bluuebunny/crossref_metadata_2025 huggingface dataset:
A Review of Optimising the Design of a New Coke Drum Skirt
Authors: Berry Alex , Brown Warren , Seijas Antonio , Cook Sarah
Published: November 2019

Coke drums are subjected to severe thermal cycling with the skirt to shell connection weld being vulnerable to fatigue cracking. It is essential this connection is well designed to ensure a long life before repairs are inevitably required. Much has been written on coke drum skirt design with the aim of reducing the thermal stresses and strains encountered at the skirt connection weld, some designs have removed the weld completely allowing the drum to sit in an “egg-in-cup” arrangement. This paper includes a short literature review discussing Coke drum skirt designs and explains skirt behaviour during the drum cycle that results in eventual skirt cracking. A case study is reviewed in detail for a new pair of coke drums, where the predicted fatigue life of the chosen welded connection is assessed using axisymmetric, quarter symmetry and half symmetry finite element analysis supported by thermocouple data. The optimised design focuses on a conventional tangential design where the effects of the essential variables such as skirt thickness, skirt connection location, skirt-to head-gap and slot design (length, location & spacing) have been modelled and optimised to obtain a skirt design that produces the longest fatigue life for the intended duty cycle. Coke drum skirts must be installed onto the shell to exacting tolerances during manufacture to ensure concentricity and minimal gap between the skirt and shell. A brief overview of how this is achieved will be presented.
The Effects of Carburisation on Creep Response of Stainless Steel Components
Authors: Cakstins J. , Ainsworth R. A. , Su M.
Published: November 2019

Stainless steel components in the UK’s Advanced Gas-cooled Reactors can undergo microstructural changes near the surface due to the reactor carbon dioxide environment. Carburisation tends to increase the material’s elastic modulus, yield strength and creep resistance. However, the ductility of the material tends to be reduced. This paper assesses the effect on the component response of the changes in local elastic, plastic and creep material properties resulting from carburisation. A pressurised carburised cylinder is modelled analytically as a set of concentric, creeping homogeneous cylinders. The results show a reduced overall deformation rate in the steady state as expected. For completeness, it is shown quite generally that steady-state deformation in a creeping component is reduced by locally increased creep resistance. The cylinder model, however, shows that the locally increased creep and plastic resistance leads to higher stresses in the carburised region than in a homogeneous cylinder, particularly during the transition before steady-state conditions are established. The transient period before steady state creep is then examined in more detail numerically by allowing the material properties to change due to carburisation during the transient phase. This leads to reduced stresses in the carburised region. The influence of the results on deformation, triaxial stress fields and associated creep damage distributions are examined and used to provide guidance on both component assessment and on evaluation of carburised material properties from deformation measurements on test specimens.
Further Improvements to ASME Section XI Code Case N-806 in a Proposed Second Revision
Authors: McGill Robert O. , Antaki George A. , Moenssens Mark A. , Scarth Douglas A.
Published: November 2019

ASME Section XI Code Case N-806, for evaluation of metal loss in Class 2 and 3 metallic piping buried in a backfilled trench, was first published in 2012. This Code Case has been prepared by the ASME Section XI Task Group on Evaluation Procedures for Degraded Buried Pipe. The Code Case addresses the nuclear industry need for evaluation procedures and acceptance criteria for the disposition of metal loss that is discovered during the inspection of metallic piping buried in a back-filled trench. In a second revision of the Code Case, several changes are proposed. First, guidance is provided for analytical evaluation of greater detail including finite element analysis methods. A new nonmandatory appendix is included to provide procedures for the evaluation of soil and surcharge loads using finite element analysis. Next, a second new nonmandatory appendix is provided giving detailed guidance on the evaluation of seismic loads. Finally, the need to evaluate the fatigue life of buried piping subjected to cyclic surface loading is now included and a design factor applied to the modulus of soil reaction is introduced. This paper presents details of the proposed changes to Code Case N-806-1 and their technical basis where applicable.
Large-Scale Parallel Thermal Elastic-Plastic Welding Simulation Using Balancing Domain Decomposition Method
Authors: Yusa Yasunori , Murakami Yuma , Okada Hiroshi
Published: November 2019

From the mechanical point of view, welding processes can be modeled as a coupling problem between heat conduction and thermal elastic–plastic problems. Such a welding mechanics problem generally requires a large amount of computational time due to its nonlinearity as well as a lot of time steps with a moving heat source. To overcome this difficulty, we are developing a large-scale welding simulator based on the domain decomposition method, which is one of parallel finite element methods. In the present paper, the methodology of the domain decomposition method that is applied to welding analysis is presented, followed by the algorithm. Then, a bead-on-plate problem, which is a popular benchmark problem in the field of computational welding mechanics, was analyzed by the simulator. The bead-on-plate problem was successfully analyzed within very small numbers of iteration steps of the Newton–Raphson and conjugate gradient methods.
Temperature Profile and its Effect on Hardness Numbers of a Mild Steel Butt Weld
Authors: Ma Qin
Published: November 2019

Fusion welding of steel joints is common through history of industrial applications. Among those, Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) are most common. Fusion welding process comprises of rapid heating and cooling cycles. Each cycle produces a non-uniform and transient temperature distribution and causes rapid thermal expansion followed by thermal contraction. Thus plastic deformation and thermal residual stresses can be induced in a welded joint when it cools down gradually to room temperature. In this study, temperature profiles of a hand-weld mild steel butt weld are analyzed by means of the finite element method (FEM) through ANSYS Mechanical APDL The moving heat source is simulated using the Gaussian distribution heat source model. A parametric study was then performed to evaluate the importance of certain key process parameters that affect the quality of a weldment. The effects of temperature profile on hardness numbers inside and away from the heat affected zone (HAZ) are discussed. It was found that the residual stress results obtained from the simulation agree with the distribution of hardness numbers tested on the weldment sample.
Forensic Estimation of Uplift of an Anchored Tank During the 2011 Earthquake Off the Pacific Coast of Tohoku
Authors: Yoshida Yuichi , Taniguchi Tomoyo , Nakashima Teruhiro , Hatayama Ken
Published: November 2019

The reconnaissance just after the 2011 earthquake off the Pacific coast of Tohoku reported the pulling out of anchor bolts of an upright cylindrical tank. Regarding the tank as an unanchored tank and employing the accelerogram recorded at 2 km off the tank, uplift of the unanchored tank during the 2011 earthquake off the Pacific coast of Tohoku was forensically examined. The time history of the uplift displacement of the tank computed by the explicit finite element analysis reveals that the unanchored tank uplifts during the earthquake and its uplift displacement is more than the length of the pulling out of the anchor bolts found by the reconnaissance. This implicitly corroborates applicability of the explicit finite element analysis to analyzing the tank rocking behavior. In addition to that, the uplift displacement of the unanchored tank was estimated by some calculation methods available to date and compared with that computed by the explicit finite element analysis. Comparison reveals that the calculation methods used herein may likely overestimate the uplift displacement of the unanchored tank and need to improve their calculation accuracy.
A Method to Estimate Cross-Sectional Stress Distributions on Reinforced Nozzle Corners Under Internal Pressure
Authors: Oh Chang-Sik , Song Tae-Kwang , Lee Sang-Min
Published: November 2019

Stress distribution through the nozzle corner cross-section may be required to calculate stress intensity factor (SIF) for a nozzle corner crack in accordance with ASME Section XI Nonmandatory Appendix G. This paper proposes a simple method to predict nozzle corner cross-section stress distributions on reinforced nozzle corners of pressure vessels under internal pressure. This method includes simplified equations for predicting stresses on the inner surfaces of the nozzle corner region. These equations are expressed in terms of stress concentration factor (SCF) and geometric variables. Approximate SCF solutions for the reinforced nozzle corners are also proposed. Stress distributions using the proposed method are compared with finite element (FE) analysis results of nozzle-vessel intersections of various geometric dimensions, and agreements are quite good within postulated crack depths. Furthermore, SIFs calculated from the estimated stress distributions in accordance with ASME Section XI Nonmandatory Appendix G are compared with those from the FE results, showing good agreement.
The Effects of Crack Growth History on Fracture Toughness
Authors: Probert M. A. , Coules H. E. , Truman C. E. , Hofmann M.
Published: November 2019

The introduction of cracks into loaded versus unloaded components has a significant effect on the apparent fracture toughness within finite element modelling. The history effects of crack introduction can be beneficial to defect assessment procedures that do not consider prior plasticity specifically from crack introduction. It is assumed that as strain energy is released due to plastic deformation during crack formation a reduction in the energy available for crack propagation under fracture conditions is experienced. This can be characterized by the formation of a plastic wake behind the crack tip and leads to significant increases in load at critical J and other crack growth parameters for modelling situations. However experimental evidence validating this apparent fracture toughness increase are needed. A beneficial increase in apparent fracture toughness can prolong the life of components that might be taken out of service prematurely if history effects are not considered.

This paper discusses a series of experimental and modelling approaches that have been taken to assess the magnitude of the benefit in increase of apparent fracture toughness by the manipulation of crack introduction history effects. An initial parametric study of material properties on the effect of introducing cracks into loaded and unloaded components indicates that most benefit be derived from high hardness, high yield materials such as Aluminum 7000 series alloys. Further work has been carried out with experimental C(T) specimens of Aluminum Alloy 7475 T7351. Cracks were introduced by fatigue into the samples. One set of specimens was fatigued with a low mean load and the other with a high mean load, this was achieved by keeping a consistent ΔKI between specimens and changing the load ratio one set of specimens. Fracture test results indicate that the influence of prior plasticity on fracture initiation is much subtler in experimental trials than in the finite element model. Crack growth resistance curves and neutron diffraction results measuring the residual stress created ahead of the crack tip by this method are be discussed and contrasted with the parametric study and finite element modelling of the two different crack introduction scenarios.
Sliding Response of Unanchored Steel Storage Tanks Subjected to Seismic Loading
Authors: Kalemi Bledar , Farhan Muhammad , Corritore Daniele
Published: November 2019

Steel storage tanks are critical components of an industrial installation due to their high seismic vulnerability and containment of hazardous materials. Failure of a which, may lead to loss of containment (LOC) triggering domino effects such as explosion, environmental pollution, loss of functionality and disruption of business. Past earthquakes have demonstrated different type of failure modes in steel storage tanks. Although there are plenty of studies related to different failure modes like elephant foot buckling or tank uplifting, there are very few efforts on the sliding behavior of tank. Large displacements caused by the tank sliding can lead to pipe detachment and release of hazardous material which might cause damage propagation. Consequently, this damage state is very important for the Quantitative Seismic Risk Assessment of industrial plants.

In order to enumerate the sliding displacement of unanchored steel storage tanks, a simplified numerical model realized with OpenSees platform is proposed. The friction model used in OpenSees is calibrated with the results obtained from ABAQUS FE model. Sliding response of tanks with different D/H ratio is analyzed using the simplified model. Fragility curves for the tank sliding damage state are analytically evaluated for different D/H ratio of the tank using the “cloud method”. Finally, a parametric study is conducted in order to comprehend the influence of different parameters on the sliding behavior such as friction coefficient, tank filling level and the influence of the vertical component of ground motions.
The Effects of Non-Proportional Biaxial Loading Paths on Ductile Fracture Initiation: A Void Growth Analysis
Authors: Jin Zhaoyu , Wang Xin
Published: November 2019

The effects of non-proportional biaxial loading paths on ductile fracture initiation toughness are studied in this paper. To this end, the growth of a cylindrical void (hole) located in front of a mode I plane strain crack has been studied using large deformation finite element analysis (FEA). A specific microstructural feature of a steel alloy was thoroughly studied by having a single void positioned at a fixed distance from the crack tip and void that was equal to 10 times the diameter of the void. In particular, the non-proportional biaxial loading path effects on the crack tip blunting, void-growth, ligament reduction and near-tip stress fields are investigated computationally. Under small-scale yielding conditions, one proportional loading and two non-proportional loading paths are applied to the modified boundary layer (MBL) model. It is observed that the non-proportional load paths have a marked effect on the void growth, crack tip blunting and their interaction. By applying the criteria for the coalescence of the crack tip and void, the ductile fracture initiation toughness is estimated. It is shown that the ductile fracture toughness is dependent on loading paths, and the T-stress ratios. Results from this study are of relevance to ductile fracture assessment of components or pressure vessels that operate under non-proportional biaxial loading conditions.
Effect of Pre-Weld Heat Treatment on Microstructure and Creep Strength of ICHAZ in Grade 91 Steel
Authors: Wang Yiyu , Zhang Wei , Feng Zhili
Published: November 2019

In this work, Grade 91 base metal was normalized with two different cooling conditions, water quenching and air cooling. The intercritical welding thermal cycle simulated by using the Gleeble system was applied to the heat-treated base metals to reproduce the intercritical heat-affected zone (ICHAZ). Microstructure, including precipitate and tempered martensite, of the base metal and ICHAZ was carefully characterized with advanced microscopy techniques. Creep strength of the simulated ICHAZs was evaluated at a high creep temperature of 650 °C with a stress of 100 MPa. A correlation between the microstructure and creep behavior of the ICHAZ is built to understand creep rupture mechanisms in the ICHAZ. The results show that more coarse carbides precipitated along the prior austenite grain boundaries after tempering in the water-quenched base metal. These carbides cannot be fully dissolved by the intercritical welding thermal cycle. The simulated ICHAZ generated from the water-quenched base metal underwent a higher grain recovery and growth during the typical post-weld heat treatment at 760 °C. Both simulated ICHAZs from two pre-weld heat treated base metals exhibit an extremely low creep resistance with a typical ductile fracture during creep testing. The faster grain growth and precipitate coarsening in the ICHAZ, simulated from the water-quenched base metal, made it even worse.
Pitch and Pattern Effects on Streamwise Fluidelastic Instability in Tube Arrays
Authors: Hassan Marwan , Weaver David
Published: November 2019

Fluidelastic instability (FEI) is well known to be a critical flow-induced vibration concern for the integrity of the tubes in nuclear steam generators. Traditionally, this has been assumed to occur in the direction transverse to the direction of flow but the tube failures at San Onofre Nuclear Generating Station (SONGS) in Los Angeles proved that this assumption is not generally valid. A simple tube-in-channel theoretical model was previously developed to predict streamwise as well as transverse FEI in a parallel triangular tube array. This predicted that this array geometry was particularly sensitive to streamwise FEI for high mass-damping parameters and small pitch ratios, the conditions in which the SONGS failures occurred. The advantage of this simple modelling approach is that no new empirical data are required for parametric studies of the effects of tube pattern and pitch ratio on FEI. The tube-in-channel model has been extended to in-line square, normal triangular and rotated square tube arrays and the stability of these geometric patterns are analyzed for the effects of varying pitch ratio and the mass-damping parameter. The results are compared with the available experimental data and conclusions are drawn regarding the relative vulnerability of these different tube array geometries to streamwise FEI.
A Development of the Technical Basis for the New Code Case “Mitigation of PWSCC and CISCC in ASME Section III Components by the Advanced Surface Stress Improvement Technology”
Authors: Cho S. W. , Yi W. G. , Mohr N. , Amanov A. , Stover C. , Tatman J. , Vasudevan V. , Kim Y. S. , Pyun Y. S. , Naralasetty H. , Kim K. T.
Published: November 2019

It is necessary for nuclear power plant operation and spent fuel canisters to provide a sound technical basis for the safety and security of long-term operation and storage respectively. A new code case for mitigation of Primary Water Stress Corrosion Cracking (PWSCC) and Chloride Induced Stress Corrosion Cracking (CISCC) in Section III components by using an advanced surface stress improvement technology (ASSIT) is being developed by Task Group ASSIT which is one of the task groups under the ASME (The American Society of Mechanical Engineers). The necessary technical reports supporting this code case are being developed as part of joint research projects conducted by Doosan Heavy Industries and Construction (DOOSAN), Electric Power Research Institute (EPRI) and Sun Moon University (SMU). A well-known approach to prevent PWSCC and CISCC are to be performed using materials resistant to PWSCC and CISCC. The objective is to eliminate residual tensile stresses, or to induce compressive residual stress using ASSIT methods such as laser peening, water jet/cavitation peening, ultrasonic peening and ultrasonic nanocrystal surface modification (UNSM). Performance and measurement criteria for mitigation of PWSCC by ASSIT will be established based on the magnitude of surface stress and depth of compressive residual stress, sustainability, inspectability and lack of adverse effects. Additionally, for mitigation of CISCC by ASSIT, the evaluation of chloride induced corrosion pitting, the depth and density of corrosion pits and stress corrosion crack initiation and growth under chloride salt chemistry conditions are also being examined. This paper explains the approach, and progress of testing and analysis. The results and details from testing and analysis will be presented in a future PVP paper upon completion.
RCC-M Code: Recent Evolutions and Perspectives
Authors: Triay Manuela , Meister Eric , Lefever Benoît , Puybouffat Sylvain , Quéré Julien , Chantelat Emmanuel , Muller David , Cadith Julien , Marie Stéphane , de Mathan Nicolas
Published: November 2019

This paper covers the general approach followed by AFCEN, the French Society for Design, Construction and In-Service Inspection Rules for Nuclear Island Components in updating the nuclear code RCC-M, from the technical and organizational points of view. The main evolutions introduced in recent editions of RCC-M code are presented and commented on, with a focus on the 2018 edition of the code, which marks the end of the 3-year program carried out to demonstrate the conformity with European essential safety requirements for pressure equipment and French requirements for nuclear pressure equipment.

In addition, the main on-going activities are presented, as well as the future activities of the RCC-M subcommittee, in the frame of the 4-year editorial program that has been launched in 2019, in line with the AFCEN 4-year strategic plan. They encompass all fields covered by the code: design and analysis rules, material procurement, fabrication and nondestructive testing. The paper highlights how the industrial experience is integrated into the RCC-M code, and also how the new projects needs are taken into account.
Study on Added Mass Coefficient and Coupling Effect of Concentric Tube Bundles
Authors: Zhang Zhenshu , Guo Kai , Zhang Tianbao , Tan Wei
Published: November 2019

The added mass coefficient is an important parameter when calculating the flow induced vibration (FIV) in heat exchangers. The calculation method of the added mass coefficient for tube bundles in triangular and square arrays had been presented in relevant standards which like GB/T 151. Presently, concentric arrays of tube bundles are applied extensively in the heat exchangers at nuclear power plants. However, the method for calculating the added mass coefficient of tube bundles in concentric arrays has not been given in these standards. In this paper, in order to calculate the added mass coefficient of a central flexible tube surrounded by rigid tubes in concentric arrays, the fluid-structure interaction models of tube bundles has been established by ANSYS CFX. The influence of the circumferential and radial distance of the tube bundles on the added mass coefficient has been studied by calculating the natural frequency. The results are expected to provide the calculation reference for added mass coefficient of the tube bundles in concentric arrays. The coupling vibration of tube bundles in concentric arrays has been studied by the other model which is made up of all the flexible tubes, and the coupling vibration of the tube bundles is simulated by the rigid wall motion of ANSYS CFX. According to simulation results, there exists a band of amplitude peaks in the coupling vibration of the tube bundles. It is shown that as the circumferential and radial distance increases, the band of amplitude peaks becomes narrow.
Ratcheting Behaviour of 3D Printed and Conventionally Produced SS316L Material
Authors: Halama Radim , Pagáč Marek , Paška Zbyněk , Pavlíček Pavel , Chen Xu
Published: November 2019

This paper shows some differences in stress-strain behavior of conventional and 3D print SS316L. First, the influence of strain rate on the monotonic curve has been investigated. Specimens produced by Selective Laser Melting technology were not so sensitive to the strain rate. Viscoplasticity has to be taken into account for cyclic loading modelling in the case of conventionally produced SS316L but not for the 3D printed material.

A set of low-cycle fatigue tests was performed on specimens from both used production technologies. Uniaxial ratcheting tests were realized under constant amplitude of stress and varying mean stress. Experimental results show a good ratcheting endurance of SS316L produced by the Selective Laser Melting technology. Biaxial ratcheting tests were realized for 3D print SS316L only. Applied Digital Image Correlation technique makes possible to get more ratcheting curves from each ratcheting test.
European Project ATLAS+: Status of the WP1 Relative to the Experimental Program on Pipes and Specimens
Authors: Le Delliou Patrick , Moinereau Dominique , Bourgeois Myriam , Szavai Szabolcs
Published: November 2019

The 4-year 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 experimental work is conducted in support to 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 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 dissimilar metal weld (DMW)

This paper presents the WP 1, the experimental programme and summarizes the first results. A companion paper [1] presents in more details the experimental programme on the ferritic steel.
A Comparison of Proximity Rules for Surface Planar Flaws
Authors: Bouydo Afaf , Dulieu Pierre , Lacroix Valéry , Hasegawa Kunio , Mares Vratislav
Published: November 2019

Flaw assessment according to Fitness-For-Service (FFS) codes is usually based on equations describing the impact of a single flaw in piping or pressure vessels components. However, when multiple flaws are detected, combination rules are to be taken into account to evaluate whether these flaws should be combined into a larger flaw or should be evaluated as separate ones. In recent years, numerous works have been done to evaluate the conservatism of the combination rules required by FFS codes and, if needed, establish new characterization rules. These new characterization rules are based on the distance between flaws, their depths, their lengths or a combination of these three parameters in order to reflect the level of interaction between adjacent flaws. A comparison, focusing on multiple surface planar flaws, between ASME B&PV Section XI current combination rules, other Fitness-For-Service codes and other combination rules established by fellow authors is presented in this paper.
Research Plan and Progress to Realize Fracture Control of Nuclear Components
Authors: Kasahara Naoto , Wakai Takashi , Nakamura Izumi , Sato Takuya
Published: November 2019

For safety improvement after Fukushima daiichi nuclear power plant accident, mitigation of accident consequence for Beyond Design Basis Events (BDBE) has become important. Authors propose application of fracture control concept for mitigation of accident consequence of nuclear plants as follows.

In the case of reactor vessels under high temperature and pressure conditions, small cracks from local failure will release internal pressure and can avoid a large scale ductile fracture of general portions.

For piping under excessive earthquake, repeated elastic-plastic deformation and ratchet deformation dissipate vibration energy and reduce input energy from floor. They can prevent collapse of piping systems or break of pipe wall. Strength of pipe supports can be designed lower than pipe itself. Controlling the failure of supports would lead to plastic deformation without the break. The ratio of the frequency of seismic loading to the natural frequency of the piping system would also affect the failure behavior of piping systems.

This paper describes research plan and progress to realize fracture control of nuclear components.

The first step is clarification of actual failure modes and their mechanisms.

Next step is development of relative strength evaluation method among failure modes.

The third step is proposals of failure control methods. One of example is a vessel under high pressure and high temperature loadings. Another example is pipe under excessive earthquake.
CCG of PE100 and Life Prediction of PE Pipe With Axial Semi-Elliptical Crack
Authors: Zhang Lei , Lin Kaiming , Fu Yang , Gao Bingjun
Published: November 2019

High density polyethylene (HDPE) is widely used in city water and gas piping system and even in nuclear engineering for its excellent properties in flexibility, impact resistance, aging and corrosion resistance, reliable connection, long service life. It is generally believed that the typical failure mode of PE pipe under long-term static pressure load is the slow crack growth (SCG) caused by creep crack initiation (CCI) and creep crack growth (CCG), which is a kind of quasi-brittle failure. Scratching often occurs during PE pipe installation due to the drag of pipe without any protection, which would leave axial cracks as the initial defect. This would harm the long term performance of pressurized HDPE pipe. In the present work, the creep crack kinetics was experimentally determined in term of C* integral, and then CCG behavior of PE pipe with axial semi-elliptical crack was discussed. With the help of a CARE electronic universal testing machine and DIC displacement measuring system, creep tests are performed with smooth bar specimen of PE100 pipe parent material. And the stationary creep law parameters were determined. The crack opening displacement (COD) rates were determined by creep cracking test with cracked round bar specimen. With the help of compliance calibration tests, the COD curves were changed into crack propagation curves and the creep crack kinetics was eventually determined in term of C* integral. By assuming an semi-elliptical crack front with nearly the same C* integral, the creep crack propagation was predicted with the determined crack kinetics. And the allowable initial crack size was also determined for the PE pipe discussed. Compared with that determined in terms of SIF, current study yields much margin for the allowable initial crack.
A Study of the Conservatism in ASME BPVC Section VIII Division 2 Opening Design for External Pressure
Authors: Millet Barry , Ebrahimi Kaveh , Lu James , Kirkpatrick Kenneth , Mosher Bryan
Published: November 2019

In the ASME Boiler and Pressure Vessel Code, nozzle reinforcement rules for nozzles attached to shells under external pressure differ from the rules for internal pressure. ASME BPVC Section I, Section VIII Division 1 and Section VIII Division 2 (Pre-2007 Edition) reinforcement rules for external pressure are less stringent than those for internal pressure. The reinforcement rules for external pressure published since the 2007 Edition of ASME BPVC Section VIII Division 2 are more stringent than those for internal pressure. The previous rule only required reinforcement for external pressure to be one-half of the reinforcement required for internal pressure. In the current BPVC Code the required reinforcement is inversely proportional to the allowable compressive stress for the shell under external pressure. Therefore as the allowable drops, the required reinforcement increases. Understandably, the rules for external pressure differ in these two Divisions, but the amount of required reinforcement can be significantly larger.

This paper will examine the possible conservatism in the current Division 2 rules as compared to the other Divisions of the BPVC Code and the EN 13445-3. The paper will review the background of each method and provide finite element analyses of several selected nozzles and geometries.
Ductile Tearing Simulations to Support Design of Large Scale Tests on Ferritic Pipes to Be Performed in the European Project ATLAS+
Authors: Nicak Tomas
Published: November 2019

The safety and reliability of all systems has to be maintained throughout the lifetime of a nuclear power plant (NPP). This requires a systematic ageing management procedure for justifying their safe long term operation. One fundamental part in this process is to demonstrate the integrity of the nuclear power plant components. The European project ATLAS+ aims to develop and validate advanced methods of structural integrity assessment applicable in the ageing and lifetime management of primary and secondary circuit components.

To support development and validation of those methods, a large scale test program was developed with the aim to investigate fracture behavior of relevant piping material at the component level.

Three of planned large scale experiments focus on the fracture behavior of ferritic piping made of material WB 36 (15 NiCuMoNb 5), that is representative of secondary feedwater lines installed in German NPPs.

In order to verify design calculations conducted by means of the classical fracture mechanics approach based on J-Integral [1], detailed local approach analyses are performed for three mock-ups with different initial defects.

The local approach analyses presented in this paper are based on the local micromechanical model proposed by Gurson and further modified by Tvergaard.

Calibration of required material parameters and prediction of the mock-up behavior during the test is discussed.

In order to support constraint investigations stress triaxiality ahead of the crack front during crack propagation in the mock-ups is evaluated and compared to the stress triaxiality in CT20 and SENT specimens. As high stress triaxiality generally limits plastic deformation and increases the crack tip constraint, it is a good parameter to look at if constraint effects are considered.
Critical Crack Sizes of Pressure Vessels Based on Failure Assessment Diagram Under Design Requirements
Authors: Li Yuebing , Jin Weiya , Zhou Mingjue , Gao Zengliang
Published: November 2019

Standards or codes for defects assessment usually accompany their own design standards, such as, ASME BPVC section VIII and API 579-1/ASME FFS-1, GB 150 and GB/T 19624. The development of defects assessment standards should be adapted to the design requirements of pressure vessels. The consistency between fitness-for-service (FFS) procedures and design requirements of pressure vessels is discussed in this work. As a key link between FFS procedures and design standards, the required material fracture toughness not only depends on the methods of FFS procedures such as failure assessment diagram, but also on the design requirements. A procedure based on failure assessment diagram under design requirements is proposed to calculate critical crack sizes. The result can give some meaningful suggestions for the development of standards or codes.
Interface Microstructure and Thermal Expansion Mismatch in Alloy N/316H Bimetallic Plates
Authors: Xiao Jia , Li Zhijun , Jiang Li , Ye Linfeng , Yu Kun , Liang Jianping , Chen Shuangjian , Chen Zezhong
Published: November 2019

Two Alloy N/316H bimetallic plates have been fabricated by explosive welding and rolling technologies respectively. Metallographic observations indicate that the rolled bimetallic plate has a straight bond interface, in which some cavities and precipitates exist. While the explosive welded plate shows a wavy bond interfaces. The interface thermal expansion mismatch between the two alloys were evaluated in the two plates at high temperature. Results show that the thermal expansion coefficient of 316H is larger than that of Alloy N. The thermal expansion coefficient of the substrate plates depends on the thickness ratio between Alloy N and 316H, which reaches the maximum when the ratio is 1:4.
Vibration of a High Energy PWR Piping System due to Vibro-Acoustic Coupling: Evaluation and Mitigation
Authors: Meyer Gregory A. , Meneely Timothy K. , Koether Jeremy R. , Smith Stephen D. , DiBasilio David C.
Published: November 2019

Vortex Shedding at pipe junctions can create pressure pulsations and flow-induced vibrations. The flow through one pipe may result in a shear layer at the junction with a second pipe. Instabilities such as vortex shedding in the shear layer can then excite acoustic modes in the second pipe, especially when the flow in the secondary pipe is stagnant or weak. The effect is the excitation of a pipe organ mode, which under certain conditions, may result in unacceptable noise and/or vibration levels. Within the nuclear industry this phenomenon has been most frequently observed in boiling water reactors (BWRs), resulting in vortex-induced, main steam line associated stand pipe acoustic resonances.

This phenomenon has not been typically observed in pressurized water reactors (PWRs), especially in primary coolant loops due to the lengths of pipe needed to support acoustic resonances in water systems relevant to driving lower order structural piping modes. However, if certain conditions exist, PWRs do contain large sections of piping which can be susceptible to such flow-induced adverse noise and vibration effects. This paper describes the evaluation and mitigation of structural vibrations due to a vortex-induced excitation of an acoustic mode of a large side branch pipe in a high-energy, water-filled, PWR piping system. Specifically, an acoustic resonance was observed and structurally significant resultant vibration levels were measured on a safety related piping system directly connected to a PWR primary reactor coolant system (RCS) between the reactor and a steam generator.

A rapidly employed evaluation program was implemented, which included significant in-situ structural vibration measurements that informed a combination of acoustic, structural, and fluid-domain numerical modeling evaluations. These evaluations were performed in concert to provide both root cause insights and candidate mitigation strategies. Candidate mitigation strategies were then evaluated prior to inplant implementation via further modeling evaluations and a model-scale testing program. This paper describes the primary vibration characteristics of interest of the affected piping system, the data analyses and modeling methods used to successfully identify the vibro-acoustic phenomena, the developed mitigation strategies, and verification of the final mitigation strategy via model-scale with final demonstration occurring in the plant prior to fuel load.
Damage Evaluation of Grade 91 Thick Cylinder Under Variable Thermal Cyclic Loading Using Continuum Damage Coupled Viscoplastic Models
Authors: Islam Nazrul , Hassan Tasnim
Published: November 2019

This study evaluates creep-fatigue damage in the modified Grade 91 thick-cylinder tested by Japan Atomic Energy Agency (JAEA), to understand the failure mechanism of critical components of Fast Reactor nuclear plants. As modified Grade 91 demonstrated creep-fatigue interaction induced failure mechanisms, finite element analysis of high-temperature components will require a unified constitutive model (UCM) that can simulate various creep-fatigue responses with reasonable accuracy. Hence, a UCM coupled with various advanced modeling features including the continuum damage modeling features is investigated to demonstrate their predictability of the fatigue, creep and creep-fatigue responses of the modified Grade 91 steel. The modified UCM is implemented into ABAQUS for analysis of creep deformation in the thick cylinder benchmark problem. Finite element analysis results are presented to demonstrate how the thermal cycling influences the creep-deformation of this high-temperature component. It is also demonstrated how thermal cycling’s influence on fatigue life can be determined based on the damage variable incorporated in the UCM.
A Method for Directly Assessing Elastic Follow Up in 3D Finite Element Calculations
Authors: Messner M. C. , Jetter B. , Sham T.-L.
Published: November 2019

Elastic follow up significantly influences the creep and creep-fatigue life of structural components in elevated temperature service. As such, assessing the amount of follow up a component sees under a given loading history is critical in properly designing a component for high temperature use. Current methods for quantifying elastic follow up based on an elastic follow up factor use simple constitutive models and are available only for simple component geometries. This work describes a method for assessing the follow up factor, as a function of position and time, from a finite element simulation. The method recovers the simple, analytic solutions for simple geometries and material models but can also provide follow up factors for complicated components, loading histories, and material models. We use this new method to assess the range of follow up factors in a variety of prototypical high temperature structural components. This information can be used to improve design methods by better understanding the magnitude of follow up present in typical high temperature components. The method can also be used to support new design methods that require time-dependent point values of the follow up factor across a component.
A Combined Model Approach for Estimating T0
Authors: Erickson Marjorie
Published: November 2019

The current best-estimate model describing the fracture toughness of ferritic steels is the Master Curve methodology standardized in ASTM E1921. Shortly following standardization by ASTM, efforts were undertaken to incorporate this best-estimate model into the framework of the ASME Code to reduce the conservatisms resulting from use of a reference temperature based on the nil-ductility temperature (RTNDT) to index the plane strain fracture initiation toughness (KIc). The reference temperature RTT0, which is based on the ASTM E1921-defined T0 value, was introduced in ASME Code Cases N-629 (replaced by Code Case N-851) and N-631 to replace RTNDT for indexing the ASME KIc curve. Efforts are continuing within the ASME Code to implement direct use of the Master Curve model; using the T0 reference temperature to index an elastic-plastic, KJc fracture toughness curve.

Transitioning to a direct T0-based fracture toughness assessment methodology requires the availability of T0 estimates for all materials to be assessed. The historical Charpy and NDT-based regulatory approach to characterizing toughness for reactor pressure vessel (RPV) steels results in a lack of T0 values for a large population of the US nuclear fleet. The expense of the fracture toughness testing required to estimate a valid T0 value makes it unlikely that T0 will ever be widely available. Since direct implementation of best-estimate, fracture toughness models in codes and regulatory actions requires an estimate of T0 for all materials of interest it is necessary to develop an alternative means of estimating T0.

A project has been undertaken to develop a combined model approach to estimating T0 from data that may include limited elastic-plastic fracture toughness KJc, Charpy, tensile, ductile initiation toughness, arrest toughness, and/or nil-ductility temperature data. Using correlations between these properties and T0 a methodology for combining estimates of T0 from several sources of data was developed. T0 estimates obtained independently from the Master Curve model, the Simple T28J correlation model, and a more complex Charpy correlation model were combined using the Mixture Probability Density Function (PDF) method to provide a single estimate for T0. Using this method, the individual T0 estimates were combined using weighting factors that accounted for sample size and individual model accuracy to optimize the accuracy and precision of the combined T0 estimate. Combining weighted estimates of T0 from several sources of data was found to provide a more refined estimate of T0 than could be obtained from any of the models alone.
Effect of Internal Pressurization on the Creep-Fatigue Performance of Alloy 617 Based on Simplified Model Test Method
Authors: Wang Y. , Jetter B. , Sham T.-L.
Published: November 2019

The Simplified Model Test (SMT) is an alternative approach to determine cyclic life at elevated temperature and avoids parsing the damage into creep and fatigue components. The original SMT concept [1] considered that the effects of sustained primary stress loading could be safely neglected because the allowable local stress and strain levels were much higher than the allowable sustained primary stress levels. This key assumption is critically evaluated on Alloy 617 using internal pressurized cylindrical SMT specimens at 950 °C. The impact of combined internal pressurization and displacement-controlled creep-fatigue loading on the SMT cycle life is demonstrated at different strain ranges. The effect of primary load on the SMT design method is discussed.
Welding Simulation Integrated With Machine Learning to Train a Meta-Model for Fast Exploration of Various Weld Sequence Scenarios
Authors: Asadi Mahyar , Mohseni Mohammad , Tanbakuei Kashani Majid , Fernandez Michael , Smith Mathew
Published: November 2019

Distortion is a common problem in welded structures, and therefore welding standards require a mitigation plan to be in place before welding. When dealing with multiple welds, an optimal intermittent weld sequence can effectively minimize the distortion by counter-balancing the transient distortion during welding. However, the process of finding an effective weld sequence is a challenging task given a large number of possible combinations, i.e. several thousand for a few welds. As an acceptable approach, welding simulation tools allow engineers to optimize a welding sequence without the need for multiple physical samples. Despite efficient simulation tools and powerful supercomputers, yet simulation tools have been limited by CPU time and therefore not mature for practical designs. To this end, we constructed and integrated an inexpensive low-fidelity machine learning (ML) algorithm with the expensive high-fidelity simulation. This ML model was then trained to increase the fidelity by a wisely chosen train set of simulation to construct a meta-model for active exploration of various weld sequence scenarios. As opposed to existing ML algorithms that require an extensive data set to train, our algorithm picks relatively small training set to construct a meta-model. We present an example of our algorithm implemented in a real welded structure project.