bluuebunny/crossref_metadata_2025 huggingface dataset:
Lower Bound Limit Loads Using the Reference Two-Bar Structure: An Improved Estimate Beyond Mura’s Lower Bound
Authors: Mahmood S. L. , Adibi-Asl R. , Daley C. G. , Seshadri R.
Published: November 2015

Mura’s lower bound limit load multiplier (m′) has been obtained on the basis of a variational formulation (Mura et al., 1965). However, m′ is equal to or less than the classical lower bound multiplier (mL). In this paper, a relationship between the m′ multiplier and the reference two-bar multiplier (Seshadri, R., and Adibi-Asl, R., 2007) is obtained. The nature of the bounds is examined in the context of several pressure components.
Construction of Dynamic Model for Free Standing Spent Fuel Rack Under Seismic Excitations
Authors: Kaneko Shigehiko , Shirai Hironao
Published: November 2015

Free standing rack designed for storing spent fuel at nuclear power station has an advantage to earthquake excitations because both fluid force and friction force can reduce the movement of a rack. However, there are various motions of FS rack such as parallel, rotational and rocking which should be taken into consideration when it is subjected to earthquake excitations. Therefore, the motion of FS rack must be precisely figured out in order to apply FS rack design concept. In this research, to investigate the motion of FS rack, 2-dimensional dynamic model considering pressure loss of gap flow was constructed. In addition, an experiment with a 1/16 scale model was conducted to validate the dynamic model. From numerical results based on the proposed dynamic model, some important features for the design of FS rack were found. Finally, case studies by real size free standing rack under the excitation of actually observed earthquake wave like The Great East Japan earthquake and The Niigata-ken Chuetsu-Oki earthquake were conducted based on the proposed method of calculation.
Effect of Cladding Residual Stress Modeling Technique on Shallow Flaw Stress Intensity Factor in a Reactor Pressure Vessel
Authors: Kusnick Joshua , Kirk Mark , Bass B. Richard , Williams Paul , Dickson Terry
Published: November 2015

Prior probabilistic fracture mechanics (PFM) analysis of reactor pressure vessels (RPVs) subjected to normal cool-down transients has shown that shallow, internal surface-breaking flaws dominate the RPV failure probability. This outcome is caused by the additional crack driving force generated near the clad interface due to the mismatch in coefficient of thermal expansion (CTE) between the cladding and base material, which elevates the thermally induced stresses. The CTE contribution decreases rapidly away from the cladding, making this effect negligible for deeper flaws. The probabilistic fracture mechanics code FAVOR (Fracture Analysis of Vessels, Oak Ridge) uses a stress-free temperature model to account for residual stresses in the RPV wall due to the cladding application process. This paper uses finite element analysis to compare the stresses and stress intensity factor during a cool-down transient for two cases: (1) the existing stress-free temperature model adopted for use in FAVOR, and (2) directly applied RPV residual stresses obtained from empirical measurements made at room temperature. It was found that for a linear elastic fracture mechanics analysis, the application of measured room temperature stresses resulted in a 10% decrease in the peak stress intensity factor during a cool-down transient as compared to the stress-free temperature model.
Evaluation of Arbitrary 3-D Crack Growth Behavior Under Residual Stress in Butt-Welded Pipe
Authors: Iwamatsu Fuminori
Published: November 2015

Arbitrary 3-D crack growth behavior due to stress corrosion cracking under residual stress was evaluated by finite element analyses. The analytical evaluation enables consideration of complicated stress distributions, such as weld residual stress, and expression of arbitrary 3-D crack shapes. The estimated weld residual stress for non-cracked components was distributed on the crack surface on the basis of the superposition principle to calculate stress intensity factors. Arbitrary 3-D crack shapes due to the crack propagation were expressed by FINAS/CRACK software. Moreover, stress corrosion cracking (SCC) crack growth evaluation under weld residual stress in a butt-welded large diameter pipe was conducted. The weld residual stress was estimated by finite element analyses considering a moving heat source during welding. An initial crack was postulated in a heat affected zone. The 3-D no planar crack growth behavior due to the complicated weld residual stress was observed by the analytical evaluation. To verify the applicability of flaw growth procedure in a fitness-for-service code on the SCC crack growth considering 3-D shape, SCC crack growth evaluation on the basis of the code procedure using a planar semi-elliptical crack shape was conducted and compared with the analytical results.
Remaining Life Prediction of Ethylene Cracking Tubes Under Carburizing and Creep Joint Action
Authors: Cao Luowei , Du Chenyang , Shao Shanshan , Xie Guoshan
Published: November 2015

Remaining life prediction model of ethylene cracking tubes (ECT) suffered joint damage of carburizing and creep have been set up in this study. Materials employed in this work were cut from Cr35Ni45-type radiation section of ECT. Layered structure, including oxide layer, carburized layer and carburizing transition layer, have been found from inside to outside of the tubes in scanning electron microscopy (SEM) images. However, no abrupt transition occurs between carburized layer and the base material. Both carburizing related layers caused the damage of the tubes, together with oxide layer. In order to facilitate the life prediction accuracy, carburizing transition layer was considered as a part of the damage layer. The remaining life of ECT was investigated by review of the microstructure and stress-rupture tests. Stress-rupture tests have been finished to obtained the rupture life of the tubes at 1000°C, 1040°C, 1080°C and 1125°C under six loading stresses (10MPa, 15MPa, 17MPa, 20MPa, 25MPa and 30MPa, respectively). In the results of stress-rupture tests, the combination of testing temperature at 1040°C and loading stress with 15MPa got the highest rupture life of 830h. Finally, a modified Larson-Miller remaining life prediction model of ECT, considering the comprehensive effect of carburizing and creep damage, has been established.
Study on Limit Load of Double Pipe Bend Combined Fittings
Authors: Zhou Changyu , Li Jian , He Xiaohua
Published: November 2015

Pipe bends and double pipe bends combined fittings including Back-to-back pipe combination (BB) and Face-to-face pipe combination (FF) play an important role in pressure pipeline system. Their carrying capacity will affect the integrity and safe operation of whole piping system directly. In this paper plastic limit loads for double pipe bends combined fittings (BB and FF) are analyzed by finite element method with elastic-perfect-plastic constitutive relation and the corresponding limit load equations are proposed which extends the range of pipe geometry λ Results show that the limit load equations available in references fail to be used for double pipe bends combined fittings and are unsafe, especially for FF combination. The limit loads increase with pipe thickness and bend radius in the meantime. The value of r/t is the main factor affecting limit load solutions. Detailed analysis also demonstrates that with applied load increasing, initial yielding appears in the FF combination firstly and finally overall yielding will happen. While the stress situation of BB combination is close to that of a single pipe bend. Eventually these proposed finite element based results are validated with experiment data and shows that finite element based solutions are believable.
Establishment and Application of Fatigue Life Prediction Models for Coiled Tubing
Authors: Tian Xiao , Zhang Hong , Duan Qingquan , Ji Yafeng
Published: November 2015

Coiled tubing (CT) technology has been developing in recent years. Analyzing the factors that affect CT fatigue life and getting a more accurate life prediction are of great significance. The work process of CT is one that goes through large deformation and multi-axial low-cycle fatigue, which suggests that the strain-life method should be used. Considering tri-axial strain state, this paper uses finite element software to fit the expression of strains in three directions so as to get equivalent strain. This paper also carries out tensile and fatigue experiments to get necessary fatigue parameters for calculating CT life. Comparing to the experiment results, the error is within 10%, which is considered to be acceptable. Based on the life prediction model above and field information, the software for predicting CT life is developed, through which the operators can store and recall data as well as export and print figures and tables. Besides, one can predict CT residual life before each operation and it shows the distribution of damage along the tube, providing basis for CT removal and repair.
Large Eddy Simulation of Fluid-Elastic Instability in Square Normal Cylinder Array
Authors: Shinde Vilas , Longatte Elisabeth , Baj Franck
Published: November 2015

Large Eddy Simulations (LES) are performed at low Reynolds number (2000 upto 6000) to investigate the dynamic fluid-elastic instability in square normal cylinder array for a single-phase fluid cross flow. The fluid-elastic instability is dominant in flow normal direction, at least for all water-flow experiments (Price et al. [18]). The instability appears even in the case of single moving cylinder in an otherwise fixed-cylinder arrangement resulting in the same critical velocity (Khalifa et al. [1]). Therefore, in the present work only a central cylinder out of 20 cylinders is allowed to vibrate in flow normal direction. The square normal (90°) array has 5 rows and 3 columns of cylinders with 2 additional side columns of half wall-mounted cylinders. The numerical configuration is a replica of the experimental setup except for the length of cylinders, which is 4 diameters (4D) in numerical setup against about 8D in the experiment facility. The single-phase fluid is water. The standard Smagorinsky turbulence model is used for the sub-grid scale eddy viscosity modeling. The numerical results are analysed and compared with the experimental results, for a range of flow velocities in the vicinity of the instability. Moreover, instantaneous pressure and fluid-force profiles on the cylinder surface are extracted from the LES calculations in order to better understand the dynamic fluid-elastic instability.
Evaluation of Residual Stresses Induced by Repairs to Small Diameter Stainless Steel Pipe Welds
Authors: Hicks Trevor G. , Mabe William R. , Miller Jason R. , Mullen John V.
Published: November 2015

Residual stresses within stainless steel pipe welds may cause or exacerbate in-service cracking. Significant investigative efforts have been devoted to the examination of piping residual stresses in large diameter piping using both finite element modeling and experimental techniques, but limited information is available for small diameter piping. Even less information is available for small diameter piping welds which have been repaired or re-worked during initial fabrication. This investigation used both experimental methods and analytical modeling to assess the impact of repair welding during initial fabrication on the residual stresses along the inner diameter (ID) of small diameter pipe specimens.

The investigation showed that tensile axial residual stresses were located in the heat affected zone (HAZ) along the ID of the pipe specimens adjacent to regions which were excavated and re-welded. Such repair welds were also shown to markedly increase the magnitude of the tensile axial residual stresses for weld configurations which otherwise had lower magnitude residual stresses.
Experimental and Numerical Study of Ductile Fracture Initiation in Aluminum 6061-T6
Authors: Rekik W. , Ancelet O. , Gardin C.
Published: November 2015

This work deals with the characterization of ductile damage in Aluminum 6061-T6 alloy.

In this paper we discuss the stress triaxiality effect on the initiation and the evolution of damage through a sequence of tensile tests conducted on round specimens with different rate of trixialities and tearing tests on precracked Compact Tension specimens. Scattering of ductility and toughness values was highlighted between the three characteristic directions studied in this topic.

Based on the experimental results, numerical simulation has been performed in order to analyze and predict ductile fracture initiation of this aluminum alloy by simulating void growth according to the Rice-Tracey micromechanical model.

The numerical simulation was conducted in two steps: first the critical void growth ratio (R / R0)c was evaluated for tensile cylindrical specimens with different degrees of triaxiality and then used to analyze crack growth initiation on Compact Tension specimen.

Due to the Al-6061-T6 highly sensitivity to triaxiality, a necessary adaptation of the Rice-Tracey model’s coefficient was made.
A Calculation Method for Torques of Large Capacity Cylinders for Tube Trailers
Authors: Deng Guide , Wang Jingxian , Jiang Yongshan , Ji Fang , Feng Jingliang
Published: November 2015

Large capacity cylinders installed in the frames of tube trailers subject to torques caused by their own curvatures and out of roundness under the action of gravity. The torques may induce additional stresses to the ends of the cylinders connecting to the frames. If the torques are big enough, the cylinders may rotate significantly, which can deform or even break the gathering and transferring pipes connecting to the cylinders. An explicit calculation method was presented to predict the maximum torques introduced by the degrees of curvatures and out of roundness of the cylinders under gravity, and the torques calculated agree with the tested results of 5 steel cylinders with a water capacity of 2250 L, which verifies the usability of the calculation method.
Structural Assessment of Main Steam Line and Containment Building Under Steam Explosion Conditions
Authors: Kim Seung-Huyn , Chang Yoon-Suk , Song Sungchu , Cho Yong-Jin
Published: November 2015

The steam explosion is a fuel-coolant interaction process where the heat transfer from the melt to water is quite intense and rapid. This phenomenon may threat integrity of nuclear components and structures. For instance, the dynamic loads on the reactor cavity and the reactor lower plenum could potentially lead to failure of the main steam lines connected to the steam generators. In addition, since the main steam line extends to the containment wall, failure of the containment building may occur. The object of present study is to examine characteristics of Main Steam Line (MSL) and containment building under the steam explosion conditions. In this context, the corresponding FE models were generated and previously determined displacements of penetration piping were used as loading conditions. Subsequent FE analyses were conducted for the main steam line and containment building to calculate stresses and crack evaluations. Finally, structural assessment of nuclear component and structure combined with concrete failure criteria was performed and their results were discussed.
Upper Bound Estimates of the Contribution of an Unknown Residual Stress Field to Stress Intensity Factor
Authors: Coules Harry , Smith David
Published: November 2015

When assessing the effect of residual stresses on the driving force for fracture of a structure containing a defect, it is necessary to determine the residual stress field either via measurement or process simulation (e.g. weld modelling). However, residual stresses can be difficult and time-consuming to measure and model, especially in welded components which are subject to complex patterns of deformation during manufacture in addition to material inhomogeneity. To avoid this, many assessment procedures provide compendia of conservative estimates of the residual stress distribution for a limited set of welded joints. Unfortunately the use of these conservative estimates can lead to unrealistic results.

In this article we propose alternative methods to account for the effect of residual stress on linear elastic defect assessments. We determine the maximum possible stress intensity factor that can be generated in a cracked component by any unknown self-equilibrating residual stress field. The limiting value of stress intensity factor can then be used to assess the acceptability of defects without the need for any residual stress data.
Structural Integrity Assessment of Notched Components Using the Master Curve Methodology and Failure Assessment Diagrams
Authors: Garcia Tiberio , Cicero Sergio , Madrazo Virginia
Published: November 2015

This paper proposes a methodology for the structural integrity assessment of notched components. It combines failure assessment diagrams and a notch analysis approach based on the application of the Master Curve methodology for the prediction of the apparent fracture toughness of ferritic-pearlitic steels in notched conditions. This approach considers a new parameter named the notch reference temperature (T0N), which is different from the reference temperature (T0) obtained in cracked specimens and varies with the notch radius. With this purpose, the methodology has been applied to a set of fracture tests on steel S275JR, with notch radii ranging from 0 mm (crack-type defects) up to 2.0 mm and testing temperatures from −120°C up to 40°C. The methodology improves significantly the results obtained under the assumption that notches behave as cracks.
Stress Intensity Factor Handbook: Comparison of RSEM and ASME XI Codes
Authors: Faidy Claude
Published: November 2015

For fracture mechanic applications at design level or during operation the basic parameter used is the elastic stress intensity factor K. This stress intensity factor can be evaluated through different methods: formulas, influence or weight functions or direct elastic finite element analysis of the cracked structure.

After a brief review of available methods to develop elastic analysis of the fracture mechanic parameter K (stress intensity factor), this paper will compare French RSE-M Appendix 5 handbook and corresponding ASME-XI draft Appendix A-3000 handbook under development for cylindrical cracked structures (pipes or vessels) in a first step. In a future step, other structures (elbows, thickness variation…) and other crack types or locations will be considered.

The cross reference validations and the technical white papers will be discussed in the paper.

A short overview of plasticity corrections proposed by these 2 different Codes will be presented, compared and discussed in accordance with the validation analysis available.

Finally, some differences between these 2 handbooks can have important safety consequences in their practical applications, some over-conservatism have to be better understand and will be discussed in term of consequences on different practical applications, like fatigue or corrosion crack growth, or critical crack size in brittle or ductile regime of nuclear components.
Automated Approach for Reciprocating Compressor Cylinders Design
Authors: Babbini Alberto , Orsi Gianni , Maleci Riccardo
Published: November 2015

The design of a brand new reciprocating compressor cylinder is a difficult and time expensive task, involving CAD, FEA and CFD tools, which can take several months. Following standard approach, usually several trials are needed in order to achieve the most suitable solution. Every time it is necessary to change some design/model features, all the following operations have to be repeated: modifying the CAD model; meshing the model; calculating new loads and/or boundary conditions; configuring the results analyses; post process the results. Following standard methods each described operation has to be performed manually by a user.

This paper describes a method to achieve the automation of most of these manual operations, transferring the workload from human to hardware resources, with a consequent saving in time needed to achieve results and related quality.

Paper will describe the process (including details about FEA and CFD analyses) to design a cylinder with this method, compared with a traditional one. The comparison will show differences in delivery time, weight and total cost (engineering + production) between the cylinders.
Study of Joule-Thomson Cooling Effect During Leakage With Application to Compressed Natural Gas Containment on Marine Vessels
Authors: Liu Yinghua , Ai Gang
Published: November 2015

As the localized temperature drop induced by the Joule-Thomson cooling effect in a leak causes a reduction in the fracture toughness at the crack front, leak-before-break approach that does not take this effect into account may be unconservative. In this paper, argon was selected as the experimental gas used in the experiment due to its incombustibility and similar Joule-Thomson coefficient to that of methane. An experimental pressure vessel with a design pressure of 250 bar was designed and fabricated. Liquid nitrogen cracking method was employed to fabricate a realistic through-thickness crack in a test plate. Under the condition of ambient temperature of 30 °C and maximum internal pressure of 91 bar, the temperature of argon at the exit of the crack and the measured lowest temperature of metal near the crack are −9.2 °C and 7.9 °C, respectively.
Effects of Chemical Content Variation on the Fracture Probability of PWR Pressure Vessel Subjected to PTS Events
Authors: Huang Pin-Chiun , Chou Hsoung-Wei , Ferng Yuh-Ming
Published: November 2015

This paper is to study the effects of copper and nickel content variations on the fracture probability of the pressurized water reactor (PWR) pressure vessel subjected to pressurized-thermal-shock (PTS) transients. The probabilistic fracture mechanics (PFM) code, FAVOR, which was developed by the Oak Ridge National Laboratory in the United States, is employed to perform the analyses. A Taiwan domestic PWR pressure vessel with varied copper and nickel contents of beltline region welds and plates is investigated in the study. Some PTS transients analyzed from Beaver Valley Unit 1 for establishing the USNRC’s new PTS rule are applied as the loading conditions. It is found that the content variation of copper and nickel will significantly affect the radiation embrittlement and the fracture probability of PWR pressure vessels. The results can be regarded as the risk incremental factors for comparison with the safety regulation requirements on vessel degradation as well as a reference for the operation of PWR plants in Taiwan.
Prediction of Fatigue Crack Initiation and Growth During Thermal Cycling
Authors: Wu Guiyi , Smith David , Tanner David
Published: November 2015

Conventional approaches to assess fatigue under combined thermal and mechanical loading often utilize a fatigue design curve. In this paper models based on the physics and mechanics for the initiation and growth of fatigue cracks in stainless steel are first explained. The models are based on experimental evidence gathered for the initiation and growth of small cracks created during strain controlled laboratory tests. This evidence is then linked with data for the growth of large fatigue cracks in stainless steel. In the paper these models are coupled with finite element analyses to explore the fatigue initiation and growth of cracks in stainless steel pipes subjected to thermal cycling. It is assumed that the material behaviour is elastic-perfectly plastic, rate independent and fatigue occurs in air.

The stress and strain fields for pipes subjected to a range of thermal loading conditions are explored. The fields are shown to be sensitive to parameters such as the Biot and Fourier numbers that include pipe dimensions, physical properties, dwell time and thermal conditions. Of particular interest is the temperature range and dwell time during thermal loading. Finite element analyses are then used to determine the stress and strain ranges created by thermal loading and these ranges are used in the crack initiation and growth models to estimate fatigue life.
Prediction of Leak Rates in Porous Braided Packing Rings
Authors: Kazeminia Mehdi , Bouzid Abdel-Hakim
Published: November 2015

The prediction of leakage is one of the most challenging tasks when designing bolted flanged connections and valves. Failure of these pressure vessel components can cause shutdowns but also accidents, loss of revenue and environmental damages. With the strict regulations on fugitive emissions and environmental protection laws new tightness-based standards and design methods are being adopted to improve the sealing performance of bolted joints and valves. However, there is a practical interest in using a reliable correlation that could predict leak rates of one fluid on the basis of tests carried out with another on compressed packings. The paper presents an innovative approach to accurately predict and correlate leak rates in porous braided packing rings. The approach is based onDarcy-Klinkenberg to which a modified effective diffusion term is added to the equation. Experimental measured gas flow rates were performed on a setof graphite based compression packing rings with a large range of leak rates under isothermal steady conditions. Leakage from three different gases namely Helium, Nitrogen and Argon were used to validate the developed correlation. In the presence of the statistical properties of porous packings, the leak rates for different gases can be predicted with reasonable accuracy.
Failure Analysis on Abnormal Thinning of Elbows in the Economizer at Waste Heat Boiler System
Authors: Wang Sheng-Hui , Luo Xiao-Ming , Yang Yu-Qing , Tang Jian , Yang Zhen-Guo
Published: November 2015

Abnormal wall thinning of elbows were detected in the economizer at waste heat boiler system. In the failure analysis, material analysis, metallographic examination, macro- and microstructure analysis and composition analysis were conducted. We analyzed the causes and mechanisms of abnormal wall thinning. The failure causes were found to be sulfuric dew point corrosion. Finally, corresponding countermeasures were suggested.
Material Test and Analysis for Pressure Vessel Rupture Study Under Fire in Plant
Authors: Itoh Yoshiyasu , Waki Yoshiyuki , Kasuya Kazuyuki
Published: November 2015

In case fire incident occurs in Oil and Gas plant, pressure vessels will be exposed to fire. Though entire system will be depressurized when the fire is detected, internal pressure may still remain in the pressure vessels. Therefore, pressure vessels, if leakage of its internal fluids will escalate the incident, shall be confirmed that they will withstand internal pressure without rupture at least until internal pressure is decreased down to safe level. For design for such critical pressure vessel, a pressure vessel rupture study is conducted in addition to design code calculations. As safer plant design is requested in recent projects, demands for the pressure vessel rupture study are also growing.

In this research, material data at high temperature range, that are necessary to obtain reliable results by the pressure vessel rupture study, were measured for carbon steel and stainless steel type304 and type304L. In addition, pressure vessel rupture studies were performed for two sample pressure vessels by means of FEM analyses and calculation methods in published design guidelines.
Hydrogen-Enhanced Fatigue of a Cr-Mo Steel Pressure Vessel
Authors: Briottet L. , Moro I. , Furtado J. , Solin J. , Bortot P. , Tamponi G. M. , Dey R. , Acosta-Iborra B.
Published: November 2015

The current international standards and codes dedicated to the design of pressure vessels do not properly ensure fitness for service of vessels used for gaseous hydrogen storage and subjected to hydrogen enhanced fatigue. In this context, the European project MATHRYCE intends to propose an easy to implement vessel design methodology based on lab-scale tests and taking into account hydrogen enhanced fatigue.

In the present document the lab-scale experimental developments and results are presented. The material considered was a commercially available Q&T low alloy Cr-Mo steel from a seamless pressure vessel. Due to the high hydrogen diffusion at room temperature in such steel, all the tests were performed under hydrogen pressure to avoid outgassing. Different types of lab-scale tests were developed and used in order to identify the most promising one for a design code. The effect of mechanical parameters, such as H2 pressure, frequency and ΔK, on fatigue crack initiation and propagation was analyzed. In particular, special attention was paid on the influence of H2 on the relative parts of initiation and propagation in the fatigue life of a component.

The second part of the work was dedicated to cyclic hydraulic and hydrogen pressure tests on full scale vessels. Three artificial defects with different geometries per cylinder were machined in the inner wall of each tested cylinder. They were specifically designed in order to detect fatigue crack initiation and fatigue crack propagation with a single test.

The final goal of this work is to propose a methodology to derive a “hydrogen safety factor” from lab-scale tests. The proposed method is compared to the full-scale results obtained, leading to recommendations on the design of pressure components operating under cyclic hydrogen pressure.
Burst Test on the Steam Generator Tube With Multiple Part-Through-Wall Flaws
Authors: Kim Jin Weon , Eom Ki Hyeon
Published: November 2015

This study carried out burst tests on steam generator (SG) tube specimens containing multiple axial part-through-wall (PTW) flaws at room temperature (RT). The specimens were machined from SG tube of Alloy 690TT with an outer diameter of 19.05mm and a thickness of 1.067mm. The flaws were made by electro-discharge machining (EDM) method on the outer surface of specimen. In the experiment, six types of multiple PTW flaws with a constant depth of 50% of wall thickness and single flaw with four different lengths were considered. The results showed that the interaction effect for collinear axial PTW flaws diminished with increasing ligament length between flaws. The ligament length had less influence on the interaction effect for longer flaws than shorter flaws. For non-aligned axial PTW flaws, however, the interaction effect was increased and remained with increase in circumferential ligament length. For parallel axial PTW flaws, the positive interaction effect appeared when the ligament between flaws was less than 2mm. However, the failure pressure decreased with increasing circumferential ligament length between flaws and reached the minimum when they were separated by about 90-degree in circumferential direction. Interaction effect was enhanced as number of flaws for collinear and non-aligned axial PTW flaws increased. Regardless of flaw configurations and ligament lengths, multiple PTW flaws of shorter length were failed by rupture at bottom of flaws followed by coalescence and unstable tearing. But, the flaws of length longer than 25.4mm were failed by rupture at bottom of one of multiple axial flaws.
A New Low Stress to Seal Conformable ePTFE Gasket Tape for Large Diameter Glass Lined Steel Equipment
Authors: Bissett Daniel C. , Jones Charlene
Published: November 2015

Glass lined steel (GLS) vessels and piping is widely used in the chemical industry primarily for processing harsh chemicals at elevated temperatures. GLS flanges have delicate surfaces that can be easily damaged by too much bolt force, yet the connection must provide a tight seal to minimize leakage of the harsh and often dangerous chemicals. This application provides a unique sealing challenge as gaskets must be chemically and thermally resistant, seal at low loads, and accommodate the rounded and wavy nature inherent of glass lined steel flange sealing surfaces. Sealing solutions made of 100% polytetrafluoroethylene (PTFE) give the broadest chemical resistance. Such solutions are commercially available to reliably seal GLS piping. This paper explores more deeply the challenges of sealing large GLS vessels and presents a new 100% PTFE sealing solution based on fundamental technical understanding of the application using finite element analysis (FEA) and confirmed by laboratory tests. This paper also provides an overview of the gasket properties and gives a brief technical review of the principle technology.
Study of the Hydrogen Embrittlement Sensitivity of an X4CrNiMo 16.5.1 Stainless Steel and the Associated Electron Beam Weld
Authors: Cusenza Florent , Ringeval Sylvain , Thiébaut Stéphanie , Buy François , Paris Thomas , Moro Isabelle , Briottet Laurent , Vignal Vincent
Published: November 2015

X4CrNiMo 16.5.1 steel (commercial name APX4) is a low carbon martensitic stainless steel known for its remarkable mechanical characteristics and its good resistance to corrosion. The use of APX4 in the manufacture of high pressure gas vessels requires a thorough understanding of its resistance to Hydrogen Embrittlement (HE) as the gas can contain traces of hydrogen, and martensitic steels, and their welds, are generally very sensitive to HE.

This paper deals with the first part of this study, involving the characterization of the microstructure and the mechanical properties of each zone of the electron beam weld (melted zone and four different heat affected zones), and the investigation of their embrittlement in a hydrogen environment. For this purpose, tensile tests were performed in hydrogen gas at various pressures on both the base metal and the welded samples.

In situ tensile tests with picture correlation analysis have been planned for the subsequent part of our study. These experiments will enable us to track the strain in the different zones and examine the effect of hydrogen on their mechanical behavior.

These results, combined with permeation tests, should lead to a complete model for predicting hydrogen location inside the vessel as a function of time and local properties, as well as the associated embrittlement.
Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Stoichiometric H2/O2/N2-Mixtures in Long and Short Pipes
Authors: Schildberg Hans-Peter
Published: November 2015

As continuation of recently published experimental work [1,2], the static equivalent pressures (“pstat“) of the different detonative pressure scenarios occurring in stoichiometric H2/O2/N2 mixtures were determined in long and short pipes at ambient initial temperatures (20 °C) and initial pressures ranging from 4 bar abs to 35 bar abs. The pipes used for the tests were about 10 m long and had radial dimensions of 48.3×2.6 and 114.3×3.6 (outer diameter [mm] × wall thickness [mm]). The O2 content was varied from about 10 vol.-% to the highest value possible in stoichiometric mixtures (33.3 vol.-%).

For the tests in the long pipes the focus was on the variation of the ratio between the static equivalent pressure at the point where transition from deflagration to detonation occurred and the static equivalent pressure in the region of the stable detonation (pstat_DDT_long / pstat_stable). The ratio attained a maximum of about 5 at 14.78 vol.-% O2 (stoichiometric H2/air) and decays to 1 when increasing the O2 content to 24 vol.-%. This drop indicates that with increasing O2 content ever less precompression is required to cause auto ignition in the precompressed gas directly ahead of the deflagrative flame front. For mixtures of H2 with N2-diluted air the ratio exhibits a slight decrease which is in contrast to what would be expected and is not yet understood. The results obtained for the ratio between pstat of scenarios 3 and 4 (stable detonation and reflected stable detonation) and the Chapman-Jouguet pressure of the investigated gas mixtures confirmed the findings presented in PVP2013-97677 for ethylene/air-mixtures.

For mixtures of H2 and slightly diluted air the load for the reflected instable detonation was found to be about 7 · pstat_stable, the load at the DDT in the short pipe is 6.6 · pstat_stable and the load for coalescence of DDT and reflection is about 14 · pstat_stable.
Energy Approach for Determine Frequency and Amplitude of Vibration of Piping With Closed Side Branches
Authors: Orynyak Igor , Dubyk Iaroslav , Batura Anatolii
Published: November 2015

This article suggests calculation method for frequency and amplitude of acoustic vibration in piping with closed side branches, caused by gaseous running flow. The calculation algorithm consists of following steps: i) local excitation system is defined; ii) different combinations of boundary conditions are formed; iii) for fixed pair of boundary conditions ratio of stored in system energy and radiated from boundaries energy is written; iv) for every frequency energy functional is maximized to find boundary conditions; v) resonance frequencies are determined from plotting a curve of maximal energy ratio vs. frequency. Energy approach was further developed to analyze amplitude of vibration. For amplitude determine balance between injected energy (which depends on the Strouhal number and is defined from experimental data for laboratory geometries), and radiated from boundaries energy is written.
Optimization of the Existing Screening Method by Introducing Fen Correlations
Authors: Métais T. , Gilman T. , Genette P. , Chinthapalli A.
Published: November 2015

In the wake of numerous experimental tests carried out in air and also in a PWR environment, both abroad and in France, an update of the current fatigue codification is underway. Proposals are currently being formulated in France [1] [2] and discussions are taking place in the frame of a French working group involving EDF, AREVA and CEA.

In parallel with these worldwide modification efforts, it is necessary to evaluate their impact on the NSSS components. In the USA, many such evaluations have already been implemented for license renewal to operate power plants beyond their initial 40 years of operation. In order to reduce the scope of the calculations to perform, a preliminary screening was carried out on the various areas of the primary loop: this screening is detailed in an EPRI report [3]. The output of this screening process is a list of locations that are most prone to EAF degradation process and it is on these zones only that detailed EAF calculations are carried out.

In France, with the approaching fourth decennial inspection of the 900 MWe (VD4 900 MWe) power plants, EDF needs also to map out the impact of these updates to the RCC-M code before initiating detailed calculation efforts.

The EPRI report was not applicable as such to the French plants due to domestic specificities and more particularly, a need for a more detailed Fen estimation. A method was therefore developed by EDF, peer-reviewed by SI with the main innovation being the introduction of correlations enabling the calculation of Fen on the basis of the geometrical dimensions and the information available in the transient document.

This paper presents how these correlations were built and proposes to benchmark them with some existing sample case problems.
Flaw Effects and Flaw Reorientation on Spent Fuel Rod Performance: A Simulation With Finite Element Analysis
Authors: Tang David T. , Rigato Antonio , Einziger Robert
Published: November 2015

While fuel cladding failures have decreased significantly over the years, fuel cladding can still develop defects in the form of cracks, blisters, and circumferential hydride precipitates when irradiated. After drying for storage, circumferential precipitates may reorient as radial hydrides. This study examines if these hydrides could potentially influence the bending performance of the rod. Using a hollow, simply supported fuel tube to simulate the limiting behavior of a spent fuel rod deprived of the flexural rigidity contribution of the pellets, effects of the hydrides presence and orientation on the fuel rod bending structural performance are assessed. Within the confines of the finite element analyses (FEAs) of a flawed bare fuel tube, the bending strength of the hollow tube is shown not to be significantly compromised by the presence of the modeled circumferential and radial hydrides.
Options for Defining the Upper Shelf Transition Temperature (Tc) for Ferritic Pressure Vessel Steels
Authors: Kirk Mark , Stevens Gary , Erickson Marjorie , Server William , Gustin Hal
Published: November 2015

This paper evaluates current guidance concerning conditions under which the analyst is advised to transition from a linear-elastic fracture mechanics (LEFM) based analysis to an elastic-plastic fracture mechanics (EPFM) based analysis of pressure vessel steels. Current guidance concerning the upper-temperature (T>c) for LEFM-based analysis can be found in ASME Section XI Code Case N-749. Also, while not explicitly stated, an upper-limit on the KIc value that may be used in LEFM-based evaluations is sometimes taken to be 220 MPa√m (a value herein referred to as KLIM). Evaluations of Tc and KLIM were performed using a recently compiled collection of toughness models that are being considered for incorporation into a revision to ASME Section XI Code Case N-830; those models provide a complete definition of all toughness metrics needed to characterize ferritic steel behavior from lower shelf to upper shelf. Based on these evaluations, new definitions of Tc and KLIM are proposed that are fully consistent with the proposed revisions to Code Case N-830 and, thereby, with the underlying fracture toughness data. Formulas that quantify the following values over the ranges of RTTo and RTNDT characteristic of ferritic RPV steels are proposed:

• For Tc, two values, Tc(LOWER) and Tc(UPPER), are defined that bound the temperature range over which the fracture behavior of ferritic RPV steels transitions from brittle to ductile. Below Tc(LOWER), LEFM analysis is acceptable while above Tc(UPPER) EPFM analysis is recommended. Between Tc(LOWER) and Tc(UPPER), the analyst is encouraged to consider EPFM analysis because within this temperature range the competition of the fracture mode combined with the details of a particular analysis suggest that the decision concerning the type of analysis is best made on a case-by-case basis.

• For KLIM, two values, KLIM(LOWER) and KLIM(UPPER), are defined that bound the range of applied-K over which ductile tearing will begin to occur. At applied-K values below KLIM(LOWER), ductile tearing is highly unlikely, so the use of the KIc curve is appropriate. At applied-K values above KLIM(UPPER), considerable ductile tearing is expected, so the use of the KIc curve is not appropriate. At applied-K values in between KLIM(LOWER) and KLIM(UPPER), some ductile tearing can be expected, so it is recommended to give consideration to the possible effects of ductile tearing as they may impact the situation being analyzed.

These definitions of Tc and KLIM better communicate important information concerning the underlying material and structural behavior to the analyst than do current definitions.
Modified Svensson’s Formula for More Accurate Burst Pressure Predictions of Thin Cylindrical Shells With Small Shell Length to Diameter Ratios
Authors: Kang Sang-Guk , Young Kuao-John
Published: November 2015

For process safety management purposes, it is often required in industries to perform burst pressure calculations for pressurized equipment subjected to internal deflagrations. In predictions of burst pressures of vessels with short cylindrical shell sections, the stiffening effects of heads are often overlooked, which may lead to underestimated results. In this paper, a new improved method is proposed for predictions of burst pressures of thin cylindrical shells with small shell length to diameter ratios (L/D) at ambient temperature. The idea is to use the Svensson’s formula, modified by a factor that accounts for the effects of small L/D ratios, head types, and materials for more accurate predictions. Tables of such factors are developed based on study results from a series of elastic-plastic Finite Element Analyses including large displacement effect for different L/D ratios, thicknesses, materials, and head types. Some example problems are presented to validate the method.
Effect of Loading History on Elastic Modulus of HDPE
Authors: Jar P.-Y. Ben
Published: November 2015

This paper presents results from an experimental investigation about the influence of loading history on the elastic modulus of high-density polyethylene (HDPE). The study uses a new approach, named two-test method, to introduce the loading history using the first test and at least one month later, to measure the elastic modulus using the second test. The period of minimum one month between the two tests is to ensure that recovery of the viscous deformation from the first tests does not affect the measured elastic modulus from the second tests. Parameters considered to vary the loading history include maximum deformation (with the area strain up to 0.5 in most cases), loading mode (monotonic, cyclic and creep tension), test speed (from 0.005 to 30 mm/min), and stress triaxiality (through the change in the specimen gauge length), in which the area strain is defined as the logarithmic ratio of the original cross sectional area (i.e., the cross sectional area of virgin specimen) to the deformed cross sectional area. All of the second tests were conducted under monotonic tension at the crosshead speed of 0.001 mm/min. The results show the general trend of decrease of the elastic modulus, measured from the second tests, with the increase of the strain applied in the first tests. The results further indicate that test speed for deformation introduced in the first tests may have a significant influence on the elastic modulus measured from the second tests. The elastic modulus is used to determine damage parameter D based on the damage concept, based on influence of the loading history on the mechanical properties of HDPE is characterized.
CASS Fracture Tests Using Flat Plate Specimens With a Surface Flaw
Authors: Hojo Kiminobu , Nishi Wataru , Hayashi Shotaro
Published: November 2015

JSME rules for fitness for service have flaw acceptance rules for cast austenitic stainless steel (CASS) pipes. They allow applying two-parameter and elastic-plastic fracture mechanics methods using Z-factor. However they do not clearly describe whether limit load method is applicable for the case of no or low thermal aging condition. The authors performed tensile fracture tests using flat plate specimens with a surface flaw and confirmed that limit load method is applicable in the conditions of no thermal aging and even fully saturated thermal aging with high ferrite number. Also the plate with a shallow flaw ruptured at the critical stress defined by nominal stress at rupture-flaw depth curve in the code case which was determined by the similar flat plate tests of stainless steel or nickel alloy specimens. These results will be reflected to the revision of the code.