bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Collapse Characteristics and CSRF Method for 45 Deg Cylinder-to-Cylinder Intersections
Authors: Honda Takuro , Kataoka Shunji , Sato Takuya
Published: August 2013

It is known that the collapse strength of complex three dimensional structures is hard to evaluate accurately with elastic analysis, and more accurate results require the use of inelastic analysis. A cylinder-to-cylinder acute lateral intersection is one of basic structures of process plants. It is known that a high stress concentration occurs at an acute lateral more than 90 deg-lateral. In general, the area replacement method and the elastic analysis are applied for the design of acute lateral. However, these results may provide overly-conservative designs.

In the previous work, the authors proposed CSRF (Collapse Strength Reduction Factor) method. The CSRF was defined as a ratio of the simple cylinder collapse pressure to the cylinder-to-cylinder collapse pressure. The proposed CSRF method provided more reasonable design than the elastic analysis.

In this paper, the concept of the CSRF was redefined by using the maximum allowable working pressure. The CSRF were evaluated on the 45 deg and 90 deg-laterals based on the area replacement method, the elastic analysis, the limit load analysis and the elastic plastic analysis to study the collapse characteristics of 45 deg-laterals. The 45 deg-laterals are weaker than 90 deg-laterals, and inelastic analysis provides greater strength of 45 deg-laterals than elastic analysis. The results of elastic plastic analysis showed that overly-large plastic strain occurs on 45 deg-laterals. This plastic strain should be evaluated in addition to the collapse pressure.
Analytical Study on Seismic Response of Piping Under Multiple Support Excitations
Authors: Kai Satoru , Otani Akihito , Kaneko Naoaki
Published: August 2013

Conventional response spectrum analysis is used for piping seismic design in Japan. When piping is supported by restraints and structures fixed on multiple buildings or floors, the envelope of the response spectra of all supporting points is typically applied for the piping under multiple excitations. The local vibration mode of long piping is difficult to excite by the far input from the vibrating part, so the analysis will overestimate the response. Considering each input from each building or floor can estimate more reasonable seismic response of the piping. The researches about seismic response analysis by multiple input excitations have been performed since 1960s and the analysis methods are used for piping design in the United State.

There are a few experimental researches to verify the validity of the analysis method by multiple excitations. So an excitation test by multiple excitations planned to verify the validity of the application. This current study was performed as a preliminary investigation for the excitation test and it was to obtain the seismic response of a piping model by multiple excitations. Several kinds of analysis methods are compared and the characteristics of them are discussed.
Influence of Circumferential Flaw Length on Internal Burst Pressure of a Wall-Thinned Pipe
Authors: Tsuji Masataka , Meshii Toshiyuki
Published: August 2013

The effect of the circumferential angle of a flaw θ on the internal burst pressure pf of pipes with artificial wall-thinned flaws is examined.

When evaluating pf of wall-thinned straight pipes, the effect of θ has been conventionally not regarded as important. Therefore, a burst pressure equation for an axial crack inside a cylinder (Fig. 1, left), such as Kiefner’s equation [1] is widely used [2], [3]. However, it should be noted that there exist the following implicit assumptions when applying the equation for planar flaws to non-planar flaws.

1) The fracture mode of a non-planar flaw under consideration is identical with that of the crack.

2) The effect of θ, which is not considered for an axial crack on pf, is small or negligible.

However, from the systematic burst test results of carbon pipes with artificial wall-thinned flaws, Meshii [4] showed that these implicit assumptions may not be correct. On the other hand, the significance of the effect of the fracture mode on pf and the condition for θ to affect pf are not clear.

Therefore, in this paper, Meshii’s experimental results are evaluated in farther detail. The purpose of the evaluation was set to clarify the effect of θ on pf. Specifically, the significance of flaw configuration (axial length δz and wall-thinning ratio t1/t) was studied in relation to θ and pf. In addition, a simulation of the effect by a Finite Element Analysis (FEA) was attempted.

From the experimental results, θ tended to affect pf in cases with large δz, and t1/t also was correlated to a decrease in pf with the increase of θ. These tendencies were successfully simulated by the elastic-plastic FEA.

This effect means the burst pressure predicted for a crack with identical ligament thickness decreases with the increase of θ, so that the effect by θ on pf should not be ignored.
Plastic Collapse Assessment Procedure in P-M Diagram Method for Pipe Bends With a Local Thin Area Under Combined Pressure and Out-of-Plane Bending Moment
Authors: Oyamada Kenji , Konosu Shinji , Ohno Takashi
Published: August 2013

Pipe bends are common elements in piping system such as power or process piping, and local thinning are typically occurred on pipe bends due to erosion or corrosion. Therefore, it is important to establish the plastic collapse condition for pipe bends having a local thin area (LTA) under combined internal pressure and external bending moment. In this paper, a simplified plastic collapse assessment procedure in p-M (internal pressure ratio and external bending moment ratio) diagram method for pipe bends with a local thin area simultaneously subjected to internal pressure, p, and external out-of-plane bending moment, M, due to earthquake, etc., is proposed, which is derived from the reference stress. In this paper, only cases of that an LTA is located in the crown of pipe bends are considered. The plastic collapse loads derived from the p-M diagram method are compared with the results of both experiments and FEA for pipe bends of the same size with various configurations of an LTA.
French Reactor Vessel Integrity
Authors: Churier H.
Published: August 2013

The French fleet comprises 58 PWR.

The integrity of the reactor pressure vessel is one of the main considerations regarding plant life extension.

The limiting damage is the irradiation embrittlement associated with brittle fracture risk.

During the operation, integrity assessment is updated every 10 years taking in account the knowledge acquired by the feedback. In addition steps have been taken to reduce irradiation. Moreover all the research and development have also led to improvements.

The purpose of the paper, based on the latest updated demonstration of the 3 loops 900 MW vessels for the period 30–40 years of service, is to develop the strategy to be implemented to go beyond 40 years and the progress in each topic.

On one hand the demonstration by analysis is the privileged axis of justification for an operating life of 60 years.

- First, by improving at the maximum deterministic approach with regard to the input data and methods to reduce uncertainties.

- Second, by a complementary probabilistic study with the aim of showing the conservatism of the deterministic approach.

On the other hand, the arrangements already taken during operation for monitoring and mitigating irradiation embrittlement are maintened and reinforced: irradiation surveillance program, in service inspection, limitation and surveillance of fluence, not to mention heating the safety injection water which remains a possibility after the improvements of data and methods.
Structural Integrity Evaluation of a Reactor Vessel Outlet Nozzle Weld Inlay
Authors: Glunt N. L. , Udyawar A. , Ng C. K. , Marlette S. E.
Published: August 2013

Nickel-base weldments such as Alloy 82/182 dissimilar metal (DM) butt welds used in Pressurized Water Reactor (PWR) nuclear power plant components have experienced Primary Water Stress Corrosion Cracking (PWSCC), resulting in the need to repair/replace these weldments. The nuclear industry has been actively engaged in inspecting and mitigating these susceptible DM butt welds for the past several years. Full and Optimized Structural Weld Overlay as well as Mechanical Stress Improvement Process (MSIP®) are some of the mitigation/repair processes that have been implemented successfully by the nuclear industry to mitigate PWSCC. Three conditions must exist simultaneously for PWSCC to occur: high tensile stresses, susceptible material and an environment that is conducive to stress corrosion cracking. These mitigation/repair processes are effective in minimizing the potential for future initiation and crack propagation resulting from PWSCC by generating compressive residual stress at the inner surface of the susceptible DM weld. Weld inlay is an alternative mitigation/repair process especially for large bore nozzles such as reactor vessel nozzles. The weld inlay process consists of excavating a small portion of the susceptible weld material at the inside surface of the component and then applying a PWSCC resistant Alloy 52/52M repair weld layer on the inside surface of the component to isolate the susceptible DM weld material from the primary water environment. The design and analysis requirements of the weld inlay are provided in ASME Code Case N-766. This paper provides the structural integrity evaluation results for a typical reactor vessel outlet nozzle weld inlay performed in accordance with the ASME Code Case N-766 design and analysis requirements. The evaluation results demonstrate that weld inlay is also a viable PWSCC mitigation and repair process especially for large bore reactor vessel nozzles.
Determination of the Interaction Between Primary and Secondary Stresses Using an Idealised Model
Authors: Horne Graeme , Smith David J.
Published: August 2013

When conducting an assessment of the integrity of a structure the user is directed to classify the stresses as either primary stress or secondary stress. Residual stresses are usually classified as secondary stresses unless they exhibit significant elastic follow-up. In this paper the authors have first summarised current methods and origins of the UK R6 structural integrity assessment methodology for combining primary and secondary stresses. Then, using an idealised model, a new approach has been developed to examine how fixed-displacement secondary stresses interact and redistribute; this model permits a combined reference stress to be determined directly. This combined reference stress is intrinsically linked to the effect of elastic follow-up within the structure and provides a direct measure of how the residual stress relaxes between the extremes of fixed-load and fixed-displacement conditions. The results have been compared with the existing approaches in R6 and it has been demonstrated that the R6 method can be either conservative or non-conservative, depending on the degree of elastic follow-up and residual stress redistribution.
A New Linear Superposition Theory and its Application in Creep Fatigue-Oxidation Crack Growth Modeling
Authors: Wei Zhigang , Yang Fulun , Lin Burt , Luo Limin , Konson Dmitri , Nikbin Kamran
Published: August 2013

Fatigue, creep, oxidation or their combinations have long been recognized as the principal mechanisms in many high-temperature failures in power plant components, turbine engines, and exhaust systems in vehicles. Depending on the specific materials and loading conditions and temperature, the role of each damage mechanism may change significantly, ranging from independent development to competing and combined creep-fatigue, fatigue-oxidation, and creep-fatigue-oxidation. In this paper a new linear superposition theory is proposed to model the cycle-dependent and time-dependent creep-fatigue-oxidation crack growth phenomena. The model can be reduced to creep-fatigue and fatigue-oxidation crack growth models previously developed by the authors as well as, under some assumptions, the current widely used linear superposition theory. The limits of the current superposition theory and the advantages of the new theory are clearly demonstrated with several worked examples. A general probabilistic analysis procedure is also proposed by introducing the uncertainties of parameters in fatigue, creep, and oxidation crack growth laws with the help of the Monte Carlo simulation.
Nodal Force Based Finite Element Method and its Application in Durability Analysis
Authors: Wei Zhigang , Yang Fulun , Yule Matthew , Dong Pingsha
Published: August 2013

In the conventional finite element methods, the stresses are obtained from the computed nodal displacements and are thus a derived quantity, which is not accurate. Additionally, equilibrium of resulted element stresses is, in general, not satisfied at every point in the conventional finite element solutions, which is one of the major reasons for severe mesh-sensitivity in stress or strain results. However, the equilibrium of nodal force is always guaranteed in all finite element solutions regardless of mesh sizes. This equilibrium of nodal force provides a good way to recovering stress with improved accuracy, and various methods, including the currently widely used structural stress procedure for fatigue life assessment, have been proposed with varying degrees of complexity and success. In this paper, a new post-processing procedure is proposed to calculate surface traction stress for 3-D solid elements in terms of nodal forces from the conventional commercial finite element analysis software, such as Abaqus and Nastran. The applicability and limitation of the nodal force based method is demonstrated by applying it to two-dimensional and three-dimensional linear elastic continuum solid elements. Finally, its application in durability analysis such as fatigue and creep life assessments is discussed.
Design Curve Construction Based on Tolerance Limit Concept
Authors: Wei Zhigang , Dogan Bilal , Luo Limin , Lin Burt , Konson Dmitri
Published: August 2013

The design curves, such as fatigue design S-N curves, required in engineering designs, are usually constructed by analyzing test data, which often exhibit large scatter. There are many methods available to construct a design curve and many of these methods, with varying degrees of conservativeness, accuracy, and simplicity, have been adopted by engineering standards, codes and guidelines, such as the ASME and ASTM codes and standards. However, to meet the increasing engineering demands, a simplified, user friendly engineering method with rigorous mathematical and physical basis is still urgently needed to accurately manage the margin of safety on one hand and decrease the cost on the other hand.

In this paper the current engineering practices for constructing a design curve is reviewed. It is followed by the tolerance limit concept for general regression cases, because of its capability to relate the design curve to sample size, probability, and confidence level. A simple approximate solution is derived for Owen’s tolerance limit approach, which previously could be solved only with a very complex procedure. Finally, recognizing the physical unsoundness of the hyperbolic shape of the design curves constructed with the Owen’s tolerance limit approach, a new simple design curve construction method is proposed based on the “equal partition principle”. The predicted results from the new method are compared with that of other methods and the advantage of the proposed procedure over other methods is demonstrated with several worked examples. Linear design curve construction with heteroscedastic characteristics (variable variance) and nonlinear design curve are also discussed.
Extreme Value Distribution Theory and its Application in Durability Analysis
Authors: Wei Zhigang , Dong Pingsha , Gao Litang , Kurth Robert
Published: August 2013

Risk based treatment of degradation and failure in engineering components is an important topic in recent years with an emphasis on obtaining more detailed information for extreme events. Fatigue damage and life degradation caused by variable amplitude cyclic loading is dominated by such extreme events, and can be properly treated with the extreme value theory, which could help understand the damage nature of the fatigue damage process as well as to provide more efficient and robust approaches for engineering applications.

In this paper, advanced extreme value theory is reviewed first. Methods such as peak counting, block maxima, and peaks over thresholds are investigated and compared in this paper with an emphasis on the relationship between the extreme value theory and the existing methods for fatigue life assessment. A few simple examples of uniaxial and multi-axial fatigue life assessment process are provided and the results are discussed. It is found that, if properly used, the extreme value theories can improve the efficiency of fatigue life assessment. Finally, a hybrid time- and frequency-based multi-axial fatigue life assessment procedure is proposed for wide band loadings.
Determination of Fiber Orientation Along the Length of Complex Composite Structures Subjected to Internal Pressure and Axial Loading
Authors: Hossain Rifat , Mertiny Pierre , Carey Jason
Published: August 2013

Axially symmetric fiber-reinforced polymer composite structures such as pressure vessels and piping are being widely used in different industrial applications where combined loading conditions may be applied. It is imperative to determine a suitable fiber angle, or a distribution of fiber angles, along the longitudinal direction of the structure in order to achieve best performance in terms of mechanical behavior and strength for structures subjected to combined loadings. To this end, a theoretical study was conducted providing the relationship between the fiber orientation and the loading conditions applied to a composite structure. The aim of this study is to determine the fiber angle variation along the length of an axially symmetric composite structure with variable cross-section considering different ratios of axial loading and internal pressure. As an initial step, netting analysis design theory was implemented in the present study.
Axi-Symmetrical Stress Analysis and Sealing Performance Evaluation of a Pipe Flange Connection Under Elevated Temperature and Internal Pressure
Authors: Omiya Yuya , Sawa Toshiyuki
Published: August 2013

The pipe flange connections have been widely used in mechanical structures and these are mainly used under internal pressure and elevated temperature. Some investigations have been performed on mechanical behaviors such as the contact gasket stress distribution of pipe flange connection under internal pressure. However, the effects of elevated temperature on the sealing performance and mechanical behavior in the pipe flange connection have not been analyzed exactly. To design a pipe flange connection, it is necessary to know the effect of elevated temperature and the detailed flange strength for the hub and the contact gasket stress distributions in the connection. In this paper, the stress analysis of a pipe flange connection under elevated temperature and internal pressure is carried out taking into account a non-linearity and hysteresis of the gasket using the axi-symmetric theory of elasticity. The contact gasket stress distributions at the interfaces, the hub stress, in the pipe flange connection under elevated temperature and internal pressure are analyzed. Using the obtained contact gasket stress distributions, the amount of gasket leakage (He gas) is estimated. Leakage tests of the pipe flange connections were also conducted and the temperature of pipe flange connection was measured using thermoelectric couples. As a result, the difference of temperature between inner and outer is about 10%. The contact gasket stress was increased as the heated temperature was increased.
The Adhesion Failure Mode in Stainless Steel Trim Spring Operated Pressure Relief Valves
Authors: Bukowski Julia V. , Gross Robert E. , Goble William M.
Published: August 2013

This paper addresses dangerous failures of stainless steel (SS) trim spring operated pressure relief valves (SOPRV) due to a particular failure mode (SS-to-SS adhesion) which is not currently being included in SOPRV failure rates. As a result, current methods for estimating or predicting failure rates for SS trim SOPRV significantly underestimate these failure rates and, consequently, overestimate the safety provided by the SOPRV as measured by its average probability of failure on demand (PFDavg) or its corresponding safety integrity level (SIL). The paper also illustrates the critical importance of root cause analysis (RCA) of dangerous SOPRV failures in understanding the impacts of various failure modes.

Over 1300 proof test results for both new and used SS trim SOPRV from the Savannah River Site (SRS) were identified. RCA was used on the failed valves to classify those failed due to SS-to-SS adhesions. Statistical analysis of the data convincingly demonstrates adhesions, previously assumed to be only an in-storage failure phenomenon, are also an in-service failure mode which needs to be included in SOPRV failure rates. The paper discusses the factors which potentially influence the adhesion failure mode and suggests a possible approach to including this mode in failure rate predictions. An example illustrates how current failure rate models overestimate SS trim SOPRV safety by one or two orders of magnitude.
Element Size Dependent Damage Modeling of Ductile Crack Growth in Circumferential Through-Wall Cracked Pipe Tests
Authors: Kim Jong-Hyun , Kim Nak-Hyun , Kim Yun-Jae , Shim Do-Jun
Published: August 2013

This paper proposes an element-size-dependent damage model to simulate ductile crack growth in full-scale cracked pipes. The proposed method is based on the stress-modified fracture strain damage model modified from stress reduction technique proposed previously by the authors. A modification is made that the critical accumulated damage for progressive cracking is assumed to be dependent on the element size. The proposed method is then compared with a circumferential through-wall cracked pipe test that was conducted during Degrade Piping Program[18].

The bending moment at crack initiation, maximum bending moment, crack extension, and J-integral values were calculated from the FE damage analysis. These results were compared with the experimental results. In addition, results obtained from an existing J-estimation scheme were provided for comparison. All results showed reasonable agreement.

The results of the present study demonstrate that the element-size-dependent damage modeling can be applied to simulate the ductile crack growth behavior of a through-wall cracked pipe.
Influence of Nozzle Transition on Leak Before Break Parameters
Authors: Baas Peter , Blom Frederic
Published: August 2013

In the framework of leak before break a circumferential through-wall crack in a pipe with nozzle is investigated by means of finite elements and compared to a pipe only geometry. A range of crack angles (3–180°) and inner radius to wall thickness ratios (Ri/t = 5, 10, 20, 50 and 100) have been analysed in order to investigate parameter sensitivity. The nozzle and pipe models are compared for the leak before break parameters stress intensity factor (KI) and Crack Opening Area (COA).

The results of the comparisons are presented as KI nozzle factor (KI nozzle / KI pipe) and COA nozzle factor (COAnozzle / COApipe). At small crack angles the KI nozzle factor is larger than unity, caused by the stress concentration at the nozzle to pipe intersection. At larger crack angles the KI nozzle factor decreases below unity, caused by the so-called bulging effect, which is apparent in the pipe only model. The COA nozzle factor is smaller than unity for all crack angles, caused by the increased stiffness of the nozzle. As the ratio Ri/t increases, both the KI and COA nozzle factors decrease since the nozzle stiffness relative to the pipe increases.

For demonstration of leak before break the nozzle has a negative influence regarding the COA as smaller leaks are more difficult to detect. However, since the KI nozzle factor decreases at larger cracks the influence of nozzles regarding leak before break is not so straight forward.
Small Scale Experiments on Boiling Liquid Expanding Vapor Explosions: Supercritical BLEVE
Authors: Laboureur Delphine , Buchlin Jean-Marie , Rambaud Patrick
Published: August 2013

The most dangerous accident that can occur in LPG storage is the boiling liquid expanding vapor explosion (BLEVE). To better understand the rupture of the reservoir and the blast wave characteristics, small scale BLEVE experiments are performed with cylinders of 95 ml, filled at 86% with propane, laid horizontally and heated from below. A weakening of the reservoirs on the upper part allows better reproducibility of the rupture. High speed visualization, blast overpressure and surface reservoir temperature are measured.

Internal pressure measurement shows that the rupture pressure and temperature are well above the critical point. The fluid is then supercritical and there is no distinction anymore between liquid and gas prior rupture. This kind of reservoir rupture is significant of a new type of BLEVE, a supercritical BLEVE. The experiments also show that the fluid behavior during rupture differs with the size of the weakened part and therefore with the rupture pressure. Finally, the measured peak overpressures are compared with literature models.
Numerical Simulation of Eccentric Explosive Forming Using Cylindrical Pressure Vessel
Authors: Iyama Hirofumi , Itoh Shigeru
Published: August 2013

Explosive forming is one of the effective metal forming methods using underwater shock wave generated by the detonation of an explosive. The experiment of eccentric spherical free metal forming by this method was carried out. This free metal forming process does not use require expensive metal die. We used simple metal die with only circular edges and considered the metal plate formed to required shape using this method. It was possible to change the pressure distribution applied on the metal plate by changing the set-up position of the explosive and the shape of the device. We have considered this method to cause lessen cost in the small production by various types of metal forming process. In this paper, we introduce the method of eccentric spherical free metal forming using underwater shock wave and present the experimental results. The numerical simulation on this method by FDM (Finite Difference Method) was carried out. In this paper, those results are discussed.
STYLE: Transferability of Fracture Material Properties - Updated Experimental and Analytical Results
Authors: Nicak Tomas , Schendzielorz Herbert , Keim Elisabeth , Meier Gottfried , Moinereau Dominique , Le Delliou Patrick
Published: August 2013

This paper describes new results of the STYLE study on investigations of transferability of fracture material properties obtained by testing of small scale specimens to a real component.

In STYLE there are three large scale mock-up tests each of them dedicated to investigate specific effects. Mock-up3 (cladded ferritic pipe with the outer diameter of 424 mm) is foreseen to investigate transferability of material data, in particular to compare fracture mechanics behavior of small specimens under different constraint conditions with a full size component. The Mock-Up3 is an original part of a surge line made of low alloy steel (20MnMoNi55 which corresponds to SA 508 Grade 3, Cl. 1).

Usually, material data necessary for fracture mechanic analyses are obtained by testing small specimens, which are subsequently used for the assessment of large scale structures (real components). This approach is believed to be conservative since the material properties are obtained on highly constrained standard specimens.

In this paper new experimental and analytical results will be presented (including tests on constraint modified specimens and a comparison of these results with the Mock-up3 test). The overall objective is to investigate the influence of specimen size, crack shape and type of loading on fracture mechanics properties like crack initiation load or amount of the crack growth by means of numerical analyses and compared with experimental results.
Benchmark Campaign on the Uncertainty Treatment Analysis Tools Developed for French Nuclear Reactor Pressure Vessels Integrity Assessment
Authors: Dautreme Emilie , Beaufils Romain , Pernot Thomas , Remy Emmanuel , Meister Eric , Fontes Jean-Philippe , Demol Thibault , Yalamas Thierry , Defaux Gilles , Izard Jean-Pierre
Published: August 2013

In France, nuclear reactor pressure vessels (RPV) integrity assessment follows a deterministic methodology and is performed according to the 1999 French regulation requirements with the use of safety coefficients. In the deterministic methodology, the input data are penalized in order to address the uncertainties.

EDF and AREVA developed some couplings between integrity assessment models and uncertainty treatment software in order to address explicitly the uncertainties on the input data.

In such analysis, the accumulation of conservatisms is replaced by a rational combination of parameters taking into account their uncertainty and variability.

This paper presents a benchmark campaign conducted jointly by EDF and AREVA to validate the couplings between the codes and to strengthen the confidence in the calculations.

The benchmark campaign was performed with several physical thermo-mechanical codes and uncertainty treatments software tools to evaluate the sensitivity of the analyses results as a function of code effects. The benchmark results are in good accordance between the several codes used. This conclusion gives confidence in the code couplings used for performing the uncertainty treatment analyses.
Shock Wave Propagation Inside of Pressure Vessel Used for Food Processing
Authors: Iyama Hirofumi , Higa Yoshikazu , Itoh Shigeru
Published: August 2013

In this study, it has aimed at the design of the pressure vessel for food processing using an underwater shock wave. This study aims at the design of a pressure vessel in which the underwater shock wave generated by the underwater explosion of high explosive was experimentally investigated by the optical observation and the pressure measurement. Therefore the pressure vessel is designed so that suitable pressure may apply on food. This designed vessel is evaluated by the numerical simulation. The interaction of the underwater shock wave, the incident wave and the reflected wave are investigated by the numerical simulation.
Detection of a Surface Flaw Using Differential Signals of MI Sensors With the Residual Magnetization Method
Authors: Kasai Naoya , Miura Keisuke
Published: August 2013

In the present study, the detection of surface flaws using differential signals with two MI sensors with the residual magnetization method was conducted. Vertical components of leakage magnetic fields generated from flaws were measured with the residual magnetization method by scanning with two MI sensors in the spatial domains around flaws. The measured differential signals indicate clear flaw images without signal processing because a flaw signal sharply changes from the signal generated from the weld zone although the signal amplitude becomes very small due to differential signals. However, in the case of a small flaw in the weld zone, the flaw was hard to detect because the noise due to weld metal was also measured. Therefore, wavelet analysis was applied, and the result after wavelet analysis indicated the improvement of the flaw detectability.
Compound and Monobloc Cylinders Incorporating Reverse-Autofrettage to Reduce External Hoop Stresses
Authors: Parker Anthony P.
Published: August 2013

Reverse autofrettage involves the application of pressure to the OD of a tube which in turn produces bore yielding and a residual stress profile equal in magnitude but opposite in sign to conventional autofrettage.

The analyses within this paper identify two potential new manufacturing procedures involving reverse autofrettage. The procedures are predicted to reduce external tensile hoop stress in an autofrettaged gun tube. This reduction should increase lifetime of tubes that are prone to OD fatigue or corrosion-related failure from manufacturing defects or notches.

The first procedure involves traditional autofrettage of an inner tube and reverse autofrettage of a larger outer tube. The outer tube is then compounded with the inner tube by thermal shrink-fitting or some equivalent process. The second procedure employs a monobloc tube which is subjected to reverse autofrettage followed by conventional internal autofrettage. Both procedures significantly reduce OD residual hoop stress but in the case of the monobloc tube there is an associated loss of compressive residual bore hoop stress.
Ductile Failure Simulation of Bending Pipes With Multiple Circumferential Surface Cracks Using an Element-Size Dependent Damage Model
Authors: Kim Jong-Hyun , Kim Nak-Hyun , Kim Yun-Jae , Hasegawa Kunio , Miyazaki Katsumasa
Published: August 2013

The purpose of this study is to simulate ductile failure of bending pipes with multiple circumferential surface cracks using an element-size dependent damage model. This method is based on the stress-modified fracture strain damage model with stress reduction technique proposed previously by the authors [9,10]. For validation, simulated results using the proposed method are compared with experimental data of Type 304SS pipes performed by Japanese researchers [19].

To calibrate the proposed method, pipe test data with a single surface crack were compared with simulated results using the damage model. Based on the calibrated damage model, the pipe tests with multiple circumferential surface cracks were simulated. The bending moment at both crack penetration and coalescence were calculated from the FE damage analysis. These results were compared with the experimental results.

In spite of its simplicity, the results show that proposed method can simulate ductile failure behavior of bending pipes with multiple circumferential surface cracks.
Weld Strength Mismatch in Strain Based Flaw Assessment: Which Definition to Use?
Authors: Hertelé Stijn , De Waele Wim , Denys Rudi , Verstraete Matthias , Van Minnebruggen Koen , Horn Anthony
Published: August 2013

Weld strength mismatch is a key factor in the strain based assessment of flawed girth welds under tension. A strength overmatching weld shields potential flaws within the weld itself from remotely applied deformations and consequently reduces crack driving force. Although this effect has been recognized for decades, different weld strength overmatch definitions exist and it is not yet fully established which of those is most relevant to a strain based flaw assessment. In an effort to clarify this unsolved question, the authors have performed a large series of parametric finite element analyses of curved wide plate tests. This paper provides an experimental validation of the model and subsequently discusses representative results. It is found that crack driving force is influenced by the shape of the pipe metals’ stress-strain curves, which influences the representativeness of two common mismatch definitions (based on yield strength and on ultimate tensile strength). It can be concluded from further observations that effects of strength mismatch on strain capacity of a flawed girth weld are best described on the basis of a flow stress, defined as the average of yield and ultimate tensile strength. Based on the observations, a framework for a new strain capacity equation is proposed.
Limit Loads for Structural Elements Made of Heterogeneous Materials
Authors: Chen Min , Hachemi Abdelkader , Weichert Dieter
Published: August 2013

A numerical method is presented for determining the limit loads of periodically heterogeneous structures subjected to variable loads. The Melan’s lower-bound shakedown theorem was applied to representative volume elements. Combined with the homogenization technique, the homogenized material properties were determined through transformation from the mesoscopic to macroscopic admissible loading domains. For the numerical applications, solid non-conforming finite element discretization and large-scale nonlinear optimization, based on an interior-point-algorithm were used. The methodology is illustrated by the application to pipes models. This way, the proposed method provides a direct numerical approach to evaluate the macroscopic strength of heterogeneous structures with periodic micro- or meso-structure as a useful tool for the design of structures.
Fatigue Limit Prediction of SUS630 Stainless Steel Matrix Based on Small Crack Mechanics
Authors: Nie Defu , Mutoh Yoshiharu
Published: August 2013

The experimentally obtained fatigue limit of high strength steel is generally a value reduced by inherent flaws, which does not characterize the resistance of high strength steel matrix to cyclic loading. To investigate the fatigue limit of matrix, fatigue tests of SUS630 stainless steel were performed. SUS630 stainless steel showed a distinct dual-stage S-N curve: one stage corresponding to high stress where crack initiated at the surface and another stage corresponding to low stress where crack initiated from the subsurface inclusion (Al2O3). Based on small crack mechanics, a model was proposed to predict the fatigue limit of SUS630 stainless steel matrix. Moreover, fatigue tests of blunt notch specimens were performed to examine the validity of this model.
Determination of Shakedown Boundary and Fitness-Assessment-Diagrams of Cracked Pipe Bends
Authors: ElSaadany Mostafa S. , Younan Maher Y. A. , Abdalla Hany F.
Published: August 2013

Determination of shakedown boundaries of 90-degree plain smooth pipe bends has recently received substantial attention by several researchers. However, scarce or almost no solid information is found within the literature regarding the determination of the shakedown boundary of cracked pipe bends. The current research presents two additions to the literature namely: determination of shakedown boundary for a circumferentially cracked 90-degree pipe bend via a simplified technique utilizing the finite element method, and introduction of Fitness-Assessment-Diagrams (FAD) in compliance with the API 579 Fitness-for-Service assessment of pressure vessel and piping components. The analyzed cracked pipe bend is subjected to the combined effect of steady internal pressure spectrum and cyclic In-Plane Closing (IPC) and opening (IPO) bending moments. Line spring elements (LSE) are embedded in quadratic shell elements to model part through cracks. Fitness assessment diagrams (FAD) are obtained through linking the J-integral fracture mechanics parameter with the shakedown limit moments of the analyzed cracked 90-degree pipe bend. The LSE outcomes illustrated satisfactory results in comparison to the results of two verification studies: stress intensity factor and limit load. Additionally, full elastic-plastic cyclic loading finite element analyses are conducted and the outcomes revealed very good correlation with the results obtained via the simplified technique. The maximum load carrying capacity (limit moment) and the elastic domain are also computed thereby generating a Bree diagram for the cracked pipe bend.
NESC VII European Project: Demonstration of Warm Pre-Stressing Effect in Biaxial Loading Conditions: Bending Tests on 18MND5 Cruciform Specimens and Their Interpretation
Authors: Jacquemoud C. , Yuritzinn T. , Marie S. , Moinereau D. , Nédélec M. , Chapuliot S.
Published: August 2013

In the framework of the NESC VII European project, a large experimental program has been dedicated to characterize the Warm Pre-Stressing (WPS) effect in different testing configurations. One of the CEA (France) contributions to this project is the realization of five point bending tests on large cruciform specimens considering different WPS loading cycles. The five cruciform specimens, sponsored by EDF (France) and IRSN (France), are made of 18MND5 steel. Two of them have been tested on a same LCF (Load-Cool-Fracture) loading cycle and two others on the same LCTF (Load-Cool-Transient-Fracture) loading cycle. The experimental results presented in this paper give a successful demonstration of the WPS effect in biaxial loading conditions either on a LCF or on a LCTF cycle. During the test interpretations, different models have then been tested and compared in order to evaluate their ability to predict the cleavage fracture in the case of different WPS loading cycles. They all provide very conservative predictions whatever loading cycle is concerned.
Defect Evolution on Coated Samples Under Severe Thermal Transients and Interfacial Characterization
Authors: Harris J. T. , Segall A. E. , Robinson D. , Carter R.
Published: August 2013

The effects of severe thermal- and pressure-transients on coated substrates with indentation-induced, blister defects were analyzed using experimental and finite-element methods. Both explicit and implicit FEA approaches were used to assess the transient thermal- and stress-states and the propensity for fracture related damage and evolution, while undergoing uniform convective heating and pressure transients across the surface. Spherical indentations along with in-situ acoustic emissions, c-scans, and finite element modeling were utilized to induce the defects, as well as quantify interfacial adhesion and cohesive zone properties. Preliminary results indicated complex interactions between the boundary conditions and their timing and the resulting propensity for damage birth and evolution. Given the need for robust coatings, the experimental and modeling procedures explored by this study will have important ramifications for coated tube designs and the evaluation of candidate materials.
Numerical Simulation of Residual Stresses Induced in Compact Tension Specimens Using Electron Beam Welding
Authors: Kapadia P. , Davies C. M. , Dean D. W. , Nikbin K. M.
Published: August 2013

In welded components residual stresses on the order of yield magnitude can exist, allowing creep damage and cracking to occur under secondary stresses at elevated temperatures. A method of inducing residual stresses in compact tension, C(T), specimens is proposed using Electron Beam (EB) welding, which is simulated using a sequential thermal-mechanical model. The thermal model has been verified by comparison to thermocouple measurements obtained from instrumented EB welding experiments on blocks made of ex-service Type 316H stainless steel. Residual stress measurements, obtained by the neutron diffraction technique, have also been used to verify the mechanical model. It has been found that in the proposed EB welding method plasticity is localised and limited to just a few millimetres away from the notch whilst at the same time exhibiting a near yield level residual stress at the crack tip. Thus this technique may allow the effects of residual stresses on creep crack growth to be investigated by the EB welding technique without material property changes due to crack tip plasticity influencing the results.
Assessment of Fatigue Crack Growth in Imperfect Lap Joint: Part 2 — Crack Propagation Analysis Using “SCANP”
Authors: Igi Satoshi , Morikage Yasushi , Wakasa Masaru , Yoshida Shoichi , Sekine Kazuyoshi , Shiratori Masaki , Tsuchida Tomohiko , Iwata Katsuki
Published: August 2013

The deck plates of single-deck-type floating roofs for large oil storage tanks are joined by single-welded Full-fillet lap joints. In areas with frequent strong winds, fatigue cracks sometimes occur in the welds of the deck plate. The aim of the present study is to investigate the effect of the gap imperfection of the lap joints on the fatigue life. In the case that tensile load acted on Full-fillet lap joints, the stress at the crack face becomes larger by gap imperfection of the lap joint. The authors have developed a software system called “SCANP (Surface Crack Analysis Program)”, a software system to evaluate the stress intensity factor, K, and to simulate fatigue crack propagation for surface cracks for arbitrarily distributed surface stresses. The fatigue life of a lap joint was predicted by the “SCANP” using the calculated stresses at the root crack face and the toe crack face. The number of loading cycles to penetration for arbitrary bending load amplitudes and tensile load amplitudes are obtained.
Stress Optimization of a Piezoelectric-Controlled Curved Beam
Authors: Vo Van , Maha Amit , Pang Su-Seng
Published: August 2013

A composite curved beam is used to represent a multitude of structures in piping, such as O-Rings, that undergo dynamic warping as a result of long term usage, thermal changes, and high pressures. A piezoelectric material can be used to design an auto-corrective process that senses the dynamic warping and induces forces to restore the shape through the Piezoelectric Effect. The orientation and placement of the piezoelectric material on a composite curved beam directly affects the deflection and stress applied to that beam. The optimal placement of the actuator in terms of these two factors was researched.
Non-Iterative Reinforced Concrete Design Methodology for Combined Axial Force and Bending Moment
Authors: Jung Se-Kwon , Harrold Joseph , Alchaar Nawar
Published: August 2013

This paper presents a non-iterative reinforced concrete design methodology that can be used to design structural components such as beam-columns, walls and slabs of reinforced concrete structures subjected to combined axial force and bending moment. The paper demonstrates that the required reinforcing area of a demand point (paired axial force and bending moment) on the interaction diagram can be accurately computed by 1) constructing two non-dimensionalized capacity curves approximated by a combination of polygon segments that are expected to bound all possible design cases including the demand point, 2) dividing the area enclosed by the lower- and upper-bound capacity segments into several four-sided capacity polygons, 3) locating a capacity polygon where the demand point is located and identifying associated lower- and upper-bound capacity segments, 4) identifying a capacity segment that passes through the demand point by linear interpolation from the given two bounding segments, and finally 5) determining the required reinforcing area for the demand point by linear interpolation between the minimum and maximum reinforcing ratios associated with the pre-defined lower- and upper-bound capacity segments, respectively. This essentially eliminates a cumbersome need to perform iterative trial and error solutions to obtain the required reinforcing area for the combined axial force and moment concrete design. Illustrative design examples per ACI 349 and ACI 359 are presented within the paper.