bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
Yeast HMO1: Linker Histone Reinvented
Authors: Panday Arvind , Grove Anne 
Published: December 2016

SUMMARY

Eukaryotic genomes are packaged in chromatin. The higher-order organization of nucleosome core particles is controlled by the association of the intervening linker DNA with either the linker histone H1 or high mobility group box (HMGB) proteins. While H1 is thought to stabilize the nucleosome by preventing DNA unwrapping, the DNA bending imposed by HMGB may propagate to the nucleosome to destabilize chromatin. For metazoan H1, chromatin compaction requires its lysine-rich C-terminal domain, a domain that is buried between globular domains in the previously characterized yeast
Saccharomyces cerevisiae
linker histone Hho1p. Here, we discuss the functions of
S. cerevisiae
HMO1, an HMGB family protein unique in containing a terminal lysine-rich domain and in stabilizing genomic DNA. On ribosomal DNA (rDNA) and genes encoding ribosomal proteins, HMO1 appears to exert its role primarily by stabilizing nucleosome-free regions or “fragile” nucleosomes. During replication, HMO1 likewise appears to ensure low nucleosome density at DNA junctions associated with the DNA damage response or the need for topoisomerases to resolve catenanes. Notably, HMO1 shares with the mammalian linker histone H1 the ability to stabilize chromatin, as evidenced by the absence of HMO1 creating a more dynamic chromatin environment that is more sensitive to nuclease digestion and in which chromatin-remodeling events associated with DNA double-strand break repair occur faster; such chromatin stabilization requires the lysine-rich extension of HMO1. Thus, HMO1 appears to have evolved a unique linker histone-like function involving the ability to stabilize both conventional nucleosome arrays as well as DNA regions characterized by low nucleosome density or the presence of noncanonical nucleosomes.