bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Multi-Axial Fatigue Test Data Using a Path-Dependent Effective Stress/Strain Definition
Authors: Wei Zhigang , Dong Pingsha , Batra Romesh C. , Nikbin Kamran
Published: January 2014

Multi-axial fatigue life assessment is important in power generation, aerospace, automotive, and many other industries. The newly developed path-dependent multi-axial cycle counting and fatigue life assessment method has been shown effective for some applications. For instance, when stress range is used as the only driving force for fatigue failure, the method correlates high cycle fatigue test data well. The method consists of two parts: (1) maximum-range (or maximum distance) based cycle counting method, so that the method can be applied to 2-D and 3-D stress or strain space, as compared to the conventional rainflow counting method, which is based on the peak-valley concept, therefore, can be applied only to uniaxial (1-D) loadings; and (2) a path-length based stress range is used as the fatigue damage parameter replacing the traditional concept of stress or strain range, which is the difference between the peak value and the valley value of a cycle. This method has been justified using the classical fracture mechanics in multidimensional stress space.

In this paper, we apply the method to analyze two additional classes of multi-axial fatigue test data reported in the literature: (1) low-cycle strain based tests, which has an important implications in high-temperature applications, such as piping/vessels in power industry, turbine, and automotive exhaust systems; (2) a series of test data that require an introduction of two parameters in either fatigue crack growth model or S-N curve based approach. For the latter, an incremental crack growth model reported earlier by the authors is recast to incorporate one additional stress based parameter to account either mean stress or maximum principle stress effects in multi-axial fatigue damage process, dependent upon material characteristics under consideration. The results show that strain-based low-cycle multi-axial fatigue data can be effectively correlated in the form of a single S-N curve using a path-dependent effective strain range definition. Furthermore, a two parameter based interpretation of the crack propagation model is capable of capturing effects of the maximum principle and mean stresses on multi-axial fatigue damage process associated with some of the test data. Finally, the physical basis of the method in these extended applications is discussed.
Design Curve Construction Based on Monte Carlo Simulation
Authors: Wei Zhigang , Luo Limin , Lin Burt , Konson Dmitri , Nikbin Kamran
Published: January 2014

Good durability/reliability performance of products can be achieved by properly constructing and implementing design curves, which are usually obtained by analyzing test data, such as fatigue S-N data. A good design curve construction approach should consider sample size, failure probability and confidence level, and these features are especially critical when test sample size is small. The authors have developed a design S-N curve construction method based on the tolerance limit concept. However, recent studies have shown that the analytical solutions based on the tolerance limit approach may not be accurate for very small sample size because of the assumptions and approximations introduced to the analytical approach.

In this paper a Monte Carlo simulation approach is used to construct design curves for test data with an assumed underlining normal (or lognormal) distribution. The difference of factor K, which measures the confidence level of the test data, between the analytical solution and the Monte Carlo simulation solutions is compared. Finally, the design curves constructed based on these methods are demonstrated and compared using fatigue S-N data with small sample size.
Effect of Thermal Ageing on Properties of Pressure Vessel Low Alloy Steel
Authors: Joly Pierre , Roch François , Primault Christophe
Published: January 2014

The shells of the PWR heavy components are made of quenched and tempered low alloy steel (type A508 cl.3). Slow thermal ageing of the steel may occur by inter-granular segregation of impurities, depending on the service temperature and the concentration of residual elements (mainly phosphorus) in the steel. This phenomenon may generate embrittlement (i.e. a shift of ductile to brittle transition temperature). The pressurizer service temperature is the highest of the primary loop (345°C), and this component may be affected by more important ageing effects than others. In order to support rules for embrittlement predictions and to anticipate the potential embrittlement of the pressure boundary of this component, AREVA launched a research program, on different materials (base materials, weld metals, and heat affected zones of welds) based on accelerated ageing (400°C up to 30,000 hours and 450°C up to 20,000 hours), and Charpy impact toughness measurements. The aim of this paper is to present available results and to analyze them in the light of the literature and the available models.
Seismic Response Analysis of Industrial Building With Viscous-Friction Hybrid Damper
Authors: Minagawa Keisuke , Fujita Satoshi , Kawamura Tatsuya , Tanaka Go
Published: January 2014

In great east Japan earthquake, resonances of structures which have long natural period by long period seismic wave were reported. The duration time of the long period seismic wave was more than a few minutes. Meanwhile many dampers have been proposed and applied to actual structures in order to suppress seismic response. However large stroke and energy absorption capacity are required for these conventional oil dampers against the long period seismic wave. In this paper, authors propose a viscous-friction hybrid damper as an effective vibration control device suitable for structures which have long natural period. In general, structures with long natural period resonate with long period ground motion. The hybrid damper consists of an oil damper and a friction damper in series. In our hybrid damper, the friction damper can absorb vibration energy as well, in the case of long period seismic wave. Thus energy absorption of oil damper is suppressed, and the damper retains good performance. In addition, the oil damper of the hybrid damper is effective for small earthquake. In this paper, a boiler building was selected as an example of industrial buildings. The boiler building was modeled as 2-degree-of-freedom for analysis. Seismic response analysis of the building with the hybrid damper was carried out. As a result good vibration control performance was confirmed.
Evaluation for Nondestructive Crack Sizing Capability on Cracked Surface Treated by Water Jet Peening
Authors: Kimura Ryuji , Yoshikubo Fujio , Ehara Kazuya , Murakami Nobuo , Kanno Akihiro
Published: January 2014

Water Jet Peening (WJP) is an approved mechanical mitigation technique that has been widely applied in Japanese nuclear power plants since 1999. WJP suppresses stress corrosion cracking (SCC) initiation in SCC susceptible materials which have been widely used in the fabrication of reactor internals [1].

Laboratory data shows that WJP is effective at mitigating or suppressing shallow crack propagation if the post application compression depth layer is deeper than the original crack depth and that WJP has no adverse effect on pre-existing cracks, such as crack propagation or acceleration of the crack propagation during and after WJP [2]. In addition, it has also been reported that WJP has no adverse effect on Ultrasonic testing (UT) sizing capability for pre-existing cracks in 304S.S. and Alloy 182 [3].

Based on these evaluation test results, Hitachi-GE Nuclear Energy, Ltd (HGNE) successfully applied WJP on the cracked surfaces of reactor internals in an operating Japanese nuclear power plant in 2011 [4].

Recently, to evaluate the applicability of this process in a PWR power plant, HGNE has performed an evaluation of Ultrasonic testing (UT) and Eddy Current Testing (ECT) sizing capabilities for surface cracks on a dissimilar metal weld coupon that had been mitigated utilizing the WJP process. No significant differences in their sizing capabilities were observed between the before and after WJP treatment test coupons. During this evaluation, it was also confirmed that surface residual stress on the coupon was improved from tensile to compressive (from max approximately 800MPa to min approximately −600MPa).

As a result of this evaluation, it was determined that WJP has no adverse effect on UT and ECT sizing capabilities. In addition, HGNE has taken this knowledge and applied it to the development of a WJP tool for PWR Bottom Mounted Instrumentation (BMI) nozzles, which accommodates all the parameters used for this testing and enables HGNE to reduce the total application time as a result of the inclusion of advanced technological improvements.
Effect of Hammer Peening Processing on Fatigue Property of Welded Joints After Overload
Authors: Morikage Yasushi , Igi Satoshi , Oi Kenji
Published: January 2014

One general method for improving the fatigue strength of welded joints is introduction of compressive residual stress by peening. However, there is concern that the fatigue strength of the welded joint may decrease if excessive preloading is applied after peening.

It has been found that fatigue strength decreased after applying compressive preloading to a welded joint due to cancellation of the compressive stress at the weld toe.

In the present research, the influence of excessive preloading on the fatigue strength of welded joints with compressive residual stress at the weld toe was clarified by experiments using hammer peening with an improved pin.

When hammer peening was applied to welded joints, increasing the radius of the weld toe reduced the decrease of compressive residual stress due to excessive preloading. As a result, the decrease of the fatigue strength of the welded joint was also reduced.
Mechanical Properties of a New Nitrogen-Strengthened Stainless Steel With Reduced Amount of Ni and Mo in High Pressure Gaseous Hydrogen
Authors: Matsumoto Kazuhisa , Ohmiya Shinichi , Fujii Hideki , Hatano Masaharu
Published: January 2014

To confirm a compatibility of a newly developed high strength stainless steel “NSSC STH®2” for hydrogen related applications, tensile and fatigue crack growth properties were evaluated in high pressure hydrogen gas up to 90MPa. At temperatures between −40 and 85°C, no conspicuous deterioration of tensile properties including ductility was observed even in 90 MPa hydrogen gas at −40°C while strength of STH®2 was higher than SUS316L. Although a slight drop of reduction of area was recognized in one specimen tested in 90 MPa hydrogen gas at −40°C, caused by the segregation of Mn, Ni and Cu in the laboratory manufactured 15mm-thick plate, it was considerably improved in the large mill products having less segregation. Fatigue crack growth rates of STH®2 in high pressure hydrogen gas were almost the same as that of SUS316L in air. Although fatigue crack growth rate in air was considerably decelerated and lower than that in hydrogen gas at lower ΔK region, this was probably caused by crack closure brought by oxide debris formed on the fracture surfaces near the crack tip by the strong contact of the fracture surfaces after the fatigue crack was propagated. By taking the obtained results into account, it is concluded that NSSC STH®2 has excellent properties in high pressure hydrogen gas in addition to high strength compared with standard JIS SUS316L.
Stability of Cylinder Arrangement in Potential Flow
Authors: Benaouicha M. , Longatte E. , Baj F.
Published: January 2014

Fluid-structure interaction and flow-induced vibration in square cylinder arrangement under incompressible, ideal and irrotational cross flow are investigated in the present paper. The purpose of this study is to contribute to better understanding of external fluid loads exerted on long thin cylinders inducing the flow perturbations. Indeed, in presence of high flow confinement, the thin cylinders could be subjected to strong vibrations, which may lead to instability development and therefore to a risk of break or collision. The dynamic instability of the mobile tube, according to some geometric and flow parameters such as reduced velocity and pitch ratio, is then studied. A semi-analytical approach is used to determine a stability criterion of the dynamical system. In addition, the influence of key physical parameters on fluid-solid dynamics interaction is quantified in the studied configuration.
Dynamic Modeling of a BWR Control Rod Insertion System for Seismic Analysis and its Experimental Validation
Authors: Koide Yuichi , Goto Yoshihiro , Sato Yuki , Ishigaki Hirokuni , Takahashi Tsuyoshi , Shiraki Tomomi
Published: January 2014

The assessment of the seismic scrammability, which means the control rod insertability during a seismic event, is one of the most important design tasks for ensuring the seismic safety of nuclear power plants in Japan. This paper discusses the dynamic modeling of the control rod insertion behavior of a boiling water reactor (BWR) during an earthquake. A dynamic model of a control rod insertion system for BWR was developed based on multi-body dynamics. The coupled vibration behavior of the fuel assemblies in the fluid was modeled as an inertial coupling system. The effect of the interaction force between the control rod and the fuel assemblies was considered in a three-dimensional contact analysis. The hydraulic control unit and the control rod drive, which provide the control rod with drive force, were modeled in the concentrated parameter system. The model parameters, such as the friction coefficient between the control rod and the fuel assembly and the discharge coefficient of the scram piping, were obtained by conducting experiments. The validity of the model was confirmed by comparing the analytical results with the experimental ones. First, the validity of the fuel assembly model was verified through a comparison with the vibration testing in an underwater condition. It was confirmed that the calculation results for the frequency response of the fuel assembly were in good agreement with the experimental ones. Second, the validity of the modeling method of the drive system consisting of the hydraulic control unit and the control rod drive was verified through a comparison with the scram testing under non-vibration condition. The calculation results for the time history of the control rod insertion, the accumulator pressure, and the flow through the scram piping were in good agreement with the experimental ones. Finally, the validity of the modeling method of the whole system consisting of the fuel assemblies, the control rod, and the drive system was verified through a comparison with the scram testing under vibration condition. The calculation results for the time history of the control rod insertion stroke and the time delay of the insertion motion during an earthquake were in good agreement with the experimental ones. The results of these comparisons show that the developed analysis model can simulate the control rod insertion behavior during an earthquake.
Stress Intensity Factors for Axial Cracks in Pressurized Cylindrical Elements Using the Boundary Element Method
Authors: Gonzalez Marco , Martinez Manuel
Published: January 2014

Pressure vessels and pipes are inspected to establish the presence of cracks that could affect their integrity for a reliable operation avoiding the possible negative impact of their failure. The Boundary Element Method (BEM) is a relatively new numerical method in this kind of applications, which is based on Integral Equations (IE), considering only the contour of the solid (meaning an easier meshing). The BEM has a good accuracy that promotes its use in stresses analysis. Crack growth modeling is one of the most important applications for the BEM, since it allows an accurate stress analysis in the crack faces and crack propagation analysis without re-meshing. This paper focuses on modeling an inside surface axial crack in a cylindrical element under internal pressure using 2D-BEM, to determine the mode I Stress Intensity Factors (KI) at the crack tip. These factors are used to predict the mechanical behavior of the element and its residual life when is subjected to cyclic loadings The BEM generates less conservative results than API 579 rules for Ri/t ≤ 10, meanwhile for Ri/t ≥ 12 the results are in a good agreement with that standard. New simple correlations to calculate KI for 5≤Ri/t≤10 and 10<Ri/t≤25, are offered.
A Testing Apparatus for SEM In-Situ Fatigue Testing of Small Scale Specimens and a Derived Application
Authors: Reiser Johannes , Maier Bernd , Guster Christoph , Gaenser Hans-Peter , Pippan Reinhard
Published: January 2014

The prediction of fatigue strength and fatigue life of materials was the key motivation in this study. Several approaches for fatigue limit prediction at mesoscopic scale have been proposed. All of them incorporate microstructure and grain features. For the purpose of studying plastic local strain accumulation and therefore fatigue behaviour at the grain scale a new testing rig was developed. A key point for understanding fatigue behaviour and crack initiation even at higher load cycles is basic knowledge on strain localization in the grain structure of the material. Till now low testing frequencies of SEM in-situ testing rigs limited tests at higher load cycles. The developed in-situ tension-compression testing apparatus for in-situ SEM use allows testing at higher frequencies and therefore to perform even higher load cycles with less time consumption. Oxygen free high conductivity copper (OFHC) grade 99,99% was chosen for investigation. In addition cuts with a focus ion beam (FIB) were made in distinct orientations representing material defects to get an idea of the influence of micro notches on fatigue behaviour and crack initiation. The results of in-situ fatigue tests will be presented.
Efficient Probabilistic Calculation of a Thermal Transient on a 3D FE Model With Variable Heat Exchange Coefficient
Authors: Demol Thibault , Izard Jean-Pierre , Tartare Nicolas
Published: January 2014

Probabilistic calculations are often used to evaluate reliability in nuclear industry. One of their main difficulties is that failure probabilities are, in this domain, very low and therefore their computations are very long. The speed of the calculations depends on the probabilistic algorithm and the complexity of the physical problem (usually modeled by a finite element analysis). The optimization of the probabilistic algorithms benefits from a wealth of literature but the physical problem is often very simplified by a lot of approximations. This paper develops a methodology to avoid some approximations. The geometry of the problem is often brought back to a 1D or 2D problem. Here, large 3D mesh can still be used thanks to transfer functions. This requires the linearity of the problem and especially a constant heat transfer coefficient for a thermo-elastic analysis. This limitation has been removed.

This article’s focus is on methodology but qualitative results of a probabilistic brittle fracture application of a reactor pressure vessel (RPV) in ferritic steel are given. Other kinds of analysis can benefit from similar methodology.
A Multi-Phase CFD Study of a Liquid Slug Ingestion in a Reciprocating Compressor
Authors: Traversari Riccardo , Bettini Bernardo , Carcasci Cosimo , Fusi Andrea
Published: January 2014

The fluid handled by reciprocating compressors has to be strictly limited to gas and, under no circumstances, can there be a liquid fraction ingestion, as this event can cause the famous “liquid hammer effect” that can generate catastrophic failures. A study was conducted to evaluate the quantitative effects of the ingestion of a liquid slug into a reciprocating compressor cylinder with the goal of calculating the pressure distribution on the piston during such an event. The Multi-phase CFD ANSYS FSI software, utilized to simulate the behavior of a mixture of gaseous and liquid hydrocarbons during the delivery phase, has shown that the pressure inside the cylinder increases up to five times the normal pressure. This new approach can be helpful in the design stage or for root cause failure analysis of large compressors such as the ones utilized in the natural gas, refining, and LDPE industries.
Experimental Determination of the Static Equivalent Pressures of Gas Phase Detonations in Pipes and Comparison With Numerical Models
Authors: Schildberg Hans-Peter , Smeulers Jan P. M. , Pape Gersom
Published: January 2014

In order to determine the effective load of gas phase detonations on pipe walls (“static equivalent pressure”), comprehensive experiments have been conducted in 48.3×2.6 and 114.3×3.6 pipes (outer diameter [mm] × wall thickness [mm]), in which deflagrative explosions of stoichiometric C2H4/O2/N2-mixtures at 20 °C underwent the transition to detonation. Initial pressures were chosen high enough to produce detonation pressures that caused significant bulging of the pipe walls.

All 8 different pressure scenarios that can be distinguished for gas phase detonations in pipes were addressed by the experiments, even the extremely rare case of having the deflagration to detonation transition occurring within about 1 pipe diameter a head of blind flange which yields the largest static equivalent pressure of all scenarios.

By these tests it was possible to (1) validate the predictions of recently developed numerical models for predicting the structural response of the pipe wall and to (2) determine the static equivalent pressure of gas phase detonations in pipes even for those detonative pressure scenarios for which a reliable pressure/space/time profile required as input for the numerical models is at present not yet available. Once the static equivalent pressure is known, the well-established pressure vessel design guidelines, which can only cope with static loads, can be applied for detonation pressure proof pipe design in all those cases where the detonation speed is not close to the propagation speed of the flexural waves in the pipe.

Furthermore, preliminary information was obtained about which of the 8 detonative pressure scenarios only depends on the Chapman-Jouguet pressure ratio of the involved mixture and which scenarios will also depend on other characteristic parameters of the involved mixture (difference between initial temperature and auto ignition temperature, ignition delay time).
System Identification and Reduction of Vibrations of Piping in Different Conditions
Authors: Hinz Gereon , Kerkhof Klaus
Published: January 2014

Safe operation, availability and lifetime assessment of piping are of utmost concern for plant operators. The knowledge on how failures in piping and its support construction are reflected in changes of the dynamic behavior (eigen-frequencies, -modes and damping) is a useful basis for System Identification and Structural Health Monitoring (SHM). Modal analysis of complex piping, the identification of system changes and the use of vibration dampers in piping still constitute challenges. In this study three different piping systems are investigated:

1. In the first piping system at a chemical plant, which is supported by a tall steel structure fixed at the base, piping-elbow forces at the top of the building cause large vibration amplitudes. Tuned mass dampers (TMD) for minimizing vibration amplitudes were first tested in the laboratory of MPA Stuttgart and then designed for the piping system in the plant for preventing failures.

2. Another piping system is reported that is excited at resonance frequency to cause failure due to in-plane bending in an elbow with local wall thinning.

3. Finally, a large piping system at a lignite power plant is investigated under ambient vibration to detect changes in boundary conditions.

Experimental Output Only Modal Analysis (OOMA) and Operational Modal Analysis (OMA), FE-model studies and model-updating are performed. Changes in the natural frequencies and corresponding mode shapes due to through-wall cracks or changing boundary conditions were observed.
Use of Nuclear Mechanical Design Codes and Fracture Mechanics Procedures for the UK EPR™ at Hinkley Point C
Authors: Gallegillo Martin , Goodfellow Andrew , Philipp Christophe , Miles Lol , Williams Anthony
Published: January 2014

Structures, systems and components that are important to nuclear safety are designed, manufactured, constructed, installed, commissioned, quality assured, maintained, tested and inspected to the appropriate standards. The codes and standards need to be evaluated to determine their applicability, adequacy and sufficiency.

The consideration of a conservative design is one important element of the Safety Case. This is generally used together with high manufacturing quality, the use of proven materials, inspection, functional testing and defect tolerability. In a UK Safety Case, the assessment of fracture risk of those mechanical components whose likelihood of gross failure is so low that can be discounted requires the determination of the actual critical defect size in order to compare it with the detectable defect size used for inspections.

For the UK EPR™ the 2007 Edition of the RCC-M Code including Addenda 2008, 2009 and 2010 will be the design code of reference and the RSE-M Code version 2010 Appendix 5 will form the basis of the methodology used for standard fracture mechanics assessments of the UK EPR™. Previously, the UK nuclear structural integrity community has used the ASME Code Section III for the UK previous PWR and the R6 procedure for fracture mechanics assessments.

This paper explains the choice of these two codes for the UK EPR™ and the work carried out to date by EDF Energy to demonstrate its compliance with the UK expectations for components critical to safety.
Online Monitoring — From Condition Monitoring to Plant Optimization and Operation Prognosis
Authors: Trieglaff Ralf , Rieck Detlef , Schulz Axel , Wagner Joël , Wernicke Robert
Published: January 2014

Operation and monitoring of thick-walled components in coal fired power plants demand special requirements: high availability, flexible loads, low maintenance costs and reliability.

In this article it is shown how, based on a strength calculation of thick-walled components potential may be expelled for a flexible, cost effective plant. The aim is to meet the requirements of the volatile energy market successfully.

By different manufacturers developed online monitoring systems are used in the European generation system. The available online monitoring systems differ in terms of the underlying rules and the measuring and evaluation methods.

The common task of all online monitoring systems is the monitoring of the fatigue condition of the power plants. Fatigue calculations represent an essential element of condition monitoring and are necessary to guarantee the plant safety. Furthermore, important business decisions on the availability of facilities are made (periodic inspection and maintenance).

In the article is shown how the existing online monitoring systems can be adapted to the changed requirements.

Potential for smart additional tools based on two planned research projects are demonstrated.
Assessment of Stress Distribution in a Buttress Type Connection for Polyethylene Autoclave Reactor
Authors: Haeri Navid , Lewis John S. , Cornah Brian A.
Published: January 2014

Background. The authors conducted a study to analyze the stress distribution in an End Cover – Buttress Strap – Cylindrical connection according to Users’ Spec.

Materials and methods. The authors created axi-symmetric finite element models in order to demonstrate the reaction loads and stress distribution on contact surfaces as well as stress distribution in the various regions of the model. They applied different design scenarios according to an operational (users’) spec to the models. The parameters investigated were the reaction loads at contact points and local and linearised stresses. Also each individual buttress groove was studied. Ratcheting and fatigue assessment were also addressed aligned with the stress results.

Results. The study results showed the behaviour of each buttress element under the operating loads. It also showed the location with the greatest local stress levels as well as the locations most vulnerable to ratcheting and fatigue cracking. A safety margin assessment also was carried out picturing the pressure-temperature enhancement possibilities.

Conclusions. The study indicates potential future design options for enhancing buttress type connections. It also contributes to the understanding of existing reactor damage and corrosion assessment, impacts which may be useful in the remaining life assessment and process optimisation. Fracture study also defines the most critical inspection points during the life of the reactor.
Multiple Cracks Interaction Model and Residual Life Assessment Methods for the High-Temperature Structure
Authors: Si Jun , Xuan Fu-Zhen , Tu Shan-Tung
Published: January 2014

Multiple cracks are often found in many high-temperature structural components. The interaction and coalescence of multiple cracks may significantly influence the service lives of these high-temperature components. The interaction effect on multiple cracks is investigated under creep conditions in this paper. The results indicated that interaction of multiple cracks is different between the time dependent fracture characterized by C*-integral and linear elastic fracture noted by SIF. The level of conservatism of the current alignment rule was discussed under creep conditions. Then combination rules and regularization of multiple cracks under creep conditions are developed. Based on these analyses, the assessment method for the residual life prediction of high-temperature structure containing multiple cracks is developed.
Basis for ASME Section XI Code Case for Flaw Tolerance Evaluation of CASS Piping
Authors: Griesbach Timothy J. , Harris David O. , Cofie Nathaniel G. , Chockie Alan , Dedhia Dilip
Published: January 2014

Thermal aging of cast austenitic stainless steel (CASS) piping is a concern for long term operation of nuclear power plants. The effects of aging in susceptible (i.e., high delta ferrite) CASS piping and components must be managed through the license renewal period. In the United States, utilities must follow the guidance for managing age-related degradation in the Generic Aging Lessons Learned (GALL) report, and this may include analyses or inspections to demonstrate that the piping systems remain flaw tolerant. The duplex structure and large grain size of the CASS materials poses challenges with non-destructive examinations (NDE) using ultrasonic inspection (UT) techniques of the CASS components which further complicates the ability to demonstrate that any existing flaws would not compromise piping integrity.

Recent analytical studies of fully aged CF8M piping have resulted in a probabilistic fracture mechanics (PFM) model that has been used to develop allowable flaw sizes based on various levels of probability of failure. This model has been utilized extensively to generate a series of flaw acceptance limits that could be equated to the service levels in the ASME Code. A proposed ASME Section XI Code Case has been developed based on this PFM methodology for flaw tolerance evaluation of CASS piping components considering the effects of aging and uncertainties in material properties. The Code Case is currently under review by the ASME Working Group on Pipe Flaw Evaluation. This paper outlines the proposed Code Case and presents a technical basis for the flaw tolerance evaluation of CASS piping components. The ultimate objective of the flaw tolerance evaluation is to determine allowable flaw sizes in CASS components and determine target flaw sizes for NDE that will ensure safe operation with these components considering possible flaw growth. The flaw tolerance evaluation could be applied for a range of piping systems including pressurizer surge lines and primary system piping made from either statically or centrifugally cast stainless steel.
Stress Analysis of Pipeline Subjected to Differential Frost Heave
Authors: Di Yan , Shuai Jian , Kong Lingzhen , Zhou Xiayi
Published: January 2014

Frost heave must be considered in cases where pipelines are laid in permafrost in order to protect the pipelines from overstress and to maintain the safe operation. In this paper, a finite element model for stress/strain analysis in a pipeline subjected to differential frost heave was presented, in which the amount of frost heave is calculated using a segregation potential model and considering creep effects of the frozen soil. In addition, a computational method for the temperature field around a pipeline was proposed so that the frozen depth and temperature variation gradient could be obtained. Using the procedure proposed in this paper, stress/strain can be calculated according to the temperature on the surface of soil and in a pipeline. The result shows the characteristics of deformation and loading of a pipeline subjected to differential frost heave. In general, the methods and results in this paper can provide a reference for the design, construction and operation of pipelines in permafrost areas.
Behavior of Bolt Force Changes of Flanged Connections Under Thermal Loading
Authors: Hiratsuka Masaaki , Kobayashi Takashi , Nishiura Kengou , Itoi Katsutoyo
Published: January 2014

When flanged connections are used at a high temperature, one of the issues is the reduction of bolt forces, especially in the cases where PTFE-based gaskets are employed. Bolt forces significantly reduce when flanged connections are heated and re-torque is necessary in many cases. It is important to estimate the residual bolt forces under thermal loading to ensure the integrity of flanged connections.

In this paper, the behavior of bolt force changes under thermal loading was experimentally examined using a flanged connection with expanded PTFE sheet gaskets. The flanged connection was heated and then cooled in an electric oven and the changes of the bolt forces were measured. It is found that the bolt forces reduce at the first thermal loading due to the gasket flow. Once the gasket is settled, the bolt force changes depend on the difference of thermal coefficients of the bolts and the gasket. It is also clarified that thinner gaskets and spiral wound gaskets are effective for elevated temperature applications.
Stress Intensity Factor Coefficients for Circumferential ID Surface Flaws in Cylinders for Appendix A of ASME Section XI
Authors: Cipolla Russell C. , Lee Darrell R.
Published: January 2014

The stress intensity factor (KI) equations for a surface crack in ASME Section XI, Appendix A are based on non-dimensional coefficients (Gi) that allow for the calculation of stress intensity factors for a cubic varying stress field. Currently, the coefficients are in tabular format for the case of a surface crack in a flat plate geometry. The tabular form makes the computation of KI tedious when determination of KI for various crack sizes is required and a flat plate geometry is conservative when applied to a cylindrical geometry.

In this paper, closed-form equations are developed based on tabular data from API 579 (2007 Edition) [1] for circumferential cracks on the ID surface of cylinders. The equations presented, represent a complete set of Ri/t, a/t, and a/l ratios and include those presented in the 2012 PVP paper [8]. The closed-form equations provide G0 and G1 coefficients while G2 through G4 are obtained using a weight function representation for the KI solutions for a surface crack. These equations permit the calculation of the Gi coefficients without the need to perform tabular interpolation. The equations are complete up to a fourth order polynomial representation of applied stress, so that the procedures in Appendix A have been expanded. The fourth-order representation for stress will allow for more accurate fitting of highly non-linear stress distributions, such as those depicting high thermal gradients and weld residual stress fields.

The equations developed in this paper will be added to the Appendix A procedures in the next major revision to ASME Section XI. With the inclusion of equations to represent Gi, the procedures of Appendix A for the determination of KI can be performed more efficiently without the conservatism of using flat plate solutions. This is especially useful when performing flaw growth evaluations where repetitive calculations are required in the computations of crack size versus time.

The equations are relatively simple in format so that the KI computations can be performed by either spreadsheet analysis or by simple computer programming. The format of the equations is generic in that KI solutions for other geometries can be added to Appendix A relatively easily.
Characterisation of A508 Steel Cleavage Initiation Sites and Local Plasticity Using Surface Matching Technique
Authors: McKenzie F. , Smith R. J. , Scenini F. , Sherry A. H.
Published: January 2014

Cleavage fracture in ferritic pressure vessel steels is preceded by local plastic deformation that initiates micro-cracks at carbides or second phase particles within the highly stressed region ahead of a crack tip. The objective of this study is to locate initiation sites of failed Compact Tension fracture mechanics specimens, tested at temperatures within the lower ductile to brittle transition region. A surface matching approach was developed to identify regions of local plastic deformation on the fracture surfaces of tested specimens, using confocal microscopy to acquire accurately mapped topographic images of both fractured surfaces, and then subtracting each pair of images in a virtual environment. This methodology is conceptually similar to the fracture surface topography analysis (FRASTA) technique but uses a home developed MATLAB software based on image correlation. The residual mismatch (interference) between the two datasets was used to identify the regions of local plasticity on both fracture surfaces of each test specimen studied that is believed to be associated with the cleavage initiation sites.

The size and location of the localised plasticity was found to be consistent with scanning electron microscopy observations of cleavage initiation sites located directly ahead of the fatigue pre-crack tips in tested specimens. Finite element modelling was used to identify the magnitude of stress at the identified regions of cleavage initiation for the specimens studied, providing new insights into the mechanism of cleavage initiation in the lower transition region. This study suggests that this is a promising methodology for the identification of the initiation sites of cleavage fracture.
Fundamental Study on Health Monitoring for Pipe by Vibration Analysis
Authors: Kawazu Shunsuke , Fujita Satoshi , Minagawa Keisuke
Published: January 2014

In the operation of industrial plant, it is important to ensure the piping integrity. One of the serious problems of pipe is wall-thinning because of erosion (mechanical process) and corrosion (chemical process). Wall-thinning causes several kind of damage to pipes, such as the wholesale destruction of pipes due to corrosion, which may result in great accident and seriously harm human and environment. In general, wall thinning of pipes is measured by ultrasonic testing. However, it takes too much time for the test because there are many observation spots due to the recent growth of plant size. For this reason, this method of inspection of wall thinning has been reconsidered.

In this study, evaluation technique of pipe integrity by measuring the flow-induced by vibration of the pipe with acceleration sensors and analyzing the vibration characteristics is proposed. If the method of this study is successfully carried out, it is expected that the condition of pipes can be figured out in a short time and the examination can be made efficiently. This paper shows some/the research findings of fundamental study.
Mechanical Behavior of Welded and Un-Welded Polyethylene Pipe Materials
Authors: El-Bagory Tarek M. A. A. , Younan Maher Y. A. , Sallam Hossam E. M.
Published: January 2014

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, HDPE, pipes to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate and specimen configuration on the mechanical behavior of welded and un-welded pipes made from HDPE. Tensile tests are conducted on specimens longitudinally cut from the pipe with thickness (10, and 30 mm), at different crosshead speeds (5–500 mm/min), and different gauge lengths (20, 25, and 50 mm) to investigate the mechanical properties of welded and un-welded specimens. Butt-fusion, BF, welding method is used to join the different parts of HDPE pipes. In the case of test specimens taken from un-welded pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of welded specimens almost occurs at the fusion zone. At lower crosshead speeds the fracture of welded specimen occurs in all specimen configurations at the fusion zone. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both welded and un-welded specimens.
Inelastic Deformation and Elastic Follow-Up
Authors: Wang Yiqiang , Smith David J. , Truman Christopher E.
Published: January 2014

A structure, when operated at high temperature and subjected to combinations of applied and residual stresses, is known to exhibit elastic follow-up (EFU). This is a consequence of the interaction between the applied and residual stresses leading to additional strain accumulation. However, current methods of determining elastic follow-up are often based on judgment and experience [1]. This research reveals that there are a range of solutions for the elastic follow-up for materials exhibiting combinations of elastic, plastic and creep behaviour. The various solutions are illustrated for an idealised two bar structure. Cases are considered for bars each having different constitutive behaviour, similar or different cross sections or operating at the same or different temperatures. We find that often solutions are given only for idealised cases and the elastic follow-up factor is a constant. The implications of the results are discussed in the context of the behaviour of practical components.
Development of Fatigue Assessment Method Based on Flaw Tolerance Concept
Authors: Asada Seiji , Shuhei Takeda , Hirasawa Taiji , Saito Toshiyuki , Saito Itaru , Dozaki Koji
Published: January 2014

The Japan Society of Mechanical Engineers (JSME) Committee on Power Generation Facility Codes recognizes the importance of fatigue evaluation methods based on the latest knowledge and is developing a fatigue evaluation method by flaw tolerance. The ASME B&PV Code Section XI has Non-mandatory Appendix L, “Operating Plant Fatigue Assessment” (hereinafter “App. L”), which provides a flaw tolerance method for fatigue evaluation when a cumulative usage factor (CUF) of a component is greater than 1.0. In order to develop a flaw tolerance method for the JSME Codes for nuclear power generation facilities, postulated initial flaws, capability of nondestructive examination, compatibility to rules and flaw tolerance codes are discussed.
Role of Soil-Structure Interaction in Base-Isolated Structures Founded on Soil Stratum Overlying Half Space
Authors: Tsai C. S. , Su H. C.
Published: January 2014

This paper attempts to assess the role of soil-structure interaction (SSI) and higher modes in base-isolated structures founded on a soil layer overlying a half space. Closed form solutions for a system that includes a superstructure, seismic isolator and soil stratum overlying a half space have been obtained. The derived formulations considering the effects of SSI and higher modes in terms of well-known frequency and impedance ratios can explicitly interpret the dynamic behavior of a base isolated structure founded on soil stratum overlying a half space. Furthermore, the SSI effects on dynamic responses of isolated structures founded on soil stratum overlying a half space were extensively investigated. The conclusions drawn by this study provide considerable information for comprehending the SSI and higher mode effects on the dynamic responses of isolated-structures especially for those founded on soil stratum overlying a half space.
Estimation of Stress Ratio From Striation’s Three-Dimensional Geometry
Authors: Yamagiwa Kenta , Sasaki Tetsuya
Published: January 2014

Striation’s width is useful to estimate stress intensity factor range. To estimate maximum and minimum stress intensity factor, the relationship between stress ratio and aspect ratio of striation obtained by Furukawa, is used. However, accuracy of that method depends on the observer’s skill. In this paper, the parameter (P.S.sum), which relates to the striation height, is proposed and method for estimation of stress ratio, which is independent of observer’s skill, is also proposed. In order to calculate P.S.sum, the frequency analysis is applied to the three-dimensional geometry of striation obtained by laser microscope. The wavelength and the power spectrum are considered to indicate the striation width and height respectively. To consider the variation of striation, P.S.sum is calculated by the integration of power spectrum. The method is applied to the fatigue fracture surface of aluminum (A2024), steel (0.25% carbon) and high-tension steels. The condition of fatigue test was ΔK constant to keep the crack growth rate constant, in other words, to make the striations of which width were same. Applying the method, almost linear relationship between stress ratio and P.S.sum was obtained. Therefore, stress ratio can be quantitatively estimated by P.S.sum.
Study on Constitutive Modeling for Large Deformation Behavior of Polyethylene Considering Strain Rate Effect
Authors: Zhong Sijia , Shi Jianfeng , Zheng Jinyang
Published: January 2014

Polyethylene (PE) pipes have been applied in transportation of key energy medium such as natural gas in the past decades. The mechanical property of PE is of great importance for better design and safer application of PE pipeline system. The large deformation behavior is a key character of PE, not only for its significant strain rate sensitivity, but also for localized necking process after yielding. In this paper, a new constitutive modeling method was proposed to charaterize the rate-denpendent large deformation behavior of PE, in which the true stress is regarded as a function of true stain and true strain rate alone. Uniaxial tensile tests of PE were conducted under various cross-head speeds, and a digital camera was used to record the real-time deformation of specimens. By separating the composite effect into respective effect of local true strain and strain rate on the local true stress in the necking region, a phenomenological model for describing the rate-dependent deformation behavior under uniaxial tension was ealstablished. Model results were validated and found in good agreement with experimental data.