Shell and tube heat exchangers are widely used in various industries for effective heat transfer between fluids. However, these exchangers often encounter challenges such as corrosion and wear, which can greatly affect their performance and lifespan. To address these issues, utilizing stainless steel (SS) made heat exchangers can significantly improve the corrosion and wear resistance of heat exchangers and their components. In this study, welding procedure specifications (WPS) for welding tube-to-tube sheet (TTS) joint mock up is qualified as per ASME IX QW 193 and ASME Section VIII Div. 1 UW-20. Experimental studies were performed on a 50 mm thick SS tube sheet (SA240 Gr TP 316 L) welded with SS tubes that have an outside diameter (OD) 19.05 mm and thickness 1.65 mm (SA 312 Gr TP 316 L). Both the tube and tubesheet materials are SS which is widely used due to their excellent corrosion resistance, strength and versatility. The welding of 10 samples was carried out using a gas tungsten arc welding (GTAW). In order to evaluate the quality of TTS joint, visual testing (VT), penetrant testing (PT) and macro-examination for minimum leak path (MLP) was performed according to welding procedure which can also satisfy the inspection standard. Furthermore, hardness test, ferrite test, and chemical analysis were also conducted to confirm the quality and integrity of the welds. The successful WPS provides a good reference (process parameters) for the welding quality control during the manufacturing SS heat exchangers for corrosion resistance.
Water hammer in long-distance pumped water transmission pipelines can cause severe safety incidents, making effective protection for pipelines and pump stations essential. However, optimizing parameters of water hammer protection devices remains challenging, as engineers often rely on time-consuming, experience-based trial-and-error methods. To address this, a multi-objective optimization framework combining random forest (RF) and nondominated sorting genetic algorithm II (NSGA- II) is proposed. An RF model is trained to map relationships between device parameters and extreme water hammer pressures. A multi-objective optimization model is developed with unidirectional surge tower water level, maximum pressure, and minimum pressure as objectives. Furthermore, Shapley additive explanations (SHAP), an interpretable machine learning method, is employed to reveal the importance and interactions of parameters. Results show that the approach rapidly identifies optimal device settings, achieving a 79% increase in minimum pressure, a 25% reduction in surge tower water level, and negligible change in maximum pressure compared with the original design. SHAP analysis quantitatively verifies that connecting pipe diameter and local resistance coefficient of the downstream air vessel are the dominant parameters governing transient pressure behavior. The nonlinear interaction of the two parameters is quantitatively characterized, showing that the increase in positive-pressure peaks induced by a larger connecting pipe diameter can be counterbalanced by a corresponding rise in local resistance coefficient, reflecting a codependent mechanism between flow inertia and local head loss. This data-driven interpretation provides quantitative insight into parameter coupling and offers practical guidance for optimizing water-hammer protection device design.
In order to improve the safety of vehicle-mounted liquid hydrogen storage and transportation and reveal the leakage and diffusion characteristics of vehicle-mounted liquid hydrogen in open space, a numerical simulation model of liquid hydrogen leakage and diffusion was established. The leakage and diffusion behavior of liquid hydrogen during transportation was studied. The influence of wind speed, leakage rate, leakage time, wind temperature, ground temperature, and other factors on the diffusion behavior of hydrogen clouds was analyzed. The results show that the flammable hydrogen cloud formed after the leakage of liquid hydrogen diffuses from the near ground to the distant air, and the volume expands rapidly, resulting in a significant increase in the potential hazard area. The combustible hydrogen cloud has typical radial concentration gradient distribution characteristics, and the hydrogen concentration decreases from the center to the periphery. The spatial diffusion range and volume change are mainly affected by wind speed, leakage rate, and leakage duration, while the influence of wind temperature and ground temperature is relatively limited.
Nondestructive evaluation techniques are increasingly applied to estimate the buckling load of shell structures without inducing failure. This study employs the force-stiffness (F-s) method to evaluate the buckling load of oblate ellipsoidal shells subjected to external pressure. Experiments are conducted on five steel shells with comparable R/t ratios, recording pressure, strains, and crown deflections up to failure. Using deflection data up to 80% of the buckling load, the F-s technique predicts buckling with similar to 90% accuracy, while incorporating crown strain data improves accuracy to similar to 95%. All shells fail within a pressure range of 2.7-3.4 MPa. The method is further validated on 3D-printed aluminum shells, showing promising consistency, though additional testing is required to refine accuracy. Finally, the F-s approach is demonstrated for real-time prediction of a large-scale shell, nearly three times larger than the experimental models, highlighting its scalability and potential for structural applications.
The mechanical behavior of three dimensional (3D)-printed polymeric materials, particularly those obtained through fused filament fabrication (FFF), has been extensively investigated over the last few years with the aim of scaling the use of these materials from prototyping purposes to structural applications. In this regard, acrylonitrile-styrene-acrylate (ASA) terpolymer emerges as a promising option, given that this polymer displays outstanding resistance to weathering agents, together with reasonable mechanical properties, both dimensional and thermal stability, and relatively good resistance to environmental stress cracking, among other properties. One of the necessary requirements when studying the structural use of a given material is to have tools for evaluating its structural integrity in the presence of defects. Thus, this paper provides an analysis of fracture loads in 3D printed (FFF) single edge notched bending (SENB) specimens containing U-notches and made of pure ASA and carbon fiber reinforced (10 wt. %) ASA. The specimens cover three different raster orientations (0/90, 45/-45 and 30/-60) and contain four different notch radii (from 0 mm up to 2 mm). The fracture loads were predicted using the failure assessment diagram (FAD) methodology in conjunction with the theory of critical distances (TCD). The results show how this FAD-TCD approach is capable of providing safe, accurate predictions of fracture loads for this type of material when containing notch-type defects. The safety of the predictions relies directly on the criterion (in terms of probability of failure) assumed to define the mechanical properties included in the FAD approach.
In ocean engineering, spherical shells often serve as common pressure vessels. Under external pressure, these shells tend to suffer from buckling damage. To ensure the stability of spherical shells and optimize their structural design, it is necessary to predict their buckling load under external pressure. However, current predictions based on the knockdown factors are relatively conservative, and predictions based on common machine learning methods lack physical orientation. Based on the energy barrier method, a physics-informed one-dimensional-convolutional neural networks (1D-CNN) model is proposed to address this problem. These newly developed physics-informed features and loss functions improve the accuracy of the model. Both metallic and nonmetallic spherical shells datasets are used to establish the models. Then, we determine the optimal hyperparameters using K-fold cross-validation and the optuna optimization framework and compare their predictive performance against models like decision trees (DT), random forests (RF), and artificial neural networks (ANN). The results indicate that our model outperforms the others in predictive accuracy. Additionally, the potential of the model, guided by the energy barrier method, is demonstrated by comparing various loss functions. For the actual spherical shell, the trained model can be used for buckling analysis and the optimized design of spherical shells in engineering practice.
The used fuel container (UFC) is a metal container for long-term management (i.e., disposal) of used nuclear fuel in a deep geological repository. The UFC employs a nonstandard closure weld joint with a shallow partial penetration. The container was constructed following the principles of ASME Boiler and Pressure Vessel Code (BPVC) Section III, Division 3, and the weld is inspected by surface and volumetric nondestructive examination (NDE) methods, i.e., eddy current testing (ET) and ultrasonic testing (UT). NDE acceptance criteria for this customized weld joint are developed based on the effect of porosity and its interaction with the partial penetration weld geometry. The safety margin of the proposed acceptance criteria is verified through tensile tests of welded specimens containing artificial defects of bounding geometry. The effectiveness of the acceptance criteria is further demonstrated in full-scale prototype manufacturing and external pressure tests.
Slender tubes are prone to buckling failure under compressive loads, which remains a critical challenge in the design of thin tubes. The fabrication of slender tubes is susceptible to manufacturing eccentricity, which reduces the buckling strength. The geometric axes of a practical 3D heat exchanger tube may not align perfectly due to manufacturing eccentricities that span multiple planes. This study introduces a novel methodology that consolidates multidirectional eccentricities into a single representative parameter, thereby enabling the application of the simplified Euler's buckling equation for strength assessment. Based on detailed buckling experiments on slender heat exchanger tubes, the proposed bracket square sum and root (BSSR)-based combination method is shown to reliably predict axial compression behavior by accounting for multiplane eccentricities within a 1.0% variation. These findings provide a robust framework for integrating experimental insights with classical theory, offering improved reliability and efficiency in the structural evaluation of buckling strength in practical three-dimensional tubular structures under compressive loads.
To develop a microdamage evaluation method applicable to in-service equipment under low-temperature conditions, this study systematically investigates the mechanical properties and fracture behavior of 09MnNiDR cryogenic steel over a broad temperature range from room temperature to -196 degrees C. The small punch test (SPT) technique is employed, supplemented by electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) for micromechanism analysis. Results indicate that under cryogenic conditions, dislocation slip is suppressed, leading to a more uniform distribution of plastic strain. Concurrently, the deformation process at low temperatures refines the grains within the plastic zone through mechanisms such as mechanical subdivision. As temperature decreases, the material strength increases linearly, exhibiting a significant cryogenic strengthening effect. The fracture mode transitions from ductile to brittle, with a ductile-to-brittle transition zone identified near -150 degrees C. An empirical formula based on SPT deformation energy is proposed to predict yield and true tensile strength, with prediction errors below 6%. By introducing a normalized energy parameter, an empirical correlation model is established between the SPT ductile-to-brittle transition temperature (DBTT) and the standard Charpy impact transition temperature. This study presents a viable methodology for safety assessment of in-service cryogenic pressure vessels through minimally invasive testing and performance prediction.
The oxidation resistance, carburization resistance, and mechanical properties of ethylene pyrolysis furnace tube alloys modified by Al/Al-W alloying were comparatively investigated with conventional alloys using various microstructural characterization techniques and mechanical property testing methods. The Al-alloyed 29Cr44Ni4AlNb+microalloy (MA) exhibits superior oxidation and carburization resistance compared to conventional 25Cr35NiNb+MA and 35Cr45NiNb+MA alloys; however, its creep rupture life was significantly reduced. Further addition of W enhanced the solid solution strengthening effect, thereby improving high-temperature tensile properties and mitigating the detrimental impact of Al on creep performance. The creep rupture life of the Al/W-modified 27Cr44Ni5W3Al+MA alloy reached levels comparable to those of conventional alloys while retaining the beneficial effects of Al in improving oxidation and carburization resistance. Through alloying strategies, this study successfully achieved a balance between corrosion resistance and mechanical properties in ethylene pyrolysis furnace tube alloys, enabling them to withstand their harsh service conditions effectively.
This study focuses on X80 pipelines and establishes a three-dimensional pipe-soil interaction model in abaqus. Based on wave theory, the loading of obliquely incident P-waves in the finite element model was implemented, and the effects of temperature, corrosion spacing, and incident angle on the stress, acceleration, and displacement responses of the pipeline were analyzed. The results indicate that at +0 degrees C, the stress response of the pipeline increases significantly due to the reduction in seismic wave velocity caused by the decrease in soil elastic modulus. When the axial spacing between double corrosion defects exceeds 4 times the wall thickness, the interaction between them becomes negligible. The stress response of the pipeline first increases and then decreases with the increase of the incident inclination angle (theta i), while it continuously increases with the increase of the incident azimuth angle (theta v). The most severe stress response and the highest safety risk occur when theta i = 60 deg and theta v = 90 deg. Additionally, the incident azimuth angle has a minor impact on the vertical acceleration and velocity of the pipeline but significantly affects the lateral and axial responses. In contrast, the incident inclination angle noticeably influences the acceleration and velocity responses in all three directions of the pipeline, with the most pronounced effect observed at theta i = 60 deg.
In shell and tube heat exchangers, welding residual stress has a crucial impact on reliability and structural integrity of the tube-to-tubesheet joints. This paper combines numerical simulation and theoretical analysis methods to investigate the welded-and-expanded process. Previous studies typically treated welding and expansion as isolated processes. This paper explains the regulation mechanism of the expansion load on the existing welding residual stress through analyzing the residual stresses on the surface of the tube sheet and at the weld root before and after expansion. The study suggests that the welding process generates high-magnitude tensile residual stress near and in the adjacent areas of the weld. The peak of this residual stress exceeds the yield strength of the material. The stress is mainly concentrated on the joint surface and gradually decays with the thickness of the tube sheet. The expansion process significantly alters the stress field induced by welding, achieving effective stress release and redistribution. A critical expansion pressure threshold was determined, approximately 280 MPa. If this threshold is exceeded, the stress relief effect will tend to saturation, and further loading may cause local yield on the surface of the tube sheet. In addition, the agreement between numerical simulations and experiments confirms the effectiveness of expansion load in mitigating welding residual stress and provides a theoretical foundation for optimizing the welded-and-expanded process.
Currently, with the increasing demands for manufacturing precision and production efficiency, the number of layers and the overall thickness of multilayered clamping high-pressure vessels have significantly increased. Building upon previous studies in linear elastic calculations, this research takes into account the strain hardening of metallic materials and adopts a bilinear hardening elastic-plastic model. Analytical expressions for the elastic-plastic stress distribution, initial yield pressure pyield, and full yield pressure py of multilayered cylinders with interlaminar gaps are derived. In the derivation process, consistent with prior elastic studies, the calculation method for the equivalent radius Req in the plastic region is proposed. Finite element verification shows that the analytical stress calculation results align well with the finite element analysis, demonstrating the high accuracy of the proposed calculation method.
The BoZi pipeline transports high-wax-content crude oil; however, the spatiotemporal evolution of wax deposition thickness along the pipeline remains poorly characterized. This study develops a modeling framework that integrates field operational data with theoretical formulations to simulate and predict pipeline production dynamics over a one-year period. The model, comprising 365 consecutive time points, accurately captures key operational phases including wax deposition growth, pigging operations, and pipeline shutdowns and restarts. Model predictions were validated against four key operational parameters: inlet pressure, outlet temperature, wax removal volume, and pigging pressure. The model exhibits high fidelity, with deviations below 1.01% for pressure, 1.9% for outlet temperature, 2% for pigging pressure, and 10.5% for wax removal volume. Based on the validated model, 11 pigging and shutdown-restart operations were implemented in the BoZi pipeline. The model further enables long-term projection of wax deposition evolution and provides a basis for optimizing pigging frequency over a 15-year horizon.
The extended finite element method (XFEM) has recently emerged as a highly effective tool for analyzing crack propagation in complex structures, but its use in pipeline fracture studies, particularly with cohesive zone models (CZMs), is still developing. Current XFEM fracture criteria are not calibrated for pipeline steels, relying on fixed fracture stress or strain to initiate crack propagation. While the stress-based criterion works for brittle fractures, it fails for ductile ones, either accelerating cracks or preventing them altogether. The strain-based criterion better predicts both fracture types, but its numerical accuracy remains inadequate, highlighting a need for further research. This numerical study explores the use of XFEM to predict crack propagation in standard fracture specimens of single edge notch bending (SENB) made of X52 pipe steels. First, an XFEM-based cohesive zone model was developed to simulate the specimens. The maximum principal strain (MAXPE) and fracture energy (Gc) were selected as key damage parameters to characterize the fracture process, controlling crack initiation and resistance to crack propagation, respectively. These damage parameters were adjusted until the model closely matched experimental results (load-crack tip opening displacement (CTOD)) for different initial notch sizes in SENB specimens. Subsequently, experimental results for CTOD-R and the strain distribution around the crack tip, both at crack initiation and during unstable crack propagation, were compared with the numerical model's predictions to validate the chosen XFEM input damage parameters. The research confirms the effectiveness of XFEM in predicting fracture characteristics (i.e., CTOD and crack growth length), particularly when using the XFEM parameters MAXPE and Gc.
This paper presents a comprehensive finite element analysis using abaqus to obtain the tensile strain capacity (TSC) of X70 and X100 pipelines with external semi-elliptical cracks in the heat-affected zone (HAZ) under tension and bending. The analysis estimates the crack driving forces using the J-integral in relation to the pipeline's remote strain. Subsequently, the evaluation of TSC was carried out employing both initiation and ductile tearing criteria. The study investigates the effects of internal pressures, HAZ softening levels, loading type, and weld strength overmatch ratios on TSC. The results reveal similar trends in TSC between the initiation and ductile tearing criteria, as well as between tension and bending for both types of steel. Notably, TSC decreases with increased HAZ softening and internal pressures, while higher overmatch ratios appear to enhance it. These findings highlight the critical influence of these factors on the structural integrity of pipeline girth welds, offering essential insights for the design and maintenance of pipeline systems.
Since the 1970s, various burn-through criteria have been proposed by numerous research institutions regarding in-service welding phenomenon. However, no widely recognized criterion has emerged to date due to the ambiguity of the burn-through mechanism, which lacks a scientific explanation and hinders the formulation of a definitive criterion. This study independently established an in-service welding test device based on the ABB automatic welding system and conducted burn-through experiments utilizing digital image correlation (DIC), high-speed photography technique, and other methods to identify critical conditions for burn-through. The reliability of numerical simulation models for in-service welding was validated through DIC strain measurements. Both experiments and numerical simulations revealed that radial deformation represents the primary mode of deformation preceding burn-through. It was indicated that the welding thermal stress would significantly weaken the influence of the medium pressure. The overall stress evolution behavior during in-service welding was mainly dominated by the welding stress. The critical condition for burn-through occurs when radial deformation transitions from an inward-convex form to an outward-convex form. Radial stress is identified as the key stress driving burn-through, with its absolute value exceeding yield strength being a critical condition for it to occur. This study elucidates mechanisms behind burn-through and develops a radial stress burn-through criterion that aligns closely with experimental values while clarifying mechanisms behind maximum inner-wall temperature criterion.
Thin-walled cylinders exhibit a significant difference between the theoretically calculated critical load and experimental buckling loads. The inconsistency arises primarily due to the presence of geometric imperfections in the shell, which cannot be accurately determined during the design process. To mitigate this, designers apply a buckling knockdown factor (KDF) to theoretical estimates when sizing such critical structures. Industry guidelines like NASA SP 8007 specify KDF, which is a lower-bound experimental data fit and is overly conservative. Recent studies have shown significant progress in the numerical estimation of KDFs for cylinders subjected to axial compression. However, other critical loading conditions, such as external pressure, remain underexplored. This paper addresses this gap by employing numerical methods to estimate KDFs for cylinders under external pressure, enabling the design of lighter structures. The applicability of energy barrier analysis (EBA) is investigated for KDF estimation, and its efficacy is validated by comparing it with experimental results. The effect of geometry on KDF estimation is studied through numerical experiments, and new KDF curves are proposed as a function of the Batdorf parameter and the L/R ratio. A comparison with a detailed dataset of various pressurized cylinder buckling experiments demonstrates the accuracy of the suggested KDF curves. The studies indicate that the KDF curves enhance the load-carrying capacity by up to 20% compared to the conservative standards. These findings contribute to the development of lighter, optimized airframe structures and enhance the understanding of buckling behavior under external pressure.
Compressed natural gas (CNG) pressure vessels are used for fuel storage in eco-friendly vehicles, providing a safe fuel supply under high pressure. Lightweighting of CNG pressure vessels while ensuring structural safety is an essential factor. In this study, liner and composite thickness designs were performed to reduce the weight of CNG pressure vessels. The stress behavior based on liner and composite thicknesses was analyzed using the commercial finite element analysis (FEA) software, ansys workbench. To improve fatigue life and durability, considering failure due to buckling and burst, autofrettage pressure was applied. Using optimal design, a minimum-weight pressure vessel was achieved, meeting criteria for structural safety, fatigue life, and cost reduction. Therefore, a 6.6% reduction in weight was achieved compared to CNG pressure vessels currently manufactured in the field.
Barrel erosion, critically limiting service life and ballistic performance, involves complex thermomechanical interactions. This study investigates the hitherto underexplored erosion mechanism induced by highly dynamic gas-solid flow and unburned propellant particles. We propose an improved two-phase flow erosion model by integrating interior ballistics theory with the barrel's transient radial heat transfer equation and established erosion models. This coupled thermal-fluid-mechanical method enables quantitative prediction of wear from particle-wall interactions under extreme thermal and mechanical loads. Simulations reveal that erosion severity is predominantly governed by particle impact velocity and angle, propellant charge mass, and combustion rate. Increased charge mass exacerbates erosion by elevating collision frequency and kinetic energy, whereas faster combustion rates mitigate wear by reducing particle residence time. Crucially, thermal softening induced by transient heat transfer markedly reduces material hardness, which amplifies the erosion ratio significantly. Furthermore, erosion thickness is minimized at lower impact angles, suggesting practical design strategies for wear reduction.
