Preparation method of SA-336F12 super pipeline drop weight test piece for drop weight test

Abstract

The invention relates to a test piece for a drop weight test, in particular to a preparation method of an SA-336F12 super pipeline drop weight test piece for a drop weight test, which comprises the following chemical components in percentage by weight: 0.10 to 0.17 percent of C, 0.30 to 0.80 percent of Mn, 0.20 to 0.50 percent of Si, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, 0.80 to 1.10 percent of Cr, 0.45 to 0.65 percent of Mo, less than or equal to 0.05 percent of Co, 0.10 to 0.30 percent of Ni and less than or equal to 0.15 percent of Cu. The balance is Fe and inevitable impurity elements; the raw materials of the chemical components are subjected to steelmaking, straight pipe forging, preheat treatment, pipe nozzle extrusion, performance heat treatment, sampling and welding to obtain the drop hammer test piece for the drop hammer test. The method is simple and easy to operate, meets the requirement of the super pipeline drop weight test, and is high in percent of pass.

Description

Technical Field

[0001] The present invention relates to the field of performance testing of metal materials, and specifically to a preparation method for SA-336F12 super pipeline drop weight test specimens for drop weight tests. Background Art

[0002] The CAP1400 main steam super pipeline stipulates that when the wall thickness of the forging > 64 mm, a drop weight test should be considered. The drop weight test should be carried out in accordance with the requirements of ASTM E208. The drop weight test specimens can be of type P-1, P-2 or P-3. Enough drop weight test specimens should be prepared at each sampling location to determine the actual nil-ductility transition temperature (NDT) of the pipeline. The actual nil-ductility transition temperature of the pipeline should not be higher than (10 - A) °C (A is a parameter related to the pipeline thickness specified in Appendix R of ASME Section III). When calculated that NDT ≤ -7 °C, the drop weight test of the super pipeline is considered qualified.

[0003] For a batch of main steam super pipelines produced according to the standard, on the premise that the conventional mechanical properties are qualified, and the -7 °C impact is 100% ductile fracture, using the current (180 - 200 A) and welding process methods recommended by ASTM E208, there are still some products that cannot meet the requirement of NDT ≤ -7 °C.

[0004] Publication No. CN 109500508 A discloses a welding method for specimens in the nil-ductility transition temperature drop weight test of ferritic steel. It provides a method for fast heat dissipation and precise welding of specimens when conducting the nil-ductility transition temperature drop weight test of ferritic steel according to GB / T6803-2008, which is convenient and fast to operate.

[0005] Publication No. CN 103808541 A discloses a surfacing welding method for specimens in the nil-ductility transition temperature drop weight test. A surfacing electrode with a diameter of 5.0 mm is used, the welding current is controlled at 180 - 200 A, and the welding speed is controlled at 30 - 50 mm / min; the length of the crack source weld bead is controlled at 12 - 16 mm, and the height of the crack source weld bead is controlled at 3.5 - 5.5 mm.

[0006] Publication No. CN 118081142A discloses a welding process for the crack source weld bead in the drop weight test of the heat affected zone of dissimilar steel joints, which mainly refines the specific requirements of the ASTM E208 standard. A crack source weld bead is built up on the specimen using an electrode, and heat dissipation is carried out by means of heat dissipation with a copper plate and / or water isolation heat dissipation during welding. The welding current is controlled as close to 180 A as possible near 180 A, the electrode is inclined at 30° - 45° during welding, and the welding process is uninterrupted.

[0007] The above-mentioned process method is mainly a refinement or quantification of the provisions of ASTM E208 or GB / T6803-2008. Using the above-mentioned process method, even when the -7°C impact has a 100% ductile fracture surface, there are still some products that cannot meet the acceptance requirement of NDT ≤ -7°C, or the margin is not large. To improve the test qualification rate and ensure the stable and reliable performance of the products, it is hoped to not only optimize and improve the welding process, but also optimize the design from aspects such as chemical composition and forging process control. In order to form a stable and reliable process method with a certain margin, reduce the nil-ductility transition temperature of SA-336F12 super pipes, and ensure the stable quality of the products.

[0008] "Fracture Science" edited by Zhong Qunpeng and Zhao Zihua (Higher Education Press) Figure 6.42 describes the relationship between typical impact absorption work, cleavage fracture surface and temperature. FTP (fracture transition plastic) is the plastic fracture transition temperature, which is the lower limit temperature of a 100% ductile (fibrous) fracture surface and also the temperature at which the impact absorption work enters the upper platform. NDT (nil-ductility temperature) is the nil-ductility transition temperature, which is the upper limit temperature of a 100% cleavage fracture and also the temperature at which the impact absorption work enters the lower platform. From the above theory, it can be seen that NDT ≤ FTP holds true anyway. For SA-336F12 materials after appropriate heat treatment, the -7°C impact is a 100% ductile fracture surface. That is, NDT ≤ FTP ≤ -7°C should hold true for this material. Therefore, we can find reasons from the welding aspect to make the test results meet the requirement of NDT ≤ -7°C. At the same time, by optimizing the chemical composition, controlling the forging process, and adopting appropriate heat treatment process methods, reduce its nil-ductility transition temperature, improve the stability and reliability of the drop weight test, and make it have a certain margin. Summary of the Invention

[0009] The purpose of the present invention is to solve the above technical problems and provide a drop weight specimen with a simple process, easy to operate, meeting the requirements of the drop weight test for super pipes, and a high qualification rate.

[0010] The technical solution is as follows: The chemical composition is as follows: The chemical composition in weight percentage is: C:

[0011] 0.10 - 0.17% (wt%), Mn: 0.30 - 0.80 (wt%), Si: 0.20 - 0.50%

[0012] (wt%), P ≤ 0.010% (wt%), S ≤ 0.010% (wt%), Cr: 0.80 - 1.10%,

[0013] (wt%), Mo: 0.45 - 0.65% (wt%), Co ≤ 0.05% (wt%), Ni:

[0014] 0.10 - 0.30% (wt%), Cu ≤ 0.15 (wt%); the balance is Fe and inevitable impurity elements;

[0015] The raw materials with the above chemical components are processed through steelmaking, forging straight pipes, preliminary heat treatment, extruding nozzles, performance heat treatment, sampling, and welding to obtain drop hammer specimens for drop hammer tests.

[0016] Before the step of forging straight pipes, the riser end and the bottom end of the ingot used for forging the blank steel pipe should be removed. The proportion of the removed weight of the riser end in the mass of the ingot is ≥ 12%, and the proportion of the removed weight of the bottom end in the mass of the ingot is ≥ 8%.

[0017] In the step of forging straight pipes, the forging ratio is controlled to be ≥ 3.

[0018] In the sampling step, the specimen blank is taken from the pipe body by means of cold machining sawing, and at least one original surface is reserved on the specimen blank for surfacing.

[0019] In the welding step, the electrode specifications are Ф3.2 or 4.0 mm.

[0020] In the welding step, the welding current is 90 - 140 A, and the voltage is 20 - 31 V.

[0021] The electrode is an EDPMn4 - 15 type electrode.

[0022] In the welding step, the electrode is baked at 350°C ± 10°C for one hour before welding.

[0023] In the welding step, continuous welding is carried out from one end of the crack source weld bead to the other end, and the welding speed is controlled at 45 - 90 mm / min.

[0024] In view of the problems existing in the background technology, the inventor has made the following improvements:

[0025] I. Composition optimization: In order to obtain appropriate strength and toughness, quenching heat treatment is required. The composition optimization should start from improving the hardenability of the steel and refining the grain size. While meeting the range specified in the SA - 336F12 standard, some components are optimized, and their content ranges are further limited:

[0026] Optimization of C element: Carbon can form precipitates with various elements to achieve the purpose of improving the creep rupture performance of the material. However, with the increase of carbon content, the hardness and strength of the material increase, but its plasticity and toughness decrease, and it also has an adverse effect on the welding performance. Therefore, the optimal control range of the carbon content in the material of the present invention is 0.10 - 0.17%.

[0027] Si element optimization: Silicon reduces the γ phase area and forms a γ phase ring, which is beneficial to improving the strength of the material matrix and the resistance to steam corrosion, and can improve the hardenability and tempering resistance of steel. However, if the content is too high, it will weaken the impact toughness and affect the non-plastic transition temperature. Therefore, the optimal control range of silicon content is 0.20-0.50%.

[0028] Ni element optimization: expand the γ phase area, form an infinite solid solution, and appropriately improve the hardenability of steel. Refine the ferrite grains, improve the plasticity and toughness of steel, especially low-temperature toughness. Therefore, the optimal control range of nickel content is 0.10-0.30%.

[0029] Cu element optimization: expand the γ phase area, but not infinite solid solution. The presence of copper in steel is inevitable. When the content is low, its effect is similar to that of nickel, but weaker. When the content is high, it is not conducive to hot deformation processing. Therefore, the optimal control range of copper content is ≤0.15%.

[0030] In addition, the lower the five harmful elements are, the better, and the content of phosphorus, sulfur, hydrogen and oxygen elements should be strictly controlled to keep them at a low level, which plays an important role in ensuring the final performance of the product.

[0031] Furthermore, the forging process is optimized: the mass ratio of the riser end of the forged steel pipe is controlled to be ≥12%, and the mass ratio of the bottom end is controlled to be ≥8%. The impurities and segregation-prone parts in the steel ingot can be fully discarded; the forging ratio of the super pipeline steel pipe is controlled to be ≥3, so that the tiny defects (shrinkage cavities, shrinkage, etc.) inside the steel ingot can be fully forged, the inclusions can be fully crushed, and its strength and plasticity indicators can be fully improved.

[0032] Furthermore, the welding procedure has been improved. The specifications of the welding electrodes are Ф3.2 or 4.0 mm. If the specifications of the welding electrodes are too small, the welding speed will be slow, the heat input will be higher, and it is not easy to operate under the premise of ensuring the height and width of the weld bead at the crack source, which will affect the quality of the specimen. If welding electrodes with larger specifications are selected, the welding current will increase, and the heat input will also be high. It is appropriate to control the current at 90 - 140 A and the voltage at 20 - 31 V. Here, the range of the controlled current is lower than the prior art. The inventor found that when the current is greater than 140 A, by dissecting the specimen, it is found that the heat input is relatively high, which will result in a relatively large heat-affected zone area on the specimen below the weld bead at the crack source. In addition to forming a martensite coarse grain zone with relatively high brittleness in the welding fusion zone, a semi-circular bainite transition zone with carbide aggregation thicker than 5 mm will be formed, and the hardness of this zone is extremely uneven, which also greatly reduces the toughness of the specimen itself. As a result, during the test, the specimen is extremely prone to cracking, directly affecting the determination of the drop weight test results. If the current is too small, the welding electrode is difficult to melt and is easily stuck to the welded part. It is preferred to use the EDPMn4 - 15 type welding electrode recommended by GB / T948, which is easy to form a crack source. During welding, the welding speed should be controlled at 45 - 90 mm / min. When the welding speed is less than 45 mm / min, the heat input will be relatively high, and the same situation as when the current is greater than 140 A is likely to occur. When the welding speed is greater than 90 mm / min, the height and width of the weld bead at the crack source cannot be guaranteed.

[0033] Beneficial effects: Through the optimization of chemical composition, the hardenability of the steel is improved, the grains are refined, and on the premise of ensuring strength, the toughness of the material, especially the low-temperature impact toughness, is improved; through the optimization of the forging process, the parts with impurities and easy segregation in the ingot are fully removed, the internal micro-defects (shrinkage cavity, porosity, etc.) in the ingot are fully forged together, and the inclusions are fully crushed, so that the strength and plasticity indexes are fully improved; by reducing the current and controlling the welding speed, the adverse effects of the weld on the microstructure of the heat-affected zone under the welding notch are reduced, and a weld bead at the crack source that meets the standard requirements is obtained, improving the accuracy of the nil-ductility transition temperature measurement; finally, a drop weight specimen that meets the corresponding drop weight test and has a high qualified rate is obtained. Specific embodiments

[0034] In the following examples, two groups of parallel tests were carried out. Unless otherwise specified, the equipment involved in the following examples is conventional equipment; the production methods involved, unless otherwise specified, are conventional methods. In the mechanical property testing methods involved: the low-temperature impact is ASTM A370-2017 "Standard Test Methods and Definitions for Mechanical Testing of Steel Products"; the drop-weight test uses ASTM E208-2017 "Standard Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels"; the grain size grading method involved is ASTM E112-2013 "Standard Test Methods for Determining Average Grain Size". The crack source weld bead shall meet the requirements of ASTM E208.

[0035] The dimensions of the standard drop-weight test specimen shall meet the requirements of ASTM E208, as shown in Table 1 below.

[0036] Table 1 Dimensions of Standard Drop-Weight Test Specimen

[0037]

[0038] As an example, for the sake of convenience of description, only the part of the SA-336F12 super pipeline related to this example is shown, and the details are as follows:

[0039] Example 1

[0040] Steelmaking: Use killed steel refined by electric arc furnace and ladle vacuum refining to produce 2 steel ingots. The chemical composition is as follows: C: 0.11% (wt%), Mn: 0.65 (wt%), Si: 0.30% (wt%), P: 0.008% (wt%), S: 0.005% (wt%), Cr: 1.0%, (wt%), Mo: 0.51% (wt%), Co: 0.03% (wt%), Ni: 0.15% (wt%), Cu: 0.07% (wt%), Sn: 0.006% (wt%), Sb: 0.005% (wt%), Pb: 0.002% (wt%), As: 0.012% (wt%), Bi: 0.001% (wt%).

[0041] Forged straight pipe: The blank steel pipe is made by using a vertical punching press and a horizontal pushing press. The forging ratio of the super pipeline blank steel pipe is 3.5, the cutting quality ratio at the riser end is 13%, and the cutting quality ratio at the bottom end is 9%.

[0042] Refer to the existing method for preliminary heat treatment, extrusion nozzle and performance heat treatment to obtain the test piece blank.

[0043] Sampling: The test piece blank is taken from the pipe body by sawing, and at least one original surface is retained. All surfaces are machined into P-2 type test pieces in Table 1.

[0044] Welding: Surfacing is carried out on the retained original surface (tensile surface), and the surface of the surfacing part is cleaned; The welding consumables are EDPMn4-15 welding consumables, with a specification diameter of Ф4.0mm. The welding rod is baked at 350℃±10℃ for one hour before welding; SMAW (manual arc welding) is used, with a current of 130A, a voltage of 20-31V, and the current polarity is DC reverse connection. A copper template is placed on the test piece. During surfacing, continuous welding is carried out from either end of the crack source weld bead to the other end, with a welding speed of 60mm / min. A water tank radiator is placed under the test piece during welding; After welding is completed, the copper template is removed after the test piece has cooled for 3 minutes, and the slag and spatter on the weld surface are cleaned with a wire brush to obtain two drop weight test pieces (test piece 1 and test piece 2).

[0045] According to the ASTM E208-2017 standard, the above drop weight test pieces are subjected to a passability test at -7℃ and a test to find the nil-ductility transition temperature. The test results are shown in Table 2:

[0046] Table 2 Drop weight test and -7℃ impact test results

[0047]

[0048] As can be seen from the above table, the NDT of the two test pieces is -22℃≤-7℃, meeting the acceptance requirements.

[0049] Example 2

[0050] Steelmaking: Killed steel is refined by an electric arc furnace for primary refining and a ladle vacuum refining process to produce 2 steel ingots. The chemical composition is as follows: C: 0.13% (wt%), Mn: 0.68 (wt%), Si: 0.25% (wt%), P: 0.010% (wt%), S: 0.004% (wt%), Cr: 0.95%, (wt%), Mo: 0.55% (wt%), Co: 0.04% (wt%), Ni: 0.18% (wt%), Cu: 0.06% (wt%), Sn: 0.007% (wt%), Sb: 0.006% (wt%), Pb: 0.001% (wt%), As: 0.010% (wt%), Bi: 0.001% (wt%).

[0051] Forged straight pipe: A blank steel pipe is produced using a vertical punching press in combination with a horizontal pushing press. The forging ratio of the super pipeline blank steel pipe is 3.5, the mass ratio of the cut-off at the riser end is 13%, and the mass ratio of the cut-off at the bottom end is 9%.

[0052] Refer to the existing method for preliminary heat treatment, extrusion nozzle, and performance heat treatment to obtain test piece blanks.

[0053] Sampling: The test piece blanks are cut from the pipe body by sawing, with at least one original surface retained. All surfaces are machined into P-2 type test pieces in Table 1.

[0054] Welding: Surfacing is carried out on the retained original surface (tension surface), and the surface of the surfacing part is cleaned. The welding consumables used are EDPMn4-15 welding consumables with a diameter of Ф3.2mm. The welding electrodes are baked at 350℃ ± 10℃ for one hour before welding. The welding method used is SMAW (shielded metal arc welding), with a current of 90A, a voltage of 20 - 31V, and a DC reverse polarity. A copper template is placed on the test piece. During surfacing, continuous welding is carried out from either end of the crack source weld bead to the other end at a welding speed of 40mm / min. A water tank radiator is placed below the test piece during welding; after the test piece has cooled for 3 minutes, the copper template is removed, and the slag and spatter on the weld surface are cleaned with a wire brush to obtain two drop-weight test pieces (test piece 3 and test piece 4).

[0055] According to the ASTM E208-2017 standard, a -7℃ passability test and a test to find the nil-ductility transition temperature are carried out. The test results are shown in Table 3:

[0056] Table 3 Drop-weight test and -7℃ impact test results

[0057]

[0058]

[0059] As can be seen from the above table, the NDT of the two specimens is -27°C ≤ -7°C, meeting the acceptance requirements.

[0060] Example 3

[0061] Steelmaking: Use killed steel refined by electric arc furnace rough melting and ladle vacuum refining to produce 2 steel ingots. The chemical composition is as follows: C: 0.16% (wt%), Mn: 0.70 (wt%), Si: 0.30% (wt%), P: 0.010% (wt%), S: 0.004% (wt%), Cr: 0.11%, (wt%), Mo: 0.60% (wt%), Co: 0.05% (wt%), Ni: 0.15% (wt%), Cu: 0.08% (wt%), Sn: 0.009% (wt%), Sb: 0.009% (wt%), Pb: 0.001% (wt%), As: 0.012% (wt%), Bi: 0.001% (wt%).

[0062] Forging straight pipe: Use a vertical punching press and a horizontal pushing press to produce a blank steel pipe. The forging ratio of the super pipeline blank steel pipe is 3.5, the cutting quality ratio at the riser end is 13%, and the cutting quality ratio at the bottom end is 9%.

[0063] Refer to the existing method for preliminary heat treatment, extrusion nozzle and performance heat treatment to obtain specimen blanks.

[0064] Sampling: The specimen blanks are taken from the pipe body by sawing, and at least one original surface is retained. All surfaces are machined into P-2 type specimens in Table 1.

[0065] Welding: Build-up welding is carried out on the retained original surface (tensile surface), and the surface of the build-up welding part is cleaned; the welding consumables are EDPMn4-15 welding consumables, with a specification diameter of Ф4.0mm. The electrode is baked at 350°C ± 10°C for one hour before welding. The welding method is SMAW (manual arc welding), the current is 140A, the voltage is 20 - 31V, and the current polarity is DC reverse connection. A copper template is placed on the specimen. During build-up welding, continuous welding should be carried out from any end of the crack source weld bead to the other end, and the welding speed is 90mm / min. A water tank radiator is placed under the specimen during welding; after the specimen cools for 3 minutes, the copper template is removed. The slag and spatter on the weld surface are cleaned with a wire brush to obtain two drop-weight specimens (specimen 5 and specimen 6) respectively.

[0066] According to the ASTM E208-2017 standard, perform the -7°C passability test and the test to find the nil-ductility transition temperature. The test results are shown in Table 4:

[0067] Table 4 Drop-weight test and -7°C impact test results

[0068]

[0069] As can be seen from the above table, the NDT of the two specimens is -17°C ≤ -7°C, meeting the acceptance requirements.

[0070] Comparative Example 1:

[0071] Except that the welding current is 180 A, the rest is the same as in Example 2, and two drop-weight specimens (Specimen 7 and Specimen 8) are obtained respectively.

[0072] The test results are shown in Table 5:

[0073] Table 5 Drop-Weight Test and -7°C Impact Test Results

[0074]

[0075] As can be seen from the above table, the NDT test results of the two specimens do not meet the requirement of NDT ≤ -7°C. Comparative Example 2:

[0076] Except that the welding current is 200 A, the rest is the same as in Example 3, and two drop-weight specimens (Specimen 9 and Specimen 10) are obtained respectively.

[0077] The test results are shown in Table 6:

[0078] Table 6 Drop-Weight Test and -7°C Impact Test Results

[0079]

[0080]

[0081] As can be seen from the above table, the NDT test results of the two specimens do not meet the requirement of NDT ≤ -7°C. Comparative Example 3:

[0082] Except that the welding speed is 30 mm / min, the rest is the same as in Example 2 or 3. The test results show that the qualified rate of the NDT test results of the specimens is only 70%. It can be seen that when the welding speed is slow, the heat input is large, which has an adverse effect on the test results.

[0083] Verification Example:

[0084] Four groups are selected from the WB36CN1 material of the same batch and the same position, and a group (three pieces) of P-2 type specimens are used for the verification test of the welding process. (The mechanical properties of this material pass the acceptance, and the -30°C drop-weight test passes the acceptance).

[0085] The welding process verification test is carried out according to Step 4 in the example, and welding is carried out by selecting currents of 90 A, 110 A, 130 A, and 140 A. The main welding process parameters are shown in Table 7.

[0086] Table 7 Welding Process Parameters

[0087]

[0088]

[0089] The notch machining and test process were carried out in accordance with the ASTM E208-2017 standard, and the test temperature was 55°C.

[0090] In the above four groups, the weld beads at the crack initiation of each of the three tests cracked when the bending deformation amount on the tensile side surface of the specimen reached the maximum deformation amount allowed by the anvil block, indicating that the welding process was effective.

[0091] The verification examples show that the welding process parameters shown in Table 3 meet the requirements of the ASTM E208-2017 standard and are effective welding process parameters.

[0092] In summary, by adopting the process method described in the present invention, optimizing the chemical composition of the SA-336F12 super pipeline, controlling the forging process, performing appropriate heat treatment, and implementing a dedicated welding process, the specimens produced have reduced the nil-ductility transition temperature of the SA-336F12 super pipeline, ensured that the drop-weight test results of the product meet the technical requirements, and have a certain margin, and can be used for CAP1400 type pressurized water reactor nuclear power units and similar units.

Claims

1. A method for preparing a SA-336F12 super pipe drop hammer specimen for a drop hammer test, characterized in that: The chemical composition is as follows: the chemical composition weight percentage is: C: 0.10-0.17% (wt%), Mn: 0.30-0.80 (wt%), Si: 0.20-0.50% (wt%), P≤0.010% (wt%), S≤0.010% (wt%), Cr: 0.80-1.10%, (wt%), Mo: 0.45-0.65% (wt%), Co≤0.05% (wt%), Ni: 0.10-0.30% (wt%), Cu≤0.15 (wt%); the balance is Fe and unavoidable impurity elements; The raw materials with the above chemical composition are subjected to steelmaking, straight pipe forging, preliminary heat treatment, nozzle extrusion, performance heat treatment, sampling and welding to obtain a drop hammer specimen for drop hammer test.

2. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 1, characterized in that: Before the straight tube forging step, the riser end and the bottom end of the steel ingot used for forging the blank steel tube should be cut off, wherein the riser end cut weight accounts for ≥12% of the steel ingot mass ratio, and the bottom end cut weight accounts for ≥8% of the steel ingot mass ratio.

3. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 1, characterized in that: In the step of forging the straight tube, the forging ratio is controlled to be ≥3.

4. The method for preparing a drop weight specimen for a SA-336F12 super pipe drop weight test according to claim 1, characterized in that: In the sampling step, the test piece blank is removed from the pipe body by cold working sawing, and at least one original surface of the test piece blank is retained for surfacing.

5. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 1, characterized in that: In the welding step, the welding rod specification used is Ф3.2 or 4.0 mm.

6. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 1, characterized in that: In the welding step, the welding current is 90-140A and the voltage is 20-31V.

7. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 5, characterized in that: The welding rod is EDPMn4-15 type welding rod.

8. The method for preparing the SA-336F12 super pipe drop weight specimen for drop weight test according to claim 5, characterized in that: In the welding step, the welding rod is baked at 350°C±10°C for one hour before welding.

9. The method for preparing a SA-336F12 super pipe drop weight specimen for a drop weight test according to any one of claims 1 to 8, characterized in that: In the welding step, continuous welding is performed from one end of the crack source weld to the other end, and the welding speed is controlled at 45-90 mm / min.

Images