bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation and Slippage Modeling for Investigating Bolt Loosening Under Harmonic Transverse Excitation
Authors: Yang Xianjie , Nassar Sayed A.
Published: August 2013

This paper presents an analytical model for deformation and self-loosening performance of a preloaded M12 threaded fastener under cyclic transverse excitation based on the calibration of the bending stiffness parameters at bolt ends using finite element method. The model describes the bolt bending deflection and the relative bending rotational angle between the male and female threads, the loosening (rotational) angle, and the local contact slippage behavior of bolted joints. The analytical results for the deformation behavior of the bolt including bending deflection and bending angle are compared with the corresponding finite element results to validate the mathematical model of the threaded bolt. The shear force-displacement response, and the clamp load decay with the number of cycles are compared with the experimental data for model validation.
Load Combination Reduction Methodology for the US EPR™ Standard Nuclear Power Plant
Authors: Jung Se-Kwon , Harrold Joseph , Alchaar Nawar
Published: August 2013

The Safety-Related structures of the U.S. EPR™ Standard Nuclear Power Plant (NPP) predominantly consist of reinforced concrete shear walls and slabs; thus they are typically modeled using shell finite elements and analyzed and designed for a large number of applicable load combinations. This paper presents a load combination reduction methodology that has been specifically developed for and applied to these types of structural elements in order to methodically reduce the full set of applicable load combinations to a manageable sub-set of load combinations, termed “controlling load combinations” for structural design purposes. Load combination reduction criteria involve code-specified section capacities (i.e., allowables), structural demands (i.e., forces and moments), and demand-to-capacity ratios (DCR) as complemented by reinforcing ratios. For a particular Safety-Related structure or portions thereof, the controlling load combination produces the most demanding forces and moments relative to design allowables in accordance with applicable codes and standards for reinforced concrete design, resulting in the highest DCR among all applicable load combinations. To facilitate the load combination reduction process, portions or segments of a particular Safety-Related structure that are in close proximity and thereby most likely to be designed for a common reinforcement pattern are identified and grouped as a single design component and termed an “evaluation level component.” It is demonstrated that the load combination reduction methodology developed herein is instrumental in narrowing down numerous applicable load combinations to a sub-set of controlling load combinations for the U.S. EPR™ Nuclear Island Safety-Related structures.
Development and Use of a Homogenized Fuel Region Model for Thermal Analysis of a Truck Package Under Normal and Fire Accident Conditions
Authors: Kamichetty Krishna Kumar , Venigalla Venkata , Greiner Miles
Published: August 2013

In the current work, a geometrically-accurate two-dimensional model is developed of an isolated fuel assembly within isothermal compartment walls. Finite difference thermal simulations are performed to determine the cladding temperature for a range of compartment wall temperatures and assembly heat generation rates. The results for zero heat generation rate are used to determine a temperature-dependent effective thermal conductivity of the fuel region. The effective volumetric specific heat of the region is determined from a lumped capacity model. These effective properties are then applied to a two-dimensional model of a legal weight truck cask with homogenized (smeared) fuel regions. Steady-state normal conditions of transport simulations are performed for a range of fuel heat generation rates. The generation rate that brings the zircaloy cladding to their radial hydride formation temperature predicted by the homogenized model is greater than that determined by an accurate geometry model. Transient regulator fire accident simulations are performed for a range of fire durations. The minimum fire durations that bring the fuel cladding to its burst rupture temperatures are estimated. These results are compared to simulations which employ cask models with geometrically-accurate fuel region models.
Implant Test Modeling for Risk of Cold Cracking Assessment During Welding Operations
Authors: Robin Vincent , Gommez Florence , Primault Christophe , Devaux Josette
Published: August 2013

Filler material used for welding operations can lead to the occlusion of hydrogen gas in the arc atmosphere into the solidifying weld metal. This amount of hydrogen as well as the one originally present in the parent metal rapidly diffuses into the various regions of the weldment due to the high temperature depending also on the microstructure evolution and trapping effects. As the welded component cools down, depending on the metal’s microstructure in the heat-affected zone, the concentration of hydrogen in weld and the level of residual stresses, the risk of hydrogen assisted cold cracking in ferritic steel can arise. One of the most effective precautions against weld hydrogen cracking is to use of preheating and post-heating in order to reduce the hydrogen content, by diffusion in the structure and degassing, when residual stresses reach higher values at the end of cooling. The implant test is a stress controlled test applied on small specimen during welding to assess the susceptibility to heat affected zone hydrogen cracking. It may be used to define preheating temperature and postheating duration in order to prevent nuclear component assemblies from cold cracking risk. This paper will first present how to couple hydrogen diffusion, thermo-metallurgical and mechanical modeling in order to simulate the implant test. Finally, a Weibull type probabilistic criterion based on numerical approaches will be proposed to improve the implant test predictive capability in the case of multi-pass welding processes involving dissimilar materials.
Shape Recovery Model of a Curved Beam Using Piezoelectric Actuation
Authors: Maha Amit , Pang Su-Seng
Published: August 2013

A thin composite curved beam under external loading is used to simulate different structures such as pressurized pipes, O-Rings etc. These products can undergo dynamic shape change and warping. A piezoelectric actuator is to be used to design for thin curved structures. Simple thin quarter circular beam geometry is analyzed with external loading at the free end. The orientation and placement of the piezoelectric material on a composite curved beam directly affects the deflection and stress applied to that beam. The optimal placement for an actuator for shape recovery was estimated.
Thermal-Creep Induced Stress Relaxation Near a Notch in Zr-2.5Nb
Authors: Wan Shuai , Daymond Mark R. , Holt Rick A.
Published: August 2013

In CANDU nuclear reactors, flaws on the surface of Zr-2.5Nb pressure tubes naturally cause stress concentration, and subsequently potentially lead to crack initiation through delayed hydride cracking. However, the concentrated stresses tend to relax due to creep, which is suggested to reduce the occurrences of cracks. In this study, C-shaped specimens with a small radius notch (15μm or 30μm) manufactured from Zr-2.5Nb pressure tubes were first preconditioned through an ex-situ creep process (Keff = 6MPam, 583K) for a series of hold times. Elastic lattice strains around the notch were measured using high energy X-ray diffraction at the Advanced Photon source. Results show that strains along the loading direction are tensile and concentrated in front of the notch tip, while those perpendicular to the loading direction are compressive and distributed symmetrically about the notch plane. The concentrated strains relax with creep time, and the larger-size notch has a higher rate of relaxation.
Evaluation of Long-Term Creep Strength of Welded Joints of ASME Grades 91, 92 and 122 Type Steels
Authors: Yaguchi Masatsugu , Matsumura Takuaki , Hoshino Katsuaki
Published: August 2013

Creep rupture data of welded joints of ASME Grades 91, 92 and 122 type steels have been collected and long-term creep rupture strength of the materials has been evaluated. Similar study was conducted by the SHC Committee in 2004 and 2005, therefore, the evaluation of the creep rupture strength was conducted with emphasis on the long-term creep rupture data obtained after the previous study, in addition to discussion of the effects of product form, welding procedure and test temperature etc. on the creep strength. Almost the same results were obtained on the welded joint of Grade 92 as the previous study, however, the master creep life equations for the welded joints of Grades 91 and 122 were lower than the previous results, especially in the case of Grade 122. Furthermore, the creep strength reduction factor obtained from 100,000 hours creep strength of welded joints and base metal was given as a function of temperature.
A Loosening Mechanism of Bolted Joints Under Repeated Transverse Displacements
Authors: Sawa Toshiyuki , Ishimura Mitsutoshi , Nagao Takanori
Published: August 2013

Loosening accidents sometimes occur under several types of loadings such as winds, vibrations, earthquakes, impact loads and thermal changes. Recently, some studies have been conducted on the screw thread loosening in bolted joints under repeated transverse displacements. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied [1]. In assembling bolted joints, double nut, spring plate washers and hexagon nuts with flange have been used. However, a few studies have been carried out on the loosening mechanism in bolted joints with the above parts for preventing the loosening. In the present paper, the effects of the double nut, spring plate washers and hexagon nuts with flange mentioned above are examined using FEM calculations. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine for validation of the FEM calculations. As the results, it is seen that the loosening speed is the maximum when the hexagon nuts with flange is used. In addition, it is also observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily in the FEM calculations. The amounts of loosening for bolted joints with double nut, spring plate washers and hexagon nuts with flange are in a fairly good agreement with the measured results. Discussion is made on the loosening mechanism of bolted joints with the above parts under repeated transverse displacements.
Prediction and Measurement of Weld Residual Stresses in Thermally Aged Girth-Welded Austenitic Steel Pipes
Authors: Muránsky Ondrej , Smith Mike C. , Bendeich Philip J. , Hamelin Cory J. , Edwards Lyndon
Published: August 2013

The current paper describes finite element simulation of the complete manufacturing and service exposure history of girth-welded austenitic steel pipes fabricated from ESSHETE 1250 material for the STYLE Framework 7 project. The simulation campaign examines the impacts of prior quenching of pipe material, fabrication of closely adjacent welds, variation in mixed isotropic-kinematic hardening material constitutive models, and high temperature (650°C) service exposure (thermal ageing). The predicted residual stresses are validated using measurements made with the deep hole drilling (DHD) and incremental deep hole drilling (iDHD) techniques.
The Sealing Characteristics of Bolted Flanged Connection With Metal Gasket
Authors: Kondo Koji , Sawa Toshiyuki , Sato Koji , Kikuchi Tsutomu , Tsubaki Shota
Published: August 2013

Metal gaskets have been used in bolted flanged connections under high pressure and high temperature conditions. However, it is difficult to estimate an amount of leakage from the metal contact interfaces in the connections. Recently, it has been noticed that a tiny leakage occurs from the gasket interfaces in bolted flanged connections. Thus, it is necessary to study on the sealing characteristics of the metal to metal contact gasket in the connections under internal pressure and high temperature.

In the present paper, for clarifying the characteristic of the metal gaskets, some experiments were conducted at room temperature. The gaskets are used aluminum, copper and mild steel flat gaskets. Firstly, according to JIS B 2490, the sealing behavior was measured taking account the surface roughness of the metal gaskets. The gaskets were compressed using a material testing machine while the amount of leakage was measured. Secondly, the amount of leakage was measured for bolted flanged connections with metal gaskets. The flange nominal diameter used was 2″. Finally, the contact gasket stress distributions in the connection were analyzed using 3-D FEM analysis. Using these results, discussion was made on the sealing behavior of the metal gaskets. In the result, it is found that plastic strain is important for the sealing performance of the metal gasket.
FEM Stress Analysis and the Sealing Performance Evaluation in Bolted Flange Connections With Ring Joint Gasket Subjected to Internal Pressure: Effect of Scatter in Bolt Preloads
Authors: Kondo Koji , Tsubaki Shota , Sawa Toshiyuki , Kikuchi Tsutomu , Omiya Yuya
Published: August 2013

Bolted flange connections with ring joint gaskets have been used to seal the inner fluid under higher internal pressure and higher temperature conditions where soft gaskets such as compressed sheet gaskets cannot be applied. Bolted flange connections are frequently tightened using torque wrench, and it is known that the values of bolt preloads are scattered. The effect of the scatter on the sealing performance for bolted flange connections with compressed sheet gasket or semi-metal gasket has been examined. However, no research on the characteristics for the bolted flange connections with ring joint gasket has been found. It is necessary to know the effect of the scattered bolt preloads on the sealing performance and mechanical behavior of the connection with ring joint gasket. In addition, it is important to know an optimum method for determining the bolt preloads taking account of the scatter in bolt preloads.

In this paper, leakage tests for bolted flange connections with octagonal ring joint gaskets were conducted for cases where the bolt preloads are uniform and scattered. The sealing performance of these connections with ring joint gaskets was measured and evaluated. In addition, the leak rate was estimated using the contact gasket stress distributions of the connections when the bolt preloads were uniform and scattered using 3-D FEM. Finally, the measured leak rate for the connection using helium gas was compared with the estimated results. The estimated results are in fairly good agreement with the measured values. It is found that the sealing performance of the connections tightened with the uniform bolt methods is better than that with scattered bolt preloads.
Material Degradation and Creep Damage of Aging Components at High Temperature
Authors: Ye Ting , Wang Zhengdong , Xuan Fu-Zhen , Tu Shan-Tung , Liu Minshan
Published: August 2013

An assessment of material property degradation is carried out in this paper for an aged material taken from turbine component subjected to high temperature. Microstructure and chemical composition analysis is conducted to evaluate the damage status of the material after 16-year term of service. Testing samples are taken from the different regions of a steam turbine rotor with different working conditions. Regular material properties tests at high temperature, creep strength tests and creep crack growth (CCG) tests are performed to investigate the material property degradation. Experimental results reveal that the damage micromechanism is sensitive to temperature and stress state. High temperature tensile properties of the rotor steel materials are degraded due to the damage. The creep deformation rate and creep crack growth rate are higher in more degraded material than that in less degraded material. The relationships between the microstructure, internal damage evolution and the material properties are discussed for the aged rotor steel. This study will provide a further support for prediction of the residual life of the component with different degree of material degradation and creep damage.
Radially Polarized and Magnetized Rotating Cylinders Under Thermal Loading
Authors: Akbarzadeh A. H. , Chen Z. T.
Published: August 2013

Analytical solutions are acquired for radially polarized and magnetized rotating magnetoelectroelastic hollow and solid cylinders. The cylinders are orthotropic and infinitely long and are subjected to a combination of thermal, magnetic, electric, and mechanical loadings. The symmetric and steady state heat conduction equation is solved based on a general form of thermal boundary conditions to give the temperature distribution along the radial direction of cylinders. The governing ordinary differential equations in terms of displacement, electric potential, and magnetic potential with considering the thermal and inertial effects are obtained and solved in an exact form using the straightforward successive decoupling method. Numerical results are illustrated to reveal influences of thermal boundary condition, angular velocity, aspect ratio, and magneto-electro-mechanical boundary condition on the multiphysical responses of the rotating hollow and solid cylinders. The results are validated with those available in the literature.
Development of a Wall Thinning Rate Model for Liquid Droplet Impingement Erosion
Authors: Morita Ryo , Uchiyama Yuta
Published: August 2013

Liquid droplet impingement erosion (LDI) is defined as an erosion phenomenon caused by high-speed droplet attack in a wet steam flow. Pipe wall thinning due to LDI is sometimes observed in a steam piping system of a power plant. In this study, for more realistic LDI evaluation in the power plant, we conducted LDI experiments in wet steam flow with steam apparatus, and tried to develop a new thinning rate prediction model (LDI model). High speed wet steam flow simulating the actual plant condition was employed in the experiments. As a result, the cushioning effect of liquid film on a material surface was observed and was incorporated into LDI model as a empirical equation with fluid parameter.
Simulation for a Floating Roof Behavior of Cylindrical Storage Tank due to Wind Load: Part 1 — CFD Analysis
Authors: Kuroda Shinichi , Uejima Hidesaku , Ishida Kazuo , Yoshida Shoichi , Shiratori Masaki , Sekine Kazuyoshi , Tsuchida Tomohiko , Iwata Katsuki
Published: August 2013

Floating roofs are used in large cylindrical storage tanks to prevent evaporation of oil. The floating roof is said to vibrate in high winds like undulation of the sea surface. The wind induced, sea-surface-undulation-like vibration may initiate fatigue cracks at welded joints in the floating roof deck. In this two-part study, the authors attempted to simulate the vibration. In Part1 wind flow over an isolated cylindrical oil-storage tank was simulated without considering the motion of the roof. Computed unsteady pressure load data were transferred to structural analyses. Response analyses of the floating roof under the wind load are dealt with in Part2. The present paper describes the wind flow simulation. The computed pressure fluctuation over the roof exhibits broadband spectra and no remarkable dominant frequency. To gain some insights into characteristics of the roof pressure fluctuation and its association with global flow structures, the Snapshot Proper Orthogonal Decomposition (POD), the Dynamic Mode Decomposition (DMD), and the Complex POD were applied.
Investigation on On-Board High-Pressure Composite Tanks Subjected to Localized and Engulfing Fire
Authors: Ou Kesheng , Zheng Jinyang , Zhao Yongzhi
Published: August 2013

Safety performance of on-board high-pressure composite tanks under fire exposure has drawn extensive attention. Vehicle fires usually lead to such tanks experiencing a term of localized and engulfing fire. During this period, the composite tank would be degraded and even burst before pressure relief device (PRD) opens to release internal high-pressure gas. In this paper, experimental investigation for the tanks subjected to localized and engulfing fire was conducted on an Aluminum liner composite tank filled with hydrogen. Based on the temperature distribution and pressure rise measured in the experiment, a three-dimensional computational fluid dynamics model is developed to study the key factors influencing PRD activation time. The effects of filling medium, tank pressure and localized fire exposure time are analyzed in detail. The experimental results showed that pressure and temperature of internal gas changed little during the localized fire. In addition, filling medium and tank pressure have weak influence on the activation time of thermally-activated PRD (TPRD), but have significant effect on the activation time of pressure-activated PRD. TPRD can respond more quickly to protect the hydrogen composite tank than pressure-activated PRD. PRD activation time increases as the localized fire exposure time extends.
Intense X-Ray Measurement of Transient Hydraulic Phenomena in Molten Pool During Laser Welding Process
Authors: Yamada Tomonori , Shobu Takahisa , Yamashita Susumu , Ogawa Takemitsu , Sugihara Kenta , Nishimura Akihiko , Muramatsu Toshiharu
Published: August 2013

Spatial temperature distribution during the laser welding process has a huge effect on any residual stress distribution. Therefore, understanding of the transient hydraulic phenomena which affect the temperature distribution in the molten pool is very important.

In this work, intense X-ray measurement at the Super Photon ring-8 GeV (SPring-8) facility well carried out to document the transient hydraulic phenomena in the molten pool during the laser welding process. Based on in-situ observation of inside material, the experimental results confirmed that the molten pool shapes, hydraulic condition such as flow velocity, etc.. In the case of laser power is 330W and spot diameter is 1mm, we observed the steady flow which consisted of downward flow and upward flow. The flow velocities were about 19.5 mm/s and 9.0 mm/s, respectively. Moreover, the rate of phase change was obtained from molten pool shape during laser welding. The rate of phase change was not constant during laser welding. Thus the interface shape might change at all time. Therefore, to evaluate the temperature distribution, it is necessary to consider not only convection but also the interface shape.

These results indicate that the intense X-ray measurement during laser welding is very effective for the understanding the molten pool phenomena.
Cyclic Visco-Plasticity Testing and Modelling of a Service-Aged P91 Steel
Authors: Hyde C. J. , Sun W. , Hyde T. H. , Rouse J. P. , Farragher T. , O’Dowd Noel P. , Leen S. B.
Published: August 2013

A service-aged P91 steel was used to perform an experimental programme of cyclic mechanical testing in the temperature range of 400°C to 600°C, under isothermal conditions, using both saw-tooth and dwell (inclusion of a constant strain dwell period at the maximum (tensile) strain within the cycle) waveforms. The results of this testing were used to identify the material constants for a modified Chaboche, unified visco-plasticity model, which can deal with rate-dependant cyclic effects, such as combined isotropic and kinematic hardening, and time-dependent effects, such as creep, associated with visco-plasticity. The model has been modified in order that the two-stage (non-linear primary and linear secondary) softening which occurs within the cyclic response of the service-aged P91 material is accounted for and accurately predicted. The characterisation of the cyclic visco-plasticity behaviour of the service-aged P91 material at 500°C is presented and compared to experimental stress-strain loops, cyclic softening and creep relaxation, obtained from the cyclic isothermal tests.
Estimation of SCC Crack Growth Behavior Under Weld Residual Stress in the Bottom of a Reactor Pressure Vessel by Finite Element Analysis
Authors: Iwamatsu Fuminori , Miyazaki Katsumasa , Mochizuki Masahito
Published: August 2013

Crack growth behavior intended for stress corrosion cracking under residual stress was estimated by repeatedly calculated 3-dimensional finite element analysis. The analytical estimation enables consideration of complicated stress distributions, such as weld residual stress, and expression of arbitrary crack shapes. Estimated weld residual stress for non-cracked components was distributed on the crack surface on the basis of superposition principle in order to calculate stress intensity factors. Specifically, the user subroutine DLOAD to specify a non-uniformly distribution load in ABAQUS was applied in the finite element analysis. Arbitrary crack shapes due to the crack propagation were expressed by applying the sub-modeling. The sub-modeling facilitated automatic modeling of cracked components. The estimation results intended for a SCC crack in the bottom of the reactor pressure vessel expressed the complicated crack growth shape along the weld metal. Moreover, crack growth behavior was estimated using the influence function method. The influence function method assumes arbitrary stress distribution and semi-elliptical crack shapes. Applicability of the influence function method was confirmed by comparisons with FEA results.
Advances in Hypercompressor Valve and Valve Spring Design
Authors: Bagagli Riccardo , Capanni Alessio , Maggi Carmelo , Tognarelli Leonardo
Published: August 2013

The life of valves is extremely important for the availability of hyper-compressors in LDPE plants.

The valves operate due to the action of the differential pressure across a moving element, typically with a poppet shape, and close due to the action of dedicated counteracting springs housed into the same valves. A proper design of the spring is a balance between ensuring the “on time” opening/closure of the valve, a low impact velocity of the poppet and low fluttering.

Particular attention shall be paid to the dynamic behavior avoiding to excite the spring and poppet-spring system close to themselves resonance frequencies. Different factors such unexpected transient conditions or vortex shedding phenomena could shorten the life of valves springs and valves bodies, since the valve spring is forced to operate out of the design conditions.

A compressor application presenting evidence of spring surge phenomena (resonance of spring itself) is presented. Frequencies exciting spring natural modes frequencies can be introduced in the process gas by vortex shedding generated along the gas outflow through the valve during the transient conditions or in regime conditions.

Since the vortex shedding frequency predictability is affected by some bias inaccuracy level coming from process variability and model approximation, then a robust design approach is to employ progressive spring that is insensitive to surge phenomena.

This paper gives an overview of progressive and non-linear springs and the benefits they offer compared to linear springs and how progressive springs has to be designed for hyper-compressor valves application. Several spring designs are analyzed with a simplified prediction model, the results (load deflection, stiffness, natural frequencies, fatigue lives) are then compared with finite element analysis and bench tests results using a specifically developed test bench allowing to measure spring natural frequencies and to conduct accelerated fatigue testing.
Reliability-Based Fatigue Design for Piping Using Spectrum Characteristics
Authors: Sakai Shinsuke , Maeda Jyunki , Takanashi Masahiro , Satoshi Izumi
Published: August 2013

A reliability-based approach can play an important role in avoiding excessive conservative design for piping. We showed a formulation for applying the limit state function method to reliability-based fatigue design at the previous PVP conference. Using this method, the reliability can be expressed by two dominant parameters: the distribution of equivalent stress and the distribution of fatigue life. If the equivalent stress under stationary random loading can be related to some specific spectrum parameters, it is expected that reliability-based fatigue design can be achieved under random loading. Fatigue damage under random loading is usually estimated using Miner’s law together with the SN diagram. In applying Miner’s law, the random wave is decomposed to the fatigue range using some counting method. The rainflow cycle counting (RFC) method is widely used as a counting method. In view of design application, however, the estimation of fatigue damage from spectrum characteristics is important, and the RFC method is not necessarily suitable for this purpose because it is rather difficult to use in the analytical treatment. Fortunately, it has been shown that the level crossing counting (LCC) method provides a more conservative estimation when compared with the RFC method and the analytical treatment for the evaluation is available. In this paper, we will show a procedure for reliability-based fatigue design which evaluates fatigue damage using the LCC method, spectrum characteristics and Miner’s law.
Experimental Investigation of In-Plane Constraint and Out-of-Plane Constraint Effects on Creep Crack Growth
Authors: Tan Jian-Ping , Wang Guo-Zhen , Xuan Fu-Zhen , Tu Shan-Tung
Published: August 2013

In order to establish an accurate integrity assessment of structures containing defects at high temperature, it is necessary to clarify the constraint effect on creep crack growth (CCG) property. However, the experimental investigation of constraint effects on creep crack growth has been little studied. In this study, the effects of the out-of-plane constraint and the in-plane constraint were investigated and considered via data obtained from compact tension (CT) specimens with different thicknesses and single edge-notched tensile (SENT) specimen. The results show that the constraint effect induced by specimen thickness (out-of-plane) and specimen types (in-plane) on CCG rate is related to load level C*. In the lower C* region, there are obvious differences in the CCG rate for different specimens, while the CCG rates of the different specimens are within a scatter band in the higher C* region. Meanwhile, the CCG rate da/dt versus C* on log-log scale is composed of two straight lines with different slops instead of a single linear relation. Because the straight line slope in the lower C* region is smaller than that in the higher C* region, it would be non-conservative if the CCG rate in the lower C* was extrapolated from that in the higher C*. Therefore, in order to conduct integrity assessment and life prediction at high temperature accurately, it is necessary to obtain the actual CCG rate in the lower C* (long-term data), and the constraint effect induced by specimen thickness and loading modes should be considered.
Development of a Web-Based RBI Program for LNG Plant Considering Cryogenic Environment
Authors: Kim Joo-Dong , Choi Song-Chun , Choi Jae-Boong
Published: August 2013

Recently, Risk-Based Inspection (RBI) evaluation technique based on API 581 has become a preferred approach to determine economic feasibility and safety to plants. However, there are limitations of applying API 581 to Liquefied Natural Gas (LNG) plant because its liquefaction process is operated in cryogenic temperature under −162 °C. It could affect the risk of main components in liquefaction process, but API code considered the temperature range of about −40∼149 °C to evaluate the brittle fracture damage factor. The objectives of this paper are to develop a RBI program based on a web-based reality environment to resolve the above issue and to evaluate the risk of equipment in LNG plant. To achieve these, Minimum Design Metal Temperature (MBDT) region of impact test exemption curves were extended to about −196 °C. Risk evaluation results considering cryogenic temperature and applicability of the proposed RBI program are fully discussed in the paper. The proposed RBI program will be useful to evaluate risk of the major components in cryogenic environment.
Error Analysis for FEM Analysis of Cracks Using Submodels
Authors: Gloger Daniel , Enderlein Marco , Kuna Meinhard
Published: August 2013

In order to assess the safety against fracture of nuclear shipping casks, drop tests are simulated using the finite element method. The simulations are based on a global model without defects. From the results positions are derived at which a crack initiation from a defect would be most likely. At each of these positions a submodel with a crack is inserted. The insertion of the crack changes the stiffness and therefore the stress of this region. Depending on the submodel size the calculated fracture mechanics parameters deviate from the reference value found without using the submodel technique.

The objective is to determine this deviation only from one submodel. A practicable method for the determination of the required submodel size is developed calculating the difference of the traction vector between the submodel with opened and with closed crack. Its scalar product with the weight function results in the contribution of the submodel boundary to the deviation. Integrated over the boundary it yields the deviation of the submodel. The shape of the submodel can be optimized by expanding sections of the submodel boundary with a high contribution.
Finite Element Modelling of Reduced Pressure Electron Beam Stainless Steel Plate and Pipe Welds
Authors: Pellereau Benjamin M. E. , Hurrell Paul R. , Gill Christopher M. , Ayres Kevin
Published: August 2013

Rolls-Royce plc is conducting work to investigate the feasibility of using Reduced Pressure Electron Beam Welding (RPEB) for thick section welded joints in power plant construction. As part of the work, simple specimens have been manufactured at TWI ltd in order to develop welding parameters and conditions and to examine the achievable weld quality. Previous work in this project has shown good correlations between measured and predicted stresses in RPEB welds in ferritic components [5,6].

This paper describes Finite Element (FE) modelling that was carried out to try to predict the residual stress field generated by the welding process in three of the specimens. The first specimen that was modelled was a full penetration butt weld in 80 mm thick Type 316L plate (W17). The other two models were of circumferential butt welds in 14 inch nominal diameter Type 304L pipe. The first pipe model (W20) was a single pass, 360° weld, while the second (W22) featured a slope-up and slope-down each lasting for 16° either side of a 360° full penetration weld, giving a total weld of 392°. The modelling was carried out in Abaqus [1] using a DFLUX user subroutine to model the welding heat input as a cylindrical heat source, due to the reduced pressure during specimen manufacture, only radiation heat losses were considered. The built-in Chaboche mixed hardening model was used for both materials during the structural analysis.

The residual stresses predicted by the FE modelling have been compared with the results of Deep Hole Drilling (DHD) that was carried out on the equivalent specimens. Full details of the measurements are reported in [4].
Code Aspects Related to Combination of Stresses due to Hydrogen Detonation: Beam and Combined Effects
Authors: Minichiello John C. , Ligon Thomas C. , Gross David J.
Published: August 2013

Stresses in piping systems subject to hydrogen detonation loading are complex. There are high-frequency localized shell-type stresses, such as hoop membrane, longitudinal through-wall bending and hoop through-wall bending due to asymmetric modes. There are low-frequency gross beam-type stresses, similar to those from a waterhammer, as the unbalanced forces excite the beam bending and bar wave modes in the piping system. From a code compliance standpoint, all the stresses need to be considered and categorized in terms of the type of failure that they can cause.

Part 1 developed a method to estimate the local shell stresses due to the detonation wave. This paper, Part 2, discusses an investigation into the global beam bending effects. It proposes a methodology for combining the beam and local shell effects, and evaluating the results in terms of complying with a typical piping code.

The gross stresses due to the propagating detonation wave can be evaluated using beam-finite element models and time-history analysis, similar to analyses for waterhammer. As with waterhammer, these stresses are typically considered “occasional” loads. However, the beam stresses can coincide with very high hoop or radial shell stresses, due to the high peak pressures involved, so that the simple comparison of using longitudinal stresses may not be an adequate design check. This paper recommends a combination of shell-equivalent stresses and beam-stress intensities that result in a conservative comparison, when compared to a full time-history analysis, but one which is not overly conservative.

With the exception of ASME Section III, Class 1, most U.S. piping codes do not provide rules for fatigue evaluation for loads other than displacement controlled loads. ASME B31.3 Appendix P provides guidance for pressure fluctuations, but the focus is primarily gross stress effects. The local effects from a detonation wave include both a “skin” stress effect on the inside surface and a through-wall bending effect due to the dynamic nature of the effects of the propagating wave. Both of these must be considered if the number of occurrences is significant. This paper proposes a method to consider these localized stresses that is patterned after the guidance in ASME Section III, NB-3600.
Effect of Ageing on Residual Stresses in Welded Stainless Steel Cylinders
Authors: Do Son , Smith David , Smith Mike
Published: August 2013

Operation of components at high temperature in power stations leads to the relaxation of residual stresses created in welded stainless steel cylinders. In this work a number of Esshete 1250 stainless steel cylinders containing girth welds and repair welds were manufactured. Two cylinders were then put to a furnace for 10,000hrs and 20,000hrs at 650°C. These conditions simulated the effects of aging.

The residual stresses in the girth welds and repair welds before and after aging were measured using a number of methods based around the Deep Hole Drilling method. This paper describes the experiments carried out to obtain the through-wall distribution of stresses.

It is evident that there was significant relaxation of the residual stresses due to aging. The peak tensile residual stress in girth welds was relaxed from 500MPa to 110MPa and the peak compressive residual stress in girth welds was relaxed from −301MPa to −135MPa after 10,000 hours at 650°C. The repair weld residual stresses were not only relaxed at the peak stresses but relaxed average levels from 220MPa to 140MPa for hoop stresses and from 180MPa to 145MPa for axial stresses. The implications of these findings are discussed in the context of future fracture tests.
Detonation and Transition to Detonation in Partially Water-Filled Pipes
Authors: Bitter Neal P. , Shepherd Joseph E.
Published: August 2013

Detonations and deflagration-to-detonation transition (DDT) are experimentally studied in horizontal pipes which are partially filled with water. The gas layer above the water is stoichiometric hydrogen-oxygen at 1 bar. For detonation cases, ignition and transition occur outside of the water-filled section. For DDT cases, ignition and transition occur over the surface of the water. Pressure and hoop strain are measured incrementally along the pipe, with pressure transducers located both above and below the water. The detonation wave produces an oblique shock train in the water, and the curvature of the pipe is seen to focus the shocks at the bottom, resulting in peak pressures that are 4–6 times higher than the peak detonation pressure. Such pressure amplification is observed for water depths of 0.25, 0.5, 0.75, 0.87, and 0.92 pipe diameters. For a water depth of 0.5 diameters, pressure is also recorded at several circumferential locations in order to measure the shock focusing phenomenon. Peak hoop strains are found to decrease with increasing water depth, and transition to detonation is seen to occur for water depths as high as 0.92 pipe diameters.
Finite Element Based Analysis of Bolted Joints Under Extreme Loading Conditions
Authors: Kummari Seetha Ramudu , Dewees David J. , Brown Robert G.
Published: August 2013

A case study is presented for a heat exchanger subjected to a postulated beyond-design basis over-pressurization. Gasket behavior is explicitly modeled with commercial FEA software, and tuned to experimental data. Material (strain-hardening plasticity) and geometric nonlinearities are also accounted for. Both two-dimensional and three-dimensional analysis is performed and compared, and all results are compared with standard ASME Code design criteria for bolted joints leakage. Recommendations for use of FEA technology to assess the behavior of bolted joints subject to extreme loading behaviors are presented.
Alternative Selections of Delayed Coke Drum Materials Based on ASME Material Property Data
Authors: Nikic Milan , Xia Zihui
Published: August 2013

Severe cyclic thermo-mechanical operating conditions during delayed coking can cause damages in the form of bulging and cracking in coke drums. As a result, the industry has to perform costly repairs and maintenance shutdowns. Therefore, it is important to understand the damage and failure mechanisms of the coke drums and to achieve more reliable coke drum design solutions. This paper explores alternative selections of clad and base material combinations for coke drum applications based on material property data provided in ASME Boiler & Pressure Vessel Code, Section II - Materials. Finite element analyses are carried out by simulating two critical loading scenarios in the coke drum operation cycle, i.e. the heating up and quenching stages. The analysis results show that the major achievement in lowering the stress level in the clad layer is due to matching of the coefficients of thermal expansion between clad and base materials. In addition, the finite element analyses indicate that the differences in Young’s modulus values play an important role in the variation of maximum stress in the coke drum shell during the quenching stage. Among eleven pairs of the clad and base material combinations studied, the combination of SA302-C as the base and nickel alloy N06625 as the cladding material is recommended.
A Full-Field Residual Stress Profile Estimation Scheme for Pipe Girth Welds
Authors: Song Shaopin , Dong Pingsha , Zhang Jinmiao
Published: August 2013

For supporting fitness-for-service (FFS) assessment, this paper presents a method for providing a full field description of through-thickness residual stress profiles for pipe girth welds, beyond weld locations (e.g., at weld centerline and weld toe). The paper starts with a brief introduction of the finite element modeling procedure used in this study. Experimental validations are performed for a pipe weld geometry on which detailed experimental data have recently become available in the literature. Then, a large number of parametric residual stress analyses are performed to identify key parameters that govern through-thickness residual stress distribution characteristics. These parameters are not only shown to uniquely contribute to some of the important residual stress distribution characteristics of interest to FFS, but also can be formulated, to the first approximation, using basic mechanics and physics principle. Finally, a detailed application of the proposed full field residual stress estimation scheme is illustrated for various girth weld conditions.
Effective Modeling of Fatigue Crack Growth in Pipelines
Authors: Polasik Steven J. , Jaske Carl E.
Published: August 2013

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.
Snubber Optimization Utilizing Gapped Struts in Nuclear Power Plants: River Bend Station
Authors: Singley Matthew P. , Gray John H. , Verma Vijay K. , Pressburger Maury A. , Chatterton Glenn
Published: August 2013

At Entergy River Bend Station (a 978 MWe BWR located near Baton Rouge, Louisiana) snubber examination and testing have become unwanted expenses with the potential to lengthen planned outages and increase ALARA concerns. This paper presents a new concept for snubber replacement which can be used to expand the “Snubber to Strut” methodology. The E-BAR is a passive gapped support fabricated to be a “drop-in” replacement for snubbers. During normal plant operation the E-BAR functions like a box support, and during dynamic loading the E-BAR limits pipe motion and functions as a seismic restraint. Combining the guidance of WRC-300 [1] (snubber to strut criteria) and the industry practice of installing box supports with 1/16″ gaps between the pipe face and steel frame, generic criteria were developed to facilitate drop in snubber replacements. Replacements based on these criteria do not require re-analysis of the piping system. At the River Bend Station 102 snubbers were identified with thermal movements between 1/16″ and 3/8″. Sixty four snubbers (> 60%) met the generic criteria and were shown to be located at appropriate locations for snubber replacement. Development and explanation of the generic criteria and their applications are discussed here-in.