Energy test of drop weight tear test of hottest pi

Abstract: This paper shows the reliability of the system through the development and research of the energy test system of the domestic hammer tear tester and the successful application of the system in the Angang chemical inspection center. The successful development of the system provides experimental support for the quantitative study of the influence of various factors on the fracture toughness of pipeline steel and the theoretical study of the fracture mechanism of pipeline steel under impact load, improves the inspection level, improves the test methods and means, fills the domestic gap, and also improves the price advantage and improves the market competitiveness of domestic drop weight testing machines

key words: Determination of energy in drop weight tear test of pipeline steel

Preface:

with the development of China's oil and gas industry, the smelting and welding technology of pipeline steel is achieving leapfrog development at an unprecedented speed, which also brings some new problems to the evaluation test of pipeline steel. For pipeline steel with high toughness and large wall thickness, the size of ordinary Charpy impact specimen is too small to reflect the stress state in the actual component, and the results are discrete, which can not meet some special requirements. The results of the pipeline steel drop weight tear test (DWTT) are quite consistent with the results of the full-scale explosion test of the steel pipe, and it is easy to operate. Therefore, the researchers proposed to use the hammer breaking energy value of the drop weight tear test to replace the Charpy impact energy value. This energy test method is more close to the service state of the material and reflects the real situation of its fracture. Therefore, the drop weight tear test is widely used in the evaluation of the fracture toughness of pipeline steel, Become one of the important quality acceptance indicators. In n.2.2 of technical conditions for spiral seam submerged arc welded pipe for West to east gas transmission project, it is required not only to evaluate the shear area of the sample, but also to provide the energy value of the drop weight tear test. However, in view of the condition of the test equipment, only a few scientific research institutions can measure the energy, while most steel mills and pipe manufacturers cannot provide accurate energy measurements. This paper shows the reliability of the system by studying the energy testing system of the domestic hammer tearing tester developed by the author 3 (discussed in more detail on the station) and the successful application of the system in the inspection center of Angang chemical. The successful development of the system provides experimental support for the quantitative study of the influence of various factors on the fracture toughness of pipeline steel and the theoretical study of the fracture mechanism of pipeline steel under impact load, improves the inspection level, improves the test methods and means, fills the domestic gap, and improves the market competitiveness of domestic drop weight testing machines

1. principle of energy measurement [1]

there are generally three methods of energy measurement: kinetic energy difference method, potential energy difference method and differential integration method. This system adopts differential integration method

the instantaneous force value f (T) in the test process is measured by the force sensor installed on the hammer, and the instantaneous speed V (T) of the sample is measured by the speed sensor installed on the testing machine. The instantaneous displacement s (T) is calculated by the system. From F (t) and S (T), the relationship f (s) between any instantaneous force and deformation can be obtained. In this way, the product of the force value f (s)) at each moment and the differential ds of its deformation is the "instantaneous work" at each instant. Integrating the work values corresponding to different times can obtain all the work values absorbed by the specimen from the beginning of deformation to complete fracture. The load deformation curve is drawn by using the computer data acquisition and the analysis system in which one end of the auxiliary oil cylinder is connected with the clamping jaw. The area under the curve is the work done by the load acting on the sample by the falling hammer in the process of striking the sample, that is, the energy absorbed by the sample; Therefore, according to the load deformation curve, the energy deformation curve can be drawn

w= ∫ f (s) ds

where: W - energy absorbed by the sample (J)

f (s) - force on the sample (n)

at more than 6 a.m. on the 20th

2. Structural design of the system

the structure of the whole test system is shown in Figure 1. The real-time speed is measured by the photoelectric sensor, and the instantaneous force value is measured by the force sensor on the hammer head, and the data of these two aspects are transmitted to the signal conditioner, Then the conditioned signal is sent to the computer through the data acquisition card, and processed by the system data acquisition and processing software to obtain various measurement data, which is fed back to the computer to print out the test report

Figure 1 Composition of the test system

3. Test curve analysis

two curves (load deformation curve and energy deformation curve) can be obtained at the same time in the test, and the two curves can also be combined. For convenience, the combined curve shown in Figure 2 is generally used in the test report

Fig. 2 test process curve

the abscissa of the curve is the displacement of the hammer head during the striking process (the displacement from the beginning of contact with the sample to the static process), and the ordinate is the force value change and energy change from the force generated by the contact between the hammer head and the sample to the complete fracture of the sample. This curve is actually equivalent to a process of high-speed compression deformation and bending deformation

4. Reliability evaluation of the test system

4.1 dynamic characteristics of the drop weight test system

the dynamic characteristics of the test system have a great impact on the test results, which can be described by the unit impulse response function, step response function, frequency response function or transfer function of the system. In order to realize the undistorted test, the amplitude frequency characteristic of the system is required to be constant within the measured frequency range. In the drop hammer test of pipeline steel, the hammering is completed in a few milliseconds to tens of milliseconds. The impact pulse itself has a wide frequency range, so the frequency response of the test system is required to be wide. The frequency response of the test system is far greater than the bandwidth of the shock pulse, which ensures that the signal will not be distorted

4.2 through the energy analysis of the non hammered sample, the performance evaluation of the test system

the sample is not hammered, indicating that the potential energy of the heavy hammer is almost absorbed by the sample. A material sample with a thickness of 43mm was tested, of which 3 samples were not broken by hammering. The test results are shown in Table 1. Figure 3 shows the test results of the sample not broken when the falling hammer falls from a height of 1.5 meters. It can be seen from the test results that the test curves of the three samples and the three unbroken samples are consistent in shape. The error between the measured energy and the theoretical potential energy of the hammer is very small (about 2%), and the test error can be kept very small in a large energy range, indicating that the test system has good reproducibility, high accuracy and good linearity

Fig. 3 test results of samples (after digital filtering)

Table 1 energy test results of a steel

test number sample thickness (mm) drop hammer height (mm) hammer potential energy (J) measured energy (J) maximum load (KN) The error of measured energy/potential energy of heavy hammer

431200 20403 20096 574 98.49% 1.51%

431500 25504 24980592 97.94% 2.06%

432000 34006 33381612 98.1% 1.9%

conclusion:

the application of this energy testing system has made the energy measurement of drop weight tear test change from qualitative to quantitative. It is the largest domestic drop weight tear test equipment with full-automatic energy test system at present. It has received good results after being installed and used in Angang chemical inspection center. The system improves the inspection standard of pipeline steel, provides experimental support for the quantitative study of the influence of various factors on the fracture toughness of pipeline steel and the theoretical study of the fracture mechanism of pipeline steel under impact load, improves the inspection level, improves the test means and methods, fills the domestic gap, and improves the market competitiveness of domestic drop weight testing machines

References:

1 Wang Shuren, Cui Zhixin Application practice of pipeline steel drop hammer 316 external insulation tear test [J] Welded pipe, 2004, 27 (4): 62 ~ 63

Wang Shuren 1st generation liberal arts 2 Shan Jingmin 3

(1. steel pipe plant of China Petroleum Pipeline administration 111000 2. Angang chemical inspection center 114001 3. Shaanxi University of science and technology 712081) (end)