bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Structural Integrity Assessment Method for Flow-Induced Vibration of Reactor Internals in PWR
Authors: Sugiura Hirokazu , Watanabe Shigeyuki , Iwasaki Akihisa , Morita Hideyuki , Sakata Hideyuki , Nishikawa Yoshito
Published: October 2018

For verifying the structural integrity of the reactor internals (RIs) in a pressurized water reactor (PWR) plant, it is important to estimate the vibration response of the core barrel (CB) due to flow turbulence. Instead of scale model test, the computational fluid dynamics (CFD) has been expected as a method to predict the turbulence forcing function for the response analysis of the CB. In this article, a hybrid approach combining empirical equations based on flow test and CFD analysis is proposed in order to predict the turbulence forcing function.

The scale model test of new RIs, which were developed by Mitsubishi Heavy Industries, Ltd., was conducted, and the pressure fluctuations for the turbulence forcing function and the vibration response of the CB were measured. The pressure fluctuations were calculated by CFD analysis, and the vibration analysis using the turbulence forcing function determined from the calculated pressure fluctuations was performed.

This article provides the scale model test data and the empirical equations of the turbulence forcing functions, and validation results of the proposed method to predict the turbulence forcing function using CFD.
Study of Mode I-II Mixed Crack Propagation in Electrofusion Joint of Polyethylene Pipe
Authors: Zhang Yue , Shi Jianfeng , Zheng Jinyang
Published: October 2018

Electrofusion joint plays an important role in connecting polyethylene (PE) pipe. In our previous study, penetrating crack failure through the fitting with an angle of about 70° was observed, and axial stress was found to be an important factor in the crack propagation. In this paper, experiments were carried out to study the crack propagation phenomena of the electrofusion joint of PE pipe. Digital Image Correlation (DIC) method was used to measure the displacement on specimen’s surface, as well as full-field strain distribution, based on which the J-integral of the crack tip was calculated. Besides, a finite element numerical simulation was conducted, and its accuracy was verified by experimental J-integral value. Through combination of experimental observations and finite element method, the phenomenon that the angle between crack propagation direction and tube axial is about 70° is detailed analysed. By comparison and analysis of the testing results, critical J-integral value during crack propagation is determined. Furthermore, critical J-integral value of crack propagation in electrofusion joint is predicted.
Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Ethylene/O2/N2-Mixtures and Cyclohexane/O2/N2-Mixtures in Long and Short Pipes
Authors: Schildberg Hans-Peter
Published: October 2018

In the recent past (PVP2013-97677, PVP2014-28197, PVP2015-45286, PVP2016-63223) we had started to determine the static equivalent pressures (pstat) of the eight detonative pressure scenarios in long and short pipes for different detonable gas mixtures. The pstat-values are of vital importance for process design: by assigning static equivalent pressures to the highly dynamic detonative pressure peaks it is possible to apply the established pressure vessel guidelines, which can only cope with static loads, in the design of detonation pressure resistant pipes. In the previous publications the parameter R was defined as the ratio between pstat at the location where transition from deflagration to detonation occurs and pstat in the region of the stable detonation. One important finding was that R depends on the reactivity of the gas mixture. So far, R cannot be predicted from first principles or from combustion parameters, but can only be determined experimentally. The ratio R has a special significance, because it not only determines pstat for the Deflagration to Detonation Transition (DDT) in long pipes (first detonative pressure scenario), but also gives a good estimate for two of the three scenarios relevant in the design of short pipes: DDT and the coalescence of DDT and reflection.

The present paper concludes the test series conducted at BASF during the last 4 years. It presents additional experimental data showing the variation of R over the entire detonative range of Ethylene/O2/N2 mixtures and along the stoichiometric line of Cyclohexane/O2/N2 mixtures. Based on the variation of R for these ternary mixtures and for the mixtures presented in the preceding publications, a typical variation of R for a general combustible/O2/N2-mixture is estimated over the entire explosive range. By means of this estimation the static equivalent pressures of the six design-relevant detonative pressure scenarios of any combustible/O2/N2-mixture can now be derived combining the parameter R with the Chapman-Jouguet pressure ratio, which can be calculated in a straightforward manner from thermodynamic properties.
Simulation of Acoustic-Structure Interaction by Using Finite Element Analysis in Reactor Pressure Vessel of PWR
Authors: Maeta Koji , Matsuyama Keisuke , Sugiura Hirokazu , Watanabe Shigeyuki , Morita Hideyuki , Iwasaki Akihisa , Nishikawa Yoshito
Published: October 2018

The reactor coolant pump (RCP) in a pressurized water reactor (PWR) plant generates pressure pulsations at multiple frequencies. These pressure pulsations excite the acoustic modes inside the reactor vessel (RV), and cause significant acoustic loads on the reactor internals (RIs). For verifying the structural integrity of the RIs, it is important to predict the acoustic loads, which is used for vibration analysis of the RIs. Traditionally, an analytical method, assuming that structures are rigid, has been used in order to predict the acoustic pressure distributions inside the RV [1]. However, water in actual PWR plant is heavy enough to influence structural response, so that it is required to use methods for a coupled structural acoustic system.

In this article, the coupled structural-acoustic analysis using the commercial software ANSYS is proposed in order to predict the acoustic loads, and the applicability of this method is discussed. The structural-acoustic interactions inside the RV are investigated by element tests and the scale model test. The acoustic pressures measured by these tests are compared with the calculated results.
Low-Cycled Fatigue Life of S30408 Stainless Steel at Liquid-Nitrogen Temperature
Authors: Wu Yingzhe , Xu Huaijian , Lu Qunjie , Zheng Jinyang , Xu Ping
Published: October 2018

This paper is concerned with the low-cycled fatigue life of S30408 austenitic stainless steel at 77 K. Strain-controlled low-cycled fatigue tests were performed in a liquid-nitrogen bath covering a strain-amplitude range of 0.4%–1.0%. The role of the reduced temperature is examined during the low-cycled fatigue tests by comparing the fatigue performance to the one at ambient temperature that was obtained in our previous work. It is found that the cryogenic low-cycled fatigue life is significantly improved by a factor of 5–10 in the low strain-amplitude range of 0.4%–0.5%, resulting from the pronounced hardening effect due to the low temperature. However, the cryogenic improvement gradually reduces with the increasing strain-amplitude. At 77 K, the cyclic stress amplitude increases rapidly at the beginning of the fatigue test, and no cyclic softening is found due to the cryogenically constrained movement of the dislocations. The fatigue hysteresis loops and fatigue stress-strain curves shows that the cyclic plastic strain at cryogenic temperature accounts for a limited proportion in the total cyclic strain, and the damage may occurs explosively at the beginning of the cyclic load at 77 K.
Analysis and Design for Fixed Type Refrigerant Chiller in LNG and Ethylene Plant
Authors: Cho Jongyoon , Zhou Runze , Ishiyama Hiroyuki , Mitarai Yasuhiro , Waki Yoshiyuki
Published: October 2018

In LNG Plant using APCI Precooled MR process [1] (Propane precooling and Mixed Refrigerant as main cooling medium, Figure 1), Natural gas and Mixed Refrigerant chillers which installed upstream of the main cryogenic heat exchanger are one of the key process equipment of the plant. Similar application is often used in other petrochemical area such as Ethylene plant using light hydrocarbon refrigerant for evaporation chiller. It is always challenging to optimize the design to reduce necessary plot area while it satisfies various process and mechanical requirements. This paper will cover an analysis of typical chiller design of 4MTPA LNG project in respect of thermal design, process scenarios and mechanical integrity. Firstly starts thermal design review for better understanding on the back ground of equipment features and its function. Then discuss about process scenarios which are used for analysis cases. For mechanical integrity analysis, FEA method, result and review will be introduced. In the last section, design cases by using different tube thickness and optimization study will be presented as suggestion for future LNG projects.
Study on the Risk Based Inspection and Evaluation System for Polyethylene Gas Pipeline
Authors: Ling Zhangwei , Xia Junfang , Cai Gangyi , Tang Ping , Chen Chang , Guo Weican
Published: October 2018

The operating environment of polyethylene (PE) gas pipeline is complex and changeable. In the process of pipeline design, construction and operation, there are many fuzzy factors inducing pipeline accidents. In the paper, the fuzzy factors causing pipeline accidents were studied and analyzed, and the risk evaluation factors of PE gas pipeline were determined. According to the theory of fuzzy comprehensive evaluation, the mathematical model of fuzzy comprehensive evaluation for PE pipeline was established. In order to pursue as much accurate results of assessment as possible, the fuzzy analytic hierarchy process was used to determine the weight of each index. The safety evaluation grade of the pipeline was given by using the risk matrix method. And then the evaluation system software of PE gas pipeline risk assessment was developed. The software has been used in the risk inspection of PE gas pipeline, which provides the basis for the risk management of the pipeline.
Finite Element Analysis for Failure of Dividing Wall of MMDI Distillation Column
Authors: Wang Jielu , Su Wenxian , Tang Xiaoying , Shi Qinghai , Yang Bo , Ding Ju , Huang Yichang , Zuo Yantian , Xue Xiaolong
Published: October 2018

A company’s isocyanate and polyether MMDI distillation column is a Dividing wall column (called DWC). During the trial operation, the dividing wall is distorted so that the distillation can not work on. Finite element method was used in this subject, considering the dividing wall with no flaw, unevenness and with initial stress, studying the deformation during the temperature loading, unloading and re-loading respectively. According to the results, main factors for the deformation of dividing wall were analyzed and possible solutions were proposed eventually.
Effect of 3-D Initial Imperfections on the Deformation Behaviors of Head Plates Subjected to Convex Side Pressure
Authors: Yada Hiroki , Ando Masanori , Tsukimori Kazuyuki , Ichimiya Masakazu , Anoda Yoshinari
Published: October 2018

Containment vessel (CV) of nuclear power plants is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. The head plate is one of the components which constitute the CV boundary. In order to develop the evaluation method of the pressure toughness of the head plate at beyond design basis events, the pressure failure tests and finite element analysis of the head plates subjected to convex side pressure were performed. In the tests, non-axisymmetric deformations with local deformation concentration were observed in post buckling behavior in the case of the thin thickness head plate. In this study, to evaluate these non-axisymmetric deformations in the test, finite element analyses using detailed 3-D solid model constructed by precise dimensions of the head plates measured by 3-D scanner were performed. Moreover, FEA using simplified model with uniform or non-uniform thickness model were performed. Through a series of FEA, it was clarified the effect of each thickness pattern on post buckling non-axisymmetric deformation.
Thermo-Mechanical Justification of the FA3 RPV Cover and Bottom Domes Under Normal and Upset, Emergency and Faulted Loading Situations
Authors: Chapuliot S. , Sportisse M. , Hardouin J. , Vidard S.
Published: October 2018

This paper describes in a synthetic manner the work performed for the thermo-mechanical justification of the FA3 cover and bottom domes. Details on the postulated defects definition, thermo-hydraulics loading determination, thermo-mechanical model definition and margin evaluation are provided.

As a conclusion it is shown that despite the presence of the Carbon macro-segregation, the mechanical justification of both domes could be achieved with significant margins.
Evaluation of Stress Rupture Factors for Grade 91 Weldments
Authors: Kimura Kazuhiro
Published: October 2018

Stress rupture factors and weld strength reduction factors for Grade 91 weldments in the codes and literatures have been reviewed. Stress rupture factors for weld metals proposed for Code Case N-47 in the mid 1980’s was defined as the average rupture strength of the deposited filler metal to the average rupture strength of the base metal. Remarkable drop in creep rupture strength of weldments is significant issue of Grade 91, especially in the low-stress and long-term regime. A premature failure of Grade 91 weldments in the long-term, however, is caused by Type IV failure which takes place in the fine grained heat affected zone (FG-HAZ), rather than fracture in the deposited weld metal. The stress rupture factor of the Grade 91 steel, therefore, was based on the creep rupture strength of cross weld test specimens. Time and temperature dependent stress rupture factors for Grade 91 have been estimated based on the average creep rupture strength of cross weld test specimen to the average creep rupture strength of base metal.
Towards a Process for the Assessment of Mixed Mode I+II Fracture Toughness
Authors: Bouydo Afaf , Lacroix Valéry , Chaouadi Rachid , Mares Vratislav
Published: October 2018

In fracture mechanics, a flaw behavior in pressure vessels is assessed with respect to the material fracture toughness.

Fracture toughness which most Fitness-for-Service (FFS) codes relies on, only considers mode-I crack opening. However, in presence of tilted flaws, like quasi-laminar hydrogen flakes, this mode-I toughness may be too severe, and a mixed mode I+II fracture toughness seems to be more appropriate.

In order to address the assessment of the fracture toughness curve, mixed mode I+II tests were performed by the authors on ferritic steel samples by adjusting the standard mode I CT specimen geometry to a geometry subjected to mixed mode I+II. Then, XFEM simulations of the mixed mode tests were performed in order to calculate the J-integral along the crack front.

Based on tests and calculations results, the paper explains how the authors work towards proposing a method to measure the material fracture toughness in case of flaws subjected to mixed mode (I+II) loading.
A Comparative Study of Pressure Area Method of Nozzle Compensation in ASME Section VIII Division 2 and PD 5500 for Restrictions in Nozzle Dimensions
Authors: Gopalakrishnan Shyam , Mathkar Ameya
Published: October 2018

Clause 4.5 of ASME Section VIII Division 2[1] provides rules for compensation of openings in cylindrical shells having fitted nozzles.

The rules provided in Clause 4.5.5 of ASME Section VIII Division 2[1] are based on pressure-area method which is based on ensuring that the reactive force provided by the vessel material is greater than or equal to the load from the pressure.

Clause 3.5.4 of PD 5500[5] provides rules for compensation of opening and nozzle connections.

Clause 3.5.4.3 provides requirements for the design of isolated openings and nozzle connections in the form of design procedure. Clause 3.5.4.4 provides requirements for groups of openings and the procedure allows the checking of chosen geometry.

Clause 3.5.4.9 of PD 5500[5] provides rules for compensation of openings by pressure-area method to those geometries which confirms to the geometric limitations specified therein. This method has extensive satisfactory use in European Code of practice and has been adopted in BS EN 13445-3 also.

The key element in applying the pressure area method is to determine the dimensions of the reinforcing zone, i.e., the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure.

In comparison to certain restrictions in PD 5500[5] there appears to be no restriction on the physical dimensions of the nozzle or shell in ASME Section VIII Division 2[1], as long as the required area AT is obtained and the stresses are within allowable limits.

It is therefore possible that all of the required area AT is obtained either from the nozzle or from the shell. While both these alternatives would be acceptable in ASME Section VIII Division 2[1] design, the actual stresses at the shell/nozzle junction may vary considerably.

The work reported in this paper — a comparative study of pressure area method of nozzle compensation in ASME Section VIII Division 2[1] and PD 5500[5] for restrictions in nozzle dimensions was undertaken to compare the results obtained from both the Codes and is an extension of work carried out and published as PVP2015-45564.
Using Virtual Testing to Study the Influence of Constraint on Fracture Properties
Authors: Seal Christopher , Ainsworth Robert
Published: October 2018

This paper presents a study in which the influence of constraint is investigated using a ductile damage model based on a stress modified failure strain. This model, proposed by Oh et al, has been used to successfully predict the J-R curve of standard compact tension (CT) test pieces for a range of different materials. Further work has shown how the model can also predict the fracture behaviour of non-standard CT test specimens, in which a blunt notch is used in place of a sharp crack.

Continuing on from this work, the paper predicts the J-R curves of single edge notch tension (SET) test pieces with both a sharp crack and blunt notches.
Assessment of Creep Crack Growth Rates for Grade 91 Weld Joint at 550°C
Authors: Kim Woo-Gon , Park Jae-Young , Lee Hyeong-Yeon , Kim Eung-Seon , Kim Seon-Jin
Published: October 2018

This study presents assessment of creep crack growth rates (CCGRs) for the base metal (BM), weld metal (WM), and heat affected zone (HAZ) of Gr. 91 weld joint, which was prepared by a shield metal arc weld (SMAW) method. A series of tensile, creep, creep crack growth (CCG) tests were performed for the BM, WM, and HAZ at the identical temperature of 550°C. The CCGR laws for the BM, WM and HAZ were constructed and compared in terms of a C*-fracture parameter. In addition, the CCGR law tested for BM was compared to that of RCC-MRx code. For a given value of C*, the WM and HAZ were almost similar in the CCGR, but they were significantly faster than the BM. This reason was closely attributed to the higher creep rate in the WM and HAZ than the BM. Currently elevated temperature design (ETD) code in French, RCC-MRx was found to be non-conservative in the CCGR when compared with the present investigation.
Effect of Simulated Post-Weld Heat Treatment on the Mechanical Properties and Microstructure of P-No. 1 Carbon Steels
Authors: Kang Yongjoon , Lee Seung-Gun , Kim Gi-Dong , Lee Sang-Hoon , Song Sang-Woo , Kang Sung-Sik
Published: October 2018

The effect of simulated post-weld heat treatment (PWHT) on the mechanical properties and microstructure of P-No. 1 materials was investigated and the suitability of the exemption requirements of simulated PWHT as specified in ASME Section III Division 1 Subsection NX-2211 was evaluated. SA-516 Gr. 60 and 70 carbon steel plates and SA-106 Gr. B carbon steel pipe were employed, and the materials were subjected to the simulated PWHT with holding temperatures of 610, 650, 690, and 730 °C for 8 hours. Both the tensile strength and lateral expansion of the materials tested in this study showed a tendency to decrease with increasing holding temperature of the simulated PWHT. In some cases, the materials after the simulated PWHT cannot satisfy those mechanical requirements.
Predicting the Effect of Low Constraint on the Onset of Upper Shelf Temperature
Authors: Seal Christopher , Sherry Andrew
Published: October 2018

It has long been recognised that a defect experiencing a state of low constraint shows improved fracture properties when compared to the same defect in a highly constrained state. Fracture test specimens have, therefore, been designed in such a way as to generate a state of high constraint at the crack tip in order to ensure that the properties measured are conservative. Where a defect, in practice, is not highly constrained then using the fracture toughness measured from a standard test piece leads to an overly pessimistic assessment. With the move toward more accurate design and assessment due to the availability of advanced computational tools, it is advantageous to take this excessive conservatism into account. A particular case that is of interest is the effect that constraint has on the onset of upper shelf temperature (OUST). The OUST is typically defined as the intersection of the fracture toughness loci representing the 5% probability of cleavage and the 50% probability of ductile initiation. This paper details a method which can be used to predict the shift in OUST using the toughness scaling method proposed by Anderson and Dodds and extended to account for the influence of constraint on ductile initiation.
Graded Creep Deformation Properties of 316H Welds and its Impact on Creep
Authors: Dey S. , Knowles D. M. , Truman C. E.
Published: October 2018

The creep damage evolution in multi-pass welds is believed to be influenced by the variation of creep rates from the weld to the base metal and through the HAZ. Material heterogeneity in a multi-pass weld leads to a non-uniform stress distribution resulting in non-uniform evolution of creep strains with strain localisation. Also, a non-uniform stress distribution may lead to highly multiaxial stress states in the weld resulting in a lower creep ductility. Since creep damage in metallic components is influenced by creep strain rate and creep ductility of the material amongst other factors, creep inhomogeneity in a weldment may significantly affect creep damage accumulation. Therefore, in order to predict creep behaviour of a multi-pass weld, it is important to take into account the gradation of creep deformation properties through the weld HAZ. Impression creep tests are useful in revealing localised creep properties in a material, where test results can be directly correlated to uniaxial creep tests. In this paper, a 2D finite element model of a multipass 316H weld with three different material sections (weld, HAZ, parent) is used to demonstrate the effects of creep deformation mismatch on stress and strain distributions. The paper also describes a series of impression creep tests planned and being conducted on an ex-service 316H weldment from a power plant steam generator with specimens taken from locations in the HAZ and at varying proximities to the weld fusion line. One specimen from the far away base metal and one from the weld centerline were also taken to serve as reference since the uniaxial creep deformation properties for the weld and the base material are known from uniaxial creep tests. By comparing the minimum creep rates for the HAZ specimens against the reference specimens from the weld and the base metal, Norton’s law creep coefficients and stress exponents will be derived for the HAZ specimens thereby revealing the gradation of creep deformation properties as a function of distance from the weld fusion line.
Prediction of the Leakage Threshold for Hertzian Contact Seals: An Experimental Approach
Authors: Van Wittenberghe Jeroen , Vande Voorde John
Published: October 2018

The prediction and evaluation of leakage and leak tightness is an important issue in a multitude of high-pressure applications, such as valves, flanges and threaded pipe connections that are used under extreme service conditions that occur in oil and gas exploration and production. Using Hertzian contact theory or finite element techniques it is possible to determine the local contact conditions at the seal on a macroscopic level (to wit the extent of the contact area and the contact pressure in this area). However, the leak tightness of such a contact depends also on the surface topology, which is a microscopic characteristic. Therefore, the assessment of leak tightness requires an evaluation criterion relating both scales. Empirical evaluation criteria have been postulated in the past, each with their own application domain. More recently the Persson method has been developed that models the contact area microscopically using contact models developed in the field of tribology. However, in its current form this model is limited to flat surfaces while in many applications, such as valves, O-ring seals or metal-to-metal seals of threaded pipe connections, the contact is Hertzian and the contact pressure distribution is not uniform but parabolic. This paper provides the experimental results that will be used to validate an extension of the Persson model to Hertzian contact seals. A set of samples for leakage experiments was produced with varying surface topology. The surface roughness of these samples is measured and the leakage behaviour under high pressure is evaluated. This paper focusses on the experimental evaluation of the influence of surface topology on leakage.
Novel Metamaterial-Based Foundation Concept Applied to a Coupled Tank-Pipeline System
Authors: Wenzel Moritz , Basone Francesco , Bursi Oreste S.
Published: October 2018

The recent advance of seismic metamaterials has led to various concepts for the attenuation of seismic waves. A particularly promising type of material is the locally resonant metamaterial, which is capable of attenuating seismic waves at wave lengths much greater than the dimensions of its unit cells. Based on this concept, the so called Metafoundation has been design. It is able to protect a fuel storage tank from ground motions at various fluid levels. In order to show the effectiveness of the proposed design, the response of the Metafoundation is compared to the response of a tank on a traditional concrete foundation. The design process of conceiving the Metafoundation, optimizing it for a specific tank, and its seismic response are described herein. Furthermore, the response of a tank during a seismic event can cause severe damages to pipelines connected to the tank. This phenomenon can be of critical importance for the design of a seismic tank protection and must be treated with care. Since the coupled structure (tank+foundation+pipeline) exerts highly non-linear behavior, due to the complexity of the piping system, a laboratory experiment has been conducted. More precisely, a hybrid simulation that uses the Metafoundation and a tank as a numerical substructure (NS) and a piping system as a physical substructure (PS) was employed. In order to make the results relatable to the current state of the art, additional experiments were performed with concave spherical bearing devices (CSBs) as an isolation system in the NS. While the Metafoundation performed better than the CSB isolated structure for some records, a clear advantage could not be concluded. However, the Metafoundation offers a clear attenuation of tank stresses and may potentially mitigate also piping stresses when tuned to the right frequency in the future.
ATLAS PLUS: Design of Large Scale Fracture Mechanics Tests on a Ferritic Pipe
Authors: Nicak Tomas , Bolinder Tobias , Keim Elisabeth , Eriksson Alexander , Le Delliou Patrick , Dahl Anna , Wallin Kim
Published: October 2018

This paper summarizes the design calculations performed by Framatome, EDF, KIWA INSPECTA and VTT for three large scale tests on ferritic pipes made of material WB 36 (15 NiCuMoNb 5).

The large scale tests will be performed on a 4-point bending test facility provided by EDF under displacement control at room temperature.

The overall goal of the planned large scale tests is to demonstrate the effect of the crack tip constraint on the fracture toughness at the component level. Results of those tests will be utilized to develop and validate advanced tools for structural integrity assessment within WP 3 particularly with respect to the transferability of material properties from small scale specimens to large scale components as well as for the development and validation of a procedure for the determination of component fracture resistance curves.

Three configurations of the initial defect with different constraint conditions (one through-wall and two surface cracks) are considered.

The design calculations are divided into two parts. In the first part an optimization of three different crack shapes is performed on basis of the standard fracture mechanics approach (based on J-Integral) without consideration of the constraint effect.

In the second part a quantification of the crack tip constraint for the selected crack configurations from part I is performed. The effect of the constraint on the crack initiation and propagation for the selected crack configurations shall be assessed and compared between each other.

Based on these calculations the final flaw configuration for each large scale experiment is selected.
Stress and Damage Analysis of Fiber-Reinforced Composite Pipe
Authors: Ramos I. , Park Y. H. , Ulibarri-Sanchez J.
Published: October 2018

Composite materials are used in many environments due to their special properties such as high strength-to-weight ratio, corrosion resistance and the ability to be tailored to specific requirements. In particular, the use of fiber reinforced composites (FRCs) for pressure vessels/pipes has increased in structural applications such as fuel tanks, pipes, vessels, and rocket motor cases. Assessing failure conditions is important to ensure that these structures do not fail under their operating condition. In this study, an analytical procedure is developed to predict the fatigue behavior of FRC. A numerical model will also be developed and applied to failure analysis under internal pressure loading.
Overview of Recent Activities Undertaken by the UK Forum for Engineering Structural Integrity (FESI)
Authors: Sharples John , Tomkins Brian , Flewitt Peter , Garwood Stephen , Daniels Brian
Published: October 2018

The United Kingdom (UK) Forum for Engineering Structural Integrity (FESI) is the membership organisation for engineering structural integrity (ESI) in the UK. This paper provides an overview of FESI in terms of summarising its recent activities with particular regard to conferences, workshops/seminars, training courses, and the strengthening of links and ties to other organisational bodies associated with elements of ESI. A commentary is included on how some of these activities relate to codes and standards to meet future demands of existing and future plants for extended periods of operation.
Comparison of Two Ductile Crack Propagation Models of GTN and CZM for Pipe Steel Fracture
Authors: Wang Junqiang , Wang Haitao , Lin Nan , Ma Honglian , Wang Jinlong
Published: October 2018

The ductile crack propagation behavior of pressure equipment has always been the focus of structural integrity assessment. It is very important to find an effective three-dimensional (3D) damage model, which overcomes the geometric discontinuity and crack tip singularity caused by cracking. The cohesive force model (CZM), which is combined with the extended finite element method (XFEM), can solve element self-reconfiguration near the crack tip and track the crack direction. Based on the theory of void nucleation, growth and coalescence, the Gurson-Tvergaard-Needleman (GTN) damage model is used to study the fracture behavior of metallic materials, and agrees well with the experimental results. Two 3D crack propagation models are used to compare crack propagation behavior of pipe steel from the crack tip shape, fracture critical value of CTOA and CTOD, constraint effect, calculation accuracy, efficiency and mesh dependence etc. The results show that the GTN model has excellent applicability in the analysis of crack tip CTOD/CTOA, constraint effect, tunneling crack and so on, and its accuracy is high. However, the mesh of crack growth region needs to be extremely refined, and the element size is required to be 0.1–0.3mm and the calculation amount is large. The CZM model combined with XFEM has the advantages of high computational efficiency and free crack growth path, and the advantages are obvious in simulating the shear crack, combination crack and fatigue crack propagation. But, the crack tip shape and thickness effect of ductile tearing specimen can not be simulated, and the CTOA value of local crack tip is not accurate.
Performance of Depressurization Devices to Dynamic Loads Generated by Arcing in Liquid Filled Transformers
Authors: Iyer Ashwin Padmanaban , Goj Anne , Ahmed Omar K.
Published: October 2018

This study provides a methodology that can be used to evaluate the dynamic performance of fast depressurization devices used in liquid-filled oil transformers. Liquid-filled transformers are susceptible to explosions due to internal arcing if the dielectric insulation fails. The internal arc vaporizes a portion of the liquid and generates a sudden pressure wave. The first peak of the pressure wave has been measured to be as high as 13 bars, with time durations on the order of milliseconds [1]. Transformer tanks have a typical static withstand limit of approximately 1 bar gauge [2]. It is thus imperative that the tank be depressurized before the static pressure reaches such a threshold. One industry-accepted Fast Depressurization System [3] used to depressurize transformers after an internal arc is based on a patented rupture disk design [4]. This study compares the dynamic performance of this disk to results from a successful test campaign using a rupture disk as the depressurization device. Limiting loading rate values from the test campaign are then used to comment on the effectiveness of the design.

The evaluation methodology is based on Pressure-Impulse (P-I) curves. The P-I curve was generated by running a series of Implicit Dynamic analysis using Code_Aster [5]. This iterative process first required establishing a failure mode that is consistent with actual observed failure in the field and observable in the Finite Element Analysis (FEA) model. The criteria were then used in interpreting the response of the Rupture Disk to a series of different half-sine wave pulse loading of varying amplitudes and time-periods.

The generated P-I curve was then compared to loading rates observed in the test campaign [1] as well as three other higher loading rates (1.28 times, 2 times, 3.8 times, and 10.25 times the reported experimental rate) to qualitatively assess the effectiveness of the design. Results indicated that disk functions extremely effectively as a Fast Depressurization System as also corroborated by the test campaign.

Although this methodology is used for the rupture disk, it is expected that this methodology can be extended to compare the dynamic performance of other depressurization devices.
The Experimental Work in Support to ATLAS+ Project
Authors: Moinereau Dominique , Le Delliou Patrick , Dahl Anna , Kayser Yann , Szavai Szabolcs , Tatar Levente , Bolinder Tobias , Serrano Marta , Besson Jacques , Nicak Tomas , Wallin Kim , Marie Stéphane
Published: October 2018

The 4-years European project ATLAS+ project was launched in June 2017. Its main objective is to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems.

The transferability of ductile material properties from small scale fracture mechanics specimens to large scale components is one of the topics of the project. A large programme of experimental work is to be conducted in support of the development and validation of advanced tools for structural integrity assessment within the framework of the work-package 1 (WP 1): Design and execution of simulation oriented experiments to validate models at different scales.

The experimental work is based on a full set of fracture mechanics experiments conducted on standard specimens and large scale components (several pipes and one mock-up), including a full materials characterization. Three materials are considered:

• a ferritic steel 15NiCuMoNb5 (WB 36)

• an aged austenitic stainless steel weld

• a VVER (eastern PWR) dissimilar metal weld (DMW)

The paper presents the WP 1, the experimental programme and summarizes the first results.
Nuclear Fatigue Codified Design Rules: Development Status, Margins and Screening Criteria
Authors: Faidy Claude
Published: October 2018

In the past 10 years, different laboratory test results lead the International Standard Development Organizations (SDO) to review their fatigue design rules in different directions, in particular to consider consequences of environmental effects on existing design rules.

The key document that ask different questions to Code developers is the USNRC NUREG 6909 report: “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials” that confirms some environmental effects on S-N fatigue tests on small specimen. The open question is: how to transfer these results to Fatigue Design Rules of plant components?

This paper will review existing codified rules in major nuclear Codes; in particular USA ASME Boiler and Pressure Vessel Code Section III and French AFCEN RCC-M Code.

The paper will make a first historical background of these Codes and analyze background of these rules by consideration of field experience and existing tests results.

To conclude, the paper will summarize to-day “fatigue road maps” to evaluate margins and screening criteria to assure reliable and safe codified design fatigue life evaluation.
Considerations of Alloy N Code Extension for Commercial Molten Salt Reactor Development and Deployment
Authors: Ren Weiju
Published: October 2018

For commercial development and deployment of the molten salt reactor, a structural alloy that provides both strength at high temperature and resistance to very corrosive molten salt environment is required. To meet this requirement, a survey is conducted on domestic and international candidate alloys. Alloy N turns out to be the sole frontrunner in readiness for qualification to enable the desired deployment within an estimated 10 years. A review of the qualification for commercial nuclear applications indicates that Alloy N has met a large portion of the requirements. Gaps in the qualification are also identified. A search for historical data is underway to retrieve information needed for filling the gaps and upgrading the qualification. Scope of the discovered historical data is briefly discussed and strategic planning for research and development pathway is suggested to ensure successful evolution in commercial deployment of the molten salt reactor system.
Uncertainty Quantification of Finite Element Analysis of Uni-Axial Strength Test of Holed Composite Laminates
Authors: Ma Li , Fong Jeffrey T. , Marcal Pedro V. , Rainsberger Robert B. , Heckert N. Alan , Filliben James J.
Published: October 2018

In the aerospace industry, open hole specimens of composite laminates have been used in standardized tests to generate design allowables. Using finite element method (FEM) based tool MicMac/FEA with AB AQUS code interface and statistical design of experiments, Shah, et al. in 2010 [11] studied average-property-based failure envelope with uncertainty estimates of open hole specimen with quasi-isotropic carbon fiber-epoxy laminate. However, their FEM model is deterministic, without uncertainty analysis. In this paper, based on Shah’s FEM model, we developed FEM model of uni-axial strength test of holed composite laminates using ABAQUS with a serious of quadrilateral S4R and trilateral S3R shell element designs. The mesh density ranges from the original 8 × 8 (very coarse) to 48 × 48 (very fine). For each of the meshes, we compute the failure strength from Hasin failure criteria. Then we use a 4-parameter logistic function nonlinear least squares fit algorithm to obtain an estimate of the failure strength at infinite degrees of freedom (d.o.f) as well as its uncertainty at 50,000-d.o.f. and relative error convergence rates. Our results are then compared with Shah’s with the additional advantage that our results have uncertainty quantification that can be compared with experimental data. The significance and limitation of our method on the uncertainty quantification of FEM model of uniaxial strength test of holed composite laminates are discussed.
A Seismic Vulnerability Analysis of a Liquefied Natural Gas Subplant
Authors: Pedot Massimiliano , di Filippo Rocco , Bursi Oreste S.
Published: October 2018

“Special risk” industrial plants can be highly vulnerable when subjected to natural phenomena such as earthquakes, flooding and explosions. In this study we focused our attention on the performance of a liquefied natural gas (LNG) terminal subjected to extreme earthquakes; an LNG terminal consists of a series of process facilities connected by pipelines of various sizes carrying hazardous chemical components. Although tanks, pipes, elbows, bolted flanges have been a major concern in terms of seismic design, generally, they have not been analyzed with modern performance-based procedures. Thus, our work has been devoted to the assessment, within the performance-based earthquake engineering (PBEE) framework, of the seismic performance of tanks, pipes, elbows and bolted flange joints by means of seismic fragility functions. Particular attention was paid to component resistance and to loss of containment (LoC) due to leakage.

A representative case study of an LNG terminal has been selected and tank, support structures and pipework, including elbows and flanges were analyzed with a detailed 3D finite elements model. Preliminary analyses identified elbow and bolted flange joints as critical components. A mechanical model, based on experimental data, defines leakage limit states for bolted flange joints. A significant effort was also devoted to identification of a leakage limit state for piping elbows, and we found the level of the hoop plastic strain to be an indicator.

On a first stage for the probabilistic seismic demand analysis (PSDA) we applied the Cloud method, due to its advantages in terms of consistency in the seismic input and of computational savings. More precisely, we studied the behaviour of critical components using a set of 36 ground motions, selected from a database of historic earthquake accelerations. The results of seismic analysis show that bolted flange joints remain significantly below their leakage threshold while elbows at the top of the LNG tank are likely to show LoC. Fragility functions show that elbows located on the tank platform are relatively unsafe against earthquakes.

On a second stage, in order to detect more complex failure scenarios, we analysed an LNG plant comprising a more complex piping substructure with respect to the original FE model. Moreover, we have treated the LoC of elbows from a probabilistic point of view by means of a Gaussian probability density function associated to a hoop strain limit state. The results provided by the aforementioned refined piping system allow for an improved and more accurate seismic risk assesment of the LNG plant.
Calculation of Inspection Intervals for an Ammonia Storage Tank Based on Design Modifications, RBI, Commissioning Inspection, and FEA
Authors: Prewitt T. J. , Finneran Shane , Ruiz-Rico Juan Carlos
Published: October 2018

One of the most critical welds in the design of a large storage tank is the weld between the bottom annular plates and shell wall. The change in direction of the material introduces a biaxial stress, and possible stress concentration. This paper evaluates a method of determining a required inspection interval based on using a combination of conservative design modifications, risk based inspection (RBI) assessments, on site construction verification, and FEA analyses. In the case study presented, a design modification was made to specify this traditionally dual fillet weld as a full-penetration fillet weld. While this exceeds the typical design requirements, exceeding the minimum requirements, inspection codes do not provide acceptance criteria for the design. A more thorough volumetric inspection was conducted, in addition to the typical magnetic particle inspection, to confirm the full penetration of the weld was achieved. In making conservative changes to the design, more robust inspections, and performing RBI methodology, a longer inspection interval can be determined due to the increased information available on the outset. These small changes at the start of the construction can lead to increased operating time without an intrusive inspection through the lifespan of the tank.
Master Curve Testing on Reconstituted Surveillance Charpy Specimens
Authors: Gillemot Ferenc , Horváth Márta , Horváth Ákos , Szenthe Ildikó , Kovács Attila
Published: October 2018

The original WWER-440 surveillance had 6 sets of specimens and each set had 12 Charpy, 12 COD (crack opening displacement) and 6 tensile specimens made from base material, weldment and HAZ (heat affected zone). The Charpy size precrack TPB (three point bend) COD specimens were located at the end of the chains, where the flux is rapidly decreasing.

During the period of 1970–90, when the WWER-440-V213 units were designed, built and started to operate, the Charpy impact transition curve measurement was the accepted method to evaluate the radiation embrittlement. The technology and the standards to use small size fracture mechanical specimens in surveillance capsules were not developed at the time period when most of the second generation reactors — including the WWER-440 V 213 type — were designed, therefore the fracture toughness specimens were considered less interesting for the utilities and the safety authorities. Fracture toughness curves were elaborated in the laboratories on large size unirradiated specimens and radiation embrittlement adjustments were made according to the Charpy shift. However, during the past 30 years fracture mechanics has rapidly developed, and the testing moved to the direction of using small and mini sized specimens. The development of the Master Curve evaluation method [4,5] allowed the use of small specimens for fracture toughness testing in surveillance programs, and the results obtained on irradiated specimens may be used directly in the lifetime evaluation. The purpose of this work was to develop a specimen production technology and testing procedure to measure these data using the remnants of irradiated surveillance Charpy specimens, and the comparison of the data calculated from CMOD and LLD on irradiated CrMoV type RPV material and weldment.