Analysis of residual stresses and distortions resulting from multi-pass welding of nozzles to cylindrical pressure vessels.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.The purpose of the present study is to obtain insight into the formation, behaviour and magnitude of welding-induced residual stresses and distortions resulting from welding nozzles onto cylindrical pressure vessels. A hybrid methodology that comprises numerical analysis, experimental measurements and empirical calculations is used in the present study. The welding process induces a high thermal gradient on the material due to non-uniform temperature distribution; thereby causing the portion of the material that is exposed to high temperatures to expand. However, the relatively cooler material portion that is away from the weld pool resists such expansion, thereby subjecting the structure to stresses and distortions around the fusion zone (FZ) and the heat-affected zone (HAZ). Over the last two decades a number of studies have been done in an effort to predict the effect of welding-induced residual stresses on the integrity of welded structures. However, to this end, such studies have focussed on analysing residual stresses on bead-on-plate, plate-to-plate and [to a less extent] on pipe-to-pipe weld joints. Fewer studies have looked at nozzle-cylinder joints of pressure vessels as is the case in this study. The second chapter gives a detailed review of applicable literature. The constitutive model described in the third chapter includes a two-phase sequentially-coupled thermo-mechanical analysis, which incorporates metallurgical effects. The non-linear transient problem is solved using an axisymmetric 2D model with ‘element birth’ technique, developed on ABAQUS. The first phase comprises the thermal analysis based on Goldak’s moving heat source model that is used to determine temperature histories. The second phase is a sequel stress/strain analysis wherein the temperature fields are used as input loads. The results discussed in chapters three and four show that there is a high concentration of residual stresses close to the weld centre-line, and these die down as distance away from centre-line increases. It is also shown that the inside surface is under tensile stresses, while the outer surface is under compressive stress, whose magnitude approaches yield strength of the material. Axial deflections of up to 0.384mm and radial shrinkage of 0.0237mm are observed. Distortion decreases as distance away from weld centre-line increases. Minimum axial shrinkage, which is close to zero, is observed at the restrained end. The analytical results show adequate corroboration and agreement with the experimental measurements. A number of mitigation techniques are suggested in order to alleviate the impact of residual stress and distortions on fatigue performance of welded structures

Англійська мова для навчання і работи. Навчальний посібник з англійської мови за професійним спрямуванням для студентів і фахівців галузі знань 0503 Розробка корисних копалин Т 1

A coursebook includes all the activities of students’ work at ESP course aimed at development of language behaviour necessary for effective communication of students in their study and specialism areas. The tasks and activities given in the coursebook are typicalfor students’ academic and professional domains and situations. The content is organized in modules that covers generic job-related language skills of engineers. The authentic texts taken from real life contain interesting up-to-date information about mining, peculiarities of study abroad, customs and traditions of English-speaking countries. Pack of self-study resources given in Part II contains Glossary of mining terms, tasks and activities aimed at developing a range of vocabulary necessary for mining, different functions and functional exponents to be used in academic and professional environment as well as tasks developing self-awareness, self-assessment and self-organisation skills. Testing points for different grammar structuresare given in Part III. Indices at the end of each part easify the use of the coursebook. The coursebook contains illustrations, various samples of visualizing technical information. The coursebook is designed for ESP students of non-linguistic universities. It can be used as teaching/learning materials for ESP Courses for Mining Engineers as well as for self-study of subject and specialist teachers, practicing mining engineers and researchers in Engineering.У посібнику представлені всі види діяльності студентів з вивчення англійської мови, спрямовані на розвиток мовної поведінки, необхідної для ефективного спілкування в академічному та професійному середовищах. Навчальний посібник містить завдання і вправи, типові для різноманітних академічних та професійних сфер і ситуацій. Структура організації змісту– модульна і охоплює загальні мовленнєві вміння інженерів. Зразки текстів– автентичні, взяті з реального життя, містять цікаву та актуальну інформацію про видобувничу промисловість, особливості навчання за кордоном, традиції та звичаї країн, мова яких вивчається. Ресурси для самостійної роботи(Том ІІ) містять глосарій термінів, завдання та вправи для розвитку словарного запасу та розширення діапазону функціональних зразків, необхідних для виконання певних функцій, та завдання, які спрямовані на розвиток навичок самооцінювання і організації свого навчання. Граматичні явища і вправи для їх засвоєння наводяться в томі ІІІ. Наприкінці кожної частини наведено алфавітно-предметні покажчики. Багато ілюстрацій та різних візуальних засобів подання інформації. Навчальний посібник призначений для студентів технічних університетів гірничого профілю. Може використовуватися для самостійного вивчення англійської мови викладачами, фахівцями і науковцями різних інженерних галузей

Heat Transfer Modeling of Roller Hearth and Muffle Furnace

In hot forming die quenching, furnaces are used to austenitize ultra high strength steel blanks. In the case of coated steels, like Usibor® 1500 P, furnace heating also transforms a protective Al-Si layer into a permanent Al-Si-Fe intermetallic coating. Modeling this process requires knowledge of the thermophysical properties of the material, specifically, radiative properties and how the sensible energy and latent heat of austenitization change with blank temperature. While the sensible energy is known, there is considerable uncertainty regarding the radiative properties and the latent heat of austenitization. In this work the effective specific heat of Usibor® 1500 P is inferred through inverse analysis of temperature data collected on coupons heated in a muffle furnace. This technique is first used to validate the heat transfer model, and then used to reveal the distribution of latent heat of austenitization at higher temperatures. The characterization of the radiative properties is carried out on Gleeble-heated coupons using a near-infrared spectrometer and a Fourier transform infrared reflectometer. Obtained thermophysical properties are employed in developing a heat transfer model for the patched blanks to gain insight into the non-uniform heating of patched blanks. The thermocouple measurements carried out in muffle and roller hearth furnaces are used to validate the modeled temperatures. Various strategies to optimize the heating process for patched blanks are proposed and evaluated, including the use of a high emissivity coating to compensate for the increased thermal mass of the patch

Optimisation of welding parameters to mitigate the effect of residual stress on the fatigue life of nozzle–shell welded joints in cylindrical pressure vessels.

Doctoral Degree. University of KwaZulu-Natal, Durban.The process of welding steel structures inadvertently causes residual stress as a result of thermal cycles that the material is subjected to. These welding-induced residual stresses have been shown to be responsible for a number of catastrophic failures in critical infrastructure installations such as pressure vessels, ship’s hulls, steel roof structures, and others. The present study examines the relationship between welding input parameters and the resultant residual stress, fatigue properties, weld bead geometry and mechanical properties of welded carbon steel pressure vessels. The study focuses on circumferential nozzle-to-shell welds, which have not been studied to this extent until now. A hybrid methodology including experimentation, numerical analysis, and mathematical modelling is employed to map out the relationship between welding input parameters and the output weld characteristics in order to further optimize the input parameters to produce an optimal welded joint whose stress and fatigue characteristics enhance service life of the welded structure. The results of a series of experiments performed show that the mechanical properties such as hardness are significantly affected by the welding process parameters and thereby affect the service life of a welded pressure vessel. The weld geometry is also affected by the input parameters of the welding process such that bead width and bead depth will vary depending on the parametric combination of input variables. The fatigue properties of a welded pressure vessel structure are affected by the residual stress conditions of the structure. The fractional factorial design technique shows that the welding current (I) and voltage (V) are statistically significant controlling parameters in the welding process. The results of the neutron diffraction (ND) tests reveal that there is a high concentration of residual stresses close to the weld centre-line. These stresses subside with increasing distance from the centre-line. The resultant hoop residual stress distribution shows that the hoop stresses are highly tensile close to the weld centre-line, decrease in magnitude as the distance from the weld centre-line increases, then decrease back to zero before changing direction to compressive further away from the weld centre-line. The hoop stress distribution profile on the flange side is similar to that of the pipe side around the circumferential weld, and the residual stress peak values are equal to or higher than the yield strength of the filler material. The weld specimens failed at the weld toe where the hoop stress was generally highly tensile in most of the welded specimens. The multiobjective genetic algorithm is successfully used to produce a set of optimal solutions that are in agreement with values obtained during experiments. The 3D finite element model produced using MSC Marc software is generally comparable to physical experimentation. The results obtained in the present study are in agreement with similar studies reported in the literature

University of Nevada, Las Vegas Transmutation Research Program Annual Report Academic Year 2006-2007

It is my pleasure to present the UNLV Transmutation Research Program’s sixth annual report that highlights the academic year 2006-2007. Supporting this document are the many technical reports and theses that have been generated over the past five years. In the sixth year of our program, we continued to see growth in the Radiochemistry Ph.D. program with a total of 13 students in the third year of the program (we anticipated eight in the program proposal). Since our inception, the program has sponsored to their conclusion 42 M.S. and 4 Ph.D. degrees. The program supported 39 graduate students, 17 undergraduates, and seven post-doctoral scholars in six academic departments across the UNLV scientific and engineering communities in the academic year 2006-2007. Our research tasks span the range of technology areas for transmutation, including separation of actinides from spent nuclear fuel, methods of fuel fabrication, reactoraccelerator coupled experiments, corrosion of materials exposed to lead-bismuth eutectic, and special nuclear materials protection and accountability. We continued our emphasis on molten metal technology and actinide chemistry in our enhancements to UNLV this year to build a foundation in areas that are in line with UNLV’s strategic growth and our ability to address student-appropriate research in the transmutation program

Fuel Injection

Fuel Injection is a key process characterizing the combustion development within Internal Combustion Engines (ICEs) and in many other industrial applications. State of the art in the research and development of modern fuel injection systems are presented in this book. It consists of 12 chapters focused on both numerical and experimental techniques, allowing its proper design and optimization

Laser assisted arc welding process for dry hyperbaric deep water application

Hyperbaric Gas Metal Arc Welding (GMAW) is an important technology for repair welding of deep sea pipelines and linking of existing pipeline networks to newer ones through tie-ins and hot-tap welding. With increasing water depth the process becomes susceptible to hydrogen assisted cracking due to the very fast cooling rate of the weld caused by higher habitat gas density and resulting higher thermal diffusivity. Maintaining sufficient heat in the welding zone is vital to avoid a potential cracking tendency especially as moisture pick-up may be difficult to avoid during hyperbaric welding operations. In addition to this, hyperbaric GMAW has a limitation of low heat input because it is operated at a short arc length or dip transfer mode to avoid process instability at high pressure. Also, the short arc length generates weld spatter that may affect weld quality. The research presented in this thesis, investigated the use of an industrial laser in conduction mode for the purpose of providing significant additional heat input to control the weld thermal cycles of GMAW. Advanced GMAW power sources such as the Fronius Cold Metal Transfer (CMT) and EWM ColdArc have also been investigated for reduced weld spatter generation. Studies were conducted to investigate the weld pool thermal cycles and resulting metallurgical phase formation in hyperbaric GMAW at different pressures ranging from 1 bar to 200 bar. This was followed by welding trials at one atmosphere to compare the process characteristics of traditional dip transfer GMAW with some advanced GMAW power sources such as CMT and ColdArc. The main experimental trials to investigate a laser assisted GMAW (CMT) process were performed at one atmosphere condition. A thermal model was developed using Abaqus software to predict the weld metal and heat affected zone thermal cycle in a laser assisted GMAW (CMT) process at one atmosphere and under high ambient pressures. Finally, investigation was carried out to evaluate the benefit of the laser assisted process in lowering diffusible hydrogen content from the weld metal. The hyperbaric GMAW experimental results showed that the weld pool cooling rate increases with pressure due to higher chamber gas density and resulting thermal diffusivity. But this effect is not prominent for thicker plates. Therefore, it was concluded that heat conduction through the steel thickness dominates convective losses to the chamber gas environment. It was also shown that the welding arc shrinks as pressure increases in order to minimise energy loss to the environment. This defined the weld bead profile; although it was found that beyond 100 bar pressure the weld penetration depth remained effectively unchanged. Apart from the hardness of the weld made at 1 bar, there was little difference between those at 18, 100 and 200 bar. However, all of the welds show hardness peaks greater than 350 HV10 recommended for offshore structures. It was observed that CMT produced the lowest weld spatter compared to the traditional GMAW and ColdArc. However, this advantage is constrained to low wire feed speed (3 to 5 m/min) beyond which it becomes relatively unstable. For the laser assisted GMAW (CMT) trials, it was shown that the laser serves as a spatially resolved heat source, reheating the weld bead and reducing the cooling rate. For the laser parameters investigated, over 200% reduction of cooling rate could be achieved when compared with GMAW alone. It was also demonstrated that the additional laser thermal input will extend the weld residence time at high temperature (over 300 °C). This will prolong the weld cooling time such that dissolved hydrogen can diffuse out before it comes to room temperature. The laser was shown to significantly reduce the weld peak hardness from about 420 HV0.5 to values below 350 HV0.5, which will be beneficial for hyperbaric welding. The model prediction of the weld thermal cycles was in good agreement with the experimental results. Therefore, it could be used to predict the weld metal and HAZ cooling rate of a laser assisted GMAW (CMT) process although the model would need to be calibrated for higher pressure data. It was also demonstrated that additional laser heat can reduce the weld hydrogen content to acceptable limits of 5 ml/100 g of weld metal even for high moisture content in the welding environment. In conclusion, the addition of laser heating to GMAW will reduce the weld cooling rate, extend the weld pool cooling time, and expel diffusible weld hydrogen. All of these would be immensely beneficial in terms of improving the quality and reliability of structures fabricated through hyperbaric GMAW

NASA thesaurus. Volume 3: Definitions

Publication of NASA Thesaurus definitions began with Supplement 1 to the 1985 NASA Thesaurus. The definitions given here represent the complete file of over 3,200 definitions, complimented by nearly 1,000 use references. Definitions of more common or general scientific terms are given a NASA slant if one exists. Certain terms are not defined as a matter of policy: common names, chemical elements, specific models of computers, and nontechnical terms. The NASA Thesaurus predates by a number of years the systematic effort to define terms, therefore not all Thesaurus terms have been defined. Nevertheless, definitions of older terms are continually being added. The following data are provided for each entry: term in uppercase/lowercase form, definition, source, and year the term (not the definition) was added to the NASA Thesaurus. The NASA History Office is the authority for capitalization in satellite and spacecraft names. Definitions with no source given were constructed by lexicographers at the NASA Scientific and Technical Information (STI) Facility who rely on the following sources for their information: experts in the field, literature searches from the NASA STI database, and specialized references