Evaluation method of welding quality of pressure transmitter flange diaphragm based on failure physics

Abstract

The present invention provides a method for evaluating the welding quality of the diaphragm of the pressure transmitter flange based on failure physics, including: performing non-destructive evaluation and testing, the non-destructive evaluation and testing is used to evaluate whether the diaphragm and the weld meet the preset quality requirements through the appearance of the diaphragm and the weld; performing destructive evaluation and testing, the destructive evaluation and testing is to perform microscopic analysis and observation from the diaphragm damage mechanism and the weld failure mechanism through destructive physical analysis, so as to evaluate the quality and reliability of the diaphragm and the weld at the ultimate strength and microscopic level; testing through a mixed stress accelerated test, the mixed stress accelerated test is based on the failure mechanism of the diaphragm and the weld, and the real use environment on site is simulated by mixed stress to perform accelerated testing, so that the life and long-term reliability of the diaphragm and the weld can be quickly evaluated. The present invention can systematically and comprehensively determine and verify the welding quality of the membrane seat assembly.

Description

Technical Field

[0001] The invention relates to a pressure transmitter, and in particular to a method for evaluating the welding quality of a flange diaphragm of a pressure transmitter based on failure physics. Background Art

[0002] Pressure transmitters are mainly used in industries such as petrochemicals, metallurgy, medicine, light industry, and electric power to measure industrial process control parameters such as pressure, differential pressure, flow, liquid level, and density of various fluids. The pressure sensing membrane seat assembly is made of a 0.08mm thick diaphragm and a corrugated flange base by precision welding. In practical applications, the membrane seat assembly is in direct contact with the measured medium, and it is necessary to measure and transmit pressure signals in special environments such as high temperature, low temperature, corrosion, vibration, or shock, and require high precision and high stability of the measurement. Therefore, the welding quality requirements for the diaphragm and flange base are relatively high.

[0003] The welded membrane seat assembly is usually leak tested using a helium mass spectrometer. If the leak rate is within the allowable range, the welding is considered qualified.

[0004] The current welding detection technology only performs helium leak detection on the membrane seat assembly after welding, which has the following disadvantages:

[0005] 1. It can only judge whether the sealing of the components is qualified, but does not start from the weld itself, and effectively inspect and evaluate the metal bonding quality after welding;

[0006] 2. If the sealing of the component is not up to standard, it is impossible to accurately locate the leakage point and determine the cause of the leakage;

[0007] 3. Existing methods are limited to assessing the current status of products and cannot reflect product life and reliability in actual applications;

[0008] 4. When conducting stress tests, only a single stress can be used, which cannot effectively simulate the actual situation on site.

[0009] In summary, the above shortcomings make it impossible for existing methods and technologies to systematically and comprehensively determine and verify the welding quality of the membrane seat assembly. Summary of the invention

[0010] In view of the defects in the prior art, the object of the present invention is to provide a method for evaluating the welding quality of the flange diaphragm of a pressure transmitter based on failure physics.

[0011] The method for evaluating the welding quality of the flange diaphragm of a pressure transmitter based on failure physics provided by the present invention includes:

[0012] Step S1: performing a non-destructive evaluation test, wherein the non-destructive evaluation test is used to evaluate whether the diaphragm and the weld meet the preset quality requirements through the appearance of the diaphragm and the weld;

[0013] Step S2: performing a destructive evaluation test, wherein the destructive evaluation test is to conduct microscopic analysis and observation of the diaphragm damage mechanism and the weld failure mechanism through destructive physical analysis, so as to evaluate the quality and reliability of the diaphragm and the weld at the ultimate strength and microscopic level;

[0014] Step S3: Testing is performed through a mixed stress accelerated test. The mixed stress accelerated test is based on the failure mechanism of the diaphragm and the weld. The mixed stress is used to simulate the actual use environment on site to perform accelerated testing, so that the life and long-term reliability of the diaphragm and the weld can be quickly evaluated.

[0015] Preferably, the non-destructive evaluation test includes any one or more of appearance inspection, sealing test, penetration test and X-ray flaw detection test.

[0016] Preferably, the destructive evaluation test includes an ultimate pressure resistance test and / or a metallographic test.

[0017] Preferably, the mixed stress accelerated test includes a pressurized temperature cycle mixed test and a pressure cycle high temperature mixed test.

[0018] Preferably, the appearance inspection includes observing whether there are pores, slag inclusions, spatter, cracks, and penetration on the weld surface, and whether the weld has a smooth transition, a uniform and fine weld wave, and a straight joint and a consistent width.

[0019] Preferably, the sealing test adopts a tracer gas method.

[0020] Preferably, the ultimate pressure test is specifically performed by applying pressure from the outside and from the inside, adjusting the pressure value until the weld or the diaphragm ruptures, and stopping, recording the process pressure value and the corresponding diaphragm or weld change status, so as to verify the pressure resistance and sealing ability of the diaphragm and the weld.

[0021] Preferably, the metallographic test includes two parts: sectioning and microscopic observation;

[0022] The slicing is specifically to perform cross-sectional cutting on the membrane seat assembly, and grind, polish and erode to prepare a cross-sectional sample of the weld;

[0023] The microscopic observation is an inspection performed by optical instruments to display the macroscopic and microscopic characteristics of the weld metal through macroscopic and microscopic inspections.

[0024] Preferably, the mixed stress includes cyclic stress and constant stress, wherein the cyclic stress will cause fatigue failure of the diaphragm and the weld, and the constant stress will cause creep failure of the material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention conducts systematic and comprehensive inspections on the diaphragm welding quality in multiple dimensions and by multiple means, from non-destructive analysis to destructive analysis, from characterization inspection to internal defect inspection, and uses mixed stress to conduct accelerated aging tests to verify the reliability level of the diaphragm and welding process in long-term operation in actual environments, thereby systematically and comprehensively determining and verifying the welding quality of the membrane seat assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0028] Figure 1 It is a flowchart of the steps of a method for evaluating the welding quality of a pressure transmitter flange diaphragm based on failure physics in an embodiment of the present invention;

[0029] Figure 2 This is a flow chart based on failure physics assessment in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0031] Figure 1 FIG. 1 is a flow chart of the steps of a method for evaluating the welding quality of a pressure transmitter flange diaphragm based on failure physics in an embodiment of the present invention. Figure 1 As shown, in the embodiment of the present invention, nondestructive analysis and destructive analysis are performed on the flange diaphragm of the pressure transmitter and the weld formed after the flange diaphragm and the flange base are welded. Based on the failure mechanism of the weld failure and the diaphragm damage, a set of systematic evaluation methods for the quality of the flange diaphragm and its weld from micro to macro are obtained. In the embodiment of the present invention, the evaluation method for the welding quality of the flange diaphragm of the pressure transmitter based on failure physics provided by the present invention includes the following steps:

[0032] Step S1: non-destructive evaluation and testing, wherein the non-destructive evaluation and testing includes any one or more of appearance inspection, sealing test, penetration test and X-ray flaw detection inspection, and the non-destructive evaluation and testing is used to ensure the basic quality requirements of the diaphragm and the weld;

[0033] Step S2: destructive evaluation and testing, wherein the destructive evaluation and testing includes an ultimate withstand voltage test and / or a metallographic test. The destructive evaluation and testing is used to conduct microscopic analysis and observation of the diaphragm damage mechanism and the weld failure mechanism through destructive physical analysis, thereby evaluating the quality and reliability of the diaphragm and the weld at the ultimate strength and microscopic level;

[0034] Step S3: Testing is performed through a mixed stress accelerated test. The mixed stress accelerated test is based on the failure mechanism of the diaphragm and the weld. The mixed stress is used to simulate the actual use environment on site to perform accelerated testing, so that the life and long-term reliability of the diaphragm and the weld can be quickly evaluated. The mixed stress accelerated test includes a pressurized temperature cycle mixed test and a pressure cycle high temperature mixed test.

[0035] When using the method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics provided by the present invention, the diaphragm and the weld are first tested in a non-destructive manner to perform a preliminary screening of basic quality requirements, such as:

[0036] Carry out basic appearance inspection on the diaphragm weld after welding to observe whether there are pores, slag inclusions, spatter, cracks, and penetration on the weld surface, and whether the weld transition is smooth, the weld wave is uniform and fine, the joint is straight, and the width is consistent;

[0037] After the appearance inspection, the welded membrane seat assembly is subjected to a sealing test. In the present invention, the tracer gas method is used to inspect the sealing of the assembly welding;

[0038] To ensure the accuracy of the inspection, based on the capillary phenomenon of the liquid and the X-ray characteristics, penetration tests and X-ray flaw detection are used to further detect defects on the weld surface such as cracks and pores.

[0039] Secondly, the diaphragm and weld are tested through destructive analysis. The purpose is to observe the diaphragm damage mechanism and weld welding mechanism, so as to evaluate the quality and reliability of the diaphragm and weld at the ultimate strength and micro level, as described below:

[0040] After completing the non-destructive analysis, the welded membrane seat assembly is subjected to an ultimate pressure test, using external and internal pressure, respectively. The pressure value is adjusted according to the characteristics of the diaphragm material and design requirements until the weld or diaphragm ruptures. The pressure value of the process and the corresponding diaphragm or weld change are recorded to verify the pressure resistance and sealing ability of the diaphragm and weld.

[0041] The metallographic test includes two parts: sectioning and microscopic observation. The membrane seat assembly is cut into sections, and then properly ground, polished and etched. After the cross-sectional specimen of the weld is prepared, low-power and high-power inspections are performed with the help of optical instruments. Macroscopic and microscopic inspections are used to display the macroscopic and microscopic characteristics of the weld metal.

[0042] If any abnormality is found in the diaphragm and weld in any of the above methods, a targeted metallographic analysis of the weld cross section is required at the abnormal position; if no abnormality is found in the above methods, a metallographic analysis is still required based on the welding process of the diaphragm and weld or possible weak points.

[0043] Finally, based on the failure mechanism of the diaphragm and weld, the accelerated test is carried out by simulating the actual use environment on site through mixed stress, and the performance of the test samples in the test is observed, so that the life and long-term reliability of the diaphragm and weld can be quickly evaluated. Mixed stress includes cyclic stress and constant stress, among which cyclic stress will cause fatigue failure of the diaphragm and weld, and constant stress will cause creep failure of the material. It is mainly reflected by two methods: pressurized temperature cycle mixed test and pressure cycle high temperature mixed test.

[0044] The theoretical model of the mixed stress accelerated test is as follows:

[0045] During the elastic deformation stage of the diaphragm and weld, no damage occurs during the cyclic loading process. After entering the plastic deformation stage, each stress cycle will cause a certain amount of plastic deformation (damage / degradation) of the material. The damage to the diaphragm and weld will continue to accumulate with the increase in the number of cycles until complete fatigue failure. Since the damage of the material after a stress cycle depends on the plastic deformation Δε pl The size of can be expressed by the power law model to represent the number of cycles to fatigue failure, that is, the fatigue life CTF:

[0046] CTF=B0(Δε pl ) -n ……(1)

[0047] The above formula is called the Coffin-Manson model, which is generally used for low-cycle fatigue, that is, CTF is less than 10 4 Second, plastic deformation Δε pl Bigger fatigue issues.

[0048] According to the actual use on site, the constant stress considered in the present invention includes two factors: pressure and temperature. Both pressure level and temperature will cause creep in the material, and its strain will gradually increase with time, causing the strength of the diaphragm and the weld to gradually decrease, eventually leading to failure of the diaphragm and the weld. In the stable creep stage, the function of creep strain changing with time ε(t) is:

[0049]

[0050] It can be seen from the above formula that the creep rate dε / dt is very important and can be expressed as

[0051]

[0052] The creep process can continue until failure occurs, and the time corresponding to failure is the failure time. Failure time (TF) refers to the time required for the total creep deformation to exceed a certain limit value (such as failure of the diaphragm and weld), t = TF, that is,

[0053]

[0054] According to formulas (3) and (4), the failure time can be obtained

[0055]

[0056] A0 and B0 are coefficients related to materials and processing technology; ε0 is the initial creep; σ is the stress, σ yield is the yield stress, which can be ignored when it is lower than σ; Q is the activation energy; K B is the Boltzmann constant; T is the temperature; the value of n can be found in Appendix Table 1.

[0057] Table 1 n values ​​of different materials

[0058] Material n Softer, less strong materials (such as lead solder and sticky glass) 1～3 Materials of average strength (such as mild steel and metal compounds) 3～6 Very strong materials and brittle materials (such as hardened steel and ceramics) 6～9

[0059] By collecting failure time data under accelerated stress conditions and extrapolating these data to actual use conditions, the failure time of the product under future service conditions can be quickly obtained. The expected failure time TF under normal conditions op Failure time TF under specific accelerated stress conditions stress The ratio of is the acceleration factor AF:

[0060]

[0061] Similarly,

[0062]

[0063] Based on the mixed stress failure mechanism, the failure mechanism acceleration model is used to design corresponding accelerated tests, which can effectively evaluate the life and reliability of diaphragms and welds.

[0064] In the embodiment of the present invention, the appearance inspection, i.e., visual inspection, specifically includes:

[0065] Inspection object: diaphragm weld after welding;

[0066] Inspection purpose: Observe whether there are pores, slag inclusions, spatter, cracks, and penetration on the weld surface, and whether the weld transition is smooth, the weld wave is uniform and fine, the joint is straight, and the width is consistent;

[0067] Evaluation basis: Observe the weld surface at 5X to 10X magnification. No obvious pores, slag inclusions, spatter, cracks, or penetration are observed. The weld transition is smooth, the weld wave is uniform and fine, the joint is straight, and the width is consistent.

[0068] The sealing test, namely the tracer gas method, specifically includes:

[0069] Inspection object: membrane seat assembly after welding;

[0070] Inspection purpose: To inspect the tightness of the welding joint of the test sample;

[0071] Basic principle: When the sealing surface of the sample leaks, the tracer gas helium and other gases will leak out from the leak hole. After the leaked gas enters the helium mass spectrometer leak detector, the leak detector has the selective identification ability, so it only gives the partial pressure signal of helium in the gas. On the basis of obtaining the helium signal value, the helium leakage amount can be obtained by comparing with the standard leakage amount;

[0072] Assessment basis: When the leak rate detected does not exceed 1.0×10 -8 Pa·m 3 / s, the inspected area is qualified.

[0073] The specific contents of the penetration test are as follows:

[0074] Inspection object: diaphragm weld after welding;

[0075] Inspection purpose: used to detect defects on the weld surface such as cracks, pores, etc.

[0076] Basic principle: Based on the wetting ability of liquid on solid and capillary phenomenon in physics, a liquid penetrant containing dye and with high penetration ability is first applied to the surface of the material to be tested. The penetrant penetrates into the open defects on the surface, and then the excess penetrant on the surface is removed. A layer of developer with strong adsorption capacity is applied to adsorb the penetrant in the defect to the surface, and the traces of the defect will be shown on the developer.

[0077] Evaluation basis: The product is qualified if there are no cracks or holes.

[0078] The withstand voltage test specifically includes:

[0079] Inspection object: membrane seat assembly after welding;

[0080] Inspection purpose: To inspect the compressive strength and sealing ability of the tested samples after welding;

[0081] Test method and evaluation basis: Observe the changes of the weld or diaphragm according to the increase of pressure value, and record the corresponding pressure value when the change occurs, and take photos of the changes of the weld or diaphragm. As shown in the following table:

[0082] Table 1 Pressure test method and evaluation basis

[0083]

[0084] Metallographic test, the specific contents are:

[0085] Inspection object: weld section;

[0086] Inspection purpose: To observe the macrostructure and microstructure of the weld cross section, and to observe the presence of welding defects such as cracks, voids, and lack of fusion;

[0087] Test method: Cut the membrane seat assembly into sections, grind, polish and erode appropriately, prepare the cross-section specimen of the weld, and then perform low-power and high-power inspections with the aid of optical instruments. Use macroscopic and microscopic inspections to show the macroscopic and microscopic properties of the weld metal. If necessary, use an EDS energy spectrum analyzer to perform component analysis on the structure of each area of ​​the weld cross section to confirm the metal fusion situation;

[0088] Evaluation basis: The product is qualified if there are no abnormalities such as cracks, looseness, pores, solid inclusions, and incomplete penetration between layers.

[0089] The high and low temperature impact test is specifically implemented as follows:

[0090] Inspection object: membrane seat assembly after welding;

[0091] Inspection purpose: To simulate the performance of the test sample in an extremely harsh temperature environment, verify the process quality of diaphragm welding, and discover and improve defects in advance;

[0092] Test method: temperature range -40℃~150℃, high and low temperature dwell time 30min, temperature conversion time 10℃ / min, and pressurize the inside of the mold base assembly (the pressurization strength is determined in combination with the pressure resistance test results and application conditions), test round 300 cycles (test time is determined according to the product service life);

[0093] Assessment basis: Take 2 nodes (150 rounds and 300 rounds) and conduct tests on items one to five respectively. Before testing, the samples must be placed at room temperature for 1 hour or until the temperature stabilizes. After passing the test, continue the test and discard those that fail until the end of the test.

[0094] In the embodiment of the present invention, a layer-by-layer progressive analysis and verification is performed from the outside to the inside, from the macroscopic to the microscopic. First, the appearance of the weld formation is observed to complete the preliminary screening; secondly, the membrane seat assembly is subjected to a sealing test, a weld penetration test, an X-ray flaw detection test, and a pressure test to further verify the density, surface defects, and pressure resistance of the weld; finally, a metallographic test is performed on the cross-section of the weld to observe the macroscopic and microscopic structures of the weld area to determine the fusion status of each area of ​​the weld;

[0095] The method proposed by the present invention is easier to find abnormal features and locations, and conduct failure analysis in a directional manner. If abnormalities are found in appearance inspection, sealing test, penetration test, etc., targeted weld metallographic analysis can be performed based on abnormal morphology, defect location, etc.

[0096] The prior art only applies a single stress, and the test evaluation results are far from the on-site application conditions. The present invention is based on the failure mechanism of the diaphragm and the weld, and ensures that no new failure mechanism is introduced. It conducts accelerated aging tests by using two methods: pressurizing and conducting high and low temperature shock tests, and high temperature and pressure cycle mixed tests. These two methods simulate the actual on-site application conditions, and can more objectively reflect the product life and reliability, and further evaluate the quality of the diaphragm's own material and the diaphragm weld in the actual environment for long-term operation.

[0097] In summary, in order to improve the shortcomings of the existing technology, the welding quality of the membrane seat assembly should be inspected more systematically, comprehensively, efficiently and accurately, the welding process should be continuously optimized, and product reliability should be improved.

[0098] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for evaluating the welding quality of flange diaphragm of pressure transmitter based on failure physics, characterized in that: include: Step S1: performing a non-destructive evaluation test, wherein the non-destructive evaluation test is used to evaluate whether the diaphragm and the weld meet the preset quality requirements through the appearance of the diaphragm and the weld; Step S2: performing a destructive evaluation test, wherein the destructive evaluation test is to conduct microscopic analysis and observation of the diaphragm damage mechanism and the weld failure mechanism through destructive physical analysis, so as to evaluate the quality and reliability of the diaphragm and the weld at the ultimate strength and microscopic level; Step S3: Testing is performed through a mixed stress accelerated test, wherein the mixed stress accelerated test is based on the failure mechanism of the diaphragm and the weld, and the mixed stress is used to simulate the actual use environment on site to perform an accelerated test, thereby quickly evaluating the life and long-term reliability of the diaphragm and the weld; The mixed stress accelerated test includes a pressurized temperature cycle mixed test and a pressure cycle high temperature mixed test; the pressure cycle high temperature mixed test is an experiment of simultaneously performing pressure cycle at high temperature, and the pressurized temperature cycle mixed test is an experiment of simultaneously performing high and low temperature shock at pressurization; The mixed stress includes cyclic stress and constant stress, wherein the cyclic stress will cause fatigue failure of the diaphragm and the weld, and the constant stress will cause creep failure of the material.

2. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 1 is characterized in that: The non-destructive evaluation test includes any one or more of appearance inspection, sealing test, penetration test and X-ray flaw detection.

3. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 1 is characterized in that: The destructive evaluation test includes an ultimate pressure resistance test and / or a metallographic test.

4. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 2 is characterized in that: The appearance inspection includes observing whether there are pores, slag inclusions, spatter, cracks, and penetration on the weld surface, whether the weld transition is smooth, the weld wave is uniform and fine, the joint is straight, and the width is consistent.

5. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 2 is characterized in that: The sealing test adopts the tracer gas method.

6. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 3 is characterized in that: The ultimate pressure test specifically adopts external and internal pressurization methods, adjusts the pressure value until the weld or diaphragm ruptures, and stops, records the process pressure value and the corresponding diaphragm or weld change status, so as to verify the pressure resistance and sealing ability of the diaphragm and weld.

7. The method for evaluating the welding quality of the pressure transmitter flange diaphragm based on failure physics according to claim 3 is characterized in that: The metallographic test includes two parts: sectioning and microscopic observation; The slicing is specifically to perform cross-sectional cutting on the membrane seat assembly, and grind, polish and erode to prepare a cross-sectional sample of the weld; The microscopic observation is an inspection performed by optical instruments to display the macroscopic and microscopic characteristics of the weld metal through macroscopic and microscopic inspections.

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