CN115931422A - Sampling method and analysis method for internal cracks of welding joint - Google Patents
Sampling method and analysis method for internal cracks of welding joint Download PDFInfo
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- CN115931422A CN115931422A CN202310044564.4A CN202310044564A CN115931422A CN 115931422 A CN115931422 A CN 115931422A CN 202310044564 A CN202310044564 A CN 202310044564A CN 115931422 A CN115931422 A CN 115931422A
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Abstract
The invention discloses a method for sampling internal cracks of a welding joint, which comprises the following steps: acquiring the position and the size of the internal crack in the welding joint, and setting an integral sampling area and a metallographic sampling area according to the position and the size; taking out the integral sampling area from the pressure vessel, and then taking out the gold-phase-containing sampling area from the integral sampling area to obtain a sample; polishing and etching the cross sections of two opposite sides of the sample until cracks appear on the surfaces of the cross sections; and setting a fracture sampling area according to the position and the size of the crack, taking the fracture sampling area out of the sample to obtain a fracture sampling sample, and opening the crack in the fracture sampling sample. The method for sampling the micro cracks in the welding joint can accurately position the micro cracks in the welding joint of the thick-wall pressure container, and analyze the properties and the reasons of the cracks, so that measures for preventing the cracks can be accurately formulated, and the safe and stable operation of the pressure container is improved.
Description
Technical Field
The invention relates to the technical field of analysis of internal defects of welding joints, in particular to a sampling method for micro cracks in the welding joints of thick-wall pressure vessels and an internal crack analysis method based on the sampling method.
Background
The thick-walled (generally, the thickness is more than or equal to 40 mm) pressure vessels are usually connected by adopting a multilayer multi-pass welding mode, and defects such as fine air holes, shrinkage cavities and incomplete fusion in the welding process are often caused by improper operation. Meanwhile, the interlayer position of the multilayer welding seam is positioned at the repeated heating position of welding heat cycle, so that the low-melting-point substance in the welding seam is easy to generate grain boundary liquefaction under the environment with higher reheating temperature, and cracks are formed. The above-mentioned fine defects and microcracks are very prone to develop into new cracks during operation. Meanwhile, the joint is subjected to the action of multiple welding thermal cycles, so that the structure and the performance of the joint are extremely uneven, new cracks are generated in the operation process of the welded joint, and the welded joint becomes a great hidden danger of safe and stable operation of the pressure container.
For defects generated in the welding process, the existing nondestructive testing technology is difficult to detect due to the fact that the thickness of parts is thick and the sizes of the defects are small. During service, internal defects of the pressure container are easy to expand and form cracks due to internal pressure, but the size of the cracks is still very fine due to the limitation of the overall size of the pressure container. The existing nondestructive detection technology can only find the position and the approximate size of the defect, and the specific property of the crack is difficult to judge, thereby threatening the safe and stable operation of the pressure vessel.
At present, the research on the cracking of the thick-wall welding joint mainly aims at the aspects of a method for preventing cracks and detection, and the analysis related to internal micro cracks is not reported. Lixinmei et al effectively avoids the formation of P92 steel weld metal microcracks by reducing the formation of brittle martensite and increasing the volume fraction of austenite converted to martensite. Wangxuyang et al studied a method for controlling cracks and air holes during the welding process of 800HT pipelines, and effectively avoided the cracks and air holes during the welding process of 800HT pipelines. The invention relates to a device for detecting the depth of cracks on the welding surface and near the surface of a poplar vibration peak, which can be quickly fixed in a large container and a pipeline and can quickly detect the depth of cracks on the welding surface and near the surface. However, the prior art does not relate to the macroscopic detection and analysis of cracks at greater depths in thick-walled joints.
Disclosure of Invention
In view of the above, in order to overcome the drawbacks of the prior art, the present invention provides a method for sampling micro-cracks inside a welded joint, which enables cracks to be acquired and analyzed macroscopically.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for sampling internal cracks of a welded joint comprises the following steps: acquiring the position and the size of the internal crack in the welding joint, and setting an integral sampling area and a metallographic sampling area according to the position and the size; taking out the integral sampling area from the pressure vessel, and then taking out the gold-phase-containing sampling area from the integral sampling area to obtain a sample; polishing and etching the cross sections of two opposite sides of the sample until cracks appear on the surfaces of the cross sections; setting a fracture sampling area according to the position and the size of the crack, taking the fracture sampling area out of the sample to obtain a fracture sampling sample, and opening the crack in the fracture sampling sample. By the method, the internal cracks can be accurately obtained, the crack properties are qualitative, and technical support is provided for defect treatment and prevention.
According to some preferred embodiments of the invention, the edge of the unitary sampling area is at least 100mm from the crack. The method and the device prevent the follow-up misjudgment of crack properties caused by the damage of the original characteristic information of the cracks in the sampling process.
According to some preferred embodiments of the invention, the edge of the metallographic sample section is at least 10 to 15mm from the crack. The defect part is completely taken out, and the subsequent polishing workload is reduced.
According to some preferred embodiments of the invention, the grinding comprises the steps of: firstly, the surface of the cross section of the sample is polished to be 0.5-1 mm away from the crack, then the surface is sequentially polished by using 100#, 400# and 800# metallographic abrasive paper until the crack appears on the surface of the cross section, and then the grinding paste is used for mechanical polishing. And (5) rapidly eliminating grinding marks to obtain crack positions and appearances.
According to some preferred embodiments of the present invention, the etching is performed by etching the mechanically polished sample with an etching solution, and the etching solution is selected according to different types of the base material and the weld joint.
According to some preferred implementation aspects of the invention, the crack is opened from the fracture sampling sample, namely the fracture sampling sample is soaked in liquid nitrogen for 10-15 min and then is rapidly taken out to open the crack. The reason for this is to make the material brittle and thus to achieve fracture opening in a room temperature environment.
According to some preferred embodiments of the present invention, the whole sampling area is removed by flame cutting; and the metallographic sampling area and the fracture sampling area are taken out in a linear cutting mode.
The invention also provides a method for analyzing the internal cracks of the welding joint based on the sampling method, which comprises the following steps: when the cracks appear on the surface of the cross section, the sample is observed and measured by using a body type microscope and a metallographic microscope, and the position, the internal appearance and the tissue condition of the cracks in the welding seam are determined.
According to some preferred embodiments of the invention, after the crack is opened, the fracture after the crack is opened is observed by using a scanning electron microscope, the morphological characteristics of the fracture of the crack along the length direction of the weld joint are determined, and the abnormal area is subjected to energy spectrum analysis.
According to some preferred embodiments of the invention, the crack position and the internal appearance, the metallographic structure and the fracture appearance of the crack are comprehensively analyzed, and the crack property and the crack generation cause are comprehensively judged.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the beneficial effects that: the method for sampling the microcracks in the welded joint can accurately position the microcracks in the welded joint of the thick-wall pressure vessel, systematically analyze the crack properties and the causes of the cracks, and accordingly accurately make measures for preventing the cracks and improve the safe and stable operation of the pressure vessel.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic sampling diagram of an overall sampling area and a metallographic sampling area in a preferred embodiment of the invention;
FIG. 2 is a schematic illustration of a sample taken from a fracture sampling area in a preferred embodiment of the present invention;
FIG. 3 is a position and topography of an end of a crack observed under a stereomicroscope and a metallographic microscope in an embodiment of the invention;
FIG. 4 is a view of the position and appearance of the crack at the other end of the crack under a stereomicroscope and a metallographic microscope in an embodiment of the invention;
FIG. 5 is a schematic illustration of the location of a crack fracture cut in an embodiment of the invention;
FIG. 6 is a fracture morphology after crack opening in an embodiment of the invention;
FIG. 7 shows the results of the fracture spectrum analysis after the crack opens in the example of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a method for acquiring and analyzing internal microcracks of a thick-wall pressure vessel welding joint, which mainly comprises the steps of positioning the internal microcracks, sampling and polishing a sample, observing and analyzing the ends of the cracks, analyzing the internal appearance and the structure of the cracks, and analyzing the appearance and the characteristic of fracture appearance of the cracks.
The method specifically comprises the following steps:
1. cleaning base material areas close to the positions of about 100mm on two sides of a welding line, removing paint, oxide skin, oil stains and the like on the surfaces, detecting a welding joint by using ultrasonic equipment, obtaining the position and the size of an internal crack in the joint, and setting an integral sampling area and a metallographic sampling area according to the position and the size, as shown in figure 1.
2. The whole sampling area containing cracks is taken out from the pressure container by utilizing the flame cutting device, and the tissue in the crack position area is not influenced by cutting heat in the cutting process.
3. And taking out the metallographic sampling area containing the cracks by using a linear cutting device to obtain a sample, ensuring that the length of the welding line is 10-15 mm longer than the length of each of two sides of each crack, and ensuring that the width of the welding line comprises 10-15 mm of base material, namely the edge of the metallographic sampling area is at least 10-15 mm away from the cracks.
4. Fixing a sample on a bench vice, polishing the cross section surface of one side of the sample by using a grinding wheel to be about 0.5 mm away from a crack, sequentially polishing by using 100#, 400# and 800# metallographic abrasive paper, rotating the sample by 180 degrees before each time of polishing by using abrasive paper, until the crack is visible to naked eyes, mechanically polishing by using No. 2.5 abrasive paste, and then etching by using an etching solution.
And observing and measuring the prepared sample by using a body type microscope and a metallographic microscope, and determining the position and the internal appearance of the crack in the weld joint and the tissue condition near the crack.
5. And repeating the step 4, and observing the crack condition of the opposite side.
6. Setting a fracture sampling area according to the position and the size of the crack, wherein the set area comprises the overall size of the crack, taking out the fracture sampling area containing the crack along the length direction of the welding seam by utilizing linear cutting (as shown in figure 2), soaking a fracture sampling sample in liquid nitrogen for 10-15 min, and rapidly taking out the fracture sampling sample and then opening the crack along the length direction of the crack.
7. And observing the fracture after the crack is opened by using a scanning electron microscope, determining the appearance characteristics of the crack fracture along the length direction of the welding line, and performing energy spectrum analysis on a part of abnormal area, wherein the abnormal area refers to the abnormal area observed on the surface of the crack fracture.
8. According to the crack position, the internal appearance and the metallographic structure in the analysis result, the initial properties of the crack, such as cold crack or hot crack, can be preliminarily judged. The types of the cracks and the reasons for the generation of the cracks can be comprehensively judged by combining the appearance characteristics of the fractures after the cracks are opened.
The technical scheme of the application is described as an example for discovering the standard exceeding defect by the nondestructive testing of the welding line of the hydrogen storage tank of a certain power plant. In order to clarify the defect type and subsequent processing, the following steps are carried out on the defect:
1. and detecting the welded joint by using ultrasonic detection, and finding that the welded joint has a crack defect with the length of about 28mm.
2. The crack sample was taken out from the hydrogen tank by a flame cutting apparatus, the cut region was 120mm × 120mm × plate thickness, and the crack defect was located at the middle position of the cut region.
3. And taking out the sample containing the cracks by using a linear cutting device to obtain a metallographic sample, wherein the size of the sample is 55mm multiplied by the thickness of the board, and the cracks are positioned in the middle of the metallographic sample.
4. Fixing the sample on a bench vice, firstly grinding the cross section surface of one side of the sample by using a grinding wheel to be about 0.5 mm away from the crack, then sequentially grinding by using No. 100, no. 400 and No. 800 metallographic abrasive paper until the crack is visible, mechanically polishing by using No. 2.5 grinding paste, and then etching by using 4% nitric acid alcohol corrosive solution. The cracks were observed using a stereomicroscope and a metallographic microscope, and the positions and morphology of the cracks are shown in fig. 3. The crack is positioned between the multilayer multi-pass welding layers, the crack generally extends in parallel along a fusion line, a ball drop-shaped micro-hole is generated after the non-metallic inclusion is remelted in an unmixed melting area, and the inside of the crack contains the S element with a low melting point.
5. And repeating the step 4, and observing the crack condition of the opposite side. The cracks were observed using a stereomicroscope and a metallographic microscope, and the positions and morphology of the cracks are shown in fig. 4. The cracks are positioned between the multi-layer and multi-pass welding layers and generally spread in parallel along the fusion line.
6. And taking out a metallographic sample containing the cracks along the length direction of the welding line according to a dotted line in the figure 5 by utilizing linear cutting, soaking the fracture sampling sample in liquid nitrogen for 10-15 min, quickly taking out the fracture sampling sample, and then opening the cracks along the length direction of the cracks.
7. And (3) placing the disconnected fracture into a scanning electron microscope, wherein the crack fracture presents the morphology characteristic of dendrites, the fracture is provided with traces of liquid phase solidification along a crystal interface and a globular solidification product, and the results are combined to carry out inspection, so that the fracture is the characteristic of the typical weld metal liquefaction crack. The fracture morphology features and the energy spectrum results are shown in fig. 6 and 7.
The analysis method integrates the analysis means of conventional ultrasonic detection, integral microscopic observation, metallographic examination, scanning electron microscope, energy spectrometer and the like, can accurately position the position of the micro-crack inside the welded joint of the thick-wall pressure container, and systematically analyzes the crack property and the generation reason, thereby accurately establishing the measure for preventing the crack and improving the safe and stable operation of the pressure container.
The above embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention by this means. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. A method for sampling internal cracks of a welded joint is characterized by comprising the following steps: acquiring the position and the size of the internal crack inside the welded joint, and setting an integral sampling area and a metallographic sampling area according to the position and the size; taking out the integral sampling area from the pressure vessel, and then taking out the gold-phase-containing sampling area from the integral sampling area to obtain a sample; polishing and etching the cross sections of two opposite sides of the sample until cracks appear on the surfaces of the cross sections; setting a fracture sampling area according to the position and the size of the crack, taking the fracture sampling area out of the sample to obtain a fracture sampling sample, and opening the crack in the fracture sampling sample.
2. A sampling method according to claim 1, wherein the edge of the global sampling area is at least 100mm from the crack.
3. The sampling method of claim 1, wherein the edge of the metallographic sampling area is at least 10 to 15mm from the crack.
4. The sampling method according to claim 1, characterized in that said grinding comprises the steps of: firstly, the surface of the cross section of the sample is polished to be 0.5-1 mm away from the crack, then the surface is sequentially polished by using 100#, 400# and 800# metallographic abrasive paper, the sample is rotated 180 degrees before each time of polishing by using the abrasive paper, and mechanical polishing is carried out by using grinding paste until the crack appears on the surface of the cross section.
5. The sampling method according to claim 4, wherein the etching is etching the sample after mechanical polishing with an etching solution.
6. The sampling method according to claim 1, wherein the crack is opened from the fracture sampling sample, and the fracture sampling sample is soaked in liquid nitrogen for 10-15 min and then taken out to open the crack.
7. The sampling method according to claim 6, wherein the whole sampling area is taken out by flame cutting; and the metallographic sampling area and the fracture sampling area are taken out in a linear cutting mode.
8. A method for analyzing cracks inside a welded joint based on the sampling method according to any one of claims 1 to 7, comprising: when the cracks appear on the surface of the cross section, the sample is observed and measured by using a body type microscope and a metallographic microscope, and the position, the internal appearance and the tissue condition of the cracks in the welding seam are determined.
9. The analysis method according to claim 8, characterized in that after the crack is opened, the fracture after the crack is opened is observed by using a scanning electron microscope, the morphological characteristics of the crack fracture along the length direction of the weld joint are determined, and the abnormal region is subjected to energy spectrum analysis.
10. The analysis method of claim 8, wherein the crack position and the internal appearance, the metallographic structure and the fracture appearance of the crack are comprehensively analyzed to comprehensively judge the crack property and the cause of the crack generation.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310044564.4A CN115931422A (en) | 2023-01-30 | 2023-01-30 | Sampling method and analysis method for internal cracks of welding joint |
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| CN202310044564.4A CN115931422A (en) | 2023-01-30 | 2023-01-30 | Sampling method and analysis method for internal cracks of welding joint |
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