of LNG Receiving Terminals》. However, these processes are carried out independently, and the detection of internal leakage of valves is not carried out in combination with the medium flow characteristics, and the detection means are scattered and inefficient. In addition, although portable detection equipment has been gradually introduced into the industrial site, the current applications are still mainly for single purposes, and a systematic multi-index comprehensive detection mode has not been formed, restricting its applicability and detection effect.

[0006] Therefore, it is an urgent technical problem to develop a valve internal leakage detection technology based on a multi-stage comprehensive detection method, make full use of the operating characteristics of the water pressure test, nitrogen purging and cryogenic precooling stages, and improve the detection accuracy and applicability through the joint analysis of multiple indicators. In view of the deficiencies in the prior art, the present invention proposes an innovative valve internal leakage detection method, which can significantly improve the detection efficiency and reliability and is applicable to complex construction site conditions. Summary of the Invention

[0007] The present invention proposes a cryogenic equipment valve internal leakage detection method based on multi-stage joint detection. Combining conventional technological processes such as water pressure test, nitrogen purging and cryogenic precooling, it uses portable detection equipment to monitor the dew point, nitrogen concentration and combustible gas concentration upstream and downstream of the valve. Through comprehensive analysis of multiple indicators, rapid diagnosis and determination of the sealing performance of cryogenic valves are realized. This method does not require complex experimental facilities, is applicable to construction site conditions, and has the advantages of convenient operation and high accuracy.

[0008] To solve the prior art, the technical solution adopted by the present invention is as follows:

[0009] 1. A cryogenic valve internal leakage detection method based on multi-stage joint. For each cryogenic valve in the pre-commissioning process system, a first monitoring valve group and a second monitoring valve group are provided upstream and downstream thereof; the method sequentially performs internal leakage detection on each cryogenic valve in the pre-commissioning process system in the water pressure detection stage, purge and drying stage and precooling stage, including:

[0010] Water pressure detection stage: The dew point difference ΔT of the water dew point of a single detection valve upstream and downstream of the first monitoring valve group is collected by a dew point detector to judge the water leakage condition of the cryogenic valve; the water dew point difference is:

[0011]

[0012] wherein, ΔT is the water dew point difference of the first monitoring valve group, is the water dew point of the first monitoring valve group at time point t1; is the water dew point downstream of the valve at time point t2; t2 and t1 are two different time points, t2 > t1, and the time interval satisfies the determination of the dew point difference;

[0013] Purge and drying detection stage: The nitrogen concentration difference ΔC of a single detection valve upstream and downstream of the second detection valve group is collected by a gaseous detector to judge the air leakage condition of the cryogenic valve; the gas concentration difference is:

[0014]

[0015] wherein, ΔC is the nitrogen concentration difference of the second monitoring valve group, The nitrogen concentration of the second monitoring valve group at time point t1; It is the nitrogen concentration of the monitoring valve group at time point t2; t2 and t1 are two different time points, t2 > t1, and the time interval satisfies the determination of the nitrogen concentration difference.

[0016] Precooling detection stage: The leakage of the valve is judged by collecting the natural gas concentration difference ΔF between the upstream and downstream single detection valves of the second detection valve group through a combustible gas detector; the natural gas concentration difference is:

[0017]

[0018] where ΔF is the natural gas concentration difference of the second monitoring valve group, The natural gas concentration of the second monitoring valve group at time point t1; It is the natural gas concentration of the second monitoring valve group at time point t2; t2 and t1 are two different time points, t2 > t1, and the time interval satisfies the determination of the nitrogen concentration difference.

[0019] Further, the process of judging the water leakage of each cryogenic valve in the water pressure detection stage includes:

[0020] 101. Inject water into the pipeline connected to the cryogenic valve to be detected and gradually pressurize it to the target value;

[0021] 102. When the water pressure rises to the target value, keep it for 10 minutes to make the pressure inside the pipeline and the cryogenic valve consistent;

[0022] 103. Every 5 minutes, collect the water dew point values of single valves in the first monitoring valve group upstream and downstream of the cryogenic valve to be detected through a dew point detector for 15 minutes, and calculate the difference ΔT of the water dew point;

[0023] 104. Judge whether the difference of the water dew point is greater than 0.5 °C. If it is satisfied, enter the purging and drying detection stage. Otherwise, repair the cryogenic valve and return to step 102.

[0024] Further, the process of judging the air leakage of each cryogenic valve in the purging and drying detection stage includes: 201. Purge the pipeline connected to the cryogenic valve to be detected for 10 - 15 minutes to ensure that there is no water vapor residue at the outlet of the detected cryogenic valve;

[0025] 202. Every 5 minutes, collect the water dew point values of single valves in the first monitoring valve group upstream and downstream of the cryogenic valve to be detected through a dew point detector for 15 minutes, and calculate the difference ΔT of the water dew point;

[0026] 203. Judge whether the difference of the water dew point is greater than -20 °C. If it is satisfied, enter the next step. Otherwise, return to step 201;

[0027] 204. Gradually inject nitrogen into the pipeline connected to the cryogenic valve to be detected and pressurize it to the target value.

[0028] 205. Every 5 minutes, collect the nitrogen concentration value of a single valve in the second monitoring valve group downstream of the cryogenic valve to be detected through a gaseous detector for 15 minutes, and calculate the obtained nitrogen concentration difference ΔC.

[0029] 206. Determine whether the nitrogen concentration difference ΔC is greater than 1%. If it is satisfied, enter the pre-cooling detection stage; otherwise, repair the cryogenic valve and return to step 205.

[0030] Furthermore, the process of judging the air leakage situation of each cryogenic valve in the pre-cooling stage includes:

[0031] 301. Gradually inject BOG evaporation gas into the pipeline connected to the cryogenic valve to be detected until the temperature drops to -110°C.

[0032] 302. Every 5 minutes, collect the natural gas concentration value of a single valve in the second monitoring valve group downstream of the cryogenic valve to be detected through a combustible gas detector for 15 minutes, and calculate the obtained nitrogen concentration difference ΔF.

[0033] 303. Determine whether the natural gas concentration difference ΔF is less than 0.3%. If it is satisfied, enter the pre-cooling detection stage; otherwise, repair the cryogenic valve and return to step 302.

[0034] Beneficial effects

[0035] 1. The detection result of the present invention for the internal leakage problem of the valve has high judgment accuracy. Through the combined analysis of three indicators: dew point difference, nitrogen concentration difference, and combustible gas concentration difference, the deviation of the detection result caused by misjudgment of a single indicator can be avoided. At the same time, the present invention can overcome the influence of environmental interference on the detection result. In each detection stage, the sampling is not less than three times, and the average value is taken for calculation to improve the accuracy and reliability of the detection.

[0036] 2. The present invention can cover the entire process flow before the commissioning of cryogenic industrial pipelines. Especially in combination with the requirements of national and industrial standards such as GB 24259 and GB / T 20801.5, while meeting the requirements of hydrostatic testing, nitrogen purging, and cryogenic pre-cooling processes, the valve sealing performance detection is synchronously completed, improving the detection efficiency and reducing the cost.

[0037] 3. The present invention is applicable to the internal leakage detection of cryogenic valves before the commissioning of LNG gasification receiving stations, and can also be extended to cryogenic industrial fields such as liquid nitrogen storage and transportation systems, liquid hydrogen storage and transportation equipment, and other cryogenic refrigeration systems. In addition, this method can also be extended to industries such as chemical engineering, natural gas transportation, and power plant steam pipe networks, and is widely applicable to the valve sealing detection and verification in industrial sites.

[0038] 4. The multi-stage leak point detection method adopted by the present invention can reasonably utilize the conventional operation steps before the pipeline is put into production, without the need to add special detection equipment, which can significantly shorten the detection cycle (reduce by more than 30%), and at the same time avoid the problem of shutdown and repair caused by internal leakage found after commissioning, thereby improving economic benefits and construction efficiency; at the same time, the present invention can discover and solve internal leakage problems before putting into production, and avoid potential safety hazards during operation.

[0039] 5. The detection method of the present invention can be flexibly adjusted according to specific working conditions. For example, in an environment where BOG precooling is not applicable, the nitrogen replacement and nitrogen precooling modes can be directly adopted to reduce the detection link of combustible gas concentration and meet the requirements of a wider range of on-site application needs.

[0040] 6. The method of the present invention can be widely applied to low-temperature industrial fields such as liquefied natural gas gasification stations, liquid nitrogen storage and transportation systems, liquid hydrogen storage and transportation equipment, and cryogenic refrigeration systems, and is also applicable to industrial pipelines and equipment that need to be subjected to hydrostatic pressure testing, nitrogen purging, and cryogenic precooling operations before commissioning.

[0041] 7. The detection technology of the present invention can be extended to industries such as chemical engineering, natural gas transportation, and power plant steam pipe networks, and is used for verifying the valve sealing performance before commissioning and detecting internal leakage in the system, with the characteristics of high efficiency, portability, and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of a method for detecting internal leakage of valves in cryogenic equipment based on multi-stage joint detection according to the present invention;

[0043] Figure 2 It is a layout schematic diagram of a method for detecting internal leakage of valves in cryogenic equipment based on multi-stage joint detection according to the present invention during commissioning;

[0044] Figure 3 It is a flow chart for processing valves in cryogenic equipment by adopting the present invention;

[0045] Figure 4 It is a schematic diagram of the water pressure-time curve related to the present invention;

[0046] Figure 5 It is a schematic diagram of the purging pressure-time curve related to the present invention;

[0047] Figure 6 It is a schematic diagram of the replacement pressure-time curve related to the present invention;

[0048] Figure 7 It is a schematic diagram of the precooling pressure-time curve related to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0049] The following is combined with the attachedFigure 1 ~Appendix Figure 7 The technical solution of the present invention will be elaborated in detail.

[0050] As Figure 1 、 Figure 2 As shown, the present invention provides a method for detecting internal leakage of cryogenic valves based on multi-stage combination. The detection method is based on the fact that a first monitoring valve group (D1, D2, D3, D4, D5, D6, D7, D8, D9, D10) and a second monitoring valve group (Z1, Z2, Z3, Z4, Z5) are provided upstream and downstream of each cryogenic valve (V1, V2, V3, V4, V5, V6, V7, V8, V9, V10) in the process system before commissioning; the method is to perform internal leakage detection on each cryogenic valve in the process system before commissioning in sequence during the water pressure detection stage, purging and drying stage, and precooling stage. In the present invention, before the LNG receiving and gasification station is put into operation, a first monitoring valve group and a second monitoring valve group are installed for each cryogenic valve in the process system to realize on-line monitoring of the sealing performance of cryogenic valves for media such as water, nitrogen, and combustible gas. The first monitoring valve group and the second monitoring valve group of the present invention can utilize the drain valves, vent valves, instrument sampling valves, etc. of the process system. The present invention can temporarily install tooling valves to ensure that each cryogenic valve has a first monitoring valve group and a second monitoring valve group. The temporary tooling valves are removed after the internal leakage detection of the cryogenic valves is completed.

[0051] In the water pressure test of the present invention, in the first monitoring valve group, the sealing performance of the cryogenic valve against water is judged by the change in dew point. The water dew point mentioned in the present invention refers to the temperature at which water vapor in air or gas cools to saturation and begins to condense into dew drops under a constant air pressure. In the first monitoring valve group, an increase in the water dew point within a certain period of time indicates that water leaks from the high-pressure side of the cryogenic valve to the low-pressure side, and there is internal leakage in the cryogenic valve. In the present invention, the sealing performance of the cryogenic valve against water is judged based on the monitoring of the dew point change within a certain period of time to determine whether there is internal leakage of water in the valve. As Figure 3 shown, it includes:

[0052] S1. Water pressure detection stage: The leakage situation of the cryogenic valve is judged by collecting the difference ΔT in water dew point inside the single detection valve upstream and downstream of the first monitoring valve group through a dew point detector; the difference in water dew point is:

[0053]

[0054] The dew point change of the cryogenic valve is detected by a dew point detector within a certain period of time; according to the magnitude of the dew point difference ΔT at a certain time interval, the internal leakage situation is judged; when ΔT > 0.5 °C, it is determined that there is internal leakage in the valve; the present invention utilizes Figure 4Medium water pressure time curve to verify the pressure stability during the detection process to ensure the accuracy of the detection results; wherein: the process of judging the water leakage situation of each cryogenic valve in the water pressure detection stage includes:

[0055] 101. Inject water into the pipeline connected to the cryogenic valve to be detected and gradually pressurize it to the target value;

[0056] 102. When the water pressure rises to the target value, keep it for 10 minutes to make the pressure inside the pipeline and the cryogenic valve consistent;

[0057] 103. Every 5 minutes, collect the water dew point value of a single valve in the first monitoring valve group of the cryogenic valve to be detected through a dew point detector, continuously for 15 minutes, and calculate the difference ΔT of the water dew point;

[0058] 104. Judge whether the difference of the water dew point is greater than 0.5°C. If it is satisfied, enter the purge and drying detection stage; otherwise, repair the cryogenic valve and return to step 102.

[0059] In the purge and drying stage of the present invention, in the second monitoring valve group, the gas tightness of the cryogenic valve under a certain pressure is judged by the change of the gasification body content. The drying gas of the present invention uses nitrogen gas. At this time, the gas tightness of the cryogenic valve of the present invention is accurately judged based on the monitoring of the change of the nitrogen content within a certain time to determine whether there is a problem of nitrogen internal leakage in the valve. Wherein:

[0060] S2. Purge and drying detection stage: Judge the air leakage situation of the cryogenic valve by collecting the gas concentration difference ΔC of a single detection valve in the second detection valve group within a certain time through a gas detector; the gas concentration difference is:

[0061]

[0062] As Figure 5 shown, detect the change of the nitrogen concentration upstream and downstream of the valve through a nitrogen detector; judge the internal leakage situation according to the size of the upstream and downstream nitrogen concentration difference ΔC; when ΔC>1%, it is determined that the valve has internal leakage; combined with Figure 6 the purge pressure time curve in, confirm the accuracy of the nitrogen purge effect and concentration change; wherein: the process of judging the air leakage situation of each cryogenic valve in the purge and drying detection stage includes:

[0063] 201. Purge the pipeline connected to the cryogenic valve to be detected for 10 - 15 minutes to ensure that there is no water vapor residue at the outlet of the detected cryogenic valve;

[0064] 202. Every 5 minutes, collect the water dew point value of a single valve in the first monitoring valve group of the cryogenic valve to be detected through a dew point detector, continuously for 15 minutes, and calculate the difference ΔT of the water dew point;

[0065] 203. Determine whether the difference in water dew point is greater than -20°C. If it is satisfied, proceed to the next step; otherwise, return to step 201.

[0066] 204. Gradually inject nitrogen into the pipeline connected to the cryogenic valve to be detected to pressurize it to the target value.

[0067] 205. Every 5 minutes, collect the nitrogen concentration value of a single valve in the second monitoring valve group of the cryogenic valve to be detected through a gaseous detector for 15 minutes, and calculate the nitrogen concentration difference ΔC.

[0068] 206. Determine whether the nitrogen concentration difference ΔC is greater than 1%. If it is satisfied, enter the pre-cooling detection stage; otherwise, repair the cryogenic valve and return to step 205.

[0069] In the low-temperature pre-cooling stage of the present invention, in the second monitoring valve group, by the change in the content of combustible gas, the sealing performance of the cryogenic valve for cryogenic combustible gas under a certain pressure is judged. For the sealing performance of the cryogenic natural gas of the present invention, whether there is a problem of internal leakage of cryogenic combustible gas is judged based on the change in the content of combustible gas within a certain time.

[0070] S3. Pre-cooling detection stage: Collect the difference ΔF in the natural gas concentration of a single valve in the second detection valve group of the cryogenic valve within a certain time through a combustible gas detector to judge the valve leakage situation; the difference in natural gas concentration is:

[0071] ΔF = F t2 -F t1

[0072] The present invention uses BOG (boil-off gas) as the test medium, monitors the change in the natural gas concentration of the valve through a combustible gas detector; judges the internal leakage situation according to the magnitude of the difference ΔF in the natural gas concentration between upstream and downstream; when ΔF > 0.3%, it is determined that the valve has internal leakage; uses Figure 4 the pre-cooling pressure-time curve in to verify the stability of pressure and the low-temperature adaptability during the detection process.

[0073] Among them: The process of judging the leakage situation of each cryogenic valve in the pre-cooling stage includes:

[0074] 301. Gradually inject BOG boil-off gas into the pipeline connected to the cryogenic valve to be detected until the temperature drops to 110°C.

[0075] 302. Every 5 minutes, collect the natural gas concentration value of a single valve in the second monitoring valve group of the cryogenic valve to be detected through a combustible gas detector for 15 minutes, and calculate the nitrogen concentration difference ΔF.

[0076] 303. Determine whether the natural gas concentration difference ΔF is less than 0.3%. If it is satisfied, enter the pre-cooling detection stage; otherwise, repair the cryogenic valve and return to step 302.

[0077] According to different pipeline commissioning methods, the present invention proposes two detection modes:

[0078] 1) When the pipeline is commissioned using BOG (boil-off gas) pre-cooling, the detection includes a three-stage combined detection of the internal leakage problem of the cryogenic valve in the water pressure stage, purging and drying stage, and pre-cooling stage;

[0079] 2) When the pipeline is commissioned using nitrogen displacement and nitrogen pre-cooling, the detection includes a combined monitoring of the water pressure stage and the purging and drying stage, reducing the detection steps related to combustible gases.

[0080] Embodiment 1: Water pressure, drying, nitrogen displacement, BOG pre-cooling

[0081] This embodiment is aimed at the working condition using BOG (boil-off gas) as the pre-cooling medium, and combines the steps of water pressure test, drying treatment, nitrogen displacement, and cryogenic pre-cooling to conduct multi-stage comprehensive detection of the valve. The specific steps are as follows:

[0082] The first stage: Preparation work for the water pressure detection stage:

[0083] Fill the pipeline with clean water and gradually increase the pressure to the design pressure P (usually 1.5 times the design pressure, such as 1.5P). In this stage, a portable dew point detector is used to monitor the dew point changes upstream and downstream of the valve in real time. Pressure stabilization step: After the water pressure rises to the target pressure, keep the pressure stable (error less than 0.05 MPa) for 10 minutes to ensure that the pipeline system and the inside of the valve reach the pressure balance state.

[0084] Detection step: After the pressure stabilization is completed, continuously monitor the dew point changes upstream and downstream for 15 minutes, take samples once every 5 minutes, take a total of 3 samples, calculate the average value of ΔT after sampling, and judge the internal leakage situation based on this.

[0085] Judgment criterion: Judge the internal leakage situation through the dew point difference ΔT. When ΔT > 0.5 °C, it is judged that the valve has internal leakage.

[0086] Unqualified treatment: If ΔT > 0.5 °C is judged as unqualified, the following measures need to be taken:

[0087] 1) Reduce the pressure and check the tightness of the pipeline and valve connection parts;

[0088] 2) Repair the leakage point or replace the relevant components;

[0089] 3) Re-conduct the water pressure detection to ensure that ΔT ≤ 0.5 °C.

[0090] The second stage: Purging stage (air)

[0091] The purging time is 10 to 15 minutes until there is no residual water vapor at the outlet and the dew point value is stabilized at -20°C.

[0092] Verification step: Monitor the drying effect through a portable dew point detector to ensure that the dew point value meets the standard.

[0093] Non-conformance handling: If the dew point value does not reach below -20°C, extend the purging time or adjust the air flow rate until the detection is qualified.

[0094] Preparation work for the nitrogen replacement stage: Inject high-purity nitrogen (purity ≥ 99.9%) from the pipeline inlet and gradually increase the pressure to the target pressure (usually 0.6P to 1.1P). A portable nitrogen detector is used to monitor the change of nitrogen concentration upstream and downstream in real time, as Figure 5 shown.

[0095] Replacement step:

[0096] 1) Divide the pipeline into several sections and conduct nitrogen replacement for each section separately;

[0097] 2) Monitor the oxygen content at the outlet in real time until the oxygen content is lower than 0.5%.

[0098] Detection step: After the replacement is completed, continuously monitor the nitrogen concentration upstream and downstream for 10 minutes, take samples every 5 minutes, and take a total of 3 samples. Judgment criterion: Judge the internal leakage situation through the nitrogen concentration difference ΔC. When ΔC > 1%, it is judged that there is internal leakage in the valve.

[0099] Non-conformance handling: If ΔC > 1% is judged as unqualified, nitrogen purging should be carried out again and re-detected until ΔC ≤ 1%.

[0100] Third stage: Preparation work for the pre-cooling detection stage: Inject BOG (boil-off gas) from the pipeline inlet and gradually reduce the pipeline temperature to -110°C. A portable combustible gas detector is used to monitor the natural gas concentration of the cryogenic valve.

[0101] Cooling step: Control the cooling rate within 10°C per minute to avoid damage to the pipeline due to thermal stress.

[0102] Detection step: After the temperature is stabilized, continuously monitor the natural gas concentration upstream and downstream for 15 minutes, take samples every 5 minutes, and take a total of 3 samples.

[0103] Judgment criterion:

[0104] Judge the internal leakage situation through the natural gas concentration difference ΔF. When ΔF > 0.3%, it is judged that there is internal leakage in the valve.

[0105] Non-conformance handling: If ΔF > 0.3%, it is determined as non-conforming. The pre-cooling operation should be suspended, and after repairing or replacing the valve, the detection should be carried out again. Implementation method 2: Hydrostatic pressure, drying, nitrogen replacement, nitrogen pre-cooling

[0106] The main difference between this implementation method and implementation method 1 is that low-temperature nitrogen is used as the cooling medium in the pre-cooling stage. The specific operation steps are as follows:

[0107] Preparation work for the nitrogen pre-cooling detection stage:

[0108] Inject low-temperature nitrogen into the pipeline, gradually reduce the pipeline temperature to -110°C, and at the same time use a portable dew point detector and a nitrogen detector to monitor the upstream and downstream dew points and nitrogen concentrations.

[0109] Cooling step: Control the cooling rate within 10°C per minute to ensure system safety.

[0110] Detection step: After the temperature stabilizes, continuously monitor the upstream and downstream dew points and nitrogen concentrations for 10 minutes, take samples every 5 minutes, and take a total of 3 samples.

[0111] Judgment criteria:

[0112] Based on the comprehensive analysis results of the dew point difference ΔT and the nitrogen concentration difference ΔC, judge the internal leakage situation.

[0113] Non-conformance handling: If the detection is unqualified, nitrogen should be re-injected and the detection should be carried out until both ΔT and ΔC meet the standards.

[0114] It should be noted that the protection scope of the present invention is not limited to the following description, but covers all improvements and deformations based on the technical solution.

Claims

1. A cryogenic valve internal leakage detection method based on multi-stage combination, characterized in that: The detection method is based on the fact that each cryogenic valve in the process system before commissioning is provided with a first monitoring valve group and a second monitoring valve group upstream and downstream; The method is to sequentially perform internal leakage detection in the water pressure detection stage, the purge drying stage and the pre-cooling stage on each cryogenic valve in the process system before commissioning, including: Water pressure detection stage: the dew point difference ΔT of water in the upstream and downstream individual detection valves of the first monitoring valve group is collected by a dew point detector to determine the leakage of the low-temperature valve; the water dew point difference is: Among them, ΔT is the water dew point difference of the first monitoring valve group, is the water dew point of the first monitoring valve group at time point t1; is the water dew point downstream of the valve at time point t2; t2 and t1 are two different time points, t2>t1, and the time interval satisfies the dew point difference determination; Purging and drying detection stage: The nitrogen concentration difference ΔC in the upstream and downstream individual detection valves of the second detection valve group is collected by the gas detector to determine the leakage of the cryogenic valve; the gas concentration difference is: Among them, ΔC is the nitrogen concentration difference of the second monitoring valve group, The second monitoring valve group nitrogen concentration at time point t1; To monitor the nitrogen concentration of the valve group at time point t2; t2 and t1 are two different time points, t2>t1, and the time interval satisfies the nitrogen concentration difference determination. Pre-cooling detection stage: The combustible gas detector is used to collect the natural gas concentration difference ΔF of the single detection valve upstream and downstream of the second detection valve group to determine the valve leakage; the natural gas concentration difference is: Among them, ΔF is the natural gas concentration difference of the second monitoring valve group, The second monitoring valve group monitors the natural gas concentration at time point t1; is the natural gas concentration of the second monitoring valve group at time point t2; t2 and t1 are two different time points, t2>t1, and the time interval satisfies the nitrogen concentration difference determination.

2. A cryogenic valve internal leakage detection method based on multi-stage combination according to claim 1, characterized in that: The process of judging the water leakage of each cryogenic valve in the water pressure detection stage includes:

101. Inject water into the pipeline connected to the cryogenic valve to be tested and gradually increase the pressure to the target value; 102. When the water pressure reaches the target value, keep it for 10 minutes to make the pressure inside the pipeline and the cryogenic valve consistent; 103. Collect the water dew point value of a single valve in the first monitoring valve group upstream and downstream of the low-temperature valve to be tested by a dew point detector every 5 minutes for 15 minutes, and calculate the difference ΔT of the water dew point; 104. Determine whether the difference in water dew point is greater than 0.5°C. If so, enter the purge and dry detection phase. Otherwise, repair the cryogenic valve and return to step 102.

3. The method for detecting internal leakage of cryogenic valves based on multi-stage combination according to claim 1 is characterized in that: The process of judging the leakage of each cryogenic valve in the purge and dry detection stage includes:

201. Purge the pipeline connected to the cryogenic valve to be tested for 10 to 15 minutes to ensure that there is no water vapor remaining at the outlet of the cryogenic valve to be tested; 202. Collect the water dew point value of a single valve in the first monitoring valve group upstream and downstream of the low-temperature valve to be tested by a dew point detector every 5 minutes for 15 minutes, and calculate the difference ΔT of the water dew point; 203. Determine whether the difference in water dew point is greater than -20°C. If so, proceed to the next step, otherwise return to step 201; 204. Gradually inject nitrogen into the pipeline connected to the cryogenic valve to be tested to pressurize it to the target value; 205. Collect nitrogen concentration values ​​of individual valves in the second monitoring valve group downstream of the cryogenic valve to be tested by a gas detector every 5 minutes for 15 minutes, and calculate the nitrogen concentration difference ΔC; 206. Determine whether the nitrogen concentration difference ΔC is greater than 1%. If so, enter the pre-cooling detection phase. Otherwise, repair the cryogenic valve and return to step 205.

4. The method for detecting internal leakage of cryogenic valves based on multi-stage combination according to claim 1 is characterized in that: The process of judging the leakage of each cryogenic valve in the pre-cooling stage includes:

301. Inject BOG evaporation gas gradually into the pipeline connected to the cryogenic valve to be tested until the temperature drops to -110°C; 302. Every 5 minutes, the natural gas concentration value of a single valve in the second monitoring valve group downstream of the low-temperature valve to be detected is collected by a combustible gas detector for 15 minutes, and the nitrogen concentration difference ΔF is calculated; 303. Determine whether the natural gas concentration difference ΔF is less than 0.3%. If so, enter the pre-cooling detection phase. Otherwise, repair the cryogenic valve and return to step 302.

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