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This paper provides further validation of the burst pressure estimation equations for multiple axial surface cracked steam generator tubes, recently proposed by the authors based on analytical local collapse load approach against systematic FE damage analysis results of Alloy 690 tubes with twin axial surface cracks. Wide ranges of the relative cra...
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Citations
... Thus, to see the effect of the crack location on the burst pressure, finite element (FE) damage analysis would be a useful method. The authors have recently applied the multi-axial fracture strain model to simulate failure behavior of the steam generator tube with single or multi axial cracks [8][9][10]. ...
... Using the commercial FE program ABAQUS with user subroutines, the above damage model and ductile failure simulation can be performed. The model and simulation technique can be found in more detail in our previously published papers [8][9][10][13][14][15]. Finally, it should be noted that the element size is important in FE damage analysis. ...
... This is because of the higher strength due to the strain hardening during the bending process. Burst pressure prediction for straight tube using FE damage analysis has been validated in our previous papers [8][9][10]. To verify → validate the burst pressure prediction considering the U-bending process, FE damage analysis results are compared with the experimental results of Bahn et al. [7]. ...
This paper presents numerical estimation of burst pressures of axial cracked U-bend tubes, considering the U-bending process analysis. The validity of the FE simulations is confirmed by comparing with published experimental data. From parametric analyses, it is shown that existing EPRI burst pressure estimation equations for straight tubes can be conservatively used to estimate burst pressures of the U-bend tubes. This is due to the increase in yield strength during the U-bending process. The degree of conservatism would decrease with increasing the bend radius and with increasing the crack depth.
This paper compares the difference and accuracy of bursting pressure prediction based on the flow stress σf prediction method, plastic collapse prediction method, and ductile damage model prediction method in Inconel 690 steam generator tube (SGT) with volume defect. The tensile and smooth tube bursting tests determine the parameters required for the three prediction methods. The three methods predict the bursting pressures for four deep volume defects in SGT. The results are compared and analyzed with the experimental data. The results show that the ductile damage model prediction method is the best to predict the SGT bursting pressure error with volume defects simulating the structure's deformation and damage failure process.
Purpose
The high-pressure accumulator has been widely used in the hydraulic system. Failure pressure prediction is crucial for the safe design and integrity assessment of the accumulators. The purpose of this study is to accurately predict the burst pressure and location for the accumulator shells due to internal pressure.
Design/methodology/approach
This study concentrates the non-linear finite element simulation procedure, which allows determination of the burst pressure and crack location using extensive plastic straining criterion. Meanwhile, the full-scale hydraulic burst test and the analytical solution are conducted for comparative analysis.
Findings
A good agreement between predicted and measured the burst pressure that was obtained, and the predicted failure point coincided very well with the fracture location of the actual shell very well. Meanwhile, the burst pressure of the shells increases with wall thickness, independent of the length. It can be said that the non-linear finite element method can be employed to predict the failure behavior of a cylindrical shell with sufficient accuracy.
Originality/value
This paper can provide a designer with additional insight into how the pressurized hollow cylinder might fail, and the failure pressure has been predicted accurately with a minimum error below 1%, comparing the numerical results with experimental data.
Tubes with local wall-thinning defects are often found in the heat exchangers of high-pressure feedwater heaters in thermal power plants. When serious damage is found in a tube, the tube is taken out of service by plugging it to prevent rupturing at the location of the local wall-thinning defect. This paper introduces a theoretical and numerical analysis of the stresses found in feedwater heater tubes with local wall-thinning defects under pressure and thermal loads. The effect of the dimensions of this defect on these stresses is also studied.
Using finite element analysis and regression, analytic equations for the hoop and axial stress on the inner surface of a tube with a local wall-thinning defect are proposed. The plugging criteria for a tube with this form of defect are also determined using von Mises stress theory. It is found that maximum stress occurs on the inner surface of the tube. The radial stress on the inner surface does not depend on the c/t and c/b ratio; rather, depth (c) is the main factor influencing overall stress (i.e., hoop, axial, and von Mises stress), with hoop and axial stress increasing as the depth increases. The longitudinal length (2b) also has an effect on hoop and axial stress. When the depth increases (c/t = 0.3-0.5), the effect of b is more prominent. The procedure used in this study is independent of the material properties and operating conditions, so it can be applied to other tube materials under various operating conditions in high-pressure feedwater heaters.
