Applied Mechanics and Materials Vol. 750

Abstract: The steam generators at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK are potentially life-limiting components. Enhancing the capability to monitor the steam generators has been identified as having the potential to provide key evidence in justifying the extension of the generating lifetime of the stations. It has been proposed to install new temperature measuring instrumentation to monitor reactor gas temperature and to provide additional data regarding steam generator operating conditions. The modification will be to introduce thermocouples to the bore of an intact steam generator tube to facilitate temperature measurement at or near to the locations of interest. The modified steam generator tube will be sealed at the feed header upstand. Between the upper surface of the superheater header tubeplate and the wall of the superheater header, the thermocouple bundle and sheath will be contained within a rigid stainless steel guide tube. The guide tube will be attached at both ends by welds, each forming a pressure boundary. At the tubeplate a weld will separate the bore of the sealed guide tube from the steam space within the superheater header; a weld between the guide tube and the superheater header will separate the steam space within the superheater header from atmosphere outside the header. In order to obtain a better design, three 3-dimentional finite element models have been created using ABAQUS. A series of cyclic pressure, and start-up and shutdown thermal transient stress analyses have been carried out to provide stress values for structural integrity assessments to be conducted using ASME III, Subsection NH and R5.

Abstract: The layered cylindrical shell is one of important structures of high pressure vessels. From 1977 to 2005 there were 8 urea synthesis reactors exploded. Seven of them were layered cylindrical shell structure. Therefore, there will be much more issues come out and waiting for us to study and explore. In this paper, we take the urea synthesis reactor exploded in 2005 in China as an example to study why and how a multi-layered exploded. Through the research work, we not only concluded why and how a multilayered vessel exploded but also established a method to analyze the serious explosion accident of complex vessels such as urea synthesis reactors.

Abstract: Jacketed polypropylene reaction kettle is the key equipment of polypropylene reaction setting. Cracks and leakage occurred in the kettle wall near the lower thermometer pipe branch, which is a widespread phenomenon in this refinery. The results showed that the cracks were caused by low cycle fatigue. High edge stress concentration resulted from incorrect design of the jacket structure is responsible for the fatigue cracks. An improved measurement which is available and simple was introduced.

Abstract: Since external loads affect the sealing performance of bolted flanged joints, this paper calculated external loads of bolted flanged joints by using CAESAR II software and evaluated the effects of external loads on the sealing performance from the viewpoint of changes in contact gasket stress and flange rotation by using ANSYS software. The FE results showed that the contact gasket stress decreases a lot at the tension side and increases a little at the compression side. The paper also evaluated the stress distribution in bolted flanged joints subjected to external loads. The results suggested that the flange rotation and the overall stress increased compared with that of flange without external loads. External loads can induce unexpected leakage and strength failure of the bolted flanged joints during operation.

Abstract: High-strength steel is often used in the design and manufacture of the pressure vessel and the failure accident often happens in the weld area after used. CF62 is chosen in this paper which is the large-scale sphere steel for manufacture and the equal-loading butt joint of whose three different sizes are designed. The weld simulations of the equal-loading joints are made by 3D FEM, then the residual stress distributions and the influence of the thickness are analyzed in this paper. The results show that the equal-loading butt joint's weld toe is without stress concentration and the equal-loading butt joint can reduce the residual stress during the welding process. The thinner equal-loading butt joint has the lower residual stress. The joint designed by the equivalent Von Mises calculation has the lower stress than the one designed by the maximum stress calculation as well and the same as the weld toe's stress concentration. But the half reinforcement width of the maximum stress calculation butt joint is smaller than that of the equivalent Von Mises joint and whose welding electrode is economical, so the maximum stress equal-loading joint fits the engineering practical more.

Abstract: Three kinds of reinforcing fillers (i.e. carbon black N330, carbon black N880 and carbon-white) were used to study effect of the reinforcing fillers on the mechanical properties of NBR materials. The NBR materials with various reinforcing fillers were fabricated, and the mechanical property tests were performed in this work. The results show that the carbon black N330 made the NBR material have better tensile strength, hardness, elongation and compression elastic modulus compared to the carbon black N880 and the carbon-white, while the carbon-white made NBR material have better heat resistance, tear strength and elongation compared to the carbon black N330 and the carbon black N880. In addition, the tensile strength, tear strength, elongation and the heat resistance property of the NBR materials increased significantly with the increase of the carbon-white, but the compression elastic modulus decreased with the increase of the carbon-white.

Abstract: The header and the multiple microchannel tubes connected to the header compose a complicated fluid network with several circuits, and the refrigerant flow into the header and is distributed to the microchannels in parallel by the refrigerant pressure driving in the inlet. So all changed details of geometry, operating conditions and thermophysical properties of the fluids lead to nonuniform refrigerant flow distribution in the microchannels. In the present work, one 6-pass 40-tube microchannel condenser as the research objective was equipped in a window type air conditioner prototype with the cooling capacity 5200W for Middle East T3 climate. A mathematical model based on fluid network theory was developed to predict flow distribution and phase separation in 9 flat tubes and their connecting headers on the second pass of the microchannel condenser. In the assumption of homogeneous flow, the mesh current analysis was employed to solve the mass flow of the loop_i+1 by that of the loop_i upon two phase pressure drop. The simulated mass flow rate distribution in 9 tubes is parabolic and approaches to uniform distribution when inlet quality comes to the median 0.45 from both directions.

Abstract: In this paper, the elastoplastic stress analysis of a novel parabola-arc-shaped head subjected to internal pressure has been carried out using finite element method. Limit loads and burst pressures are obtained for various geometric parameters and compared with the conventional torispherical and ellipsoidal heads. For the same middle diameter and thickness, the novel parabola-arc-shaped head shows better mechanical performance than the torispherical head. The burst pressure is mainly determined by the size of cylinder and the burst always occurs in cylinder. The head can improve the burst load when the cylinder is relatively short. The improvement of the novel parabola-arc-shaped head is almost the same as the ellipsoidal head, while the torispherical head is slightly inferior. As the novel parabola-arc-shaped head can be more easily formed with less material consumed compared to the conventional ones, it should thus be applicable in engineering practice.

Abstract: Fatigue failure analysis on key components of bladder accumulators was conducted. Failure fracture of the key components, which included the shell, the support ring and the oil inlet valve body in the accumulators, was investigated by optical microscope (OM) scanning electron microscope (SEM). According to the metallographic analysis and micro-hardness determination at the crack profile, crack initiation and propagation direction was confirmed. By simulation using the finite element method, it was detected that the peak stress of the key components applied on the contact surfaces. Obvious plastic deformation was observed at the region with high stress. However, the fatigue crack did not initiate at the contact surface, but occurred on the second high stress area without contact.

Abstract: During the analysis of stability heat conduction in the composite pipes, firstly, when the heat equation contained fuzzy and random uncertain parameters, interval equations of the heat conduction are presented in the rough set. Secondly, the error expecting of heat conduction equation is presented. Finally, with upper (lower) approximation in rough set, a new method of the rough set analysis to deal with the stability heat conduction is presented.