bluuebunny/crossref_metadata_2025 huggingface dataset:
A Dislocation-Based Cleavage Initiation Model for Pressure Vessel Steels
Authors: Cochran Kristine B. , Erickson Marjorie , Williams Paul T. , Klasky Hilda B. , Bass B. Richard
Published: August 2013

Efforts are under way to develop a theoretical, multi-scale model for the prediction of fracture toughness of ferritic steels in the ductile-to-brittle transition temperature (DBTT) region that accounts for temperature, irradiation, strain rate, and material condition (chemistry and heat treatment) effects. This new model is intended to address difficulties associated with existing empirically-derived models of the DBTT region that cannot be extrapolated to conditions for which data are unavailable. Dislocation distribution equations, derived from the theories of Yokobori et al., are incorporated to account for the local stress state prior to and following initiation of a microcrack from a second-phase particle. The new model is the basis for the DISlocation-based FRACture (DISFRAC) computer code being developed at the Oak Ridge National Laboratory (ORNL). The purpose of this code is to permit fracture safety assessments of ferritic structures with only tensile properties required as input. The primary motivation for the code is to assist in the prediction of radiation effects on nuclear reactor pressure vessels, in parallel with the EURATOM PERFORM 60 project.

This paper begins with a brief overview of the strategy for implementing the new model into the DISFRAC computer code. The balance of the paper focuses on efforts to model the nucleation of a carbide particle crack near an existing macrocrack under applied load. The carbide microcrack initiation model applies dislocation mechanics to assess the stress intensity exerted on a stiff, elastic carbide particle embedded in an elastic-plastic ferrite matrix near a macrocrack tip. The paper derives and discusses the governing equations for the model; including (1) computation of a slip band dislocation pileup distribution by enforcing equilibrium with the macrocrack-induced elastic-plastic stress field, (2) calculation of the mode I stress intensity on the particle crack plane due to the dislocation pileup and (3) determination of the particle fracture toughness. Together, these calculations provide the basis for determining the applied load required to initiate particle fracture. This paper demonstrates how the prediction of particle fracture depends on various microstructure parameters.
Examining Computational Techniques to Simulate the Effects of External Chemical Explosions Using Explicit Finite Element Analysis
Authors: Prueter Phillip E. , Dewees David J. , Brown Robert G.
Published: August 2013

Understanding the dynamic response of structures such as storage tanks or pressure vessels due to external chemical explosions is a critical aspect in determining the possible damage resulting from such an event. Furthermore, accurately simulating the overpressure or shock wave associated with a given explosion is equally important in order to achieve accurate results. Assessing the possible damage from an overpressure wave can provide valuable information about protecting structures from external explosions and improving designs. Such analyses become all the more important should the contents of the tank or vessel pose a risk to humans or the surrounding environment. This paper examines multiple computational techniques for simulating the load acting on a structure due to an external blast. In the past, blast parameters such as overpressure amplitude, spatial decay, arrival time, and blast duration had to be defined by the user. Recent development of more advanced computational tools, such as the CONWEP charge property in Abaqus, provides a means to accurately simulate blast loading on a structure, including reflection effects, without having to model the acoustic medium. The explicit computational methods discussed herein provide predictions of blast parameters and permit realistic evaluations of structures due to external explosions.
Non-Cyclic Methods for Shakedown Analysis of Cracked Structures
Authors: Vlaicu Dan
Published: August 2013

Fatigue calculation of nuclear components under cyclic loading in the inelastic domain is a complex task involving nonlinear material models capable of predicting the strain-stress relationship beyond the yield limit. In this context, the ratcheting boundary that is the cyclic plastic strain accumulation under primary and secondary cyclic loads is a key criterion for structural design. A cyclically loaded structure made of elastic-plastic material is considered elastic shakedown if plastic straining occurs in the first few cycles and the sequent response is wholly elastic. In this paper the finite element calculations of a straight pipe with a notch is used to develop upper and lower bounds limits for the elastic shakedown of structures under periodic loading conditions. Linear methods using elastic compensation approach and the residual stress method derived from Melan’s theorem are used to generate the lower bound limit for the shakedown load while the upper bound is found through a method derived from Koiter’s theorem. Furthermore, the global classical theorems are complemented by local shakedown calculations within the regions near the cracks in terms of stress intensity factors that are evaluated from fracture mechanics theory. The presence of the stress singularity in a cracked structure is breaking down the classical shakedown theory and the conventional shakedown limit for a cracked structure should be zero due to the singularity within the stress field. In this methodology it is considered that the plastic deformation is confined to a relatively limited region around the root of a stationary crack and the energy released rate is associated with the change in the elastic stress field outside of the plastic flow region. Furthermore, probabilistic methods are employed for presenting the response surface plots of the shakedown limit in terms of the maximum accumulated strain and fatigue life against the strain hardening and yield limit.
Cross-Weld Creep Comparison of Power Plant Steels CrMoV, P91 and P92
Authors: Tanner David W. J. , Sun Wei , Hyde Thomas H.
Published: August 2013

Results obtained from high temperature creep tests of ferritic steel CrMoV, P91 and P92 cross-weld specimens are compared. Data is presented normalized with the results of the corresponding parent metals in order to compare the materials tested at different temperatures and stresses, and to identify characteristic cross-weld material trends.

All cross-weld failures occurred in the heat-affected zone (HAZ) adjacent to the parent metal, known as type IV, at earlier test durations than for the parent material specimens. The relative performance of the cross-welds was found to decrease with decreasing stress.

The CrMoV cross-weld specimens showed by far the lowest weld strength reduction factors and greatest notch strengthening, determined by testing uniaxially loaded bars with semi-circular circumferential notches located in the heat-affected zone.

The P91 and P92 cross-weld specimens were found to have similar (high) weld strength reduction factors and showed little or no notch strengthening. It was observed that the failure time of a P92 cross-weld specimen relative to the P92 parent material could be estimated using data from P91 cross-weld and relative parent material tests.
Parametric Study of External Pressure on Steam Generator Tube Bends
Authors: Hokazono Mitch , Smith Clayton T.
Published: August 2013

Integral light-water reactor designs propose the use of steam generators located within the reactor vessel. Steam generator tubes in these designs must withstand external pressure loadings to prevent buckling, which is affected by material strength, fabrication techniques, chemical environment and tube geometry. Experience with fired tube boilers has shown that buckling in boiler tubes is greatly alleviated by controlling ovality in bends when the tubes are fabricated. Light water reactor steam generator pressures will not cause a buckling problem in steam generators with reasonable fabrication limits on tube ovality and wall thinning. Utilizing existing Code rules, there is a significant design margin, even for the maximum differential pressure case. With reasonable bend design and fabrication limits the helical steam generator thermodynamic advantages can be realized without a buckling concern. This paper describes a theoretical methodology for determining allowable external pressure for steam generator tubes subject to tube ovality based on ASME Section III Code Case N-759-2 rules. A parametric study of the results of this methodology applied to an elliptical cross section with varying wall thicknesses, tube diameters, and ovality values is also presented.
Welding Simulation: Relationship Between Welding Geometry and Determination of Hardening Model
Authors: Mullins Jonathan , Gunnars Jens
Published: August 2013

It is generally acknowledged that the material hardening model exerts a considerable effect on predicted weld residual stress fields. For this reason the choice of hardening model has attracted interest among analysts, particularly during recent validation studies. Nevertheless there is still lack of evidence for a hardening model which is generally applicable for all welding geometries. In this work we examine the predictions of nonlinear kinematic, isotropic and mixed hardening models for two different geometries: a single bead on plate weld, and a multi-bead girth weld. Hardening parameters are based on the same openly available mechanical test data. Deformation histories for the two welding geometries are presented. Predicted residual stress profiles are compared with experimental measurements. It is noted that nonlinear kinematic hardening results in good predictions for the single bead welding simulation where hardening in the weld and HAZ is dominated by a single heating and cooling cycle. Isotropic hardening results in good predictions for the 42 bead girth weld, where hardening in the weld and HAZ is heavily influenced by several heating and cooling cycles from the addition of several weld beads and where some relaxation of residual stress is possible. Mixed hardening can result in good predictions for both welding geometries. Additional strategies for development of material models based on isotropic and kinematic hardening and relevant test data are discussed with particular attention paid to intermediate weld geometries.
Gasket Design and Assembly for Large Diameter Glass Lined Vessel Flanges
Authors: Waterland A. Fitzgerald
Published: August 2013

Large glass lined vessel flanges pose unique sealing challenges that in many cases require non-conventional gasket designs and flange assembly procedures in order to provide high gasket tightness, and overall long term flanged connection reliability. Recent experiences with a large glass lined process vessel with a history of poor sealing performance are detailed in this paper.
Nuclear Plant License Renewal Status in the U.S.
Authors: Young Garry G.
Published: August 2013

As of January 2012, the NRC has renewed the operating licenses for 71 nuclear units, which will allow for up to 60 years of safe operation. In addition, the NRC has license renewal applications under review for 15 units and nuclear plant owners of more than 14 units have announced plans to submit applications over the next six years [1]. This brings the total of renewed licenses and announced plans for license renewal to over 96% of the 104 currently operating nuclear units in the U.S.

This paper presents the status of the U.S. license renewal process and the U.S. efforts associated with the option of seeking a second license renewal for up to 80 years of safe nuclear plant operation. Currently there are 9 operating nuclear plants that are eligible to seek a second license renewal. It is likely that applications for a second renewal will be submitted to the NRC within the next few years. The factors that contributed to the positive and the negative trends for both the first license renewals for 60 years and the second renewals for 80 years of safe operation are presented and discussed.
Effects of Programming Temperature on the Efficiency of Self-Healing Polymers
Authors: Yougoubare Yves Quentin , Okoro Ifeanyi Janarus , Pang Su-Seng
Published: August 2013

Self-healing shape memory polymers possess the ability to heal macro and micro cracks by autonomic processes or when subjected to a suitable external stimulus. Recent advancements in the field have shown that the healing capabilities of self-healing polymers can be improved, thus yielding to high healing efficiencies. Depending on the application, the efficiency may refer to shape fixity, shape recovery ratio, dimensions recovery, strength regain, crack healing, etc. Based on test results, it is established that there is an intrinsic correlation between pre-strain levels, shape fixing and free shape recovery of samples programmed above the glass transition temperature (Tg). For samples programmed at multiple temperatures (above and below the glass transition temperature), the absence of lateral and 3D confinements lead to poor to no crack healing. Better compressive strength properties were, however, achieved by samples programmed at higher temperatures above Tg.
Effects of Shape Geometry on the Efficiency of Self-Healing Polymers
Authors: Okoro Ifeanyi J. , Yougoubare Yves Q. , Pang Su-Seng
Published: August 2013

Autonomic smart self-healing composites are being developed and tested to deal with the problems of crack propagation and eventual damage. The recovery and self-healing efficiencies of these composite structures varies with changes in different physical properties such as temperature and shape geometry.

The foremost steps in creating a self-healing composite are mixing and programming and recovery. This paper explores the relationship between a composite’s programming processes against its shape-geometry. Improving the programming and recovery would lead to an improved self-healing polymer. To this end, samples of self-healing shape-memory polymers of different aspect ratios are tested after programming and recovery, and their compressive strengths are compared. The results show a direct relationship between the compressive strengths and aspect ratio.
Creep Life Simulation and Assessment of High Temperature Piping Systems and Components
Authors: Rose Brian , Widrig James
Published: August 2013

High temperature piping systems and associated components, elbows and bellows in particular, are vulnerable to damage from creep. The creep behavior of the system is simulated using finite element analysis (FEA). Material behavior and damage is characterized using the MPC Omega law, which captures creep embrittlement. Elbow elements provide rapid yet accurate modeling of pinching of piping, which consumes a major portion of the creep life. The simulation is used to estimate the remaining life of the piping system, evaluate the adequacy of existing bellows and spring can supports and explore remediation options.
Implications of Revised Seismic Spectra for Eastern North America on Response of Nonstructural Components and Piping
Authors: Mohammed Hesham H. H. , Mekky Waleed
Published: August 2013

The seismic response and qualification of nuclear power plant related building structures and non-structural components are affected by the sub-systems’ dynamic properties as well as the external excitation level and characteristics; to which these subsystems are subjected in a seismic event. Recently a great interest in the seismic characteristics of Eastern North America has resulted in the revision of the methodology used to develop response spectra for Nuclear Power Plant (NPP) sites including Eastern Canada. Currently site specific Uniform Hazard Spectra (UHS) are developed based on updated data that is specific to the continental East North America region and modified ground motion prediction equations. The revised UHS exhibit higher amplification in the high frequency range as compared to standard spectral shapes traditionally used in CSA/CAN3 289.3 for 1981. This paper presents the numerical results and observations for an investigation aimed at identifying the effect of these revised UHS spectral shape on the response on non structural components including piping typically requiring seismic qualification in NPPs.
Blast Analysis, Design and Research: A Canadian Perspective
Authors: Mekky Waleed , El-Dakhakhni Wael
Published: August 2013

In order to protect structures against accidental or deliberate blast loads, special expertise and knowledge are necessary to ensure adequate performance of the structural systems. Although the structure may require an extensive repair following a blast event, the main goal of the protective design is to avoid structural progressive collapse and minimize fragments. Blast loading is very different from other forms of dynamic loading generally analyzed by structural engineers. Peak pressures are several orders of magnitude higher than those associated with other typical dynamic loads, and blast load durations are usually much shorter than the fundamental period of the structure. This paper will focus on the blast loading phenomena, analysis procedures and design implications as specified by the two recently developed North America’s codes, ASCE SEI59-11 (2011) and CAN CSA S850-12 (2012). In addition, the results of an ongoing multi-year large-scale experimental and analytical program at McMaster University, Canada will be highlighted.
Development of Elastic-Plastic Constitutive Models for the Evaluation of Nuclear Piping Systems Under Severe Cyclic Loading
Authors: Takahashi Yukio , Tanaka Yoshihiko
Published: August 2013

It is essential to predict the behavior of nuclear piping system under seismic loading to evaluate the structural integrity of nuclear power plants. Relatively large stress cycles may be applied to the piping systems under severe seismic loading and plastic deformation may occur cyclically in some portion of the systems. Accurate description of inelastic deformation under cyclic loading is indispensable for the precise estimation of strain cycles and accumulation potentially leading to the failure due to fatigue-ratcheting interaction. Elastic-plastic constitutive models based on the nonlinear kinematic hardening rule proposed by Ohno and Wang were developed for type 316 austenitic stainless steel and carbon steel JIS STPT410 (similar to ASTM A106 Gr.B), both of which are used in piping systems in nuclear power plants. Different deformation characteristics under cyclic loading in terms of memory of prior hardening were observed on these two materials and they were reflected in the modeling. Results of simulations under various loading conditions were compared with the test data to demonstrate the high capability of the constitutive models.
Spent Nuclear Fuel Transportation Package Seals in Beyond Design Basis Temperature Excursions
Authors: Gonzalez Felix , Bajwa Christopher , Einziger Robert , Easton Earl , Yang Jiann , Hnetkovsky Edward
Published: August 2013

The US Nuclear Regulatory Commission (NRC) is studying the performance of seals in spent nuclear fuel (SNF) transportation packages exposed to fires that could exceed the hypothetical accident condition fire described in Title 10 of the Code of Federal Regulations, Part 71, such as the Baltimore Tunnel Fire that occurred in 2001, or the MacArthur Maze fire that occurred in 2007. The performance of package seals is important for determining the potential for release of radioactive material from a package during a beyond-design-basis accident. Seals generally have lower temperature limits than other package components and are the containment barrier between the environment and the radioactive package contents. The NRC Office of Nuclear Regulatory Research contracted the National Institute of Standards and Technology to conduct small-scale thermal testing to obtain experimental data of the performance of seals during extreme temperature exposures. The experimental testing consisted of several small-scale pressure vessels fabricated with a modified ASME flange design and tested metallic and polymeric seals, similar to those that might be used on an actual SNF transportation package. The vessels were heated in an electrical oven to temperatures as high as 800°C (1472°F), exceeding the rated temperatures of the seals in question. This paper will provide a summary of the testing conducted and present test results and conclusions.
Initial Quantification of the Effect of Ambient Humidity on the Strength of Non-Metallic Repairs of Piping and Pressure Vessels
Authors: Gribble David J. , Walker Roger H. , French Jesse J.
Published: August 2013

Composite repairs of pressure vessels and transmission pipelines are installed in a wide variety of ambient conditions. The installation of epoxies utilized can range from arid environments with almost no humidity to tropical conditions of nearly 100% humidity or even completely submerged in water. This paper presents the methodology and results from an initial effort to determine the effects of humidity on the strength of certain epoxy matrix composite repairs.

The effect on final strength of a composite repair specimen cured under a variety of ambient humidity is presented from experimentation with specimens cured below 20% humidity and at approximately 96% humidity in a climate controlled chamber. The effects on final strength, stiffness, and hardness, are observed and recorded to note the difference between the varying conditions. The compilation of data is analyzed to determine what considerations need to be made for various levels of humidity at the time of installation for composite repairs installed on pressure vessels and piping.

Results are presented to show that prediction of curing time and final strength are achievable with reasonable accuracy given sufficiently accurate humidity measurement during the curing process.
Life Cycle Management of Bolted Joints on Oil and Gas Assets for Leak Free Start Up and Operation
Authors: Noble Robert
Published: August 2013

A typical Oil and Gas Asset will have a minimum of 10,000 bolted connections with larger assets exceeding 100,000 joints. Yet a leak on any one of those joints could result in disaster. The need for a management system using the power of modern computing is therefore evident. The paper will use the Energy Institute guidelines for managing the integrity of bolted joints for pressurized systems (ISBN 978 0 85293 461 6) [6] as its core theme, highlight its correlation with ASME PCC-1-2010 [1] and describe a number of case studies where implementation has successfully achieved the goal of reducing Hydrocarbon escapes. The guidelines [6] develop 8 Essential Elements of a management system. Ownership - Technology and Practice - Criticality Assessment - Training and Competence - Records Data Management and Tagging - In service inspection - Management of Leaks - Analysis Learning and Improvement. The relevance and implementation of each of these elements will be explained.
A Sensitivity Analysis of NRC Welding Residual Stress Validation Program International Round Robin Program
Authors: Goldak John A. , Tchernov Stanislav , Zhou Jianguo , Downey Dan
Published: August 2013

The sensitivity of the residual stress distribution to variations in several weld process parameters are computed for the dissimilar metal nozzle weld in the NRC/EPRI welding residual stress (WRS) program Phase II. The design parameters variations evaluated are; weld power ±20%, weld pass start positions at 0, 90, 180 and 270 degrees, delay times between weld passes of 0 and 3 minutes, temperature dependent yield stress and hardening modulus. The analyses are 3D nonlinear transient. The 3D residual stress results are compared to published measured data and published averaged FEM results which are mostly 2D axisymmetric analyses.
A Round Robin Program of Master Curve Evaluation Using Miniature C(T) Specimens: First Round Robin Test on Uniform Specimens of Reactor Pressure Vessel Material
Authors: Yamamoto Masato , Kimura Akihiko , Onizawa Kunio , Yoshimoto Kentaro , Ogawa Takuya , Chiba Atsushi , Hirano Takashi , Sugihara Takuji , Sugiyama Masanari , Miura Naoki , Soneda Naoki
Published: August 2013

Reference temperature evaluation method by Master Curve approach for the fracture toughness evaluation had been standardized recently in Japan, and expected to be a powerful tool to ensure the reliability of long term used RPV steels. In order to get sufficient number of data for the Master curve approach coexistent with the present surveillance program for RPVs, the utilization of miniature specimens, which can be taken from broken halves of surveillance Charpy specimens, is important. CRIEPI had developed the test technique for the miniature C(T) specimens (Mini-CT), whose dimensions are 4 × 10 × 10 mm, and verified the basic applicability of Master Curve approach by means of Mini-CT for the determination of fracture toughness of typical Japanese RPV steels. A round robin program is organized with the participation of Japanese academia, industries and a government institute. The program aims to verify the reliability and robustness of experimental data of Mini-CT, and to pick out further investigation items to be solved before the actual application of the technique. As the first step of this program, four institutes separately carried out a series of Master Curve evaluation in conformity to ASTM E1921-10e1 by means of Mini-CT specimens, whose material (Japanese RPV material, SFVQ1A), machining process and pre-cracking process are in common in all the specimens. Valid reference temperature T0 could be successfully obtained in all of the institutes by means of Mini-CT specimen. However, the value, T0, have large difference with maximum of 34 °C among the institutes. The difference shows strong correlation with the difference in loading rate, which is selected by each organization to be meet the testing standard ASTM E1921-10e1.
Investigation on the Allowable Temperature During Electrofusion Welding of Polyethylene Pipe
Authors: Zhong Sijia , Shi Jianfeng , Guo Weican , Zheng Jinyang
Published: August 2013

Polyethylene (PE) pipe material may degrade into lower carbon number volatiles quickly during the electrofusion welding process when the welding temperature rises up to more than about 370°C. Meanwhile, PE may also degrade into lower molecular weight (MW) polymer when subject to a lower temperature. As a result, the allowable temperature during electrofusion welding is uncertain. In this paper, a typical PE100 material was chosen to conduct thermogravimetic analysis (TGA) and Gel permeation chromatography (GPC) test. The thermal degradation behavior of PE100 was investigated in Dynamic and isothermal mode. And the composition of the thermal degradation residue was determined through MW and molecular weight distribution (MWD) measurements of the residue. Based on the experimental results, the initial temperature of thermal degradation with volatilization was derived and the thermal degradation process was studied in detail. To limit the thermal degradation degree of PE in a required range in thermal welding process, the preliminary allowable welding temperature for typical commercial PE100 material was determined. In addition, some regular information was obtained, which could promote the ultimate determination of the allowable welding temperature.
Prediction of Ratchet Boundary for 90-Degree Smooth and Mitred Pipe Bends
Authors: Korba Ahmed G. , Megahed Mohammad M. , Abdalla Hany F. , Nassar Mohamed M.
Published: August 2013

The present paper attempts to predict ratchet boundary for 90-degree mitred and smooth pipe bends subjected to sustained pressure and cyclic in-plane bending. The methodology utilizes a recently published technique known as the “Uniform Modified Yielding” (UMY) technique, which relies on generation of a virtual structure with inhomogeneous reduced yield strength, whose magnitude and distribution depend on the elastic stress field due to the cyclic load. The collapse load of this virtual structure determines the threshold steady load necessary for commencement of “incremental collapse”. The technique is applied first to predict ratchet boundaries for two benchmark problems possessing analytical descriptions of ratchet boundary and uni-axial states of stress; the two-bar structure problem and the Bree cylinder. Predicted ratchet boundaries exactly coincided with the corresponding published analytical descriptions, and reasons for this correlation were discussed in this paper. The technique was then applied to three 90-degree pipe bends with similar geometries as follows: smooth pipe bend (SPB), single mitred pipe bend (SMPB), and three weld mitred pipe bend (3WMPB). Certain assumptions are adopted to enable treatment of the problem as a quasi-uniaxial one. Conservative estimates are obtained for ratchet boundaries in pipe bends that correlates well with elastic shakedown/ratchet boundary of the same problems as predicted by a recently developed non-cyclic direct technique.
Application of Risk Evaluation in Increasing the Operating Pressure of Etherification Reactors
Authors: Ma Xin
Published: August 2013

Due to process changes, the operating pressure of three double-layer reactors (DLRs) containing flammable dimethyl ether and poisonous chloromethane needs to be increased to 6.3% above the design pressure, which is not in conformity with the regulations and standards in China. To evaluate the effect of the operating pressure increase on the risk of a vessel rupture, the safety margin for the wall thickness of all DLR structural components was evaluated at the increased pressure. A safety assessment employing risk-based inspection (RBI) methodology was carried out on the DLRs to evaluate the risk in the case of failure of the DLRs. The probability of failure (PoF) and consequence of failure (CoF) were analyzed using the first-order-second moment theory and the vapor cloud explosion model, respectively. The analysis results showed that the inner shell, the inner torispherical head and all nozzles were sufficiently strong to withstand the increased operating pressure of 2.66 MPa, and the knuckle of inner torispherical head was the weakest component, with a minimum safety margin of 5.64%. The assessment data showed the PoF of the DLRs was level 4, the CoF was level C, and the risk overall risk level for the DLRs was medium high.
Pressure Tests for Thickness Management of Wall Thinning Tees
Authors: Teshima Kaina , Iwamoto Yoichi , Hojo Kiminobu , Oka Tomoyuki , Kobayashi Kunihiro , Tsuno Syuichi
Published: August 2013

Although the minimum thickness of pipe wall required (tsr) of T-joints (tees) of class 2, 3 and lower classes of nuclear power plants in Japan is calculated from the design pressure and temperature, there is no rule or standard of wall thinning T-joints for thickness management.

This paper describes the pressure tests procedure and six test results with parameters of T-joint geometry such as outer diameter D, thickness T and T/D to establish structural integrity of wall thinning T-joints. Based on the fracture surface observation, a ductile crack initiation of each test mock-ups was confirmed.
Comparison Between Pressure Tests and Simulations for Thickness Management of Wall Thinning T-Joints
Authors: Teshima Kaina , Ochi Mayumi , Asada Seiji , Hojo Kiminobu , Suzuki Takahiro , Kugimoto Mitsuo
Published: August 2013

Although the required minimum thickness (tsr) of T-joints (tees) is calculated from the design pressure and temperature for design, there are no rules or standards for thickness management of wall thinning T-joints for facilities maintenance.

This paper describes the comparison between the five pressure test results of T-joints and their numerical simulations using FE analysis and confirms the failure criterion. The investigation for the numerical simulation and the experimental tests showed that ultimate tensile stress (σu) is the most suitable criterion for the burst of T-joints.
A Method to Characterize the Fracture Resistance of Dissimilar Metal Welds
Authors: Blouin A. , Chapuliot S. , Marie S.
Published: August 2013

Characterization of the fracture resistance of weld joints, and in particular dissimilar metal welds (DMW), is a huge and difficult work where no standard currently exists. As a consequence, characterizations of materials have to be done prior to the fracture tests in order to consider the mechanical aspects of the material mismatch via F.E. analysis in the fracture toughness determination. However, performing these characterization tests may imply using a lot of material, which is sometimes not available, and can be expensive. Most studies are usually realized on reduced sized mock-ups.

The considered experimental mock-ups are pipes composed of a ferritic pipe welded to an austenitic one. The weld joints are made of Ni base alloys. A few small tensile samples have been extracted so that each material, even the heat affected zone (HAZ), can be characterized at low temperature. A fast method using laser sensors and a specific specimen shape has been developed and is used to identify these materials strain-stress curves at −125°C. Afterwards, these data have been used to simulate multi-material compact specimen tensile tests and single edge notch tension specimen, representing a conventional defect in the HAZ. Also, these two kinds of specimen have been extracted and the tests performed in order to compare the experimental results to the F.E. analysis. This paper presents the experimental work, the related specific devices, the F.E. analyses and the experimental analysis.
Constraint and Failure Assessment Diagram Under Biaxial Loading on Semi-Elliptic Surface Cracks
Authors: Wang Zhongxian , Zhang Ruifeng , Chao Yuh J. , Lam Poh-Sang
Published: August 2013

Three-dimensional finite element analysis has been performed for several configurations of the semi-elliptic surface crack in an X100 pipeline steel plate under various biaxial loading conditions. The biaxial loading ratio (λ) is defined as the ratio of loading parallel to the crack face in the plate width direction to the loading perpendicular to the crack. The constraint level and the J-integral along the semi-elliptic crack front were calculated with J-A2 constraint theory in fracture mechanics, in which A2 is considered as the constraint parameter. It was found that λ influences the J values along the crack front. As λ varies from −1 to 0 then to +1, the location of the maximum J has a tendency to move from the deepest point of the crack to a location near the surface as the load increases, especially for a deeper crack. The constraint level (A2) along the crack front behaves similarly to the J-integral. At λ = −1, the value of A2 increases from the near surface to the deepest penetration when the load increases. In the case of uniaxial tension (λ = 0), the A2 values do not vary significantly except near the surface. When the equibiaxial condition is reached (λ = 1), the location of the highest constraint moves to the near surface. However, in this region the higher constraint level is unable to maintain as the load increases (i.e., the peak value of A2 decreases with increasing load). Finally, the failure assessment diagrams (FAD) at the deepest point of the semi-elliptic crack were constructed with the J-A2 fracture theory. The crack stability regions are apparently smaller in the cases of λ = −1 and 2 than those for λ = 0 (uniaxial tension) or λ = 1 (equibiaxial tension).
Dynamic Finite Element Analysis of Drum-Type Shipping Packages for Radioactive Materials
Authors: Han Zenghu , Shah Vikram N. , Liu Yung Y.
Published: August 2013

The US Department of Energy (DOE) often uses Type AF and Type B drum-type packages for shipment of radioactive materials (RAM), both of which shall be designed and certified to meet the regulatory requirements specified in 10 CFR 71, to ensure safety, public health and protection of environment. In particular for the hypothetical accident conditions (HAC) prescribed in 10 CFR 71.73, RAM packages are subjected to sequential tests of 30-ft drop, crush, puncture, engulfing fire, and water immersions. Packages shall maintain structural integrity of containment, radiation shielding, and criticality control following these HAC tests. The structural evaluation (i.e., drop, crush, and puncture) of packages should address different combinations of test conditions, such as drop orientations, sequence, temperature and payload during the drop, crush and puncture tests. The combinations to be considered are those which would produce most damage to the package, challenge the most vulnerable packaging components, and cause the most cumulative damages. The evaluation of the most damage should also consider the effects of fire and water immersions following the structural tests. In this paper, the structural evaluation details of two drum-type packages, Model 9979 Type AF and Model ES-3100 Type B(U)F, are discussed. The design and performance of these packages were evaluated by physical testing of full-size prototype units. However, it is not practical to account for the worst test conditions and sequence in physical testing. Therefore, confirmatory finite element analyses have been performed to determine whether the cumulative damage resulting from the worst test sequence and conditions is acceptable. It was found for the 9979 package, the corner drop followed by corner crush causes most damage, and most unfavorably challenges its split-ring closures; for the ES-3100 package, the containment vessel (CV) experiences maximum strain following the sequence of bottom-to-lid slapdown and side crush. Although a lower temperature does not compromise their structural performance, the ES-3100 CV does experience slightly more strain because the impact limiter imparts more impact load because of its higher stiffness at lower temperature. In summary, the confirmatory analysis results show that the structural performance of the packages meets the regulatory requirements.
R6 V, Vg and RSE-M Estimates of Experimental Failure for Combined Loading
Authors: James Peter , Madew Colin , Goodfellow Andrew , Gallegillo Martin
Published: August 2013

Engineering components which are considered in safety case assessments contain either real or hypothetical crack-like defects that experience combinations of primary and secondary stresses during service. A number of assessment procedures contain simplified numerical approaches to detail the interaction of these stresses under in-service or fault conditions including the R6 procedure used in the UK and the RSE-M Appendix 5.4 (RSE-M) assessment code adopted in France.

The R6 procedure and RSE-M approaches are shown to be relatively similar for cases which do not contain secondary loading but differ when treating secondary stresses. It is generally accepted that the R6 procedure in terms of ρ or V is conservative compared to finite element analyses and plant experience; which has driven the development of a new formalism of the R6 V factor, Vg. This new formalism is seen to be more aligned to the RSE-M approach but differs in some cases.

The aim of this paper is twofold: 1) to demonstrate the main divergence between the procedures, and 2) to provide experimental comparison between the R6 V, the newly formalised Vg, and the RSE-M approaches under test cases within literature that contain combined primary and secondary loading.
Evaluation of Airblast Loads on Structures in Complex Configurations
Authors: Vaughan David , Levine Howard , Hassig Paul , Smilowitz Robert
Published: August 2013

A common terrorist threat worldwide is the use of large vehicle bombs to attack high value targets. Detonation of large yield devices can cause significant damage to nearby buildings, facilities and infrastructure with potentially high loss of life and large economic losses. Blast pressures can have major consequences on critical facilities such as nuclear power plants, causing economic loss, environmental damage and system failure. Closely spaced structures in a dense configuration provide a complicated setting for evaluating airblast pressures caused by explosive devices. The presence of multiple buildings can channel the airblast, resulting in significant effects on load magnitudes at range from the detonation. Buildings reflect propagating blast waves causing increased loading at some locations and reduced loads elsewhere due to shielding from direct blast waves. The complex interaction between structures, streets, alleys and geographical terrain can have a major impact on structural loads. Currently, the most common way to estimate airblast pressures resulting from above ground explosive detonations is to use fast running, approximate blast tools such as CONWEP. These simplified tools may not provide accurate guidance on airblast pressures in complex environments. The following paper illustrates the use of Computational Fluid Dynamics (CFD) calculations of complex building configurations to quantify the resulting blast environment. Comparisons with simplified methods are presented. An approach to using a database of CFD simulations, customized for a specific site, to provide a fast running blast assessment tool is described. This approach provides a convenient, fast running tool for designers and security planners to visualize and accurately quantify the hazard from any threat size and location within the area of interest.
Deformation Versus Modified J-Integral Resistance Curves for Ductile Materials
Authors: Zhu Xian-Kui , Lam Poh-Sang
Published: August 2013

The J-integral resistance curve (or J-R curve) has been widely used as material property in fracture mechanics methods for structural integrity assessment. ASTM E1820 provides the standard fracture toughness test methods to measure JIc and J-R curves. The conventional J-R curve utilizes the J-integral parameter proposed by Rice [1] based on the deformation theory of plasticity. Due to crack-tip constraint effect, J-R curves of a material depend on specimen size, geometry type and crack length. In order to obtain size-independent resistance curves, Ernst [11] introduced a modified J-integral or Jm to minimize the size dependence and to characterize the resistance curve for large crack extensions beyond the limitation of deformation J-R curves. In the late 1980s and in the early 1990s, different experimental results showed the modified Jm-R curves were still size-dependent and may even behave worse than the deformation J-R curves. However, to date, the Jm-R curves are still regarded as “size-independent” in fracture mechanics analysis. To clarify this, the present paper gives a brief historical review of ductile resistance curves in terms of deformation J-integral and the modified Jm-integral, and evaluates the size dependence using experimental results for various steels and specimens, including A285 carbon steel and SENB specimens. A suggestion how to use the resistance curves is made accordingly.
FE Residual Stress Analysis in a Narrow Gap Dissimilar Metal Weld
Authors: Obermeier Florian , Courtin Stéphan , Nicak Tomas , Keim Elisabeth
Published: August 2013

In the nuclear industry narrow gap welding techniques are used to perform junctions between ferritic low alloy steel heavy section components and austenitic stainless steel piping systems. The residual stresses in Dissimilar Metals Welds (DMW) may influence the lifetime and functionality of the welded components. In Pressurized Water Reactor (PWR) piping systems, weld residual stresses in particular increased the susceptibility to primary water stress corrosion cracking (PWSCC) in the past. It is therefore necessary to develop and validate methods for a reliable residual stress and distortion prediction.

Numerical welding simulations for predicting residual stresses are commonly used in nuclear industry and their development is progressing fast during the recent years. As part of the European project STYLE — Structural Integrity for Lifetime Management — a case study was launched to assess the capability of such simulations.

The mock-up in this case study is provided by AREVA NP SAS. It is a pipe with a narrow gap dissimilar metal weld. The pipe thickness is about 40 mm and the outer diameter is 352 mm after final machining. In this assembly a 316L austenitic pipe is welded to an A508 Class 3 ferritic pipe by means of Alloy 52 Gas Tungsten Arc (GTA) narrow gap weld which is representative for PWR primary circuit piping. This mock-up is in the scope of a continuation of the ADIMEW – Assessment of Aged Piping Dissimilar Metal Weld Integrity - project and deals with the improvement of the assessment for DMW and Leak-before-break (LBB) procedures. The fracture test on this mock-up is planed to be performed at 300 °C with an initial through-wall defect. Apart from the LBB demonstration this mock-up is also dedicated for the validation of the applied fracture mechanics approach, extension of material data basis and validation of the weld simulation procedures applied within AREVA.

This paper presents the results of the finite element residual stress analysis related to this STYLE narrow gap weld case study. The two finite element codes ABAQUS and SYSWELD were used to predict the weld residual stresses and the shrinkage in axial direction. The major difference between the here presented methods is that SYSWELD accounts for phase transformation and the method used with ABAQUS does not. The results are compared between each other and with data obtained by deep-hole drilling techniques (DHD) at several locations.
Assessment of Constraint Effects on the Local Behaviour of a Propagating Crack Under Cyclic Loading
Authors: Goldthorpe M. R. , Sherry A. H.
Published: August 2013

During operation, reactor components experience a range of static and cyclic loading that have the potential to result in environmental-fatigue crack initiation and growth. Recent experimental work has indicated that the ASME XI fatigue ‘in air’ design curves are non-conservative for fatigue cracks propagating in primary water environments at fixed temperatures of relevance to the plant. The approach adopted to assess these tests has, to date, followed current best practice: in which global Linear Elastic Fracture Mechanics (LEFM) loading parameters are used to quantify crack growth rates.

To help establish an improved understanding of these data, and to assist in their application to assess plant components, a local crack-tip finite element model has been developed. The model incorporates material constitutive behavior that simulates cyclic deformation of austenitic steel, can take account of plasticity-induced crack closure and can take into consideration cracks in structurally-representative geometries via the T-stress constraint parameter.

The results of studies using the model suggest that highly compressive values of the T-stress constraint parameter tend to promote less severe reverse loading of the crack tip compared with high constraint geometries such as pre-cracked compact tension and bend test specimens. These findings indicate that rates of corrosion-fatigue in actual structural geometries might be different from those observed in pre-cracked test specimens.