A numerical model that predicts high temperature pressure vessel rupture was developed. The finite element method of analysis was used to determine the effects that various parameters had on pressure vessel failure. The work was concerned with 500, 1000 and 33000 US gallon pressure vessels made of SA 455 steel. Experimental pressure vessel fire tests have shown that vessel rupture in a fully engulfing fire can occur in less than 30 minutes. This experimental work was used both to validate the numerical results as well as to provide important vessel temperature distribution information. Due to the fact that SA 455 steel is not meant for high temperature applications, there was little published high temperature material data. Therefore, elevated temperature tensile tests and creep rupture tests were performed to measure needed material properties. Creep and creep damage constants were calculated from SA 455 steel’s creep rupture data. The Kachanov One-State Variable technique and the MPC Omega method were the creep damage techniques chosen to predict SA 455 steel’s high temperature time-dependent behaviour. The specimens used in the mechanical testing were modeled to numerically predict the creep rupture behaviour measured in the lab. An extensive comparison between the experimental and numerical uniaxial creep rupture results revealed that both techniques could adequately predict failure times at all tested conditions; however, the MPC Omega method was generally more accurate at predicting creep failure strains. The comparison also showed that the MPC Omega method was more numerically stable than the One-State Variable technique when analyzing SA 455 steel’s creep rupture. The creep models were modified to account for multiaxial states of stress and were used to analyze the high temperature failure of pressure vessels. The various parameters considered included pressure vessel dimensions, fire type (fully engulfing or local impingement), peak wall temperature and internal pressure. The objective of these analyses was to gain a better understanding of the structural failure of pressure vessels exposed to various accidental fire conditions. The numerical results of rupture time and geometry of failure region were shown to agree with experimental fire tests. From the fully engulfing fire numerical analyses, it was shown that pressure vessels with a smaller length to diameter ratio and a larger thickness to diameter ratio were inherently safer. It was also shown that as the heated area was reduced, the failure time increased for the same internal pressure and peak wall temperature. Therefore, fully engulfing fires produced more structurally unstable conditions in pressure vessels then local fire impingements. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-07-04 10:55:32.008

In this work a cooling system connected to a reactor pressure vessel has been studied using the CFD method for the purpose of investigating the strengths and shortcomings of using CFD as a tool in similar fluid flow problems within nuclear power plants. The cooling system is used to transport water of 288K (15°C) into a nuclear reactor vessel filled with water of about 555K (282°C) during certain operating scenarios. After the system has been used, the warm water inside the vessel will be carried into the cooling system by buoyancy forces. It was of interest to investigate how quickly the warm water moves into the cooling system and how the temperature field of the water changes over time. Using the open source CFD code OpenFOAM 2.3.x and the LES turbulence modelling method, a certain operating scenario of the cooling system was simulated. A simplified computational domain was created to represent the geometries of the downcomer region within the reactor pressure vessel and the pipe structure of the cooling system. Boundary conditions and other domain properties were chosen and motivated to represent the real scenario as good as possible. For the geometry, four computational grids of different sizes and design were generated. Three of these were generated using the ANSA pre-processing tool, and they all have the same general structure only with different cell sizes. The fourth grid was made by the OpenFOAM application snappyHexMesh, which automatically creates the volume mesh with little user input. It was found that for the case at hand, the different computational grids produced roughly the same results despite the number of cells ranging from 0,14M to 3,2M. A major difference between the simulations was the maximum size of the time steps which ranged from 0,3ms for the finest ANSA mesh to 2ms for the snappy mesh, a difference which has a large impact on the total time consumption of the simulations. Furthermore, a comparison of the CFD results was made with those of a simpler 1D thermal hydraulic code, Relap5. The difference in time consumption between the two analyses were of course large and it was found that although the CFD analysis provided more detailed information about the flow field, the cheaper 1D analysis managed to capture the important phenomena for this particular case. However, it cannot be guaranteed that the 1D analysis is sufficient for all similar flow scenarios as it may not always be able to sufficiently capture phenomena such as thermal shocks and sharp temperature gradients in the fluid. Regardless of whether the CFD method or a simpler analysis is used, conservativeness in the flow simulation results needs to be ensured. If the simplifications introduced in the computational models cannot be proved to always give conservative results, the final simulation results need to be modified to ensure conservativeness although no such modifications were made in this work.

Orientador: Fernando de Azevedo Silva / Banca: Alvaro Manoel de Souza Soares / Banca: Silvana Aparecida Barbosa / Resumo: Este trabalho estuda a distribuição de tensões através do método dos elementos finitos em componentes típicos de um vaso de pressão. As diretrizes e metodologia utilizadas nas análises estão de acordo com o código ASME. O vaso de pressão foi estudado para suportar as cargas mais comuns previstas em um projeto de equipamento de processo deste porte. As análises numéricas foram feitas com o software comercial ANSYS e comparados com resultados analíticos previstos no código ASME para os casos mais simples, onde foi obtida a validação dos resultados. Os casos mais complexos foram analisados apenas por soluções numéricas. Todos os casos obtiveram resultados abaixo das tensões admissíveis e de acordo com a metodologia do código, confirmando a viabilidade de análises deste tipo para os casos onde a solução analítica se torna muito conservativa. / Abstract: Riveted lap joints represent a critical element in metallic airframe construction when designing against fatigue. These elements are widely used in the aerospace industry, so the study of the fatigue's properties and variables has been increasingly broad. The variable that has shown to have a high influence on the fatigue strength of riveted joints is the clamping force applied to the riveting process. The life of the part tends to be higher when the clamping force applied is increased. The finite element method, which is a calculation tool applied in various fields of activity and has become an indispensable step of mechanical design, is used in this dissertation for the analysis of a riveted lap joint of aeronautic use. The joint is simulated considering the stages of the manufacturing process and application, in order to perform analysis of mechanical behavior and calculate the fatigue life. Through an experimental test of monotonic tensile, strain values were obtained with strain-gauges, and is made the correlation of these data with the numerical model to validate the modeling. Finally two more tests are made with different clamping forces, in order to check the influence of this variation in fatigue life of the joint. / Mestre

No description available.

The behavior of cryogenic double-walled pressure vessels, such as thoseused in space launch vehicle infrastructure, under blast loading is a somewhatunderstudied topic. This is of interest due its implications on, among otherthings, launch site design and safety in the event of a launch vehicle failure.The detonation of a 100 kg charge of TNT at a distance of 1 m from a simplifiedmodel of a horizontal cryogenic (double-walled) pressure vessel was simulatedusing Ansys Mechanical and AUTODYN. As a result, the inner and outershells of the pressure vessel underwent significant deformation which, in thecase of the outer shell, reached one third of its radius. No rupture occurred.Various other structural parameters, such as von Mises equivalent stress, strain,and element velocity were also studied. The results presented in this reportimply that cylindrical cryogenic pressure vessels are highly resistant to blastoverpressure, but does not take surrounding piping, valves, supports, and other infrastructure into account.

The project is a research on liquid methane. It is stored in a standing and static pressure vessel specially calculated for cryogenic purposes. All the simulations have been done using the finite element method.  The  finite  element  method  (FEM)  or  finite  element  analysis  (FEA)  is  a  numerical technique to find approximate solutions for partial differential equations and it is used to simulate the strength of materials. FEM allows the user to visualize the distribution of stresses and displacements. There is a wide range of software to do FEM simulations, the software chosen for the project is Pro/Engineer Wildfire 4.0.  Pro-Engineer  is  a  CAD/CAM/CAE  software  developed  by  Parametric  Technology Corporation (PTC).  It provides solid modeling, assembly modeling and finite element analysis.  The  results  obtained  in  the  mechanical  analysis  executed  with  the  application  Pro-mechanica show that the designed container holds the loads applied and stands stable.  The thermal analysis of the insulation verifies that the amount of heat exchanged with the environment is on acceptable levels. Finally, to protect the integrity of the structure the proper paints have been selected.

The welding of austenite stainless steel often results in large amount of welding distortion due to its high thermal expansion coefficient and low thermal conductivity. This has created great difficulty in the dimensional control of the welded stainless steel structure, ending up with high manufacturing cost. Researches on the welding distortion of stainless steels were very limited, especially for large weld structures with complex component shapes. The studies of this thesis were initiated with focus on the stainless steel nozzle-to-shell-can weld structures, a very typical structural configuration for pressure vessels used in petrochemical and nuclear power generation industries. Both the experimental and the FEA (finite element analysis), i.e. computational simulation, approaches were taken in the studies which addressed the influences of the welding fixture, the welding sequence, and the welding process on the distortion caused by stainless steel nozzle-to-shell welding. The investigations employed single and multi-nozzle weld test models (called mockups in the thesis) or FEA models. Manual GTAW (gas tungsten arc welding) and SMAW (shielded metal arc welding) processes were selected to represent the most common practice for stainless steel nozzle welding. The FEA simulations were conducted with ABAQUS program using sequentially coupled transient analysis method with lumped weld passes to achieve high computing efficiency. The investigations on the effect of the welding fixture concluded that the contour fixtures introduced in the thesis be effective for reducing the welding distortion for both the single and the multi-nozzle welding. The contour fixtures tend to localize the welding distortion, hence yield less impact on the global distortion of the whole weld structure. The rib-bar fixture, a more common fixture type for multi-nozzle welding, was found resulting in a big jump in the shell plate distortion when the fixture was removed. The studies on the influence of the welding sequence revealed that a progressive approach was more favorable for distortion control under the given nozzle-to-shell weld structure configurations. The best sequence suggested is to start welding at one nozzle, firstly on shell OD (outside diameter) side then on ID (inside diameter) side, then proceed to next neighboring nozzle. The effect of the welding direction of each weld pass was found affecting only the nozzle angular distortion. The experimental data showed that the manual GTAW process developed much higher shell plate distortion than the SMAW process. The reason would be that a higher percentage of the welding heat had been consumed on the base metal. The influence of the weld bead size didn???t appear to be significant. In the FEA study on the effect of the size of the lumped weld pass, the increase in weld bead size even resulted in a decrease in weld distortion. From the FEA simulation point of view, using large lumped pass would be a highly efficient choice without compromising too much in the precision of the distortion prediction. The FEA study confirmed that a decrease in cooling time after welding would result in more welding distortion. The large scale multi-nozzle mockup with rib-bar fixture demonstrated a maximum out-of-plane shell distortion of 16.4mm after the welding of 10 nozzles with GTAW+SMAW process, which suggests that additional measures should be developed to further control the welding distortion.

Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-15Bitstream added on 2014-06-13T19:37:16Z : No. of bitstreams: 1 mendonca_dp_me_guara.pdf: 3863927 bytes, checksum: cfef071bb77c53f8b78223c45a6d65a3 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho estuda a distribuição de tensões através do método dos elementos finitos em componentes típicos de um vaso de pressão. As diretrizes e metodologia utilizadas nas análises estão de acordo com o código ASME. O vaso de pressão foi estudado para suportar as cargas mais comuns previstas em um projeto de equipamento de processo deste porte. As análises numéricas foram feitas com o software comercial ANSYS e comparados com resultados analíticos previstos no código ASME para os casos mais simples, onde foi obtida a validação dos resultados. Os casos mais complexos foram analisados apenas por soluções numéricas. Todos os casos obtiveram resultados abaixo das tensões admissíveis e de acordo com a metodologia do código, confirmando a viabilidade de análises deste tipo para os casos onde a solução analítica se torna muito conservativa. / Riveted lap joints represent a critical element in metallic airframe construction when designing against fatigue. These elements are widely used in the aerospace industry, so the study of the fatigue’s properties and variables has been increasingly broad. The variable that has shown to have a high influence on the fatigue strength of riveted joints is the clamping force applied to the riveting process. The life of the part tends to be higher when the clamping force applied is increased. The finite element method, which is a calculation tool applied in various fields of activity and has become an indispensable step of mechanical design, is used in this dissertation for the analysis of a riveted lap joint of aeronautic use. The joint is simulated considering the stages of the manufacturing process and application, in order to perform analysis of mechanical behavior and calculate the fatigue life. Through an experimental test of monotonic tensile, strain values were obtained with strain-gauges, and is made the correlation of these data with the numerical model to validate the modeling. Finally two more tests are made with different clamping forces, in order to check the influence of this variation in fatigue life of the joint.

The project is an analysis of technology production of pressure pipes made of aluminum alloys. The basis is a literary study of TIG technology, aluminum heat-tretable and non-heat-treatable materials. The flange-material is EN AW 5083 and the pipe is made of EN AW 6005A. The design of the welding is compromise between the preparation, the cleaning of the welding edges and the weld metal backing strip. Weld was made in real production. Examined impacts are evaluated on the basis of destructive and non-destructive welding test methods. After heating process of weldment material exhibits better mechanical properties. Using the economical and technological evaluation were selected sutiable proces parameters. The result is a suitable weld of the pressure vessel. Further optimization is possible through automation and robotics.

The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C. SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.