Fabrication Of Vessels Research Articles

Methodology for the structural design of single spoke accelerating cavities at Fermilab

Fermilab is planning to upgrade its accelerator complex to deliver a more powerful and intense proton-beam for neutrino experiments. In the framework of the so-called Proton Improvement Plan-II (PIP-II), we are designing and developing a cryomodule containing superconducting accelerating cavities, the Single Spoke Resonators of type 1 (SSR1). In this paper, we present the sequence of analysis and calculations performed for the structural design of these cavities, using the rules of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC). The lack of an accepted procedure for addressing the design, fabrication, and inspection of such unique pressure vessels makes the task demanding and challenging every time. Several factors such as exotic materials, unqualified brazing procedures, limited nondestructive examination, and the general R&D nature of these early generations of cavity design, conspire to make it impractical to obtain full compliance with all ASME BPVC requirements. However, the presented approach allowed us to validate the design of this new generation of single spoke cavities with values of maximum allowable working pressure that exceeds the safety requirements. This set of rules could be used as a starting point for the structural design and development of similar objects.

Surface Integrity of SA508 Gr 3 Subjected to Abusive Milling Conditions

SA508 Gr 3, a bainitic forging steel employed in the fabrication of nuclear pressure vessels has been characterised after dry-milling to investigate extent of machining abuse on the surface. A detailed study of the evolution of residual stresses, microstructure, micro-hardness and roughness in relation to different milling parameters is presented. A central composite orthogonal (CCO) design of experiments (DoE) was used to generate a statistic model of the milling process. Deformation of the sub-surface layer was assessed via SEM BSE imaging. The developed statistical model is discussed aiming to illustrate availability of different cost-effective manufacturing techniques meeting the high standards required by the industry.

Local vacuum electron beam welding for pressure vessel applications

Welding of thick section components such as pressure vessels used in the nuclear industry is traditionally performed using arc welding techniques, requiring multiple weld passes, with interstage non-destructive examination (NDE) and preheating of the component to reduce the risk of hydrogen cracking. Electron beam (EB) welding offers the opportunity to weld thick section components in a single pass and negates the need for interstage NDE, resulting in saving significant time and cost in the fabrication of nuclear vessels. Furthermore, elimination of the preheat step may be possible since the EB process is carried out in a vacuum environment. However, due to the physical size and geometry of nuclear vessels, traditional vacuum chambers would be prohibitively expensive when considering the low volume of output in the nuclear industry. Rolls-Royce and TWI are working on a local vacuum, or ‘out of chamber’, EB welding system, which eliminates the need of such a vacuum chamber and brings the vacuum to the component, thus making EB welding of nuclear vessels more practical and financially viable.

On-site determination of an uncommon cracking mechanism due to composition gradients in a nickel steel weld

This article analyzes a 3.5% Ni steel cryogenic cylindrical vessel, after the detection by nondestructive inspection of cracks in a circumferential weld. Possible in-service damage mechanisms are discussed, in particular, vibration, low cycle thermal fatigue and hydrogen embrittlement. On-site experimental analysis allowed defining that cracks were due to a manufacturing problem. A final weld bead with much greater concentration of Ni generated an uncommon mechanism of thermal fatigue. In Ni alloyed steels, small variations of Ni around 36% involve variations of almost an order of magnitude in the coefficient of thermal expansion. Proposed actions for integrity assurance of the vessel and lessons learned for fabrication of future vessels are briefly discussed.

Applicability of the ASME Exemption Curve for Chinese Pressure Vessel Steel Q345R

Q345R steel is the most commonly used material in fabrication of the pressure vessels and boilers in China, due to its excellent properties. In 2010, ASME code case 2642 accepted Q345R steel for use in construction of pressure vessels. The code case specified impact test exemption curve A for the impact test requirements for Q345R. However, this provision severely limits the application of this material at low temperature, since most of the minimum design metal temperature (MDMT) of curve A is above the freezing point. In this paper, a series of tests (such as uniaxial tensile test, impact test, and fracture toughness test) were carried out at low temperature to investigate the mechanical properties of Q345R steel plates with thickness of 36–80 mm. This study of low temperature usage of Q345R steel was conducted using the fracture mechanics assessment procedure of API 579-1/ASME FFS-1. The fracture toughness is given by master curve (MC) method in the transition regime. The results show that Q345R can be used at lower temperature and that classifying Q345R steel into curve D is appropriate.

Characterization and preparation of bio-tubular scaffolds for fabricating artificial vascular grafts by combining electrospinning and a 3D printing system.

The last decade has seen artificial blood vessels composed of natural polymer nanofibers grafted into human bodies to facilitate the recovery of damaged blood vessels. However, electrospun nanofibers (ENs) of biocompatible materials such as chitosan (CTS) suffer from poor mechanical properties. This study describes the design and fabrication of artificial blood vessels composed of a blend of CTS and PCL ENs and coated with PCL strands using rapid prototyping technology. The resulting tubular vessels exhibited excellent mechanical properties and showed that this process may be useful for vascular reconstruction.

Development of Grounding Device to Reduce Current Variation in Submerged Arc Welding Process for Pressure Vessel Fabrication

This study developed a device to solve welding problems that occur in the manufacturing of a pressure vessel for cryogenic applications under the ASME Section VIII Division 1. The cylindrical body of the vessel was assembled with short pre-fabricated cylinders and caps using submerged arc welding. The rotatable grounding electrode was mounted to the top half of the spherical cap. However, the relatively long distance between the welding and the electrode grounding locations, especially in longer vessels, restricts the flow and the distribution of the electrical current. Radiographic testing identified lack of fusion as the major reason for the restricted flow of the electrical current. This also caused additional work on welding repair. To address this issue that compromised both top-outer and bottom-inner vertical positions for circumference welding, a new grounding device was developed to reduce the flow distance. The electrical conductivity was also improved through a series of welding tests. The investigation showed that a greater average welding current increased arc stability. Radiographic testing confirmed that the vessels were welded completely suggesting the grounding device utility for increasing welding joint soundness of the circumference weldment.

Evaluation of vascular grafts based on polyvinyl alcohol cryogels.

The present study designed and developed blood vessel substitutes (BVSs) composed of polyvinyl alcohol (PVA) cryogels. The in vitro results demonstrated that the coating of the polymer with lyophilized decellularized vascular matrix (DVM) greatly enhanced the adhesion of human umbilical vein endothelial cells (HUVECs). However, when PVA̸DVM BVSs were implanted into the abdominal aorta of Sprague‑Dawley rats, DVM was identified as a highly thrombogenic surface resulting in the mortality of all animals 3‑4 days after surgery. By contrast, all rats implanted with PVA survived and were sacrificed after 12 months. The luminal surface of the explanted grafts was completely covered by endothelial cells and the inner diameter was similar to that of the original vessel. In conclusion, the present study indicated that PVA may be considered as a promising biomaterial for the fabrication of artificial vessels.

Phenomenology of Hydrogen Flaking in Nuclear Reactor Pressure Vessels*

Abstract Recently, the problem of hydrogen flaking resurfaced, when internal defects were detected in the reactor pressure vessels of two Belgian nuclear power plants. These defects turned out to be hydrogen flakes formed during the fabrication of these pressure vessels. The goal of this publication is to provide important insights into the phenomenon of hydrogen flaking, the different parameters that play a role in the mechanism, as well as the typical morphology and location of these flakes. Therefore an extensive literature study was combined with a detailed metallurgical characterization of a significant number of flakes. Hydrogen flaking is a fabrication problem, which is strongly linked with segregation phenomena. A combination of a sufficient amount of hydrogen, stresses and a sensitive microstructure causes hydrogen flaking. For these reasons hydrogen flakes inside large reactor pressure vessels are found in the so-called ghost lines, which originate from segregation processes during casting.

Investigations of Microstructure and Mechanical Properties of 60-mm-Thick Type 316L Stainless Steel Welded Plates by Multipass Tungsten Inert Gas Welding and Electron Beam Welding for Fusion Reactor Applications

Austenitic Type 316L stainless steel plates of very large thicknesses are considered for use in vacuum vessel fabrication in advanced fusion reactors. The possible options for welding of higher-thickness plates are multipass tungsten inert gas (TIG) welding, narrow gap–TIG welding, and electron beam welding (EBW). The manufacture of double-wall vacuum vessel inner components like keys, shells, and ribs are planned to be fabricated using EBW, and some components like field joints are to be fabricated using TIG welding processes. The present paper reports the fabrication of 60-mm-thick Type 316L stainless steel welded samples with multipass TIG welding and EBW processes and sample property characterization studies. The fabricated weld samples have been tested for weld defects with nondestructive tests using X-ray radiography and ultrasonic scan tests. The welded samples have been characterized for mechanical properties such as tensile, bend, Vickers hardness, and Charpy V-notch impact tests. Microstructure analysis has been carried out for both welded samples for the base metal, heat-affected zone, and weld zone. Impact-tested sample fracture analysis has been done by scanning electron microscopy.

Shape Evolution of Multicellular Systems; Application to Tissue Engineering

Organs are in high demand. Tissue engineering and regenerative medicine might be the answer to this challenge of the 21st century. Towards this goal our objective is to optimize the conditions for cells to self assemble into functional structures, such as tissues and eventually organoids. To facilitate self-assembly we employ the technology of bioprinting. To maintain the extended cellular assemblies, they need to be vascularized. Thus we first concentrate on the fabrication of blood vessels. We prepare convenient bioink particles, multicellular units composed of the relevant cell types and we deposit them into a geometry, consistent with the shape of the vessels. Self-assembly and the maturation of the construct takes place post-printing in special-purpose bioreactors by the fusion of the bioink units and the rearrangement of the cells within them. The time to achieve near physiological biomechanical properties has so far been found by trial and error. We have developed an experimental-theoretical-computational framework to optimize the postprinting maturation process, in particular the fusion of the bioink units. This paper focuses on the experimental component of this formalism, in particular on the fusion of spherical and cylindrical bioink units. The connection between experiments and computer simulations are guided by theory. Here we report the results of extended fusion experiments and on their comparison with predictions of the theory. The excellent agreement we find, on one hand, provides a verification of the theoretical component of the formalism, and, on the other hand, the input for the computational component of the formalism. Specifically, our experiments, together with the theory, allow the calibration of the basic simulation parameters, which in turn allows to fully implement the computational component of the formalism to optimize the fabrication of blood vessels through the bioprinting process.

Experimental investigation on submerged arc welding of Cr–Mo–V steel

Welding aspects of a high-quality Cr–Mo–V steel are investigated in the present work. Cr–Mo–V steel can be suggested as a best choice for fabrication of pressure vessels to be operated in high-temperature operating conditions. Welding of this group of steel demands very critical attention on the parameters setting of chosen welding process. Only a few researchers had carried out research on the optimization aspects of the submerged arc welding of Cr–Mo–V steel. In the present work, complete experimental analysis is carried out on the submerged arc welding of Cr–Mo–V steel. The important input process parameters considered are welding current, voltage, welding speed, and wire feed. The effect of these input parameters is studied on various responses related to weld bead geometry and few mechanical properties. Taguchi’s L9 orthogonal array is used for design of experiment and the mathematical models are developed for the responses using MINITAB 15 software. The models developed are validated by conducting more experiments. Optimised parameter setting is also obtained by using a recently developed teaching–learning-based optimization algorithm.

Effect of temper and hydrogen embrittlement on mechanical properties of 2,25Cr–1Mo steel grades – Application to Minimum Pressurizing Temperature (MPT) issues. Part II: Vintage reactors & MPT determination

Standard and Vanadium-alloyed 2,25Cr–1Mo steel grades (EN 10028-2 12CrMo9-10/ASTM A387 gr. 22 and 13CrMoV9-10/ASTM A542 tp. D) are commonly used for the fabrication of heavy pressure vessels for applications in petroleum refining plants.These reactors are made of heavy plates, forged shells, forged nozzles and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high temperatures and high hydrogen partial pressures). A primary concern for end-users is the definition of the Minimum Pressurizing Temperature (MPT) of the equipment. This temperature is the lowest temperature at which the vessel can be repressurized after shutdown and insures no risk of brittle failure of the containment body. The MPT is defined by fracture mechanics and/or CVN approaches and calculations.This second part of the paper presents the methodology of MPT determination and the particular case of vintage reactors. MPT determination methodology is explained by using a virtual pressure vessel representative of vessels found in petroleum refineries. A special focus is also set on the evolution of embedded defects.

Effect of temper and hydrogen embrittlement on mechanical properties of 2,25Cr–1Mo steel grades – Application to Minimum Pressurizing Temperature (MPT) issues. Part I: General considerations & materials' properties

Standard and Vanadium-alloyed 2,25Cr–1Mo steel grades (EN 10028-2 12CrMo9-10/ASTM A387 gr. 22 and 13CrMoV9-10/ASTM A542 tp. D) are commonly used for the fabrication of heavy pressure vessels for applications in petroleum refining plants.These reactors are made of heavy plates, forged shells, forged nozzles and fittings. They are subjected to thermal cycles (stop and go) and to severe service conditions (high temperatures and high hydrogen partial pressures). A primary concern for end-users is the definition of the Minimum Pressurizing Temperature (MPT) of the equipment. This temperature is the lowest temperature at which the vessel can be repressurized after shutdown and insures no risk of brittle failure of the containment body. The MPT is defined by fracture mechanics and/or CVN approaches and calculations.This first part of the paper presents the impact of thermal aging and exposure to hydrogen on materials' mechanical properties and consequently on the value of MPT.

Studies on fracture toughness of cold wire addition in narrow groove submerged arc welding process

Due to the faster joint completion rates coupled with good mechanical properties, narrow gap submerged arc welding (NGSAW) is widely used for fabrication of thick-walled pressure vessels. Several researchers are working on further increase in productivity in NGSAW. In this paper, we propose to increase the quality and productivity in NGSAW through cold wire addition without addition of heat input. Further toughness at sub-zero temperature is also enhanced. The improvement in toughness in cold wire NGSAW is demonstrated through different tests such as impact energy test, fracture toughness tests, plane strain fracture toughness test K Ic, and crack tip opening displacement test.

Effect of Large Cross-Section Oxygen-Propane Flame Cutting on Microstructure in Heat-Affected Zone

Many metal-manufacturing industries include oxyfuel gas cutting among their manufacturing processes because cutting was often used in metal-cutting processes, specifically in the large castings and forgings and the fabrication of pressure vessels. The oxyfuel gas cutting process uses controlled chemical reactions to remove preheated metal by rapid oxidation in a stream of pure oxygen. Previous research has demonstrated microstructure in heat-affected zone varied depending on the gas used for the combustion as well as the cutting speed (Vc) used during the process. In this research, 34CrNiMo6 steel of 900 mm in thickness and 45 carbon steel of 450 mm in thickness were cut using an oxygen-propane flame cutting process. Then, macroscopic morphology and microstructure test were done to analyze the influence of the thickness of cutting cross-section. The results showed, in general, the width of heat-affected zone increased with the thickness of cutting cross-section. Also, it was demonstrated that heat-affected zone in the bottom and top section was wider than others.

Long-term testing and properties of acrylic for the Daya Bay antineutrino detectors

The Daya Bay reactor antineutrino experiment has recently measured the neutrino mixing parameter sin22θ13 by observing electron antineutrino disappearance over kilometer-scale baselines using six antineutrino detectors at near and far distances from reactor cores at the Daya Bay nuclear power complex. Liquid scintillator contained in transparent target vessels is used to detect electron antineutrinos via the inverse beta-decay reaction. The Daya Bay experiment will operate for about five years yielding a precision measurement of sin22θ13. We report on long-term studies of poly(methyl methacrylate) known as acrylic, which is the primary material used in the fabrication of the target vessels for the experiment's antineutrino detectors. In these studies, acrylic samples are subjected to gaseous and liquid environmental conditions similar to those experienced during construction, transport, and operation of the Daya Bay acrylic target vessels and detectors. Mechanical and optical stability of the acrylic as well as its interaction with detector liquids is reported.

Rotational Molding of Polyamide-6 Nanocomposites with Improved Flame Retardancy

Abstract The aim of this work was to develop polyamide-6/ organic-modified montmorillonite (omMMT) nanocomposites for the production of hollow parts by rotational molding. Particular emphasis was placed on the mechanical and flame retardancy properties needed for the fabrication of vessels for flammable liquids. The morphology of the melt compounded nanocomposites, produced by melt compounding, was investigated by X-ray diffraction measurements (WAXD), and Transmission Electron Microscopy (TEM) showed an exfoliated structure. Rheological measurements were used in order to verify whether the viscosity of materials was adequate for rotational molding. While thermomechanical analysis has revealed that neat PA6 and its nanocomposites were not suitable for rotational molding, due to the very low thermal stability of the polymer, the addition of a thermal stabilizer, shifted the onset of degradation to higher temperatures, thus widening the processing window of both PA6 and PA6 nanocomposites. Large-scale vessel prototypes were obtained by rotational molding of thermo-stabilized PA6 and its nanocomposites, and samples extracted from the rotomolded parts were characterized with respect to physical and mechanical properties. It was found that the PA6 nanocomposites exhibited significant improvements at cone calorimeter tests in comparison with neat PA6.

Acrylic target vessels for a high-precision measurement of θ13 with the Daya Bay antineutrino detectors

This paper describes in detail the acrylic vessels used to encapsulate the target and gamma catcher regions in the Daya Bay experiment's first pair of antineutrino detectors. We give an overview of the design, fabrication, shipping, and installation of the acrylic vessels and their liquid overflow tanks. The acrylic quality assurance program and vessel characterization, which measures all geometric, optical, and material properties relevant to ν̄e detection at Daya Bay are summarized. This paper is the technical reference for the Daya Bay acrylic vessels and can provide guidance in the design and use of acrylic components in future neutrino or dark matter experiments.

Effect of filler materials on the performance of gas tungsten arc welded AISI 304 and Monel 400

Dissimilar metal welding involving AISI 304 and Monel 400 finds widespread use in marine and offshore environments for the fabrication of heat exchangers, evaporators, piping and vessels in petrochemical and power generation industries. However studies on the performance of such weldments are scantly found in the literature even though the individual metals have higher corrosion resistance and strength. This paper reports the work carried out on welding of AISI 304 and Monel 400 using Gas Tungsten Arc Welding (GTAW) technique to examine the weldability, mechanical and metallurgical properties. Investigations have been carried out on the hot corrosion behavior of these joints subjected to cyclic air oxidation and K2SO4+NaCl (60%) molten salt environment at 600°C. A comparative analysis was carried out on these weldments for two different filler metals such as E309L and ENiCu-7. The oxide scales formed on the various zones of the weldment have been characterized systematically using surface analytical techniques. Weld zone was found to be more susceptible to degradation than base metals used. The effect of filler materials on the hot corrosion is discussed. The studies reported in this paper would be beneficial for fabricators embracing this type of dissimilar weldments in the petrochemical and power generation industries.