bluuebunny/crossref_metadata_2025 huggingface dataset:
Flange Gasket Behavior Characterization for Service in Arctic Environment
Authors: Lejeune Hubert , Javanaud Stéphane , Richard Kevin
Published: October 2018

With Oil and Gas exploration and production in low temperature arctic environment, new concerns arise concerning the application of the existing design rules for these conditions. Most codes and standards for bolted flange calculation do not include specific rules concerning application at low temperature. Especially, gasket performances under low temperature are neither tabulated nor easily available from other public sources.

In this context, in collaboration with TOTAL, SCHLUMBERGER and SAIPEM sponsors, the CETIM has performed a program called ARCTICSEAL to characterize the flange gasket behavior in arctic environment. The goal is to check that gasket references, commonly used by these companies, are still usable under low temperature arctic conditions without main performance loss.

The test program involves mechanical and sealing tests performed on 4 gasket types (sheet fiber based, sheet PTFE based, sheet graphite based and graphite spiral wound) with both NPS 8 and NPS 16 gasket sizes. Gasket performances are determined at −60°C, after loading at −25°C. Additional test involving hot/cold thermal cycling ageing (simulation of intermittent hot process fluid in the bolted flange) have also been performed. The result shows the ability of the tested gasket references to maintain good sealing behavior in most cases. Moreover, the hot/cold thermal cycling ageing improves the sealing performances for some of the tested gasket references. Moreover, a dedicated test stand has been developed to study the behavior of NPS 8 flange connection exposed to quick heat-up after exposure to low temperature environment.
Reversing the Chell Model to Predict Using Monte Carlo Simulations the Original Fracture Toughness of Ferritic Steels
Authors: Van Gelderen Derreck , Booker Julian
Published: October 2018

Warm pre-stress (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture.

Various models exist to predict this type of enhancement, with the Chell model being one of the most widely used within industry. Previous research conducted by Van Gelderen et al. have reformulated the Chell model to create a method of undertaking Monte Carlo Simulations (MCS) to study the effect of WPS on brittle fracture.

Following on from this research, the Chell model could effectively be reversed providing a means of predicting the underlying fracture toughness from experimental WPS data. It also offers the possibility of assessing whether or not a specific specimen has indeed seen an enhancement, solely based on its experimental apparent toughness post WPS.

The reverse Chell model was applied to different experimental data and provided reasonable estimates of the original fracture toughness. In the same way that the traditional Chell model offers conservative estimates, the reverse Chell model also provides “reverse conservative” estimates of the original fracture toughness. It was also used to provide confidence that a typical fatigue pre-cracking procedure performed according to ASTM standard E399 would not be sufficient to induce a WPS benefit on the specimens. This type of check can be of particularly interest when manufacturing small scale specimens (small scale Single Edge Notch Bend (SENB) or miniature sized Compact Tension C(T) specimens); a practice often favoured by industry to maximise the number of tests possible.
Fundamental Modelling of Mechanisms Contributing to Tertiary Creep in Copper at 215 and 250°C
Authors: Sui Fangfei , Sandström Rolf
Published: October 2018

Extensive creep tests have been performed on oxygen free copper with 50 ppm phosphorus at both low and high temperatures. It is the candidate material for storage of spent nuclear fuel in Sweden. Basic models without fitting parameters have been formulated to reproduce primary and secondary creep. For a long time, only empirical models existed for fitting of tertiary creep. To understand the role of creep damage, including recovery, cavitation and necking, basic models that do not involve adjustable parameters are in urgent demand. Only recently, basic models taking the relevant mechanisms into account have been developed. These models were used to predict the tertiary creep for copper at 75°C. The modelled results were compared with experimental creep curves and good agreement has been found. In the present paper, the models are applied to creep tests at higher temperatures (215 and 250°C). A similar representation with good accuracy is obtained. This demonstrates that the fundamental model for back stress is applicable for the higher temperature tests as well.
Effect of Hydrogen on Creep Behavior of a Vanadium-Modified CRMO Steel and its Continuum Damage Analysis
Authors: Zhou Yu , Chen Xuedong , Fan Zhichao , Xu Peng , Liu Xiaoliang
Published: October 2018

Creep properties both in hot hydrogen and in air of a vanadium-modified CrMo steel 2.25Cr1Mo0.25V, widely used in hydroprocessing reactors in petrochemical industry, were investigated to determine the effect of hydrogen on high-temperature creep behavior of the low-alloy ferritic steel. The minimum creep strain rate in hydrogen is higher than that in air, whereas the creep strain at failure in hydrogen is relatively smaller. Many tiny spherical cavities are dispersively distributed in the ruptured specimen under hydrogen, which has relatively higher Vickers hardness. Based on the thermodynamics theory, the pressure of methane generated by the so-called “methane reaction” in the vanadium-modified CrMo steel can be calculated by using corresponding thermodynamic data, assuming that methane can reach its equilibrium state during cavitation. Meanwhile, a creep constitutive model based on continuum damage mechanics (CDM) was proposed, taking methane pressure into consideration. The results show that methane pressure increases nonlinearly with increase of hydrogen pressure while it decreases gradually with increase of temperature. The constitutive model considering the damage induced by methane pressure can be used to predict the effect of hydrogen pressure and temperature on creep life, indicating that the influence of hydrogen at elevated temperatures becomes smaller when increasing temperature or decreasing hydrogen pressure.
Assessment of Master Curve Material Inhomogeneity Using Small Data Sets
Authors: Wallin Kim
Published: October 2018

The standard Master Curve (MC) deals only with materials assumed to be homogeneous, but MC analysis methods for inhomogeneous materials have also been developed. Especially the bi-modal and multi-modal analysis methods are becoming more and more standard. Their drawback is that these methods are generally reliable only with sufficiently large data sets (number of valid tests, r ≥ 15–20). Here, the possibility of using the multi-modal analysis method with smaller data sets is assessed, and a new procedure to conservatively account for possible inhomogeneities is proposed.
Long Term Creep Life Prediction of New and Service Exposed P91 Steel
Authors: Ejaz Muneeb , Ab Razak Norhaida , Morris Andrew , Lockyer Scott , Davies Catrin M.
Published: October 2018

P91 steels are widely used in high temperature components for power generation. Creep data is often generated through accelerated short term creep tests, for practical reasons, via increasing stress or temperature though this may alter the creep behaviour. Through normalising the creep test stress by tensile strength the Wilshire models reduce the batch to batch scatter in the creep data and enable the prediction of long term creep data from relatively short term test results. In this work it is shown that the Wilshire models fitted to uniaxial creep rupture data can be used to predict failure in both as cast and service exposed multiaxial tests. This is provided that the equivalent stress is the rupture controlling stress, as is the case for the P91 tests examined, and the tensile strength is measured as part of the test programme.
Application of Finite Element in Accurate Calculations of Stresses in Expansion Joints
Authors: Ganguly Sudip
Published: October 2018

In order to evaluate the stiffness and perform detailed stress analysis of thick wall flange and flued expansion joint, a computer program based on finite element method was developed in C++, using 8-node axisymmetric element. Traditionally the analysis of expansion joints had been performed using the plate and beam theory which had several limitations and lead to inaccurate estimation of expansion joint stiffness and stresses. In this paper, initially the finite element mathematical model will be discussed, followed by comparison of the results of the stiffness calculations and stress analysis from the past method and that of the above-mentioned finite element model, and finally summarized by some discussions on the dependency of the accuracy of the results on the mesh density of the finite element model. The aforementioned finite element engine would be integrated to the pressure vessel and heat exchanger mechanical design software, AutoPIPE Vessel in the near future.
Investigation of Blast Wave Effects on Containment Wall and Steam Generator
Authors: Kim Tae Jin , Chang Yoon-Suk
Published: October 2018

When a sudden rupture occurs in high energy lines such as MSL (Main Steam Line) and safety injection line of nuclear power plants, ejection of inner fluid with high temperature and pressure causes blast wave, and may lead to secondary damage of adjacent major components and/or structures. The objective of this study is to assess integrity of containment wall and steam generator due to the blast wave under a postulated high energy line break condition at the MSL piping. In this context, a preliminary analysis was conducted to examine the blast wave simulation using coupled Eulerian-Lagrangian technique. Subsequently, a finite element analysis was carried out to assess integrity of the structures. As typical results, strain and stress values were calculated at the containment wall and steam generator, which did not exceed their failure criteria.
Flamanville EPR RPV’s Heads Carbon Segregation: Tests Program Definition to Characterize the Mechanical Properties of the Carbon Segregation
Authors: Marie Stéphane , Demarecaux Jérôme , Fichot Philippe , Keim Elisabeth , May Johannes , Lambrecht Marlies , Chaouadi Rachid , Birkett Peter , Hajjaj Mejido , Miller Cecile
Published: October 2018

To characterize the mechanical properties of the residual carbon segregation of the Flamanville EPR RPV heads, a testing program have been organized by Framatome and performed in 3 laboratories (Wood, Framatome technical center of Erlangen and SCK Mol).

This paper presents the tests program, how it has been defined and its goals. The main issue was the impact of the carbon content on the toughness properties. A procedure was defined to characterize specifically the toughness distribution in the upper part of the brittle-to-ductile transition. The ductile regime was also investigated. These tests were completed with tensile, Charpy and drop weight tests, representing a final total of approximatively 1700 mechanical tests.
The Notched C-Ring Test to Evaluate Reheat Cracking Susceptibility of CGHAZ in 2¼Cr-1Mo-¼V Steel Welded Joints
Authors: Huang Yu , Xu Chi , Chen Jin , Liu Chang-Jun , Chen Jian-Jun , Zhang Li
Published: October 2018

2¼Cr-1Mo-¼V steel is used for manufacturing and producing hydrogenation reactors. The coarse-grained heat affected zone (CGHAZ) of welded joints using 2¼Cr-1Mo-¼V steel have a higher reheat cracking susceptibility than the conventional 2¼Cr-1Mo steel. But there is no simple and effective method evaluating reheat cracking susceptibility of CGHAZ in 2¼Cr-1Mo-¼V steel welded joints at present. Based on Weld C-Ring Test and Gleeble® Thermo-Mechanical Test, a new Notched C-Ring Test to evaluate reheat cracking susceptibility of CGHAZ in 2¼Cr-1Mo-¼V steel was studied in this paper. According to the fitting relationship between RoA and critical stress, a criteria was proposed preliminarily to determine the reheat cracking susceptibility of 2¼Cr-1Mo-¼V steel CGHAZ using “not susceptible” and “slightly susceptible”.
A Proposed Guideline for Applying Waterhammer Predictions Under Transient Cavitation Conditions: Part 1 — Pressures
Authors: Stewart Matthew , Walters Trey W. , Wunderlich Greg , Onat Erin A.
Published: October 2018

Waterhammer analysis (herein referred to as Hydraulic Transient Analysis or simply “HTA”) becomes more complicated when transient cavitation occurs (also known as liquid column separation). While standard HTA transient cavitation models used with analysis based on the Method of Characteristics show good correlation when compared to known test/field data, the great majority of test/field data are for simple systems experiencing a single transient. Transient cavitation in more complicated systems or from two or more independently initiated transients have not been validated against data.

Part 1 of this paper describes the various safety factors already provided by ASME B31.3 for pressure containment, provides criteria for accepting the results of HTA calculations that show the presence of transient cavitation, and makes recommendations where the user should include additional safety factors based on the transient cavitation results.

Situations are discussed where waterhammer abatement is recommended to reduce hydraulic transient pressures and forces, and for increasing confidence in HTA results in specific cases. The result is a proposed comprehensive and pragmatic guideline which practicing engineers can use to perform waterhammer analysis and apply pressure predictions to pipe stress analysis.
A Proposed Guideline for Applying Waterhammer Predictions Under Transient Cavitation Conditions: Part 2 — Imbalanced Forces
Authors: Stewart Matthew , Walters Trey W. , Wunderlich Greg
Published: October 2018

Waterhammer analysis (herein referred to as Hydraulic Transient Analysis or simply “HTA”) becomes more complicated when transient cavitation occurs (also known as liquid column separation). This complication is exacerbated when trying to predict imbalanced forces as this often involves comparing pressure times area (“PxA”) forces at two locations (for example at elbow pairs). Whereas the pressure at each elbow location has increased uncertainty because of transient cavitation, the difference in PxA forces at elbow pairs involves subtracting one potentially uncertain pressure from another uncertain pressure. Exacerbating this uncertainty yet further, the existence of vapor in a liquid system can dramatically affect the fluid wavespeed and, hence, the timing of the pressure wave travel between two locations such as elbow pairs; so the pressure calculated at each location would not actually occur at exactly the same time.

This Part 2 discusses methods of accounting for uncertainty in HTA imbalanced force predictions due to cavitation. The criteria in this paper assume that cavitation in the HTA has been assessed and accepted per the criteria in Part 1 of this paper.

A guideline is proposed for accepting and applying such results and, in particular, makes recommendations on safety factors to use in pipe stress analysis for different cases. The specific recommendations depend on numerous factors including:

• Presence or absence of cavitation in hydraulically connected or isolated parts of the system

• If cavitation occurs, whether the peak forces occur before or after cavitation first occurs

• Size of the cavitation vapor volumes with respect to the computing volumes

• Use of point forces as a conservative substitute in place of potentially less certain elbow pair forces or the manual assessment of maximum envelope values for the force.

Situations are discussed where waterhammer abatement is recommended to reduce hydraulic transient forces, and for increasing confidence in HTA results in specific cases. The result is a proposed comprehensive and pragmatic guideline which practicing engineers can use to perform waterhammer analysis and apply imbalanced force predictions to pipe stress analysis.
Demonstrate ASME Section XI Appendix G Margins for Pressurized Water Reactor Inlet and Outlet Nozzle Corner Regions
Authors: Udyawar Anees , Hall J. Brian , Webb Justin , Carolan Alexandria
Published: October 2018

Since the implementation of pressure-temperature (P-T) limit curves in the 1960s for light water reactors, the P-T limit curves have been based on the limiting locations in the reactor coolant system, which are typically the irradiated reactor pressure vessel (RPV) region adjacent to the core (beltline) and the closure head flange. Recently, it has been questioned as to whether the reactor vessel inlet or outlet nozzle corners could be more limiting due to the stress concentration at these locations. The discussion presented in this paper provides technical justification that the RPV nozzle corner P-T limit curves are bounded by the traditional P-T limit curves for the pressurized water reactors (PWRs).

The current approach in evaluating the Pressurized Water Reactor Inlet and Outlet nozzle corner regions with respect to plant heatup and cooldown Pressure Temperature Limit Curves contains a number of conservatisms. These conservatisms include postulation of a large 1/4T flaw at the nozzle corner region, use of RTNDT (reference nil-ductility temperature), and fracture toughness prediction based on plane strain fracture toughness. The paper herein discusses several factors that can be considered to improve the pressure temperature limit curves for nozzle corners and increase the operating window for nuclear power plant operations.

Prior to the 2013 edition, the ASME Section XI Appendix G did not require the use of a 1/4T flaw for the nozzle corners; furthermore, a smaller postulated flaw size is permissible. Based on inspection capability and experience, a smaller flaw size can easily be justified. The use of a smaller flaw size reduces the stress intensity factors and allows for the benefit of being able to take advantage of increased material toughness due to the loss of constraint at the nozzle corner geometry. The analysis herein considers the calculation of stress intensity factors for small postulated nozzle corner flaws based on a 3D finite element analysis for Westinghouse PWR inlet and outlet nozzle corner regions. The Finite Element Analysis (FEA) stress intensity factors along the crack front are used in the determination of allowable pressures for the cooldown transient Pressure-Temperature limit curves.
Study on the Simplified Method of Special Supporting Structure for Steam Generator Tubes
Authors: Tan Wei , Jiang Songyuan , Li Zhao , Jia Zhanbin , Liu Liyan
Published: October 2018

The flow induced vibration of tubes in the steam generator gradually attracts great attention. The natural frequency of the tube is the basic parameter for vibration analysis. The supporting structures of the tube bundle in steam generator are the cinquefoil orifice-baffle and the anti-vibration bar which is different from the common baffle plate. The issue that researchers focus on is how these supporting structures affect the natural frequency. A simplified method of the special support in the tube bundle was studied based on the numerical simulation. According to the characteristics of supporting structures, the effect of stiffness of the supporting structures on the natural frequency was studied by the spring element constraints. The results show that when the stiffness of the support structure is larger than the magnitude of 105 N/m, the stiffness has no influence on the natural frequency. The frictional force of the circumferential constraint inside the plane is too weak to constrain the tube so we need to pay more attention on the vibration inside the plane. Through changing the contact length of the support component and tubes, the effect of the contact condition on the natural frequency is studied. The results show that the contact condition has a certain effect on the natural frequency. When the support is simplified as simple support, the influence on natural frequency is small and the deviation is less than 1.5%. And there is a certain safety margin under the simplified method. In the calculation process, the special support can be simplified as simple support and the calculation results are relatively accurate and conservative.
Experimental Investigation of Post-Fire Mechanical Properties of Quenched and Tempered High Strength Steel 07MnMoVR
Authors: Shao Shanshan , Jia Guodong , Cao Luowei , Zhuang Fakun
Published: October 2018

Quenched and tempered high strength steel 07MnMoVR with a better combination of mechanical properties and low susceptibility to welding crack has attracted attention for applications in engineering fields. Exposure to fire will subject steel to thermally induced environmental conditions that may alter the material’s properties. The residual strength after a fire event is important to assess the extent of the fire damage and the potential reusability of the vessel. This paper presents the details of an experimental investigation on the post-fire mechanical properties of 07MnMoVR steel. Uniaxial tension tests and Charpy impact tests were performed on coupons exposed to elevated temperatures varying from 550°C to 850°C for half an hour to 8 hours and then naturally cooled in air or cooled by water. The post-fire stress-strain curves, strength, ductility and impact toughness of 07MnMoVR steel are discussed. The results show that the yield plateau in post-fire stress-strain curves disappears when the exposure temperature is higher than 700°C. The residual yield strength and ultimate strength decrease firstly and increase afterward with increasing exposure temperature. The influences of duration time on the residual strength are considerable for exposure at 650°C. The post-fire impact toughness of 07MnMoVR steel at −20°C degrades drastically with increasing duration time when the exposure temperature reaches 700°C. The effects of cooling methods on strength and toughness become significant when the exposure temperature exceeds 750°C. The critical tempetature for the mechanical properties deterioration is 650°C. This study can provide basis data and guidelines for the fitness for service assessment of 07MnMoVR steel suffered from fire accident.
Modeling the Interfacial De-Bonding Behavior Between Steel Wire and Adhesive
Authors: Shi Jun , Shi Jianfeng , Nie Xinyu , Zhang Yue , Li Guangzhong , Chen Hanxin , He Yibin , Wang Qingjun
Published: October 2018

A polyethylene pipe reinforced by winding steel wires (PSP) has been widely used in petroleum, chemical engineering, and water supply, etc. The PSP has outstanding mechanical properties due to its unique composite structure. However, according to earlier research, interfacial de-bonding between steel wire and adhesive is the cause for bulging failure of PSP joint, which is more likely to occur when the temperature and inner pressure increases to some extent in the application. In this study, the interfacial behavior between steel wire and adhesive was investigated and the interfacial failure process was analyzed. The pull-out test was conducted using specimens that were manufactured following PSP process parameters. Finite element models were established to represent the mechanical behavior and the de-bonding failure process of the steel-polymer interface. Contact surface with cohesive behavior based cohesive zone model was utilized to characterize the interfacial properties. The interfacial de-bonding failure process included stick-slip interaction and frictional sliding interaction. Both the stick-slip interaction and the adhesive-friction transition were modeled in the simulation. Results were presented in terms of pull-out load-displacement relationships, maximum pull-out force, and nonlinear stress distributions. The simulation result agreed well with the experimental result.
On the Design of Contact Member Surface Shape of Bolted Joints to Minimize Clamping Load Loss
Authors: Zhu Linbo , Hou Yifei , Bouzid Abdel-Hakim , Hong Jun
Published: October 2018

Metal to metal contact between joint surfaces is widely used in bolted joints to obtain a rigid and a high performance connection. However, a significant amount of clamping load is lost when the joint is subjected to mechanical and thermal loading including creep and fatigue. In practice, to prevent bolt loosening, additional parts such as spring washers, double nut, spring lock washers, Nyloc nut and so on are used. Those methods are costly and influence the stability of the joint and affect its structural integrity.

It is well established that a small compression displacement in clamping parts leads to a big clamping load loss in stiff joints. This paper discusses the relationship between connection stiffness and clamping load and presents a method that improves clamping load retention during operation by a careful design of the member contact surface shape. A single bolted joint with two clamping parts is modeled using finite element method (FEM). A method is proposed to obtain a specific stiffness by an optimized geometrical shape of the joint contact surfaces. The result shows that the contact surface shape based on a gradually varying gap can improve the retention of the initial clamping load. Furthermore, a formula of the connection stiffness based on the curve fitting technique is proposed to predict residual clamping load under different external load and loosening.
Prediction of the Leakage Threshold for Hertzian Contact Seals: A Cellular Automata Model
Authors: Vande Voorde John , Van Wittenberghe Jeroen
Published: October 2018

The prediction and evaluation of leakage and leak tightness is an important issue in a multitude of high-pressure applications, such as valves, flanges or threaded connections. Through the use of finite element techniques it is in general possible to determine the local contact conditions at the seal on a macroscopic level (to wit the extent of the contact area and the contact pressure in this area). However, the leak tightness of a contact area depends also on the surface topology, which is a microscopic characteristic. Therefore the assessment of leak tightness requires an evaluation criterion relating both scales. Over the years a lot of empirical evaluation criteria have been developed, each with their own application domain. However, in terms of modelling the leakage a big step forwards was made only in the last decades. The Persson method models the contact area microscopically using contact models developed in the field of tribology. This contact evaluation is then combined with results from percolation theory, which state that for a sufficiently large contact area and a uniform contact pressure leakage will occur beyond a well-specified threshold. This has yielded a potent way of evaluating leakage, but the application is limited by the requirement that the contact pressure be uniform. In many applications, such as valves or O-ring seals, the contact is Hertzian and the contact pressure distribution is not uniform but parabolic. This paper will report the first results of an effort to extent such models to Hertzian contact seals. A set of samples for leakage experiments was produced with varying surface topology. The surface of these samples is measured and the leakage behaviour under high pressure is evaluated. At the same time a cellular automata model was built and used to model percolation under non-uniform contact pressures in an effort to adapt the Persson model. Finally the experiments and the modelling results are brought together via a finite element model and compared to each other.

This paper will focus on the development of the cellular automata model and the obtained simulation results.
Fracture Toughness of Defects Orientated Parallel to a Dissimilar Metal Weld Boundary
Authors: O’Connor A. N. , Davies C. M. , Nikbin K. M.
Published: October 2018

Dissimilar Metal Welds (DMWs) are used in many industries to increase the service life of components. Typically a corrosion resistant material is bonded to the internal surface of a second material, this is often referred to as cladding. This type of composite component provides the desired mechanical properties and corrosion resistance without excessive cost. Structural integrity assessments can be used to estimate the remaining life of critical components but these methods are complicated and results are dependent on factors such as: material properties, defect size, defect location and the direction of defect propagation. The cladding process is generally conducted via welding which results in yield strength residual stresses. The interaction between primary and secondary stresses on crack driving force (CDF) are not well understood, particularly at the interface between multiple materials where the microstructure is not homogeneous. These unknown factors contribute to overly conservative structural integrity assessments. This work investigates the fracture toughness of defects orientated parallel the interface of a dissimilar metal clad weld using experimental and finite element (FE) methods. A nuclear grade austenitic clad ferritic steel was investigated. A fracture toughness test was conducted on a CT specimen and the influence of the materials boundary on crack propagation was examined using digital image correlation (DIC). DIC of the fracture toughness test shows that high amounts of strain exist both in the region immediately surrounding the crack tip and in the ferritic material at the material boundary. Post-test analysis of the specimen showed two defects initiated at the root of the notch on the outer surface of the specimen. One longer notch was found internally. Two-dimensional plane stress and plane strain FE analyses were conducted and compared to the experimental results.
RCC-M Code: Main Evolutions From the 2016 to 2018 Editions
Authors: Triay Manuela , Lefever Benoit , Quéré Julien , Gobert Jean-Luc , Chantelat Emmanuel , Puybouffat Sylvain , Cadith Julien , Meister Eric
Published: October 2018

The paper will cover the general approach followed by nuclear code RCC-M [1] of AFCEN, the French Society for Design, Construction and In-Service Inspection Rules for Nuclear Island Components, in codes and standards setting, from the technical and organizational points of view. After reminding the main modifications introduced in the 2016 & 2017 editions, the main evolutions expected in the 2018 edition of RCC-M code will be explained and commented, as well as the main new topics of activity of RCC-M subcommittee. The presentation highlights how the industrial experience is currently integrated into the RCC-M code. It also develops how the substantial effort carried out by AFCEN for the last three years, to demonstrate the conformity with European and French regulatory requirements, led not only to the development of dedicated guides and modifications in regulatory appendices of the code, but also to improvements in the main parts of the code.
Application of the FAVOR-OCI Fracture Mechanics Computer Program to ASME Code Section XI, IWB-3610 Flaw Acceptance Criteria Evaluations
Authors: Dickson Terry L. , Williams Paul T. , Bass B. Richard , Klasky Hilda B.
Published: October 2018

This paper presents an overview of added features in a new version of the FAVOR (Fracture Analysis of Vessels Oak Ridge) computer code called FAVOR-OCI. The original FAVOR code was developed at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) under the sponsorship of the US Nuclear Regulatory Commission (NRC). FAVOR is applied by US and international nuclear power industries to perform deterministic and probabilistic fracture mechanics analyses of commercial nuclear reactor pressure vessels (RPVs). Applications of FAVOR are focused on insuring that the structural integrity of aging, and increasingly embrittled, RPVs is maintained throughout their licensed service life. Based on the final ORNL release of FAVOR, v16.1, FAVOR-OCI extends existing deterministic features of FAVOR while preserving all previously-existing probabilistic capabilities of FAVOR.

The objective of this paper is to describe new deterministic features in FAVOR-OCI that can be applied to analytical evaluations of planar flaws. These evaluations are consistent with the acceptance criteria of ASME Code, Section XI, Article IWB-3610, including Subarticles IWB-3611 (acceptance based on flaw size) and IWB-3612 (acceptance based on applied stress intensity factor). The linear elastic fracture mechanics (LEFM) capabilities of FAVOR-OCI also incorporate the analytical procedures presented in the Nonmandatory Appendix A, Analysis of Flaws, Article A-3000, Method of KI Determination, for both surface and subsurface (embedded) flaws.

The paper describes a computational methodology for determining critical values of fracture-related parameters that satisfy ASME Code Section XI acceptance criteria for flaws exposed to multiple thermal-hydraulic transients. These compute-intensive analyses can be carried out with a single execution of FAVOR-OCI. The new methodology determines critical values by solving for either the point of tangency or point of intersection between applied KI versus time histories and a user-selected cleavage initiation toughness material property (e.g., ASME KIc, FAVOR Weibull KIc, or Master Curve Weibull KJc) for surface or subsurface flaws. Situations where warm prestress conditions apply can also be addressed. The paper highlights a need for this new capability via applications to a recent independent review of safety cases for RPVs in two Belgian nuclear power plants (NPPs). That review required ASME Section XI assessments of several thousand embedded, quasi-laminar flaws in the wall of each RPV Analysis results provided by the new capability contributed to the technical bases compiled from several sources by the Belgian nuclear regulatory agency (FANC) and eventually used by FANC to justify the restart of these NPPs.
Effects of Crack Introduction History on Fracture Initiation in Residually Stressed Components
Authors: Probert Molly A. , Coules Harry E. , Truman Christopher E.
Published: October 2018

If a crack is introduced progressively into an elastic-plastic material containing a residual stress field, the incremental relaxation of the residual stress field causes the formation of a plastic wake along the crack boundaries. This leads to the reduction in the J parameter for a crack of a given size, compared to a crack with the same dimensions which has been introduced instantaneously, having the crack faces released simultaneously along the whole length, a 40% reduction is observed in the current analysis. This reduction in J is due to the dissipation of strain energy which is otherwise available for further crack extension, as in the instantaneously introduced crack. This is important for the current J-based fracture assessment common in the nuclear and petrochemical industries such as EDF Energy’s R6 and BS7910:2013 as they currently assume instantaneous insertion of cracks as this is inherently more conservative. Although many studies demonstrating this effect in FE are available, there is little experimental evidence for this phenomenon. Especially those including rigorous comparisons with specimens that have been ‘instantaneously’ cracked. This may be due to the difficulty inherent in manufacturing such a specimen as manufacturing processes rely on the incremental removal of material. The aim of this paper is to detail analysis of a novel method of crack introduction that aims to replicate the deformation behavior of an instantaneously introduced crack tip in a model that has had the nodes released in a progressive manner. This will allow specimens to be machined in a way that replicates ‘instantaneous’ cracking allowing for experimental techniques to be developed to display the difference between instantaneous and progressively introduced cracks.
A Study on the Fracture Toughness at Different Locations of SMAW Welded Joint of Primary Coolant Piping
Authors: Yu Weiwei , Fan Minyu , Shi Jinhua , Xue Fei , Chen Mingya , Chen Xu
Published: October 2018

Two primary coolant pipes were narrow-gap multipass circumferentially butt welded by shielded metal arc welding (SMAW) method and then subjected to micro-hardness tests to distinguish the base metal (BM), heat affected zones (HAZs), fusion zones (FZs) and weld metal (WM). Subsequently, uniaxial tensile tests were performed to investigate the tensile properties on each area in SMAW welded joints. The fracture toughness has been investigated at the above four different locations of the SMAW welded joints. Then the 0.2mm offset line method and the stretch zone width method have been both employed to determine the critical initial fracture toughness Ji. The results indicate that the fusion zones (FZs) have the worst fracture toughness compared with other locations over weld joints.
Improved Model Tests to Investigate the Failure Modes of Pipes Under Beyond Design Basis Earthquakes
Authors: Nakamura Izumi , Kasahara Naoto
Published: October 2018

In order to investigate the failure modes of piping systems under the beyond design basis seismic loads, the authors proposed an experimental approach to use pipes made of the simulation material instead of steel pipes in the previous study. Though the ratchet-collapse (ratchet and subsequent collapse) was successfully obtained as the failure mode through the shaking table test using the pure lead (Pb) pipes as the simulation material pipe specimens, there was concern that characteristics of pure lead was somewhat extreme considering the analogy with the stress-strain relationship of steel. In order to resolve such concern, a modified experimental procedure has been developed. In the modified procedure, lead-antimony (Pb-Sb) alloy is used as the simulation material. Through the shaking table tests on single elbow pipe specimens made of Pb-Sb alloy, it is found that the typical failure mode is the ratchet and subsequent collapse, as same as the results by the shaking table tests of the Pb pipe specimens. The results indicate that the lower input frequency than the specimen’s natural frequency is prone to cause failure to the specimen, while the higher input frequency hardly causes the failure. The tendency of the global behavior of specimens is similar each other between the Pb pipe specimens and the Pb-Sb alloy specimens, but the strength of self-weight collapse of the Pb-Sb alloy pipe specimen is much higher than that of the Pb pipe specimen. Due to such higher strength of Pb-Sb alloy pipes, a prospect to conduct an excitation test on a more complicated piping system model is obtained.
Constraint Assessment for Cruciform Specimens With a Semi-Elliptical Crack
Authors: Cao Yupeng , Qian Guian , He Yinbiao , Chao Yuh J.
Published: October 2018

A real crack to be assessed in a RPV is generally a shallow crack subjected to biaxial far-field stresses. However, the fracture toughness Kc or Jc, which is an important material property for the structural integrity assessment of RPV containing cracks, are usually tested on deep cracked compact tension [C(T)] or single-edged bending [SE(B)] specimens under uniaxial loading. The fracture toughness data do not reflect the realistic biaxial loading state that the cracks are subjected to. Cruciform bending [CR(B)] specimen is therefore developed to simulate the biaxial stress state. In this paper, a series of finite element (FE) simulations of the CR(B) specimens containing different semi-elliptical cracks are conducted. Stress-strain curves of materials of different yield strength and hardening behavior reflecting the variation in the mechanical properties of RPV steels due to aging or temperature change are implemented into the finite element models. The J-A2 theory is applied to analyze the crack tip constraint. The results show that the biaxial effect is material property dependent and affected by load levels.
Experimental Study on Mechanical Properties and Microstructure of 2.25Cr1Mo0.25V Steel by the Influence of Heat Treatment and Welding
Authors: Li Qing , Cheng Guangxu , Qin Mu , Zhang Zaoxiao
Published: October 2018

In this paper, the mechanical properties and microstructural changes of 2.25Cr1Mo0.25V steel under different heat treatment and welding process were investigated. The heat treatment of steel during practical processing is taken as a reference. Different heat treatment time are used to obtain samples with different condition. Automatic submerged arc welding was used to obtain welding sample. The mechanical properties of different samples are obtained by tensile test; the evolution of microstructure and precipitates of different sample with heat treatment and welding was studied on scanning electron microscopy. The experimental results show that with the increase of heat treatment time, the strength of the samples decreases and the plasticity remains nearly constant. Heat treatment also affects the precipitation of carbides; the longer the heat treatment time is, the more precipitates are. Compared with the base metal, the welding metal sample has higher strength. The amount of precipitates in welding metal is much larger than it in base metal. The research on precipitation shows that there are different kinds of precipitates which have different morphologies in welding metal.
An Improved Phased Array Ultrasonic Testing Technique for Thick-Wall Polyethylene Pipe Used in Nuclear Power Plant
Authors: Qin Yinkang , Shi Jianfeng , Zheng Jinyang
Published: October 2018

With the application of High-density polyethylene (HDPE) pipe with thick wall in nuclear power plant (NPP), great attention has been paid to the safety of the pipeline’s joints, which can be assessed by phased array ultrasonic testing (PAUT). PAUT creates constructive interference of acoustic waves to generate focused beams according to delay law based on time-of-flight. However, due to the existence of acoustic attenuation and dispersion, waveform distortion occurs when ultrasonic pulse propagates in HDPE, which will accumulate with the increase of propagation distance, and then results in imaging errors. In this paper, the relationship of acoustic attenuation and dispersion in HDPE was obtained by numerical simulation in Field II®, which can be verified by the experiment of our previous work. Besides, the investigation of the waveform distortion revealed the linear relation between peak offset and propagation distance. Considering the relation, an improved delay law was proposed to increase the intensity of ultrasonic field. This improved delay law was compared with the conventional one by numerical simulation of ultrasonic field and PAUT experiments, which showed that the improved delay law could increase the image sensitivity.
Study on the Response Behavior of Large Steel Seamless Cylinder Pressure Relief Devices Under Different Fire Conditions
Authors: Bo Ke , Zhao Baodi , Ding Chunhui , Deng Guide , Ji Fang
Published: October 2018

The pressures relief devices (PRDs) are widely used on long tube trailers, and can automatically open in a fire accident to relieve pressure when the pressure exceeds the set value to keep the cylinder safe from explosion. However, there is a big difference in the structure selection of PRDs and the calculation methods of the effective discharge area between different standards such as GB/T33215, API521 and CGA S-1.1. The overall fire test and local fire test of large capacity steel seamless cylinder were carried out to obtain the response behavior of different PRDs with different discharge areas, and the change law of temperature and pressure during the pressure relief process. Results showed that the requirements of safety release of cylinders in the fire environment were satisfied by the effective discharge area calculated by API521, CGA S-1.1 and GB/T33215, and the inner temperature and pressure were greatly affected by the different discharge orifices. In the same cases that the PRD were isolated from fire by steel plate, the single rupture disk device has a faster response than the combination rupture disk/fusible-plug devices.
Plastic Collapse Evaluation of Fuel Channel Assembly in Pressurized Heavy Water Reactor
Authors: Choi Jun Hyeok , Kang Seok Jun , Choi Jae-Boong
Published: October 2018

400 fuel channel assemblies are there in a PHWR. Each assembly consist of a CT as outer tube, a PT as inner tube, and 4 GSs to prevent contact between two tubes. The fuel bundles, inserted into PT of fuel channel assembly, heat the coolant to high temperature by nuclear fission. Furthermore, the pressurizer compresses the coolant not to boil in high temperature. From this, high pressure and high temperature condition happened in the PT. So, the integrity of PTs needs to be guaranteed. Although large number of previous researches were performed, they assumed a PT as single tube and did not take into account the constrained effect. In actual behavior, PT contact with CT, GS or both. In addition, its structural shape made bending restraint effect to the PT. Since the contact force and bending restraint effect make limit in behavior of the PT, previous evaluation results are not accurate. In order to obtain more accurate result, it is needed for the PT to be modeled as fuel channel assembly including CT and GSs. For this, 3D FE model of fuel channel assembly is proposed and validated by comparing with previous creep analysis result in previous study. In this study, fracture mechanical FE analysis is conducted for the PHWR fuel channel with circumferential surface or through-wall crack at the PT. Parameters of PIP geometry and bending restraint effect which can apply to plastic collapse evaluation of the PHWR fuel channels are extracted.
Numerical Study on Buckling Strength of Vertical Vessel Skirts With Access Opening
Authors: Takahashi Takuma , Miyashita Toshikazu , Kataoka Shunji , Uno Yoshiaki , Sato Takuya
Published: October 2018

Vertical vessel skirts generally have access openings. The evaluation for buckling of vertical vessel skirts shall consider the effect of the opening. On the other hand, evaluation methods of buckling in present design codes are established based on the theory for a cylindrical shell without any opening. There is no method to assess effects of openings on buckling strength.

The purpose of this paper is to establish a new design method of vertical vessel skirts with access openings, by evaluating the effects of openings on buckling strength of cylindrical shells. The finite element analyses of buckling strength for cylindrical shells with and without openings were conducted by an eigenvalue analysis. A study was conducted on the effects of geometric parameters, such as skirt diameter, thickness, opening shape and application of reinforcements. The effects of openings on buckling strength were revealed by comparing the analysis results. Based on these results, the new design factor, Buckling Strength Reduction Factor (BSRF), was proposed for evaluating buckling strength. BSRF is the ratio of buckling strength of a cylindrical shell with an opening to that of a cylindrical shell without an opening. BSRF provides a practical simplified method to evaluate how an access opening affects skirt buckling strength.