Alloy 82/182/600, which is used in light-water reactors, is known to be susceptible to stress-corrosion cracking. The depth of some of these cracks may exceed the value of half-length on the surface. Although the stress intensity factor (SIF) for cracks plays an important role in predicting crack propagation and failure, Section XI of the ASME Boiler and Pressure Vessel Code does not provide SIF solutions for such deep cracks. In this study, closed-form SIF solutions for deep surface cracks in plates are discussed using an influence coefficient approach. The stress distribution at the crack location is represented by a fourth-degree-polynomial equation. Tables for influence coefficients obtained by finite element analysis in the previous studies are used for curve fitting. The closed-form solutions for the influence coefficients were developed at the surface point, the deepest point, and the maximum point of a crack with an aspect ratio a / c ranging from 1.0 to 8.0, where a is the crack depth and c is one-half of the crack length. The maximum point of a crack refers to the location on the crack front where the SIF reaches a maximum value.

This paper focuses on the expansion process of twinning-induced plasticity (TWIP) steel tubular undergoing the large circumferential plastic deformation in expandable tubular technology. The expansion process was performed by propagating a mandrel through the tubular mechanically. This paper aimed at developing the mathematical models to predict the expansion force required for the radial expansion of the TWIP steel tubular using the rigid-perfectly plastic model and the linear hardening rigid plastic model, respectively. The volume incompressible condition together with the Tresca yield criterion was used to describe the plastic behavior of the tubular material in the expansion process. Besides, the finite element analysis of the expansion process was developed using the commercial software abaqus to validate the theoretical results and determine the scope of application of the derived expansion force formula. Further to this, the effect of the process parameters, such as the expansion ratio, friction coefficient and the cone angle, on the expansion force was investigated. It was found that the expansion force difference of two models have similar variation trend. The accuracy and applicability of the expansion force formula using the linear hardening rigid plastic model improve as the expansion ratio increases and the expansion cone angle decreases.

Rupture of steel pipelines leads to the loss-of-containment that may be accompanied with loss of life or damage to property and environment. Therefore, the understanding of the fracture characteristics of steel grades used in the pipelines is essential for a safe and reliable design. In this study, a set of small-scale fracture tests was designed and conducted in order to characterize the fracture of X65 steel grade. The experimental results show that not only is the fracture strain dependent on the triaxial stress condition but also the three-dimensional nature of the stress field considerably affects the ductile fracture toughness. Moreover, parallel finite element (FE) simulation of experiments were conducted and a hybrid experimental–numerical approach was used to calibrate the Mohr–Coulomb fracture criterion and obtain the equivalent plastic strain to fracture of X65 steel as a three-dimensional function of stress triaxiality and Lode angle. An engineering application friendly ductile fracture model is proposed for X65 steel pipelines.

Corrosion perforation occurs frequently in oil field pipelines under strong oxidation environment. The causes for the failure of spray cooler after approximately 87,600 h in service have been investigated. To determine the failure mechanisms of pipes, material characterization and numerical analysis are conducted on the inlet pipeline. Ultrasonic thickness measurement is performed to check the corrosion rate and corrosion type of the pipe. Scanning electron microscopy is employed to observe the microscopic corrosion morphology of the pipeline. The microstructure of the corrosion products and the cause of corrosion are investigated using energy dispersive spectroscopy (EDS). Chemical composition and metallographic structure investigations are conducted to study the characteristics of the materials. Finite element analysis of the pipeline is employed to evaluate the deformation and stress distribution of the corrosion product film with a fluid–solid coupling model. Results of this investigation indicate that the reason of failure was the existence of strong oxidizing substances and the uneven distribution of corrosion rate that resulted from fluid accelerating corrosion.

The Advanced Power Reactor 1400 (APR1400) Steam Generator (SG) uses alloy 690 as tube material and SA-508 Grade 3 Class 1 as tubesheet material to form tube-to-tubesheet joint through the hydraulic expansion process. Failures in SGs have been identified to occur due to poorly formed tube-to-tubesheet expansion joint or due to Stress Corrosion Cracking (SCC) of the tube resulting from high residual tensile stresses in the transition zone. This paper investigates this residual stresses. Both theoretical and Finite Element Methodology (FEM) was used to assess and compare the contact pressure in the tube-to-tubesheet joint. In addition, the expansion joint axial strength was assessed by comparing the pull-out force against the joint contact force and an iterative method in FEM used to determine the limit autofrettage pressure. A single U-tube hole and tubesheet with ligament thickness were taken as a single cylinder and plane strain condition assumed. The results obtained shows that the maximum residual longitudinal tensile stress occurs at the inner surface of the tube with a value of 230.32MPa and the maximum residual hoop stress also occurs at the inner surface with a value of 151.76MPa. The joint contact force was estimated to be 20 times more than the pull-out force and the limit autofrettage pressure was estimated to be 141.85MPa.

Fatigue tests were conducted to analyze the fatigue behavior and diameter growth of large-diameter coiled tubing under the combined loads of bending and internal pressure. The experimental results reveal that mechanical limitations on the allowable diameter growth mean that the effective working life of CT at high pressures is only a fraction of the available fatigue life. The finite element software ABAQUS is used to further research the changes in diameter growth and to analyze the sensitivity of CT diameter growth to the main influencing factors, including internal pressure, tubing OD, wall thickness, yield strength, and bending radius. For coiled tubing with a diameter larger than 2-in, the diameter growth is sensitive to the above factors. As the number of bending and straightening cycles increases, the OD of the CT increases in association with obvious ovalization deformation, and the increase in the OD is closely related to the internal pressure load. The redistribution of material causes the wall thickness of the CT to become universally thinner. The ovality of the CT and the uneven decrease in wall thickness reduce the resistance to external extrusion. Therefore, it is becoming increasingly necessary to account for diameter growth as one of the key elements when predicting CT life or determining when to retire a string from service.

In this paper, numerical formulations are presented; these permit full thermal simulation of an arbitrary plane axisymmetric residual stress field encompassing hoop, radial, and axial stresses. Earlier formulations were based upon the determination of a temperature profile within the tube that could only replicate radial and hoop stresses; in general, axial stresses were incorrect. This new thermal simulation provides all three stresses and is achieved by incorporating orthotropic coefficients of thermal expansion that themselves vary with radius. Results are generally highly accurate. Crucial near-bore hoop and axial stresses can be replicated within 1%. Near-bore behavior is discussed in detail. These formulations will permit subsequent determination of stress intensity factors (SIF) for arbitrarily orientated cracks within pressure vessels in the presence of pre-existing residual stresses. Note that these thermal solutions mimic known, residual stress profiles; they do not predict residual stress profiles.

In this study, based on the rod tensile model, a conversion relationship between three-point bending specimen with fixed constraints (TPBSF) and uniaxial creep data in the large deformation stage is defined by the reference stress method. Using finite element method, conversion coefficients are determined. Then it is verified by the creep test data of A7N01 at 350 °C (Zhuang, F. K., 2014, “Research on Creep Test Method of Small Specimen Based on Beam Bending Theory,” Ph.D. thesis, East China University of Science and Technology, Shanghai, China). The results show that creep stress exponent n is the same, but creep constant B obtained by rod tensile model is much closer to uniaxial creep than beam bending model. Finally, effects of geometric parameters and friction on conversion coefficients are investigated. On this basis, the specimen cross section aspect ratio greater than 1 and the indenter radius larger than 1 mm are recommended to minimize the influence of TPBSF geometric parameters on conversion coefficients. The influence of friction on conversion coefficients can be negligible.

Pipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to growing socio-economic requirements. Most of the water mains are buried in shallow depths where the soil is partially saturated with significant spatial and temporal variations. Even though the behavior of buried pipes in such unsaturated soil condition is substantially different when compared to dry or fully saturated soil, the effect of soil saturations is overlooked in the current pipe stress prediction methods, leading to unrealistic predictions of the pipe stresses. In this study, three-dimensional (3D) finite element (FE) method was employed with advanced constitutive soil models to analyze the behavior of pipes buried in unsaturated soil condition. Having validated the FE model using reported field test data, an analytical model was proposed to predict the maximum stress in buried pipes considering soil saturation effect using a series of 3D FE analyses. Results from the FE analyses reveal that the maximum pipe stress can be significantly different when soil is in unsaturated condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in the prediction of maximum pipe stress when they are buried under realistic (i.e., nondry) soil conditions.

This paper presents a numerical study of plastic hardening models used in the stress, strain, and fatigue life simulations of a pipeline elbow under operating pressure and cyclic in-plane bending. To determine more accurate stresses, strains, and fatigue life of the elbow in cyclic loading, the material plastic hardening response and the Bauschinger effect need to be considered properly in the numerical simulation. The isotropic, kinematic, and combined isotropic/kinematic hardening models are, thus, evaluated in the elastic-plastic finite element analysis (FEA) of a benchmark beam. On this basis, those plastic hardening models are applied to simulate the elbow under combined loading of constant internal pressure and cyclic in-plane bending. With the FEA results and selected fatigue models that are commonly used in the pipeline industry, fatigue life of the elbow is predicted for each hardening model. As such, the appropriate plastic hardening model and fatigue life model to predict fatigue life of the elbow are determined.

Finite element analysis (FEA) of bolted flange connections is the common methodology for the analysis of bolted flange connections. However, it requires high computational power for model preparation and nonlinear analysis due to contact definitions used between the mating parts. Design of an optimum bolted flange connection requires many costly finite element analyses to be performed to decide on the optimum bolt configuration and minimum flange and casing thicknesses. In this study, very fast responding and accurate artificial neural network-based bolted flange design tool is developed. Artificial neural network is established using the database which is generated by the results of more than 10,000 nonlinear finite element analyses of the bolted flange connection of a typical aircraft engine. The FEA database is created by taking permutations of the parametric geometric design variables of the bolted flange connection and input load parameters. In order to decrease the number of FEA points, the significance of each design variable is evaluated by performing a parameter correlation study beforehand, and the number of design points between the lower and upper and bounds of the design variables is decided accordingly. The prediction of the artificial neural network based design tool is then compared with the FEA results. The results show excellent agreement between the artificial neural network-based design tool and the nonlinear FEA results within the training limits of the artificial neural network.

In this study, the integrity of a manhole structure made of a 78 in. high density polyethylene (HDPE) stub-end, steel ring, and blind flange, sealed with a compressed nonasbestos fiber (CNAF) gasket is investigated by means of a parametric finite element analysis (FEA). A coupled thermomechanical nonlinear FEA model is built, comprising of a heat transfer and a structural model, which allows modeling the complex thermal and mechanical loads and their interactions present during the operation of the manhole. The temperature-dependent elastic–plastic HDPE material constitutive behavior and the temperature-dependent nonlinear response of the CNAF gasket are accounted for in the model. Factors influencing the performance and integrity of the manhole such as stud-bolt pretorque level (T b ), internal pressure (P i ), and outer temperature (T o ) are considered. Based on the results, the integrity and performance of the structure are assessed in view of a leakage through the gasket criterion and a yielding of the HDPE stub-end criterion. The FEA results reveal that both T b , P i , and T o significantly influence the performance (i.e., leakage) of the gasket and the integrity (i.e., yielding) of the HDPE stub-end. At 40 °C, it is possible to find a safe operational window for a range of T b and P i values, where no leakage through the gasket or yielding of the stub-end occurs. However, as the temperature is increased this safe operational window decreases considerably, and at 80 °C safe operation cannot be guaranteed where leakage, yielding, or both simultaneously, will lead to loss in performance and integrity of the manhole structure.

The behavior of aboveground storage tanks subjected to seismic excitation was investigated using numerical methods by taking flexibility of foundation into account. The hydrostatic load due to stored liquid has an axisymmetric distribution on the tank shell and base. However, during seismic events, the hydrodynamic load originating from the seismic acceleration of liquid in the tank starts to act in the direction of the earthquake motion. This leads to a nonaxisymmetric loading distribution, which may result in buckling and uplifting of the tank structure. Finite element models were created having nonlinear material properties and large deformation capabilities. Three different tank geometries with liquid height to tank radius aspect ratios of 0.67, 1.0, and 3.0 were selected representing broad, nominal, and slender tanks. These tanks were subjected to two different hydrodynamic loading based on Housner's and Jacobsen–Veletsos' pressure distributions, which forms the basis of design provisions used in American Petroleum Institute API 650 and Eurocode 8, respectively. These pressure distributions were formulated under the assumption of rigid tank wall and base. Furthermore, each tank for a given geometry was subjected to two different foundations: (1) representing a rigid foundation and (2) representing a flexible foundation. The flexible foundation was created using a series of compression-only elastic springs attached to tank base having equivalent soil stiffness. Static analysis corresponding to maximum dynamic force was performed. The finite element results for circumferential and longitudinal stress in the shell were compared with the provisions of API 650. It was found that the effect of foundation flexibility from the practical design point of view may be neglected for broad tanks, but should be considered for nominal and slender tanks.

In this study, failure pressure prediction was conducted in a pipeline with localized corrosion in base metal (BM), heat-affected zone (HAZ), and welding bead (WB) by finite element (FE) analysis. In the gas pipeline industry, there are methods (B31G, RESTRENGH, Shell, DNV, PCORR, and Fitnet FFS) and authors' approaches (Choi and Cronin) to determine the failure pressure. However, one disadvantage of these methods is that their equations do not consider damage corrosion at the HAZ or WB. They consider corrosion only in the BM. The corrosion shape is rectangular with a radius at the edges. In this study, the corrosion defect depth (d) was varied. The corrosion defect length (L) and the corrosion defect width (W) were equal. A type of rectangular corrosion defect with a radius at the edges in the longitudinal and circumferential directions was proposed. True stress–strain curves for BM, HAZ, and WB of an API 5 L X52 were introduced in the FE program. The results show that the pressure decreases as d, L, and W increase. This is because the damage corrosion is more severe as it grows, which causes the failure pressure to decrease.

Based on the detailed three-dimensional (3D) finite element (FE) limit analyses, the present study investigates the plastic limit loads of complex-cracked pipes with two-layered materials for determining maximum load-carrying capacity or critical crack length of pipes with two-layered materials. The complex cracks in pipes with two-layered materials consist of a partial through-wall crack and 360-deg circumferential surface crack in the inner side of pipe in the same plane in pipe, which could be developed in the preemptive weld overlay region on the dissimilar metal weld (DMW) of nuclear pipe. In terms of FE limit analyses for complex-cracked pipes with two-layered materials, total thickness of pipe, depth of 360-deg internal surface crack, length of partial through-wall crack and the effect of strength mismatch between two materials are systematically considered in the present study. As for loading conditions, axial tension, global bending moment, and internal pressure are employed in the present FE analyses, and then, the confidence of the present FE procedure is confirmed by comparing the FE results with the existing solutions for complex cracks in single material. The results of the present FE plastic limit loads are compared with the existing solutions for complex-cracked pipes with two-layered materials. Also, a simple approach using equivalent single material based on the weighted average concept instead of using the properties of two materials is suggested for predicting plastic limit loads of two-layered materials. The present results can be applied to leak-before-break (LBB) analyses of nuclear piping with weld overlay.

Multilayered cylindrical structures subject to pressure and thermal loading are commonly seen in many industries. In this study, the formulas for multilayered cylinders under pressure and thermal loading are derived with an assumption that the cylinders meet generalized plane strain condition, i.e., there is no external constraint in the axial direction and the axial growths of the cylindrical layers are the same. A numerical solution procedure for double-layered cylinders subject to both pressure and thermal load is developed and implemented in a mathcad program. To validate the solution, a finite element model for a double-layered cylinder is prepared with abaqus , and its responses under pressure and thermal loading are compared to those from the mathcad program. The algorithm of the method can be extended to three or more layered cylinders. The method developed in this study allows quick optimization and efficient design refinement for multilayered cylinders without running finite element analysis (FEA).

In this paper, we developed an exact analytical 3D elasticity solution to investigate mechanical behavior of a thick multilayered anisotropic fiber-reinforced pressure vessel subjected to multiple mechanical loadings. This closed-form solution was implemented in a computer program, and analytical results were compared to finite element analysis (FEA) calculations. In order to predict through-thickness stresses accurately, three-dimensional finite element meshes were used in the FEA since shell meshes can only be used to predict in-plane strength. Three-dimensional FEA results are in excellent agreement with the analytical results. Finally, using the proposed analytical approach, we evaluated structural damage and failure conditions of the composite pressure vessel using the Tsai–Wu failure criteria and predicted a maximum burst pressure.

Deciding the boundary conditions is the most difficult part of developing an effective finite element model. Incorrect boundary conditions can cause significant errors in analysis. The finite element analysis has become a popular method of design validation for the transformer tank but the boundary conditions to be used for simulating the pressure test by finite element analysis are not clear. The pressure test analysis is carried out by assuming the bottom surface of the transformer tank to be fixed. This common practice has not been validated and requires verification. In this work, a generalized model of the transformer tank under the pressure was solved to eliminate the assumption, and the results were compared with those of the usual practice. It was found that there was significant difference in the results of the two models indicating the incorrectness of the usual practice.

In this paper, a novel visual experimental apparatus for simulating seafloor hydrothermal venting is proposed. The instrument consists mainly of an acrylic pressure vessel and a hydrothermal fluid syringe pump, which provided a 360 deg view of the simulated hydrothermal venting and plumes. Theoretical calculation and finite element analysis (FEA) were conducted to demonstrate the appropriateness of material selection and structural design for the acrylic pressure vessel. The experimental apparatus was tested at elevated temperature and pressure of up to 300 °C and 12 MPa. Hydrothermal venting experiments were successfully carried out with this apparatus, and clear images of hydrothermal plumes were obtained.

This paper proposes simplified methods to evaluate fatigue damage in a component subjected to cyclic thermal loads to visualize damage distribution by using typical computer-aided engineering systems. The objective is to perform the evaluations on a standard desktop PC within a reasonably short computation time. Three simplified methods for defining elastic stress ranges are proposed in place of the method in the ASME Subsection NH procedures. A thermal fatigue test that was previously performed using a type-304 stainless steel (304SS) cylinder is simulated to validate the proposed methods. Heat transfer and elastic analyses are conducted. Simultaneously with the analyses, fatigue usage factors are calculated using user subroutines formulated in this study, including the three simplified methods and the ASME NH-based method. The calculated values of the fatigue usage factor are visualized using a graphical user interface (GUI) incorporated into a commercial finite-element analysis (FEA) code. The fatigue usage factor distribution obtained using the simplified methods could be calculated without requiring large amounts of memory and long computation time. In addition, the distribution of the fatigue usage factor was consistent with the distribution of cracks observed in the test.