bluuebunny/crossref_metadata_2025 huggingface dataset:
Deterministic Prediction of Stress Corrosion Crack Growth Rates in High Temperature Water by Combination of Interface Oxidation Kinetics and Crack Tip Asymptotic Field
Authors: Shoji Tetsuo , Lu Zhanpeng , Takeda Yoichi , Murakami Hiroyoshi , Fu Chaoyang
Published: July 2009

Proper disposition of the environmentally assisted crack growth rate in terms of key engineering parameters is crucial for safe and economic long term operation of light water reactors. Accurately predicting stress corrosion crack growth rate requires the quantification of crack tip mechanics, crack tip oxidation kinetics and their interactions. Crack tip strain rate has been categorized as a fundamental parameter for stress corrosion cracking of austenitic alloys in light water reactor environments. Continuum mechanics is applied to quantify crack tip strain rate based on the crack tip asymptotic field. A general oxidation kinetics formulation is proposed based on solid state mass transport theory. Stress corrosion crack growth rates of austenitic alloys in high temperature water environments are formulated as a function of various engineering parameters by combination of interface oxidation kinetics and the crack tip asymptotic field. Recent experimental results of stress corrosion crack growth rates in simulated boiling water reactor and pressurized water reactor environments are analyzed and reflected in the model development and application. The importance of surface integrity on plant safety is emphasized. The plant material aging management methodology is applied to the recent cracking issues in light water reactors.
Plastic Collapse Evaluation for Multiple Circumferential Flaws in a Pipe
Authors: Machida Hideo , Takahashi Yoshiaki , Nakagawa Yusuke
Published: July 2009

Multiple stress corrosion cracks initiate in a weld joint of primary loop recirculation system (PLR) piping in many cases. To prepare a stability assessment method for a pipe with these flaws is one of the major interests for Fitness-for-Service (FFS) Codes of Japan Society of Mechanical Engineers (JSME). This paper presents plastic collapse assessment method of a pipe with multiple circumferential flaws and proposals to revise FFS Codes. Plastic collapse strength of a pipe with multiple circumferential flaws is evaluated with respect to the weakest axis where the minimum plastic collapse moment is obtained, and a program assessing the weakest axis is presented in this study. A ratio of collapse strength corresponding to the weakest axis to that putting all cracks together is defined as strength correction factor, FMC. The strength correction factors when the number of flaws is two and three are summarized in the assessment diagrams, and proposals to revise FFS Codes are reported based on these results.
Finite Element Analysis of Load Distribution of Threaded Connections Made of Dissimilar Materials in High Pressure Facilities
Authors: Sato Takuya , Yamamoto Kenji , Li Rixing , Ando Hiroteru
Published: July 2009

Threaded connections are often used for pressure vessels in high pressure services, and they must be designed to resist the shear forces due to initial tightening and internal pressure. Many investigations of the load distribution in threaded connections have been conducted. One of the most basic investigations was the work of Sopwith, and a design formula was developed. The High Pressure Gas Safety Institute of Japan (KHK) design guide provides design methods based on a modification of Sopwith’s formula for threaded connections. These methods are limited to threads made of similar materials. However, in order to prevent such problems as seizing or corrosion, threaded connections sometimes use dissimilar materials for the female and male threads. In this case, it is necessary to determine whether the modified Sopwith formula can be applied or not. In this paper, linear finite element analyses were performed to calculate the load distribution in threaded connections of dissimilar materials, and the results were compared with those of the modified Sopwith formula. The contact pressure and the friction forces on the surfaces of the threads were considered in the analyses. Two load conditions, the initial tightening and the internal pressure, were considered. From these analyses, the following conclusions were obtained: (1) In practical material combinations with an elastic modulus ratio of 0.5∼2.0, the load concentration factor for threaded connections of dissimilar materials was almost the same as that for threaded connections of similar materials. In other words, it is not necessary to consider the effects of the material combinations in threaded connection design. (2) The load concentration factors were dependent on the load type. The load concentration factor under internal pressure was smaller than that under initial tightening.
Fracture Assessment for Weldment of Piping for BWR Reactor Internal With Circumferential Through Wall Crack
Authors: Itatani Masao , Kanazawa Yasushi , Tanaka Norihiko , Shitara Chikashi , Nakagawa Yusuke
Published: July 2009

A fracture assessment method for piping of BWR reactor internals with a circumferential crack is described in the JSME Code, Rules on Fitness-for-Service for Nuclear Power Plants 2004 Edition. According to this code, limit load is calculated assuming a/t = 1 for through wall crack. It has been desired to demonstrate the adequacy of this equation experimentally. Furthermore, the crack path in weld HAZ between a header and a piping is not straight and has some curvature. It is important to assure the applicability of fracture assessment method to such a case. The fracture tests were conducted for pipes with a circumferential through wall crack between header and pipe to demonstrate the applicability of the current JSME method. Limit load analyses by FEM were also conducted. It was confirmed that the limit load equation in the current JSME Code is possible to apply to the pipe with a circumferential through wall crack even if the crack path was curved along the weld line between header and sparger pipe. In the JSME FFS Code, limit load analysis is required for piping of reactor internals. On the other hand, elastic-plastic fracture mechanics using Z-factor is required for class 1 piping. The present results show that it is enough to assume Z = 1 for the fracture assessment of weldment in austenitic steel piping with medium diameter.
Creep Damage, Ductility and Expected Life for Materials With Defects
Authors: Auerkari Pertti , Holmstro¨m Stefan , Rantala Juhani , Salonen Jorma
Published: July 2009

Defects can pre-exist and grow by creep in structures subjected to loading at high temperatures. As structural integrity is not necessarily conveniently predicted and managed by applying design and life assessment techniques intended for nominally defect-free material, it is important that methods are available for quantified and safe assessment of defects. In addition to the assessment methods, also materials behaviour will affect the likely outcome. In particular, ductility of the materials is important, and unfortunately ductility tends to decrease when shifting from short-term testing to long term creep conditions. In this paper, two examples are shown of materials with such ductility effects when combined with defects. The first example involves 316H stainless steel subjected to creep loading with an extensive crack-like defect, resulting in a transformation from microscopically ductile to brittle intergranular cracking within a relatively modest time span. The second example will demonstrate a corresponding shift in OFP copper that shows a radical ductility and life reduction in creep when including so small weld defects that they would be undetectable in conventional NDT.
Experimental Evaluation of Piecewise Exact Solution for Structure Isolated With Sliding Type Isolators Under Bidirectional Earthquake
Authors: Tsai C. S. , Chiang Tsu-Cheng , Lin Yung-Chang
Published: July 2009

In recent years, the base isolation technology has been recognized as a popular and an efficient way to upgrade the earthquake proof capability of a conventional fixed-base structure. Because the first mode of a base-isolated structure participates the most part of the seismic response from the point view of the modal analysis, it is reasonable to develop a simple method to evaluate the seismic responses of a base-isolated structure by assuming that the superstructure behaves as a rigid body during earthquakes. In this study, a piecewise exact solution for a structure isolated with a sliding type of isolators under bidirectional earthquakes has been developed. The comparisons between the experimental results and the piecewise exact solutions show that the proposed method can well simulate the nonlinear behavior of a structure equipped with sliding-type isolators when subjected to bidirectional earthquakes.
Nondestructive Inspection of Pressure-Bearing Equipment in China
Authors: Yuan Rong , Chen Xuedong , Guan Weihe
Published: July 2009

JB4730-94 “nondestructive inspection of pressure vessels” is a mandatory backbone standard for Chinese pressure equipment sector. However, several problems have also been found in the course of its implementation. Chinese government decided to make revision to JB4730 standard and officially promulgated JB/T4730-2005 “Nondestructive inspection of pressure equipment” in July 2005 and published its English version at the same time. The new standard has made significant modification based on 94 edition, it extends the scope of application to the entire category of pressure equipment, the standard covers such five conventional NDT techniques as RT, UT, MT, PT and eddy-current inspection, adds the content of the types of defects (point defect, surface defect) determined by UT, and UT of austenitic stainless steel welds is also included. As the major drafting unit of the standard, in this paper the modification condition, modification content and modification reason of this standard are exhaustively introduced, which provides certain help and guidance in learning the development and present situation of NDT techniques of Chinese pressure equipment sector. Exhaustive introduction provides certain help and guidance for learning the development and present situation of NDT technology of Chinese pressure-bearing equipment sector.
Prevention of Transformer Tank Explosion: Part 2 — Development and Application of a Numerical Simulation Tool
Authors: Brady Ryan , Muller Se´bastien , de Bressy Gae¨l , Magnier Philippe , Pe´rigaud Guillaume
Published: July 2009

Power transformers rank highly among the most dangerous electrical equipments because of the large quantity of oil they contain in direct contact with high voltage elements. Low impedance faults resulting in arcing can appear in transformer tanks if the oil loses its dielectric properties. Vaporization of the oil generates pressurized gas because the liquid inertia prevents expansion. The pressure difference between the gas bubbles and the surrounding liquid oil generates dynamic pressure waves which propagate and interact with the sealed tank structure. Simultaneously, the static pressure inside of the tank climbs and causes the tank to explode, resulting in fires and very expensive damages for electricity facilities. Despite all these risks, and contrary to usual pressure vessels, no specific standard exists as of yet to protect sealed transformer tanks subjected to large dynamic overpressures. This paper describes a complete numerical model for transformer explosions, which helps to understand all processes involved in such dramatic events, and helps design and optimize an efficient explosion prevention technology. Such a model includes various physical phenomena from the electrical arc description to the evaluation of the stress loads the transformer tank must withstand. The simulation tool kernel is based on a reduced 5 equation model introduced by Kapila et al. [8] to describe the hydrodynamic behavior of compressible 2-phase flows. It consists of a set of conservation laws for each phase partial-mass, the mixture momentum and energy, and volume fraction evolution equation. The closure is isobaric, and both phases have the same velocity at a given point. Each phase is described by its own equation of state. Physical effects such as electromagnetic forces, viscosity, thermal and gravity effects are also taken into account. These equations are solved on complex 3D transformer geometries using a finite volume strategy with unstructured meshes. Computer simulations are then used to study a fast-direct-tank-depressurization-based method to prevent the transformer explosions. Numerical results compare well with experimental results collected during arcing tests in oil filled transformers.
Evaluation of Stress Intensity Factor for Transverse Cracks in Weld Joint of BWR Shroud Support and Its Application to the Evaluation of Trapezoidal Crack
Authors: Itatani Masao , Saito Toshiyuki , Hayashi Takahiro , Narazaki Chihiro , Ogawa Kazuo
Published: July 2009

Since the weld joints of BWR shroud support are made of Ni-base weld metal that has susceptibility to SCC in the BWR water, the SCC crack prefers to grow in weld metal rather than base metal of Ni-base alloys. It is important to prepare the evaluation method for SCC crack initiated in these alloys. To develop the flaw evaluation method for shroud support, stress intensity factor of postulated axial cracks in H10 weld of shroud support in BWR were analyzed by FEM. Results were compared with simplified SIF solutions in codes and standards to confirm the applicability of these simplified methods. It was understood that these simplified methods were available to evaluate the SIFs of axial crack in H10 weld although the thickness of H10 weld is not constant and is tapered. In the present study, SIF for trapezoidal crack was also analyzed because the front shape of stress corrosion crack in the weld metal of Ni-base alloy is not always semi-elliptical and is thought to have complex shape. It was found that the trapezoidal crack could be substituted by elliptical crack for conservative evaluation when the crack is deep and the ratio of upper base 2d to lower base 2c is small. Based on this result, the authors analyzed SIF for more number of trapezoidal cracks in a plate and compared with SIF of semi-elliptical crack which has the same depth a and surface length 2c of trapezoidal crack to investigate the effective range of substitution by an elliptical crack. It was found that the SIF of deepest point KA of semi-elliptical crack becomes larger than that of trapezoidal crack when d/c becomes smaller than about 0.37. These results show the substitution of trapezoidal crack with small d/c by semi-elliptical crack makes conservative SIF evaluation and it is very useful because the SIF solutions for semi-elliptical crack provided in many codes and handbooks can be applied.
Characterization of Sealing Behavior of Gaskets for the Leak Rate Based Design of Gasketed Bolted Flanged Connections
Authors: Kobayashi Takashi
Published: July 2009

This paper discusses the sealing behavior of gaskets according to the gasket testing procedure HPIS Z104 established in Japan. The testing procedure consists of eleven gasket stress levels while the internal pressure is constant. It takes about 3 hours to complete one test, which is acceptable for gasket manufacturers. The test method is going to be effective as the Japanese Industrial Standard (JIS) soon. Several sheet gaskets and spiral wound gaskets were tested based on the test method HPIS Z104 and test results are compared and discussed in this paper. Based on the test results, experimental formulas are proposed to approximate the sealing behavior of gaskets. It is shown that the sealing behavior of gaskets can be well characterized using the proposed testing procedure and the experimental formulas. The formulas have the possibility of application to the design of gasketed bolted flanged connections. It is also shown that the sealing performance of spiral wound gaskets with graphite and PTFE fillers is as good as that of sheet gaskets under an equal gasket load.
Principal Bases of the VERLIFE – Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs During Operation
Authors: Brumovsky Milan
Published: July 2009

Main goal of the project within the European Community 5th Framework Program was in a preparation, evaluation and mutual agreement of a “Unified Procedure for Lifetime Assessment of Components and Piping in WWER Type Nuclear Power Plants”. This procedure should be based on former Soviet rules and codes, as WWER components were designed and manufactured in accordance with requirements of these codes and from prescribed materials. Then, critical analysis of possible application of some approaches used in PWR type components was performed and such approaches have been incorporated into the prepared procedure as much as possible with the aim of a harmonization of WWER and PWR Codes and procedures. Preparation of a Unified Procedure for WWERs operating in Finland, Czech Republic, Slovak Republic, Hungary and Bulgaria will increase the level of lifetime/integrity evaluation in these countries and will help to elaborate a unified approach and fully comparable results between individual plants and countries. Then, harmonization with PWR codes allows to obtain results that will be comparable, reliable and more sophisticated as similar approaches will be used in both types of reactors. The paper described main principles, approaches and achievements of the “Unified Procedure...”. mainly in the part of lifetime, non-ductile failure assessment, defect allowance and reactor dosimetry. Next, paper describes also the continuation on the VERLIFE upgrading and updating that was performed within another EU project COVERS with the participation of experts also from the EU countries.
Ways for Extending the Reactor Pressure Vessel Lifetime
Authors: Brumovsky Milan
Published: July 2009

Reactor pressure vessels are components that usually determine the lifetime of the whole nuclear power plant and thus also its efficiency and economy. There are several ways how to ensure conditions for reactor pressure vessel lifetime extension, mainly: - pre-operational, like: • optimal design of the vessel; • proper choice of vessel materials and manufacturing technology; - operational, like: • application of low-leakage core; • increase of water temperature in ECCS; • insertion of dummy elements; • vessel annealing; • decrease of conservatism during reactor pressure vessel integrity assessment e.g. using direct use of fracture mechanics parameters, like “Master Curve” approach. All these ways are discussed in the paper and some qualitative as well as quantitative evaluation is given.
Simulation of Quenching in Aluminium and Comparison With Neutron Diffraction Measurements
Authors: Dennis R. J. , Phillips S. , Truman C. E. , Stiles A. , Plant R.
Published: July 2009

The through life integrity of engineering components are routinely assessed using complex finite element methods. A critical input to such an assessment is an understanding of the operating environment, including service loading and temperature. Significant effort is expended identifying and understanding the effect of service loads on component integrity however there are many cases where service loading in isolation cannot account for premature failure of components during testing or in-service. A key assumption is that components in the as-built condition are often treated as stress and defect free and of nominal dimensions. This approach can however be inadequate and there are many documented cases where residual stress has influenced the in-service integrity of components. In this paper the magnitude and distribution of residual stresses are investigated in a quenched Aluminium 2014A TB test specimen. The test specimen has been specifically designed to contain design features representative of pressurised aerospace components which are quenched during manufacture. The specimen has two sections, one cylindrical (65mm internal diameter) and one oval (125mm largest internal diameter). The outer wall thickness is 10mm and the overall specimen length is 200mm with the two sections joined by a 30mm bridge section. The specimen has been subject to solution heat treatment at 505°C for five hours. Following heat treatment the specimen is rapidly quenched in cold water at 10°C with the cylindrical end entering the water first. Non-linear finite element methods have been developed to simulate the quenching process making use of user defined subroutines to enhance the standard features available in the finite element code. The accuracy of the predicted residual stresses has been assessed by comparison with neutron diffraction measurements at a range of critical locations. The work provides an extremely useful insight into how non-linear finite element methods can be successfully used to predict the residual stresses that are generated as a result of the quenching process. Where residual stresses are a potential integrity concern an understanding of the magnitude and spatial distribution of residual stress can be used to influence both the design and in-service operation of components.
A New Heat Treatment Technology for On-Site Life Extension of High Energy Pipe Weldments Degraded by Creep Damage
Authors: Sakata Fumitoshi , Ozaki Masashi , Takeuchi Ko , Nishimura Nobuhiko , Shiibashi Akira , Kobayashi Masahiro , Tezuka Hideshi
Published: July 2009

This report presents the development of technology enabling temporary countermeasures for the on-site application of life-extending induction heating to high energy pipe weldments having experienced degradation due to creep. The results of an investigation into the cross-sectional structure thus suggested that material life can be extended by the application of regenerative heat treatment. The life-extending effect of regenerative heat treatment is greatest toward the short-life vicinity of the pipes outer surface, thus providing an efficient life extension. The remaining life converted for an actual installation from the result of real scale creep burst test increased from 63,000hrs before treatment to 200,000hrs after treatment, confirming that life can be extended by approximately 130,000hrs.
Structural Evaluation of Degraded Containment Penetration Sleeves
Authors: Vasquez Daniel J. , Smith Amy J. , Dwivedy Keshab K.
Published: July 2009

The design of a nuclear plant includes “hot” containment penetration assemblies designed to protect the containment building concrete walls from the effects of localized high temperature and degradation due to thermal cycling resulting from the process piping. Typically, a penetration assembly is jacketed by coolers inside and outside a sleeve originating at a flued head on the process pipe and penetrating the containment wall. The coolers are supplied by either chromated component cooling (CC) or raw service water. Recently, a minor leak of chromated water from the penetration coolers rendered the Class 3 safety-related CC system inoperable and was isolated. Subsequently, Non-Destructive Examination (NDE) inspections of the sleeve were conducted and significant degradation was noted. The root cause of the degradation under the jacketed cooler was due to raw service water, which was used in the cooler prior to switching to CC water. Weld repairs were subsequently performed to restore degraded areas. The coolers were also removed since the air gap could provide adequate insulation to keep the sleeve below a threshold temperature for degradation of concrete. An evaluation of past functionality was still required, however, to demonstrate that the degradation did not affect the structural integrity of the sleeve and breach containment boundary. The NDE data was processed to characterize the degradation for analysis. A novel application of ASME Section XI Non-mandatory Appendix C with a simple extension of the methodology was used in the evaluation to assist the operability determination. The paper concludes that a simple extension of the code methodology was useful in establishing plant operability.
Evaluation of the Corrosion Rate for Acidic Bottom Plates of an Aboveground Oil Tank by the AE Method
Authors: Kasai Naoya , Park So Soon , Utatsu Kentaro , Sekine Kazuyoshi , Kitsukawa Shigeo , Mitsuta Tsukasa
Published: July 2009

An AE method is an effective technique that can inspect corrosion damage of tank bottom plates to prevent leakage accidents of oil storage tanks. However, a correlation between AE signals and the corrosion behavior for bottom plates is not fully clarified. In this study, the authors considered that the corrosion regions in bottom plates become a strong acid environment by chloride ions as shown our previous work. The correlation between the AE signals and the corrosion behavior with a potentiostat for test pieces was examined in the environment. The polarization resistance was measured with an AC impedance method using a frequency response analyzer. It was clear that the polarization resistance indicated the corrosion rate for a test pieces in the experiments. While measuring the AE signals, the corrosion rate was monitored with a test piece. As a result, the AE signal showed the good correlation with the corrosion rates of the test pieces.
Flaw Assessment in a Petro-Chemical Spherical Shell by Using FAD Method
Authors: Cho Doo-Ho , Chang Yoon-Suk , Choi Jae-Boong , Kim Young-Jin , Han Sang In
Published: July 2009

As the increase of operating times of petro-chemical facilities, possibility of flaw occurrences has been rapidly increased also. From a recent in-service inspection, three different sized surface cracks (crack depths of 4.5, 9.9 and 14.2 mm) were detected in welding parts of a spherical shell in Korea. While API579 code provides corresponding assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked spherical shell to investigate effects of complex geometry, analysis model and residual stress. From detailed finite element analysis, stress distributions are determined for the full three-dimensional model. Then, stress intensity factors are calculated for simplified model by employing the well-known influence stress function technique. Finally, parametric structural integrity evaluation of the cracked spherical shell is conducted by using failure assessment diagram method. And the numerical results reflecting different geometry, analysis model and residual stress are fully discussed.
The Measurement and Modelling of Residual Stresses in a Stainless Steel Pipe Girth Weld
Authors: Ogawa K. , Chidwick L. O. , Kingston E. J. , Dennis R. , Bray D. , Yanagida N.
Published: July 2009

This paper presents results from a program of residual stress measurements and modelling carried out for a pipe girth weld of 369 mm outer diameter and 40 mm thickness. The component consisted of two 316 stainless steel pipe sections joined together using a “single-V” nickel base alloy (alloy 82) weld. The residual stresses were measured using the Deep-Hole Drilling (DHD) technique and modelled using ABAQUS. Biaxial, through-thickness residual stresses were measured through the weld centreline at a total of 6 different locations around the component. At three of the measurement locations the DHD process was carried out from the outer surface of the component with the remaining three, one of which coinciding with the weld start/stop position, carried out from the inner surface of the component. The differences in DHD process application (i.e. outer-to-inner or inner-to-outer) was carried out as a sub-objective to investigate the sequence of residual stress relaxation and its influence on the measured results. Good measurement repeatability was found between all locations. The hoop residual stresses were tensile at the outer surface, increasing to a maximum of 350 MPa at 10 mm depth, then decreasing to a minimum of −325 MPa at a depth of 34 mm, before increasing again towards the inner surface. The axial residual stresses were found to be similar in profile to the hoop residual stresses albeit lower in absolute magnitude by roughly 100 MPa. For this component it was found that the hoop residual stresses showed an influence of process direction, whereas for the axial residual stresses no influence was found. The modelling of the residual stresses generated was undertaken using a 2D axisymmetric finite element analysis containing 25 discrete weld beads. Each of the 25 weld beads were analysed sequentially using the following stages: heat source modelling, thermal analysis, elastic-plastic mechanical analysis. The sensitivity of the residual stresses generated with respect to the material hardening model used was investigated (i.e. kinematic, isotropic and mixed mode – kinematic/isotropic). Generally, the isotropic hardening model produces the highest predictions, the kinematic hardening model produces the lowest predictions with the mixed mode model lying in-between. Good agreement was found between the measured and modelled residual stresses. The main discrepancy existed in the hoop direction with the modelled residual stresses being the most tensile by roughly 200 MPa at depths within 15 mm of the outer surface of the pipe.
The Measurement and Modelling of Residual Stresses in a Full-Scale BWR Shroud-Support Mock-Up
Authors: Ogawa K. , Kingston E. J. , Smith D. J. , Saito T. , Sumiya R. , Okuda Y.
Published: July 2009

This paper presents results from a programme of residual stress measurements and modelling carried out in Japan on a full-scale mock-up of the hemi-spherical base of a Boiling Water Reactor (BWR) pressure vessel. The shroud support mock-up consisted of four main parts: pressure vessel, support plate, support cylinder and support legs. The mock-up was manufactured using a combination of ferritic steel and nickel base alloy (i.e. alloys: 82, 182 and 600) in a similar manner to that of the actual component. Overall the mock-up had an outer diameter of 6.6m and a height of 3.4m. The residual stresses generated by the nickel alloy welds during manufacture were measured using the Deep-Hole Drilling (DHD) [1–3] and Sectioning [4, 5] techniques, and modelled using ABAQUS. Presented here are measurement and modelling results from three weld locations within the mock-up: at one location through the “double-bevel” butt-weld joining the top of the support leg to the support cylinder (named H10) and at two locations through the “asymmetric double-V” weld joining the bottom of the support leg to the cladded pressure vessel (named H11a and H11b). The semi-destructive DHD technique was carried out first at all three locations on-site in Japan before the fully destructive Sectioning technique was used. Both techniques measured the biaxial (i.e. mock-up-hoop and -axial) residual stresses. The DHD and Sectioning techniques were not carried out at the exact same locations, rather similar locations due to the axisymmetry of the mock-up. Modelling of the residual stresses generated was undertaken for each weld location using a 2D axisymmetric finite element analysis containing between 40–50 discrete weld beads. The modelled residual stresses were generated using thermal load modelling followed by elastic-plastic mechanical analysis under kinematic hardening rules. Overall there is excellent agreement between the measured and modelled residual stresses at all locations. At all locations the measured peak tensile residual stresses (i.e. H10 = 410MPa, H11a = 260MPa and H11b = 230MPa) were found to be in the hoop direction just below the inner weld cap surface. The modelled peak tensile residual stresses were again found in the hoop direction near the inner weld capped surface, however, they were found to be approximately 155MPa greater than the measured residual stresses, and for locations H10 and H11a similar peaks were found near the outer weld cap surface as well.
Analytical and Numerical Evaluation of the Impact Limiters Design of a Research Reactors Spent Fuel Transportation Package Half Scale Model Under 9 M Drop Tests
Authors: Mattar Neto Miguel , Miranda Carlos A. J. , Fainer Gerson , Moura˜o Roge´rio P.
Published: July 2009

Since 2001, under the IAEA (International Atomic Energy Agency) support, some regional projects have been developed in Latin America to assess storage and transportion options for the research reactors spent fuel in the region. One of the projects tasks is the design and testing of a half scale model of a dual purpose (transportation and storage) package for research reactors spent fuel. Considering one of the hypothetical accident conditions, the 9 m drop test, this paper presents the impact limiters design evaluation of the above mentioned half scale model of the dual purpose package based on the impact limiters materials characterization, on the analytical assessment of the impact limiters sizing (dimensions and expected package acceleration levels) and on numerical simulations of the drop tests using a finite element explicit code. Conclusions and comments are addressed based on the obtained results.
Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI
Authors: Tabatabaie Mansour , Ballard Thomas
Published: July 2009

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.
Three Dimensional Aspects of Computational Weld Modelling
Authors: Brust Frederick W. , Rudland David L.
Published: July 2009

Many computational weld models and the corresponding solutions are performed using two dimensional models. For instance, many models of circumferential pipe welding use the axis-symmetric assumption since the predicted residual stresses tend to be upper bound. Hence, when performing a stress corrosion crack growth prediction the results tend to be conservative. However, there are many instances where full three dimensional analyses are required. Distortion predictions of large structures require full three dimensional analyses. Pipe repair analyses often require 3D solutions since the repair may only be 90-degrees of the circumference. Many other examples exist. This paper discusses circumstances where such three dimensional solutions are required. Moreover, discussions of when full moving arc solutions versus lump pass solutions suffice, and many other 3D analysis assumptions are summarized. Several examples of full three dimensional analyses are discussed. These include a partial circumferential pipe repair, an industrial weld fabrication, and ship structure weld analyses.
Dynamic Analysis of Hanford Unirradiated Fuel Package Subjected to Sequential Lateral Loads in Hypothetical Accident Conditions
Authors: Wu Tsu-Te , Gorczyca Jennifer L. , Leduc Daniel R. , England Jeffery L.
Published: July 2009

Large fuel casks present challenges when evaluating their performance in the Hypothetical Accident Conditions (HAC) specified in the Code of Federal Regulations Title 10 part 71 (10CFR71). Testing is often limited by cost, difficulty in preparing test units and the limited availability of facilities which can carry out such tests. In the past, many casks were evaluated without testing by using simplified analytical methods. This paper presents a numerical technique for evaluating the dynamic responses of large fuel casks subjected to sequential HAC loading. A nonlinear dynamic analysis was performed for a Hanford Unirradiated Fuel Package (HUFP) [1] to evaluate the cumulative damage after the hypothetical accident Conditions of a 30-foot lateral drop followed by a 40-inch lateral puncture as specified in 10CFR71. The structural integrity of the containment vessel is justified based on the analytical results in comparison with the stress criteria, specified in the ASME Code, Section III, Appendix F [2], for Level D service loads. The analyzed cumulative damages caused by the sequential loading of a 30-foot lateral drop and a 40-inch lateral puncture are compared with the package test data. The analytical results are in good agreement with the test results.
Potential Effects of Recent Road Transportation Accidents on Radioactive Material Shipments
Authors: Bajwa Christopher S. , Easton Earl P. , Dunn Darrell S. , Shewmaker Robert E.
Published: July 2009

In 2007, two severe transportation accidents, involving primarily long-haul tractor trailers, occurred in the State of California. In the first, which occurred in Oakland in the “MacArthur Maze” section of Interstate 580, a tractor trailer carrying gasoline impacted an overpass support column and burst into flames. The subsequent fire, which burned for over 2 hours, led to the collapse of the overpass onto the remains of the tractor trailer, due to the loss of strength in the steel exposed to the fire. The second incident was a chain-reaction accident involving several tractor trailers in the I-5 “Newhall Pass” truck bypass tunnel in Santa Clarita. This accident also involved an intense fire that damaged the tunnel and required the closing of the tunnel for repairs to the concrete walls. The US Nuclear Regulatory Commission is studying both these accidents to examine any potential regulatory implications related to the safe transport of radioactive materials and spent nuclear fuel in the United States. This paper will provide a summary of that effort.
An Analytical Framework for the Solution of Autofrettaged Tubes Under Constant Axial Strain Condition
Authors: Hosseinian E. , Farrahi G. H. , Movahhedy M. R.
Published: July 2009

Autofrettage is a technique for introducing beneficial residual stresses into cylinders. Both analytical and numerical methods are used for analysis of the autofrettage process. Analytical methods have been presented only for special cases of autofrettage. In this work, an analytical framework for the solution of autofrettaged tubes with constant axial strain conditions is developed. Material behavior is assumed to be incompressible and two different quadratic polynomials are used for strain hardening in loading and unloading. Clearly, elastic-perfectly plastic and linear hardening materials are special cases of this general model. This material model is convenient for description of the behavior of a class of pressure vessel steels such as A723. The Bauschinger effect is assumed fixed and total deformation theory based upon von-Mises yield criterion is used. An explicit solution for the constant axial strain conditions and its special cases such as plane strain and closed-end conditions is obtained. For open-end condition for which axial force is zero the presented analytical method leads to a simple numerical solution. Finally, results of the new method are compared with those obtained from other analytical and numerical methods and excellent agreement is observed. Since the presented method is a general analytical method, it is believed that it could be used for validation of numerical solutions or analytical solutions for special loading cases.
A New Approach to Assessing the Reliability of Applying Laboratory Fracture Toughness Test Data to Full-Scale Structures
Authors: Chao Yuh J. , Fong Jeffrey T. , Lam Poh-Sang
Published: July 2009

In this paper, we propose a two-step approach to addressing the question of how reliable the practice of applying laboratory data on fracture toughness to full-scale structures and components is. In the first step, we construct a two-level eight-factor 16-run-plus-a-center-point fractional factorial orthogonal design of experiments and conduct an analysis using literature fracture toughness and parameter data, where the eight factors are: (1) the Young’s modulus, E, (2) a material property constant, α, as defined in a Ramberg-Osgood stress-strain model, (3) the work hardening exponent, n, of the same model, (4) the yield stress, σy, (5) the critical local fracture stress, σf, (6) a chemical composition parameter in the form of the ratio of manganese to carbon content, Mn/C, (7) the crack depth/width ratio, a/W, and (8) the critical microstructural distance, rc, from the crack tip. Based on the 17-run data and the design of experiments analysis, we first obtain a ranking of the relative importance of those eight factors and then select two most important ones, to be named “key parameters”, to perform a multi-linear least square fit of the fracture toughness data as a function of those two key parameters. This simplification allows us to calculate, for the number of tests equal to N (= 17), the best estimate of the fracture toughness with 95% confidence prediction intervals. In the second step, we apply the statistical concept of a tolerance interval for a fixed sample size N and three coverages, 90%, 95%, and 99%, to a conversion of the results of the first step (the prediction intervals) to a set of tolerance intervals for the fracture toughness of a full-scale structure. Significance and limitations of this novel approach to answering the question of reliability from laboratory data to full scale structures are discussed at the end of this presentation.
Utilization of Minimal Material Data in Design
Authors: Marriott Douglas L. , Westerkamp E. J.
Published: July 2009

This paper is a statement of intent rather than the description of a piece of completed work. It outlines a proposed Internet based material database to be developed for the specific purpose of collecting and communicating information of acknowledged variable quality, for use in situations where more detailed information is lacking. The proposed system will consist of two main modules. The first is a freeform database with open access for both contributing and consulting information. The second will be a compilation of methods developed by practical problem solvers in dealing with materials related problems in the presence of inadequate, unreliable or even nonexistent data.
Evaluation of Thermal Conductivity of Installed-in-Place Polyurethane Foam Insulation by Experiment and Analysis
Authors: Smith Allen C. , Gupta Narendra K. , Hardy Bruce J. , Eberl Kurt R.
Published: July 2009

In the thermal analysis of the 9977 package, it was found that calculated temperatures, determined using a typical thermal analysis code, did not match those measured in the experimental apparatus. The analysis indicated that the thermal resistance of the overpack in the experimental apparatus was less than that expected, based on manufacturer’s reported value of thermal conductivity. To resolve this question, the thermal conductivity of the installed foam was evaluated from the experimental results, using a simplified analysis. This study confirmed that the thermal resistance of the experimental apparatus was lower than that which would result from the manufacturer’s published values for thermal conductivity of the foam insulation. The test package was sectioned to obtain samples for measurement of material properties. In the course of the destructive examination a large uninsulated region was found at the bottom of the package, which accounted for the anomalous results. Subsequent measurement of thermal conductivity confirmed the manufacturer’s published values. The study provides useful insight into the use of simplified, scoping calculations for evaluation of thermal performance of packages.
S-N Curves in Pressure Vessel Steels Using Theory of Critical Distances
Authors: Chattopadhyay Somnath
Published: July 2009

The S-N technology used in the ASME Code and similar design criteria includes both crack initiation and crack propagation phases of fatigue failure. Some of the pressure vessel construction codes have used the simplified fatigue initiation criterion based on stresses calculated at a distance of 0.05 mm from the surface crack. In this work such techniques have been assessed for pressure vessels in light of the theory of critical distances. This method has been used to generate S-N curves for typical materials such as medium carbon steels, nickel chrome steels and stainless steels. Separate techniques have been highlighted for obtaining the number of cycles to nucleate a crack from a free surface, and also the number of cycles to drive the nucleated surface crack to propagate to a length equal to the critical distance parameter related to the process zone. The two estimates on the number of cycles when combined constitute a reasonable estimate of the number of cycles to initiate a crack and form the basis of the S-N design curves. The method requires the material property information on elastic-plastic fracture toughness and short crack propagation characteristics including crack closure effects.
Investigation, Analysis and Mitigation of Combustion Driven Vibration in a Sulfur Recovery Burner Assembly
Authors: Porter M. A. , Fenton M. C. , Martens D. H.
Published: July 2009

During initial operation, one of three identical Claus furnace burners of a large Sulfur Recovery Complex was observed to develop a vibration at certain operational conditions that affected the reliability of some of the instruments attached to the burner front. The resonance was not sufficient to lead to mechanical damage of the burner or the instruments but led to spurious operational trips and corresponding plant shutdowns. The observed vibration, first considered to be a result of mechanical resonance within the burner assembly, was found to be the direct result of acoustic excitation of a burner pressure head by the natural acoustical frequencies present in the attached furnace during the combustion process. The investigation included gathering field operational conditions, field vibration measurements, and analytical computations using finite element methods. This paper reports the investigation process, results obtained, and the modifications that were determined necessary to sufficiently reduce the vibration of the instruments.