bluuebunny/crossref_metadata_2025 huggingface dataset:
Grade 11 High Temperature Steam Header Case History and Benchmark
Authors: Dewees Dave
Published: December 2016

The cost and complexity of design method validation at the component level makes actual and comprehensive benchmark cases challenging to obtain. This is especially true of elevated temperature design methods where component and material response is complicated by time-dependent creep and possibly creep-fatigue behavior. To support current Design-by-Analysis modernization development within Section I of the ASME Boiler & Pressure Vessel Code, service examples that are comprehensive enough to allow method validation, while still being tractable in complexity have been identified. To this end, the case history of a Grade 11 high temperature steam outlet header that was retired after 23 of years of service is presented. Detailed damage and deformation information is available which allows validation of creep material models, as well as future evaluation of candidate elevated temperature design method performance.
Crack Growth Simulation Under Complicated Stress Field Using S-Version FEM
Authors: Masaki Koichi , Osakabe Kazuya , Takahashi Akiyuki , Wada Yoshitaka , Kikuchi Masanori
Published: December 2016

In the S-version finite element method (S-FEM), a local detailed finite element mesh (local mesh) is superimposed on a coarse finite element model (global mesh) representing the global structure. In the S-FEM developed by Tokyo University of Science, the virtual crack closure integral method is employed to evaluate the stress intensity factor, and a local mesh is re-meshed automatically, which enables easy simulations of crack growth by users. Using S-FEM, crack growth can be simulated in both two- and three-dimensional stress fields, under thermal stress field, under welding residual stress field, and in multiple materials. This paper reports the latest results of the simulations of crack growth in the presence of complicated stress fields.
Fatigue Analysis of Cladded HPHT Pressure Containing Equipment
Authors: Karpanan Kumarswamy , Gatherar Nicholas
Published: December 2016

Large, pressure-containing equipment used in subsea production, including Christmas trees (XTs), gate valves, flowloops, jumpers, and connectors, are constructed of low-carbon steel and cladded with corrosion resistant alloys such as Alloy 625. Cladding is a welding process that generates high tensile residual stresses on the cladded layer and on the heat affected zone (HAZ). High pressure high temperature (HPHT) equipment for subsea applications, designed to operate above 15 ksi internal pressure and 350°F, is also cladded. This equipment experiences severe working conditions in the field, plus cyclic loading during operations, such as riser loads, installation, intervention and, most importantly, startup and shutdown sequences. Per API 17TR8 guidelines, all HPHT equipment be hydrostatically tested to 1.5 times the equipment rated working pressure (RWP). For 20 ksi equipment, the hydrostatic test pressure is 30 ksi, which can significantly deform any highly localized stressed regions. These regions deform plastically when test pressure is applied. When the pressure is bled, these regions experience high compressive stresses due to surrounding materials that are still elastic.

This paper analyzes a simplified HPHT cladded gate valve (GV) body for fatigue loading (pressure cycles only) using the ASME Sec VIII, Div-3 method. The fatigue stress amplitude is calculated using an elastic-plastic material (E-P method) finite element analysis. In this method, first, the residual stress from the cladding process is simulated, and then the hydrotest is simulated on the component. During the hydrostatic test, fatigue sensitive regions (FSRs) or highly localized stressed regions such as the valve cavity and seat pockets, deform plastically, and the initial weld tensile residual stress turns to compressive (similar to autofrettage). Later, when these components are subjected to working pressure cycles (startup and shutdown), the shear stress range remains the same but the mean stress on the FSR reduces significantly. By considering all types of residual stresses, the high cycle fatigue life can be predicted with a high degree of accuracy.
Correlation on Scatter Between Torque Coefficient and Bolt Preload in Pipe Flange Connection
Authors: Omiya Yuya , Fujii Masahiro
Published: December 2016

In this paper, a mechanism of variation in axial bolt force in pipe flange connection during bolt tightening process is investigated. Especially, Correlation between torque coefficient and bolt preload is investigated. The actual pipe flange connection is tightened by a wrench due to the torque control method. Axial bolt forces were measured in the tightening process. The three types of gasket are chosen in this paper. As a result the good relationships are seen between torque coefficient and axial bolt force. The effect of gasket material on the relationships between torque coefficient and bolt preload is not seen.
Thermal Stress Calculation Based on Enhanced 3-Dimensional Green’s Function Approach Considering Temperature-Dependent Effect
Authors: Surh Han-Bum , Choi Shin-Beom , Kim Jong-Wook , Ko Han-Ok
Published: December 2016

In this paper, an enhanced 3-dimensional (3D) Green’s function approach (GFA), which can be utilized more practically in fatigue monitoring systems, is proposed. The proposed approach can not only calculate the accurate thermal stress history since it considers the temperature-dependent effect, but it also enables a robust calculation of the thermal stress since the steady state term is separated. To verify the proposed approach, thermal stresses of the System integrated Modular Advanced ReacTor (SMART) shutdown cooling system (SCS) nozzle subjected heat-up transient are calculated based on the proposed 3D GFA, and are compared with results computed by a detailed finite element (FE) analysis considering the temperature-dependent material properties. Since the comparison results are in good agreement with each other, it is concluded that the proposed approach enables an accurate thermal stress evaluation in fatigue monitoring.
Measurement of Hydride Precipitation and Dissolution Kinetics Using Synchrotron X-Rays
Authors: Shiman Oksana , Tulk Eric , Daymond Mark R.
Published: December 2016

Structural components of nuclear reactors made from zirconium alloys are subject to degradation mechanisms associated with hydrogen pickup during their operating life. Even small amounts of hydrogen isotopes (∼tens of wt. ppm) can significantly reduce the material’s fracture toughness and make it susceptible to a sub-critical crack growth mechanism known as Delayed Hydride Cracking (DHC). The mitigation of potentially costly failures of these components requires assessments based upon not only the bulk concentration of hydrogen, but the concentration of hydrogen precipitated as hydrides, and in solution. The behaviour of the zirconium-hydrogen system near ∼100 ppm hydrogen concentration continues to be the subject of research, primarily due to its otherwise complex behaviour and critical role in nuclear plant operations. There is an anisotropic volumetric expansion associated with the precipitation of zirconium hydride, and this precipitation event results in plasticity in the surrounding matrix and compressive strain in the hydride phase. This leads to both a pronounced solubility hysteresis upon dissolution and precipitation, as well as variances in solubility behaviour depending on the prior thermal and mechanical history.

In the present study, high-energy synchrotron x-ray diffraction is used to study the evolution of hydrogen solubility in Zr-2.5 wt% Nb pressure tube material with different hydrogen concentrations in situ during thermal cycling between 100 and 400°C. This technique provides the ability to directly measure the amount of hydride in a given sample at different temperatures, and to evaluate zirconium-hydrogen precipitation and dissolution kinetics.
Weld Residual Stress and Creep-Fatigue Analysis of a Furnace Roll in a Continuous Hot Dip Coating Line
Authors: Yang Yu-Ping , Mohr William C.
Published: December 2016

A catastrophic furnace roll failure was observed in a continuous hot dip line. The failure occurred in the weld joining an end bell to a roll shell and resulted in the complete separation of the end bell from the roll shell. The roll had been in service for approximately 7 months before failure. Typically, rolls in this furnace roll position have a short life, less than 1 year. The roll shell and the end bell were made of high-temperature alloy. The journal was made of stainless steel. Inconel welding electrode was used as the weld filler material. The roll shell and the end bells were shrink fitted before welding. The welding process was flux-cored arc welding (FCAW). Upon completion of welding post-weld heat treatment (PWHT) was applied for 3 hours at 1093°C to the entire roll. To extend the roll life, a new design and a new welding method, electron beam welding (EBW) without filler metal, were proposed. To evaluate the effectiveness of the new design and the new welding process, four kinds of numerical analyses were conducted on the new design for both FCAW and EBW which included a weld residual stress analysis, a PWHT analysis, a heat transfer analysis, and a creep-fatigue analysis. Analysis results showed that the new design with EBW has lower stress and creep strain than with FCAW, which could improve the roll creep-fatigue life.
Probabilistic Failure Assessment of a Complex Nozzle Structure With Flaw Defect Based on FITNET Procedure
Authors: Wang Yan , Wang Yan-Wei , Chen Hanxin , Ma Linwei
Published: December 2016

A probabilistic failure assessment based on the fracture and fatigue modules of European FITNET procedure is presented in this work. Analysis of the leak probability of a complex nozzle structure with postulated flaw defect under thermal mechanical loading is performed. Crack growth is calculated using FITNET fatigue module, in which the crack driving force ΔKeq considering mixed-mode load is applied. For the structural safety evaluation, the failure assessment diagram (FAD) within the frame of FITNET fracture module is utilized with the parameter Keff combing KI and KII. The fracture mechanical parameters are calculated using finite element (FE) method because of the complex geometry and load conditions. To meet the needs of probabilistic analyses, formulas calculating crack driving force are developed specific for this nozzle structure through nonlinear regression based on the FE results. With an initial crack depth of 5 mm, the nozzle failure probability in form of leak comes to 1.84×10−4 in next fifty years. The good agreement of the results of Monte Carlo simulation and stratified sampling technique confirms that the crack growth parameter C and the initial crack shape ratio c/a have considerable effect on the structural failure probability.
Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Affected by Hydrogen Flakes: Refined X-FEM Analyses
Authors: Dulieu Pierre , Lacroix Valéry
Published: December 2016

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, specific ultrasonic in-service inspections revealed a large number of quasi-laminar indications in the base metal of the reactor pressure vessels, mainly in the lower and upper core shells. The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process.

As a consequence, a Flaw Acceptability Assessment had to be performed as a part of the Safety Case demonstrating the fitness-for-service of these units.

In that framework, detailed analyses using eXtended Finite Element Method were conducted to model the specific character of hydrogen flakes. Their quasi-laminar orientation as well as their high density required setting up 3D multi-flaws model accounting for flaw interaction.

These calculations highlighted that even the most penalizing flaw configurations are harmless in terms of structural integrity despite the consideration of higher degradation of irradiated material toughness.
Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs Linear Elastic and Elastic-Plastic X-FEM Calculations Performed for Large Scale Tests
Authors: Lacroix Valéry , Dulieu Pierre
Published: December 2016

In the framework of the hydrogen flakes issue concerning the reactor pressure vessels of the two Belgian NPP’s Doel 3 and Tihange 2, the Federal Agency of Nuclear Control required to perform tests on large scale specimens taken from a block representative of the pressure vessels with the double objective of validating the structural integrity approach and of verifying the load capacity of the specimens affected by flakes.

The large scale tests were led on many kinds of specimens: 4 points bending specimens, CT specimens and tensile specimens containing hydrogen flakes or flawed with EDM notches. All of these tests have been simulated using extend finite element method (XFEM).

The paper describes the linear elastic and elastic-plastic fracture mechanics calculations performed in the frame of these large scale tests using XFEM and presents the comparison between simulations and experiments.

A focus is done on the XFEM capabilities to model 3D complex shaped flaws like hydrogen flakes.
Effect of the Thickness on Re-Characterisation of Subsurface to Surface Flaw: Application on Piping and Vessels
Authors: Lacroix Valéry , Katsumata Genshichiro , Li Yinsheng , Hasegawa Kunio
Published: December 2016

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule.

The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes in different countries. However, the specific criteria of the recharacterizations are different among the FFS codes.

The authors have proposed a new subsurface-to-surface flaw proximity rule based on experimental data and equivalent fatigue crack growth rates.

Recently, the authors have highlighted through numerous fatigue crack growth calculations that, on one hand, the proximity rule provided in the current ASME Boiler and Pressure Vessel Code Section XI (ASME Code Section XI) can provide non conservative fatigue lives for thin wall components like pipes and, on the other hand, for thick wall components like vessels, the current proximity rule and the proposed one provide relatively similar fatigue lives.

It appears therefore that the flaw-to-surface factor should be updated according to the thickness of the component or according to the type of component i.e. pipe or vessel.

In this study, fatigue crack growth calculations were carried out on additional flaw configurations in thick wall pipes and thin wall vessels in order define the best limit for the thickness-dependence of the fatigue lives.

Finally, a new subsurface to surface proximity rule depending on the thickness of the component is proposed.
The Effects of the Downstream Vane on the Torsional Vibration of the Upstream Vane
Authors: Takeyama Daiki , Shioyama Tsutomu , Osaki Kenji , Watanabe Masanobu , Nakazono Masahiko
Published: December 2016

Some hydraulic turbines sometimes have severe flow-induced vibrations on their vanes. One is the torsional vibration of the stay vane. This vibration occurred despite the stay vane profile was selected to avoid generating large Karman vortex. This vibration was influenced by the guide vane. In this paper, the effects of the attack angle of the downstream vane on the torsional vibration of the upstream vane were examined by about 1/20 scale stay vane experimental equipment. First, the relationships between the attack angle of vanes and the limit of the reduced flow velocity inducing the torsional vibration of the upstream vane were examined. The large torsional vibration of the upstream vane did not occurred without downstream vane. But, the large torsional vibration occurred when the reduced flow velocity exceeds a critical value with the downstream vane. It was substantiated the limit of the reduced flow velocities were 1.5 and 3.0. The large vibration was only generated under a specific velocity range. The dominant torsional vibration frequency slightly increased from 35Hz to 45Hz with the reduced flow velocity. When the attack angle of the upstream vane and the downstream vane were series along streamline, the vibration became large. Next, the torque coefficient and Strouhal number of the upstream vane were evaluated. The torque coefficient for the upstream vane attack angle with the downstream vane was positive. This result showed the upstream vane will occur. And, Strouhal number was 0.35 at the reduced flow velocity 3.0. Strouhal number is near to 0.3 which is result of the previous study of stay vane. There is a possible of the generating vortex.
Fluid-Structure Interaction in the Nozzle of Collunarium Container
Authors: Yamaguchi Daisuke , Inaba Kazuaki
Published: December 2016

Nasal administration of the vaccine is in the spotlight and the medicine has been developed in recent years. The medication is carried out by spraying the medicine in the nasal cavity by collunarium container. The top nozzle part of a common collunarium container consists of three parts, nozzle tip having an exit, cylindrical nozzle, and stepped center rod which is inserted into the nozzle. We confirmed that the spray of collunarium container consists of two stages phenomena (initial jet and its disintegration, and steady spray stage) by visualization with high-speed video camera. Since we found that the initial jet impacted with larger droplet size than later sprayed droplet, we examined the initial jet and steady spray stage in experiments and numerical simulations to study the effect of material and dimension of the rod. The dimensions of the center rod affected the acceleration of the initial jet front and the spray angle in experiments. In numerical simulations including fluid-structure interaction (FSI), lower density rod moved at faster speed and excited higher flow velocity at the exit in the jet stage. Moreover we confirmed that the acceleration of the jet was initiated by the water hammer wave propagation inside the nozzle.
Research on Tightness Performance of Corrugated Gasket Bolted Flanged Connections System
Authors: Li Xiang , Yao Cheng , Li Jiepu
Published: December 2016

A finite element calculation and a leakage rate test were carried out in order to investigate the tightness performance of a corrugated gasket bolted flanged connections system. Based on a detailed finite element model of the bolted flange connection, gasket stresses and deformations were determined for room temperature operating conditions. Leakage testes were then performed to acquire leakage data at different gasket compression stresses and different internal pressures. The data was fit to a leakage rate formula. Additional analysis was performed to investigate the influence of temperature.
Applicability of the Taylor Forge Method for Flange Design to High Pressure Bolted Joint Flanges With Lens Ring Gaskets
Authors: Fuenmayor David , Wink Rolf
Published: December 2016

The design-by-formula methodology used by the ASME Code for bolted-flange joints offers no guidance for the determination of flange stresses for high-pressure applications. More specifically, it offers no guidance for bolted joint connections using lens ring gaskets. The Taylor Forge Method adopted by the Code in Appendix 2 of Division 1 and Paragraph 4.16 of Division 2 has well known limitations, most notably: (a) the joint elements are modeled using simplified plate and shell theory and neglecting pressure inflation effects, (b) the nozzle-neck axial pressure stress is omitted in the calculation of the longitudinal hub stress, and (c) the pressure end load HD is assumed to act through the mid-thickness of the large end of the hub. In addition, the so called maintenance factor m, and the design seating stress y, are not defined for this type of partially self-sealing gasket. Lens ring gaskets are line contact seals based on the unsupported area principle. According to this principle, the internal pressure acting on the uncompensated lateral surface forces the lens towards the edge of the cone increasing the load on its sealing surfaces. The calculation of the forces and moment exerted on the flange as a result of this loading is also not considered in the methodology used by the ASME Code. In this article a study of the state of stresses for High Pressure Bolted Joint Flanges with Lens Ring Gaskets is carried out by means of Finite Element Analysis. The results of the numerical analysis are compared to those obtained by applying the formulae in Appendix 2 of ASME VIII Division 1 in order to determine to which extent these analytical expressions can be used while preserving the safety margins seen for regular flanges.
Assessing the Behaviour of Subsea Pipes Under Impact
Authors: Fareed Shamsoon , Cotsovos Demitrios M. , Laghrouche Omar
Published: December 2016

Subsea steel pipes are often used to form extensive networks for transporting oil and gas over large distances. Such pipes can potentially be subjected to actions characterized by high loading rates and intensities stemming from accidental loads, due to high-mass low-velocity impacts. In order to ensure that such networks can continue to operate even after being subjected to such extreme loading conditions, it is essential that the behavior of the pipes is characterized by a certain level of resilience. The present study aims to investigate numerically, via dynamic nonlinear finite element analysis, the effect of various parameters on the dynamic response exhibited by pipes under impact loading. The considered parameters are associated with the impacting object, the geometry and the support conditions of the pipes, the level of axial loading as well as the internal and the external pressures imposed onto the walls of the pipes.

The numerical predictions, which are validated against relevant published test data, reveal that the above parameters, which are associated with the in-situ conditions imposed onto subsea pipes throughout their operational life, can significantly affect, often detrimentally, the behavior exhibited under impact loading. Existing assessment methods employed in practice for predicting the level of damage sustained by pipes during impact do not accurately consider the effect of the above parameters. As a result, questions are raised concerning the ability of such guidelines to realistically predict the level of damage sustained by subsea pipes under impact.
Testing System Set-Up to Evaluate Acoustic Induced Vibration
Authors: Mann J. Adin , Eilers Daniel , Jackson Trent , Swindell Rob , Middleton Christopher , Arnett David , Horder Nicolas , Izuchi Hisao , Evans Geoff
Published: December 2016

A consortium of companies is collaborating in a Joint Industry Project (JIP) for Acoustic Induced Vibration (AIV). Laboratory testing is one of the work areas of the JIP. The goals of the tests are to evaluate typical pipe fittings for AIV induced fatigue, to rank order their AIV risk and to obtain data for validation of computational models. An NPS6x8 (6R8) pressure safety valve was the flow and noise input to a 10S piping system, which consisted of an NPS12 tailpipe input into an NPS12x20 tee. Small bore connectors (SBCs) were included in both the NPS12 tailpipe and the NPS20 header. The type of fitting used as the connection between the SBC and the pipe was varied. The system was operating in a Carucci-Mueller acoustic power of around 175 dB. Vibration acceleration response of the system was measured, and dynamic strain data was also gathered to evaluate fatigue life. The piping and data acquisition system setup will be discussed along with the type of results that are being obtained.
Validating FEA Simulations of Structural Collapse of a Complex Vessel Geometry
Authors: Mann J. Adin , Yost Brandon , Westwater Gregory , Johnson Christopher R. , Pollock Brett , Liu Katharine
Published: December 2016

Part 5 in Section VIII Division 2 of the ASME Boiler & Pressure Vessel Code provides methods for evaluating stresses in pressure vessel components using Finite Element Analysis (FEA). Both linear elastic and inelastic methods are provided. Validating the FEA simulations can be challenging because of testing procedures as well as variation between the test parts. Control valve bodies, which have a complex geometry, were tested to pressures far beyond the maximum allowable working pressure to evaluate behavior at structural collapse. The test bodies were scanned so that the true geometry was used in the FEA simulations. FEA simulations were used to perform a linear elastic evaluation and inelastic evaluations. The inelastic evaluation included various material models. The difference between a point by point comparison and outcome based validation are discussed.
Applicability of Stress Intensity Factor Solution for Flat Plate to Nozzle Crotch Corner Flaw
Authors: Iwamatsu Fuminori , Miyazaki Katsumasa , Masuda Minoru , Hirokawa Fumihito
Published: December 2016

The applicability of a stress intensity factor (SIF) solution for a flat plate with a surface flaw (flat plate model) to nozzle crotch corner flaw is investigated by using a 3-D finite element method (FEM). Flaws due to stress corrosion cracking (SCC), fatigue, etc. are frequently postulated or detected at discontinuity regions. To evaluate the structural integrity of flawed components, it is important to calculate fracture mechanics parameters rationally and appropriately. SIF is one of the key fracture mechanics parameters for linear elastic fracture mechanics evaluation. Therefore, almost all fitness-for-service codes, e.g. ASEM BPVC Section XI, JSME FFS Code and R6 provide SIF solutions. However, they essentially provide SIF solutions only for flat plates or cylinders with flaws. Since nozzle crotch corner suffers from stress concentration and there are a lot of nozzle geometry parameters, there is no direct SIF solution for arbitrary nozzle geometries. To estimate SIFs for nozzle crotch corner flaws rationally and appropriately, the applicability of the SIF solution for the flat plate model needs to be verified. SIFs were calculated by using 3-D FEM for a flawed nozzle, and the results were compared with those calculated by equations and coefficients in the code solution. Our comparison showed that the flat plate model is applicable to nozzle crotch corner flaws rationally and conservatively.
Water Hammer Event on Aboveground Section of Oil Piping During Hydro Test
Authors: Orynyak Igor , Batura Anatolii , Dubyk Iaroslav
Published: December 2016

In this article we have analyzed a water hammer event that occurred during the hydrostatic test of an oil pipeline. As a result of a significant dynamic loading event the piping was thrown off of its supports. We have performed dynamic calculations in the frequency domain with two models. The first model is a 2-DOF mass-spring model, used to perform an engineering assessment of the pipeline. The second model is a complex piping model of the aboveground section, which matches the real pipeline geometry and physical properties as well as possible. The Duhamel integral was used to calculate the transient response of the pipeline to the local water hammer impulse loading. The analysis results were used to estimate the pipeline displacement, and to develop certain practical recommendations to prevent such damage in the future.
Technical Basis for Proposed ASME Section XI Code Case on Beyond Design Bases Earthquake
Authors: Donavin Paul R. , Gilada Ramiz , Gustin Harry , Vo Truong , Pace Raymond
Published: December 2016

This paper will provide the bases for the requirements in the Beyond Design Basis Events (BDBE) evaluation performed in accordance with the American Society of Mechanical Engineers (ASME), Boiler and Pressure Vessel Code (BPVC), Section XI, Code Case (CC). The CC provides rules to facilitate the affected components Return to Service (RTS) after a BDBE magnitude Earthquake. The paper describes the bases for the examination of Reactor Coolant Pressure Boundary (RCPB) Structures, Systems and Components (SSCs) for determining the actual seismic loading and magnitude. The implications of the examination data based on design allowable stress values. The pipe loads determined shall be used to calculate stresses on the pumps and valves.

The paper also describes the methodology for seismic events lasting longer than 100 cycles.

The Cumulative Usage Factor (U) due to the event is calculated from individual cycles as; U = U1 + U2 + U3 + ... + Un. Aftershocks are accounted for in the methodology. Fatigue usage from the event that increases the total U to a value greater than 0.8 shall be included as high risk location(s) in the ASME BPVC, Section XI, Inservice Inspection (ISI) Program.
Validation of Axial Crack Stability Assessment Methods in xLPR Version 2.0 Code
Authors: Kalyanam S. , Brust F. W. , Wilkowski G. , Shim D. J. , Rudland D.
Published: December 2016

As part of the xLPR (Extremely Low Probability of Rupture) project, validation efforts were conducted to assess the predictive capability of axial surface crack (Ax-SC) and axial through-wall crack (Ax-TWC) stability modules employed for making the crack stability assessment. For the Ax-SC, the plastic collapse solution/criteria from the Ductile Fracture Handbook (DFH) was selected and employed after making detailed comparisons between the solutions obtained from the DFH and API-579/ASME FFS-1 solution methods. Experiments from past tests conducted for the Atomic Energy Commission (AEC) and by MPA-Stuttgart were used to validate the performance of the implemented axial SC stability module.

Similarly, for the axial TWC stability assessment, a Limit Load solution, and a numerical analysis procedure for an elastic-plastic fracture mechanics (EPFM) based method employing a J-integral fracture mechanics parameter approach using a GE/EPRI type J-estimation equation, and tabulated plastic influence functions based on pipe dimension and Ramberg-Osgood material parameters, were used. Experimental results from past pipe tests conducted for the AEC, others conducted for the PRCI, and by Tokyo Gas involving larger diameter pipes were used to validate the performance of the implemented axial TWC stability module.

In this paper, the selection of stability criteria/solutions, their performance and implications for the xLPR 2.0 code are discussed. The impact of using different flow stresses (function of yield and ultimate stresses), and stress magnification factor (Folias bulging factor) expressions, on the predictions is highlighted. Further, a conservative basis for the assessment of axial crack stability in welds is proposed. In closing, additional empirical corrections that can be incorporated without overly biasing the deterministic solutions/criteria that feed into a probabilistic analysis are highlighted.
Three Dimensional Weld Residual Stress Simulations of Piping Butt Welds: Influence of Boundary Conditions and Start/Stop Positions on Axisymmetry
Authors: Bonnaud Etienne , Gunnars Jens
Published: December 2016

Weld residual stress simulations have become an essential tool in structural integrity assessments. In piping, two dimensional axisymmetric simulations generally give good estimations of residual stresses but clearly cannot capture the three dimensional nature of the welding process: the start/stop effects and the constant change in mechanical restraint during a weld pass. In this study, three dimensional welding simulations have been carried out for piping butt welds, first on a dissimilar metal weld in a thin-walled pipe and second on a narrow gap weld in a thicker stainless steel pipe. The effects of mechanical boundary conditions and start/stop positions have been investigated and stress fields are shown to markedly deviate from axisymmetry. As an illustration, a fracture mechanical analysis of a partial internal surface crack reveals noticeable changes in critical crack sizes.
Ultra-Low-Cycle Fatigue Behavior of Full-Scale Straight Pipes Under Alternating Bending
Authors: Pereira João C. R. , Van Wittenberghe Jeroen , Jesus Abílio , Thibaux Philippe , Fernandes António A.
Published: December 2016

Ultra or extreme low-cycle fatigue of steels has been deserving increasing interest by the researchers since it corresponds to a fatigue domain not fully understood nor explored. It has been recognized that fatigue damage under extreme loading conditions is representative of several practical applications (e.g. seismic actions, accidental loads) and pipelines are a type of components that could undergo such extreme loading conditions. In addition, concerning the pipelines, reeling could also contribute to significant plastic cycles. ULCF damage corresponds to a transition damage behavior between the LCF and monotonic ductile damage. Therefore studies on ULCF usually needs to cover those bounding damage processes. ULCF testing exploring large-scale specimens is rare. The aim of this paper is to investigate the ultra-low-cycle fatigue of large-scale straight pipes subjected to cyclic pure bending tests which were performed under the framework of the ULCF European/RFCS project. In detail, two steel grades used on pipelines manufacturing were investigated, namely the X60 and X65 piping steels, respectively with the following nominal diameters of 16” (w.t. 9.5 mm) and 8 5/8” (w.t. 5.59 mm). A specifically developed testing setup was used to perform the cyclic bending of the straight pipes, combined with internal pressure, until the pipes collapse. The failure was preceded by local plastic instability (buckling), motivating the concentration of cyclic plastic deformation leading to macroscopic crack initiation and propagation. In addition to the full-scale tests, the plain material was investigated under monotonic and ULCF conditions using both smooth and notched specimens. In order to assess the stress/strain fields in the straight pipes, finite element models of the straight pipes were developed and simulations were performed under the experimental displacement histories. Nonlinear plasticity models with kinematic hardening, inputted on finite element simulations, were calibrated by means of small-scale data. Moreover, the test data of small-scale tests was used on the identification of damage models constants (e.g. Coffin-Manson), which in turn were applied to simulate the failure cycles of the tested straight pipes. The ASME B&PVC VIII Div.2 procedures were also used to compute the failure cycles for the straight pipes to allow an assessment of these existing procedures.
Impact of Near-Fault Ground Motions on the Efficiency of Viscous-Damping Systems
Authors: Huang Yin-Nan , Liu Chia-Ren
Published: December 2016

Energy dissipation systems can effectively reduce the seismic demands of structures and protect them from damage. However, the effectiveness of the systems is not entirely independent from the dynamic characteristics of ground motions and may be challenged by long-period velocity pulses in near-fault ground motions. The major focus of this study is to clarify the impact of the characteristics of near-fault ground motions on the effectiveness of energy dissipation systems, particularly, structures equipped with viscous dampers. A series of response-history analyses are conducted using single degree-of-systems (SDOF) with periods varying between 0.2 and 5 seconds and damping ratios between 5% and 50% and subjected to fault-normal components of 91 sets of near-fault ground motions identified in a literature prepared by Prof. Jack Baker in 2007. The effectiveness of damping in reducing seismic demands of SDOF systems subjected to near-fault motions are discussed and a model are proposed to describe their relationship.
Manufacturing Conditions of French Reactor Pressure Vessels to Avoid the Occurrence of Hydrogen Flakes
Authors: Miller C. , Champigny F. , Frund J. M.
Published: December 2016

The formation of hydrogen flakes in Reactor Pressure Vessels (RPV’s) forgings is a well known phenomenon that can affect forging components during manufacturing. Following recent data from Belgium, it has been the object of important assessments during the last 3 years. We will present in this paper elements pertaining to the RPV’s of the French nuclear fleet.

A thorough review of fabrication processes and specifically of ultrasonic examination of forgings, including the oldest ones has demonstrated that the risk of leaving undetected hydrogen flakes in RPV’s forgings is not a problem in French RPVs. The French Regulator also clearly shared this position point in 1985. Parts with defects were once again observed at the beginning of 2012 but the defects were attributed to errors in hydrogen measurement at the steel maker shop. Those hydrogen induced defects were detected at an early manufacturing stage (before quality heat treatment) by ultrasonic examination, and the concerned parts were consequently rejected through the normal quality control process.
Case Study of Seismic Response for Shell Key Gasification Equipment Based on Transient Dynamic Analysis
Authors: Shen Jun , Wu Yunlong , Peng Heng , Liu Yinghua
Published: December 2016

Coal gasification is a key technology for clean coal conversion with high efficiency. During the past decade, more than twenty Shell Key Gasification Equipments (SKGE) used in the Shell Coal Gasification Process (SCGP) have been built in coal-to-chemicals industry in China. SKGE is composed of Gasifier and Syngas cooler which are connected by Transfer duct. The support skirt of the Gasifier base is fixed, while the Syngas cooler side is supported by a constant hanger (floating support).

In this paper, a FE model of the largest 2000-ton SKGE system in China is established by using ANSYS. The global dynamic response under the seismic load is simulated. In order to verify the correction of the calculation, the results are also compared with that by using ABAQUS.

Compared to the traditional static analysis, it can be found that the deformation and stress distribution, the force and moment on several specified cross sections of SKGE change over time under seismic load based on the transient dynamic analysis.

As the result of the seismic analysis is the prerequisite and foundation for accurate calculation of each key part (e.g. connection between Transfer duct and Gas reversal chamber), the seismic analysis is one of the most important analyses in the Gasification design, which will ensure the essential safety of SKGE system.
Material Properties of Reactor Pressure Vessel Shells Affected by Hydrogen Flaking
Authors: Gérard Robert , De Smet Michel , Chaouadi Rachid
Published: December 2016

During the summer outages of 2012, large numbers of nearly-laminar indications were found in the core shells of the Doel 3 and Tihange 2 reactor pressure vessels (RPV). As a consequence, both units remained in cold shutdown with their core unloaded. A series of examinations, tests and inspections were performed leading to the conclusion that the indications are hydrogen flakes and that they do not affect the structural integrity of the RPV, regardless of the operating mode, transient or accident condition. All this was documented in the Safety Case reports issued in December 2012 and in the Safety Case Addenda issued in April 2013 [1]. Based on those reports, the Belgian Federal Agency for Nuclear Control (FANC) authorized the restart of both units which went back on-line in June 2013.

A key input required for this Safety Case was the definition of the appropriate material properties, in particular fracture toughness, for the RPV shells affected by hydrogen flakes. A material testing program on non-irradiated materials evaluated aspects like the possible effects of macro-segregations and local segregations (ghost lines) and of specimen orientation on the fracture toughness. The irradiation embrittlement sensitivity of the zone of macro-segregation in which the flakes are located was evaluated on the basis of the maximum enrichment in Cu, P and Ni in macro-segregations based on literature data. This was the basis of the trend curve of RTNDT evolution vs. fluence used in the Safety Cases submitted in 2012–2013.

The restart authorization in 2013 was accompanied by a number of “mid-term” requirements, to be completed during the first operating cycle after the restart. One of these requirements was the mechanical testing of irradiated specimens containing hydrogen flakes, in order to confirm the conservativeness of the RTNDT trend curve used for the structural integrity analyses.

After a first irradiation campaign of a material containing hydrogen flakes in the BR2 reactor of the Belgian Nuclear Research Center SCK.CEN, atypical results were obtained and the utility decided to shut down the units in March 2014. Detailed investigations involving three additional irradiation campaigns in BR2 including other reference materials, among which another material affected by hydrogen flakes, were performed in order to characterize this atypical behaviour and to derive a new conservative RTNDT trend curve. The resulting trend curve was accepted by the FANC and was used in the 2015 Safety Cases [1]. An overview of the Doel 3 and Tihange 2 safety cases is given in [6].

The paper summarizes the results of the material investigations on non-irradiated and irradiated materials and the process leading to the definition of this conservative RTNDT trend curve.
Technical Basis for Code Case N-853: A600 Branch Connection Weld Repair for SCC Mitigation
Authors: Waskey David , McCracken Steven
Published: December 2016

The NRC Issued a Regulatory Issue Summary (RIS 15-10) which was an inquiry to the ASME Code Committee to review the in-service inspection requirements for Alloy 600 full penetration branch connections. This NRC request resulted in the initiation of two PWROG projects, PA-MSC-1283 and 1294.

PA-MSC-1283 is a Fracture Analysis to evaluate the crack growth rate of the various existing A600 configurations, heat treat conditions and operating loads. The results from this study would provide the technical basis for in-service inspection method and frequency.

PA-MSC-1294 is a project to consider contingency repair techniques and provide a bounding analysis for all nozzle configurations of the selected repair technique. The selected repair approach to be analyzed was a weld buildup referred as a Branch Connection Weld Metal Buildup (BCWMB) in the ASME Code Case (N-853) developed to provide the rules for design, implementation and inspection. Included in this project was a proof-of-principle phase to demonstrate that the repair methodology is implementable and assist in establishing the potential on component repair duration and anticipated dose.
Thermal Hot Spot Damage Assessment in Pressure Vessels
Authors: Adibi-Asl R. , Seshadri R.
Published: December 2016

Local hot spots occur in some pressure vessels and piping systems used in power and process plants. This type of damage is typically caused by loss of refractory lining on the inside wall of pressure components or due to a maldistribution of the flow within vessels containing catalysts and reactive fluids. In general, this form of damage can be detected by thermography or temperature sensitive paints on the outside of the vessel. Hot spot damage can reduce the overall load carrying capacity of a pressurized component due to lower yield strength of the damaged region resulting from localized increase in temperature. This paper investigates hot spot damage assessment by reviewing the available solutions. Various pressure vessel profiles including cylindrical, spherical and conical vessels are discussed.
Uncertainty Management in Lebesgue Sampling-Based Fault Diagnosis and Prognosis
Authors: Yan Wuzhao , Zhang Bin
Published: December 2016

This paper develops the uncertainty management of fault diagnosis and prognosis (FDP) in Lebesgue sampling (LS)-based framework with an application to helicopter drivetrain gearbox. In the developed LS-based FDP system, a particle filtering-based FDP algorithm, fault diagnostic model, failure prognostic model, and uncertainty management are discussed. Although uncertainty management has been developed in the traditional Riemann sampling (RS)-based FDP, it needs to be analyzed and managed in a totally different way since the working principle of LS-FDP is fundamentally different from that of RS-FDP. Inaccurate model structure and parameter, measurement noise, process noise, and unknown future loading are major contributing factors of uncertainties in LS-FDP framework. Since the noise in LS-based prognosis is a distribution on time axis while the noise in RS-based prognosis is one on fault state axis, this paper studies the transpose of noise distribution from state domain to time domain. In order to reduce the uncertainty in the prediction of remaining useful life (RUL), model noise and measurement noise terms are adjusted based on a short-term prediction with n steps and correction loop. In this scheme, the priori time distribution at the (t + n)-th Lebesgue state is predicted and stored at the t-th Lebesgue state. Then, at the (t + n)-th Lebesgue state, when the posteriori distribution becomes available, it is compared with the stored priori distribution to manage the uncertainty. The methods for uncertainty management are illustrated by a case study of the prediction of RUL of gearbox. The experimental results show that the uncertainty in the diagnosis and prognosis process of gearbox is properly managed and the confidence interval is decreased, which enhances the confidence level for decision-making and condition-based maintenance.
Leak-Before-Break Assessment of a Cracked Reactor Vessel Nozzle Using 3D Crack Meshes
Authors: Thorwald Greg , Parietti Lucie
Published: December 2016

A postulated surface crack near a reactor pressure vessel nozzle is evaluated using finite element analysis (FEA) to compute the fatigue crack growth rate, evaluate crack stability, and examine the possibility of a leak-before-break (LBB) condition. For a pressurized vessel with cyclic loading, determining if the crack may have a LBB condition is desirable to allow for the possibility of leak detection leading to corrective action before catastrophic failure.

A fatigue crack growth analysis is used to determine how the surface crack dimensions develop before re-categorizing the surface crack as a through thickness crack and evaluating its stability for LBB. To evaluate if a particular crack is unstable and may cause a structural failure, the Failure Assessment Diagram (FAD) method provides an evaluation using two ratios: brittle fracture and plastic collapse. The FAD method is described in the engineering best practice standard API 579-1/ASME FFS-1. The FAD curve and assessment ratios can be obtained from crack front J-integral values, which are computed using 3D crack meshes and elastic and elastic-plastic FEA. Computing custom crack solutions is beneficial when structural component geometries do not have an available stress intensity or reference stress solution.