bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Implications of High Energy Density Welding of Corrosion Resistant Alloy Heat Exchanger Tubing
Authors: O’Donnell Dave , Karlen Nicole , Kettermann Carl
Published: January 2011

The advent of Laser Beam Welding (LBW) has had a significant impact on resultant metallurgical performance of stainless steel welded heat exchanger tubing. While productivity enhancements are well recognized the metallurgical benefits are not. The low total heat input combined with the very high energy density results in ultra-fast quenching of molten metal, super-cooling past normal primary ferrite solidification in common 304/304L and 316/316L grades directly to austenite resulting in weldments with no retained delta ferrite and some inherent corrosion advantages. The same low total heat input and high energy density generates dramatically smaller dendrite spacing making subsequent homogenization by the combined efforts of cold work and solution annealing dramatically more effective. It should be recognized that this paper deals with issues relating to tube production where welds are autogenous or made without filler metal addition and are subsequently cold worked and solution annealed. Resulting benefits of laser welding include a seamless metallographic appearance, and improved field performance. The benefits and limitations of these enhancements are explored relative to other common stainless steel grades, as are alloy characteristics affecting performance.
Effect of External Bending Moment on the Sealing Performance of Pipe Flange Connection
Authors: Takagi Yoshio , Torii Hiroyasu , Sawa Toshiyuki , Omiya Yuya
Published: January 2011

Since an external bending moment affects the sealing performance of pipe flange connection, it is important to investigate this effect. This paper analyzed the contact gasket stress distribution of pipe flange connections and evaluates the effect of external bending moment on the sealing performance from the viewpoint of changes in contact gasket stress. The study includes the FE analyses and the experimental leakage tests. The FE analyses suggested the large decrease of contact gasket stress at tension side and small increase at compression side. The difference in change in contact gasket stress was caused by the non-linear hysteresis characteristics of stress-displacement curve of gasket. The FE analyses also suggested that the loading order, internal pressure and external bending moment, also affected the sealing performance due to the non-linear deformation characteristic of the gasket. The sealing performance when the external bending moment applied prior to the internal pressure was degraded more than when the internal pressure was applied prior to the external bending moment. The experimental leakage tests using helium (He) gas were analyzed by the finite element method and discussed. This paper also evaluated the stress distribution in the pipe flange under external bending moment. The results suggested that the hub stress dominated the flange structure and the most important factor in designing the flange.
A Study on the Temperature Calibration for a Small Electrical Resistance Furnace
Authors: Baek Un Bong , Lee Hae Moo , Lee Yun-Hee , Nahm Seung Hoon
Published: January 2011

A severe thermal stress occurs during start up/shutdown transients in thick walled components of high temperature power plants. Thus, a precise consideration of this issue is very important. Many researchers have studied low-cycle fatigue at high temperatures and small box-type electrical resistance furnaces have been developed for small-sized fatigue specimens. However, these small-scale electrical resistance furnaces need precise temperature calibrations because temperature control is difficult in a small space. Thus, a method for the temperature calibration of a box-type electrical resistance furnace is investigated and calibration procedures are proposed in this study.
Effects of Continuous Strain Rate Changing on Environmental Fatigue for Stainless Steels in PWR Environment
Authors: Nomura Yuichiro , Asada Seiji , Nakamura Takao , Tanaka Masakazu
Published: January 2011

The strain rates in actual transients of operating plants are not constant and changing momentarily. A large number of fatigue tests under stepwise strain rate changing conditions were performed to develop a method for evaluating fatigue life under varying strain rate conditions. Based on these test results, a strain base integral model known as the named the modified rate approach method was developed and verified. However it was reported recently that in the case of sine wave fatigue tests in BWR environment, the fatigue life was two to six times longer than the fatigue life predicted by the modified rate approach method. For this paper, in order to confirm whether the same tendency is observed in PWR environment, fatigue tests of sine wave were performed of SS316 in simulated PWR water environment. As the result, the difference of fatigue life by sine wave test reported in BWR environment was not observed between experimental and predicted life in PWR environment and the modified rate approach method was applicable under continuous strain rate changing condition.
A Modified Weld Structure of Layered Urea Reactor Based on Stress Analysis and Leak Detection
Authors: Xu Shugen , Wang Weiqiang , Li Mengli , Song Mingda
Published: January 2011

In this paper, a modified weld structure of the layered urea reactor has been provided. In the modified structure, new circumferential weld can improve the stress status of the urea reactor. It has the both advantage of separated and integrated layered pressure vessel. This modified design is based on the stress status analysis and the requirement of leak detection. In order to evaluate the modified structure, stresses of original and modified urea reactor shell with interlayer gaps were calculated via Finite element software ANSYS 12.0. The calculation result shows that the maximum stress of the modified structure is reduced obviously in the same condition, and the leak of liner also can be detected effectively.
Uncertainties in Probabilistic Fracture Mechanics Calculations
Authors: Simonen F. A.
Published: January 2011

This paper addresses uncertainties in probabilistic fracture mechanics (PFM) calculations for pressure boundary components at commercial nuclear power plants. Such calculations can predict the probability that a component will have failed after a specified period of operation, but with large uncertainties that are difficult to quantify. PFM models only approximate details of as-built components as well as actual operating conditions over the lifetime of the component. Statistical distributions used as inputs to the calculations are subject to uncertainties, which also results in large uncertainties in calculated failure probabilities. This paper describes from the author’s perspective various uncertainties that are associated with PFM calculations. Efforts to quantify PFM uncertainties are described along with their impacts on calculated failure probabilities. Many uncertainties are explicitly addressed by statistical distributions for input parameters to the PFM models (e.g. crack growth rates, material strengths, probabilities of flaw detection, etc.). Other calculations have gone further by estimating uncertainties in the parameters of these statistical distributions along with uncertainties in parameters treated as deterministic inputs to the PFM models. Examples from the author’s experience with uncertainty analyses for pressure vessels and piping components are described.
Quantifying the Crack Tip Oxidation Kinetics Parameters and Their Contribution to Stress Corrosion Cracking in High Temperature Water
Authors: Shoji Tetsuo , Lu Zhanpeng , Xue He , Qiu Yubing , Sakaguchi Kazuhiko
Published: January 2011

Stress corrosion cracking is the result of the interaction between crack tip oxidation kinetics and crack tip mechanics. Oxidation kinetic processes for austenitic alloys in high temperate water environments are analyzed, emphasizing the effects of alloy composition and microstructure, temperature, water chemistry, etc. The crack chemistry is investigated with introducing the effect of aging on reactivity of crack sides and the throwing power of bulk water chemistry. Oxidation rate constants under various conditions are calculated based on quasi-solid state oxidation mechanism, which are incorporated in the theoretical growth rate equation to quantify the effects of several key parameters on stress corrosion cracking growth rates of austenitic alloys in high temperature water environments, especially the effect of environmental parameters on stress corrosion cracking of Ni-base alloys in simulated PWR environments and stainless steels in simulated boiling water environments.
Plunger Failure on a Second Stage Cylinder of a Hyper Compressor
Authors: Megens Bas , Colaris Bert
Published: January 2011

In February 2006 a tungsten carbide plunger of the second stage cilinder of a hyper compressor fractured. The failure occurred on the part of the plunger that is running in the high pressure packing. After the incident a failure and unknown cause analysis (UCA) was conducted. It was concluded that the main cause for the failure were heat cracks that initiated a fatigue crack over 60% of the cross section of the plunger prior to final fracture. It appeared that the use of a more wear resistant sealing ring material and poor lubrication conditions during high leak gas caused the initiation of the heat cracks. The more wear resistant ring material was used in all of our compressors. An operation, monitoring and replacement strategy was developed to assure a safe operation. In this way a scheduled replacement of the rings by a non sensitive ring material was possible and production loss was minimized. In the paper all aspects of this case will be discussed.
Potential Detrimental Consequences of Excessive PWHT on Pressure Vessel Steel Properties
Authors: Chauvy Ce´dric , Coudreuse Lionel , Toussaint Patrick
Published: January 2011

During fabrication of Pressure Vessels, steels undergo several heat treatments that aim to confer the required properties on the entire equipment, including welds and base metal. Indeed, the Quality heat treatment of the base material, which leads to achieve the target properties, is most of the time followed by Post Weld Heat Treatment (PWHT). The aim of such treatments is to insure a good behaviour of the welded zones in terms of residual stresses and obviously properties such as toughness. Generally, many simulated PWHT (up to 4 or more) are required for the testing of the base material, which can affect its properties and even lead to non acceptable results. In some cases for fabrication purposes an intermediate Stress relieving treatment can be required. Special attention is paid on C-Mn steels (e.g. SA/A516 from ASME BPV Code) with the effect of thickness and Ceq (IIW Carbon equivalent formula: see page 3) requirements on the final compromise between properties and heat treatments. In particular, toughness and UTS are the critical parameters that will limit the acceptance of too high PWHT. Although micro-alloying is a mean to increase the resistance to PWHT, this leads to difficulties in softening the heat affected zones. This solution is therefore not the best one considering the whole equipment optimisation. Finally, the manufacturing process can play a major role when specifications are stringent. Quenching and tempering can indeed provide better flexibility in terms of PWHT and improved toughness for given Ceq and thickness. The case of Cr-Mo(-V) steels, which are widely used in the energy industry, is also addressed. Indeed, PWHT requirements for increasing the toughness in the weld metal can lead to decrease the base metal properties below the specification limits. For example, the case of SA/A387gr11 is very typical of metallurgical changes that can occur during these high PWHT leading to a degradation of toughness in the base metal. Another focus is made on the Vanadium Cr-Mo grade SA/A542D that must withstand very high PWHT (705°C and even 710°C) because of welds toughness issues. Optimisation has therefore to be done to increase the resistance to softening and to guarantee acceptable microstructure, especially in the case of thick wall vessels. Some ways for improvement are proposed on the basis of the equivalent LMP tempering parameter concept. The basic philosophy is to fulfil the need for discussion between companies involved in pressure vessels fabrication so that the best compromise can be found to ensure the best and safest behaviour of the equipment as a whole.
Finite Element Damage Analyses for Predictions of Creep Crack Growth
Authors: Oh Chang-Sik , Kim Nak-Hyun , Min Sung-Hwan , Kim Yun-Jae
Published: January 2011

This paper provides the virtual simulation method for creep crack growth test, based on finite element (FE) analyses with damage mechanics. Creep tests of smooth bars are used to quantify the constants of creep constitutive equation. The reduction of area resulting from creep tests of smooth and notched bar is adopted as a measure of creep ductility under multiaxial stress conditions. The creep ductility exhaustion concept is adopted for calculating creep damage, which is defined as the ratio of creep strain to the multiaxial creep ductility. To simulate crack propagation, fully damaged elements are forced to have nearly zero stresses using user-defined subroutine UHARD in the general-purpose FE code, ABAQUS. The results from 2D or 3D FE analyses are compared with experimental data of creep crack growth. It is shown that the predictions obtained from this new method are in good agreement with experimental data.
Analysis of Fracture Specimen Failure of Inconel 600: Elastic-Plastic Calculations and Thermo-Plastic Energy Fracture Parameter
Authors: Rossillon Fre´de´rique , Me´zie`re Yves
Published: January 2011

The integrity of structures exhibiting flaws in nuclear power plants, and in particular for class 1 components (pipes, vessels, internals), has to be assessed to meet safety criteria. Technical rules along with simplified assessment methods are available in various standards: ASME, RSE-M, RCC-MR, R6 etc…. They rely on conservative hypotheses and parameters (loading, material properties, failure diagram). They are developed using analytical or numerical approaches and are validated with adequate demonstrative experimental testing. In particular, RSE-M and RCC-MR codes include a large set of compendia for the calculation of the fracture parameter J, depending on component and defect geometries, loading and material characteristics. However, it is essential first to consider the type of failure that the structure is likely to undergo and then to apply the proper assessment methods with the criteria required by the safety rules. For structures made of a material with a high strain-hardening behavior combined with a large enough value of ductile tearing resistance, it is not so easy to identify properly the failure mode between ductile failure or plastic collapse. This paper deals with the fracture mechanical test on a specimen made on Inconel 600 up to the ultimate failure of the sample. Due to the high mechanical properties of this material, the determination of ductile fracture initiation and propagation is quite difficult. Nonetheless the tests were carried out on a Center Cracked specimen under Tension (CCT). A numerical analysis of this experiment is provided using Finite Element (FE) calculations. In this case, the small-scale-yielding hypothesis is not verified and a complex load path is observed. The classical fracture mechanics parameter J-integral is not relevant anymore. The use of an energy fracture parameter in thermo-plasticity, called GTP, seems to be a more adequate parameter to describe correctly the effect of the crack growth. Different models are evaluated and a comparison with more classical parameters in a Non-Linear Elastic (NLE) behavior is done.
A Novel Approach to Energy Based Evaluations of Ultra High-Pressure Waterjets
Authors: Chillman A. , Hashish M. , Ramulu M.
Published: January 2011

Ultra high-pressure waterjets (UHP-WJ) have been emerging as a viable method for surface texturing, cleaning, and peening of metallic materials. Previous experimental studies have suggested that removal of material can be related to the energy density of the waterjet impinging upon the workpiece, rather than the net energy. The net energy transferred to the workpiece is a function of four key process parameters, namely i.) orifice diameter, ii.) orifice geometry, iii.) supply pressure, and iv.) traverse rate. The energy density also incorporates jet spreading as well as flow rate and impulse pressure distributions within the waterjet. In this paper, a novel representation of the power distribution within the waterjet is presented, as well as a relationship governing jet-material interaction. Empirical validation on a Ti-6Al-4V titanium alloy is presented, with good correlation noted between the predicted and experimental results.
Evaluation of Creep-Fatigue Damage for Prototype Process Heat Exchanger of the NHDD Plant
Authors: Lee Hyeong-Yeon , Song Kee-Nam , Kim Yong-Wan , Hong Sung-Deok , Park Hong-Yune
Published: January 2011

A process heat exchanger (PHE) transfers the heat generated from a nuclear reactor to a sulfur-iodine hydrogen production system in the NHDD (Nuclear Hydrogen Development and Demonstration), and was subjected to very high temperature up to 950°C. An evaluation of creep-fatigue damage, for a prototype PHE, has been carried out from finite element analysis with the full three dimensional model of the PHE. The inlet temperature in the primary side of the PHE was 950°C with an internal pressure of 7MPa while the inlet temperature in the secondary side of the PHE is 500°C with internal pressure of 4MPa. The candidate materials of the PHE were Alloy 617 and Hastelloy X. In this study, only the Alloy 617 was considered because the high temperature design code is available only for Alloy 617. Using the full 3D finite element analysis on the PHE model, creep-fatigue damage evaluation at very high temperature was carried out, according to the ASME Draft Code Case for Alloy 617, and technical issues in the draft Code Case were raised.
An Experimental and Numerical Methodology to Investigate Crack Growth in a 304L Austenitic Stainless Steel Pipe Under Thermal Fatigue
Authors: Bouin Pauline , Fissolo Antoine , Gourdin Ce´dric
Published: January 2011

This paper covers work carried out by the French Atomic Energy Commission (CEA) to investigate on mechanisms leading to cracking of piping as a result of thermal loading existing in flow mixing zones. The main purpose of this work is to analyse, with a new experiment and its numerical interpretation, and to understand the mechanism of propagation of cracks in such components. To address this issue, a new specimen has been developed on the basis of the Fat3D experiment. This thermal fatigue test consists in heating a 304L steel pre-cracked tube while cyclically injecting ambient water onto its inner surface. The tube is regularly removed from the furnace for a crack characterisation. Finally, the crack growth is evaluated from the crack length differences between two stops. In parallel, a finite element analysis is developed using the finite element Cast3M code. A pipe with a semi-elliptical crack on its inner surface is modelled. A cyclic thermal loading is imposed on the tube. This loading is in agreement with experimental data. The crack propagates through the thickness. A prediction of the velocity of the crack is finally assessed using a Paris’ law type criteria. Finally, this combined experimental and numerical work on 304L austenitic stainless steel pipes will enable to improve existing methods to accurately predict the crack growth under cyclic thermal loadings in austenitic stainless steel pipe at the design stage.
STYLE: Project Overview
Authors: Nicak Tomas , Keim Elisabeth
Published: January 2011

The purpose of this paper is to introduce a new EUROATOM project focusing on the structural integrity assessment of reactor coolant pressure boundary components (RCPB) relevant to ageing and life time management. The project started in January 2010 and will last 4 years. The project is coordinated by AREVA NP GmbH with 20 partner organizations from Europe, one collaborator from USA and one collaborator from Russia: AEKI, Hungary; AREVA NP GmbH, Germany (coordination, WP2 leader); AREVA NP SAS, France; Bay Zoltan, Hungary; British Energy Generation Ltd., UK (WP7 leader); CEA, France (WP1 leader); EDF, France; IdS, France; INR, Romania; IWM, Germany; JRC, Netherlands (WP4 leader); NRI, Czech Republik; NRG, Netherlands; SCK-CEN, Belgium; Serco Assurance Technical Services, UK (WP3 and WP5 leader); University of Bristol, UK; University of Manchester, UK; Technatom, Spain; Vattenfall, Sweden (WP6 leader); VTT, Finland. Within STYLE (Structural integrity for lifetime management – non-RPV components) realistic failure models for some of the key components will be identified. The range of assessment tools considered will include those for assessment of component failure by advanced fracture mechanics analyses validated on small and large scale experiments, quantification of weld residual stresses by numerical analysis and by measurements, stress corrosion crack initiation/ growth effects and assessment of RCPB components (excluding the reactor pressure vessel) under dynamic and seismic loading. Based on theoretical and experimental results, performance assessment and further development of simplified engineering assessment methods (EAM) will be carried out considering both deterministic and probabilistic approaches. Integrity assessment case studies and large scale demonstration experiments will be performed on Mock-ups of safety-relevant components. These will include a repair weld in an aged butt-welded austenitic pipe, a dissimilar narrow gap TIG weld (following the EPR design) and a cladded ferritic pipe. Moreover experiments on specimens and feature test pieces will be carried out to support the large scale Mock-up analyses. The end product of the project (“STYLE TOOLS”) will comprise best practice guidelines on the use of advanced tools, on improvement and qualification of EAM as a part of European Leak-before-break (LBB) procedures and on life time management of the integrity of RCPB components in European nuclear power plants. The project will interact with the European Network of Excellence NULIFE.
Modification of the Failure Assessment Diagram for Non-Sharp Defects
Authors: Horn Anthony J. , Sherry Andrew H.
Published: January 2011

Current defect assessment procedures assume all flaws to be sharp. While this assumption may be appropriate for fatigue cracks, in other cases such as voids, mechanical dents or welding defects it can be an over-conservative assumption that can lead to pessimistic assessment of structures and significant under-estimation of their safety margin against fracture. This study has developed an assessment procedure for predicting the cleavage fracture resistance of structures containing non-sharp defects. The new assessment method was developed using the Weibull stress based toughness scaling model and an approach based on a modification of the Failure Assessment Diagram (FAD). In the new assessment procedure, the notch driving force is described by the notch J-integral, the notch tip loading severity by the elastic notch tip opening stress σN, the notch geometry by a load-independent parameter βN, and the sensitivity of the material toughness to the notch effect by the material parameters γ and l. Finite element analysis of SE(B) specimens containing U-notches was used to demonstrate that the notch J-integral can be estimated using existing expressions in fracture toughness testing standards intended for pre-cracked specimens. A test programme of SE(B) specimens containing U-notches was used to validate the new assessment procedure. Failure predictions of the SE(B) specimens using the notch-modified FAD approach result in significantly reduced conservatism compared to the standard FAD assessment approach for sharp cracks.
Research of Weld on Axial Buckling Stress of Multilayer Combined Cylindrical Shells
Authors: Yu Chulin , Chen Zhiping , Yang Licai
Published: January 2011

Large welded steel tanks for oil storage (oil tank for short in following text) are usually constructed by welding together several varying thickness cylindrical shells. The generated welding residual stress and deformation may affect the buckling behavior of oil tanks. Learning the influence of welding residual stress and deformation on axial buckling helps accounting for discrepancy between elephant’s foot buckling critical stress and classic theoretical solution. A buckling analysis method considering welding residual stress and deformation is established. Inherent strain finite element method is illustrated as the proper method to simulate welding residual stress and deformation in buckling analysis and its detail setting procedures in ABAQUS are given. A small model cylinder is analyzed under three conditions (one circumferential weld only, one meridian weld only, and one circumferential weld with two meridian welds), leading to several important conclusions. One of these conclusions is that the extent to which welding residual stress and deformation reduces axial buckling critical stress depends on the weld type greatly. Then the established buckling analysis method is applied to an actual oil tank with patterned welds. Result shows that patterned welds decrease axial buckling critical stress significantly. At last several recommendations are given to decrease the effect of welding residual stress and deformation on axial buckling of oil tanks.
Numerical Simulation and Experiment for Underwater Shock Wave in Newly Designed Pressure Vessel for Food Processing
Authors: Shibuta Manabu , Hamashima Hideki , Itoh Shigeru
Published: January 2011

Modern eating habits depend in large part on the development of food processing technology. Thermal treatments are often performed in the conventional food processing, but it can cause discoloration and loss of nutrients of the food by thermal processing or treatment. On the other hand, food processing using an underwater shock wave has little influence of heat and its processing time is very short, preventing the loss of nutrients. In this research optical observation experiment and the numerical simulation were performed, in order to understand and control the behavior of the underwater shock wave in the development of the processing container using an underwater shock wave for the factory and home. In this experiment a rectangular container was used to observe the behavior of the underwater shock wave. In the experiment, the shock wave was generated by using explosive on the shock wave generation side. The shock wave, which passed through the phosphor bronze and propagated from the aluminum sidewall, was observed on the processing container side. Numerical simulation of an analogous experimental model was investigated, where LS-DYNA software was used for the numerical simulation. The comparative study of the experiment and the numerical simulation was investigated. The behavior of a precursor shock wave from the device wall was able to be clarified. This result is used for development of the device in numerical simulation.
Experimental Investigation on Coupling Focusing Ultrasonic Technique for Inspection of Polyethylene Butt-Fusion Joint
Authors: Guo Weican , Zheng Jinyang , Liu Zhongqiang , Shi Jianfeng , Ding Shoubao , Zuo Shangzhi
Published: January 2011

The butt fusion process is a widely used method for connecting Polyethylene (PE) pipes. Conventional ultrasonic test is unable to detect defects due to heavy ultrasonic attenuation, disturbance by the structure of the joint, and the weak acoustic response caused by lack of fusion. A new technique named coupling focusing ultrasonic technique used for testing PE butt fusion joints is developed in this paper. The key of the technique is to get a special couplant, which is a mixture of glycerinum, sodium silicate, water, and defoamer, with almost the same sound velocity and acoustic impedance of PE. Through the couplant, sound beam is converged by spherical lens, entering the PE material with focusing zone overlapping the fusion area of the joint. It is proved that the technique has a good testing ability for defects of typical lack of fusion, gas holes with 1mm in diameter and crack with 1mm in height, based on the results of detection experiments of test sample accompanied with typical defect. It is also proved that its sensitivity is better than TOFD technique and traditional contact angle wave ultrasonic technique as well.
Development of High Cycle Thermal Fatigue Evaluation Method Based on Time Interval of Peak-to-Peak of Fluid Temperature
Authors: Kimura Nobuyuki , Kobayashi Jun , Kamide Hideki
Published: January 2011

Hot and cold fluids are mixed at the core outlet of sodium cooled fast reactors. The temperature fluctuation causes high cycle thermal fatigue in structural components. The temperature fluctuation at the core outlet region does not have always a sinusoidal waveform but a sharp edged waveform. The temperature shows intermittent and sudden decrease and recovery like a spike form. It is necessary to take into account the spiky waveform of temperature fluctuation for the construction of an evaluation method of the high cycle thermal fatigue. The conventional method uses the amplitude and cycle number of waves without reference to the frequency of temperature fluctuation. In this study, the time interval of each wave based on the rainflow method was applied to consider frequency characteristics against the conversion from fluid temperature to thermal stress in structure. The thermal stress obtained from the new method was compared to the results of FEM analysis. It was found that the consideration of frequency characteristics of waves could evaluate the fatigue damage in structure. Furthermore, the frequency characteristics of waves in this method were expressed as the unified curve independent of the velocity. Hereby the new evaluation method could evaluate the thermal fatigue in the reactor.
Evaluating the Mechanical Behavior of 316 Stainless Steel at the Microscale Using Finite Element Modelling and In-Situ Neutron Scattering
Authors: Li Dong-Feng , O’Dowd Noel P. , Davies Catrin M. , Zhang Shu-Yan
Published: January 2011

In this study, the deformation behavior of an austenitic stainless steel is investigated at the microscale by means of in-situ neutron diffraction (ND) measurements in conjunction with finite-element (FE) simulations. Results are presented in terms of (elastic) lattice strains for selected grain (crystallite) families. The FE model is based on a crystallographic (slip system based) representation of the deformation at the microscale. The present study indicates that combined in-situ ND measurement and micromechanical modelling provides an enhanced understanding of the mechanical response at the microscale in engineering steels.
Stress Concentration and Stress Intensity for Pressurized Eroded Autofrettaged Thick Cylinders With Bauschinger Effect
Authors: Ma Q. , Levy C. , Perl M.
Published: January 2011

Our previous studies have shown that stress intensity factors (SIFs) are influenced considerably from the presence of the Bauschinger Effect (BE) in thick-walled pressurized cracked cylinders. For some types of pressure vessels, such as gun barrels, working in corrosive environment, in addition to acute temperature gradients and repetitive high-pressure impulses, erosions can be practically induced. Those erosions cause stress concentration at the bore, where cracks can readily initiate and propagate. In this study, The BE on the SIFs will be investigated for a crack emanating from an erosion’s deepest point in a multiply eroded autofrettaged, pressurized thick-walled cylinder. A commercial finite element package, ANSYS, was employed to perform this type of analysis. A two-dimensional model, analogous to the authors’ previous studies, has been adopted for this new investigation. Autofrettage with and without BE, based on von Mises yield criterion, is simulated by thermal loading and the SIFs are determined by the nodal displacement method. The SIFs are evaluated for a variety of relative crack lengths, a0/t = 0.01–0.45 emanating from the tip of the erosion of different geometries including (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, t; (b) arc erosions for several dimensionless radii of curvature, r′/t = 0.05–0.4; and (c) semi-elliptical erosions with ellipticities of d/h = 0.5–1.5, and erosion span angle, α, from 6 deg to 360 deg. The effective SIFs for relatively short cracks are found to be increased by the presence of the erosion and further increased due to the BE, which may result in a significant decrease in the vessel’s fatigue life. Deep cracks are found to be almost unaffected by the erosion, but are considerably affected by BE.
Probabilistic Approach for Fatigue Life Assessment Based on S-N Curve
Authors: Wei Zhigang , Kurth Robert E. , Forte Thomas P.
Published: January 2011

Components in pressure vessels and pipes are usually subjected to mechanical and thermal cyclic loadings, which cause fatigue failure. The statistic and probabilistic assessment of these components based on S – N or ε–N curves is of great importance for fatigue design. Recently, the standard practice, as adopted by ASTM, BS, DNV and many other standards, for statistical analysis of linear or linearized stresslife (S – N) and strain-life (ε–N) fatigue data has been critically reviewed. The shortcomings of the standard procedure based only on the variation of cycles have been clearly demonstrated by examining the general trend of a large amount of S-N data. A new deterministic statistical method based on the equivalency between the changes of stress range and cycles to failure has been subsequently proposed and validated. In this paper a probabilistic approach based on the equivalency method is developed to quantify the uncertainty of engineering structures subjected to inherent randomness in material properties, and its effectiveness is also demonstrated.
Consideration of Hydraulic Loads in the Load and Resistance Factor Design (LRFD) of Class 2 and 3 Nuclear Pipes
Authors: Avrithi Kleio
Published: January 2011

Recently, work was done to develop Load and Resistance Factor Design equations for Class 2 and 3 straight nuclear pipes for loads that cause primary stress. Unlike the Allowable Stress Design (ASD) method, used traditionally in the ASME B&PV Code, the Load and Resistance Factor Design (LRFD) method results in a known reliability index or probability of failure, Pf, for the piping. LRFD may provide other benefits for the design of piping too, such as design consistency with other industries (ACI, AISC, etc.) and sections of the ASME B&PV Code (e.g., Section XI), facilitation of risk analysis of piping systems, and elimination of unnecessary conservatisms. This paper presents the format of the LRFD equations and load combinations that address mechanical (hydraulic) loading, result of sudden valve closure for Service Levels B, and C or Loss-Of-Coolant Accident (LOCA) for Service Level D for straight pipes. Sample partial safety factors are provided for different values of piping reliability. Results address both carbon and stainless steel material for piping and operation temperature up to 600°F.
Plastic Response of Thin-Walled Tubes to Detonation
Authors: Karnesky J. , Damazo J. , Shepherd J. E. , Rusinek A.
Published: January 2011

Elastic and plastic deformation of tubes to internal detonations and the shock waves produced by their reflection were investigated. The study included experimental measurements as well as computational modeling. Tests with stoichiometric ethylene-oxygen mixtures were performed at various initial pressures and strain was measured on thin-walled mild-steel tubes. The range of initial pressures covered the span from entirely elastic to fully plastic deformation modes. A model for the pressure load on the tube wall was developed and tested against experimental measurements. This model was applied as a boundary condition in both a single degree of freedom model of the tube cross section and a finite element model of the entire tube. Comparison of computational and experimental results showed reasonable agreement if both strain-rate and strain-hardening effects were accounted for. A unique mode of periodic radial deformation was discovered and explained through modeling as the result of flexural wave interference effects.
Review and Assessment of Ratcheting Considerations for Design and Analysis
Authors: Garud Yogendra S.
Published: January 2011

This paper presents theoretical, practical, and computational considerations of significance in assessing the strain ratcheting under combined cyclic loads. Different aspects of ratcheting are covered comparing uniaxial versus multiaxial loading. Since ratcheting and (elastic or plastic) shakedown are generally influenced by the same underlying factors, the conditions under which shakedown is more likely to be the end result are reviewed with reference to the material response versus the structural response. A simple two-bar model is used to illustrate the key characteristics of ratcheting and the essential factors or conditions responsible for the ratcheting. For example, the role of material strain hardening vs. kinematic hardening, and the effects of non-symmetry in loading or material yielding are examined. The role of structural constraint in determining the actual ratcheting response of components as compared to the material (point) response is discussed. Based on the review and assessment of these observations the resulting practical considerations in limiting the impact of ratcheting are discussed. The ratcheting considerations in this paper are limited to the time independent deformation or plasticity, excluding the additional effect of time-dependent phenomena such as the material creep or stress relaxation.
Estimation Procedures for J and CTOD Fracture Parameters Experimental Evaluation Using Homogeneous and Mismatched Clamped SE(T) Specimens
Authors: Moreira Felipe C. , Donato Gustavo H. B.
Published: January 2011

Experimental evaluation of geometry-dependent material’s fracture resistance using constraint-designed SE(T) specimens has proved to be an accurate option to assess the structural integrity of pipelines and pressure vessels reducing excessive conservatism. In this context, this work presents procedures for experimental J-integral and CTOD (δ) evaluation using the eta (η) method applied to tension clamped SE(T) specimens made of homogeneous materials and also containing mismatched joints. Initially, the conceptual background is presented, followed by the description of the refined non-linear finite element models developed, which provide the necessary evolution of load with increased load-line displacement and crack mouth opening displacement. As results, are presented a variety of η factors for J -integral and CTOD calculations, which are not available in current standardized procedures. The main objective is to allow fracture resistance experimental evaluation using specimens of different a/W-ratios, material flow properties, weld joint configurations and levels of weld strength mismatch. The main motivation is the possibility of enhancing accuracy of pressure vessels and piping integrity assessments, since these later present very close fracture conditions if compared to SE(T) specimens. The present results, when taken together with previous developments, extend the knowledge about the use of clamped SE(T) specimens. The reader should enhance the studies about the topic with the complimentary paper with the same title beginning but involving pin-loaded SE(T) specimens.
Life Prediction of Composite Pressure Vessels Using Multi-Scale Approach
Authors: Ha Sung Kyu , Tsai Stephen W. , Kim Seong Jong , Hayat Khazar , Jin Kyo Kook
Published: January 2011

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multiaxial fatigue loading acting at laminate is determined from finite element analysis (FEM) of composite pressure vessel, and ply stresses are computed using a classical laminate theory (CLT). The micro-scale stresses are calculated in each constituent (i.e. matrix, interface, and fiber) from ply stresses using a micromechanical model. Micromechanics of failure (MMF) was originally developed to predict the strength of composites and now extended to prediction of fatigue life. Two methods are employed in predicting fatigue life of each constituent, i.e. an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner’s rule. Each fiber is assumed to follow a probabilistic failure depending on the length. Using the overall micro and macro models established in this study, Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent and manufacturing winding helical angle.
Microstructural Evolution of Alloy 617 and Alloy 230 Following High Temperature Aging
Authors: Mo Kun , Lovicu Gianfranco , Tung Hsiao-Ming , Chen Xiang , Stubbins James F.
Published: January 2011

Alloy 617 and Alloy 230 are solid-solution strengthened nickel based superalloys, which have been considered two of the most promising structural materials for the Very-High-Temperature Reactor (VHTR). In order to have a better understanding of the degradation process of the materials in the VHTR, long-term aging experiments have been carried out to investigate the dynamic process of microstructure evolution at 900 and 1000°C for Alloy 617 and Alloy 230. The microstructural evolution process in different aging periods (up to 3000 hours) was analyzed by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD). A diffusion-controlled precipitation and coarsening of carbide particles (mainly M23C6 and M6C) for both alloys was observed. The corresponding characteristics of the precipitates, i.e. type, size and coherence, were analyzed. The coarsening rate of the intergranular precipitates in Alloy 617 was found to be much faster compared to Alloy 230’s. The inhomogeneous precipitation process in the transverse plane of Alloy 617 was observed, which may be attributed to the alignment of the inclusion particles induced by the hot rolling. Hardness and tensile tests were carried out to investigate the aging impacts on materials’ strength. Both alloys obtained increased hardness and strength during early stages of aging and softened after elongated time. The results of mechanical tests were in a good agreement with the microstructure evolution process.
Stress Analysis and Qualification of Vessels Containing Sizeable Internal Vessels and Piping: Applications
Authors: Hamaoui Amir , Sviatoslavsky Greg , Dunlap Bryan , Prakash Ajay
Published: January 2011

Stress analysis and qualification of a parent vessel with sizeable internal vessels, extensive internal piping and associated supporting structures is performed using a single finite element model. A single model is desirable because of the coupling and interaction between various sized components, particularly for seismic, hydrodynamic and thermal evaluations. Qualification of the various types of components (shells, nozzles and beams) requires multiple design codes. Examples of some unique features and challenges encountered in the process of qualifying such vessels are presented.
The Application of Harmonic Finite Elements in the Seismic Response Spectrum Analysis of a Skirt Supported Vessel
Authors: Antaal Bikramjit Singh , Hari Yogeshwar , Williams Dennis K.
Published: January 2011

This paper describes the finite element considerations employed in a seismic response spectrum analysis of a skirt supported, liquid containing pressure vessel. Like many axisymmetric cylindrical vessels, the gross seismic response to an input response spectrum can be categorized by a simplified lump mass model that includes both the mass of the vessel proper in combination with the associated mass of multiple fluid levels. This simplified response may be utilized to determine the initial sizing of the supporting configuration, such as a skirt, but lacks the ability to properly address the fluid-structure interaction that creates sloshing loads on the vessel walls. The most obvious method to address the fluid-structure interaction when considering the finite element method is to build a three-dimensional model of the vessel proper, including, but not limited to the shell courses, the top and bottom heads (for a vertical vessel), and the support skirt. The inclusion of the fluid effects may now be incorporated with a “contained fluid” finite element, however, for vessels of any significant volume, the number of finite elements can easily exceed 100,000 and the number of degrees of freedom can sore from as few as 300,000 to as many as 500,000 or more. While these types of finite element analysis problems can be solved with today’s computer hardware and software, it is not desirable in any analysis to have that volume of information that has to be reviewed and approved in a highly regulated nuclear QA environment (if at all possible). With these items in mind, the methodology described in this paper seeks to minimize the number of degrees of freedom associated with a response spectrum analysis of a liquid filled, skirt supported vertical pressure vessel. The input response spectra are almost always provided in Cartesian coordinates, while many, if not most liquid containing pressure vessels are almost always axisymmetric in geometry without having benefit of being subjected to an axisymmetric load (acceleration in this case) due to the specified seismic event. The use of harmonic finite elements for both the vessel structure and the contained fluid medium permit the efficiencies associated with an axisymmetric geometry to be leveraged when the seismic response spectrum is formulated in terms of a Fourier series and combined to regain the effects of the two orthogonal, horizontally applied accelerations as a function of frequency. The end result as discussed and shown in this paper is a finite element model that permits a dense mesh of both the fluid and the structure, while economizing on the number of simultaneous equations required to be solved by the chosen finite element analysis.