bluuebunny/crossref_metadata_2025 huggingface dataset:
Creep Damage Formation and Crack Initiation / Growth Behavior of Notched Specimen for Directionally Solidified Ni-Base Superalloy by Interrupted Observation
Authors: Ozeki Go , Yokobori A. Toshimitsu , Matsuzaki Takashi
Published: December 2016

Directionally solidified Ni-base superalloy is used for gas turbine blades for high efficiency thermal power plant. Since gas turbine blades are subject to high temperature creep condition due to the high speed rotation of rotor, it is important to evaluate the creep strength. There are many studies using the smooth specimen for directionally solidified Ni-base superalloy. However, these are not so many researches which concern the mechanical behavior of a notched specimen. Therefore, the researches of creep damage formation and the crack growth behavior around a notch tip have not yet been clarified. Recently, electron backscatter diffraction (EBSD) method has been conducted to evaluate the creep damage for Ni-base superalloy. However, most of the studies also use the smooth specimen. When the materials are practically used for the component of structures, creep damage or crack may be originated at the site of stress concentration of equipment such as cooling holes. Therefore, in order to evaluate the creep damage formation and the crack growth behavior, it is important to conduct the research using notched specimens from the view point of application to actual components.

In this study, creep damage formation and crack growth behavior of a notched specimen for directionally solidified Ni-base superalloy CM247LC under high temperature creep condition were investigated by conducting experiment and mechanical analysis. The interrupted observational test of creep crack growth was conducted to investigate the damage formation and the crack growth behavior around notches. In addition, the In-situ observation and the metallographical investigations were conducted for creep damaged specimens using SEM / EBSD analysis. Furthermore, in order to clarify the mechanism of creep damage formation behavior, the designed two-dimensional elastic-plastic creep finite element analysis was conducted for the model with various distributed grains obtained by EBSD analysis. And this analytical results were compared with experimental results.

As a result, the micro creep crack around a notch tip was found to be caused by accumulation of micro damage and voids. In addition, macro cracks were found to initiate just before final unstable fracture.

However, it is necessary to take into account for the variety of mechanical properties of each crystal orientation, the designed two-dimensional elastic-plastic creep finite element analysis was found to well represent the creep damage formation observed in experiments.
Effect of Gaseous Hydrogen Charging on Nanohardness of Austenitic Stainless Steels
Authors: Zhang Lin , An Bai , Iijima Takashi , San Marchi Chris
Published: December 2016

Understanding of hydrogen effect on local mechanical properties of metals is important for understanding hydrogen embrittlement mechanisms. The effect of thermal gaseous hydrogen precharging on the nanomechanics of SUS310S and SUS304 austenitic stainless steels has been investigated using a combination of nanoindentation and atomic force microscopy (AFM). It is observed that hydrogen precharging decreases the first excursion load in load versus displacement curves and enhances the slip steps around indentations for both the materials, which experimentally support the hydrogen-enhanced localized plasticity (HELP) mechanism. The nanohardness in SUS310S stable austenitic stainless steel is increased by hydrogen precharging while that in SUS304 metastable austenitic stainless steel is decreased by hydrogen precharging. The hydrogen-induced hardening in SUS310S and softening in SUS304 are discussed in terms of the hydrogen/deformation interaction and the effect of hydrogen on strain-induced martensite transformation.
Fatigue Life Investigation of a High Pressure Inner Casing Under In-Service Conditions
Authors: Hong Hui , Wang Weizhe , Cai Zhenwei
Published: December 2016

The fatigue life of a specific inner casing of an ultra-supercritical steam turbine was investigated under a half year in-service conditions. The Ramberg-Osgood model and Manson-Coffin-Basquin strain-life equation were used to describe the stress-strain behavior and calculate the fatigue damage. A temperature comparison was performed to validate the reliability of finite element model. The results showed that fluctuating steam pressure rather than temperature had more significant effect on the variation of stress in the casing. Locations with high stress level were prone to cause larger fatigue damage. Statistical analysis was carried out to reveal that over half fluctuations of steam pressure could cause damage.
FEM Stress Analysis and the Sealing Performance Evaluation of Bolted Pipe Flange Connections With Large Nominal Diameter Subjected to Internal Pressure
Authors: Muramatsu Akira , Sato Koji , Khan Maksud Uddin , Sawa Toshiyuki
Published: December 2016

The gasket fundamental characteristics such as the stress-strain curves of compressed sheet gaskets (CSG) and the spiral wound gaskets (SWG) and the relationship between the average gasket stress and the leak rate using rigid platens were measured. Then, using the measured data of the gasket properties, the mechanical characteristics of bolted pipe flange connections under internal pressure are examined such as the contact gasket stress distribution, hub stress and changes in axial bolt forces (the load factor) using FEM. FEM code employed is ABAQUS. Using the obtained gasket stress distributions and the fundamental gasket relationship between the gasket stress and the leak rate, the leak rates of bolted pipe flange connections are predicted. In addition, the effect of nominal diameters (from 2” to 24”) on the mechanical characteristics is examined. For verification of the FEM calculations, experiments to measure the load factor, the hub stress and the leak rates were performed using 2” and 24” bolted pipe flange connections. The FEM results of the load factor, the hub stress and the leak rate are in a fairly good agreement with the measured results. The value of the load factor is found to be positive for 2” pipe flanged joints, while it is negative for 24” pipe flanged connection due to the flange rotation. It is noticed that the values of the load factor decreases with an increase of the nominal diameter of pipe flanges. The hub stress is kept constant when the gasket stress is held constant for each connection with each nominal diameter while it increases as the nominal diameter increases according to ASME codes. In addition, the leak rate increases as the nominal diameter increases.
Environmental Effect on Fatigue Crack Initiation and Growth of Stainless Steel for Flaw Tolerance Assessment
Authors: Kamaya Masayuki
Published: December 2016

Fatigue life can be divided into cycles of crack initiation and those in which the initiated crack grows to macroscopic size. In crack growth analysis, it is possible to consider the effect of the strain or stress gradient in the depth direction on the fatigue life. Therefore, flaw tolerance assessments allow reasonable fatigue life prediction. The fatigue life is reduced in the primary water environment of pressurized water reactor (PWR) nuclear power plants, and the correction factor Fen is used for considering the fatigue life reduction in fatigue damage assessments. To apply the flaw tolerance concept to a PWR water environment, the correction factor must be applied not to the fatigue life but to the number of cycles for crack growth. In this study, the fatigue life reduction in the PWR environment was correlated to the crack growth acceleration for a flaw tolerance assessment. The crack growth rates were obtained from fatigue life tests and crack growth tests performed in the PWR environment using Type 316 stainless steel. Then, the fatigue life was estimated by predicting the crack growth from an initial depth of 20 μm. It was concluded that a reasonable flaw tolerance assessment can be performed by using the strain intensity factor. The fatigue life reduction was successfully replaced with the crack growth acceleration.
J-R Fracture Toughness of Nuclear Piping Materials Under Excessive Seismic Loading Condition
Authors: Kim Jin Weon , Choi Myung Rak , Lee Sang Bong , Kim Yun Jae
Published: December 2016

This study investigated the loading rate effect on the fracture resistance under cyclic loading conditions to clearly understand the fracture behavior of piping materials under excessive seismic conditions. J-R fracture toughness tests were conducted under monotonic and cyclic loading conditions at various displacement rates at room temperature (RT) and the operating temperature of nuclear power plants (NPPs), i.e., 316°C. SA508 Gr. 1a lo w-alloy steel (LAS) and SA312 TP316 stainless steel (SS) piping materials were used for the tests. The fracture resistance under a reversible cyclic load was considerably lower than that under monotonic load regardless of test temperature, material, and loading rate. Under both cyclic and monotonic loading conditions, the fracture behavior of SA312 TP316 SS was independent of the loading rate at both RT and 316°C. For SA508 Gr. 1a LAS, the loading rate effect on the fracture behavior was appreciable at 316°C under both cyclic and monotonic loading conditions. However, the loading rate effect diminished when the cyclic load ratio (R) was −1. Thus, it was recognized that the fracture behavior of piping materials, including seismic loading characteristics, can be evaluated when tested under a cyclic load of R = −1 at a quasi-static loading rate.
Studies on Influence of Tantalum Addition in TP310HCbN
Authors: Furuya Kazuki , Nagao Mamoru , Miyamura Takeo , Nanba Shigenobu
Published: December 2016

SA-213/SA-213M TP310HCbN (UNS S31042) has excellent creep properties. The superior creep strength of this alloy is achieved by precipitation of fine niobium based Z-phase. It is well established that niobium and tantalum have similar physical and chemical properties. We evaluated mechanical properties of tantalum added TP310HCbN, to investigate whether tantalum could be substitute for niobium. It is concluded that niobium can be replaced by tantalum in TP310HCbN.
Fatigue Lives of Multiple Flaws in Accordance With Combination Rule
Authors: Lu Kai , Li Yinsheng , Hasegawa Kunio , Lacroix Valery
Published: December 2016

When multiple flaws are detected in structural components, remaining lives of the components are estimated by fatigue flaw growth calculations using combination rules in fitness-for-service codes. ASME, BS7910 and FITNET Codes provide different combination rules. Fatigue flaw growth for adjacent surface flaws in a pipe subjected to cyclic tensile stress were obtained by numerical calculations using these different combination rules. In addition, fatigue lives taking into account interaction effect between the two flaws were conducted by extended finite element method (X-FEM). As the calculation results, it is found that the fatigue lives calculated by the X-FEM are close to those by the ASME Code. Finally, it is worth noticing that the combination rule provided by the ASME Code is appropriate for fatigue flaw growth calculations.
Assessment Method to Account for the Rise Time of Complex Waveforms in Stainless Steel Environmental Fatigue Crack Growth Calculations
Authors: Emslie Julian , Gill Chris , Wright Keith
Published: December 2016

The reference Fatigue Crack Growth (FCG) rate behaviour for austenitic stainless steel in a deaerated Pressurised Water Reactor (PWR) environment is provided in ASME Section XI Code Case N-809. This FCG law is dependent on temperature, R ratio and environment, which is defined through a load rise time parameter. The basis for this law is contained within a large dataset of testing carried out by various industry sources.

Code Case N-809 defines rise time as the time for which the stress is increasing during a stress cycle, based on specimen testing in which sawtooth loading (typically 85% rise/15% fall) was primarily used. However it was found from testing of more complex waveforms carried out by Amec Foster Wheeler, which is reported in a separate paper at this conference, that the FCG rate is not always well characterised by this definition of rise time and was often found to be overly conservative. A number of different waveforms were considered, including simplified two-stage linear waveforms where the loading rate is different in the top and bottom half of the cycle, and those more representative of plant transients.

This paper presents a method to account for the environmental enhancement of complex waveforms with variable loading rate by weighting the loading rate according to its position within the loading cycle. In this way an effective rise time can be obtained for use in Code Case N-809. This method was found to give good agreement with the experimental data generated using complex waveforms.
Analysis of the Small Punch Test Capability to Evaluate the Response of High Strength Steels Facing HIC or SCC
Authors: Arroyo B. , Álvarez J. A. , Lacalle R.
Published: December 2016

This work is about evaluating the behavior facing HIC of high strength steels by means of the Small Punch Test (SPT). It can be considered as a quasi-non-destructive test in comparison to structural integrity analysis of large components. It was developed during the 80’s with the purpose of estimating the embrittlement grade of nuclear components reducing the amount of material employed. During the last years it has been successfully employed in the evaluation of mechanical properties of different materials and creep behavior. Also approximations for the fracture properties estimations have been carried out using this method. Although a reference standard that includes the tensile and fracture parameters estimations by SPT does not exist, a European Code of Practice (CWA 15627:2008) was recently developed. In addition a European standard is in preparation, including the ultimate research and the backup of the most relevant groups.

In this work, high strength steels behavior facing stress corrosion cracking (SCC) or hydrogen Embrittlement (HE) processes are analyzed by means of the Small Punch Test (SPT). The evaluation of the response of materials facing environmental damage processes requires a different consideration if cracks are present on the material or not. In a first stage the study carried out tries to analyze the behavior without cracks, using the threshold stress (σscc) parameter. The aforementioned parameter is obtained from slow strain rate tensile tests (SSRT), which involves its own particular disadvantages. Thus the aptitude of the SPT to obtain the threshold stress is studied, evaluating the influence of variables such as the solicitation rate.

In the second part of the work, specimen geometry and test conditions are proposed for the SPT, in order to evaluate the susceptibility facing SCC and HE in presence of cracks for the materials studied. In this case, the fracture toughness parameter that describes the crack initiation process (Khe) will be evaluated and validated by conventional tests based on fracture mechanics. The influence of variables, such as test solicitation rate on the results, is analyzed in order to obtain a qualitative methodology to evaluate mechanical-environmental damage processes by SPT means. For the SPT tests carried out, common Small Punch specimens of 10×10 mm of section and 0,5 mm of thickness are used for σscc determination.
Warm Pre-Stress Tests of the Irradiated RPV Base Material of Beznau Unit 1
Authors: Obermeier Florian , Heußner Stefan , Hägeli Heinz , Schendzielorz Herbert , Kaiser Marco , Keim Elisabeth
Published: December 2016

According to the pertinent regulations, the integrity of a reactor pressure vessel (RPV) of a nuclear power plant is to be assessed by fracture mechanics for postulated flaws under most severe loading conditions. In such an analysis usually loss of coolant accidents are assumed to cause highest possible loading of the structural material of the RPV. This is due to the fact that such a pressurized thermal shock (PTS) event during which cold emergency coolant is injected into the primary system generates additional thermal stresses in the RPV wall. Based on the applicable regulation, the initiation of postulated flaws is to be excluded by the comparison of the calculated crack tip loading and the fracture toughness of the particular material.

This kind of assessment was motivation of various research projects in the last decades addressing both evaluation approaches and experimental testing. A crucial result in this context is the existence of the so-called warm pre-stress effect (WPS) on the resulting fracture toughness. Generally, it is known as the increase of the apparent fracture toughness of a flaw in a specimen or structure after loading at high temperatures, generally in the upper shelf region, followed by a reloading at a lower temperature. This represents the typical loading scenario postulated for the assessment of a RPV during a PTS event.

Experiments were performed to quantify this effect in the case of the irradiated reactor pressure vessel base material of the nuclear power plant Beznau unit 1. This paper presents the results of the Master Curve tests to determine the reference temperature (according to ASTM E 1921) and the design and testing of the warm pre-stress experiments using irradiated 10×10 mm reconstituted single edge notch bend (SE(B)) specimens.

The design of these warm pre-stress tests was based on the loading transients for postulated surface and sub-surface flaws investigated within the scope of the assessment of the Beznau unit 1 reactor pressure vessel against brittle failure. Finite element simulations were performed to transfer the loading conditions at the crack tip of the RPV determined during the brittle fracture safety assessment onto the SE(B) specimen.

The simulation results were used to control the loading conditions as a function of time and temperature during the experimental tests. The fracture toughness values of the warm pre-stress specimens were finally compared with the original fracture toughness values determined in the absence of a warm pre-stress effect to demonstrate the increase of the safety margin when the warm pre-stress effect is taken into account.
Further Post Test Analysis and Comparison of STYLE MU-2 Test Results
Authors: James Peter , Ford Michael
Published: December 2016

Within the EU 7th framework programme, STYLE, a number of large-scale tests have been performed. One of these tests, Mock-Up 2 (MU-2), was performed on a through wall crack located at a repair weld adjacent to a multi-pass girth weld. The aim of MU-2 was to investigate ductile crack growth under conditions with significant levels of welding residual stress.

Post-test analysis of these tests has been presented by different partners within the programme. This has led to some differences in the interpretation of the results and a degree of scatter in the resulting predictions. The post-test analyses performed at the different UK establishments indicated that the ductile initiation may have been influenced by the presence of the residual stress field. However, the different investigations do not provide consistent estimates of the magnitude of this effect, nor do they provide equivalent results when considering the load-deformation of the pipe. It was therefore agreed that it would be beneficial to understand the source of these differences in order to provide an improved prediction.

Further post-test finite element analyses of the MU-2 test have therefore been performed to consider: 1) potential variations in material properties adopted, 2) the approach to better include the predicted residual stress field, and 3) the introduction of the defect into the stress field. This range of analyses has helped clarify the differences in the analyses performed and has provided further insight to the test results.
Leakage Rates Through Non-Linear Through Wall Cracks Obtained From Finite Element Analysis
Authors: Gill Peter , Ford Mike , Budden Peter
Published: December 2016

This paper presents work that has been carried out to extract leakage rates from finite element models. The benefit of using a more sophisticated leak rate model in combination with finite elements is the increased accuracy in leakage rate calculation for more complex crack shapes and loading conditions. The methodology involves extracting the crack opening displacement (COD) from the Extended Finite Element Method (XFEM) and standard finite elements, then outputting the data to an Excel spreadsheet. A polynomial is then fitted to the data and this is inputted into a MATHCAD code which calculates leakage rate using the Ordinary Differential Equation (ODE) model developed in a previous paper. Test cases were considered which were based on a thick plate with a central crack under various loading conditions. These included primary membrane loading, through-wall bending, and a residual-stress field. The through wall bending and residual stress fields were induced from a temperature field imposed on the plate. A difference of 20% in leak rate is observed between results from the DAFTCAT (Reference 1) code and the ODE method for the residual stress field considered. The paper concludes with recommendations for improved guidance in R6 Section III.11 (Reference 2) for cases when complex crack shapes and loading are present.
A Study of the Effects of Scaling on Structural Integrity Assessment and Feasibility of Physical Validation
Authors: Orrock Paulo , Truman Christopher E.
Published: December 2016

For nuclear welded components the complex nature of the stresses involved means it is often advantageous to produce mock-ups in order that the structural integrity and performance may be assessed. The weight and size of these components can make the production of mock-ups prohibitively expensive and impractical, and so the use of scaled models is considered here. The scaling laws encountered affecting the applied loads, residual stresses and crack driving forces that are of interest are investigated using numerical analyses and finite element simulations. Of particular interest is the physical validation of these laws and the statistical difficulties that may be encountered.

The scaling of applied loads required to obtain the same residual stress fields and stress intensity factors are investigated using simulated four point bends. The statistical nature of fracture introduces uncertainty into fracture measurements which this paper takes into consideration in preparation for physical validation, ensuring that the random nature of fracture will not make the described laws impractical to validate.
A Case Study on the Normality of Monte-Carlo Simulation Results
Authors: Tsembelis Konstantinos , Eom Seyun , Christodoulou Nicholas , Pandey Mahesh , Jin John
Published: December 2016

In order to address the risks associated with the operation of ageing pressure boundary components, many assessments incorporate probabilistic analysis methodologies for alleviating excessive conservatism of deterministic methodologies. In general, deterministic techniques utilize conservative upper bound values for all critical parameters. Equally, defense-in-depth assessments for the nuclear industry employ probabilistic methods in order to estimate potential risks associated with unanticipated events to demonstrate adequate margins associated with the licensed activity.

Probabilistic approaches typically invoke the Monte-Carlo (MC) approach where a set of critical input variables, assumed independent, are randomly distributed and inserted in deterministic computer models. Estimates of results from probabilistic structural integrity assessments are then compared against assessment criteria, at times, based on the assumption that these results follow normal distributions. However, this assumption is not always valid, as normality depends both on the initially assumed distributions of the input variables and linearity, or lack thereof, of the deterministic model. In particular, the characteristic of a system function (either a linear or a non-linear system function) and the sampling region of input parameters affect the level of normality of the MC simulation results.

As a proof of principle, a specific case study is presented. A system function is chosen based on the steady-state thermal creep of Zr-2.5Nb Pressure Tube (PT), instead of a full deterministic computational model, to show whether it can give rise to MC results that deviate from normality. The consequence of the deviation from normality when compared against assessment criteria is briefly discussed. It is noted that this study does not deal with analysis of Probabilistic Safety Assessments, also known as PSAs.
Thermo-Mechanical Response of Multi-Layered Cylinders Under Pressure and Thermal Loading With Generalized Plane Strain Condition
Authors: Kang Sang-Guk , Young Kuao-John
Published: December 2016

Multi-layered cylindrical structures subject to pressure and thermal loading are commonly seen in many industries. In this study, the formulas for multi-layered cylinders under pressure and thermal loading are derived with an assumption that the cylinders meet generalized plane strain condition, i.e., there is no external constraint in the axial direction and the axial growths of the cylindrical layers are the same. A numerical solution procedure for double-layered cylinders subject to both pressure and thermal load is developed and implemented in a MathCAD® program. To validate the solution, a finite element model for a double-layered cylinder is prepared with ABAQUS®, and its responses under pressure and thermal loading are compared to those from the MathCAD® program. The algorithm of the method can be extended to three or more layered cylinders.
Tensile Characterization of Narrow Gap Bimetallic Weld Ferritic-Austenitic Steel With a New Measurement System for Tensile Testing
Authors: Ancelet O. , Chapuliot S.
Published: December 2016

Ferritic steel 2 ¼ Cr is a candidate material for future pressure component in nuclear fields. In order to validate this choice, it is necessary, firstly to verify that it is able to withstand the planned environmental and operating conditions, and secondly to check if it is covered by the existing design codes, concerning its procurement, fabrication, welding, examination methods and mechanical design rules. A large R&D program on 2 ¼ Cr steel has been undertaken at CEA and Areva in order to characterize the behavior of this material and of its welded junctions.

In this frame, a new measurement system for tensile testing was developed in the LISN laboratory of the CEA (French atomic commission), in order to characterize the local behavior of the material during a whole tensile testing. Indeed, with the conventional measurement system (typically an extensometer), the local behavior of the material can only be determinate during the stable step of the testing. So, usually the behavior of the material during the necking step of the step is unknown.

This new measurement is based on the use of some laser micrometers which allow measuring the minimum diameter of the specimen and the curvature radius during the necking phase with a great precision. Thanks to the Bridgman formula, we can evaluate the local behavior of the material until the failure of the specimen.

This new system was used to characterize the tensile propriety of a bimetallic welded junction of 2 ¼ Cr steel and austenitic stainless steel 316L(N) realized with inconel filler metal.

These works lead to propose a tensile curve for each materials of the welded junction at room temperature and the effect of postweld heat treatment.
Hydrogen Effects on Fatigue Crack Growth Rates in Pipeline Steel Welds
Authors: Ronevich Joe A. , Somerday Brian P.
Published: December 2016

Fatigue crack growth rate (da/dN) versus stress intensity factor range (ΔK) relationships were measured for various grades of pipeline steel along with their respective welds in high pressure hydrogen. Tests were conducted in both 21 MPa hydrogen gas and a reference environment (e.g. air) at room temperature. Girth welds fabricated by arc welding and friction stir welding processes were examined in X65 and X52 pipeline grades, respectively. Results showed accelerated fatigue crack growth rates for all tests in hydrogen as compared to tests in air. Modestly higher hydrogen-assisted crack growth rates were observed in the welds as compared to their respective base metals. The arc weld and friction stir weld exhibited similar fatigue crack growth behavior suggesting similar sensitivity to hydrogen. A detailed study of microstructure and fractography was performed to identify relationships between microstructure constituents and hydrogen accelerated fatigue crack growth.
Nuclear-Related Materials and Technology Research at ANSTO
Authors: Law Michael , Bendeich Philip J. , Muránsky Ondrej , Payten Warwick M. , Hamelin Cory J.
Published: December 2016

Current and future nuclear technologies such as fission and fusion reactor systems depend on well characterized structural materials, underpinned by reliable material models. ANSTO is pursuing research into the nuclear power cycle on many fronts, including: modelling and measurement of weld residual stresses; simulation of radiation damage by molecular dynamics modelling; assessment of radiation, cycling and aging effects in power plant structural materials; and characterization of materials for the next generation of nuclear power plants. Several examples of past and current research activities are used to highlight the potential of ANSTO facilities, techniques and capabilities available for collaborative research in the nuclear space.
Monitoring the Fatigue Life of Offshore Subsea HPHT Components
Authors: Gilman Timothy
Published: December 2016

This paper presents the transference of a well-established nuclear power industry technique to perform environmentally-assisted fatigue monitoring for application to offshore, subsea High Pressure, High Temperature (HPHT) components using existing instrumentation. Applying fatigue monitoring is an effective way to manage these assets against the threat of fatigue failures and meet regulatory expectations during the service life. Our objective is to provide the background and overview of the approach so that design engineers better understand and evaluate its potential in contrast to traditional design changes that may actually produce an unintended consequence that increases the fatigue potential associated with heavy section thicknesses. This paper describes the overall analysis approach that may be used to perform fatigue monitoring of an HPHT component. At the conclusion, recommendations are provided for further research and development to close existing gaps.
Weld Joint Efficiency in Design by Analysis
Authors: Seipp Trevor G.
Published: December 2016

In the original ASME Section VIII, Division 2, no consideration was given to partial weld joint efficiencies (values of the factor E less than 1.0) because that version required full radiography and only permitted weld joint efficiencies of unity. In the new (post-2007) Section VIII, Division 2, partial weld joint efficiencies as small as 0.85 are now permitted. Furthermore, much Design By Analysis work is performed on vessels fabricated to ASME Section VIII, Division 1 and the ASME B31 Codes, which all permit partial weld joint efficiencies. However, no guidance is provided on how to account for these values in Deign By Analysis to ASME Section VIII, Division 2, Part 5.

This paper provides the technical justification for the proposed changes to ASME Section VIII, Division 2, Part 5 and API RP-579/ASME FFS-1 regarding weld joint efficiency. Guidance is also provided on how to incorporate this change into ASME Section VIII, Division 1 by way of U-2(g) and the B31 Codes.
Specimen Size Effect on Fracture Toughness of Reactor Pressure Vessel Steel Following Warm Pre-Stressing
Authors: Iwata Keiko , Tobita Tohru , Takamizawa Hisashi , Chimi Yasuhiro , Yoshimoto Kentaro , Nishiyama Yutaka
Published: December 2016

The effect of warm pre-stressing (WPS) on fracture toughness was evaluated for a reactor pressure vessel steel. Various types of thermomechanical loadings were applied to 1T-CT specimens. The results were compared with predictions from several analytical WPS engineering models. The specimen size effect was subsequently investigated under the load-unload-cool-fracture transient condition using 1T-, 0.4T-, and 0.16T-CT specimens. Analyses of the plastic zone distribution and residual stress were conducted to identify the difference in the WPS effect among the specimens.
3D Residual Stress Simulation of an Excavate and Weld Repair Mockup
Authors: Ku Francis H. , Riccardella Pete C. , McCracken Steven L.
Published: December 2016

This paper presents predictions of weld residual stresses in a mockup with a partial arc excavate and weld repair (EWR) utilizing finite element analysis (FEA). The partial arc EWR is a mitigation option to address stress corrosion cracking (SCC) in nuclear power plant piping systems. The mockup is a dissimilar metal weld (DMW) consisting of an SA-508 Class 3 low alloy steel forging buttered with Alloy 182 welded to a Type 316L stainless steel plate with Alloy 82/182 weld metal. This material configuration represents a typical DMW of original construction in a pressurized water reactor (PWR). After simulating the original construction piping joint, the outer half of the DMW is excavated and repaired with Alloy 52M weld metal to simulate a partial arc EWR. The FEA performed simulates the EWR weld bead sequence and applies three-dimensional (3D) modeling to evaluate the weld residual stresses. Bi-directional weld residual stresses are also assessed for impacts on the original construction DMW. The FEA predicted residual stresses follow expected trends and compare favorably to the results of experimental measurements performed on the mockup. The 3D FEA process presented herein represents a validated method to evaluate weld residual stresses as required by ASME Code Case N-847 for implementing a partial arc EWR, which is currently being considered via letter ballot at ASME BPV Standards Committee XI.
Bayesian Statistical Analysis on Chemical Composition Contributing to Irradiation Embrittlement at High Fluence Region
Authors: Takamizawa Hisashi , Nishiyama Yutaka
Published: December 2016

It has been accepted that neutron irradiation embrittlement of reactor pressure vessel is caused by irradiation-induced formation of solute clusters (SCs) and matrix damages (MDs). In the present study, to analyze the contribution of chemical composition contained in SCs to irradiation embrittlement at high fluence region, statistical analysis using the Bayesian nonparametric (BNP) method was performed for Japanese PWR surveillance data. The significance of P, Si and Mn contents, which are not necessarily included in embrittlement correlations unlike the Cu and Ni content, was evaluated. The BNP method can learn the complexity of the statistical model itself from the input data and infer the predicted data with individual probability distribution of predict condition. The result suggested that irradiation embrittlement was most affected by the Si content in three examined elements at high fluence region.
Development of Analytical Evaluation Methods for Creep Failure in Weldments of High Chromium Steels and Application to Full Scale Pipe Experiments
Authors: Takahashi Yukio , Nishinoiri Satoshi , Yaguchi Masatsugu
Published: December 2016

Creep strength Enhanced Ferritic (CSEF) steels containing chromium of 9 to 12 weight percent are widely used in fossil power plants operated all over the world under ultra-super critical (USC) steam condition. Type-IV cracking has been observed in weldments of these steels in a number of plants using these materials and prediction of failure due to such cracking or damage is of critical importance for operators of these plants. In order to address such a need, analytical life estimation methods are under development by the authors. Creep strain equations for different parts of welded joints have been developed based on the creep test data of small-sized specimens for both typical 9 Cr and 12Cr type steels designated Grade 91 and Grade 122. Failure criteria based on inelastic strain as well as inelastic strain energy density have also been developed based on the test data on small-sized cross-weld specimens. Finite element analyses incorporating them have been performed on the full-scale hot reheat pipes of Grade 91 and Grade 122 with circumferential weldments tested under inner pressure and bending moment. Reasonable agreements have been obtained between the time of local failure predicted by a newly developed energy-based approach and the time at which indications were detected by ultrasonic testing firstly.
Failure Analysis of High Pressure Rupture Discs and Effective Counter Measures
Authors: Rüsenberg Stefan , Vonnahme Georg
Published: December 2016

For the production of LDPE, high process pressures (>1000 bar up to 3500 bar and above) as well as high temperatures (>100 °C up to 300 °C and above) are required. In order to ensure a safe production process the autoclaves and compressors have to be protected against dangerous overpressure. Rupture discs are typically used to protect this high pressure process itself, as well as the employees, and the environment. Traditionally rupture discs for high pressure applications are manufactured by a weld seam which has an influence on the burst pressure. After installation the applied pressure is nearly fully-loaded on the welding joint. Additionally, the welding joint is another unwanted influencing factor. This increases the possibility of an unexpected failure which leads to an unwanted rupture disc response or, in critical cases, to a rupture disc failure recently after initial operation of the process even at lower pressures than the defined burst pressure. This, in turn, leads to a reduced life time of the disc. A special version of a rupture disc, a High Pressure Rupture Disc (HPRD) is developed specifically for this application. This long life version for high pressure applications has a lifetime which is 5–10 times higher than that of a standard rupture disc, that saves money and installation time.

The differences are explained in some minor geometrical changes. This safety device allows a protection of high pressures up to 4000 bar and beyond. The HPRD is a forward acting rupture disc and the burst pressure is adjusted by a combination of material thickness, the height of the dome, and, of course, of the chosen material. An easy and simple geometrical change eliminates the welding joint as an influencing factor, thus eliminating any unwanted responding of the rupture disc. The tolerances for high pressure rupture discs are +/−3% and lower and the HPRD can be used for all kind of different high pressure applications.
An Experience on the Elimination of Check Valve Chattering in a NPP
Authors: Kim Tae Ryong
Published: December 2016

Tapping noise and vibration was observed at a swing check valve located on an auxiliary cooling water line during operation in a nuclear power plant. For the identification of the main cause and its elimination of continuous tapping noise in check valve, site inspection, vibration measurement and flow field analysis was done. FLUENT code was used to analyze the flow field in piping and elbow. It can be concluded as follows from inspection, measurement and analysis: A check valve should be installed so that the axis of hinge is perpendicular to the plane of the curved pipes, considering the secondary flow to be formed in the cross-section of the pipe. In this configuration the secondary flow impinged to the front side of valve disk could increase the effective incidence angle, which makes the disk kept in the fully open position.
Microflow Leakage Through the Clearance of a Metal-Metal Seal
Authors: Anwar Ali A. , Ritos Konstantinos , Gorash Yevgen , Dempster William , Nash David
Published: December 2016

The motivation behind this study is to simulate high pressure gas flow through the clearance between a valve seat and disc when in a closed position using a representative model. This leakage phenomenon is common in metal-to-metal seal pressure relief valves. As a pressure relief valve reaches the set pressure, it is known for the leakage to increase. The representative model that we studied is of an ideal-gas flow through a 2D microchannel in the slip flow regime. We used a laminar continuum flow solver which solved the mass, momentum and energy equations. In addition, we applied low pressure slip boundary conditions at the wall boundaries which considered Maxwells model for slip. The channel height was varied from 1μm to 5μm while the length remained at 1.25 mm, this means the length to height ratio varied from 1250 to 250. Inlet pressure was varied from a low pressure (0.05 MPa) to a high pressure (18.6 MPa), while the outlet remained constant at atmospheric. The calculated mass flow rate is compared to an analytical solution giving very good agreement for low pressure ratios and high length to height ratios.
The Effects of Nonproportional Loading on the Elastic-Plastic Crack-Fronts Fields
Authors: Jin Zhaoyu , Wang Xin
Published: December 2016

In this paper, the loading path effect on the elastic-plastic crack-front stress field in a thin plate is investigated. There different loading sequences include one proportional loading and two non-proportional loading paths are applied to the 3-D modified boundary layer (MBL) model under small-scale yielding conditions. For the same external displacement field applied at the outer boundary of the 3-D MBL model, the mode I K field and T-stress field combined as the different loading path is applied to investigate the influence of the nonproportional loading. The results show that for either the compressive or tensional T-stress, the loading path which applied K field followed by T field generates the lower crack-tip constraint. There is only slightly difference between the proportional loading path and the T-stress field following by K field loading path. The results show that it is very important to include the load sequence effects in fracture analysis when dealing with nonproportional loading conditions.
Fatigue Crack Growth Rates for Ferritic Steels Under Negative R Ratio
Authors: Hasegawa Kunio , Mares Vratislav , Yamaguchi Yoshihito , Li Yinsheng
Published: December 2016

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN vs. Kmax, It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1 and −2. In addition, the da/dN increases with decreasing R ratio for R < −2.

This paper converts from da/dN vs. Kmax to da/dN vs. ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN vs. ΔKI is better equation than da/dN vs. Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.
3D Measurement and FFS Assessment for LTA in Pressure Equipment According to WES2820:2015
Authors: Tahara Takayasu , Shimura Yoshiharu , Niimura Minoru
Published: December 2016

The corrosion of pressure equipment such as corrosion under insulation, CUI, is the most common problem in refinery and petrochemical plants in recent years.

Fitness-For-Service, FFS, assessment technologies for pressure equipment have been studied in recent 15 years, and standardization of a FFS assessment procedure for local thin area, LTA, has been expected by maintenance engineers of process industries.

Based on the verification using extensive burst tests and FEM analysis of LTA, the Japan Welding Engineering Society, JWES, developed new FFS standard WES2820 in June 2015.[1]

This paper presents high lights of WES2820 and a FFS assessment system consisted with 3D optical measurement method and FFS software for LTA in pressure equipment as a new tool for effective inspection and reliable maintenance activities.
Comparison of Plastic Collapse Load of Isolated Piping Part and Pipe Run
Authors: Reinhardt Wolf
Published: December 2016

The analysis of plastic collapse may be used in the fitness-for-service analysis of piping parts. Typically, such an analysis is performed by first determining the loads on the part in question by piping analysis, and then applying the load or load combination to an isolated elastic-plastic model of the part to obtain the collapse load. Plastic load redistribution that would occur if a plastic collapse analysis of the entire pipe run was performed is not considered in the common analysis approach.

This paper compares the results of pipe run and piping part plastic collapse analyses for a typical illustrative example under various loading conditions.
Uncertainty Sampling of Weld Residual Stress Fields in Probabilistic Analysis: Part I — Theory
Authors: Kurth Robert E. , Sallaberry Cédric J. , Brust Frederick W. , Kurth Elizabeth A. , Benson Michael L. , Rudland David L.
Published: December 2016

NRC Standard Review Plan (SRP) 3.6.3 describes Leak-Before-Break (LBB) assessment procedures that can be used to assess compliance with the 10CFR50 Appendix A, GDC-4 requirement that primary system pressure piping exhibit an extremely low probability of rupture. SRP 3.6.3 does not allow for assessment of piping systems with active degradation mechanisms, such as Primary Water Stress Corrosion Cracking (PWSCC) which is currently occurring in systems that have been granted LBB approvals.

US NRC staff, working cooperatively with the Electric Power Research Institute through a memorandum of understanding, conducted a multi-year project that focused on the development of a viable method and approach to address the effects of PWSCC in primary piping systems approved for LBB. This project, called eXtremely Low Probability of Rupture (xLPR), defined the requirements necessary for a modular-based probabilistic fracture mechanics assessment tool to directly assess compliance with the regulations [1].

Using the lessons learned from the pilot study [2] the production version of this code, designated as Version 2.0, focused on those primary piping systems previously approved for LBB [3]. In this version the appropriate fracture mechanics-based models are employed to model the physical cracking behavior and a variety of computational options are provided to characterize, categorize and propagate problem uncertainties.

One of the most influential sources of uncertainty on risk in the xLPR code is the one associated with weld residual stresses (WRS). WRS plays a key role in both crack initiation and crack growth. PWSCC is mainly driven by tensile stresses, whose major contributors are the tensile weld residual stresses that develop during fabrication of the piping system.

Handling the uncertainty involved with WRS within a probabilistic framework is quite challenging. This paper presents the selected approach to represent uncertainty within the framework of the xLPR code while respecting a set of requirements in term of smoothness of profile, efficiency of (potential) importance sampling and (for axial WRS) equilibrium. The current WRS sampling scheme employs correlation in order to smooth the shape of the WRS fields through the thickness of a dissimilar metal weld. This method presents an enrichment of the Cholesky decomposition on the correlation matrix, in order to satisfy the other two requirements.