bluuebunny/crossref_metadata_2025 huggingface dataset:
Embrittlement Trend Curves for Notch and Fracture Toughness of 15Kh2MFAA Type Steel
Authors: Brumovsky Milan , Kopřiva Radim , Kytka Miloš
Published: October 2017

Reactor pressure vessel integrity and lifetime evaluation is based on the use of fracture mechanics apparatus but most of the material vessel material data and their degradation during operation are based on results from Charpy V-notch impact tests. Then, empirical correlations between transition shift of temperature dependence of notch toughness and fracture toughness are applied.

Elaboration of „Master Curve“ approach for fracture toughness experimental data analysis allows to use fracture toughness data directly to the reactor pressure vessel integrity evaluation. Wider use of this approach is limited by the lack of appropriate database from surveillance specimen test data, as mostly only Charpy impact specimen are included into the Surveillance specimen programs. Fortunately, all WWER Surveillance programs contain also fracture toughness specimens, either pre-cracked Charpy size or CT-0.5.

Thus, database of fracture toughness data from Surveillance programs of WWER-440/V-213C type reactor pressure vessels, operated in the Czech Republic, Slovakia and Hungary and manufactured only by one manufacturer - SKODA JS, was collated and analyzed.

These vessels were manufactured from 15Kh2MFAA type steel and appropriate weld metal, both of Cr-Mo-V type with low content of detrimental impurities — P and Cu. Analysis of the data in fluence interval up to 6×1024 m−2 (with neutron energies En larger than 0.5 MeV) show that transition temperature shifts in fracture toughness temperature dependence are higher than for Charpy impact tests.

Several formulae have been applied for fitting these shift dependencies with chemical composition of materials and finally new Embrittlement Trend Curves for Charpy shifts have been corrected. Additionally, new Embrittlement Trend Curves for fracture toughness shifts based on “Master Curve” approach have been also proposed. Both trends are using simple power law on fluence with exponents around 0.6 and depend on phosphorus and copper contents even though effect of other elements has been also checked.
Leak Detection in Pressure Vessels Using Ultrasonic Techniques
Authors: Ranzolin Piazzetta Guilherme , Costa Flesch Rodolfo César , Schalata Pacheco Antonio Luiz
Published: October 2017

Non-destructive evaluation is an important part of the process to assure the quality of goods in manufacturing lines. This paper presents a comparative study of two methods of leak testing using acoustic waves. The objective of the experiment is to evaluate the response of ultrasonic-based techniques for leak testing. The first method is based on an active arrangement, which detects leaks by analyzing acoustic data generated by the gas leakage, which is measured by an ultrasound transducer. The second one is also based on ultrasonic signals, but it uses a passive arrangement in which an ultrasound emitter is placed inside the vessel. The leakage is then detected because the fluid from inside the vessel conducts the sonic signal to an external ultra-sound detector through the discontinuity. Data from a practical case study are presented and, based on the experimental results with real defective parts, strong points and weaknesses of each method are discussed and evaluated.
Remaining Life Assessment of an External Pressure Vessel in Creep Range and Inspection Findings
Authors: Ishizaki Yoichi , Yonekawa Futoshi , Yumoto Takeaki , Suzuki Teppei , Hijikawa Shuji
Published: October 2017

As widely recognized in the industry, it is important to evaluate the creep damage of an elevated temperature vessel so that the mechanical integrity of the vessel can be achieved through the adequate repair and replacement planning. This is quite straight forward procedure for internal pressure vessels.

For an external pressure vessel, it is not easy to assess the creep damage due to the complexity of the creep buckling analysis. Eventually, creep cavity evaluation technique without identifying the correct stress distribution has been used so often. However, due to the uncertainty of the technique itself plus conservative mindset of the inspectors, it tends to leads to an excessive maintenance most of the cases. In order to conduct a reasonable remaining life assessment, it is desirable to use the creep cavity inspection in conjunction with another assessment technique such as FEM creep analysis as stated in API 579-1/ASME FFS-1 10.5.7.

In this paper, comprehensive approach with FEM and field inspection such as creep cavity evaluation to reinforce the uncertainty of each method will be demonstrated.
Closed-Form Stress Intensity Factor Solutions for Deep Surface Cracks in Cylinders Subjected to Global Bending
Authors: Azuma Kisaburo , Li Yinsheng , Hasegawa Kunio , Shim Do Jun
Published: October 2017

Materials made of alloy 82/182/600 used in pressurized water reactors are known to be susceptible to primary water stress corrosion cracking. The depth, a, of flaws due to primary water stress corrosion cracking can be larger than half of the crack length c, which is referred to as cracks with large aspect ratios. The stress intensity factor solution for cracks plays an important role to predict crack propagation and failure. However, Section XI of the ASME Boiler and Pressure Vessel Code does not provide the solutions for cracks with large aspect ratio.

This paper presents the stress intensity factor solutions for circumferential surface cracks with large aspect ratios in cylinders under global bending loads. Finite element solutions were used to fit closed-form equations with influence coefficients Ggb. The closed-form solutions for coefficient Ggb were developed at the deepest points and the surface points of the cracks with aspect ratio a/c ranged from 1.0 to 8.0.
A Method for Stress Analysis of Cylinders With Loadings From Attached Rectangular Sections With an Aspect Ratio Greater Than Four
Authors: Millet Barry , Kirkpatrick Kenneth , Miller George , Mosher Bryan
Published: October 2017

This paper provides designers a methodology for determining membrane and bending stresses in cylinders with loads applied through rectangular attachments having a length to width aspect ratio greater the four (4). This paper extends the original work done by Bijlaard [1] and Dodge [2] as well as the work published in Welding Research Council WRC Bulletins. Bulletins 107 [3] and 537 [4] are limited to aspect ratios of four (4) and Bulletin 198 [2] is limited to aspect ratio of ten (10). This method provided also adds more precision to the Kellogg [5] method which was based on the work of Roark [6]. The data, curves and formulas presented in this paper are the result of a parametric finite element study across the geometry range. Attachments were analyzed with a slender attachment orientation parallel and perpendicular to the axis of the cylinder. Geometric parameters were varied over a range of cylinder diameter & thickness and attachment length & width. This study is limited to small displacement theory. This paper also provides a methodology for analysis of the attachment from the loadings.
Combinational Influence of Internal Flow and External Annular Axial Flow on Instability of Cantilevered Double Wall Pipes
Authors: Fujita Katsuhisa , Moriasa Akinori
Published: October 2017

When flexible pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In this paper, the pipe is subjected to internal flow and external flow at the same time. The dynamic stability of a double wall pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures for the development of a piping system in the field of ocean mining, and in the field of fluid energy generation, and so on. In this paper, the pipe structures are assumed to be composed of the cantilevered elastic tube structure. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence are added to are applied. Changing the flow direction and the fluid velocity as for the internal flow and the external flow, the dynamic stability of the double wall pipes is investigated and discussed. Moreover, changing the flow rate and the density of a fluid and a structure, these effects on the stability of double wall pipes are investigated.
Characterisation of Polytetrafluoroethylene and Fiber Based Gaskets Under Creep and Thermal Ratcheting
Authors: Kanthabhabha Jeya Rahul Palaniappan , Bouzid Abdel-Hakim
Published: October 2017

The objective of this research work is to typify PolyTetraFluoroEthylene (PTFE) and fiber based gaskets. Recurrent employment of Teflon based gaskets as asbestos gasket replacement in certain applications is due to their effective leak tightness and excellent chemical resistance. The research investigates the effect of cyclic and determinant temperature on the phenomenon of creep and thermal ratcheting under compressive load. The tests are performed at 4000 and 6000 psi compressive stress on virgin PTFE (vPTFE) and expanded PTFE (ePTFE) along with Inorganic Fiber Gaskets (IFG) at different temperatures. The Universal Gasket Rig (UGR) is utilized to perform the convoluted analysis of creep-thermal ratcheting coupling at different stress levels on selected gasket materials. The actual cumulative damage due to thermal ratcheting is separable into upper and lower bound regions indicating the highest and lowest of ratcheting temperature regions. The effect of thermal ratcheting tends to saturate after 12 and 15 cycles for expanded PTFE and fiber gaskets while no saturation is observed with virgin PTFE gaskets even after 20 thermal cycles. IFG and virgin PTFE gaskets exhibited similar percentage of thickness reduction under different applied stresses while expanded PTFE showed a maximum reduction under the least applied stress. The influences of temperature and load are manifested in the compressive creep property which in turn dictates the magnitude of cumulative damage due to thermal ratcheting. Lastly, the impact of creep and thermal ratcheting on the Coefficient of Thermal Expansion (CTE) is evident as the magnitude of CTE upsurges with the extent of induced damage.
Development of Software for the Implementation of Elastic and Simplified Inelastic Rules for Design of Class A Nuclear Components in Elevated Temperature Service
Authors: Swindeman Michael , Sham T.-L. , Jetter Robert I.
Published: October 2017

Software is being developed to aid assessment procedures of components under specified loading conditions in accordance with the elevated temperature design requirements for Class A components in ASME Boiler and Pressure Vessel Code, Section III, Rules for Construction of Nuclear Facility Components, Division 5, High Temperature Reactors, Subsection HB, Subpart B (HBB). There are many features and alternative paths of varying complexity in HBB. The initial focus of this program is a basic path through the various options for a single reference material, 316H stainless steel. However, the program will be structured for eventual incorporation all of the features and permitted materials of HBB. This paper focuses on a description of the overall program, particular challenges in developing numerical procedures for the assessment, and an overall description of the approach to computer program development.
The Effectiveness of Non-Loosening Fasteners
Authors: Shoji Yasumasa
Published: October 2017

Many people know that bolted fasteners are loosened and they sometimes suffer from the loosening. It is also the case for any plants who have hundreds of thousands of bolts.

Any of these bolts may cause serious problems when they are loosened.

Many countermeasures are proposed to prevent bolt loosening, but few of them are really effective.

So far, only three bolting systems passed NAS 3350 tests. They are Eccentric nuts, based on nut eccentricity, Lock’n bolt, based on outer expansion of bolt threads, and L/R nut, whose principle is not open.

As L/R nut is unknown how it works, this paper addresses the effectiveness of the Eccentric nuts and Lock’n bolts and compare them in simulation.

The author have been working in bolt system loosening for a long time and succeeded the simulation of the phenomenon. This paper is the continuous work of this research.
ORNL Evaluation of Safety Cases for Two Belgian Reactor Pressure Vessels Containing Quasi-Laminar Defects
Authors: Klasky Hilda B. , Bass B. Richard , Dickson Terry L. , Gorti Sarma B. , Nanstad Randy K. , Sokolov Mikhail A. , Server William L. , Williams Paul T.
Published: October 2017

The Oak Ridge National Laboratory (ORNL) performed a detailed technical review of the 2015 Electrabel (EBL) Safety Cases prepared for the Belgium reactor pressure vessels (RPVs) at Doel 3 and Tihange 2 (D3/T2). The Federal Agency for Nuclear Control (FANC) in Belgium commissioned ORNL to provide a thorough assessment of the existing safety margins against cracking of the RPVs due to the presence of almost laminar flaws found in each RPV. Initial efforts focused on surveying relevant literature that provided necessary background knowledge on the issues related to the quasi-laminar flaws observed in D3/T2 reactors. Next, ORNL proceeded to develop an independent quantitative assessment of the entire flaw population in the two Belgian reactors according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI, Appendix G, “Fracture Toughness Criteria for Protection Against Failure,” New York (both 1992 and 2004 versions). That screening assessment of the EBL-characterized flaws in D3/T2 used ORNL tools, methodologies, and the ASME Code Case N-848, “Alternative Characterization Rules for Quasi-Laminar Flaws”.

Results and conclusions derived from comparisons of the ORNL flaw acceptance assessments of D3/T2 with those from the 2015 EBL Safety Cases are presented in the paper. The ORNL screening analyses identified fewer flaws than EBL that were not compliant with the ASME Section XI (1992) criterion; the EBL criterion imposed additional conservatisms not included in ASME Section XI. Furthermore, ORNL’s application of the updated ASME Section XI (2004) criterion produced only four non-compliant flaws, all due to design-basis loss-of-coolant loading transients. Among the latter, only one flaw remained non-compliant when analyzed using the warm-prestress (WPS) cleavage fracture model typically applied in USA flaw assessments. ORNL’s independent refined analysis of that flaw (#1660, which was also non-compliant in the EBL screening assessments) rendered it compliant when modeled as a more realistic individual quasi-laminar flaw using a 3-dimensional XFEM (eXtended Finite Element Method) approach available in the ABAQUS© finite element code. Taken as a whole, the ORNL-specific results and conclusions confirmed the structural integrity of Doel 3 and Tihange 2 under all design transients with ample margin in the presence of the 16,196 detected flaws.
FEM Stress Analysis and Mechanical Characteristics of Bolted Pipe Flange Connections With PTFE Blended Gaskets Subjected to External Bending Moments and Internal Pressure
Authors: Sato Koji , Sawa Toshiyuki , Morimoto Riichi , Kobayashi Takashi
Published: October 2017

In designing of pipe flange connections with gaskets, it is important to examine the mechanical characteristics of the connections subjected to external bending moments due to earthquake such as the changes in hub stress, axial bolt forces and the contact gasket stress distribution which governs the sealing performance. One of the authors developed the PTFE blended gaskets and the authors examined the mechanical characteristics of the connections with the PTFE blended gaskets under internal pressure. However, no research was done to examine the mechanical characteristics of the connections with the newly developed PTFE blended gasket subjected to external bending moment due to earthquake. The objectives of the present study are to examine the mechanical characteristics of the connection with PTFE blended gasket subjected to external bending moment and internal pressure and to discuss the difference in the load order to the connections between the internal pressure and the external bending moments. The changes in the hub stress, the axial bolt force and the contact gasket stress distribution of the connection are analyzed using FEM. Using the obtained the gasket stress distribution and the fundamental data between the gasket stress and the leak rate for a smaller test gasket, the leak rate of the connection with the gasket is predicted under external bending moment and internal pressure. In the FEM calculations, the effects of the nominal diameter of pipe flanges on the mechanical characteristics are shown. In the experiments, ASME class 300 4 inch flange connection with 2m pipes at both sides is used and the test gasket is chosen as No.GF300 made by Nippon Valqua Industries, ltd. Four point bending moment is applied to the connection. The FEM results of the hub stress and the axial bolt forces are in a fairly good agreement with the experimental results. In addition, the FEM results of the leak rate are fairly coincided with the measured results.
Investigation of Leakage Rates in Pressure Retaining Piping
Authors: Silber Fabian E. , Schuler Xaver , Weihe Stefan , Laurien Eckart , Kulenovic Rudi , Schmid Stefan , Heckmann Klaus , Sievers Jürgen
Published: October 2017

Within the break preclusion concept, leak-before-break (LBB) behavior must be demonstrated for safety relevant pressure retaining piping systems in nuclear power plants (NPP) [1]. This requires leak detection systems in NPP with the capability to detect leak rates below the maximum allowable leak rate calculated by the LBB assessment according to nuclear standards, like the German KTA rule 3206 or the U.S. Standard Review Plan (SRP). An important part of the LBB assessment is the availability of accurate calculation models to predict the leak rate under normal operating conditions for postulated through wall cracks. Current leak detection systems in NPP are capable of reliably detecting liquid leak rates 0.05 kg/s. However, most of the available experimental leak rate data published in literature focus on the range between 0.2 kg/s and 2 kg/s, which is significantly above the detection limit. Therefore, additional experimental investigations are necessary to develop and verify leak rate calculation models for smaller leaks.

In order to investigate such types of leaks, a modular test facility (fluid-structure-interaction test loop) has been developed and installed at MPA University of Stuttgart within the framework of a research project sponsored by the German Ministry of Education and Research (BMBF). The test rig includes a leakage piping module which includes artificially machined slits and fatigue through-wall cracks. It allows the variation of the significant influencing parameters such as crack size, surface roughness and the system parameters pressure and temperature up to 75 bar and 280 °C and also the measurement of the pressure gradient across the crack surface at two locations. This is important to develop a better understanding of the two-phase flow and pressure drop across the leak channel.

A first test series has been performed and the results were used to evaluate existing leak-rate models. Within this paper an overview of the test facility, the testing procedure, and the results of the investigations will be presented and discussed.
Technical Basis for Conversion of Non-Mandatory Appendix F of Section III of the ASME Boiler and Pressure Vessel Code to a Mandatory Appendix: Part I — Appendix Rewrite
Authors: Wen Jie , McKillop Suzanne , Adams Timothy M. , Keating Robert
Published: October 2017

In 1974, the Level D Service Limits for Section III, Division 1, Class 1 components were published in Non-Mandatory Appendix F titled “Rules for Evaluation of Service Loading with Level D Service Limits”. Over the past 40 years, the scope of Appendix F has been expanded to be applicable to certain Class 1, Class 2 and Class 3 components and supports in Division 1 as well as in Division 3 and Division 5. With each addition, the organization and implementation of the rules in Appendix F became more cumbersome for the user and consistency between the Appendix and the Code Books1 was not maintained. At the same time, the use of these rules has evolved to the point where the non-Mandatory Appendix is essential the default for Level D Service Limits. Starting in the 2017 Code edition, the component design rules will reference Mandatory Appendix XXVII when Design by Analysis is used to determine Level D Service Limits. This paper describes the methodology utilized to convert Non-Mandatory Appendix F to Mandatory Appendix XXVII which includes the history of the Level D Rules in the ASME Code, the philosophy taken to convert Non-Mandatory Appendix F to Mandatory Appendix XXVII, and an overview of the new Appendix XXVII. The approaches to ensure identical safety margins are maintained and the basis for adding or clarifying three allowable stress limits are also included.
Effects of Finite Strains and Residual Stresses on Path Independence of the J-Integral for Ductile Cracks
Authors: Zhu Xian-Kui , McGaughy Tom
Published: October 2017

Large plastic deformation and residual stresses exist in mechanical damages to pipelines. If a crack occurs in the damages, residual stresses will affect mechanics behavior of the crack and path independence of the J-integral, and so the J-integral may lose capacity to describe fracture driving force.

This paper theoretically investigates basic conditions required for the path independence of the J-integral and major factors affecting the path independence, including the incremental plasticity, finite strains and residual stresses. Residual stress modified J-integrals are then introduced for ensuring the path independence. With use of a notched beam, detailed elastic-plastic finite element analyses are performed in terms of the incremental plasticity for a crack subject to three-point bending. The path dependence of the J-integral due to the three major factors is then evaluated. Numerical results show that the residual stress modified J-integral is path-independent, and able to describe the fracture driving force for ductile cracks in a residual stress field. This provides a new technology to assess pipeline integrity for cracks coupling residual stresses.
Confidence Bounds for Fatigue Distribution Functions
Authors: Harlow D. Gary
Published: October 2017

The effect of uncertainty is critical in the design of complex engineered systems, components, and structural materials subjected to fatigue. Uncertainty in fatigue life prediction is a combination of several factors. In fact, it cannot be eliminated from experimentation due to material and loading variability, manufacturing processing, and imprecise scientific modeling. Consequently, uncertainty must be characterized and managed. The impact of uncertainty is exacerbated especially when high reliability must be assured. One of the ways to estimate the effect of uncertainty is to consider confidence bounds for fatigue life prediction, specifically, for cumulative distribution functions associated with life. The purpose of this paper is to investigate the statistical variability and appropriately model that variability for life in fatigue using appropriate cumulative distribution functions, and subsequently, evaluate a variety of statistical methods to estimate confidence bounds. Specifically, the confidence bounds will be estimated using mean square error, Dvoretzky-Kiefer-Wolfowitz, and pointwise Normal approximation methods. Since high reliability and long life is typically desired, extra emphasis will be placed on estimation in the lower tails of the distribution functions. The ensuing analyses are based on data for a cold-rolled, low carbon, extra deep drawing steel, ASTM A969, and creep strengthened 9Cr-1Mo steel.
An Exploration of Achievable Tightness in ASME B16.5 Standard Flanges for Various Gasket Technologies
Authors: Bausman Anita R. , Waterland A. Fitzgerald , Rice Dale A.
Published: October 2017

Many industrial plant sites have assembly torque tables for standard ASME B16.5 flanges as part of their internal procedures for bolted flanged joints. It is common for end-users to change gasket materials and gasket designs to reduce costs and/or improve reliability or as processes evolve and change. As environmental awareness and regulations continue to increase, it is important to understand the different levels of tightness that can be achieved from various gasket technologies. Gaskets do not seal equally at the same assembly load. All bolted flanged joints sealed with a gasket have some emissions rate, albeit some vanishingly small on very tight joints.

The tightness parameter has an inverse relation to leakage; the tighter a joint, the less leakage it has. The less leakage, the less emissions result. Where emissions monitoring is intense, tighter gasket technologies are preferred. These tighter technologies are often more expensive. Where emissions are less a concern, river water as an example, more economical gasket selections are preferred. This paper explores gasket tightness performance of a number of materials and construction types common for industrial and power use. Material classes that will be explored include compressed fiber, polytetrafluorethylene (PTFE), flexible graphite (FG), and flexible vermiculite (FV). Construction types that will be explored include sheet materials, composites with metal inserts (flat or corrugated), grooved metal with soft facings (“kammprofile”), and spiral wound gaskets.

For the purposes of comparison, an example assembly torque table will be used. The table includes ASME B16.5 Class 150 flanges, sizes ½” through 24”, using A105 carbon steel flanges and high strength A193 B7 fasteners. With a better understanding of the general capability of a gasket class — the end user can more quickly select gasket materials and constructions suitable for a particular application. This work follows and expands earlier work done with more limited flange sizes. [1]
Combined Load and Displacement Controlled Testing to Support Development of Simplified Component Design Rules for Elevated Temperature Service
Authors: Wang Yanli , Jetter Robert I. , Messner Mark C. , Mohanty Subhasish , Sham T.-L.
Published: October 2017

Combined load and displacement controlled test results are being used to develop and verify a simplified component design methodology for elevated temperature service. A key feature of the proposed design methodology is the use of rules for the evaluation of strain limits that are based on the application of elastic-perfectly plastic (EPP) analysis method with a pseudo yield stress to bound component response to applied loadings. The resulting strain ranges would then be used as input to the evaluation of creep-fatigue damage. This paper describes testing with two separate servo-hydraulic machines that are electronically coupled in parallel to represent combined loading effects on a two-bar test configuration.
A Method to Estimate Process Plant Seismic Resilience
Authors: Caputo Antonio C. , Paolacci Fabrizio
Published: October 2017

Resilience is a concept encompassing both the system ability to survive perturbating events which may lead to a disruption of its operations, and the rapidity in restoring system capacity after the disruptive event has occurred. While the concept of resilience has been dealt with from a number of different perspectives and in different contexts, from supply chains to networked utilities to civil infrastructures and building, research about resilience estimation of industrial facilities is lacking. In this paper a quantitative method to assess plant resilience is developed with reference to process plants and disruptive events represented by natural events such as earthquakes. The proposed method is easy to apply and amenable to both deterministic and probabilistic analysis. It provides a direct estimation of capacity loss after the disruptive event, and the time trend of recovery as well as the related economic loss. Therefore, it may provide a decision making support to facility planners and emergency managers in the process industry.
Environmental Fatigue Evaluation for Interface of Dissimilar Metal Welded Piping
Authors: Lee Dae Geon , Kim Dae Soo , Yang Kyeong Jin , Lee Joon Ho , Jang Seong Cheol
Published: October 2017

Environmental fatigue evaluation is a key technology to extend Nuclear Power Plant design life. Since USNRC issued the RG 1.207 in 2007, many studies on fatigue evaluation in Light water Reactor coolant environments have been carried out by referencing documents such as NUREG/CR-6909, EPRI-TR-1025823, ASME BPVC Sec. III NB-3600/3200 Code, ASME Code Case, and so on. These documents presented environmental fatigue evaluation methods about each single-metal such as carbon steels, low-alloy steels, nickel-chromium-iron (Ni-Cr-Fe) alloys, and austenitic stainless steels. However, the environmental fatigue evaluation method for interface of dissimilar metal welding is mostly insufficient. Dissimilar metal welding has been widely used in nuclear industry. If environmental fatigue analysis method for dissimilar metal welding is developed, it will facilitate the design of piping for more safety. Therefore, the development of environmental fatigue evaluation for the interface of dissimilar metal welding should be studied. This paper presents environmental fatigue evaluation for the interface of dissimilar metal welded piping. The environmental fatigue evaluation for a dissimilar metal welded piping model was performed based on above documents.
Case Study of Shakedown Evaluation of a Shell With Nozzle Based on Elastic-Plastic Analysis
Authors: Shen Jun , Peng Heng , Wan Liping , Tang Yanfang , Liu Yinghua
Published: October 2017

In the past, shakedown evaluation was usually based on the elastic method that the sum of the primary and secondary stress should be limited to 3Sm or the simplified elastic-plastic analysis method. The elastic method is just an approximate analysis, and the rigorous evaluation of shakedown normally requires an elastic-plastic analysis. In this paper, using an elastic perfectly plastic material model, the shakedown analysis was performed by a series of elastic-plastic analyses. Taking a shell with a nozzle subjected to parameterized temperature loads as an example, the impact of temperature change on the shakedown load was discussed and the shakedown loads of this structure at different temperature change rates were also obtained. This study can provide helpful references for engineering design.
Non-Proprietary Application of ASME Code Section III, Appendix N, to SONGS Replacement Steam Generators
Authors: Blevins R. D.
Published: October 2017

Flow-induced vibration analysis of the San Onofre Nuclear Generating Station (SONGS) Replacement Steam Generators is made using non-proprietary public data for these steam generators on the Nuclear Regulatory Commission public web site, www.NRC.com. The analysis uses the methodology of Appendix N Section III of the ASME Boiler and Pressure Vessel Code, Subarticle N-1300 Flow-Induced Vibration of Tubes and Tube Banks. First the tube geometry is assembled and overall flow and performance parameters are developed at 100% design flow, then analysis is made to determine the flow velocity in the gap between tubes and tube natural frequencies and mode shapes. Finally, the mass damping and reduced velocity for tubes on the U bend are assembled and plotted on the ASME code Figure N-11331-4 fluid elastic stability diagram.
Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 6 — Proposal of New Type of Hysteresis Model for Ultimate Behavior
Authors: Fukasawa Tsuyoshi , Okamura Shigeki , Yamamoto Tomohiko , Watakabe Tomoyoshi
Published: October 2017

This paper describes a new type of hysteresis model applied for seismic response analysis, which provides restoring force characteristics containing various types of hysteresis loops generated by calculating differential equations, based on static breaking tests regarding thick rubber bearings. In order to reduce residual risk, there is increasing necessity to accurately predict seismic response against both design-basis ground motion and ground motion exceeding design-basis. This process of seismic response prediction is called seismic Probabilistic Risk Assessment (PRA). In general, a restoring force of rubber bearing under large deformation due to a major earthquake has strong non-linear characteristics containing the hysteresis loops. To improve the accuracy of seismic response predictions up to the ultimate behavior in PRA, a new hysteresis model to be applicable up to the breaking point in horizontal and vertical directions is proposed by the authors. The features of the proposed hysteresis model are as follows: (1) The hysteresis characteristics obtained by the proposed model have smooth curves as substantive hysteresis loops measured in breaking tests. (2) The various types of hysteresis characteristics can be captured efficiently as initial value problems since the proposed model, consisting of differential equations, directly allows the skeleton function, and unaffected by hysteresis law such as Masing law. This paper indicates applicability of the proposed hysteresis model to seismic response analysis through comparison of results of the static breaking test with results of analytical, and also describes the breaking mode obtained by the seismic response analysis.
Application of the Extended Finite Element Method (XFEM) to Simulate Crack Propagation in Pressurized Steel Pipes
Authors: Lin Meng , Agbo Sylvester , Cheng J. J. Roger , Yoosef-Ghodsi Nader , Adeeb Samer
Published: October 2017

The extended finite element method (XFEM) has recently become a very effective method to investigate the propagation of cracks in various structures under complex loading conditions. However, its use in the pipeline industry has been limited. This paper aims to apply XFEM to model our previous experimental results on NPS 12 grade of X52 steel pipes in which circumferential cracks with different sizes were pre-machined near the middle length and then eccentric tension was applied to the pressurized pipe specimens. Our previous experiments showed that the propagation of a surface crack was affected by the original crack configuration, the internal pressure level, and the external loading applied. The crack depth showed greater influence than the crack length on the burst load and the tensile strain capacity of the pipe. In this paper, the fracture criterion for modelling crack propagation using XFEM was defined by two damage parameters, the maximum principle stress and the fracture energy. The values of the damage parameters were varied until excellent agreement was obtained between one of our previous experiments and its numerical model. Then, this set of damage parameters was used to model another one of the experiments for verification. This paper describes our methodology for validation of XFEM and the adequate values of the damage parameters required to model crack propagation in X52 pipes.
Molecular Dynamics Simulation of Hydrogen-Activated Coalescence and Growth of Nano-Voids
Authors: Zheng Yao-Ting , Zhang Zaoxiao , Cheng Guang-xu , Xuan Fu-Zhen , Wang Zhengdong
Published: October 2017

The understanding of hydrogen embrittlement (HE) is of significant importance and fundamental interest owing to its negative effects on industrial metallic materials. The effect of solute H on the void coalescence and growth needs to be clarified. Using molecular dynamics simulation, the evolution of preexisting nano voids is studied in the presence of H atoms. As the per unit area concentration of trapped H atom on void surface reaches 0.45 /Å2, the movement of void is observed. It proceeds along with the interdiffusion of H and Fe atoms around the voids. Strain-mediated diffusion of H atoms from void surface to the zone between nearest voids occurs at first. Then the Fe atoms are affected by migrated H and diffuse in the opposite direction following the principle of energy minimization. Such mechanism can help us understand the formation of high pressure bubble at nano scale. Based on this useful information, some methods could be obtained to prevent the growth of voids further, such as strengthening the stability of metal lattice around voids by dopant etc.
Investigation on Acoustic Propagation of Ultrasound in Polyethylene Pipe Used in Nuclear Power Plant
Authors: Sheng Xiong , Hou Dongsheng , Zheng Jinyang
Published: October 2017

Polyethylene (PE) pipe, particularly high-density polyethylene (HDPE) pipe, has been successfully utilized to transport cooling water for both non-safety-related applications and safety-related applications in nuclear power plant (NPP). However, concerns of a lack of non-destructive examination (NDE) procedures and qualifications specialized for HDPE pipe impede its broader application. Traditional approximation without considering effects of acoustic dispersion could work for PE pipe with a small inspection depth. But for PE pipe of large size used in nuclear power plant, effects of acoustic attenuation and dispersion accumulate with depth, and have influence on waveforms of target pules, which brings great challenges to the energy concentration when performing ultrasonic phased-array inspection for PE pipe in NPP. In this paper, a theoretical method applying Szabo’s causal convolutional propagation operator based on causality theory was presented to obtain wave equations of ultrasound in PE considering both attenuation and dispersion, in which attenuation coefficient and phase velocity were used to separately characterize acoustic attenuation and dispersion. Then, an experimental method using ultrasonic spectroscopy technology was proposed to confirm the proposed model, and a good agreement was obtained. The results indicated that attenuation coefficient of PE had an approximately linear relation with frequency and that phase velocity rose logarithmically with frequency. Finally, effects of attenuation and dispersion on amplitude spectrum and waveform in time domain of the target signal were investigated. Frequency downshift and time delay shift had an influence on image resolution and focus capability, and were believed to be a restriction of current inspection technology. This work also theoretically proved that lower testing frequencies (less than 2.5MHz) could improve the inspection effectiveness of the applied inspecting systems for HDPE pipes in NPP applications.
Temperature Effects on Fracture Thresholds of Hydrogen Precharged Stainless Steel Welds
Authors: Ronevich Joseph A. , San Marchi Chris , Balch Dorian K.
Published: October 2017

Austenitic stainless steels are typically used in hydrogen environments due to their resistance to hydrogen embrittlement; however, the behavior of welds is not as well understood and can vary from wrought base materials due to chemical composition differences and the presence of ferrite in the fusion zone of the weld. Applications of welded austenitic stainless steels exposed to hydrogen are not limited to room temperature but also include sub-ambient environments, which can have an additional effect on the degradation. In this study, fracture thresholds were measured of three different austenitic stainless steel welds in the hydrogen-precharged condition. Forged 304L, 316L, and 21Cr-6Ni-9Mn stainless steels were gas tungsten arc welded with 308L filler metal and machined into 3-pt bend bars for fracture testing. Crack growth resistance (J-R) curves were measured of the three welds in the hydrogen-precharged condition at ambient (293 K) and sub-ambient (223 K) temperatures to determine the effects of temperature on fracture threshold. Fracture thresholds were determined using elastic-plastic fracture mechanics through development of J-R curves to determine the stress intensity factor following standard practice for determination of fracture toughness. Fracture threshold tests for the welds revealed significant susceptibility to subcritical cracking when tested in the hydrogen-precharged condition. The 21-6-9/308L and 304L/308L welds exhibited some variability in fracture thresholds that did not appear to trend with temperature, while the 316L/308L weld exhibited a reduction of over 50% in fracture threshold at the lower temperature compared to room temperature.

In addition to fracture testing, mini-tensile specimens were extracted from the weld region and tested at 293 K and 223 K in the hydrogen-precharged condition. Hydrogen-precharging slightly increased the yield strength relative to the as-welded condition for all three welds at both temperatures. For all three welds, hydrogen reduced the total elongation by 3–11% at 293 K, whereas reductions in total elongation from 50–64% were observed at 223 K (relative to room temperature without hydrogen). The role of slip planarity on hydrogen-induced degradation of ductility and fracture resistance is discussed as a function of temperature, nickel content, and hydrogen. The fracture surfaces were examined to elucidate the observed differences and similarities in mechanical properties.
Improvements in the Welding Technology for Heavy Wall Pressure Vessels 2 ¼ Cr 1Mo ¼ V Low Alloy Steels
Authors: Fusari Fausto , Marangoni Paolo , Musti Michele , Alberini Stefano
Published: October 2017

The standard practice recommended for high pressure vessels, having heavy walls, requires the implementation of weld joint preparation with narrow gap technique; this generally calls for a ‘two beads per layer’ sequence alongside the use of the submerged arc welding process. This process provides a high quality and uniformed weld joint whilst also reducing the residual stresses after welding.

In refinery equipment that are subjected to high pressures and are exposed to hydrogen environment, high strength materials such as 2 1/4 Cr 1 Mo 1/4 V are commonly used.

A recent study conducted on this material, and the process of submerged arc welding with narrow gap technique ‘two beads per layer,’ had identified a potential issue in complying with ASME Code specified creep resistance properties. In another setting, with regards to the properties of toughness in weld joints, other possible inconsistencies, in the narrow gap weld joint, between the weld centerline and center bead, were found.

In order to overcome the deficiencies stated above, an innovative welding technology is presented in this paper which is based on the preparation of a narrower groove than the commonly used narrow gap technique. Such groove has been designed to implement the ‘single bead per layer’ approach.

This paper illustrates that the use of this new technique results in improved quality of weld seams as applied in heavy wall high pressure vessels used in creep regime. The welding process considered is that of tandem submerged arc welding with two wires. The mechanical characteristics and results obtained by comparing the two techniques ‘two beads per layer’, and the new innovative one ‘single bead per layer’ will be evidenced and discussed.
On-Line Monitoring and Warning of Important In-Service Pressure Equipment Based on Characteristic Safety Parameters
Authors: Chen Xuedong , Yang Tiecheng , Fan Zhichao , Lv Yunrong
Published: October 2017

Characteristic safety parameter refers to the parameter that reflects the inherent safety margin of pressure equipments subjected to certain failure mechanism. It has three main characteristics. Firstly, it is sensitive to the change in failure mechanism. Secondly, the safety of pressure equipments can be guaranteed by controlling this parameter. Thirdly, it is easy to measure. By real-time monitoring of this characteristic safety parameter, the quantitative assessment of the structural integrity and furhter the diagnosis and warning on the safety of in-service pressure equipments can be realized. In this paper, the definition of characteristic safety parameter is given first for the pressure equipments subjected to several typical failure modes. After that, the selection principle, measurement technique and determination of its critical value, etc., are then introduced by analyzing typical examples. In combination with the technical concepts of the Internet of Things and Big-Data, some research suggestions are proposed with respect to the remote monitoring and diagnosis techniques based on the characteristic safety parameter, including the sensing measurement, monitoring and analysis of big data, real-time diagnosis and early warning of safety condition, etc.
Effects of Creep Deformation Model of Gr. 91 Steel at 600°C on Creep Fracture Mechanics Parameters
Authors: Won Min-Gu , Huh Nam-Su , Lee Hyeong-Yeon , Kim Woo-Gon , Choi Jae-Boong
Published: October 2017

The present paper investigates the effect of creep deformation model of Gr. 91 Steel at 600 °C on creep fracture mechanics parameters. Three types of creep deformation model were considered, i.e. Garofalo’s model and RCC-MRx model for primary-secondary creep region, and modified omega model for primary-secondary-tertiary creep region. The parameters for each creep deformation model were characterized from experiment results. Reference Stress (RS) method was used to estimate creep fracture mechanics parameters, C(t)-integral and COD rate for each creep model. Furthermore, elastic-creep finite element (FE) analyses were carried out to verify the results of RS method. Finally, the effect of creep deformation model was investigated by comparing the results of C(t)-integral and COD rate.
On the Influence of Flows in Clearances for Thermal Shocks in a Globe Valve
Authors: Meunier Sébastien , Ferrari Jérôme , Rit Jean-François , Hersant David , Mathieu Jean-Philippe
Published: October 2017

In a nuclear power plant, the functionality of valves must be proven under severe operating conditions. Thermal shocks of approximately 225°C are part of the qualification tests, that fulfill this demonstration.

Such shocks are studied here on a large globe valve (nominal diameter: 150 mm), experimentally and numerically.

The experimental campaign is carried out on the testing loop “CYTHERE” of EDF. 14 thermal shocks are performed successively in pressurized cold and hot water. The tested valve is equipped with 37 thermocouples distributed over its entire height. The 12 studs of the body-bonnet flange are instrumented with strain gauges, which allow the tracking of the clamping forces evolution in the flange.

A 3D numerical simulation of such a shock in the valve is performed. It is carried out by a chained multiphysics simulation: fluid, heat conduction and finally mechanics. The mechanical simulation models around 40 different parts with numerous contacts. Two versions of this simulation are presented, the second one takes into account a heat transfer taking place in clearances.

A good agreement between simulation and experiment is shown for temperature in the studs. For clamping forces, only the second simulation manage to reproduce tightening variations observed experimentally at the beginning of cold and hot shocks.