bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Testing Environment on SP Creep Rupture Lives
Authors: Kobayashi Ken-ichi , Takei Sho
Published: January 2014

Small Punch (SP) Creep test has been recognized as a semi destructive testing method to examine residual life of creep in high temperature components. Employing 2.25Cr-1Mo steel (SCMV4), SP creep tests were conducted at 600°C both in air and in high vacuum to examine the influence of oxidation on the long-term rupture life of the SP creep tests. As a test result, the creep rupture life in air was shorter than that in vacuum when the rupture life was less than 1000 hours. Reduction of rupture lives in air was approximately a half of them tested in vacuum. However when the creep rupture life was longer than 1000 hours, little difference emerged even if the testing atmosphere was different. A thickness of the oxide scale formed on SP creep specimens in air increased with the test duration. The experimental test results showed that the oxide scale affected on a coefficient of friction between the loading ball and the SP creep specimen. Furthermore the oxide scale formed in air did not always peel off from the test specimen, and the thick oxide scale endured a part of applied load in the longer life test.
Mitigating Failures in Ferritic-Austenitic Dissimilar Metal Joints in Petrochemical Industry
Authors: Penso Jorge A. , Belanger Patrick
Published: January 2014

There are several failure mechanisms that might affect ferritic-austenitic dissimilar metal welds (DMWs) in petrochemical plants and refineries. Examples are cracking due to creep, stress corrosion cracking (SCC), sulphide SSC, thermal fatigue, brittle fracture, pitting corrosion, and hydrogen embrittlement. Of these, creep, SCC, and hydrogen embrittlement are perhaps of greater interest.

Industry has many lessons learned; however, still experiences high consequence failures. This work describes the most common failure mechanisms in dissimilar ferritic-austenitic welds and summarizes a guidance to prepare welding procedures and reduce the likelihood of failures. This guidance is based on a literature review and industry experience.

The metallurgical characteristics of the damage observed in both service and laboratory test samples indicate that creep rupture is the dominant failure mode for Dissimilar Metal Welds (DMW) in some high temperature service conditions. However, it has also been observed that temperature cycling contributes significantly to damage and can cause failure even when primary stress levels are relatively low.

Therefore, a creep-fatigue assessment procedure is required as part of a remaining life calculation. API 579-1/ASME FFS-1 2007 Fitness-For-Service standard includes a compendium of consensus methods for reliable assessment of the structural integrity of equipment containing identified flaws or damage. Part 10 of API 579-1 includes a method for protection against failure from creep-fatigue. In the assessment of DMW, a creep-fatigue interaction equation is provided to evaluate damage caused by thermal mismatch, sustained primary stresses, and cyclic secondary loads [Ref.1].

Failures due to hydrogen embrittlement cracking (HEC) mechanisms are not uncommon and are also described in this paper [Ref. 2].

Finally, a case history of a DMW failure in a steam methane furnace, which is common in the petrochemical industry, is described and shown as an example of a failure mitigation approach.
Mathematical Expressions of Helical Thread Geometry and Cross Sectional Areas of Various Shaped Thread Forms and Finite Element Analysis
Authors: Yanase Kenya , Fukuoka Toshimichi
Published: January 2014

Distinctive mechanical behavior of bolted joints is caused by the helical shape of thread geometry. Mathematical expression of the helical thread geometry of a single-thread screw has successfully been derived in the previous study. Using the derived equations, finite element models were constructed by taking account of the effect of the helix, and it is clarified how the stress distributes along the thread root and where the maximum stress occurs. Meanwhile, there are various thread forms other than a single-thread triangular screw. In this study, mathematical expressions of the helical thread geometry and the cross sectional areas of multiple-thread screws, pipe thread, trapezoidal thread and rectangular thread are derived in the same manner as in the case of a single-thread screw. Using the equations so obtained, finite element models with multiple-thread screws are constructed. From the numerical results, it is found that the maximum axial stress occurred in the bolted joints on a double-thread screw is slightly larger than the case of a single-thread screw, although the stress distribution patterns are almost identical in both types of screw geometry.
Failure Analysis of Expansion Bellows Serving in Steam Pipe Network
Authors: Huang Yichang , Tang Xiaoying , Yu Houde , Qian Yaozhou , Wu Ruqing
Published: January 2014

The failure of Type 316L stainless steel expansion bellows serving in steam pipe network has been analyzed. The expansion bellows cracked after approximately 4-year service in steam network at 230°C. The caustic stress corrosion cracking (caustic-SCC) resulting from a combined function of caustic concentrating, metal temperature and residual stress was responsible for the failure. Cracking initiated on the inside surface of the bellow at the peak where served as stress raiser by observation of sample taken from failed expansion bellows. The pattern of cracking was shown as a spider web of several small cracks in photomicrographs. The metallographic examination also indicated that cracks were predominantly transgranular. The oxides on the surface of cracks can be confirmed to be caustic NaOH through X-ray diffraction (XRD) examination.
Fatigue Crack Growth for Subsurface Flaws Near Component Surface and Proximity Rules
Authors: Hasegawa Kunio , Li Yinsheng , Miyazaki Katsumasa , Saito Koichi
Published: January 2014

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a flaw-to-surface proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the criteria of the re-characterizations are different among the FFS codes. Cyclic tensile experiment was conducted on a carbon steel flat plate with a subsurface flaw at ambient temperature. The objective of this paper is to compare the experiment and calculation of fatigue crack growth behavior for a subsurface flaw and the transformed surface flaw, and to describe the validity of the flaw-to-surface proximity rule defined by ASME Code Section XI, JSME S NA1 Code and other codes.
Basic Study on Vibrational Behavior of System Supporting Large-Scale Structures Subjected to Multiple Random Inputs Using Probabilistic Vibration Theory
Authors: Shintani Atsuhiko , Tsujita Keishi , Ito Tomohiro , Nakagawa Chihiro
Published: January 2014

In this study, the vibrational behavior of a system supporting large-scale structures that are subjected to multiple random inputs is investigated based on probabilistic vibration theory. The analytical model (FEM) of a system that is subjected to white noise is constructed first. Pipings are assumed to be supported by a nonlinear elastoplastic damper. The vibrational behavior of the structures subjected to multiple random inputs is calculated via numerical simulations. After calculating the stress, energy absorption, etc., the dynamic reliability is calculated based on random theory. Finally, the effects of the supporting location and supporting capacity on the dynamic reliability are investigated.
Development of BWR Steam Dryer Loading Evaluation Methods Through Scale Model Tests Under Actual Steam Conditions
Authors: Takahashi Shiro , Okuyama Keita , Tamura Akinori , Mabuchi Yasuhiro , Kubota Teppei , Yoshikawa Kazuhiro
Published: January 2014

It has been demonstrated that intense fluctuating pressures acted on the steam dryer in a boiling water reactor (BWR) at higher velocity flows than in normal operation through actual BWR plant tests [1] and scale model air tests [2]. The cause of the dryer loading was considered as flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). Acoustic resonance was considered to be generated by interaction between the sound field and an unstable shear layer across the closed side branches of the SRV stub pipes.

We have started a research program on BWR dryers to develop their loading evaluation methods. Some air scale tests were conducted and those are useful for evaluation of occurrence of acoustic resonance in SRV stub pipes and characteristics of fluctuating pressure in MSLs. However, it is a possibility that differences in pressure conditions and fluid proprieties caused the dryer loading to be underestimated. In the present study, we conducted scale tests under actual steam conditions to evaluate the scale model test methods for BWR dryer loading estimation.

The Hitachi Utility Steam Test Leading facility (HUSTLE) was used for the scale model steam tests of MSLs and a steam dryer. Steam which was at the same pressure and temperature conditions as an actual BWR was used in the tests. The test apparatus consisted of the steam dryer, steam dome and 4 MSLs with 20 SRV stub pipes.

We demonstrated that acoustic resonance occurred in the SRV stub pipes and fluctuating pressure which propagated from the SRVs to the dryer caused fluctuating stress on the steam dryer at the SRV resonance frequency. The increasing of fluctuating pressure due to the double vortex mode which occurred at a Strouhal number (St) from 0.8 to 0.9 could be clearly seen in the scale model steam tests unlike in the air tests. It was possible that self excited acoustic resonance was affected by the low pressure conditions and different fluid proprieties for the scale model air tests. However, no significant influence from steam pressure was seen at more than 3MPa. Normalized fluctuating pressure was almost the same regardless of pressure. We verified that normalization by dynamic pressure in the main pipe was a reasonable approach for evaluation of fluctuating pressure in the SRV stub pipes. Increasing of fluctuating pressure due to the double vortex mode was clearly distinguished for SRV stub pipes but became smaller for MS pipes and had insignificant impact on the dryer loading.
A Comparison Between Probabilistic and Deterministic Fracture Mechanics Assessments of the Structural Integrity of a Reactor Pressure Vessel Subjected to a Pressurized Thermal Shock Transient
Authors: Gao Zengliang , Li Yuebing , Lei Yuebao
Published: January 2014

Both probabilistic and deterministic methods are used in structural integrity assessment of reactor pressure vessels (RPV) under pressurized thermal shock (PTS) conditions. The deterministic assessment is normally performed using flaw assessment procedures based on linear elastic or elastic-plastic fracture mechanics. Over the past two decades, the probabilistic assessment approach, which is based on probabilistic fracture mechanics (PFM), has undergone continuous development, mostly driven by the desire to address some of the weaknesses of the deterministic approach and to facilitate increasing the life and safety of nuclear power plants. In this paper, structural integrity assessments for a selected RPV subjected to a typical PTS transient are performed using the deterministic approach according to different flaw assessment codes. The failure probabilities corresponding to the deterministic facture mechanics method with defined safety factors are evaluated and compared with the failure probability value determined using the PFM method. Several sources of uncertainty that affect the assessment of the structural integrity of an RPV under PTS, including uncertainties in the material property values, the fracture toughness and the flaw size are incorporated in the failure probability evaluation. The response distribution of crack driving force is obtained from the PFM analysis and the failure probability is calculated using Monte Carlo simulation, where the failure criteria used in the deterministic assessment are adopted. The results of analysis from the two approaches are compared and discussed. The results show that the defined safety factor in the deterministic methods does affect the limit failure probability implied by the method. However, there is no unique relationship between safety factor and the limit failure probability.
EC FP7 Structural Performance of MULTI-METAL Component: Project Overview
Authors: Karjalainen-Roikonen Paivi , Keim Elisabeth , Gilles Philippe , Blasset Sébastien
Published: January 2014

The purpose of this paper is to introduce a new EUROATOM project focusing on the structural integrity assessment of dissimilar metal weld. The project started in February 2012 and will last 3 years. The project is coordinated by VTT with 10 partner organizations from Europe: Technical Research Centre of Finland, Finland (VTT) - Coordinator AREVA NP, France and Germany (ANP) Commissariat à l’Énergie Atomique et aux energies alternatives, France (CEA) Joint Research Centre of the European Commission, Belgium (JRC) EdF-Energy, United Kingdom (BE) Bay Zoltán Foundation for Applied Research, Hungary (BZF) Electricité de France, France (EDF) TECNATOM, Spain (TEC) Jožef Stefan Institute, Slovenia (JSI) Studsvik Nuclear AB, Sweden (STU). Within MULTIMETAL, the main objectives are:

- Develop a codification for fracture resistance testing in multi-metal specimens.

- Develop harmonized procedures for dissimilar metal welds integrity assessment.

The underlying aim of the project is to provide recommendations for a good practice approach for the integrity assessment (especially testing) of dissimilar metal welds as part of overall integrity analyses including leak-before-break (LBB) procedures.

The project will promote the development of a common understanding for structural integrity assessment of dissimilar metal welds (DMWs) in existing and future nuclear power plants (NPPs) in EU member states. It will provide the technical basis for the development of harmonized European codification for multi-metal components, which is currently non-existing. A trainee program will be finally developed and text book as well as learning materials will be issued. The project will interact with the European Network of Excellence NULIFE and NUGENIA.
Alternate Requirements for Protection Against Pressurized Thermal Shock (PTS)
Authors: Parker Stephen M. , Palm Nathan A. , Pitoiset Xavier
Published: January 2014

Plants in the United States (U.S.) and many plants outside of the U.S. are required to meet the regulations of the Pressurized Thermal Shock (PTS) Rule, 10 CFR 50.61. The Alternate Pressurized Thermal Shock (PTS) Rule (10 CFR 50.61a) was approved by the U.S. Nuclear Regulatory Commission (NRC) and included in the Federal Register, with an effective date of February 3, 2010. This Alternate Rule provides a new metric and screening criteria for PTS. This metric, RTMAX-X, and the corresponding screening criteria are far less restrictive than the RTPTS metrics and screening criteria in the original PTS Rule (10 CFR 50.61).

The Alternate PTS Rule was developed through probabilistic fracture mechanics (PFM) evaluations performed for selected U.S. pilot plants. A Generalization Study was also performed which determined that the plants used for these evaluations were representative of and applicable to the U.S. Pressurized Water Reactor (PWR) nuclear power plant fleet.

Plants outside of the U.S. may be interested in implementing the Alternate PTS Rule. However, direct implementation of the Alternate PTS Rule may not be possible due to differences in plant design, embrittlement prediction techniques, inservice inspection requirements, etc. The objective of this paper is to explore the use the Alternate PTS Rule by PWR plants outside of the U.S. by proposing methods to account for the potential differences mentioned above.
Investigation on Shear Strength of Steel-Polymer Interface in Plastic Pipe Reinforced by Cross Helically Wound Steel Wires
Authors: Shi Jun , Shi Jianfeng , Zheng Jinyang
Published: January 2014

Shear strength of fibre-matrix adhesive interface is crucial important to the mechanical performance of fibre-reinforced plastic pipes and fittings, due to its function for load transfer between the fibre and the matrix. In this study, pull-out tests of steel-polymer specimens were carried out with different embedded lengths. Ultrasonic scanning was adopted to monitor the failure procedure of the interface. From the analysis of UT scanning graphs, it could be determined that the studied steel-polymer interface failed rapidly on the whole embedded length under the maximal pull-out force, but not in the manner that crack initiated from a stress concentration point under a relatively small pull-out force and then propagated gradually. Different kinds of pull-out analytical models were discussed. Finally the analytical model of yielding interface was applied to characterize the steel-polymer interfacial adhesive property. Combing with experimental results of pull-out tests of different embedded lengths, the nominal bond shear strength was calculated out.
Evaluation of Growth of Subsurface Crack by Fatigue: Simulation of Penetration of Internal Flaw to Surface of the Structure
Authors: Kikuchi Masanori , Yamada Shinya , Serizawa Ryousuke , Li Yulong
Published: January 2014

In nuclear power plant, there is a proximity rule to evaluate subsurface crack, which exists near free surface of the structure. If the distance between this subsurface crack to free surface exceeds some limit, this subsurface crack is transformed to surface crack, and residual fatigue life is evaluated. Subsurface crack has many parameters, such as, crack length, crack depth, distance between crack front to free surface, and aspect ratio of subsurface crack. As a result, proximity rule is proposed by many organizations, and each rule is different from each other largely. It is necessary to verify which is more preferable, but to determine it experimentally is very difficult due to existence of many parameters. Numerical simulation is needed for this purpose.

This problem is simulated using S-version FEM. Using S-FEM, subsurface is modeled independently from global structure, and crack growth is easily simulated. In maintenance code of nuclear power plant, initial defects are modeled as elliptical cracks in a normal plane to tension loading direction, and growth rate is estimated in this plane. But by using S-FEM, real defect shape is modeled realistically, and crack growth by fatigue is simulated. Usually, such small defects are subjected to multi-axial loading, and crack growth behaviors are very complicated. Finally, detect shape becomes elliptical or circular crack in a plane normal to tension loading direction in the structure. Fatigue cycles for these growing processes are calculated, and conservativeness of this maintenance code is discussed. Then subsurface crack growth is simulated. Inner subsurface crack grows toward free surface, penetrate to free surface and grows as a surface crack. These processes are simulated smoothly by S-FEM. Parametric studies are conducted for this problem, and proximity rules are verified with numerical results.
Flange Tightening Evaluation Method for Flat Face Flange With Full Face Gasket
Authors: Mori Masako , Nebu Akira , Kanno Takashi
Published: January 2014

Appropriate flange tightening methods for flat face flanges with full face gaskets are discussed to improve the sealing performance of the bolted flange joints and the workability of flange tightening work.

In general, relatively larger tightening torque is required for a flat face flange with a full face gasket compared to the flange with a ring gasket when we calculate the required tightening torque based on the latest Non-mandatory Japanese Industrial Standard (JIS) evaluation method, “JIS B 2205-1991, Basis for calculation of pipe flanges”[1].

Especially, for the flat face flanges with large diameter and with fewer tightening bolts, this tendency becomes stronger.

This problem sometimes causes a conflict when the flange torque calculation of the minimum required torque value to resist hydrostatic end force at the maximum design pressure of the flange is larger than the maximum allowable torque derived from flange or bolt strength.

So, in this paper, surface stress of several diameter flange faces were measured to clarify whether or not the required stress is applied on the surface of the flat face flanges with full face gaskets.

In addition, pressure tests were carried out to clarify the sealing performance under the condition of circumferentially non-uniform tightening load in each diameter flat face flange with full face gasket.

Based on these test results, minimum flange-tightening bolt axial loads have been summarized to ensure the sealing performance of the flat face bolted flanges with full face gaskets.
A Predictive Model for Gas Flow Through a Bore-Piston Ring Contact
Authors: Hallouin Baptiste , Lasseux Didier
Published: January 2014

We report on the derivation of a simplified but accurate model to describe gas flow through a bore-piston ring contact. This is achieved by making use of a scale analysis on the classical mass, momentum and energy equations assuming that the gas obeys ideal gas law. The main regime of interest for practical application in reciprocating machines, corresponding to the compressible flow with inertia is identified and is shown to be free of unsteady terms in the simplified flow equation. For this regime, a quasi analytical solution is further provided that allows the estimation of the axial gas flow rate through the contact. This predictive model is successfully compared to direct numerical simulations of the complete initial set of balance equations performed on a model aperture field of sinusoidal shape. This simplified quasi analytical solution is of particular practical interest since it allows an accurate gas flow rate estimate through a real contact using the aperture field as the only input datum which would not permit a tractable direct numerical simulation otherwise.
A Study of Applicability of Finite Displacement Analyses With Semi-Analytical Finite Elements for Analyzing Uplift Displacement of Flat-Bottom Cylindrical Shell Tanks Statically
Authors: Nakashima Teruhiro , Taniguchi Tomoyo
Published: January 2014

The rocking motion of tanks due to earthquakes causes the large uplift deformation of the tank bottom plate that has been considered to contribute to the various damages of the tanks. For analyzing the uplift displacement of the tank bottom plate statically and precisely, this paper develops a shell element, ring element and spring element partially attached to the ring element. These elements are defined as a semi-analytical finite element. Fourier series give its circumferential displacement function, while the polynomial gives its radial displacement function. In addition, the ring element can deal with effects of the large deformation, while the spring element enables to express the partial contact between the tank bottom plate and foundation. On the other hand, the loads considered are dead load, hydro-pressure and inertia force due to earthquakes acceleration as well as dynamic pressure of fluid induced by bulging and rocking motion of the tank. The numerical analyses model of the LNG Storage Tank was created using the semi-analytical finite elements shown here, and the uplift displacement of the tank bottom plate accompanying the tank rocking motion was calculated with the static analyses. For evaluating analytical accuracy of the proposed method, numerical results of the proposed method are compared with that of the explicit FE Analysis.
On Some Aspects of Fluid-Structure Interaction in Two-Phase Flow
Authors: Benaouicha M. , Astolfi J. A.
Published: January 2014

The paper presents a theoretical model of the fluid-structure interaction effect in two-phase inviscid flow. A time-space variation of the fluid density at the interface between a fluid and a rigid section is considered. The coupled problem is then written as a Laplace equation for the pressure with a boundary condition at the fluid-structure interface depending on the acceleration, the velocity of the structure and on the rate of change of flow density. It is shown that contrary to the homogeneous flow, the added mass operator is not symmetrical and depends on the flow through fluid density variation. The model shows also an added damping operator related to the rate of change of flow density. Added damping coefficients are found to be positive or negative, indicating the possibility of instability development into the dynamics of the structure.
Investigation of Stress Stabilization Behavior of Type 316 Steel
Authors: Hormozi Mohammad R. , Biglari Farid , Nikbin Kamran M.
Published: January 2014

Some materials are designed to operate at high temperature environments with high thermal gradients and will be subject to thermal and mechanical cyclic strains. Under these cyclic temperatures and strains, thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) failure occur which will lead to the initiation of damage and cracking and subsequent crack growth. In this paper the numerical and experimental investigations of stress stabilization of 316FR steel subjected to strain cycling in the temperature range of 400–650 °C has been presented. The material exhibited both cyclic and nonlinear kinematic hardening behavior. In this paper the finite element analysis of cyclic loading of the materials was based on a direct method to use the test data from a stabilized cycle in combination with the hysteresis strain energy concept for damage derivation.
Pressure Energized Gasket (PEG) Behavior and Seating Stress
Authors: Reeves David , Ruffin Mark
Published: January 2014

This paper summarizes the effect pressure and temperature have on a Pressure Energized Gasket’s (PEG’s) ability to seal, or more specifically the PEG’s gasket seating stress.
Dynamic Response of a Piping System Under Harmonic Excitations Considering Pipe-Support Friction With Variable Normal Loads
Authors: Argüelles José , Casanova Euro
Published: January 2014

Dynamic loads in piping systems are mainly caused by transient phenomena generated by operating conditions or installed equipment. In most cases these dynamic loads may be modeled as harmonic excitations e.g. pulsating flow. On the other hand, when designing piping systems under dynamic loads, it’s a common practice to neglect strong nonlinearities such as shocks and friction between pipe and support surfaces, mainly because of the excessive cost in terms of computational time and the complexity associated with the integration of the nonlinear equations of motion. However, disregarding these nonlinearities for some systems may result in overestimated dynamic amplitudes leading to incorrect analysis and designs. This paper presents a numerical approach to calculate the steady-state response amplitudes of a piping system subject to harmonic excitations and considering dry friction between the pipe and the support surfaces, without performing a numerical integration. The proposed approach permits the analysis of three dimensional piping systems where the normal forces may vary in time and is based in the Hybrid Frequency-Time Domain method (HFT). Results of the proposed approach are compared and discussed with those of a full integration scheme, confirming that HFT is a valid and computationally feasible option.
Interfacial Blister Evolution of Coated Surfaces Under Severe Thermal and Pressure Transients
Authors: Harris J. T. , Segall A. E. , Robinson D. , Carter R.
Published: January 2014

The effects of severe thermal- and pressure-transients on coated substrates with indentation-induced, blister defects were analyzed using experimental and finite-element methods. An explicit FEA approach was first used to assess the transient thermal- and stress-states and the propensity for fracture related damage and evolution, under uniform convection and pressure transients across the surface; cohesive zone properties were evaluated in a previous study before being applied in an implicit indentation simulation. The indentation simulation results then served as the initial conditions for explicit modeling of interfacial flaw evolution due to thermal and pressure transients. Various conditions were analyzed including thermal and gun tube boundary conditions, and the effects of coating thermal capacitance. Given the need for robust coatings, the experimental and modeling procedures explored by this study will have important ramifications for coated tube design.
AIV Evaluation With Sound Pressure and Fabrication Quality Standards
Authors: Mann J. Adin , Fagerlund Allen C. , Eilers Daniel
Published: January 2014

Criteria for evaluating acoustic induced vibration damage (AIV) has been based on available data, often referred to as the Carucci-Mueller approach1. The Carucci-Mueller approach has been developed with several variances, but all approaches apply the internal sound power formula used with that original published data. However, the equation is an approximation to sound power which is used in very few other applications. This paper will show a correlation between the Carucci-Mueller data and the related design curve to one generated using the IEC 60534-8-3 Control Valve Aerodynamic prediction noise standard2. Additional corrections for fabrication quality will be reviewed. Using internal sound power and the coupling to pipe wall vibration, the resulting external sound pressure can be directly related to strain and thus fatigue failure criteria which are material based. Utilizing the IEC noise standard as well as standards which give corrections for fabrication quality can move the AIV evaluation techniques to methods that are documented in international standards.
Classification of Thin-Walled Conical Vessels for Design Against Axisymmetric Plastic Collapse Under External Pressure
Authors: Meehan Patrick , Frith Robert
Published: January 2014

This paper presents the results of a study that investigates the propensity of thin walled vessels with cone-cylinder junctions to plastically collapse under external pressure. The investigation focuses on the conical portion of the vessel collapsing in an axisymmetric mode prior to buckling in a classical lobar mode. Using a parametric study, comparison is made between the factor of safety afforded by design-by-rule approaches such as that offered in ASME Section VIII Div. 1, ASME Section VIII Div. 2 Part 4.4 and elastic-plastic design by analysis approaches prescribed by ASME Section VIII Div.2 Part 5. Further, the results of the parametric study are used to determine the key parameters that result in the occurrence of an axisymmetric collapse mode before the classical lobar buckling mode. The research has led to the development of a set of criteria to indicate susceptibility of geometry to axisymmetric collapse prior to classical lobar buckling.
Development of 2012 Edition of JSME Code for Design and Construction of Fast Reactors: (4) Creep–Fatigue Evaluation Method for Modified 9Cr–1Mo Steel
Authors: Takaya Shigeru , Nagae Yuji , Asayama Tai
Published: January 2014

This paper describes a creep–fatigue evaluation method for modified 9Cr–1Mo steel, which has been newly included in the 2012 edition of the JSME code for design and construction of fast reactors. In this method, creep and fatigue damages are evaluated on the basis of Miner’s rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. Investigations using material test results are conducted, which show that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data is hardly obtained. These results confirm that the creep–fatigue evaluation method in the code has implicit conservatism.
Estimates of Plastic Limit Loads of Thick-Walled Cylinders With Non-Idealzied Through-Wall Cracks
Authors: Han Tae-Song , Huh Nam-Su , Shim Do-Jun
Published: January 2014

In order to assess a structural integrity of cracked components made of highly ductile material based on fully plastic fracture mechanics concept, an accurate plastic limit load of components of interest is crucial element. Such a plastic limit load can also be applied to estimate elastic-plastic J-integral based on the reference stress concept. In this context, during last several decades, many efforts have been made to suggest plastic limit load solutions of cracked cylinder.

Recent works for evaluating rupture probabilities of nuclear piping indicate that the only use of idealized circumferential through-wall crack leads to very conservative results which in turn gives higher rupture probabilities of nuclear piping, thus the considerations of more realistic crack shape during crack growth due to primary water stress corrosion cracking (PWSCC) and fatigue and axial through-wall crack were recommended to come up with more realistic rupture probabilities of nuclear piping. Then, the needs of fracture mechanics parameters of non-idealized through-wall cracks both in axial and circumferential directions have been raised.

In the present work, the plastic limit loads of thick-walled cylinder with non-idealized axial and circumferential through-wall cracks are proposed based on detailed 3-dimensional finite element analyses. The present results can be applied either to assess structural integrity of thick-walled nuclear piping with non-idealized through-wall cracks or to calculate elastic-plastic J-integral using the reference stress concept.
Structural Integrity Evaluation of High Strength Anchor Bolt for Supporting Steam Generator and Reactor Coolant Pump in Nuclear Power Plants
Authors: Lim Eun-Mo , Huh Nam-Su , Shim Hee-Jin , Oh Chang-Kyun , Kim Hyun-Su
Published: January 2014

In Korea, a fitness-for service evaluation for assuring structural integrity of high strength anchor bolts which support nuclear components such as steam generator and reactor coolant pump, has been one of the important issues in nuclear industry. The main failure mechanism of high strength anchor bolts supporting nuclear components might be degradation due to stress corrosion cracking and brittle fracture. In the present work, the structural integrity of high strength anchor bolts which are used to support steam generator and reactor coolant pump of one of the Korean older vintage nuclear power plants is evaluated by adopting a procedure proposed by Electric Power Research Institute (EPRI) based on an elastic fracture mechanics concept. In this EPRI’s procedure, an accurate estimation of nominal stress acting on the cross section of the bolt is a crucial element since a structural integrity of an anchor bolt is evaluated in the EPRI’s procedure using this nominal stress incorporating reference flaw factors reflecting effects of stress concentration due to bolt thread and reference sized surface crack. In this context, detailed elastic finite element stress analyses are firstly performed on the anchor bolt assemblies to come up with nominal stress in the cross-section of anchor bolt. As for loading condition, bolt pretention as well as normal and faulted loads of the anchor bolts were considered. In addition, the structural integrity of the anchor bolts is demonstrated by comparing nominal stresses of anchor bolts with the maximum allowable stresses obtained by using the EPRI’s reference flaw factors and critical fracture toughness. Furthermore, the accuracy of EPRI’s reference flaw factors which are derived on the assumption that reference sized surface crack is existed on the thread roots is investigated using 3-dimensional elastic finite element fracture mechanics analyses.
The Application of Cohesive Elements in Numerical Simulations of the Intergranular Fracture in Voronoi Cellular Models
Authors: Zhang Fan , Zhao Jianping
Published: January 2014

The 2D Voronoi algorithms were used for geometric modeling of crystalline grains. A cohesive interface model was used to simulate the process of grain-boundary separation. Polycrystalline aluminum was chosen as the research object. Under the condition of no defects while the uniaxial stretching load was applied, damage and failure of the grain boundaries as well as the stress distribution of the whole model were investigated. Based on this, a comparative study on grain-boundary damage and stress distribution was carried out in the case of defective while uniaxially stretched. It has been found that in the case of uniaxial stretch continuous failure elements appeared on the grain boundary perpendicular to the stretching direction, closest to the loading surface. This led to the formation of the so-called intergranular fracture ‘crack’. The simulation results showed that as the uniaxial tensile load increased the damage to the grain boundaries of polycrystalline aluminum would exacerbate. Due to the effect of number and distribution of the defects in grain boundaries on stress distribution of the entire model, different cohesive elements showed a different variation in stress value with the increase of the load.
Stress Analysis of Pipe Support Attachments: A Comparison of Analytical Methods and Finite Element Analysis for Circular and Non-Circular Attachments
Authors: Bhattacharya Anindya
Published: January 2014

Despite the availability of special purpose FE codes with post processing facilities as per rules of ASME SEC VIII Division 2, use of simple analytical methods like ring loading around a circumference or more complex methods like Welding Research council bulletins 107 and 297, will continue to be used in the industry for a significant period of time for stress analysis of pipe support attachments. The reasons are few: not all engineering companies have such custom made FE codes, lack of trained personnel to work with general purpose FE codes, ease of implementation of the available methods and their successful design history, cost and time issues with FE analysis etc. In this paper these available methods will be reviewed based on their theoretical background, their range of applicability w.r.t the typical design parameters and their comparison with FE analysis. More recent analytical methods based on mathematically accurate space curves of intersections for circular attachments will also be discussed. This study will include both circular as well as non-circular attachments. This paper will highlight the strengths and weaknesses of the conventionally used methods especially with respect to their mathematical limitations to make an analyst aware of the potential over conservatism and under conservatism of these analytical methods. Finite element analysis models will be discussed in detail specifically in relation to elements used, element parameters, boundary conditions and post processing.
Experimental and Numerical Investigation of Pipe T-Junctions Under Strong Cyclic Loading
Authors: Papatheocharis Theocharis , Diamanti Kalliopi , Varelis George E. , Perdikaris Philip C. , Karamanos Spyros A.
Published: January 2014

Tee pipe junctions are piping components widely used in industrial and pipeline applications. Their performance under severe loading conditions may be critical for the structural integrity of an industrial facility. When these components are subjected to repeated loading associated with cyclic plasticity, failure is possible. The present work is a combined experimental and numerical effort which examines the behavior of piping branch T-junctions subjected to strong cyclic out-of-plane bending. The first part of this paper describes the experimental investigation of the junction performance. Tests are conducted in a constant and varying amplitude displacement-controlled mode resulting to failure in the low-cycle fatigue range. The overall behavior of each specimen in terms of fatigue life, as well as the evolution and concentration of local strains are monitored throughout the testing procedure.

The experimental investigation is supported by finite element modeling, developed to simulate the experiments. Advanced cyclic plasticity material models are employed and emphasis is given on the local strains developed at the critical part of the T-junctions where first cracking occurs.
A New Generalized Nonlinear Superposition Theory and its Applications in Modeling Corrosion-Fatigue
Authors: Wei Zhigang , Luo Limin , Rybarz Marek , Nikbin Kamran
Published: January 2014

Corrosion-fatigue and stress corrosion cracking have long been recognized as the principal degradation and failure mechanisms of materials under combined corrosive environment and sustained/cyclic loading conditions. These phenomena are strongly material and environment dependent, and cycle-dependent fatigue and time-dependent matter diffusion/chemical reaction at the crack tip can be operational simultaneously. How to include these cycle-dependent and time-dependent phenomena in a single model and how to study the failure mechanisms interaction are big challenges posed to material scientists and engineers.

In this paper the current linear superposition theories for modeling cycle-dependent and time-dependent corrosion-fatigue and stress corrosion cracking phenomena are reviewed first. Subsequently, a generalized nonlinear superposition theory is proposed to incorporate possible nonlinear interaction or synergistic effect among the underlying mechanisms. The unified model derived from the new theory, depending on the specific materials and loading condition and environment, can be reduced to pure corrosion, pure fatigue, stress corrosion cracking and corrosion-fatigue. Finally, for the first time, a new breakthrough parameter is defined in this paper to quantitatively describe the interaction or synergistic effect between two different operating mechanisms, such as time- and cycle-dependent mechanisms.
Conceptual Design of a Spiral Wound Pipeline With Manufactured Residual Stresses
Authors: Scott Colin , Finneran Shane
Published: January 2014

There are several common engineering composites that are designed to take advantage of manufactured residual stresses. Concrete may be designed with pre-stressed steel tendons. Engineering ceramic composites may be designed with mismatch in thermal properties of the components to produce residual stresses and enhance crack deflection properties. Metal matrix composites may also be designed with mismatch in elastic properties of the component to enhance crack deflection properties.

The objective of this work is to explore the possibility of designing a spiral wound pipe with enhanced mechanical properties. Consider a sheet of steel wound into a spiral in preparation for welding into pipe. Consider then that it is twisted prior to and during welding of the spiral. When the weld solidifies and the torque is released, the pipe would, in principle, maintain some of the stress of the twist. The spiral could be twisted either “inwards” or “outwards” prior to the weld, and the result would be residual tension or compression.

This work is based entirely on theory and analysis. Analyses are performed that predict the residual stresses incurred during the proposed manufacturing technique, and the resulting stresses due in-service conditions. In principle, pipe design and manufacture could be adjusted for either onshore pipelines subject to internal pressure, or offshore pipelines subject to hydrostatic pressures at depth. Both possibilities are considered.
Simplified Equations for Predicting Secondary Stress Around Pipe’s Circumference
Authors: Wang Junkan , Saraswat Rajil , Mirzaee-Sisan Ali
Published: January 2014

This paper examines the magnitude and location of the maximum residual stress induced in pipes after the process of bending, reverse-bending and straightening. Dimensional analysis is used to establish generalized equations relating the maximum residual stress magnitude and location to the pipe geometry, maximum bending curvature and pipe material’s yield stress. 64 design cases based on an analytical solution assuming elastic-perfectly-plastic material behavior have been conducted. Regression analysis has revealed that the magnitude of the maximum residual stress can be conservatively approximated by a simplified quadratic equation involving the maximum axial bending strain, whereas the location of the maximum residual stress can be approximated by a linear function based on the same. Both equations are expected to be valid and conservative for X65 and X70 grade steel pipes under global maximum axial strain between 1% and 3%. Non-linear finite element analysis based on a realistic design example with isotropic hardening material is used to validate the prediction results based on the simplified equations.
Case Studies in Local Heat Treatment of Pressure Vessels Applying WRC-452 Principles
Authors: Miller George , Kirkpatrick Kenneth , Antalffy Les P.
Published: January 2014

The Welding Research Council (WRC) Bulletin 452 titled “Recommended Practices for Local Heating of Welds In Pressure Vessels”(1) was first published in June 2000. This document considers various issues associated with the local heating of welds in pressure vessels and addresses the application of controlled heat in the weld metal, heat affected zone (HAZ) and a limited volume of base metal around the weld.

ASME Boiler and Pressure Vessel Code Section VIII Division 1, paragraphs UW-40, (a) 3 and 8 require that post weld heat treatment (PWHT) be carried out in a manner such that the thermal gradients are not harmful. WRC Bulletin 452 provides guidelines for local PWHT to satisfy this requirement.

This paper provides examples of local PWHT (if not heated as a whole vessel in a furnace) based upon utilizing a soak band and calculated heated band and gradient band widths based upon WRC 452 recommendations. The paper addresses both circumferential and spot PWHTs and demonstrates that the guidelines provided in WRC 452 can also be used as a starting point for determining the band widths for spot PWHT.
Determination of Transitional Size of Metal Clusters
Authors: Park Y. H. , Hijazi I.
Published: January 2014

We investigated the transitional size of metal clusters where the electronic effect and the size effect on the ground state structure become weaker. Identification of a transitional size cluster provides the means to efficiently determine the ground state structure of large clusters using density functional theory. Beyond the critical size of clusters, geometrical effects become important and the putative global minimum obtained from an empirical method can be used to determine the true ground state structure where the size effect on structures is less significant. We identified the lowest-energy structure using a first principles method in combination with the global search algorithm. We then used the similarity function to quantify structural difference and similarity between the global minimum obtained from an empirical method and the true ground state structure. Two structures become similar beyond a certain critical size. To investigate low-lying structures of metal clusters, we used a Monte Carlo simulated annealing method which employs the Aggregate-Volume-Bias Monte Carlo (AVBMC) algorithm. Incorporated in the Monte Carlo method is an Embedded Atom Method (EAM) potential developed by the authors.