Engineering Estimation Method for Stability Analysis of Pressure Vessel and Pipeline LBB Dong Yamin, Feng Feng, Huang Kezhi (Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China) Approximate relationship, constructing engineering approximate relationship between tear instability and plastic instability stress under composite loading Expression: For the four materials and 40 crack configuration conditions, the instability evaluation is calculated: compared with the results obtained by the fine analysis method proposed by P, the general deviation does not exceed 4%, which meets the engineering evaluation requirements. In view of the fact that the engineering estimation method of LBB stability analysis is easy to be mastered and accepted by non-professionals, and can save time and effort, it is expected to play an important role in the development of LBB evaluation technology.
1LBB stability analysis method review 1.1 LBB stability analysis technology research and application In order to ensure the safe operation of pressure vessels and pipelines, LeakBefore Break analysis technology has been proposed in recent years to prevent double-end shear fracture of pipelines; In LBB analysis technology, crack propagation stability analysis is the most important link.
In 1984, the US Nuclear Regulatory Commission issued the LBB line elastic acceptance criteria 'it was established based on the principle of linear elastic fracture mechanics. Due to the linear elastic fracture initiation mechanism, the bearing capacity of crack stability expansion could not be exploited and it could be used for primary safety review.
The British CEGB/R6 method and the US GE-EPRI method can be used for elastoplastic fracture analysis. The former uses the evaluation curve for stability analysis, and the latter is evaluated for instability by the J-integration stability evaluation chart. The lack of a feasible evaluation curve, or the lack of sufficient J-integral finite element solution, makes the LBB elastoplastic stability analysis technique difficult.
The full-plastic J-integral numerical solution of the complete hoop-through crack under composite loading provides the crack propagation stability analysis technique under composite loading, which enables the LBB evaluation technology to be carried out smoothly.
1.2 Application prospects of engineering estimation methods for LBB stability analysis According to the engineering approximate relationship expression of tear instability and plastic instability stress under composite loading, it makes the LBB stability analysis process much better than the detailed analysis method provided. Simplified, easy to be accepted by non-professionals, saves time and effort, can ensure the accuracy of assessment, and meet engineering requirements, it is expected that its application prospects are broad.
2 Pipe-ring through-crack under composite loading, engineering approximate relationship between tear instability stress and plastic instability stress 2.1 Simple load and composite loading, J-integral expression of circumferential through crack J-integration under the combined loading of bending, bending, and bending, as in the formula G): heart = go r-. to (one ring 4r+1 corpse 0 good, ugly *, ugly * is the J-integral full plasticity under the corresponding loading mode solution.
Plastic fracture assessment; based on the small amount of total plastic solution provided, the J-integral fully plastic solution of the complete hoop-through crack under composite loading is constructed and provided, and the crack propagation stability analysis technique under composite loading is established, which is stable for LBB. Sexual analysis method.
2.2 Under various loading modes, the plastic instability expression of the circumferential penetrating crack is the plastic instability expression of the circumferential penetrating crack under the combined loading of tension, bending and bending, as in the formula (2): from the failure mechanism The crack-containing configuration may be a tear instability failure or a plastic instability failure. After detailed tear instability and plastic instability assessment, the failure stress in the component can be determined.
2.3 Under simple loading, the approximate relationship between the torsional stress and the plastic instability stress of the circumferential through-crack tear is the engineering approximate approximation of the force and plastic instability stress: the optimization method of the elastoplastic fracture evaluation of the equation (1) and EPRI It is obtained by evaluating the instability; cr is the plastic instability stress of the crack configuration under simple tensile and pure bending loading, which can be calculated according to the expression (2).
The expression (3) has sufficient accuracy to meet the engineering evaluation requirements, and it is the basis for establishing the approximate relationship between the tear instability stress and the plastic instability stress engineering under the composite loading.
2.4 Under the cyclically penetrating crack composite loading, the expression of the approximate relationship between the tear instability stress and the plastic instability stress engineering has been established: under simple loading, the torsional instability stress and plastic instability stress of the circumferential penetration crack have engineering approximation. Relationship (3> For composite loading, the total stress of tear instability and the total stress of plastic instability can be written as (*T, +a), respectively, and the expression (3) can be trusted. Under certain conditions, It should be possible to establish a similar engineering approximation relationship with sufficient accuracy, as shown in the expression (4): the bending stress under the failure of the composite load under the tear failure; 4 is the plastic instability failure under the composite loading The bending stress underneath; the reason why the expression (4) can be established clearly and clearly is based on the following considerations: According to the numerical calculation results of the fine analysis method of LBB stability, it is found that the expression (4) is only pulled at the left end. The change in tensile stress changes slowly. When =cr, /(T.<0.375, it is basically stable, that is, within a certain range, the left end of expression (4) is weakly related to *7.
When crf->0, the expression (4) is connected with the expression (3), which lays the foundation for the establishment of the expression (4).
A series of fine analysis of stability can be performed on various materials and various crack configuration conditions, and engineering estimation is performed at the same time according to the expression (4), and the reliability of the expression (4) is confirmed by comparison.
The processing on the right side of expression (4) can alleviate the effects of 0/0 and their respective errors.
The numerical calculation shows that the expression (4) is reliable and can meet the engineering evaluation requirements.
3Comparison of the engineering estimation method of the LBB stability analysis and the calculation result of the fine analysis method under the composite loading According to the expression (4), the expression of the tear instability stress 54 under the compound loading is: firstly according to the proposed optimization method The tearing instability evaluation is performed on the simple loading such as stretching and bending, and then the parameters are calculated. Therefore, the bending instability stress under the composite loading can be calculated according to the engineering estimation formula (5) 5 (4. 3.1 Mechanical properties of the material and The mechanical properties and crack geometry of the four kinds of crack geometry are as follows: 3.2 The tearing instability stress obtained by the engineering estimation method and the instability stress (5=Â¥) obtained by the fine analysis method are as shown in Table 1. Table 1 Comparison of the results of the estimation method and the fine analysis method In Table 1, the tearing instability stress under the combined loading of 40 kinds of cracks in four kinds of materials, the maximum deviation is = 4.4%, which indicates that the established project The estimation method is guaranteed to be accurate and can meet the engineering evaluation requirements. Because the estimation process is more simplified than the fine analysis method and is easily accepted by non-professionals, it is expected to be in the LBB stability analysis. Play an important role.
IV. Engineering Estimation of Stability Analysis of Pipeline Circumferential Cracks under Combined Loading. Estimation and Determination: The maximum bending moment value of the tear instability.
According to the working pressure; the tensile stress during normal operation can be obtained as follows: According to the optimization evaluation method, it can be calculated: it can be calculated: and: and: then, the maximum bending moment for inducing the tear instability is: estimated engineering estimation The error is not more than 5 5 Conclusion 1. With the simple approximation, the engineering approximate relationship between the torsional stress and the plastic instability stress of the circumferential through crack is established, and the engineering approximate relationship under the combined loading condition is established. Engineering estimation method for LBB stability analysis.
2. Compared with the results obtained by the LBB stability analysis method, it shows that the engineering estimation method can ensure the accuracy of the evaluation and meet the accuracy requirements of engineering evaluation.
3. In view of the engineering estimation method provided in this paper, the evaluation process is more concise and convenient than the fine analysis method, and is easy to be accepted by non-professionals. It is expected to play an important role in LBB stability analysis.
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