CN112903827A - Preparation method of thermal fatigue crack simulation test block - Google Patents
Preparation method of thermal fatigue crack simulation test block Download PDFInfo
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- CN112903827A CN112903827A CN202110322287.XA CN202110322287A CN112903827A CN 112903827 A CN112903827 A CN 112903827A CN 202110322287 A CN202110322287 A CN 202110322287A CN 112903827 A CN112903827 A CN 112903827A
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Abstract
The invention discloses a preparation method of a thermal fatigue crack simulation test block, and belongs to the technical field of preparation of nondestructive testing test blocks. Firstly, processing a through pipe hole in the middle of a test block, and processing a plurality of crack induction points around the pipe hole on one surface of the test block; then, the test block is rapidly cooled after being repeatedly and rapidly heated to high temperature, so that thermal fatigue cracks are generated on the test block; and finally, reaming the pipe hole, removing the crack induction tip, polishing the detection surface of the test block until the roughness is consistent with that of the detected workpiece, and finishing the preparation of the thermal fatigue crack simulation test block. The thermal fatigue crack simulation test block prepared by the method can be used for verifying and evaluating a detection system and a detection process, improves the identification, positioning and quantification capabilities of the detection system on thermal fatigue cracks or other defects with thermal fatigue crack characteristics, finds out the high-temperature steam main pipe harmfulness defects, and ensures the safe operation of a power station unit.
Description
Technical Field
The invention belongs to the technical field of preparation of nondestructive testing test blocks, and relates to a preparation method of a thermal fatigue crack simulation test block.
Background
Along with the continuous increase of temperature and pressure parameters of thermal power generating units at home and abroad, the increase of the service time of the thermal power generating units in service and the deep peak shaving of the thermal power generating units, in recent years, the thermal power generating units have steam main pipe leakage accidents caused by thermal fatigue cracks near a high-temperature steam pipeline sampling pipe hole and a desuperheater for many times. The thermal fatigue cracks in the vicinity of the sampling pipe hole of the high-temperature steam pipeline and the desuperheater exist in two forms: the thermal fatigue crack of the inner wall of the pipeline and the radial thermal fatigue crack around the drain pipe hole of the inner wall of the pipeline exist simultaneously in some cases. The development of thermal fatigue cracks is generally characterized by fatigue cracks, which have a time course including three stages, namely crack initiation, crack propagation and final transient fracture. Typical fractures are composed of these three parts, with typical scalloped or beach-like striations. During these three phases, the load goes through a certain cycle. It should be noted that the ultimate failure of fatigue is instantaneous and extremely dangerous. Thermal fatigue cracks generally grow on the inner wall and gradually develop to the outer wall to form through cracks, and steam main pipes are leaked. Therefore, nondestructive testing of the crack in the stages of crack initiation and propagation is particularly important for the safety of the device.
However, the radial thermal fatigue cracks around the pipe hole on the inner wall of the pipeline exist at the lower part of the fillet weld of the pipe seat, the cracks are distributed around the pipe hole on the inner wall of the pipeline and are vertical to the inner wall of the pipe hole to form radial distribution, the position structure is complex, the cracks and the structural signals in different directions and positions are difficult to identify although the traditional detection method has great advantages, and the quantification is inaccurate. However, the ultrasonic detection or phased array detection process verification on the thermal fatigue crack simulation test block to further improve the detection process is an effective way for improving the detection capability and solving the problems of defect identification, positioning and quantification. The thermal fatigue crack simulation test block can be obtained from sample pieces which are found to contain natural defects in the previous detection, but the method has high randomness and cannot be manufactured in batches, and the sample pieces obtained at different detection positions have overlarge differences and have no contrast.
Disclosure of Invention
In order to solve the above problems, the present invention aims to provide a method for preparing a thermal fatigue crack simulation test block, which can be used for verifying and evaluating a detection system and a detection process, improve the identification, positioning and quantification capabilities of the detection system on thermal fatigue cracks or other characteristic defects with thermal fatigue cracks, find out the harmfulness defects of a high-temperature steam main pipe, and ensure the safe operation of a power station unit.
The invention is realized by the following technical scheme:
the invention discloses a preparation method of a thermal fatigue crack simulation test block, which comprises the following steps:
step 1: processing a through pipe hole in the middle of the test block, and processing a plurality of crack induction points around the pipe hole on one surface of the test block;
step 2: heating the test block to 1000 +/-50 ℃ and then preserving heat;
and step 3: putting the test block into a cooling medium with the temperature of 5-35 ℃ for cooling for 10-20 min;
and 4, step 4: taking out the test block and naturally drying in the air;
and 5: repeating the step 2 to the step 4 until visually identifiable cracks appear on the surface of the test block; and (4) reaming the pipe hole, removing the crack induction tip, polishing the detection surface of the test block until the roughness is consistent with that of the detected workpiece, and finishing the preparation of the thermal fatigue crack simulation test block.
Preferably, the material of the test block is the same as that of the workpiece to be detected, and the curvature radius of the workpiece to be detected is 0.9-1.5 times of that of the test block.
Preferably, the test block is the cuboid, and 4 apex angles departments of test block all are equipped with the connecting hole, and the connecting hole on the test block passes through the connecting piece to be fixed on the base, is equipped with the insulating layer between test block and the base.
Preferably, in the step 1, the crack inducing tips are uniformly distributed around the pipe hole, and the number of the crack inducing tips is 8-16.
Preferably, in step 1, the angle of the crack-inducing tip is 10 ° to 30 °, the length of the crack-inducing tip is 0.1 to 0.15 times the diameter of the tube hole, and the depth of the crack-inducing tip is 0.025 times the thickness of the test block and is not greater than 1 mm.
Preferably, in step 2, a flexible ceramic resistance track sheet heater is used for heating.
Preferably, in the step 2, the heat preservation time is 20-30 min.
Preferably, the cooling of step 3 is performed in a cooling tank, the cooling medium in the cooling tank is water, and the maximum immersion depth of the cooling tank is 400 mm.
Further preferably, the cooling medium in the cooling tank is circulated, and the temperature rise of the cooling medium in the effluent water is not more than 20 ℃.
Preferably, in step 4, the time for natural drying in air is not less than 5 min.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the preparation method of the thermal fatigue crack simulation test block disclosed by the invention, through repeated rapid heating to high temperature and rapid cooling, the generated crack has the typical characteristics of the thermal fatigue crack, can be used for verifying the coverage condition of ultrasonic detection and ultrasonic phased array detection on a detection object, is beneficial to verifying the ultrasonic detection and ultrasonic phased array detection process, and ensures the effective detection of the thermal fatigue crack. Because the parts which are easy to generate fatigue sources generally have the parts with the abrupt change of the cross sections of the parts, and the impurities exist on the surface or in the material, the surface treatment defects and other factors, the crack induction tip which is manually processed can accelerate the generation speed of thermal fatigue cracks, reduce the cost of manpower and material resources and shorten the preparation period. And (4) reaming the pipe hole after the thermal fatigue crack is generated, removing the crack induction tip, and avoiding generating interference during detection. The thermal fatigue crack simulation test block prepared by the method can be used for verifying and evaluating a detection system and a detection process, improves the identification, positioning and quantification capabilities of the detection system on thermal fatigue cracks or other defects with thermal fatigue crack characteristics, finds out the high-temperature steam main pipe harmfulness defects, and ensures the safe operation of a power station unit.
Furthermore, the material of the test block is the same as that of the detected workpiece, and the curvature of the test block is similar to that of the detected workpiece, so that the detection system can better simulate the spare workpiece and optimize the detection process.
Further, the base can play the effect of rigidity restraint to the test block, makes the test block produce bigger alternating stress when thermal cycle, and the insulating layer can guarantee to make test platform not heat up thereupon when the test block heaies up.
Furthermore, the crack induction points are uniformly distributed around the pipe hole, the number of the crack induction points is 8-16, thermal fatigue cracks can be generated more quickly, and the test time is shortened. The generated cracks are ensured to have radial shape and are close to the characteristics of real cracks.
Further, the heating adopts flexible ceramic resistance track sheet heater, can heat to higher temperature on the one hand, on the other hand also can laminate better when the test block has certain camber, guarantees the heating effect.
Further, the heat preservation time is 20-30 min, so that the whole test block can reach the set temperature.
Furthermore, cooling is carried out in a cooling tank, the maximum immersion depth of the cooling tank is 400mm, the test block can be ensured to have enough entry depth, the phenomenon that temperature rise is too fast due to too shallow cooling medium is avoided, and meanwhile, the manufacturing cost of equipment is reduced; the cooling medium in the cooling tank is water, so that the cost is low, the fluidity is good, and the cooling effect is good.
Furthermore, the cooling medium in the cooling tank flows circularly, the temperature rise of the outlet water of the cooling medium is not more than 20 ℃, and good cooling effect can be ensured.
Furthermore, the time for natural drying in the air is not less than 5min, so that the water and the water vapor on the test block are ensured to be evaporated, and the next heating is carried out.
Drawings
FIG. 1 is a flow chart of a method for preparing a thermal fatigue crack simulation test block according to the present invention;
FIG. 2 is a schematic diagram of the overall structure of the test block of the present invention;
FIG. 3 is a schematic top view of a test block according to an embodiment of the present invention;
FIG. 4 is a view A-A of FIG. 3;
fig. 5 is a partially enlarged view B of fig. 3.
In the figure, 1-test block, 2-connecting hole, 3-tube hole, 4-crack inducing tip.
Detailed Description
The theoretical basis of the invention is as follows:
the structural material bears alternating repeated load, the peak stress in a local high strain area exceeds the yield strength of the material, and the grains are subjected to scratching and dislocation to generate micro cracks and gradually expand to form fatigue cracks. Including fatigue cracks caused by alternating working loads, thermal fatigue cracks caused by cyclic thermal stresses, and corrosion fatigue cracks caused by the combined action of cyclic stresses and a corrosion medium.
Thermal stress is stress caused by a change in temperature, which leads to cracking and plastic deformation of the material. First consider a homogeneous and isotropic rod that is uniformly heated or cooled, i.e., there is no temperature gradient in the rod. For free expansion and contraction, the rod is unstressed. However, thermal stresses can occur if the axial movement of the rod is constrained from being supported by the rigid end. From T0Temperature change to TfThermal stress generated by temperature
σ＝Eαl(T0-Tf)＝EαlΔT (2)
In which E is the modulus of elasticity, alphalIs the linear thermal expansion coefficient.
In the heating (T)f＞T0) The stress is a compressive force (σ < 0) because the expansion of the rod is constrained. Obviously, if the rod is in the process of cooling (T)f＜T0) Tensile stress (σ > 0) will be generated. The stress in equation (1) is required to be elastic compression and elongation during temperature change.
The non-uniform distribution of internal temperature when a solid is heated or cooled depends on its size and shape, the thermal conductivity of the material and the speed of temperature change. Thermal stress may come from temperature gradients within the object. The creation of a temperature gradient is typically rapid heating and cooling, in which case the outside of the object changes more rapidly than the inside, and the resulting difference in dimensional changes constrains the free expansion or contraction of adjacent regions. For example, when heated, the sample is hotter on the outside, and therefore expands more than on the inside, and the surface develops compressive stress, balanced with internal tensile stress. Conversely, upon rapid cooling, tensile stresses develop in the surface. From the formula (1), it is found that a steel material having a high elastic modulus and a high linear thermal expansion coefficient is more likely to cause thermal fatigue cracking.
The test block 1 is manufactured by machining. The parts which are easy to generate fatigue sources generally have the parts with abrupt changes of the cross sections of the parts, inclusions exist on the surface or in the material, and the surface treatment defects exist. The crack-inducing tip 4 is artificially worked around the tube hole 3 in order to more easily generate cracks therein
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, the method for preparing a thermal fatigue crack simulation test block of the present invention comprises the following steps:
step 1: as shown in fig. 2, a through-hole 3 is formed in the middle of a test block 1, and a plurality of crack-inducing tips 4 are formed around the through-hole 3 on one surface of the test block 1. The test block 1 is a cuboid, connecting holes 2 are formed in 4 vertex angles of the test block 1, and the connecting holes 2 in the test block 1 are fixed on the base through connecting pieces; a heat insulation layer is arranged between the test block 1 and the base. The base is a steel plate slightly larger than the test block 1, and handles for moving the base are arranged at two ends of the base. Preferably, the material of the test block 1 is the same as the workpiece to be tested, and the curvature of the test block 1 is equal to the curvature of the workpiece to be tested.
Preferably, the crack-inducing tips 4 are uniformly distributed around the tube hole 3, and the number of the crack-inducing tips 4 is 8-16. The angle of the crack inducing tip 4 is 10-30 degrees, the length of the crack inducing tip 4 is 0.1-0.15 times of the diameter of the tube hole 3, and the depth of the crack inducing tip 4 is 0.025 times of the thickness of the test block 1 and is not more than 1 mm.
Step 2: heating the test block 1 to 1000 +/-50 ℃ and then preserving the temperature. Preferably, a flexible ceramic resistance track sheet heater is adopted for heating; the heat preservation time is 20-30 min.
And step 3: and (3) putting the test block 1 into a cooling medium with the temperature of 5-35 ℃ for cooling for 10-20 min. Preferably, the cooling is carried out in a cooling tank, the cooling medium in the cooling tank is water, and the maximum immersion depth of the cooling tank is 400 mm; the cooling medium in the cooling tank is in circulation flow, and the temperature rise of the discharged water of the cooling medium is not more than 20 ℃.
The cooling bath can be designed to be connected with inlet tube and outlet pipe respectively for both ends, the position design of inlet tube and outlet pipe is for advancing the height more for low, inlet tube and outlet pipe are connected to the coolant source, be equipped with the control valve respectively on inlet tube and outlet pipe, be equipped with a plurality of temperature sensor in the cooling bath, control valve and temperature sensor all are connected to control system, control system passes through temperature sensor real-time supervision coolant's temperature rise, control valve control coolant's temperature rise through on inlet tube and the outlet pipe, guarantee the cooling effect of test block.
And 4, step 4: the test block 1 was taken out and naturally dried in the air. Preferably, the time for natural drying is not less than 5 min.
And 5: repeating the step 2 to the step 4 until the surface of the test block 1 has visible cracks; and (3) reaming the pipe hole 3, removing the crack induction tip 4, polishing the detection surface of the test block 1 until the roughness is consistent with that of the detected workpiece, and finishing the preparation of the thermal fatigue crack simulation test block.
The invention is further illustrated by the following specific examples:
the tested workpiece is a 660MW reheating hot section steam pipeline, the material is SA 335P 91, the specification is phi 682 multiplied by 25mm, and the specification of the sampling tube is phi 46 mm.
1) Selecting materials, wherein the material of the simulation test block is as same as the tested workpiece or similar to the acoustic performance as possible, SA 335P 91 or 10Cr9Mo1VNbN can be selected, and the material is uniform, has no impurities and has no other defects influencing the use;
2) processing a test block 1, namely processing the test block 1 according to the size on the figure 3; the test block 1 is in the specification size of 300 multiplied by 20mm, the diameter of a connecting hole is 10mm, the diameter of a pipe hole is 40mm, the length of a crack induction tip is 3mm, the angle is 30 degrees, and the depth is 0.5 mm;
3) generating and applying thermal stress, and fixing the test block 1 on the base by using 4 bolts;
4) heating, namely heating the test block 1 by using a flexible ceramic resistance track sheet heater, and preserving heat for 20min when the temperature of the whole test block 1 reaches 1000 ℃;
5) cooling, namely rapidly immersing the base and the test block 1 into water flowing in a water tank at the temperature of 5-35 ℃ for water bath, wherein the maximum immersion depth is 400mm, and adjusting water flow to ensure that the temperature rise of outlet water during the test is not more than 20 ℃;
6) drying, namely rapidly cooling the test block 1 in a water tank for 10min, and then immediately taking out the test block, and standing in the air for not less than 5 min;
7) test block 1 was observed after exposure to air for the presence of cracks. If the crack exists, stopping the test; if no crack exists, repeating the processes of the steps 4) to 6) until a visually identifiable crack appears, and stopping the test;
8) machining the expanded tube hole from 3 phi 40mm to 46mm, polishing oxide skin on the back of the test block 1 until metal luster is exposed, wherein the roughness is consistent with that of a detected workpiece, and verifying thermal fatigue cracks by using an ultrasonic detector or a phased array detector.
It should be noted that the above description is only one embodiment of the present invention, and all equivalent changes of the system described in the present invention are included in the protection scope of the present invention. Persons skilled in the art to which this invention pertains may substitute similar alternatives for the specific embodiments described, all without departing from the scope of the invention as defined by the claims.
Claims (10)
1. A preparation method of a thermal fatigue crack simulation test block is characterized by comprising the following steps:
step 1: processing a through pipe hole (3) in the middle of the test block (1), and processing a plurality of crack induction points (4) around the pipe hole (3) on one surface of the test block (1);
step 2: heating the test block (1) to 1000 +/-50 ℃ and then preserving heat;
and step 3: putting the test block (1) into a cooling medium with the temperature of 5-35 ℃ for cooling for 10-20 min;
and 4, step 4: taking out the test block (1) and naturally drying in the air;
and 5: repeating the step 2 to the step 4 until the surface of the test block (1) has visible cracks; and (3) reaming the pipe hole (3), removing the crack induction tip (4), polishing the detection surface of the test block (1) until the roughness is consistent with that of the detected workpiece, and finishing the preparation of the thermal fatigue crack simulation test block.
2. The method for preparing a thermal fatigue crack simulation test block according to claim 1, wherein the material of the test block (1) is the same as that of the workpiece to be tested, and the radius of curvature of the workpiece to be tested is 0.9 to 1.5 times the radius of curvature of the test block (1).
3. The method for preparing the thermal fatigue crack simulation test block according to claim 1, wherein the test block (1) is a cuboid, the 4 top corners of the test block (1) are respectively provided with a connecting hole (2), the connecting holes (2) on the test block (1) are fixed on a base through connecting pieces, and a heat insulation layer is arranged between the test block (1) and the base.
4. The method for preparing a thermal fatigue crack simulation test block according to claim 1, wherein in the step 1, the crack inducing tips (4) are uniformly distributed around the pipe hole (3), and the number of the crack inducing tips (4) is 8-16.
5. The method of preparing a thermal fatigue crack simulating test block according to claim 1, wherein in step 1, the angle of the crack inducing tip (4) is 10 ° to 30 °, the length of the crack inducing tip (4) is 0.1 to 0.15 times the diameter of the tube hole (3), and the depth of the crack inducing tip (4) is 0.025 times the thickness of the test block (1) and is not more than 1 mm.
6. The method for preparing a thermal fatigue crack simulating test block according to claim 1, wherein in the step 2, a flexible ceramic resistance track sheet heater is used for heating.
7. The method for preparing a thermal fatigue crack simulation test block according to claim 1, wherein in the step 2, the heat preservation time is 20-30 min.
8. The method of preparing a thermal fatigue crack-simulating test block according to claim 1, wherein the cooling of step 3 is performed in a cooling bath, the cooling medium in the cooling bath is water, and the maximum immersion depth of the cooling bath is 400 mm.
9. The method of claim 8, wherein the cooling medium in the cooling bath is circulated and the cooling medium has a water temperature rise of not more than 20 ℃.
10. The method for preparing a thermal fatigue crack simulating test block according to claim 1, wherein the natural drying time in air in step 4 is not less than 5 min.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115201339A (en) * | 2022-09-19 | 2022-10-18 | 河北铁达科技有限公司 | Detection device, turnout rail bottom flaw detection equipment and method |
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2021
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| CN110441405A (en) * | 2019-07-26 | 2019-11-12 | 大唐东北电力试验研究院有限公司 | Nearby heat fatigue cracking detects reference block to the hydrophobic pore of high temperature steam pipeline |
| CN111521507A (en) * | 2020-04-30 | 2020-08-11 | 江苏师范大学 | Test method for thermal fatigue surface crack propagation rate of environment-friendly stainless steel weld joint |
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| 许海峰 等: "Sr和Ce对镍基高温合金高温力学及热疲劳性能的影响", 《山东农业大学学报（自然科学版）》 * |
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| CN115201339A (en) * | 2022-09-19 | 2022-10-18 | 河北铁达科技有限公司 | Detection device, turnout rail bottom flaw detection equipment and method |
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