Numerical predictions of crack growth in a pressure vessel with welded nozzles

Most structural elements that represent parts of equipment and machines in the process industry are subjected to strength calculations. Structural materials and welded joints typically contain flaws and microcracks, from which cracks are initiated. Exploitation conditions can lead to the occurrence of cracks, even in cases when there are no flaws in the material, typically at locations with stress concentration. Penetration of two cylinders is the most commonly encountered form of geometric discontinuity of cylindrical surfaces which results in stress concentration. On a pressure vessel with two nozzles of different geometries, critical areas (i.e. stress concentration areas) are determined by experimental 3D Digital Image Correlation (DIC) method. Then, the numerical analysis of the equivalent 3D model is performed and the obtained results are comparable to experimental values. Since the fatigue cracks are expected in the high stress areas, in one of them - next to the nozzle in the numerical model - a crack has initiated. Then, crack growth is simulated using extended finite element method (XFEM). The aim of this paper is to show that it is possible to predict the crack growth direction and critical length of the crack which can occur in the pressure vessel, based on values of stress intensity factors (SIFs) evaluated in the numerical simulation

structural optimization of pressure vessels using FEA

The main aim of many researchers is to solve the problem of shape optimization of the pressure vessels in order to save materials and energy during manufacturing, but preserve reliability during exploitation. Structural optimization of several parameters that have main impact on stress, strain and deformation state of the pressure vessels is presented in this research. Modern approach of stress and strain analysis on pressure vessels involves numerical and experimental testing. Experimental 3D Digital Image Correlation (DIC) method for analyzing full field of surface strain and stress including camera system in combination with Aramis software was used. After determination of areas with highest von Mises stresses and strain concentrations, numerical analysis of equivalent 3D model was performed in Ansys Workbench software. Results in critical areas were compared and they showed good agreement. Then, several parameters were chosen for optimization in order to reduce stresses and mass weight of pressure vessel. Response Surface Optimization (RSO) method was used to optimize geometry of the pressure vessel parts (shell, head and nozzles). It is shown that carried out optimization gives the minimum weight of pressure vessel with optimized wall and nozzle thicknesses for the given load

Numerical predictions of crack growth in a pressure vessel with welded nozzles

Most structural elements that represent parts of equipment and machines in the process industry are subjected to strength calculations. Structural materials and welded joints typically contain flaws and microcracks, from which cracks are initiated. Exploitation conditions can lead to the occurrence of cracks, even in cases when there are no flaws in the material, typically at locations with stress concentration. Penetration of two cylinders is the most commonly encountered form of geometric discontinuity of cylindrical surfaces which results in stress concentration. On a pressure vessel with two nozzles of different geometries, critical areas (i.e. stress concentration areas) are determined by experimental 3D Digital Image Correlation (DIC) method. Then, the numerical analysis of the equivalent 3D model is performed and the obtained results are comparable to experimental values. Since the fatigue cracks are expected in the high stress areas, in one of them - next to the nozzle in the numerical model - a crack has initiated. Then, crack growth is simulated using extended finite element method (XFEM). The aim of this paper is to show that it is possible to predict the crack growth direction and critical length of the crack which can occur in the pressure vessel, based on values of stress intensity factors (SIFs) evaluated in the numerical simulation

FE analysis of the support assembly of the port bay bridge

Port bay bridge (PBB) presents unique challenges in design and construction compared to the conventional bridge. This research aims to present a 3D finite element analysis of the PBB supports. At all points of supporting parts (wheels, plate, and pin) where one tunnel is in a contact with another tunnel, the same supporting elements are used, and what differs at these points are loads that have to be carried. Since it is expected that pins will be the load-carrying elements with the highest stress, the safety factors will be evaluated according to the stress calculated on pins. Reactions forces will be applied on both wheels equally; that is, any reaction force must be divided by two first (since there is pair of supports at all points), and then obtained value must be divided again by two (since there are two wheels on each support). The moment on the pin equals zero when F1 and F2 are equal (this is an ideal case); otherwise, the twisting moment (torque) occurs. Possible values of twisting moments are also analyzed and presented later in this paper

Fem analysis of pressure vessel with an investigation of crack growth on cylindrical surface

To ensure reliability of pressure vessels during service it is necessary to (1) know properties of materials used in their design and (2) evaluate vessels' behaviour under different working conditions with satisfying accuracy. Due to various technical and/or technological requirements, nozzles are usually welded on vessel's shell producing geometrical discontinuities that reduce the safety factor. To evaluate their influence, vessels with two different nozzles were experimentally studied and critical areas for crack initiation have been identified by 3D Digital Image Correlation (DIC) method. After that, the numerical analysis of equivalent 3D finite element model was performed and obtained results were compared with experimental values. In the most critical area, next to the one of the nozzles, crack was initiated and then growth of the damage was simulated using extended finite element method (XFEM). In this paper evaluation of stress intensity factors (SIFs) along crack path is presented, as well as the most probable direction of the crack propagation on the shell. Based on SIFs values, critical length of the crack and number of pressure cycles to the final failure were estimated

Thermogravimetric study on the pyrolysis kinetic mechanism of waste biomass from fruit processing industry

The detailed kinetic analysis of slow pyrolysis process of apricot (Prunus armeniaca L.) kernal shells has been estimated, under non-isothermal conditions, through thermogravimetric analysis and derivative thermogravimetry. Thermal decomposition was implemented using four different heating rates (5, 10, 15, and 20 degrees C per minute), with consideration of how this parameter effects on the process kinetics. The higher heating rates provoke the shift of thermoanalytical curves towards more elevated temperatures. Using isoconversional differential method, the variation of activation energy, Ea, with conversion fraction, a, was detected, and pyrolysis reaction profile was discussed. After resolving the pyrolysis rate curves of individual biomass constituents, the temperature and conversion ranges of their thermal transformations were clearly identified. In the latter stage of analysis, every identified reaction step was considered through mechanistic description, which involves selection of the appropriate kinetic model function. The comparison of the results as well as discrepancies between them has been discussed. The corresponding rate-law equations related to thermal decomposition reactions of all biomass constituents present in the tested agricultural waste material have been identified

Thermogravimetric kinetic study of solid recovered fuels pyrolysis

In the Republic of Serbia there are significant quantities of coffee and tire wastes that can be utilized as Solid Recovered Fuel (SRF) and used as an additional fuel for co-combustion with coal and biomass in energy production and cement industry sectors. Differences between SRF and base fuel are a cause of numerous problems in design of burners. The objective of this study was to determine the kinetic parameters for the thermochemical conversion of selected SRF using Simultaneous Thermal Analysis (STA). Samples of coffee and tire waste were used for the experimental tests. Thermal analysis was carried out in nitrogen atmosphere at three different heating rates 10, 15 and 20 K/min for each sample, while it was heated from room temperature up to 900 degrees C. Two sample sizes x lt 0.25 mm and 0.25 lt x lt 0.5 mm of each SRF were used in experiments, in order to obtain reliable Thermal Gravimetric Analysis (TGA) data for estimation of kinetic parameters for SRF pyrolysis. Experimental results were used for determination of pre-exponential factor and activation energy according to methods presented in the literature. Presented research provides valuable data of coffee and tire waste that can be used for the burners design

Thermogravimetric study on the pyrolysis kinetic mechanism of waste biomass from fruit processing industry

The detailed kinetic analysis of slow pyrolysis process of apricot (Prunus armeniaca L.) kernal shells has been estimated, under non-isothermal conditions, through thermogravimetric analysis and derivative thermogravimetry. Thermal decomposition was implemented using four different heating rates (5, 10, 15, and 20 degrees C per minute), with consideration of how this parameter effects on the process kinetics. The higher heating rates provoke the shift of thermoanalytical curves towards more elevated temperatures. Using isoconversional differential method, the variation of activation energy, Ea, with conversion fraction, a, was detected, and pyrolysis reaction profile was discussed. After resolving the pyrolysis rate curves of individual biomass constituents, the temperature and conversion ranges of their thermal transformations were clearly identified. In the latter stage of analysis, every identified reaction step was considered through mechanistic description, which involves selection of the appropriate kinetic model function. The comparison of the results as well as discrepancies between them has been discussed. The corresponding rate-law equations related to thermal decomposition reactions of all biomass constituents present in the tested agricultural waste material have been identified

test pressures and stresses for pressure vessels according to new regulation 87/11

With the enforcement of Regulation on Technical Requirements for Design, Development and Conformity Assessment of Pressure Equipment and Regulations on the Inspections of Pressure Equipment During the Lifetime (Službeni glasnik RS, No. 87/2011), the Regulation on Technical Normatives of Stable Pressure Vessels has ceased to be valid (Službeni glasnik RS, no. 16/83). New Regulations have brought novelties regarding the essential requirements – allowable stresses and test pressures. In this paper, test pressure values and stresses resulting from these pressures are calculated. Differences in pressures and stresses generated by applying the “new” and “old” Regulations which are applied to pressure vessels designed under old Regulations, are analysed and discussed

Determination of internal pressure value causing pipe branch model to plastically deform

Složenost geometrije posuda pod pritiskom obično predstavlja uzrok pojave koncentracije napona i deformacija. Savremeni pristup analize stanja napona i deformacija uključuje numerička i eksperimentalna ispitivanja. Svako eksperimentalno testiranje na realnoj konstrukciji može ugroziti samu konstrukciju. Stoga, pravljenje modela neke konstrukcije ima velike prednosti. Umanjeni model račve A6 trećeg cevovoda na HE Perućica, Nikšić je izrađen kako bi bio podvrgnut detaljnom eksperimentalnom testiranju. Cilj je bio da se odredi vrednost unutrašnjeg pritiska koji dovodi do plastične deformacije na modelu račve i da se ovi rezultati koriste za određivanje pritiska koji će stvarnu konstrukciju dovesti do plastičnog deformisanja bez ikakvih merenja na samoj konstrukciji. Eksperimentalna merenja su sprovedena metodom mernih traka. Merne trake su pozicionirane na kritične zone. Numerički model i rezultati dobijeni metodom konačnih elemenata (FEM) potvrđeni su eksperimentalnim rezultatima (u oblasti elastičnosti). Nakon verifikacije u elastičnoj oblasti, povećanjem pritiska, eksperimentalno određena je kritična vrednost unutrašnjeg pritiska koji je izazvao plastičnu deformaciju modela račve. Na osnovu ponašanja modela račve i nakon određivanja odnosa između modela i stvarne konstrukcije, procenjuje se maksimalna izračunata vrednost unutrašnjeg pritiska na koju se realna konstrukcija može izložiti. Pored toga, slabe tačke na konstrukciji su potvrđene dobijanjem istih rezultata kroz eksperiment i proračun, što daje dobre smernice za praćenje ove konstrukcije tokom eksploatacije, s obzirom na to da je ovakvom analizom moguće smanjiti broj mernih mesta za praćenje (u smislu da se kontrolišu tačno ona merna mesta koja su se pokazala kao najkritičnija).Complexity of pressure vessels geometry usually causes stress and strain concentrations. Modern approach of stress and strain analysis involves numerical and experimental testing. Every experimental testing on the construction could endanger construction itself. Therefore, making a model of the construction has great benefits. Sub-sized model of the pipe branch of A6 third pipeline at Hydropower Plant Perućica, Nikšić was made in order to be subjected to a detailed experimental testing. The aim was to determine internal pressure value causing pipe branch model to plastically deform, and, to use these results for determining pressure causing real structure to plastically deform, without any measurements on the structure itself. Experimental measurements were carried out using strain gauge method. Strain gauges are positioned in critical zones. Numerical pipe branch model and results obtained by using finite element method (FEM) was verified with experimental results (in elasticity area). After verification in elastic area, experimentally by increasing pressure value, critical internal pressure causing plastic deformation of pipe branch model was determined. Based on the pipe branch model behaviour, and after determination of relation between the model and the real structure, maximum calculated internal pressure value to which the structure may be subjected in exploitation is assessed. Besides, weak spots on the structure were verified by obtaining the same results through experiment and calculation, which gives good guidelines for monitoring of this structure during usage, since it is possible, by using this analysis, to decrease the number of measurement locations for monitoring (in order to control exactly those measurement locations, which proved to be the most endangered)