Test method for high grade pipeline steel ctod resistance curve
By using a multi-sample method and fitting formula, the problem of uniformity in the CTOD resistance curve test of high-grade pipeline steel was solved, achieving rapid and accurate standardized test results, which are applicable to the detection and evaluation of high-grade pipeline steel.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA NAT PETROLEUM CORP
- Filing Date
- 2021-12-24
- Publication Date
- 2026-06-02
Smart Images
Figure CN116337590B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to experimental techniques for fracture toughness of pipeline steel, specifically a test method for the CTOD resistance curve of high-grade pipeline steel. Background Technology
[0002] A significant trend in the development of oil and gas pipelines, especially natural gas pipelines, is the adoption of large-diameter, high-pressure transportation and the use of high-strength steel. Increasing the operating pressure and pipeline diameter improves transportation efficiency and the economic benefits of pipeline operation. However, as the operating pressure of oil and gas pipelines increases and the pipe diameter continues to grow, the risk of ductile fracture also increases. This necessitates that high-strength pipeline steel possesses sufficient toughness to ensure the safety of pipeline operation while simultaneously increasing pipeline transportation capacity.
[0003] In the field of pipeline steel, toughness is typically tested and evaluated using CVN (Crack Thrusting Test), DWTT (Drop Weighing Test), and CTOD (Crack Tip Opening Displacement Test). CVN samples are easy to prepare and operate, and are often used as a quality control and inspection method. DWTT is mostly used to evaluate the crack arrest performance of materials, while CTOD is often used to evaluate the crack resistance of materials.
[0004] The CTOD value reflects the crack tip material's resistance to cracking. A higher value indicates better crack resistance, i.e., better toughness. The main testing methods for CTOD resistance curves are the multi-sample method and the single-sample method. The multi-sample method involves loading a series of specimens of identical nominal size to different pre-selected displacement levels and measuring the corresponding crack propagation. Each specimen becomes a point on the resistance curve. The single-sample method uses elastic compliance or other techniques to obtain multiple points on the resistance curve through testing a single specimen; the multi-sample method is preferred in resistance curve testing. However, the testing procedures are not standardized, and the obtained CTOD resistance curve results cannot be directly compared.
[0005] However, in the multi-sample method, there is no unified method for determining the displacement value to be applied to each sample. Summary of the Invention
[0006] To address the problems existing in the prior art, this invention provides a test method for the CTOD resistance curve of high-grade pipeline steel, offering a new approach for the detection, evaluation, and standardization of CTOD tests on high-grade pipeline steel.
[0007] This invention is achieved through the following technical solution: a test method for the CTOD resistance curve of high-strength pipeline steel, wherein the method is used when conducting experiments on the CTOD resistance curve of high-strength pipeline steel.
[0008] S1, sample processing is performed on the material to be tested, and the sample is selected through sample processing;
[0009] S2, the temperature of the sample is controlled within the set range by the testing machine;
[0010] S3, pre-cracks are made on the sample according to the length of the sample;
[0011] S4. CTOD test was conducted using the multi-sample method to obtain δ-Δa data points that meet the requirements.
[0012] S5. Fit the resistance curve to the experimental data point δ-Δa to obtain the fitted curve.
[0013] Furthermore, the material to be tested in S1 is high-strength and high-toughness pipeline steel.
[0014] Furthermore, for the sample processing of S1, a sample block was cut from a high-strength and high-toughness pipeline steel of the same material, and it was processed into a three-point bending CTOD sample by mechanical processing method, with a quantity of n pieces.
[0015] Furthermore, the testing machine selected in S2 is the MTS testing machine.
[0016] Furthermore, when controlling the sample temperature, S2 controls the test temperature deviation within ±2℃.
[0017] Furthermore, the pre-crack length a0 of S3 is 0.5W, the ratio of minimum to maximum force during the pre-crack process is 0.1, the span S is 4W, and the diameter of the support roller is ≥0.5W.
[0018] Furthermore, in S4, a multi-sample method is used to obtain the CTOD resistance curve, where,
[0019] A set of identical specimens were loaded to different pre-selected displacement levels, and the corresponding crack propagation Δa for each specimen was measured. The crack propagation Δa was then combined with the corresponding δ to form a resistance curve δ-Δa. During the test, the first specimen was loaded until the force dropped to 85%-90% of the maximum force, and then unloaded. The unloading displacement of the other specimens was calculated based on the unloading displacement of this specimen. s2 is the displacement value at the maximum force, and s6 is the displacement value when the force drops to 85%-90% of the maximum force. The distance between s2 and s6 was divided into four equal parts, each with a length of Δ. s1 was taken before s2, and its value is given by formulas 1 to 5.
[0020]
[0021] s1 = s2 - Δ + 0.1 (Formula 2)
[0022] s3 = s2 + Δ (Formula 3)
[0023] s4 = s2 + 2Δ (Formula 4)
[0024] s5 = s2 + 3Δ (Formula 5)
[0025] The selected displacement values are s1, s2, s3, s4, s5, and s6 in sequence. Tests are conducted based on the selected displacement values s1, s2, s3, s4, and s5, and the corresponding crack propagation amount Δa and crack tip opening displacement δ are measured for each specimen.
[0026] Furthermore, S5 fits the δ-Δa data points that meet the standard requirements in the software, and the fitting formula is:
[0027] y = a + bx c (a≥0, b≥0, 1≥c≥0), the resistance curve is calculated.
[0028] Furthermore, the software can be Origin software.
[0029] Compared with the prior art, the present invention has the following beneficial technical effects:
[0030] 1. The test method provided by this invention can quickly and accurately determine the displacement value of each point in the CTOD resistance curve, saving a lot of test time.
[0031] 2. To standardize the test method for CTOD resistance curves, so that the test results of CTOD resistance curves obtained by each laboratory can be directly compared. Attached Figure Description
[0032] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0033] Figure 1 A schematic diagram for selecting CTOD sample images;
[0034] Figure 2 Force-displacement curve;
[0035] Figure 3 For X80 pipeline steel force-displacement curve;
[0036] Figure 4 This is a graph showing the resistance curve of the X80 pipeline steel. Detailed Implementation
[0037] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.
[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.
[0042] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0043] In a preferred embodiment of the present invention, the following technical solution is adopted:
[0044] The first step is to select X80 high strength and toughness pipeline steel as the test material, specifically Φ1422×38.5mmX80 PSL2 straight seam submerged arc welded steel pipe, the pipe body of which is transverse.
[0045] like Figure 1 As shown, in the second step, a sample block is cut from the high-strength and high-toughness pipeline steel of the same material, and it is processed into a three-point bending CTOD specimen by mechanical processing method, with W / B=2 and the specimen size being 20mm×40mm×200mm; the quantity is 10 pieces; the size and quantity selected in this step are determined according to the actual situation.
[0046] The third step is to conduct experiments using an MTS testing machine based on the selected steel pipe.
[0047] The fourth step is to control the test temperature at 0℃ during the CTOD test, with a specific deviation of ±2℃.
[0048] The fifth step is to pre-crack the sample. The pre-crack length a0 = 20 mm, the minimum to maximum force ratio during the pre-crack process is 0.1, the span S = 160 mm, and the diameter of the support roller is 20 mm.
[0049] like Figure 3 As shown, in step six, a CTOD test is conducted using the multi-sample method. Specifically, the first sample is loaded until the force value drops to 85% of the maximum force, then unloaded. The unloading displacement of the other samples is determined based on the unloading displacement of this sample; s2 = 3.3 mm, s6 = 6.9 mm. The distance between s2 and s6 is divided into four equal parts, each with a length Δ = 0.9 mm. Therefore, s1 = 2.5 mm, s3 = 4.2 mm, s4 = 5.1 mm, and s5 = 6.0 mm.
[0050] The experiment was conducted based on the selected displacement values s1, s2, s3, s4, and s5, and the corresponding crack propagation amount Δa for each specimen was measured. The value of δ was obtained according to the formula in GB / T 21143-2014, and the results are shown in Table 1.
[0051] Table 1 - CTOD Test Results of X80 Pipeline Steel
[0052]
[0053]
[0054] The six δ-Δa data points obtained meet the requirements of GB / T 21143-2014.
[0055] Step 7: Fitting the resistance curve
[0056] like Figure 4 As shown, to fit the δ-Δa data points in Origin, the drag curve is obtained; δ-Δa drag curve: δ=0.010+0.705Δa 0.435 .
[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
Claims
1. A method of testing the CTOD resistance curve of a high-grade pipeline steel, characterized in that, The experiment passed when testing the CTOD resistance curve of high-grade pipeline steel. S1, Sample processing of the material to be tested, and selection of samples through sample processing; S2, the temperature of the sample is controlled within the set range by the testing machine; S3, pre-cracks are made on the sample according to the length of the sample; S4, CTOD test was conducted using the multi-sample method to obtain samples that meet the requirements. Data points; among them, the method of CTOD test by multiple specimens is as follows: a set of specimens of the same size are loaded to different pre-selected displacement levels, and the corresponding crack propagation amount of each specimen is measured. Corresponding to it Composition of resistance curve During the test, the first specimen was loaded until the force dropped to 85%-90% of the maximum force, then unloaded. The unloading displacement of the other specimens was calculated based on the unloading displacement of this specimen. s2 is the displacement value under maximum force, and s6 is the displacement value when the force drops to 85%-90% of the maximum force. The distance between s2 and s6 is divided into four equal parts, each with a length of... ;s1 is taken before s2, and its value is shown in formulas 1 to 5; (Formula 1) (Equation 2) (Formula 3) (Formula 4) (Formula 5) The selected displacement values are as follows: s 1、 s 2、 s 3、 s 4、 s 5、 s 6. Based on the selected displacement value s 1、 s 2、 s 3、 s 4、 s 5. Conduct the test and measure the corresponding crack propagation amount for each specimen. ; Crack tip opening displacement ; S5, performing a fit of the resistance curve to the experimental data points to obtain a fitted curve.
2. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, The material to be tested in S1 is high-strength and tough pipeline steel.
3. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, S1 samples were prepared from high-strength and high-toughness pipeline steel of the same material. Sample blocks were cut and machined into three-point bending CTOD samples using mechanical methods. The number of samples was n.
4. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, The testing machine selected in S2 is the MTS testing machine.
5. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, When controlling the sample temperature, S2 ensures that the test temperature deviation is controlled within ±2℃.
6. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, The pre-crack length of S3 is a0=0.5W, the ratio of minimum to maximum force during the pre-crack process is 0.1, the span is S=4W, and the diameter of the support roller is ≥0.5W, where W is the width of the sample.
7. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 1, characterized in that, S5 the data points are fitted in software to a formula of the form: Data points were fitted in software to a formula of the form: , a > 0, b > 0, 1 > c > 0, the resistance curve is calculated.
8. A method of testing the CTOD resistance curve of a high-grade pipeline steel according to claim 7, characterized in that, The software used is Origin.