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This paper presents the estimation of the reliability levels associated with a cracked pipe found acceptable as per the failure assessment diagram (FAD) based acceptance criteria of ASME Section XI, Appendix H. This acceptance criterion is built on the concepts of fracture mechanics. The parameters which enter the acceptance criteria are piping geometry, applied loading, crack size, and the material properties (tensile and fracture). Most of these parameters are known to exhibit uncertainty in their values. The FAD used also has an associated modeling bias. The code addresses these uncertainties by providing a factor of safety on the applied load. The use of a common factor of safety for a variety of pipe sizes, crack configuration, load combination, and materials may not ensure consistent level of safety associated with the piping component being evaluated. This level of safety can be evaluated by using structural reliability concepts. This paper analyzes the reliability level which is achieved if a cracked pipe passes the acceptance criteria prescribed by the code. The reliability is evaluated for a range of pipe and crack geometry, different load combination, and different materials using Monte Carlo method. The realistic assessment of reliability also requires the assessment of modeling bias associated with the FAD. This bias is also evaluated using the results from the published fracture experiments. [ABSTRACT FROM AUTHOR]

Nuclear power plant safety under seismic conditions is an important consideration. The piping systems may have some defects caused by fatigue, stress corrosion cracking, etc., in aged plants. These cracks may not only affect the seismic response but also grow and break through causing loss of coolant. Therefore, an evaluation method needs to be developed to predict crack growth behavior under seismic excitation. This paper describes efforts conducted to analyze and better understand a series of degraded pipe tests under seismic loading that was conducted by Japan Nuclear Energy Safety Organization (JNES). A special "cracked-pipe element" (CPE) concept, where the element represented the global moment-rotation response due to the crack, was developed. This approach was developed to significantly simplify the dynamic finite element analysis in fracture mechanics fields. In this paper, model validation was conducted by comparisons with a series of pipe tests with circumferential through-wall and surface cracks under different excitation conditions. These analyses showed that reasonably accurate predictions could be made using the abaqus connector element to model the complete transition of a circumferential surface crack to a through-wall crack under cyclic dynamic loading. The JNES primary loop recirculation piping test was analyzed in detail. This combined-component test had three crack locations and multiple applied simulated seismic block loadings. Comparisons were also made between the ABAQUS finite element (FE) analyses results to the measured displacements in the experiment. Good agreement was obtained, and it was confirmed that the simplified modeling is applicable to a seismic analysis for a cracked pipe on the basis of fracture mechanics. Pipe system leakage did occur in the JNES tests. The analytical predictions using the CPE approach did not predict leakage, suggesting that cyclic ductile tearing with large-scale plasticity was not the crack growth mode for the acceleration excitations considered here. Hence, the leakage was caused by low-cycle fatigue with small-scale yielding. The procedure used to make predictions of low-cycle fatigue crack growth with small-scale yielding was based on the Dowling ΔJ procedure, which is an extension of linear-elastic fatigue crack growth methodology into the nonlinear plasticity region. The predicted moments from the CPE approach were used using a cycle-by-cycle crack growth procedure. The predictions compare quite well with the experimental measurements. [ABSTRACT FROM AUTHOR]

In spite of the fact that coke drums are subjected to cyclic thermal and mechanical loads, generally, they are not designed for cyclic loads. Thus, their operational life is much shorter than other pressure equipment in refineries. Due to information developed from surveys, it was determined that the major typical location of failure due to thermal fatigue in coke drums is the shell-to-skirt junction area. This paper focuses on temperature and stress characteristics and also the thermal fatigue life of the junction area. The main objective of this paper was to explore effect of the switching temperature on thermal fatigue life of the junction area. Four coke drums, currently in service have been considered in the analyses, named drums A, B, C, and D, identical in dimensions and with an operating cycle period of 48 h. Operational temperatures and strains have been measured and collected every minute. The number of measured cycles of coke drum A, B, C, and D were 52, 53, 53, and 54 cycles, respectively. Thus, a total of 212 cycles have been analyzed. The operational temperatures and strains were examined. Finite Element Method (FEM) analyses have been performed on the selected cycles in order tofind the most severe location in the junction area. The strain history and FEM results were used to assess thermal fatigue life. The thermal fatigue lives were calculated based on low cycle fatigue properties using engineering steels for high temperature components issued by National Institute for Materials Sciences (NIMS) in Japan. The number of cycle tofracture versus switching temperature for the coke drums was then plotted. The curve best fitting criteria was then used to develop an equation relating the number of cycle tofracture as a function of switching temperature. The results show that the switching temperature strongly affects the number of cycle tofracture. These results can be used to provide the necessary information to operate coke drums safely in order to extend their useful lives. [ABSTRACT FROM AUTHOR]

In this paper, line- and ring-notched small punch test (SPT) specimens were studied; a three-dimensional (3D) model of a ring-notched SPT specimen was established using the contour integral method, and the validity of the model was verified using ring-notched specimens. The stress and strain fields were analyzed using numerical simulations of a ring-notched SPT specimen, and the change in the stress gradient during deformation was considered. To verify the finite element model, the results of the numerical simulations were compared with those of three-point bending tests and a Gurson-Tvergaard-Needleman (GTN) model. Compared with the line-notched specimen, the ring-notched specimen was more suitable for notch propagation analysis and fracture toughness evaluation. The results of the numerical simulations were in good agreement with those of the experiments, which showed that the numerical model used in this study was correct. For a notch that initiated when the load reached its maximum value, the value of the J integral was 335 × 10-6 kJ/mm², and at time 0.85Pmax, the value of the J integral was 201 × 10-6 kJ/mm², and the difference from the result of the three-point bending test was 14.4%. For a notch that initiated during the stretching deformation stage, the relevant fracture toughness was 225 × 10-6 kJ/mm², and the difference from the result of the three-point bending test was 3%. [ABSTRACT FROM AUTHOR]

Cracking in 25Cr35NiNb pyrolysis furnace tubes is difficult to detect in engineering production. This paper presents a metal magnetic memory technique for inspecting cracks. To verify the effectiveness of the proposed technique, positions where abnormal magnetic signals existed were rechecked by penetration testing and scanning electron microscopy. Magnetic memory technique results agree well with penetration testing and scanning electron microscope results, providing an effective method to detect cracks in 25Cr35NiNb pyrolysis furnace tubes. However, further research is required for the magnetic memory technique to attain full maturity for use in engineering applications. [ABSTRACT FROM AUTHOR]

Long-distance offshore pipelines always suffer large plastic deformation during installation and operation. Accompanied by high internal pressure, potential flaws are found to initiate from the girth welds, and this brings a significant challenge to the structural integrity of the pipelines. The currently used procedures for fracture assessment of pipelines are usually stress based, which are unsuitable for application to cracked pipeline subjected to large plastic deformation. Therefore, the aim of this paper is to investigate the fracture assessment of pipeline subjected to large plastic deformation and identify and understand the critical parameters influencing the fracture responses under actual loading conditions. The evolution of crack tip opening displacement (CTOD) of a pipeline segment with an embedded canoe shape crack located in the middle of the girth weld is investigated under pure bending and biaxial loading through 3D elastic-plastic finite-element simulations. The effects of crack width, crack length, pipeline thickness, material hardening, and internal pressure on fracture response are discussed. Finally, a strain-based failure assessment diagram (FAD) is developed, and comparison between fracture assessment by BS7910:2013 and finite-element simulations concludes that the former produces conservative predictions for deep crack. [ABSTRACT FROM AUTHOR]

The behavior of crack growth of polymeric materials is affected by several operating conditions such as crosshead speed, specimen thickness, load line, and specimen configurations, which reverse the behavior of crack from stable to unstable crack growth behavior. The main objective of the present paper is the determination of plane strain fracture toughness (KIC) for polyvinyl chloride (PVC) used in piping water transmission systems. The dimensions of the PVC pipe are outside diameter, Do = 315 mm, standard dimensions ratio, SDR = 13.23, ratio between outside to inside radii Ro/Ri = 1.179, and pipe thickness, t = 24 mm. Curved specimens are prepared from a pipe by cutting 12 mm thickness ring segments. The curved specimens are divided into two specimen configurations, namely, curved three-point bend (CTPB) and C-shaped tension (CST) specimens. All specimens are provided artificially with a precrack. CTPB specimen is further cut into five 72 deg sectors with each being centrally notched to a depth approximately a = 0.479 of the wall thickness. CST specimen configuration is characterized by the eccentricity X = 0, and 0.5 W, of the loading holes from the bore surface. The linear elastic fracture mechanics theory (LEFM) is used to predict the plane strain fracture. The tests are carried out at room temperature, Ta equal 20℃, and different crosshead speeds of (10-500 mm/min). The numerical analysis carried out within the frame of the present work is done using the finite element program Cosmos 2.6. Finite element method (FEM) is used to compute the stress intensity factor KQ surrounding the crack tip. The computed stress intensity factor can then be compared with that obtained by theoretical equation. The experimental fracture test results reveal that the crosshead speed has been proven to affect the mode of failure and mode of fracture. At lower crosshead speeds, the mode of failure is ductile, while at higher crosshead speeds, it is brittle. The specimen configuration also affects the fracture toughness. CST specimens show higher fracture toughness in the case of pin loading location X = 0.5W than X = 0 by about (12%). The transitional crosshead speed is affected by specimen geometry. CST specimens (CST) at X = 0 and 0.5W have higher transitional crosshead speed compared with the CTPB specimen configuration. [ABSTRACT FROM AUTHOR]

This paper presents numerical ductile tearing simulation results of four complex cracked pipes made of two materials, performed at Battelle, Columbus, OH. In ductile tearing simulation, stress-modified fracture strain model is used, which is determined from tensile test results and fracture toughness test data. Overall good agreement is found in comparing simulation results with experimental load, crack length, and crack mouth opening displacements versus load-line displacement (LLD) data. The effect of the complex crack on J-resistance curves is discussed. [ABSTRACT FROM AUTHOR]

This paper describes the structure and application of a software system that automates the fatigue initiation and crack propagation analysis based on finite element method (FEM). The system automatically performs necessary procedures to track propagation history of cracks: insertion of a crack and updating of three-dimensional (3D) finite element mesh in accordance with the crack propagation. The system is equipped with a function to automatically perform fatigue analyses using the stress-strain histories at nodes of a 3D FEM model. Some analyses for several examples were carried out for validation. The important example is the surface crack propagation in steel pipes with residual stress. [ABSTRACT FROM AUTHOR]

This paper describes the structure and application of a software system that automates the fatigue initiation and crack propagation analysis based on finite element method (FEM). The system automatically performs necessary procedures to track propagation history of cracks: insertion of a crack and updating of three-dimensional (3D) finite element mesh in accordance with the crack propagation. The system is equipped with a function to automatically perform fatigue analyses using the stress-strain histories at nodes of a 3D FEM model. Some analyses for several examples were carried out for validation. The important example is the surface crack propagation in steel pipes with residual stress. [ABSTRACT FROM AUTHOR]

The main purpose of the present paper is to investigate the effect of crosshead speed, specimen thickness, and welding on the fracture toughness. The material of the investigated pipe is a high density polyethylene (HDPE), which is commonly used in natural gas piping systems. The welding technique used in this study is butt-fusion (BF) welding technique. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45 mm for both welded and unwelded specimens at room temperature, Ta = 20 °C. Curved three point bend (CTPB) specimens were used to determine KQ. Furthermore, the results of fracture toughness, KQ, will be compared with the plane-strain fracture toughness, JIC, for welded and unwelded specimens. The experimental results revealed that KQ increases with increasing the crosshead speed, while KQ decreases as the specimen thickness increases. The investigation reveals that the apparent fracture toughness, KQ, for HDPE pipe of unwelded specimen is greater than that of corresponding value for welded specimen. The same trend was observed for the plane-strain fracture toughness, JIC. At lower crosshead speeds there is a minimum deviation in KQ between welded and unwelded specimens, while the deviation becomes larger with increasing crosshead speed. [ABSTRACT FROM AUTHOR]

If a subsurface flaw is located very near a component surface, the subsurface flaw is categorized as a surface flaw. The boundary of the subsurface and surface flaws is required for flaw evaluation. The subsurface flaw is transformed to a surface flaw in accordance with a flaw-to-surface proximity rule. The recharacterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the specific criteria of the recharacterizations 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 the paper is to compare the experiment and calculation of fatigue crack growth behavior for a subsurface flaw and the transformed surface flaw, and to check the validity of the flaw-to-surface proximity rule defined by ASME Code Section XI, JSME S NA1 Code and other codes. [ABSTRACT FROM AUTHOR]

A probabilistic fracture mechanics (PFM) code, PRAISE-CANDU 1.0, has been developed under a software quality assurance (QA) program in full compliance with Canadian Standards Association (CSA) N286.7-99, and was initially released in June 2012 and officially approved for use in August 2013. Extensive verification and validation has been performed on PRAISE-CANDU 1.0 for the purpose of software QA. This paper presents the fatigue benchmarking against NURBIM (nuclear risk based inspection methodology for passive components) fatigue cases between PRAISE-CANDU 1.0 and six other PFM codes. This benchmarking is considered to be an important element of the validation of PRAISE-CANDU. Excellent agreement is observed in spite of the differences between the codes. The comparison of the predicted leak probability at the 40th year shows that PRAISE-CANDU not only captures the same trend but also bounds (higher predicted failure probability) the majority of the NURBIM results. In addition to the leak probability, the rupture probability, and uncertainty analysis, which were not reported in the NURBIM Project, are also calculated with PRAISE-CANDU and presented. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the crack growth of primary water stress corrosion cracking (PWSCC) is mainly driven by the weld residual stress (WRS) within the dissimilar metal weld. The existing stress intensity factor (K) solutions for surface cracks in pipe typically require a fourth order polynomial stress distribution through the pipe wall thickness. However, it is not always possible to accurately represent the through thickness WRS with a fourth order polynomial fit and it is necessary to investigate the effect of the WRS fitting on the calculated Ks. In this paper, two different methods were used to calculate the K for a semi-elliptical circumferential surface crack in a pipe under a given set of simulated WRS. The first method is the universal weight function method (UWFM) where the through thickness WRS distribution is represented as a piece-wise monotonic cubic fit. In the second method, the through thickness WRS profiles are represented as a fourth order polynomial curve fit (both using the entire wall thickness data and only using data up to the crack-tip). In addition, three-dimensional finite element (FE) analyses (using the simulated weld residual stress) were conducted to provide a reference solution. The results of this study demonstrate the potential sensitivity of Ks to fourth order polynomial fitting artifacts. The piece-wise WRS representations used in the UWFM were not sensitive to these fitting artifacts and the UWFM solutions were in good agreement with the FE results. In addition, in certain cases, it was demonstrated that more accurate crack growth calculations of PWSCC are made when the UWFM is used. [ABSTRACT FROM AUTHOR]

The natural crack growth analysis (sometimes referred to as advanced finite element analysis (AFEA)) methodology has been developed by the US NRC and the nuclear industry to evaluate the natural crack growth due to primary water stress corrosion cracking (PWSCC) in nickel-based alloy materials. The natural crack growth (or AFEA) methodology allows the progression of a planar crack subjected to typical stress corrosion cracking (SCC)-type growth laws by calculating stress intensity factors at every nodal point along the crack front and incrementally advancing the crack front in a more natural manner. This paper describes the step-by-step procedure enhancements that have been made to the existing AFEA methodology. A significant enhancement was the feature to evaluate axial crack growth, where the crack was contained within the susceptible material. This methodology was validated by performing an AFEA evaluation for the axial crack that was found in the V.C. Summer hot-leg dissimilar metal weld (DMW). Other enhancements to the AFEA methodology include: feature to handle nonidealized circumferential through-wall cracks, mapping of weld residual stress for crack growth, and determination of limiting crack size using elastic-plastic J-integral analysis that included secondary stress (weld residual stress and thermal transient stress) effects. [ABSTRACT FROM AUTHOR]

Leaks in general and hydraulic leaks in specific are one of the major failure modes for mobile equipment. In-plant leak rates may range from 1% to 25%, while field leaks may range from 1% to 13% depending on the complexity of the system, assembly process, and parts quality. In this paper, the main potential leak causes are discussed and the performance of different types of fittings is compared, including JIC 37 flare fittings, O-ring boss seal, and O-ring face seal. Several potential improvement actions related to assembly process, torque specifications, and quality of manufactured fittings are proposed to reduce leaks. Among the many benefits leak reduction will result in improved customer safety and satisfaction, assembly down time reduction, cost and warranty reduction, and environmental impact reduction. [ABSTRACT FROM AUTHOR]

The development of new toughness requirements for carbon and low alloy steels was a major part of the effort to rewrite the ASME B&PV Code, Section VIII, Division 2. The new toughness rules in this code were established using the fracture mechanics assessment procedures in API 579-1/ASME FFS-1 (Fitness-For-Service), Part 9. The major change in the toughness rules when compared to older editions of Section VIII, Division 2 (2004 and prior) and the current edition of Section VIII, Division 1 are for carbon and low alloy steel materials excluding bolting. The new toughness rules in Section VIII, Division 2 are based on a Charpy V-Notch impact requirement of 20 ft-lb (27 J) consistent with European practice and the beneficial effects of post weld heat treatment are included consistent with the procedures in API 579-1/ASME FFS-1. This paper provides a technical background to the new toughness rules including the development of material toughness requirements and the development of impact test exemption rules. [ABSTRACT FROM AUTHOR]

The available design formulas for flat heads and blind end closures in the ASME Code, Section VIII, Divisions I and 2 are based on bending theory and do not apply to the design of thick flat heads used in the design of high pressure vessels. This paper presents new design formulas for thickness requirements and determination of peak stresses and stress distributions for fatigue and fracture mechanics analyses in thick blind ends. The use of these proposed design formulas provide a more accurate determination of the required thickness and fatigue life of blind ends. The proposed design formulas are given in terms of the yield strength of the material and address the fatigue strength at the location of the maximum stress concentration factor Introduction of these new formulas in a nonmandatory appendix of Section VIII, Division 3 is recommended after committee approval. [ABSTRACT FROM AUTHOR]

Cracks are popular defects initiated in structural components and their accurate evaluation is very important to assure the reliability of various plants. The direct-current electrical potential difference method is known as one of the most effective methods for the evaluation of the cracks. In this paper a method of three-dimensional identification of a semi-elliptical crack existing on the back surface of a conductive plate by the direct-current electrical potential difference method with a multiple-probe sensor is proposed. The geometrical condition of the crack was specified by six parameters, the surface and inward angles of the crack plane, θsur and θin, the length and depth of the crack, c and a, and the two-dimensional location of the crack center (yc, zc), on the back surface. The identification was carried out based on the distribution of electrical potential difference on the surface of the plate measured with a sensor composed of grid-arranged multiple probes called the "multiple-probe senso," As an approximate cracked body and a quick analysis method were used, a number of repeated electrical potential field analyses necessary for the identification of the crack became possible within a practical time. The validity of the method was numerically confirmed by carrying out the identification based on the result of the finite element analysis. The proposed method could be extended to the online monitoring of a semi-elliptical crack initiated on the inner surface of tubular components by means of the multiple-probe sensor placed on the outer surface. [ABSTRACT FROM AUTHOR]

Since environmentally assisted cracking (EAC) is an important degradation mechanism affecting the structural materials of nuclear power plants, numerous EAC experiments have been performed in the past three decades using standard specimens in simulated high temperature water environments to evaluate the various core materials used in light water reactors (LWRs). However, the environment, the condition of the material, and the mechanical properties near flaws in LWR components are not absolutely equivalent to those near the crack tip in standard specimens; thus, more research needs to be done before EAC growth in an actual LWR component can be accurately estimated using existing experimental EAC data. By combining the film slip-dissolution/oxidation model with the elastic-plastic finite element method and existing experimental EAC data, we have derived a method by which an estimation of EAC growth at flaws in actual LWR components can be made. In this paper we propose and discuss the use of this method. The results show that this new method basically concurs with the Fracture Research Institute (FRI) model in evaluating EAC growth across a semi-elliptic crack front under a simple tensile load and is also in approximate agreement with the experimental results obtained in evaluating EAC growth along a semi-elliptic crack front under complex loading conditions. The approach is expected to form a bridge between predicting EAC growth rate in core materials and evaluating EA C growth in key structural components in LWRs, and it is also expected that it can be used as a pre-analytical tool for EAC experiments using nonstandard specimens. [ABSTRACT FROM AUTHOR]

This paper presents the results of a numerical study undertaken to assess the influence of residual stresses on the ductile tearing behavior of a~ high strength low roughness aluminum alloy. The Gurson-Tvergaard model was calibrated against `conventional fracture toughness data using parameters relating to void nucleation, growth, and coalescence. The calibrated model was used to predict the load versus ductile tearing behavior of a series of full-scale and quarter-scale wide-plate tests. These center-cracked tension tests included specimens that contained a self-balancing residual stress field that was tensile in the region of the through-wall crack. Analyses of the full-scale wide-plate tests indicated that the model provides a good prediction of the load versus the ductile tearing behavior up to approximately 3 mm of stable tearing. The influence of residual stress on the load versus the crack growth behavior was accurately simulated. Predictions of the load versus the crack growth behavior of full-scale wide-plate tests for crack extensions greater than 3 mm and of the quarter-scale tests were low in terms of predicted load at a given amount of tearing. This was considered to result from (i) the "valid" calibration range in terms of specimen thickness and crack extension, (ii) the development of shear lips, and (iii) the differences in the micromechanism of ductile void formation under plane strain and under plane stress conditions. [ABSTRACT FROM AUTHOR]

The quantitative prediction of environmentally assisted cracking (EAC) or stress corrosion cracking (SCC) is essential in order to predict service life and also the structural integrity and safety assessment of light water reactors. During the last 3 decades many of the research results obtained on the quantitative prediction of the EA C crack growth rate have been based on linear fracture mechanics. in order to investigate EAC behavior in the high strain zone of important structures in light water reactors, the approach taken in this paper is one in which quantitative calculations of the EA C crack growth rate, incorporating the SCC deformation loxidation model and the elastic-plastic finite element method (EPFEM), are carried out. This approach can be used for the quantitative prediction of EA C crack growth rate. in both the low, and high strain zones of key structures in light water reactors. The crack growth behavior of sensitized type 304 stainless steel with a IT-CT specimen in simulated boiling water reactor (BWR) environments is analyzed based on this approach. The effect of several environmental, material, and mechanical parameters on the EAC crack growth rate of nickel based alloys in high-temperature aqueous environments is also discussed. [ABSTRACT FROM AUTHOR]

The angled crack problem has been given special attention in the recent years by fracture mechanics investigators due to its close proximity to realistic conditions in engineering structures. In the present paper, an investigation of fatigue crack initiation and propagation in line pipes containing an inclined surface crack is presented. The inclined angle of the surface crack with respect to the axis of loading varies between 0 deg and 90 deg. Based on the concept of the effective stress intensity factor range Δkeff, the rate of fatigue crack propagation db/dN is postulated to be a function of the effective strain energy density factor range ΔSeff. This concept is applied to predict the crack growth due to fatigue loading. Furthermore, the threshold condition for nongrowth of the initial crack was established and assessed based on the experimental data. [ABSTRACT FROM AUTHOR]

The radial second mode of sloshing in a circular cylindrical oil storage tank induces an out-of-plane deformation of the floating roof deck. The radial contraction of the deck due to this out-of-plane deformation contains modal components with circumferential wave numbers 0 and 2, thereby causing an elliptical deformation of the pontoon, which encloses the deck. In a previous paper, the stress caused by this elliptical deformation was analyzed by regarding the radial contraction of the deck as an enforced displacement of the whole pontoon. This paper presents an improved method for this stress analysis by considering the radial contraction of the deck as an enforced displacement of the joint between the deck and the pontoon. First, the effectiveness of the previous method in estimating the hoop membrane stress at the joint with the deck is confirmed by comparing the results obtained from the previous and improved method. Next, the improved method is used to predict also the other stress components in each portion of the pontoon. Numerical results reveal that the bending stresses are magnified locally near the joint with the deck and that the hoop membrane stress in the outer portion of the pontoon sensitively depends on the geometry of the cross-section of the pontoon. It is found that the hoop membrane stress near the joint between the outer rim and the top (or bottom) of the pontoon can be significantly reduced by increasing the slope of the top (or bottom) of the pontoon. [ABSTRACT FROM AUTHOR]

Tightening torque is one of the main factors that could affect the connection quality in threaded connections. On the basis of elastic mechanics and thick cylinder theory, this paper established a new analytical model based on the geometric parameters of thread tooth and the calculation method of tightening torque on P-110S threaded connections was also obtained by calculating the frictional torque on each threaded surface. In this paper, the friction coefficient on the real contact thread tooth was measured by the developed experimental equipment that could be used to simulate the contact of threaded surfaces approximately. By applying the new method on P-110S threaded connection and comparing the results obtained by analytical model with the true make-up torque in application, it could be found that the analytical model and the calculation method proposed in this paper are reasonable. The new method was also validated by using the finite element analysis method to the same sample. The new method proposed in this paper is practical and convenient because it can be applied to calculate the tightening torque just with geometric parameters and thread numbers, which is easier to implement in application. [ABSTRACT FROM AUTHOR]

Integrity evaluation methods for nuclear reactor pressure vessels (RPVs) under pressurized thermal shock (PTS) loading are applied by French Utility. They are based on the analysis of the behavior of relatively shallow cracks under loading PTS conditions due to the emergency cooling during small break loss of coolant accident (SBLOCA) transients. This paper presents the research and development program started at EDF on the computational fluid dynamics (CFD) determination of the cooling phenomena of a PWR vessel during a pressurized thermal shock. The numerical results are obtained with the thermal-hydraulic tool CodSaturne, in combination with the thermal-solid code SYRTHES to take into account the coupled effect of heat transfer between the fluid flow and the vessel. Based on the global and local thermal-hydraulic analysis of a small break loss of coolant accident transient, this paper presents mainly a parametric study that helps to understand the main phenomena that can lead to better estimating the margin factors. The geometry studied represents a third of a PWR pressure vessel, and the configuration investigated is related to the injection of cold water in the vessel during a SBLOCA transient. Conservative initial and boundary conditions for the CFD calculation are derived from the global thermal-hydraulic analysis. Both the fluid behavior and its impact on the solid part formed by cladding and base metal are considered. The main purpose of the numerical thermal-hydraulic studies is to accurately estimate the distribution of fluid temperature in the downcomer and the heat transfer coefficients on the inner RPV surface for a fracture mechanics computation, which will subsequently assess the associated RPV safety margin factors. [ABSTRACT FROM AUTHOR]

The failure assessment diagram (FAD) is a simplified and robust flaw assessment methodology, which simultaneously connects two dominant failure criteria: linear elastic fracture mechanics on one end and plastic collapse on the other end. This interaction is in the realm of elastic-plastic fracture mechanics. It is popularly known as the R6 approach, which graphically characterizes the impact of plasticity on crack driving force. In recent years, there has been continuous interest in using FADs to assess the failure of cracked structures subjected to biaxial loadings. Biaxiality is defined as the ratio of stress applied parallel and normal to the crack. Some pressure loaded aircraft components operate under negative biaxial ratios up to -0.5. In this paper, a detailed study on FAD was conducted using finite element analysis computed J-integral methods to investigate the effect of biaxial loading using different FAD approaches for geometries with notches. Geometries with a crack that emanates at a fillet region were simulated with various biaxial loading ratios from -0.5 to +0.5 using 2014-T6 material. FAD curves were numerically generated for cracks at notched regions subjected to various biaxial loadings using J-integral values from finite element analyses. These results were compared with standard FAD approaches. All comparison studies were made between uniaxial and biaxial loading cases with FAD curves created using four different crack sizes. Under small scale yielding, this study clearly shows that FAD curves are not influenced by negative biaxial loading at low load (up to 40% of yield strength). It was clearly confirmed that the majority of previously developed analytical FAD curves do not effectively account for notch and plasticity effects due to negative biaxiality. Based on this study, tension normal to the crack and compression parallel to the crack is the worst combination, and it has a very pronounced effect on FAD curve shapes. The standard analytical FAD curves are nonconservative compared with the approach recommended here, particularly under the worst case condition. FAD curves developed are shown to predict lower failure loads as compared with the currently accepted analytical FAD approaches defined in existing standards, e.g., R6 and API 579. The impact of negative biaxial loading can be investigated directly using a J-integral FAD approach but can be compared with ease by plotting both approaches in a FAD format. [ABSTRACT FROM AUTHOR]

In order to calculate the fatigue life of cylinders subjected to internal pressure using the fracture mechanics approach, the stress intensity factors (SIFs) for internal semi-elliptical cracks are needed. Nowadays, the most accurate procedure for fatigue life calculation consists in starting from a postulated internal semi-elliptical crack and updating the flaw aspect ratio during the crack propagation. In this sense, assuming a semi-elliptical shape during crack propagation, SIFs both at the deepest crack point and at the surface point must be calculated in order to update the crack aspect ratio through its fatigue propagation. This continuous crack shape updating cannot be done using the conventional tabulated solutions, as those provided in the main design codes and SIF handbooks. This paper presents a number of closed-form equations, which very accurately fit the tabulated results in ASME Boiler and Pressure Vessel Code, Section VIII, Division 3, to calculate the SIF for internal semi-elliptical cracks in cylinders subjected to internal pressure. These equations can be used to avoid the use of the tabulated solutions, and, as a consequence, an automatic numerical integration of the propagation law can be done. [ABSTRACT FROM AUTHOR]

The reeling technique presents an economical pipeline installation method for offshore oil and gas applications, especially for thick-wall (low D/t) pipelines. During reeling, the pipe is subjected to large plastic bending strains up to 3%. In thick-wall pipes, the tensile fracture response of the pipeline/girth weld would normally be the governing limit state. Seamless line pipes are preferred for the reeling applications in which the Lüders plateau is often exhibited in materials stress-strain response. In this paper, the fracture response of such pipelines is investigated from a continuum perspective using a nonlinear 3D finite element analysis. A typical pipeline with a hypothetical defect is considered, with the material having a range of Lüders strains and strain hardening indices. Results show that the Lüders plateau modifies the shape of the moment-strain response curves of the pipe, as well as the J-integral fracture response. It is observed that the response is always bounded between two limiting material models, which are (i) the elastic-perfectly plastic stress-strain response and (ii) the conventional elastic-strain hardening plasticity response, without a Lüders plateau. Also, the Lüders plateau was observed to decrease the crack opening stress ahead of the crack tip and thus the crack tip constraint. On the other hand, the presence of a Lüders plateau elevates the near tip plastic strain and stress triaxiality fields, thus promoting ductile fracture. A micromechanical damage integral model coupled with a modified boundary layer analysis was incorporated to study this aspect. Based on the findings of this study, it is believed that the presence of Lüders plateau could significantly alter the fracture response and toughness of pipes subject to relatively high strains. [ABSTRACT FROM AUTHOR]

Cold welding is the most dangerous defect in the electrofusion joint of polyethylene (PE) pipes. A proprietary method was developed to detect the degree of cold welding by using an Eigen-line, which was discovered in our previous study. To understand when, where, and how the Eigen-line would appear, the forming mechanism was investigated in this paper. Three factors, i.e., micro-air-bubbles, difference of acoustic impendence of PE in the melted and unmelted region, and small-crowded crystals in the region of the interface of melted and unmelted region, may cause the appearance of the Eigen-line. It was found that the number of Eigen-lines was the same as that of welding times when rewelded with decreasing welding time, and only one Eigen-line could be observed when rewelded with increasing welding time. The result showed that small-crowded crystals in the region of the interface of melted and unmelted region may be the dominating factor. This was then verified by the temperature analysis and differential DSC tests, and the forming process of the small-crowded crystals was discussed in detail. [ABSTRACT FROM AUTHOR]

Significant changes were made in design limits for pressurized vessels in the 2007 version of the ASME code (Sec. VIII, Div. 3) and 2008 and 2009 Addenda, and these are now a part of the 2010 code. There is now a local damage-mechanics based strain-exhaustion limit, including the well-known global plastic collapse limit. Moreover, Code Case 2564 (Sec. VIII, Div. 3) has recently been approved to address impulsively loaded vessels. It is the purpose of this paper to investigate the plastic collapse limit as it applies to dynamically loaded spherical vessels. Plastic instabilities that could potentially develop in spherical shells under symmetric loading conditions are examined for a variety of plastic constitutive relations. First, literature survey of both static and dynamic instabilities associated with spherical shells is presented. Then, a general plastic instability condition for spherical shells subjected to displacement-controlled and short-duration dynamic pressure loading is given. This instability condition is evaluated for six plastic and viscoplastic constitutive relations. The role of strain rate sensitivity on the instability point is investigated. Conclusions of this work are that there are two fundamental types of instabilities associated with failure of spherical shells. In the case of impulsively loaded vessels, where the pulse duration is short compared with the fundamental period of the structure, one instability type is found not to occur in the absence of static internal pressure. Moreover, it is found that the specific role of strain rate sensitivity on the instability strain depends on the form of the constitutive relation assumed. [ABSTRACT FROM AUTHOR]

In this paper, the classic coupled thermoelasticity model of hollow and solid cylinders under radial-symmetric loading condition (r,t) is considered. A full analytical method is used, and an exact unique solution of the classic coupled equations is presented. The thermal and mechanical boundary conditions, the body force, and the heat source are considered in the most general forms, where no limiting assumption is used. [ABSTRACT FROM AUTHOR]

Mechanical damage in transportation pipelines is a threat to their structural integrity. Failure in oil and gas pipelines is catastrophic as it leads to personal fatalities, injuries, property damage, loss of production, and environmental pollution. Therefore, this issue is of extreme importance to pipeline operators, government and regulatory agencies, and local communities. As mechanical damage can occur during the course of pipeline life due to many reasons, appropriate tools and procedures for assessment of severity is necessary. There are many parameters that affect the severity of the mechanical damage related to the pipe geometry and material properties, the defect geometry and boundary conditions, and the pipe state of strain and stress. The main objective of this paper is to investigate the effect of geometry, material, and pressure variability on strain and stress fields in dented pipelines under static and cyclic pressure loading using probabilistic analysis. Most of the published literature focuses on the strain at the maximum depth for evaluation, which is not always sufficient to evaluate the severity of a certain case. The validation and calibration of the base deterministic model was based on full-instrumented full-scale tests conducted by Pipeline Research Council International as part of their active program to fully characterize mechanical damage. A total of 100 cases randomly generated using Monte Carlo simulation are analyzed in the probabilistic model. The statistical distribution of output parameters and correlation between output and input variables is presented. Moreover, regression analysis is conducted to derive mathematical formulas of the output variables in terms of practically measured variables. The results can be used directly into strain based assessment. Moreover, they can be coupled with fracture mechanics to assess cracks for which the state of stress must be known in the location of crack tip, not necessarily found in the dent peak. Furthermore, probabilities derived from the statistical distribution can be used in risk assessment. [ABSTRACT FROM AUTHOR]

High Cr ferritic heat resisting steels have been widely used for boiler components in ultrasupercritical thermal power plants operated at about 600°C. In the welded joint of these steels, type-IV crack initates in the fine-grained heat affected zone during long-term use at high temperatures and their creep strength decreases. In this paper, creep properties and creep crack growth (CCG) properties of P92 welds are presented. The CCG tests are carried out using cross-welded compact tension C(T) specimens at several temperatures. The crack front was located within the fine-grained HAZ region to simulate type-IV cracking. Finite element analysis was conducted to simulate multiaxiality in welded joints and to compare experimental results. The constitutive behavior for these materials is described by a power-law creep model. C* and Q* parameters are used to evaluate CCG rate of P92 welds for comparison. C* parameters can characterize approximately 20% of the total life of CCG in P92 welds, and Q* parameters can characterize approximately 80% of the total life. Q* parameter is one of the useful parameters to predict CCG life in P92 welds. [ABSTRACT FROM AUTHOR]

In the present paper, calculations of the stress intensity factor (SIF) in the linear-elastic range and the J-integral in the elastoplastic domain of cracked structural components are performed by using the shell-to-solid submodeling technique to improve both the computational efficiency and accuracy. In order to validate the submodeling technique, several numerical examples are analyzed. The influence of the choice of the submodel size on the SIF and the J-integral results is investigated. Detailed finite element solutions for elastic and fully plastic J-integral values are obtained for an axially cracked thick-walled pipe under internal pressure. These values are then combined, using the General Electric/Electric Power Research Institute method and the reference stress method, to obtain approximate values of the J-integral at all load levels up to the limit load. The newly developed analytical approximation of the reference pressure for thick-walled pipes with external axial surface cracks is applicable to a wide range of crack dimensions. [ABSTRACT FROM AUTHOR]