Experimental device and method for creep test of weld joint of all-welded plate heat exchanger

Abstract

The invention belongs to the technical field of material mechanical property test and pressure vessel safety inspection, and particularly relates to an experimental device and method for a weld creep test of an all-welded plate heat exchanger. The problems that a traditional uniaxial creep testing machine cannot reproduce the real thermal-mechanical coupling service condition of a heat exchanger, a test object is disjointed with an actual structure, and the data supporting capacity is insufficient are solved. The device comprises an all-welded plate heat exchanger test piece, a pressure supply system, a temperature control system, a high-precision strain gauge arranged on a key welding seam and a multi-channel data acquisition system, the test method is implemented step by step through test piece preparation and installation, sensor calibration, temperature field establishment, pressure application, creep data acquisition and safe unloading. According to the method, the actual service condition of the heat exchanger welding seam can be accurately reproduced, the creep damage evolution law of the welding seam can be captured, key parameters such as the steady-state creep rate can be obtained, and reliable experimental basis is provided for all-welded plate heat exchanger welding seam life evaluation, welding process optimization and in-service safety inspection.

Description

Technical Field

[0001] This invention belongs to the field of material mechanical property testing and pressure vessel safety inspection technology, specifically an experimental device and method for creep testing of weld seams in fully welded plate heat exchangers. Background Technology

[0002] All-welded plate heat exchangers, with their compact structure and excellent heat transfer performance, have become key heat exchange equipment in petrochemical, nuclear power, and energy conversion industries, and their operational stability directly affects the safety and efficiency of industrial processes. This heat exchanger is formed by welding multiple corrugated metal plates together with sealed welds around its perimeter; however, the welded area (especially the heat-affected zone) can easily become a weak point under harsh operating conditions.

[0003] During long-term operation, fully welded plate heat exchangers must withstand internal pressures of up to 2.5 MPa and temperatures ranging from 100°C to 600°C (0.3-0.5 times the melting point of materials such as stainless steel). Under these thermo-mechanical coupling conditions, the material will experience creep (slow accumulation of plastic deformation under constant stress at high temperature), leading to micro-cracks in the welds that gradually propagate and may eventually cause safety accidents such as media leakage and equipment explosion.

[0004] Currently, the industry mainly relies on traditional uniaxial creep testing machines to evaluate creep performance, but such equipment has significant limitations in testing welds of fully welded plate heat exchangers: 1. The test specimens are out of touch with the actual structure: The use of homogeneous material standard specimens cannot reflect the true geometric characteristics of the weld and the non-uniformity of the material, and the stress concentration effect is ignored, resulting in a large deviation between the test results and the actual service conditions. 2. Limited load application mode: It can only achieve uniaxial tensile or compressive loading, and cannot simulate the multiaxial stress state (in-plane pressure, edge bending stress, thermal expansion constraint stress, etc.) that the equipment actually bears, making it difficult to induce real creep damage; 3. The test environment does not match reality: Most tests are conducted in static air environments, without considering the "corrosion-creep coupling" damage caused by the internal flowing medium of the equipment, resulting in low reliability of the test results; 4. Lack of complete structural testing capability: It is impossible to directly test the heat exchanger core with complete welds. The equipment performance can only be indirectly inferred from the material sample data. The data extrapolation is uncertain and it is difficult to support the equipment life assessment.

[0005] In summary, existing technologies are significantly different from the actual service conditions of fully welded plate heat exchangers, and cannot meet the industrial sector's needs for accurate equipment life prediction and reliable safety assessment. Developing creep testing devices and methods that can reproduce real operating conditions and target complete welds has become an urgent need to ensure the safe service of equipment. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies and solve the aforementioned technical problems, this invention proposes an experimental apparatus and method for testing the creep of weld seams in fully welded plate heat exchangers.

[0007] The technical solution adopted by this invention to solve its technical problem is to propose an experimental device for creep testing of weld seams in fully welded plate heat exchangers. The device includes a fully welded plate heat exchanger specimen, a pressure supply system for applying and maintaining pressure inside the specimen, a temperature control system for providing a high-temperature environment to the specimen, strain measuring elements arranged in the weld seam area of ​​the specimen, and a data acquisition system that is signal-connected to the pressure supply system, the temperature control system, and the strain measuring elements, respectively. The pressure supply system and the temperature control system work together to simulate the thermo-mechanical coupling load of actual service in the weld seam area of ​​the specimen. The data acquisition system is used to record pressure, temperature, and strain data to monitor the creep behavior of the weld seam.

[0008] Furthermore, the pressure supply system includes a water tank, pipelines, pressure stabilizing components, a check valve, a flow meter, a pressure sensor, and a back pressure valve; The pipeline is used to connect the inlet and outlet of the water tank and the fully welded plate heat exchanger specimen to form a fluid circulation path; The check valve is installed on the pipeline from the water tank to the inlet of the test specimen to prevent backflow of fluid in the pipeline; The flow meters are respectively installed on the inlet and outlet pipelines of the test specimen to monitor the fluid flow rate in the pipeline; The pressure sensor is installed on the pipeline at the inlet of the specimen to collect the pressure value in the pipeline in real time. The back pressure valve is located on the pipeline from the specimen outlet to the water tank. It is used to discharge air from the pipeline during the water injection stage and to close the pipeline during the pressurization stage to establish a stable pressure environment. The pressure stabilizing component adjusts the pressure based on the feedback signal from the pressure sensor to maintain stable pressure within the pipeline, thereby providing continuous pressure to the interior of the specimen.

[0009] Furthermore, the temperature control system includes a temperature controller and a thermocouple sensor; the thermocouple sensor is used in conjunction with the surface and weld area of ​​the fully welded plate heat exchanger specimen to monitor temperature data at different locations of the specimen; the temperature controller is connected to the thermocouple sensor signal and adjusts the heating power based on the temperature data fed back by the thermocouple sensor, so that the ambient temperature of the specimen can be kept constant within a set range.

[0010] Furthermore, the temperature control system has a temperature control range of 100℃ to 600℃, and the pressure stabilizing component in the pressure supply system can maintain the pressure in the pipeline at the rated test pressure of 2.5MPa.

[0011] Furthermore, the strain measurement element is a high-precision strain gauge; the strain gauge is arranged at least at the main sealing weld between the plates and the fillet weld of the inlet and outlet pipe seats of the fully welded plate heat exchanger specimen; the measurement accuracy of the strain gauge meets ±0.5%FS and is used to collect creep deformation data in the weld area.

[0012] Furthermore, the data acquisition system is a multi-channel data acquisition system; the sampling frequency of the data acquisition system is 1Hz, which can automatically record the pressure data collected by the pressure sensor, the temperature data collected by the thermocouple sensor, and the strain data collected by the strain gauge, and simultaneously generate the load-time-strain relationship curve; the data acquisition system also includes a data abnormal fluctuation early warning function, which triggers an early warning when the data exceeds the preset allowable range.

[0013] An experimental method for creep testing of weld seams in fully welded plate heat exchangers includes the following steps: Step 1: Specimen Preparation and System Installation: Select a fully welded plate heat exchanger that meets industrial manufacturing standards as the test specimen. Clean the surface of the specimen and check the integrity of the welds. Install the specimen into the experimental device frame. Connect the specimen to the water tank, check valve, flow meter, pressure sensor and back pressure valve of the pressure supply system through pipelines. At the same time, connect the specimen to the thermocouple sensor circuit of the temperature control system and the signal circuit of the strain measurement element, ensuring that each interface meets the high temperature and high pressure sealing requirements. Step 2: Sensor Arrangement and System Initialization: Strain gauges are arranged at the main sealing weld between the plates of the specimen and at the fillet weld of the inlet and outlet pipe seats. Thermocouple sensors are arranged on the surface of the specimen and in the weld area. The strain gauges, thermocouple sensors, and pressure sensors are all connected to the multi-channel data acquisition system. The system is powered on and self-tested. The sensors are zero-point calibrated, and the stability of the signal path is verified. Step 3: Pressure Application and Maintenance: Open the back pressure valve of the pressure supply system, start the pressure stabilizing component to continuously inject water into the pipeline until water continuously flows out of the specimen outlet pipeline to expel residual air in the pipeline; close the back pressure valve, and gradually increase the pressure in the pipeline at the set rate until the internal pressure of the fully welded plate heat exchanger specimen reaches the rated test pressure of 2.5MPa; after the pressure reaches the standard, the system enters the automatic pressure maintenance mode, and adjusts the pressure stabilizing component through real-time feedback from the pressure sensor to maintain pressure stability; Step 4: Temperature Field Establishment: Activate the temperature control system, set the heating rate to 5℃ / min, and gradually raise the ambient temperature of the specimen to the preset target test temperature. After reaching the target temperature, enter the heat preservation state for 1–2 hours to ensure uniform temperature distribution within the specimen and achieve complete thermal equilibrium. Throughout the heating and heat preservation process, the system is equipped with an electric back pressure valve for automatic pressure regulation. The pressure threshold is set to 2.5MPa. When the system pressure exceeds this set value, the back pressure valve automatically opens to release pressure, thereby stabilizing the system pressure below 2.5MPa.

[0014] Step 5: Creep data acquisition: The temperature data of the thermocouple sensor, the pressure data of the pressure sensor, and the weld strain data of the strain gauge are continuously recorded at a sampling frequency of 1Hz through a multi-channel data acquisition system, and the load-time-strain relationship curve is generated simultaneously. Step 6: Test Termination and Unloading: When the preset termination conditions are met, stop the heating function of the temperature control system, and unload the pressure in the pipeline in stages according to the preset program through the pressure stabilizing component until the pressure drops to zero; after the fully welded plate heat exchanger specimen cools naturally to room temperature, the experiment ends. The preset termination conditions include any one of the following: the pressure sensor detects a sudden drop in load value exceeding 10% of the set threshold; or the strain gauge detects that the strain value in the weld area reaches the preset limit; or the cumulative test time reaches a predetermined value.

[0015] Furthermore, in step 1, the fully welded plate heat exchanger specimen is a heat exchanger core with a complete weld structure, which can reflect the geometric characteristics and material inhomogeneity of the weld under actual service conditions.

[0016] Furthermore, in step 4, the target test temperature is any set value within the range of 100℃ to 600℃, specifically determined according to the actual service temperature of the all-welded plate heat exchanger.

[0017] Furthermore, in step 5, the multi-channel data acquisition system monitors data fluctuations in real time while recording data; when the data fluctuation exceeds the preset allowable range, it automatically triggers an anomaly warning to remind the operator to check the system status.

[0018] The beneficial effects of this invention are as follows: 1. The experimental apparatus and method for creep testing of weld seams in fully welded plate heat exchangers, as described in this invention, simultaneously applies an adjustable high temperature of 100°C to 600°C and a constant pressure of 2.5 MPa. Combined with back pressure valve exhaust control, thermocouple precise temperature measurement, and pressure feedback adjustment of pressure stabilizing components, a thermo-mechanical coupled load simulation environment is constructed. This reproduces the actual service conditions of weld seams in fully welded plate heat exchangers, solving the problem that traditional uniaxial creep testing machines can only simulate a single load and static air environment, which is out of sync with the actual service conditions of the equipment and results in low reference value. 2. The experimental apparatus and method for creep testing of weld seams in fully welded plate heat exchangers described in this invention use a heat exchanger core with a complete weld seam structure conforming to industrial standards as the test object. Strain gauges with an accuracy of ±0.5%FS are directly monitored at key locations such as the main sealing weld seam between plates and the fillet weld seam of the inlet and outlet pipe seats. This captures the creep deformation law and damage evolution characteristics of the actual weld seam (including the heat-affected zone). This solves the problem that traditional tests use homogeneous material standard samples, which cannot reflect the geometric discontinuity of the weld seam, material inhomogeneity, and stress concentration effects, and cannot support the structural life assessment of the equipment. 3. The experimental apparatus and method for creep testing of weld seams in fully welded plate heat exchangers, as described in this invention, continuously records temperature, pressure, and strain data at a sampling frequency of 1Hz through a multi-channel data acquisition system, synchronously generates load-time-strain curves, and has an anomaly warning function, ensuring data integrity and reliability, and accurately extracting key performance parameters such as steady-state creep rate and creep fracture time. This solves the technical problems of discontinuous test data acquisition and incomplete parameter extraction in existing tests, which make it difficult to support the optimization of welding processes for fully welded plate heat exchangers and accurate prediction of the remaining service life of in-service equipment. Attached Figure Description

[0019] The invention will now be further described with reference to the accompanying drawings.

[0020] Figure 1 This is a flowchart illustrating the principle of the present invention; Figure 2 This is a schematic diagram of the installation of the experimental apparatus of the present invention; Figure 3 This is a flowchart of the experimental method of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figures 1-3 As shown, the experimental apparatus and method for creep testing of weld seams in a fully welded plate heat exchanger, according to the present invention, is based on "simulating thermo-mechanical coupled load + accurately monitoring creep behavior". Specifically, it includes a fully welded plate heat exchanger specimen, a pressure supply system, a temperature control system, strain measurement elements, and a multi-channel data acquisition system. These components work together to form a complete testing system. The pressure supply system consists of a water tank, pipelines, pressure stabilizing components, check valves, flow meters, pressure sensors, and back pressure valves. The pipelines connect the water tank to the inlet and outlet of the specimen to form a circulation path. The check valves prevent fluid backflow, the flow meters monitor flow stability, the pressure sensors collect inlet pressure in real time, the back pressure valves realize water injection, air release, and pressure boosting and sealing, and the pressure stabilizing components maintain a constant test pressure of 2.5 MPa based on feedback from the pressure sensors, providing a stable pressure load for the specimen. Temperature control system: includes a temperature controller and thermocouple sensors. The thermocouple sensors are placed on the surface of the specimen and the weld area to monitor the test temperature. The temperature controller adjusts the heating power based on thermocouple feedback to achieve a constant high temperature environment in the range of 100℃ to 600℃, providing a precise temperature load for the specimen. Strain measurement elements: High-precision strain gauges with an accuracy of ±0.5%FS are used and arranged at the main sealing weld between the plates of the specimen and the fillet weld of the inlet and outlet pipe seat to directly collect creep deformation data in the weld area; Multi-channel data acquisition system: Connects to pressure sensors, thermocouple sensors, and strain gauges, automatically records pressure, temperature, and strain data at a sampling frequency of 1Hz, synchronously generates load-time-strain relationship curves, and has an early warning function for abnormal data fluctuations to ensure the integrity and reliability of test data.

[0023] Experimental method scheme: The experimental method of this invention is based on the above-mentioned experimental apparatus and is implemented step by step according to the logic of "preparation-calibration-loading-monitoring-termination". The specific steps are as follows: Step 1: Specimen preparation and system installation: Select a heat exchanger core with complete welds that meets industrial standards as the specimen, clean the surface and check the integrity of the welds, connect the specimen to the pipelines and lines of the pressure supply system (water tank, check valve, etc.) and temperature control system (thermocouple, etc.), and ensure that the interface is sealed under high temperature and high pressure. Step 2: Sensor placement and system initialization: Place strain gauges at key welds, place thermocouples on the specimen surface and weld area, connect all sensors to the data acquisition system, and complete power-on self-test, zero-point calibration and signal path verification. Step 3: Pressure application and maintenance: Open the back pressure valve to inject water and vent air. After water is continuously flowing from the outlet, close the back pressure valve. Gradually increase the pressure to 2.5MPa through the pressure stabilizing component and enter the automatic holding mode. The pressure is maintained stable by relying on the feedback of the pressure sensor. Step 4: Temperature Field Establishment: Activate the temperature control system, set the heating rate to 5℃ / min, and gradually raise the ambient temperature of the specimen to the preset target test temperature. After reaching the target temperature, enter the heat preservation state for 1–2 hours to ensure uniform temperature distribution within the specimen and achieve complete thermal equilibrium. Throughout the heating and heat preservation process, the system is equipped with an electric back pressure valve for automatic pressure regulation. The pressure threshold is set to 2.5MPa. When the system pressure exceeds this set value, the back pressure valve automatically opens to release pressure, thereby stabilizing the system pressure below 2.5MPa.

[0024] Step 5: Creep Data Acquisition: Continuously record pressure, temperature, and strain data through the data acquisition system to generate load-time-strain curves; Step 6: Test termination and unloading: When any of the following situations occur, such as "load drop exceeding 10%, strain reaching the preset limit, or cumulative time reaching the predetermined value", heating is stopped and pressure is released in stages. The experiment ends after the specimen cools down.

[0025] To make the technical solution, operation process, and implementation effect of the present invention clearer and easier to understand, the following describes specific embodiments and... Figures 1-3 The experimental setup and testing procedures of this invention are described in detail below, and those skilled in the art can reproduce the testing process of this invention based on this embodiment.

[0026] The specific setup of the experimental apparatus: In this embodiment, all components of the experimental apparatus for testing the weld creep of the fully welded plate heat exchanger are selected from industrial-grade standard equipment. The specific specifications, models, and connection relationships are as follows: (I) Selection and parameters of core components: 1. Fully welded plate heat exchanger specimen: A 316L stainless steel fully welded plate heat exchanger core conforming to GB / T28712.3-2012 standard was selected as the test specimen. The plate thickness was 1.5mm, the corrugation type was herringbone (with an included angle of 60°), and a single core group contained 10 plates. The length of the main sealing weld between the plates was 800mm, and the diameter of the fillet weld of the inlet and outlet pipe seats was 50mm. Before installation, the surface of the test specimen was wiped with acetone to remove oil stains, and the weld was checked by penetrant testing (PT) to ensure that there were no defects such as cracks and pores.

[0027] 2. Pressure supply system: Water tank: 50L capacity, made of 304 stainless steel, equipped with a level gauge and water inlet to ensure sufficient fluid during the experiment; Piping: Φ20mm 316L stainless steel pipe, pressure rating ≥10MPa, and graphite gaskets are used to seal the joints (high temperature resistance ≤650℃). Check valve: nominal pressure 1.6MPa, medium temperature ≤600℃, installed on the pipeline from the water tank outlet to the test piece inlet to prevent fluid backflow from disrupting pressure stability; Flow meter: An electromagnetic flow meter is selected, with a measurement range of 0.1-10 m³ / h and an accuracy of ±0.5%. It is installed on the inlet and outlet pipes of the test specimen to monitor the fluid circulation flow rate in real time. Pressure sensor: Measurement range 0-25MPa, accuracy ±0.1%FS, installed on the inlet pipeline of the test specimen (100mm from the inlet flange), providing feedback on the pipeline pressure; Back pressure valve: Adjustment range 0-5MPa, medium temperature ≤600℃, installed on the pipeline from the specimen outlet to the water tank, used for water injection, air release and pressure boosting and sealing; Pressure stabilizing component: An electro-hydraulic servo pressure stabilizing valve is adopted, with a response time of ≤0.1s. It can automatically adjust the pressure according to the feedback signal of the pressure sensor to maintain a constant pressure of 2.5MPa in the pipeline.

[0028] 3. Temperature control system: Temperature controller: Temperature control range 0-800℃, accuracy ±1℃, supports programmed temperature rise (temperature rise gradient of 5℃ / min can be set). Heating element: A wound electric heating belt (power 2kW / m) is used, which is wrapped around the outside of the specimen core, and the heating power is controlled by a temperature controller; Thermocouple sensors: Measurement range -200-1300℃, accuracy ±2.5℃, a total of 6 are arranged - 4 of which are attached to the main sealing weld between the plates (evenly distributed along the length of the weld), and 2 are attached to the fillet weld of the inlet and outlet pipe seats, used to monitor the temperature of key areas of the test piece.

[0029] 4. Strain measurement element and data acquisition system: Strain gauge: Grid length 3mm, sensitivity coefficient 2.08±1%, working temperature ≤600℃, a total of 8 gauges are bonded - 3 gauges on each side of the main sealing weld (spaced 200mm), 1 gauge on each side of the pipe seat fillet weld. Before bonding, the weld surface is sanded (roughness Ra≤1.6μm), and fixed with high temperature adhesive (model CH-311); Multi-channel data acquisition system: 32 channels, sampling frequency 0-10kHz (set to 1Hz in this embodiment), supports synchronous acquisition of pressure, temperature and strain signals, can automatically generate "load-time-strain" relationship curve, and triggers audible and visual warning when data fluctuation exceeds ±5% (preset threshold).

[0030] (ii) Device connection relationship (e.g.) Figure 2 (as shown) Fluid circuit: Water tank outlet → check valve → inlet flow meter → pressure sensor → specimen inlet → internal flow channel of specimen → specimen outlet → outlet flow meter → back pressure valve → water tank inlet, forming a closed loop; Control and monitoring circuitry: The output of the temperature controller is connected to the heating belt, and the input is connected to 6 thermocouple sensors; the input of the multi-channel data acquisition system is connected to the pressure sensor, 8 strain gauges, and 6 thermocouple sensors respectively, and the output is connected to the computer (for data storage and analysis); the signal end of the pressure stabilizing component is connected to the pressure sensor and the data acquisition system to realize closed-loop pressure control.

[0031] II. Specific operating procedures for the experimental test: This embodiment takes "simulated weld creep test of 316L stainless steel fully welded plate heat exchanger under operating conditions of 450℃ and 2.5MPa" as an example. The specific operation is as follows: (1) Specimen preparation and system installation: 1. Hoist the heat exchanger specimen that has passed the PT test to the test bench (the bench can bear a load of ≥500kg) and adjust the levelness of the specimen (the deviation is ≤0.1mm / m). 2. Install pipes and lines according to the above "device connection relationship". Tighten all pipe joints with a torque wrench. Protect the signal lines of strain gauges and thermocouple sensors with high-temperature resistant sleeves (temperature resistance ≤600℃) to avoid direct contact with heating wires. 3. Perform an airtightness test on the entire fluid circuit: Close the back pressure valve, pressurize the pipeline to 3MPa through the pressure stabilizing component, maintain the pressure for 30 minutes, and observe the pressure sensor reading—if the pressure drop is ≤0.05MPa, the seal is qualified. If there is leakage, tighten the interface again or replace the sealing gasket.

[0032] (2) Sensor placement and system initialization: 1. After confirming that the strain gauges and thermocouple sensors are firmly attached, turn on the power of the multi-channel data acquisition system, perform zero-point calibration on all strain gauges (zeroing error ≤ ±2με), and perform temperature calibration on the thermocouple sensors (compared with a standard thermometer, error ≤ ±1℃). 2. Start the temperature controller and voltage regulator and perform a system self-test: Set the temperature controller to a small-range temperature rise cycle of "room temperature → 50℃ → room temperature" to verify that the heating belt and thermocouple are working properly; set the voltage regulator to a pressure cycle of "0 → 1MPa → 0" to verify that the pressure sensor and back pressure valve are responding properly.

[0033] (3) Pressure application and maintenance: 1. Slowly open the back pressure valve (50% opening), start the pressure stabilizing component to inject water into the fluid circuit (water injection rate 0.5m³ / h), and observe the outlet flow meter and outlet pipeline. When water flows continuously from the outlet for 5 minutes and no air bubbles are discharged, it is determined that the air in the pipeline has been purged. 2. Close the back pressure valve and gradually increase the pressure to 2.5 MPa at a rate of 0.2 MPa / min through the pressure stabilizing component. During the pressure increase process, monitor the pressure sensor reading and the appearance of the specimen in real time (no abnormal deformation or leakage). 3. Once the pressure reaches 2.5MPa, the pressure stabilizing component switches to "automatic holding mode" and adjusts the valve opening based on real-time feedback from the pressure sensor (sampling interval 0.1s) to maintain pressure fluctuation ≤ ±0.02MPa.

[0034] (4) Temperature field establishment: 1. Set the heating program in the temperature controller: raise the temperature from room temperature to 450℃ at a rate of 5℃ / min, and then enter the heat preservation mode after reaching 450℃ for 1.5 hours. 2. During the heat preservation process, the temperature values ​​of 6 thermocouples are monitored in real time through the data acquisition system. When the deviation of all thermocouple readings is ≤2℃, the specimen is judged to have reached thermal equilibrium (if the deviation exceeds 2℃, the heating belt power is adjusted locally to compensate for the temperature).

[0035] 3. During the heating process, when the pharmacological pressure exceeds the set value, the back pressure valve automatically opens to release pressure, maintaining the system pressure at 2.5MPa.

[0036] (5) Creep data acquisition: 1. After the pressure stabilizes, activate the "continuous acquisition" function of the multi-channel data acquisition system and record the following data at a sampling frequency of 1Hz: Pressure data: Real-time pressure values ​​from the pressure sensor; Temperature data: Real-time temperature values ​​of 6 thermocouples (average value is taken as the overall temperature of the specimen); Strain data: Real-time strain values ​​of 8 strain gauges (with a focus on strain changes in the main sealing weld). 2. During the experiment, data is exported every 24 hours to generate a "time-strain" curve and observe the strain evolution trend of the weld (initial rapid deformation → mid-term steady-state deformation → late-term accelerated deformation). If abnormal fluctuations occur in the data (such as a sudden increase in strain of 10%), the system sealing and sensor connection status should be checked immediately.

[0037] (6) Test termination and unloading: 1. In this embodiment, "cumulative test time of 1000 hours" is set as the termination condition. When the data acquisition system displays that the test time has reached 1000 hours, the termination command is automatically triggered. 2. Perform the unloading process: First, turn off the heating belt and set the cooling program from 450℃ to room temperature using the temperature controller (cooling rate 3℃ / min to avoid thermal stress on the specimen due to excessive temperature difference); at the same time, the pressure stabilizing component gradually depressurizes at a rate of 0.1MPa / min until the pressure drops to 0MPa. 3. After the specimen has cooled naturally to room temperature (temperature difference from the environment ≤ 5℃), turn off the power to all equipment, remove the sensors and pipelines, and perform a second PT test on the weld of the specimen. Compare the changes in weld defects before and after the test to verify the creep damage.

[0038] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An experimental apparatus for creep testing of weld seams in fully welded plate heat exchangers, characterized in that, The system includes a fully welded plate heat exchanger specimen, a pressure supply system for applying and maintaining pressure inside the specimen, a temperature control system for providing a high-temperature environment to the specimen, a strain measurement element arranged in the weld area of ​​the specimen, and a data acquisition system that is signal-connected to the pressure supply system, the temperature control system, and the strain measurement element, respectively. The pressure supply system and the temperature control system work together to simulate the thermo-mechanical coupling load of actual service in the weld area of ​​the specimen. The data acquisition system is used to record pressure, temperature, and strain data to monitor the creep behavior of the weld.

2. The experimental apparatus for creep testing of weld seams in a fully welded plate heat exchanger according to claim 1, characterized in that, The pressure supply system includes a water tank, pipelines, pressure stabilizing components, check valve, flow meter, pressure sensor, and back pressure valve; The pipeline is used to connect the inlet and outlet of the water tank and the fully welded plate heat exchanger specimen to form a fluid circulation path; The check valve is installed on the pipeline from the water tank to the inlet of the test specimen to prevent backflow of fluid in the pipeline; The flow meters are respectively installed on the inlet and outlet pipelines of the test specimen to monitor the fluid flow rate in the pipeline; The pressure sensor is installed on the pipeline at the inlet of the specimen to collect the pressure value in the pipeline in real time. The back pressure valve is located on the pipeline from the specimen outlet to the water tank. It is used to discharge air from the pipeline during the water injection stage and to close the pipeline during the pressurization stage to establish a stable pressure environment. The pressure stabilizing component adjusts the pressure based on the feedback signal from the pressure sensor to maintain stable pressure within the pipeline, thereby providing continuous pressure to the interior of the specimen.

3. The experimental apparatus for creep testing of weld seams in a fully welded plate heat exchanger according to claim 1, characterized in that, The temperature control system includes a temperature controller and a thermocouple sensor; the thermocouple sensor is used in conjunction with the surface and weld area of ​​the fully welded plate heat exchanger specimen to monitor temperature data at different locations of the specimen; the temperature controller is connected to the thermocouple sensor signal and adjusts the heating power based on the temperature data fed back by the thermocouple sensor, so that the ambient temperature of the specimen can be kept constant within a set range.

4. The experimental apparatus for creep testing of weld seams in a fully welded plate heat exchanger according to claim 3, characterized in that, The temperature control system has a temperature control range of 100℃ to 600℃, and the pressure stabilizing component in the pressure supply system can maintain the pressure in the pipeline at the rated test pressure of 2.5MPa.

5. The experimental apparatus for creep testing of weld seams in a fully welded plate heat exchanger according to claim 1, characterized in that, The strain measurement element is a high-precision strain gauge; the strain gauge is arranged at least at the main sealing weld between the plates and the fillet weld of the inlet and outlet pipe seats of the fully welded plate heat exchanger specimen; the strain gauge is used to collect creep deformation data in the weld area.

6. The experimental apparatus for creep testing of weld seams in a fully welded plate heat exchanger according to claim 1, characterized in that, The data acquisition system is a multi-channel data acquisition system; the data acquisition system automatically records the pressure data collected by the pressure sensor, the temperature data collected by the thermocouple sensor, and the strain data collected by the strain gauge, and synchronously generates the load-time-strain relationship curve; The data acquisition system also includes a data anomaly fluctuation early warning function, which triggers an early warning when data is detected to exceed a preset allowable range.

7. An experimental method for creep testing of weld seams in fully welded plate heat exchangers, applicable to the experimental apparatus for creep testing of weld seams in fully welded plate heat exchangers as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Specimen Preparation and System Installation: Select a fully welded plate heat exchanger that meets industrial manufacturing standards as the test specimen. Clean the surface of the specimen and check the integrity of the welds. Install the specimen into the experimental device frame. Connect the specimen to the water tank, check valve, flow meter, pressure sensor and back pressure valve of the pressure supply system through pipelines. At the same time, connect the specimen to the thermocouple sensor circuit of the temperature control system and the signal circuit of the strain measurement element, ensuring that each interface meets the high temperature and high pressure sealing requirements. Step 2: Sensor arrangement and system initialization: Strain gauges are arranged at the main sealing weld between the plates of the specimen and at the fillet weld of the inlet and outlet pipe seats. Thermocouple sensors are arranged on the surface of the specimen and in the weld area. The strain gauges, thermocouple sensors and pressure sensors are all connected to the multi-channel data acquisition system. Complete the system power-on self-test, perform zero-point calibration on the sensor, and verify the stability of the signal path; Step 3: Pressure Application and Maintenance: Open the back pressure valve of the pressure supply system, start the pressure stabilizing component to continuously inject water into the pipeline until water continuously flows out of the specimen outlet pipeline to expel residual air in the pipeline; close the back pressure valve, and gradually increase the pressure in the pipeline at the set rate until the internal pressure of the fully welded plate heat exchanger specimen reaches the rated test pressure of 2.5MPa; after the pressure reaches the standard, the system enters the automatic pressure maintenance mode, and adjusts the pressure stabilizing component through real-time feedback from the pressure sensor to maintain pressure stability; Step 4: Temperature Field Establishment: Activate the temperature control system, set the heating rate to 5℃ / min, and gradually raise the ambient temperature of the specimen to the preset target test temperature. After reaching the target temperature, enter the heat preservation state for 1–2 hours to ensure uniform temperature distribution within the specimen and achieve complete thermal equilibrium. Throughout the heating and heat preservation process, the system is equipped with an electric back pressure valve for automatic pressure regulation. The pressure threshold is set to 2.5MPa. When the system pressure exceeds this set value, the back pressure valve automatically opens to release pressure, thereby stabilizing the system pressure below 2.5MPa. Step 5: Creep data acquisition: Through a multi-channel data acquisition system, continuously record the temperature data from the thermocouple sensor, the pressure data from the pressure sensor, and the weld strain data from the strain gauge, and simultaneously generate load-time-strain relationship curves; Step 6: Test Termination and Unloading: When the preset termination conditions are met, stop the heating function of the temperature control system, and unload the pressure in the pipeline in stages according to the preset program through the pressure stabilizing component until the pressure drops to zero; after the fully welded plate heat exchanger specimen cools naturally to room temperature, the experiment ends. The preset termination conditions include any one of the following: the pressure sensor detects a sudden drop in load value exceeding 10% of the set threshold; or the strain gauge detects that the strain value in the weld area reaches the preset limit; or the cumulative test time reaches a predetermined value.

8. The experimental method for creep testing of weld seams in a fully welded plate heat exchanger according to claim 7, characterized in that, In step 1, the fully welded plate heat exchanger specimen is a heat exchanger core with a complete weld structure.

9. The experimental method for creep testing of weld seams in a fully welded plate heat exchanger according to claim 7, characterized in that, In step 4, the target test temperature is any set value within the range of 100℃ to 600℃, specifically determined according to the actual service temperature of the all-welded plate heat exchanger.

10. The experimental method for creep testing of weld seams in a fully welded plate heat exchanger according to claim 7, characterized in that, In step 5, the multi-channel data acquisition system records data while monitoring data fluctuations in real time; when the data fluctuation exceeds the preset allowable range, it automatically triggers an anomaly warning.

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