International Journal of Pressure Vessels and Piping最新文献

To satisfy the requirements of hardness and corrosion resistance for laser additive manufacturing of hydraulic supports, this study applied the synergistic addition of C, B, Cr, Ni, Nb and Mo elements in Fe-based alloys. The multi-phases, martensite + austenite + ferrite were designed. The microstructure, hardness and corrosion resistance of the coatings were analyzed. Increasing the C and B contents could significantly increase the hardness of the coatings, while the corrosion resistance was decreased. The corrosion resistance of the coatings was determined by the Cr contents. However, increasing the Cr contents to 20.0 wt % resulted in the ferrite structure with lower hardness (21 HRC). The coatings with 0.25 wt % C, 1.2 wt % B and 19.0 wt % Cr showed the optimal matching of hardness (56 HRC) and corrosion resistance (survived in neutral salt spray test≥300h). The resulted coatings were mainly consisted of dendritic structure. Fine lath martensite phase was dominant in the dendrite regions. The interdendritic regions were consisted of nano-sized intermetallics with a mixture of σ+Nb + FeNb + Cr₂Nb+(Fe,Cr)₂B + NbC compounds. These interdendritic regions (14.2 GPa) showed higher hardness than that of the dendritic regions (7.1 GPa). The high Cr contents with finer dendritic structures were the major mechanisms for the excellent combination of hardness and corrosion resistance. The precipitation and growth mechanisms of the interdendritic phases were elaborated. This work provides a valuable reference for laser hot-wire cladding to prepare Fe-based alloys with high hardness and excellent corrosion resistance.

Austenitic stainless steel welds (ASSWs) suffer from severe pre-strain during assembly process, which threatens the long-term operation safety of pipelines in nuclear power plant. In this work, the 316L weld metals (WMs) with 0 % and 8 % pre-strain were thermally aged at 400 °C for up to 39000 h to investigate the pre-strain effect on thermal aging of ASSWs. The results showed that the pre-strain caused work hardening and further promoted the hardening of thermally aged ferrite. After thermal aging for 39000 h, the nano-hardness increment of ferrite with 8 % pre-strain was about 1.6 GPa more than that without pre-strain. By microstructure characterization, it is found that the high dislocation density induced by pre-strain promoted spinodal decomposition and G-phase precipitation. The spinodal decomposition morphology and corresponding element concentration fluctuations were more obvious in the WM with 8 % pre-strain. Moreover, the size and density of G-phase along dislocations were larger in the ferrite with 8 % pre-strain than those without pre-strain.

The presence of cracks on pipelines poses a potential threat to their operational status, and it is critical to assess the permissibility of pipelines containing cracks. The dimensional analysis combined with the finite element method is applied to investigate the fracture behavior of circumferential crack on the internal surface of pipe under internal pressure and large axial deformation. Dimensionless parameters are determined to represent the effects of crack size, pipe geometry, pipe material, and external load on the crack front driving force, and a strain-based J-integral formulation is obtained by a stepwise coefficient fitting approach rather than a polynomial fitting method. This J-integral formula can be used to quickly assess the crack front driving force of a pipe in service condition and subjected to axial displacement. The diameter-to-thickness ratio of the pipe and the dimensionless pressure of the pipe are found to act together in a combined form on the crack front driving force. Increases in dimensionless crack depth, dimensionless crack length, the ratio of circumferential stress to yield strength of the pipe, and strain hardening exponent cause an increase in the crack front driving force. The effect of dimensionless crack depth on crack front driving force is more significant than other dimensionless parameters. Changes in the other dimensionless parameters do not significantly change the crack front driving force when the dimensionless crack depth is small. Other dimensionless parameters have a progressively greater influence on the crack front driving force as the crack dimensionless crack depth increases. Large deformations in the ligament zone and increasing axial stress are the main reasons for the high crack front driving force. The J-integral formula has a similar form to that of the J-integral in the Electric Power Research Institute (EPRI) method when the effect of internal pressure is not considered. It can be reduced to predict the crack front driving force of a surface cracked plate subjected to uniaxial tensile loading. For the interaction between an internal surface crack and an embedded crack, re-characterizing the crack size using BS 7910 will overestimate the equivalent crack depth, and a more accurate equivalent crack size can be obtained using the J-integral formula proposed.

The shift from metallic to composite pressure vessels for storing compressed natural gas (CNG) is driven by the goal of reducing environmental impact by using lighter higher-performing structures. This work focuses on enhancing the internal pressure strength of a type IV composite overwrapped pressure vessel (COPV) by optimising the stacking sequence of the overwrapping composite layers. Parametric finite element (FE) models are developed to reveal symmetry effects. In these models, both the thickness build-up and fibre angle variation at the turnaround zones are accurately modelled. Subsequently, the stacking sequence is optimised with the objective function of maximising burst strength. The parametric modelling demonstrates that representing the COPV as an axisymmetric continuum reduces computational costs in 5400× while yielding results comparable to full 3D continuum models. Experimental burst tests are carried out to validate the numerical predictions, and the difference in pressure between them is 12.6 %.

This study investigated the failure behavior of ceramic egg-shaped shells under external pressure. Four ceramic egg-shaped shells with two thicknesses were manufactured and then subjected to geometric measurements, hydrostatic pressure tests, analytical validations, and numerical simulations. The experimental results were compared with the simulation results to validate the feasibility of the numerical modeling. Furthermore, the effects of thickness and shape on ceramic egg-shaped shells were explored. The research findings indicate that ceramic egg-shaped shells have excellent compressive properties. The performance ratio of these ceramic egg-shaped shells is approximately 10 and 5 times higher than those of resin and steel egg-shaped shells, respectively. This finding highlights the crucial role that affordable ceramic materials can play in facilitating the widespread use of submersibles in deep waters.

Three-dimensional free bending technology (3D-FBT), as an innovative tube forming process, can achieve complex spatial tube components. However, caused by springback problem how to optimize its forming accuracy for the spatially curved components of tubes is still a major issue. In this study, a springback compensation model for variable curvature tube bending components is constructed and validated based on a developed discretization methodology. The central axis curve of the tube is discretized, and the spatial compensation angles in different cylindrical helix elements were incrementally calculated by a springback analysis model, in which the stress neutral layer offset on the cross-section of the tube induced by axial thrust force. Finally, the validation and accuracy of the proposed methodology is proved through a typical 3D tube component of AL6061. By comparing the numerical and experimental results, it is found that the average shape error of the 3D component is 2.62 mm (24.52 mm without compensation).

Stress Corrosion Cracking (SCC) presents a substantial challenge within industries where materials confront both mechanical stresses and corrosive environments. This work comprehensively examines SCC, incorporating the collection and analysis of a diverse dataset. The dataset encompasses pivotal parameters, including time to failure, corrosion rates, and electrochemical data. These parameters are meticulously garnered through Slow Strain Rate Testing on carefully prepared smooth, round tension specimens. The experiments are vigilantly overseen through a condition-based data acquisition and logging system, employing various Potentiostatic loads to mirror real-world electrochemical conditions. This research elucidates the intricate interplay between mechanical stresses, electrochemical processes, and corrosive conditions, rendering crucial insights for industries dependent on material integrity amidst formidable environmental challenges. Findings show that AISI 4340 Steel specimens exposed to a $+400mV$ potential in NS4 solution exhibit an extended time to failure of approximately 7.4 days. Conversely, a $-1200mV$ potential in NS4 accelerates the failure to around 5.24 days. In a $3.5wt\%$ NaCl solution at $0mV$, the time to failure is approximately 5.76 days. On the other hand, an applied potential of $+400mV$ increases the failure time to approximately 6.16 days. And an applied potential of $-1200mV$ accelerates the failure time to approximately 4.77 days. Specifically, the study reflects on structures submerged in water and those buried underground, represented by NS4 (Near Neutral Soil Simulating Solution) and $3.5w.t.\%$ NaCl solutions, simulating real-world corrosive conditions. Through a deeper comprehension of SCC, industries can better anticipate and mitigate the risks associated with material failure in harsh environmental conditions, advancing the safeguarding of critical infrastructures.

Residual stresses were induced in the fabrication of thin-walled Inconel 718 specimens through selective laser melting (SLM) due to rapid heating and cooling, which yield distortion and have a detrimental impact on their mechanical performance. Reducing the process-induced residual stress and distortion is of great importance for practical applications. For achieving this aim, accurate measurement of residual stress and distortion is required. In the present work, residual stresses of SLMed samples were measured through hole drilling method (HDM), taking into account their anisotropic features. The distortion induced by the release of residual stress after manufacturing was measured using digital image correlation (DIC). The effect of thickness of thin-walled samples on residual stress and distortion was investigated. The results indicate that by reducing the thickness of sample, the residual stress could be reduced, whereas the distortion was increased. Furthermore, it was revealed that by manufacturing a pair of side samples in one printing job, the distortion and residual stress of the thin-walled component fabricated by SLM can be evidently reduced. The obtained results were clarified by using thermal-mechanical simulations of SLM.

An imaging technique using a scanning laser source (SLS) was applied to detect deposits inside pipes, which are necessary for the safe decommissioning of the Fukushima Nuclear Power Plant. Experimental results showed that the more firmly adhered the deposit on the back surface of a flat plate, the clearer it is to obtain an image of the deposit. This result is as expected because the imaging by an SLS technique is dependent on the bending stiffness of the thin plate structure. Furthermore, even epoxy putty as large as 50 mm in diameter adhered to the inner surface of the pipe could be imaged, and even when the receiver device was changed from a piezoelectric device to a non-contact laser doppler vibrometer, the image of the deposit could be obtained properly with some degradation of the image due to the effect of a lower signal-to-noise ratio.

Estimating bolt stress within high-temperature bolted connection systems is crucial for determining bolt preload and assessing bolt assembly integrity. This work proposes a theoretical model for estimating high-temperature bolt load under combined tension, bending, torque, and shear loads, considering the characteristics of bolt stress distribution and relaxation. To assess the model's accuracy, finite element analysis was employed to examine the impact of various creep parameters and load combinations on bolt stress relaxation. The results indicate that the introduction of bending moments, torque, and shear loads accelerates axial stress relaxation in bolts. Under a high-temperature load for 300,000 h, the stress relaxation predicted by the theoretical model aligns well with the results from finite element analysis.