International Journal of Pressure Vessels and Piping最新文献

Confining pressure has a significant effect on the mechanical properties of solid propellant, and it is crucial to develop a refined structural integrity analysis and assessment method considering confining pressure effect and nonlinearity of propellant material for the design of propellant grain of a solid rocket motor (SRM), especially for the design of high charge modulus. In this work, an existing viscoelastic-viscodamage constitutive model considering confining pressure effect was implemented as a user-defined material subroutine and verified using a few experiments under various confining pressures. The mechanical responses and safety factor of a typical variable cross-section propellant charge SRM with various charge modulus under ignition pressurization load and room temperature were analyzed and evaluated. The results show that the user-defined material subroutine can well describe nonlinear mechanical responses of solid propellant under different experimental conditions. The Von Mises stress and minimum safety factor considering the confining pressure effect are higher than the value without considering the confining pressure effect, while the Von Mises strain is opposite. In addition, regardless of whether the confining pressure effect is considered or not, the maximum Von Mises stress and strain show a nonlinear increasing relationship with the charge modulus, and the minimum safety factor decreases with charge modulus. However, when analyzing the structural integrity of high charge modulus, using two evaluation methods will yield completely different evaluation results. It is believed that this research can support structural integrity analysis and design of high charge modulus SRM.

This study aims to enhance the sealing performance of non-metallic gaskets by incorporating shape memory fibers. The analytical exploration focuses on analyzing the thermomechanical behavior of Nitinol fibers in their woven state within the gasket. Specifically, the investigation examines the variation of phase transformation zones across the wire cross-section with changes in temperature. Subsequently, a series of SMA fiber-reinforced gasket samples were fabricated, and experimental investigations were conducted to assess the impact of Nitinol fibers on composite gaskets using a helium gas leak test. The results demonstrate that the integration of shape memory alloy wires into the composition of gaskets can significantly improve their sealing performance. Moreover, this study examines a number of pivotal factors such as fiber volume fraction, temperature application, woven fiber arrangement, leakage rates, gasket deformation, contact stress, and structural bending. These comprehensive investigations may provide valuable insights into the efficacy of Nitinol fibers in enhancing gasket sealing performance.

The control of phase ratio and residual stress is a crucial subject for the structural integrity of duplex stainless steel welded components. Therefore, this paper aims to clarify the evolution of phase ratio and its effect on residual stress for duplex stainless steel multipass welded joints by a thermo-metallurgical-mechanical coupled welding model, alongside the crucial experiments which contribute to the development and validation of the coupled model. The developed model takes both the precipitation and dissolution behavior of austenite under repeated thermal cycles into consideration, thereby demonstrating a remarkable ability to predict the distribution of phase ratio and residual stress. The influencing mechanism of solid-state phase transformation on residual stress is discussed extensively. The results reveal that, for the duplex stainless steel welded joints by gas tungsten arc welding, excessive austenite is often formed within the welding zone particularly for the middle passes, while it is the occurrence of ferritization at the heat affected zone. The effect of phase transformation on residual stress is mainly presented by the change of mechanical properties and phase volume. The overtransformation from ferrite to austenite tends to induce a higher tensile residual stress, vice versa, compressive stress. In addition, it is challenging to achieve phase balance through heat input alone. However, a smaller heat input is recommended to minimize residual stress while ensuring welding penetration. This paper serves as a theoretical foundation for controlling the phase ratio and mitigating residual stress during the welding of duplex stainless steel, thereby contributing to the enhancement of weld quality and structural reliability.

In recent years, the waning of creep rupture ductility in the long term, and sensitivity to creep damage tolerance of creep strength-enhanced ferritic (CSEF) steels were put under the spotlight. The loss of ductility and damage accumulation at stress concentrations may result in early failures of boiler components, and potentially result in severe economic impact and/or safety concerns. To address the potentially undesirable materials performance, the ASME Boiler and Pressure Vessel Code has recently introduced rules for identification of damage intolerant behavior by means of testing, and for design of boiler components with creep damage-intolerant CSEF steels, as Code Case 3048. As of today, only Grade 91 Type 2 material has been classified as a damage tolerant steel.

The Thor® 115 (T115) CSEF steel has entered the market in recent years and has since been used for the construction of several combined cycle power plants. This CSEF steel was developed as an evolution to Grade 91, with chemical composition modifications to enhance the resistance to steam oxidation while ensuring long-term microstructural stability, and therefore permitting its use for the higher temperature boiler components, as an alternative to stainless steels. While chemical composition and manufacturing precautions prescribed for Grade 91 Type 2 also apply to T115, an assessment of the materials’ damage tolerance following design standards criteria, and including extensive metallurgical characterization, has not yet been published.

This work presents up-to-date uniaxial creep testing results of T115 CSEF, and the derived creep-rupture ductility and damage tolerance parameter evaluation. In addition, results from notched bar creep testing are presented, illustrating the material's response to multiaxial stress states. Post-test metallographic examination of ruptured specimens was also performed and findings are discussed.

Recently, considerable effort has been directed at the development of laser welding with wire filler addition as an alternative manufacture technique for the substantial productivity gains it would offer to the nuclear pressure vessels fabrication. However, single wire filler such as 52M and 308 L addition is difficult to take into account many properties such as the strength, toughness and resistance to stress corrosion cracking at the same time. In this work we evaluate the feasibility of applying 52 M/308 L dissimilar double wires filler addition for the multi-pass narrow gap laser welding (NGLW) of SA508/316 L dissimilar metals. The objectives of this paper is to regulate the microstructure of the welded joint by adjusting the ratio of the 52 M/308 L double wires filler. The results showed that welded joints without crack and lack-of-fusion were acquired. An excellent comprehensive property welded joint with relative high hardness and low residual stresses is acquired when the 52 M/308 L double wires proportion was 75 %:25 %. The results also indicated that a certain proportion of 308 L stainless steel wire filler addition was conducive to reducing the microhardness of the welded joint. However, when that ratio of the 308 L wire was up to 75 %, harmful element S was obtained in the precipitation zone, which might reduce the mechanical properties of the welded joints.

Failures in piping systems during earthquakes have resulted in operational disruptions and financial losses for critical facilities, such as nuclear power plants and hospital infrastructure. Past earthquake events have shown that failures in piping systems occur primarily at discontinuities, such as T-joints, elbows, and nozzles. Therefore, it is important to understand the behavior of piping joints under cyclic loading to mitigate the impact of such failures. This manuscript investigates the behavior of piping T-joints under cyclic loading. The behavior of these joints under cyclic loading is greatly influenced by the material properties of the piping components. Any variation in material properties can alter the responses of the piping joints, eventually affecting the seismic fragility of the piping system. This manuscript uses data from laboratory experiments to characterize and quantify uncertainties in material properties that influence the seismic fragility of piping systems. Additionally, this manuscript uses the data from laboratory experiments to validate a new limit state for characterizing the failure of piping joints under cyclic loading. In addition, it explores the effects of uncertainties in material properties on the performance function used to characterize the new limit state for failures at T-joint connections. In summary, this study provides insights into the influence of uncertainty in material properties on the seismic fragility of a piping system with an intent to improve the resiliency of piping systems in critical infrastructure facilities.

Flexible composite pipes have the advantages of light weight, corrosion resistance, scale resistance, and low cost compared to carbon steel pipes, and have attracted much attention in the application of onshore oil and gas gathering and transportation systems. Understanding the relationship between the pressure-bearing mechanical properties of composite pipes and their structural characteristics is crucial for guiding their process application. To investigate the mechanical behavior of flexible composite pipes under internal pressure loads, discrete and combined finite element models were established to analyze the stress-strain characteristics of flexible composite pipes. The bursting strength was predicted, and the influence of winding angle and number of reinforcement layers on the pressure-bearing capacity of flexible composite pipes was revealed. The applicability of the two models in the analysis of internal pressure resistance of flexible composite pipes was evaluated using whole pipe strain testing and instantaneous hydrostatic burst experiments. The results showed that the reinforcement layer is the main pressure-bearing layer of flexible composite pipes, and the innermost reinforcement layer bears the highest pressure. The pressure-bearing capacity of flexible composite pipes significantly increases when the winding angle is greater than 53°, and the increase in pressure-bearing capacity slows down when the number of reinforcement layers exceeds 3. Under the combination model, the strain and bursting strength of flexible composite pipes were closer to the experimental results. The study clearly defines the stress-strain characteristics of flexible composite pipes under internal pressure load and the impact of process parameters, providing a basis for the optimization design of single well oil transmission pipelines in Xinjiang oilfield.

This paper presents some developments performed by EDF and FRAMATOME with the objective to define criteria for the consideration or not of Welding Residual Stresses within the Fracture Mechanics Assessment of nuclear components.

The paper is organised in two parts. In the first part, a literature survey is proposed, showing that major part of available results is at low temperature in the Brittle to Ductile transition where the effect of Welding Residual Stresses is known to be significant. This temperature domain is not relevant for nuclear applications; however, all those results are providing very important recommendations regarding the preparation of new testing.

In the second part, a numerical study is proposed for showing the relevance of the local approach for evaluating the impact of Residual Stresses on brittle fracture, and to initiate some criteria for defining the domain where they have a significant effect.

In this research, microstructural characterization and mechanical properties of 9%Cr, 0.4%Ni (including W and Mo) steel weld metal with alloyed cobalt were investigated. Due to their strong creep resistance, oxidation resistance, and low thermal expansion, 9%Cr steels are used in nuclear power plants, petrochemical industries, and fossil fuel-powered power plants that operate in high temperature conditions. In this context, weld metals comprising 0.5 %, 1 % and 1.5 % cobalt and cobalt-free weld metal were produced by SMAW (shielded metal arc welding) technique. Microstructure of the weld metals were characterized with optical microscope (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Also, XRD analysis was performed on the bulk samples and precipitated carbide/nitride phases extracted from the weld metals. In addition, differential scanning calorimetry (DSC) was used to determine the phase transformations. Thermo-Calc modeling study was also performed. Hardness, tensile and Charpy-V impact tests were carried out to determine the mechanical properties. The hardness did not change significantly when cobalt up to 1.5 % in the weld metal. However, with the increase of cobalt, the yield and tensile strength increased without affecting the elongation value too much. In the Charpy impact tests performed at different temperatures (−40 °C, −20 °C, +20 °C, +40 °C, +60 °C), the amount of cobalt increased toughness, especially at +40 and + 60^oC temperatures. Ductile brittle transformation temperature (DBTT) of the weld metal with 1.5 % Co decreased from 29 °C to 15 °C compared to cobalt free weld metal. It is thought that this may be caused by the further separation of C, Cr and W from the matrix through forming precipitate by the cobalt effect. Besides the mechanical properties, microstructure was also affected by adding Co with inhibition of delta ferrite formation which decrease the toughness. Curie temperature increased with increasing cobalt content detected by DSC.

This present study is aimed to produce high-strength dissimilar joints of AA5083-O and AA7075-T6 alloys through optimization in the friction stir welding (FSW) process parameters. In this work, we have employed the response surface methodology (RSM) iteratively to generate 20 different welding process parameter combinations. These parameters are used to manufacture dissimilar weld joints, and the impact of these process parameters on the mechanical properties of the weld joints is evaluated by performing a series of mechanical tests such as tensile and microhardness. The microstructural evolution of the welded joints is studied using optical and SEM techniques. EBSD analysis is performed to understand the grain size, orientation, and changes in microstructure. The weld nugget zone reveals the presence of finer grains measured as 0.3 μm–0.7 μm. The specimen manufactured using FSW optimized process parameters of rotational speed 1100 rpm, welding speed 50 mm/min, and tool tilt angle 2° shows the ultimate tensile strength of 417 MPa, weld nugget hardness of 189 HV_0.1, and weld efficiency 80.65 %. The tensile fractured surface of specimens is also inspected using SEM to determine the mode of failure reached in the welded joints.

© 2001 Elsevier Science. All rights reserved.