bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improvement of Leak Tightness Analysis of Bolted Closure Systems in Pressure Equipment
Authors: Billon F. , Batmale G. , Drevon B. 
Published: August 2013

The aim of this work is to study the Leak Tightness of the closure systems of nuclear pressure equipment during all situations including in-service operating, emergency and accidental conditions. The analysis is performed using a complete 3-dimensional finite element model of the closure system including : the studs, the gasket, the contacts between the gasket and their seating surfaces (contact elements), the nuts, the cover, the part of the shell on which the opening is located and the tightening preload of the studs. It comprises 2 main phases:
(a) Using the 3D model, with non linear internal parameters converted in appropriate linear that allows performing linear analyses, we select, with respect to leaktightness, the most critical thermal and pressure transient among a large amount of transient. This selected transient presents the weakest compressing force between the gasket and its seating surfaces, which is the selection criterion.
(b) Then, using the 3D model we perform a full non-linear analysis of the selected transient, taking into account the non linearity of the contacts as well as the non linearity of the gaskets and the tightening preload of the studs.
Thus for this transient, we obtain the history of the compressive forces on the gasket and particularly the history of the metal-metal contact for the gaskets multi-ring type (metallic-graphite-metallic) and we can check if compressive forces remain effective.
An important consequence is the re-calculation of the tightening preload applied to the studs if the intensity of the metal-metal contact is not sufficient.
The Improved Measurements and Stress Analysis of Cylinder / Pipe With Out-of-Roundness
Authors: Orynyak Igor V. , Lokhman Igor V. , Bohdan Andrii V. 
Published: August 2013

The API 579 defines an out-of-roundness as the geometrical imperfection of a shell which is assumed to be constant in the longitudinal direction. In general, there are three types of out-of-roundness imperfections — a) the offset weld misalignment (misalignment of radius in the point of the circumference); b) angular misalignment (misalignment of the first derivative of the radius at some point); c) regular imperfection (radius is the continuous function along the circumference).
The document API 579 [1] contains the procedure (or requirements) of the imperfections measurement as well as their analytical treatment in case of inner pressure loading. Regretfully, at least two principal drawbacks of the document should be pointed out: the formula for regular imperfection description based on the discrete measurements of the surface point is inaccurate. Besides, nothing is said about how to extract the values of the misalignments from them. It should be kept in mind that misalignments cannot exist alone without the continuous deforming of the remaining part of the circumference; notions of the local as well as the global peaking (angular lumps) is confusing. It is practically impossible to discern them physically. Furthermore, the two equal angular misalignments should lead to the same additional stresses irrespective of how we name this misalignment — be it local or global one. In both cases the formulas are incorrect.
The proposed paper gives the solutions for the abovementioned problems. The results of the real measurements of the cross section form of different pipes are presented. The general approach for treating the out-of-roundness is given and an example of measurement of real pipe cross-section is presented. The stress calculation part of the procedure is based on the results presented in work [2].
Pipeline Health Integrity Monitoring (PHIM) Based on Acoustic Emission Technique
Authors: Giunta Giuseppe , Budano Sergio , Lucci Antonio , Prandi Luca 
Published: August 2013

The Acoustic Emission (AE) technique allows taking under control the damage as superficial flaws (S-Flaws) occurred during service operation of remarkable zones of steel components, monitoring the initiation and the propagation of critical defects, submitted to static or variable stresses and aggressive environment exposure.
In the framework of the eni gas&power research project oriented to the development of a “AE methodology” for monitoring critical sections of gas transmission pipelines, a study has been carried out jointly with Centro Sviluppo Materiali (CSM), aimed to investigate reliability and applicability of the AE technique to steels used in the Oil&Gas industry.
Steel grades API 5L X65, X80 and X100, representative of traditional and new gas pipelines, have been selected. The project was scheduled investigating the potential of these steels to release elastic waves generated by sources of damage related to ductile or brittle fracture mechanisms.
Hydraulic tests until failure were carried out on single pipes using steel grade API 5L X65 for monitoring the growing of the damage on the tip of artificial surface notches (S-flaw), machined on the wall thickness [1]. Water was used as internal fluid and temperature effect was considered as well. The capability of the AE technique to discriminate ductile and brittle fractures, the essential information to approach an integrity assessment procedure, was achieved. This paper, respect to the previous ones [1], extends the AE methodology for monitoring pipelines supplying both oil and gas. In fact a third burst test was carried out filling the pipe by air and the results on this item are presented.
The Effect of Bi-Axial Stress on Limit Loads of Structures Containing Surface-Breaking Flaws and its Influence on Structural Integrity Assessments
Authors: Wei Liwu , Hadley Isabel 
Published: August 2013

Fracture assessment diagram (FAD) based fracture assessment procedures are universally adopted by standards/documents including BS7910, R6, API579-1/ASME FFS-1 and FITNET. In the use of a FAD for structural integrity assessment, one important consideration is to determine the load ratio (Lr) which is defined by two equivalent definitions: Lr is either defined as the ratio of reference stress (σref) to yield strength (σY) as in BS7910, or as the ratio of applied load to plastic limit load as in R6. The solutions of reference stress or limit load are given in the assessment procedures for commonly encountered flawed structures such as a plate containing a surface crack and a cylinder containing an external surface crack. Although the solutions given in the various standards are not all the same, they were invariably derived on the basis of analysis of the force and moment equilibrium with regard to a flawed section and none of them has taken into account the effects of bi-axial stressing on a flawed section, thus leading to the likelihood of an overly conservative assessment.
In this work, finite element analysis (FEA) of various flawed geometries (plate and cylinder containing surface cracks) was performed to compute plastic limit load, with the focus on understanding the effects of bi-axial stressing on plastic limit load. The geometries assessed include a plate with a surface crack subjected to both uni-axial and bi-axial loading, and a cylinder with circumferentially internal and external surface cracks sustaining a combination of axial loading and internal pressure. The investigation of these cases has demonstrated a significant increase in plastic limit load arising from bi-axial stressing. Comparison of the results of plastic limit load obtained from FEA with those derived from BS 7910 reference stress solutions was carried out to assess the extent of conservatism when the standard solutions are used in the applications containing bi-axial stresses. The implication for structural integrity assessment due to bi-axial stressing was also addressed. A comparison between BS 7910 Level 2B (material-specific FAD) and Level 3C (based on a FAD generated with FEA) procedures was also made and it was shown that whether the Level 3C procedure can reduce the conservatism in an assessment is dependent on individual cases.
A Dislocation-Based Cleavage Initiation Model for Pressure Vessel Steels
Authors: Cochran Kristine B. , Erickson Marjorie , Williams Paul T. , Klasky Hilda B. , Bass B. Richard 
Published: August 2013

Efforts are under way to develop a theoretical, multi-scale model for the prediction of fracture toughness of ferritic steels in the ductile-to-brittle transition temperature (DBTT) region that accounts for temperature, irradiation, strain rate, and material condition (chemistry and heat treatment) effects. This new model is intended to address difficulties associated with existing empirically-derived models of the DBTT region that cannot be extrapolated to conditions for which data are unavailable. Dislocation distribution equations, derived from the theories of Yokobori et al., are incorporated to account for the local stress state prior to and following initiation of a microcrack from a second-phase particle. The new model is the basis for the DISlocation-based FRACture (DISFRAC) computer code being developed at the Oak Ridge National Laboratory (ORNL). The purpose of this code is to permit fracture safety assessments of ferritic structures with only tensile properties required as input. The primary motivation for the code is to assist in the prediction of radiation effects on nuclear reactor pressure vessels, in parallel with the EURATOM PERFORM 60 project.
This paper begins with a brief overview of the strategy for implementing the new model into the DISFRAC computer code. The balance of the paper focuses on efforts to model the nucleation of a carbide particle crack near an existing macrocrack under applied load. The carbide microcrack initiation model applies dislocation mechanics to assess the stress intensity exerted on a stiff, elastic carbide particle embedded in an elastic-plastic ferrite matrix near a macrocrack tip. The paper derives and discusses the governing equations for the model; including (1) computation of a slip band dislocation pileup distribution by enforcing equilibrium with the macrocrack-induced elastic-plastic stress field, (2) calculation of the mode I stress intensity on the particle crack plane due to the dislocation pileup and (3) determination of the particle fracture toughness. Together, these calculations provide the basis for determining the applied load required to initiate particle fracture. This paper demonstrates how the prediction of particle fracture depends on various microstructure parameters.
Cross-Weld Creep Comparison of Power Plant Steels CrMoV, P91 and P92
Authors: Tanner David W. J. , Sun Wei , Hyde Thomas H. 
Published: August 2013

Results obtained from high temperature creep tests of ferritic steel CrMoV, P91 and P92 cross-weld specimens are compared. Data is presented normalized with the results of the corresponding parent metals in order to compare the materials tested at different temperatures and stresses, and to identify characteristic cross-weld material trends.
All cross-weld failures occurred in the heat-affected zone (HAZ) adjacent to the parent metal, known as type IV, at earlier test durations than for the parent material specimens. The relative performance of the cross-welds was found to decrease with decreasing stress.
The CrMoV cross-weld specimens showed by far the lowest weld strength reduction factors and greatest notch strengthening, determined by testing uniaxially loaded bars with semi-circular circumferential notches located in the heat-affected zone.
The P91 and P92 cross-weld specimens were found to have similar (high) weld strength reduction factors and showed little or no notch strengthening. It was observed that the failure time of a P92 cross-weld specimen relative to the P92 parent material could be estimated using data from P91 cross-weld and relative parent material tests.
Nuclear Plant License Renewal Status in the U.S.
Authors: Young Garry G. 
Published: August 2013

As of January 2012, the NRC has renewed the operating licenses for 71 nuclear units, which will allow for up to 60 years of safe operation. In addition, the NRC has license renewal applications under review for 15 units and nuclear plant owners of more than 14 units have announced plans to submit applications over the next six years [1]. This brings the total of renewed licenses and announced plans for license renewal to over 96% of the 104 currently operating nuclear units in the U.S.
This paper presents the status of the U.S. license renewal process and the U.S. efforts associated with the option of seeking a second license renewal for up to 80 years of safe nuclear plant operation. Currently there are 9 operating nuclear plants that are eligible to seek a second license renewal. It is likely that applications for a second renewal will be submitted to the NRC within the next few years. The factors that contributed to the positive and the negative trends for both the first license renewals for 60 years and the second renewals for 80 years of safe operation are presented and discussed.
Effects of Shape Geometry on the Efficiency of Self-Healing Polymers
Authors: Okoro Ifeanyi J. , Yougoubare Yves Q. , Pang Su-Seng 
Published: August 2013

Autonomic smart self-healing composites are being developed and tested to deal with the problems of crack propagation and eventual damage. The recovery and self-healing efficiencies of these composite structures varies with changes in different physical properties such as temperature and shape geometry.
The foremost steps in creating a self-healing composite are mixing and programming and recovery. This paper explores the relationship between a composite’s programming processes against its shape-geometry. Improving the programming and recovery would lead to an improved self-healing polymer. To this end, samples of self-healing shape-memory polymers of different aspect ratios are tested after programming and recovery, and their compressive strengths are compared. The results show a direct relationship between the compressive strengths and aspect ratio.
Initial Quantification of the Effect of Ambient Humidity on the Strength of Non-Metallic Repairs of Piping and Pressure Vessels
Authors: Gribble David J. , Walker Roger H. , French Jesse J. 
Published: August 2013

Composite repairs of pressure vessels and transmission pipelines are installed in a wide variety of ambient conditions. The installation of epoxies utilized can range from arid environments with almost no humidity to tropical conditions of nearly 100% humidity or even completely submerged in water. This paper presents the methodology and results from an initial effort to determine the effects of humidity on the strength of certain epoxy matrix composite repairs.
The effect on final strength of a composite repair specimen cured under a variety of ambient humidity is presented from experimentation with specimens cured below 20% humidity and at approximately 96% humidity in a climate controlled chamber. The effects on final strength, stiffness, and hardness, are observed and recorded to note the difference between the varying conditions. The compilation of data is analyzed to determine what considerations need to be made for various levels of humidity at the time of installation for composite repairs installed on pressure vessels and piping.
Results are presented to show that prediction of curing time and final strength are achievable with reasonable accuracy given sufficiently accurate humidity measurement during the curing process.
Pressure Tests for Thickness Management of Wall Thinning Tees
Authors: Teshima Kaina , Iwamoto Yoichi , Hojo Kiminobu , Oka Tomoyuki , Kobayashi Kunihiro , Tsuno Syuichi 
Published: August 2013

Although the minimum thickness of pipe wall required (tsr) of T-joints (tees) of class 2, 3 and lower classes of nuclear power plants in Japan is calculated from the design pressure and temperature, there is no rule or standard of wall thinning T-joints for thickness management.
This paper describes the pressure tests procedure and six test results with parameters of T-joint geometry such as outer diameter D, thickness T and T/D to establish structural integrity of wall thinning T-joints. Based on the fracture surface observation, a ductile crack initiation of each test mock-ups was confirmed.
Comparison Between Pressure Tests and Simulations for Thickness Management of Wall Thinning T-Joints
Authors: Teshima Kaina , Ochi Mayumi , Asada Seiji , Hojo Kiminobu , Suzuki Takahiro , Kugimoto Mitsuo 
Published: August 2013

Although the required minimum thickness (tsr) of T-joints (tees) is calculated from the design pressure and temperature for design, there are no rules or standards for thickness management of wall thinning T-joints for facilities maintenance.
This paper describes the comparison between the five pressure test results of T-joints and their numerical simulations using FE analysis and confirms the failure criterion. The investigation for the numerical simulation and the experimental tests showed that ultimate tensile stress (σu) is the most suitable criterion for the burst of T-joints.
A Method to Characterize the Fracture Resistance of Dissimilar Metal Welds
Authors: Blouin A. , Chapuliot S. , Marie S. 
Published: August 2013

Characterization of the fracture resistance of weld joints, and in particular dissimilar metal welds (DMW), is a huge and difficult work where no standard currently exists. As a consequence, characterizations of materials have to be done prior to the fracture tests in order to consider the mechanical aspects of the material mismatch via F.E. analysis in the fracture toughness determination. However, performing these characterization tests may imply using a lot of material, which is sometimes not available, and can be expensive. Most studies are usually realized on reduced sized mock-ups.
The considered experimental mock-ups are pipes composed of a ferritic pipe welded to an austenitic one. The weld joints are made of Ni base alloys. A few small tensile samples have been extracted so that each material, even the heat affected zone (HAZ), can be characterized at low temperature. A fast method using laser sensors and a specific specimen shape has been developed and is used to identify these materials strain-stress curves at −125°C. Afterwards, these data have been used to simulate multi-material compact specimen tensile tests and single edge notch tension specimen, representing a conventional defect in the HAZ. Also, these two kinds of specimen have been extracted and the tests performed in order to compare the experimental results to the F.E. analysis. This paper presents the experimental work, the related specific devices, the F.E. analyses and the experimental analysis.
R6 V, Vg and RSE-M Estimates of Experimental Failure for Combined Loading
Authors: James Peter , Madew Colin , Goodfellow Andrew , Gallegillo Martin 
Published: August 2013

Engineering components which are considered in safety case assessments contain either real or hypothetical crack-like defects that experience combinations of primary and secondary stresses during service. A number of assessment procedures contain simplified numerical approaches to detail the interaction of these stresses under in-service or fault conditions including the R6 procedure used in the UK and the RSE-M Appendix 5.4 (RSE-M) assessment code adopted in France.
The R6 procedure and RSE-M approaches are shown to be relatively similar for cases which do not contain secondary loading but differ when treating secondary stresses. It is generally accepted that the R6 procedure in terms of ρ or V is conservative compared to finite element analyses and plant experience; which has driven the development of a new formalism of the R6 V factor, Vg. This new formalism is seen to be more aligned to the RSE-M approach but differs in some cases.
The aim of this paper is twofold: 1) to demonstrate the main divergence between the procedures, and 2) to provide experimental comparison between the R6 V, the newly formalised Vg, and the RSE-M approaches under test cases within literature that contain combined primary and secondary loading.
FE Residual Stress Analysis in a Narrow Gap Dissimilar Metal Weld
Authors: Obermeier Florian , Courtin Stéphan , Nicak Tomas , Keim Elisabeth 
Published: August 2013

In the nuclear industry narrow gap welding techniques are used to perform junctions between ferritic low alloy steel heavy section components and austenitic stainless steel piping systems. The residual stresses in Dissimilar Metals Welds (DMW) may influence the lifetime and functionality of the welded components. In Pressurized Water Reactor (PWR) piping systems, weld residual stresses in particular increased the susceptibility to primary water stress corrosion cracking (PWSCC) in the past. It is therefore necessary to develop and validate methods for a reliable residual stress and distortion prediction.
Numerical welding simulations for predicting residual stresses are commonly used in nuclear industry and their development is progressing fast during the recent years. As part of the European project STYLE — Structural Integrity for Lifetime Management — a case study was launched to assess the capability of such simulations.
The mock-up in this case study is provided by AREVA NP SAS. It is a pipe with a narrow gap dissimilar metal weld. The pipe thickness is about 40 mm and the outer diameter is 352 mm after final machining. In this assembly a 316L austenitic pipe is welded to an A508 Class 3 ferritic pipe by means of Alloy 52 Gas Tungsten Arc (GTA) narrow gap weld which is representative for PWR primary circuit piping. This mock-up is in the scope of a continuation of the ADIMEW – Assessment of Aged Piping Dissimilar Metal Weld Integrity - project and deals with the improvement of the assessment for DMW and Leak-before-break (LBB) procedures. The fracture test on this mock-up is planed to be performed at 300 °C with an initial through-wall defect. Apart from the LBB demonstration this mock-up is also dedicated for the validation of the applied fracture mechanics approach, extension of material data basis and validation of the weld simulation procedures applied within AREVA.
This paper presents the results of the finite element residual stress analysis related to this STYLE narrow gap weld case study. The two finite element codes ABAQUS and SYSWELD were used to predict the weld residual stresses and the shrinkage in axial direction. The major difference between the here presented methods is that SYSWELD accounts for phase transformation and the method used with ABAQUS does not. The results are compared between each other and with data obtained by deep-hole drilling techniques (DHD) at several locations.