Typical Pressure Vessel Research Articles

Wafer to wafer nano-imprinting lithography with monomer based thermally curable resin

Nano-imprinting lithography is one of the most promising key technologies for mass production of devices with nano-sized patterns. It is regarded as a tool for the next generation lithography (NGL). In this study, a thermally curable monomer solution was used for the imprinting process in order to lower imprinting pressure and temperature. A unique pressure vessel type imprinting system was used to imprint patterns as small as 150 nm over a whole 6 in. diameter wafer at a relatively low temperature (80 °C) and pressure (20 atm). Near zero residual layer under the trenches was successfully demonstrated over the whole 6 in. active area.

Full wafer scale near zero residual nano-imprinting lithography using UV curable monomer solution

The nano-imprinting lithography is regarded as one of the most promising technologies for nano-sized pattern fabrication and is being focused as a key technology for the mass production. However, significant progress must be made to improve uniform imprinting over large area, low temperature and low pressure operation and imprinting with minimized residual layer. A unique pressure vessel type imprinting system was used to imprint the patterns as small as 150 nm over whole 4-in. diameter wafer with near zero residual layer. To cover the whole surface of 100 mm diameter Si wafer, an array of 18 mm by 18 mm quartz stamps was used as an imprint stamp. UV curable benzylmethacrylate (C 11H 12O 2) based monomer solution is used as an imprinting resin in this study. Near zero residual nano-imprinting over 100 mm diameter Si wafers was successfully demonstrated with 25 atm of imprinting pressure by using liquid state monomer based UV curable resin.

Response of half–full horizontal cylinders under transverse excitation

The present work investigates the response of half–full horizontal cylindrical vessels under external excitation in the transverse direction. A two dimensional mathematical model is developed to describe sloshing effects in rigid vessels. The velocity potential is expressed in a series form, where each term is the product of a time function and the associated spatial function. In this geometrical configuration the spatial functions are not orthogonal and the problem is not separable. Application of the boundary conditions results in a system of ordinary linear differential equations, which are solved numerically. Sloshing frequencies of half–full horizontal cylinders are computed, and hydrodynamic forces are calculated. Under harmonic excitation, the formulation results in a system of linear equations, allowing for a semi-analytical solution. A simplified version of the mathematical model is also developed, which considers the first two terms of the series and results in an elegant solution. Furthermore, assuming a beam-type deformation of the container, the simplified formulation can be extended to approximate the coupled response of the container-liquid system. Using this formulation, the response of a typical pressure vessel under ground-motion excitation is calculated and the effects of wall deformation are demonstrated.

Modeling of welded joints for design against fatigue

Historically, design against fatigue of welded joints is widely based on the nominal stress approach with categorized structural details and appropriate S-N-curves without any need of detailed numerical analysis. Recently, local approaches based on structural and notch stresses are of growing importance for the lifetime assessment of components without post-weld treatment for dominant elastic material behavior in high cycle fatigue (HCF), and for design against the endurance limit. Finally, high quality weld seams submitted to post-weld treatment such as grinding and TIG or plasma dressing and/or operating conditions in low cycle fatigue (LCF) with high plastic deformations are advantageously considered within a strain-based approach. A concept-conforming modeling strategy as a relevant module of lifetime assessment is required to ensure reliable and reproducible analysis results for all local approaches of design against fatigue. A unique modeling strategy based on an adaptive nominal weld seam contour is derived covering a wide range of typical welded pressure vessel joints for stress and strain based approaches. An alternative method for the determination of structural stresses is proposed to avoid the uncertainties of extrapolation and description of structural stiffness.

Intensive Quenching Theory and Application for Imparting High Residual Surface Compressive Stresses in Pressure Vessel Components

An alternative method for the hardening of steel parts has been developed as a means of providing steel products with superior mechanical properties through development of high residual compressive stresses on the part surface, and involves the application of intensive quenching during heat treatment. This processing method, termed “Intensive Quenching,” imparts high residual compressive stresses on the steel surface, thus allowing for the use of lower alloy steels, reduction or elimination of the need for carburization and shot peening, and providing for more cost-effective heat treating. Intensive quenching also provides additional environmental benefits, as the process uses plain water as the quenching media in contrast to traditional heat treatment practices which typically employ hazardous and environmentally unfriendly quenching oil. This paper presents an overview of the theory and application of intensive quenching, as well as provides experimental and computational data obtained for a variety of steel products. Also presented will be results of computer simulations of temperature, structural and stress/strain conditions for a typical pressure vessel during intensive quenching.

Fatigue lifetime assessment procedures for welded pressure vessel components

Design against fatigue of welded pressure vessel components is usually based on structural or notch stress approaches. Post weld treatment methods such as grinding or TIG dressing provide significant improvements of the fatigue behaviour by blunting of the weld toe notches and by using materials of higher strength. Although well established on the level of welding technologies, fatigue design rules for improvement methods are not yet available within design codes. The local strain approach can be applied as a method of lifetime assessment in these cases. The methodology is demonstrated for cylinder-to-cylinder intersections and butt welded joints as typical pressure vessel structures. Concept-conforming modelling and numerical stress and strain analysis are relevant modules of the procedure. The derivation of fatigue curves for special weld details is shown under the aspect of practical application. Once determined, these fatigue curves can be used in the same sense as the traditional nominal stress approach.

Stress intensity factors for circumferential cracks in pressure vessel door closures

Bandlock pressure vessel door closures and many other commonly used engineering geometries can be simplified to that of a tube with an axisymmetric internal projection. When the projection is axially loaded, the maximum stress is seen at the start of the fillet between the tube and the projection, and this is the site of potential fatigue crack growth. Stress intensity factors for circumferential cracks in tubes with axially loaded axisymmetric internal projections are presented for a wide range of geometries, governed by five parameters: tube diameter, projection depth and length, fillet radius and crack length. The dominant mode is shown to be mode I. Results are presented to allow the variation of Y I, with fillet radius, tube diameter, projection depth, projection length and crack length, to be determined. Y I is shown to vary widely, between 0.59 and 12.65, and is seen to be strongly dependent on projection depth. Y I is dependent on fillet radius for short crack lengths, but for crack lengths approaching half the tube wall thickness, it becomes independent of fillet radius. Y I results for the simplified loaded projection are compared with results from a finite element analysis of a typical pressure vessel door closure, and the results are seen to correlate to within 3.2%.

Recent progress in understanding reactor pressure vessel steel embrittlement

This paper reviews the current understanding of the basic mechanisms of irradiation embrittlement in reactor pressure vessel steels. Radiation enhanced diffusiona at operating temperatures around 290°C leads to the formation of various ultrafine scale hardening phases, including copper rich and copper catalysed manganese-nickel rich precipitates. Other nanofeatures that do not require copper, so-called matrix defects, include alloy phosphides and carbonitrides as well as defect cluster-solute complexes. Matrix defects that are thermally unstable (anneal) under irradiation play a very important role in mediating flux and temperature effects. The balance of features depends on the composition of the steel and the irradiation conditions. Copper enriched phases, which are the dominant embrittling feature in alloys containing significant trace quantities of this element, are fairly well understood. In contrast, the detailed identity and etiology of the matrix defects and manganese-nickel rich phases that may form in very low copper steels has not yet been established. Embrittlement of typical (Mn-Mo-Ni) pressure vessel steels, manifested as shifts in Charpy V-notch transition temperature, can generally be related to yield stress increases. Yield stress increases from copper rich precipitates are consistent with predictions using defect-obstacle interaction theory coupled with a new model for superposition of the hardening from both pre- and post-irradiation sources of strength. Details of the strengthening contributions from the other irradiation features are not as well established, but appear to be reasonably consistent with theory. These concepts have led to the development of thermodynamic-kinetic-micromechanical models that are broadly consistent with experiment, and rationalize the highly synergistic effects of important irradiation (e.g., temperature, flux, fluence) and metallurgical (e.g., copper, nickel, manganese, phosphorous and heat treatment) variables on both irradiation hardening and hardening recovery during post-irradiation annealing. Open questions can be addressed with a hierarchy of new theoretical and experimental tools, which range from atomistic modeling to tomographic methods of observing the sequence-of-events leading to fracture. Advanced microstructural evolution, microstructure-property and micromechanical models, validated and calibrated by well designed experiments, will greatly enhance our ability to predict pressure vessel embrittlement and to resolve out-standing technical issues.

A Simple Upper-Bound Method for Calculating Approximate Shakedown Loads

A simple approach for calculating upper-bound shakedown loads is described. The method is based on a series of iterative elastic finite element analyses (the elastic compensation procedure) applied to Koiter’s upper-bound shakedown theorem. The method is demonstrated for a typical pressure vessel application; an axisymmetric nozzle in a spherical shell. Several geometrical configurations are investigated. The calculated upper-bound shakedown loads are compared with lower-bound results obtained by the authors, simple shakedown criteria, and various results given in the literature.

Development of miniaturized specimens for the study of neutron irradiation/plasma exposure synergistic effects on candidate fusion reactor materials

The aim of this work is to choose a miniaturized specimen version relevant for testing candidate fusion reactor materials including mechanical testing after combined neutron irradiation/plasma exposure in a fission reactor. The material examined was reactor pressure vessel type steel in irradiated and aged (unirradiated) conditions. Comparative standard impact, three point bend and small punch tests were conducted. It is established that there is a possibility of miniaturization of irradiated steel experimental specimens by means of proper specimens type choice with mass reducing from ≈ 40 (Charpy) to 0.4 g (small plates).

Elastic-plastic fracture assessment using a J- R curve by direct method

In the elastic-plastic evaluation methods, based on J integral and tearing modulus procedures, an essential input is the material fracture resistance ( J- R) curve. In order to simplify J- R determination direct, a method from load-load point displacement records of the single specimen tests may be employed. This procedure has advantages such as avoiding accuracy problems of the crack growth measuring devices and reducing testing time. This paper presents a structural integrity assessment approach, for ductile fracture, using the J- R obtained by a direct method from small single specimen fracture tests. The J- R direct method was carried out by means of a developed computational program based on theoretical elastic-plastic expressions. A comparative evaluation between the direct method J resistance curves and those obtained by the standard testing methodology on typical pressure vessel steels has been made. The J- R curves estimated from the direct method give an acceptable agreement with the approach proposed in this study which is reliable to use for engineering determinations.

Simulation of vented pressure vessel tests for organic peroxides

It is current practice to classify the transportation hazards category of organic peroxides using a variety of test methods including a vented pressure vessel test (PVT). This test procedure can be simulated analytically provided certain thermal calorimetry data are available for the peroxide of interest. It is the purpose of this paper to illustrate important insights into the pressure vessel test procedure which can be gained through simulation. Through simulation of the test procedure one finds sensitivities to sample size and concentration which are not readily apparent from many typical pressure vessel test results.

A reliability assessment of reactor pressure vessels

A theoretical investigation is presented on the reliability assessment of nuclear reactor pressure vessels. In the analysis, a Poisson-type random walk model is assumed to represent the randomly occurred transients, which have randomly distributed stresses. These transient stresses cause a predominant initial crack size to grow and, therefore, degrade the reliability of a pressure vessel. Following the probabilistic fracture mechanics approach, the variability of the material properties is considered. A numerical calculation is carried out based on available empirical data. It is found that for a typical BWR pressure vessel, the failure probability lies in the order of 10 −6 and the failure rate is approximately in the order of 10 −8 per vessel year. The result is in agreement with other published results.

On the application of probabilistic fracture mechanics to the reliability and inspection of pressure vessels

A probabilistic fracture mechanics model was developed to analyse the failure probability of a typical high power density reactor pressure vessel. The major causes for the nuclear reactor pressure vessel failure include fatigue, corrosion fatigue and brittle failure. All these causes are greatly affected by the stress loading conditions, material properties (aged by neutron damage), and defects embedded in the structure. Both an analytical first-order second-moment approximation and a hybrid methodology were employed in this study. In addition to the static scatter of the pre-existing cracks and material properties, a random walk model based on the operating history was introduced to represent the random occurrence of the abnormal transient stresses. The failure mode is defined as the brittle failure caused by a critical crack, meaning the stress intensity factor around a critical crack exceeding the fracture toughness of the pressure vessel material. Through a sample study on a typical high power density nuclear power plant, it was found that the vessel failure probability is about 4 × 10 −4 at the 40th year of operation and the failure rate is in the order of 5 × 10 −6 per vessel per year, which had reasonable agreement with the value of 10 −4−10 −6 as reported based on real-world statistics. In addition to the failure probability caused by fatigue crack growth, the reliability of a Low Temperature Overpressure incident was also evaluated.

Heavy-section steel irradiation program summary

In light-water-cooled nuclear power plants, a steel reactor pressure vessel (RPV) forms the primary containment boundary for the nuclear fuel assembly. Since a failure of the RPV carries the potential of major contamination release and severe accident, it is imperative to safe reactor operation to understand and be able to accurately predict realistic failure models of the vessel material. A major known risk arises from irradiation-induced degradation of the RPV fracture resistance which occurs as a result of normally occurring neutron flux during the service life of the reactor. Better understanding of the irradiation degradation of the vessel material will provide better input to improve the engineering models vital for prediction of RPV integrity and safe service life. For this reason, the Heavy-Section Steel Irradiation (HSSI) Program has been established with its primary goal to provide a thorough, quantitative assessment of the effects of neutron irradiation on the material behavior, and in particular the fracture toughness properties, of typical pressure vessel steels as they relate to light-water RPVs. The program includes the direct continuation of irradiation studies previously conducted within the Heavy-Section Steel Technology Program augmented by enhanced examinations of the accompanying microstructural changes. Effects of specimen size, material chemistry, product form and microstructure, irradiation fluence, flux, temperature and spectrum, and postirradiation annealing are being examined on a wide range of fracture properties including fracture toughness ( K 1c and J 1c), crack-arrest toughness ( K 1a), ductile tearing resistance (d J/da), Charpy V-notch impact energy, dropweight nil-ductility temperature (NDT), and tensile properties. Models based on observations of radiation-induced microstructural changes using field ion and high-resolution transmission electron microscopy provide a firmer basis for extrapolating the measured changes in fracture properties to wider ranges of irradiation conditions. The principal materials examined within the HSSI Program are highcopper welds since their postirradiation properties are most frequently limiting in the continued safe operation of commercial RPVs. In addition, a limited effort Will focus on stainless steel weld overlay cladding, typical of that used on the inner surface of RPVs, since its postirradiation fracture properties have the potential for strongly affecting the extension of small surface flaws during overcooling transients. Results from the HSSI studies will be integrated to aid in resolving major regulatory issues facing the U.S. Nuclear Regulatory Commission which involve RPV irradiation embrittlement such as pressurized-thermal shock, operating pressure-temperature limits, low-temperature overpressurization, and the specialized problems associated with low upper-shelf welds. Taken together the results of these studies also provide guidance and bases for evaluating both the aging behavior and the potential for plant life extension of light-water RPVs.

Transformation Plasticity and Residual Stresses in Single-Pass Repair Welds

Prediction of the residual stresses caused by welding is important when post-weld stress relief is not feasible. Phase changes and transformation plasticity have a significant effect on the residual stresses generated by welding and heat-treatment of some alloys. Transformation plasticity occurs when the stresses generated by the transformation of individual grains interact with the macroscopic stress state to produce plastic strains. Heuristic methods requiring empirical constants have been used in the past. A method based on the fundamental laws of plasticity and basic material properties is proposed to incorporate transformation plasticity in a finite element program. The transformation plasticity which occurs depends on the stress state. During any increment the stress state can change substantially. If the step size is too large, the analysis may become unstable. A method which allows larger steps while eliminating the instability and improving the convergence is presented. A three-dimensional (3D) analysis of a short longitudinal pipe weld in a typical pressure vessel steel is shown. The significance of this phenomenon in welds is demonstrated by comparing the residual stress states predicted with and without transformation plasticity.

Indigenous development of fatigue and creep resistant steels: Ramaswamy, V. and Mediratta, S.R. Trans. Indian Inst. Met. 1989 42, (Suppl.). S83–S92

This paper aims to examine an eventual effect of neutron flux, sometimes referred to as dose rate effect, on irradiation hardening of a typical A533B reactor pressure vessel steel.Tensile tests on both low flux (reactor surveillance data) and high flux (BR2 reactor) were performed in a large fluence range. The obtained results indicate two features. First, the surveillance data exhibit a constant (∼90 MPa) higher yield strength than the high flux data. However, this difference cannot be explained from a flux effect but most probably from differences in the initial tensile properties. The hardening kinetic of both low and high flux is the same. Annealing at low temperature, 345 °C/40 h, to eventually reveal unstable matrix damage did not affect both BR2 and surveillance specimens. This is confirmed by other annealing experimental data including both tensile and hardness measurements and tensile data on A508 forging and weld. It is suggested that the absence of flux effect on the tensile properties while different radiation-induced microstructures can be attributed to thermal ageing effects.

Crack initiation and growth resistance in pressure vessel materials

The crack initiation and propagation has been studied in two typical pressure vessel alloys ( 1 2 Mo and 2 1 4 Cr −1 Mo ) in the temperature range of 30–400°C using elastic-plastic fracture mechanics approaches. The study has also been conducted in the heat affected zone (HAZ) of weldments from these alloys. The J and CTOD crack growth resistance curves have been obtained based on average crack growth as well as the maximum crack growth approaches. The latter approach may be used to obtain a conservative estimate of crack growth resistance from subsize specimens. With increasing temperature the crack initiation toughness and tearing resistance are found to vary in different manners, i.e. the initiation toughness increases though crack growth resistance decreases and vice versa. The HAZ toughness appears to be less than that of the base metals.

ARGOS PHWR 380: Argentine offer of a safer pressurized heavy-water reactor of 380 MW: “…a many-eyed guardian…” concerned about nuclear power plant safety

Argentina introduces a newly designed nuclear power plant named “ARGOS PHWR 380”, an acronym for Argentine Offer of a Safer Pressurized Heavy Water Reactor of 380 MWe. The current version is based upon a reactor of the pressure vessel type of which the main technical characteristics are similar to those of the Atucha NPPs.

High pressure cell for magneto-optical experiments

High pressure equipment designed for low temperature magneto-optical experiments is described. The piston and cylinder type of pressure vessel was adapted to allow photocurrent experiments to be carried out at low temperatures and high magnetic fields. With a sapphire window the cell can be used in the far infrared region (3 mm-25 mu m wavelength) and in the near infrared at wavelengths shorter than 5.5 mu m. Hydrostatic pressures up to 1.8 GPa can be achieved at 4.2K. A suitable choice of window material allows the cell to be used in all spectral regions from far infrared to ultraviolet and over a temperature range from liquid helium to 500K. The use of a carbon bolometer allows transmission experiments to be performed.