bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture Properties of a Cr-Mo Ferritic Steel in High-Pressure Gaseous Hydrogen
Authors: Iijima Takashi , Itoga Hisatake , An Bai , San Marchi Chris , Somerday Brian P.
Published: November 2015

Recently, the measurement of threshold stress intensity factors for various low alloy ferritic steels was performed in high-pressure hydrogen gas, and it was revealed that the threshold for subcritical crack extension under rising displacement was lower than that for crack arrest under constant displacement. We previously examined the threshold for subcritical crack extension of ASME SA-372 Grade J ferritic steels using an unloading elastic compliance method in gaseous hydrogen at pressure up to 115 MPa, and reported that the cracking thresholds under the unloading elastic compliance method are consistent with the cracking threshold under the continuously rising displacement method. In the current study, the threshold stress intensity factor of JIS SCM 435 steel with yield strength of 700 MPa was measured using the unloading compliance method in high-pressure hydrogen gas. The roles of environmental (gas pressure) and testing (displacement rate) parameters were evaluated. The hydrogen gas pressure ranged from 10 to 115 MPa, and the displacement rate was varied between 2×10−3 and 2×10−5 mm/s. The measured values of the threshold for subcritical crack extension, KJIC,H, decreased with either increasing hydrogen gas pressure or decreasing displacement rate. When the hydrogen pressure was 115 MPa, however, the cracking threshold showed a modest dependence on displacement rate, varying from 63 to 43 MPa m1/2. These results demonstrate that the measurement conditions, such as the hydrogen pressure and the displacement rate, affect values of the subcritical cracking threshold under rising displacement.
Development of a Modified A286 Alloy With Improved Strength at Elevated Temperature and an Evaluation of Its Hydrogen Embrittlement Susceptibility
Authors: Sato Shinya , Takasawa Kouichi , Kayano Rinzo
Published: November 2015

A modified A286 alloy was developed with the aim of improving elevated temperature strength. The alloy was evaluated using a tensile test and a creep rupture test. Microstructure observations of the modified A286 alloy revealed that W and Ti carbides were precipitated at the grain boundaries and that no η phases were observed. The modified alloy showed higher tensile strength in a test at 625°C and a longer rupture time in a creep rupture test at 650°C relative to the conventional A286 alloy. Hydrogen embrittlement susceptibility was evaluated using a low-strain-rate tensile test with hydrogen-charged specimens. From a comparison of the reduction of area, it was determined that the hydrogen embrittlement resistance of the modified A286 was equal to or greater than that of conventional A286.
Effects of Trace Pb on Creep and Fracture of 25Cr35Ni-Nb Alloy
Authors: Chen Tao , Xuedong Chen , Lv Yunrong , Ye Juan , Hao Xiyun
Published: November 2015

The centrifugal casting 25Cr35Ni-Nb ethylene pyrolysis furnace tubes with different contents of Pb were selected to study the effects of Pb content on the creep and fracture properties. Both the high temperature rupture test at 1100 °C /17 MPa and the slow straining test at 850 °C with different loading rates show that the increase of Pb content significantly degrades the high temperature creep properties of centrifugal casting 25Cr35Ni-Nb alloy furnace tubes. The fractographic observation and the chemical composition analysis show that Pb segregates to the grain boundary at high temperature. It shows that the segregation of Pb to grain boundary occurs even when the content of Pb is several ppm, which leads to the reduction of grain boundary surface energy at high temperature. The initiation of creep cavities becomes easier. The creep cavities coalesce together under the local stress, forming cracks and finally causing the early failure of furnace tubes.
Stress Intensification Factor for Large Diameter Welding Tee Connections
Authors: Ranjbaran Sadjad , Ghalelar Akbar Daneshvar
Published: November 2015

Stress Intensification Factors (SIFs) are factors relating to fatigue characteristics of piping components. SIF is fatigue correlation which compares fatigue life of a typical piping component such as a tee and elbow to the reference fatigue life, that is girth butt welds in straight pipe subjected to bending moments. In order to calculate localized stress of such piping component, above mentioned figured out SIF shall be multiplied by nominal stress. ASME B31 contains several formulas for stress intensification factors considering limitation that those formulas are valid only for D/T≤100 (diameter to thickness). Extending the valid range mentioned in ASME B31 this paper is dedicated to SIF calculation for D/T≤100 and also for D/T>100 by utilizing Finite Element Analyzing (FEA) for welding tee. The computed SIF for D/T>100 welding tee can now be placed to typical pipe stressing program which analyzes piping system using beam elements. In addition, this paper investigates the effect of Rx (the magnitude of corner radius of shoulder at branch) on SIF of Welding Tee Connections.
Inner Pressure/Bending Creep Test on Circumferentially Welded Large Diameter Pipe of Grade 122 Steel: Failure Life Prediction
Authors: Takahashi Yukio , Nishinoiri Satoshi , Yaguchi Masatsugu
Published: November 2015

Estimation of failure lives for welded joints in piping made of creep strength enhanced ferritic steel is of great importance for ensuring safe and sound operation of ultra-supercritical fossil power plants using this type of material. As a part of the various efforts for developing the procedure meeting this need, a large scale pipe test was performed on grade 122 pipe with circumferential welds, in order to grasp its fracture behavior as well as its predictability. Finite element analysis as well as damage calculation were performed on this test. By using creep strain equations, as well as failure criterion newly developed for this material and welded joint, both creep deformation and failure life were successfully predicted with reasonable accuracy.
Design of a Tornado Missile Resistant Shield for the Angra Nuclear Plant
Authors: Reich Alton , Moon Jason
Published: November 2015

The Angra site contains the only two operational nuclear power plants in Brazil and one that is under construction. When Angra Unit 1 was designed the risk of tornadoes was deemed to be vanishingly small and tornadoes were not included in the design basis for the plant. When the question of environmental hazards was revisited for the design basis of Angra Unit 3, tornadoes were included as part of the design basis. Based on this change in philosophy for the Angra site, a review was performed and it was determined that the Raw Water Storage Tank and Reactor Make-up Water Tank, both of which are located outdoors at Angra Unit 1 required protection from tornado driven missiles. The tanks contain water that may be used for emergency cooling, and the water must be available for use during a design basis event. This paper provides an overview of the methodology used to design the tornado missile resistant shield structure for these two tanks.
Repercussion of Autofrettage on the Fatigue Crack Growth in the Vicinity of Catalyst Entry Opening for Polyethylene Autoclave Reactor
Authors: Haeri Navid , Cornah Brian A.
Published: November 2015

Background. The authors conducted a study to analyse the impact of autofrettage practice on the fatigue crack growth in the vicinity of the catalyst entry nozzle in a MK.15 ICI LDPE autoclave reactor.

Methods. The authors created 3-D finite element models of the quadrant of the opening. Elastic-plastic analysis was carried out to evaluate the residual stresses from the autofrettage which were then used as an input to the fracture mechanics analysis. Linear Elastic Fracture Mechanics (LEFM) methodology was then deployed associating a Radial Direction, Quarter-Circular Corner Crack pattern as per API 579/ASME VIII Div.3 for the purpose of calculating the crack tip stress intensity. A number of hypothetical pressure cycles were considered in order to calculate the crack growth rate as per ASME Div.3 (Paris’ Law) both with and without residual stresses from autofrettage analysis.

Results. The study results showed the change in the crack behaviour as a result of adding the autofrettage residual stresses onto the model and discussed the implications of such a practice on the design life for autoclave reactors.
System Stiffness and Restraint Effects on Circumferential Crack Opening Displacements: A Rotational Stiffness Approach
Authors: Young Bruce A. , Olson Richard J.
Published: November 2015

Current crack opening displacement (COD) solutions for leak-before-break (LBB) analyses assume the ends of the cracked pipe, which is subjected to remote bending and internal pressure, are free to rotate. However, in plant piping systems, the pressure induced bending and imposed rotations are restrained, because the ends of the pipe are constrained by the rest of the piping system and other components. Hence, existing evaluation procedures, theoretically overestimate the COD values of a circumferential through-wall crack (TWC) in a piping system. These overestimations comprise one of the uncertainties in an LBB analysis, as it leads to an under-prediction of the leakage-size-crack length of a postulated leaking TWC for a prescribed leakage detection limit in a plant, and thus, results in a non-conservative estimation of the crack stability from an LBB perspective.

Historical efforts on the effects of restraint on COD have focused on a restraint distance from the crack to restrain the rotation of the pipe. This study provides a fundamentally different approach in that the underlying theory develops a relationship between the apparent rotational stiffness of a pipe with unrestrained ends and the material modulus as a function of crack length and pipe geometry. Thus, the local system stiffness from a plant structural model can be used to modify the unrestrained value of COD.
Design Procedure of Spring Washers for Flanged Joints
Authors: Shatla Mahmoud Nagi
Published: November 2015

Flanged joints may experience leaks due to rapid increases or decreases in process temperatures. The mode of failure of a flanged joint during a rapid temperature increase is usually manifested in the form of gasket crushing or bolt rupture. On the other hand, the mode of failure of a flanged joint during a rapid cooling event occurs as bolt loosening causing the bolts to lose the necessary pretention required for joint tightness. In the present work, a systematic procedure has been proposed to design/select spring washers to prevent gasket leaks during thermal upsets of flanged joints. The procedure is based on the maximum allowable bolt load which is equal to the minimum of the load that will overstress the bolt, the load that will overstress the flange, or the load that will crush the gasket. The procedure considers the minimum allowable bolt load which is equal to the maximum of the required bolt load for operating conditions and required bolt load for gasket seating conditions. Moreover, the proposed procedure considers the design for rapid heating or rapid cooling events of flanged joints. The proposed procedure is based on the load-deflection characteristics of spring washer assemblies (series, parallel and series-parallel arrangements). The procedure has been applied successfully to design spring washer assemblies for flanged joints that suffer critical temperature excursions.
Inner Pressure/Bending Creep Test on Circumferentially Welded Large Diameter Pipe of Grade 122 Steel: Experimental Procedure and Results
Authors: Nishinoiri Satoshi , Shan Lin , Takahashi Yukio , Yaguchi Masatsugu
Published: November 2015

In this study, an inner pressure/bending creep test on a circumferentially welded, large diameter pipe of grade 122 steel was carried out under conditions where the test temperature was 923 K and the expected rupture time was 8,700 h to investigate creep damage mechanisms and the applicability of nondestructive evaluation techniques for the detection of creep damage. Deformation of the specimen rapidly increased at 7,894 h, and the creep test was interrupted. Surface cracks were observed on the lower part of the specimen along the circumferentially welded line where axial tensile stress was applied. As a result of phased array ultrasonic inspection, indications of internal defects were detected along welded lines where no indication was detected in previous inspection at 6,520 h, and it was predicted that cracks propagated along the fine-grained heat-affected zone (HAZ) from within the specimen to near the inner and outer surfaces. The indications of internal defects were in good agreement with observations from sectional views of the welded joints.
Effect of Reverse Yielding on the Residual Contact Stresses of Tube-to-Tubesheet Joints Subjected to Hydraulic Expansion
Authors: Bouzid Abdel-Hakim , Kazeminia Mehdi
Published: November 2015

The analytical prediction of the contact stress in tube-to-tubesheet joints subjected to hydraulic expansion is conducted without any consideration to reverse yielding that can occur inside the tube. Most existing models consider the tube and tubesheet to unload elastically when the expansion pressure is released. These models are therefore less conservative as the overestimate the contact pressure.

An analytical model that considers strain-hardening material behavior of the tube and tubesheet and accounts for reverse yielding has been developed. The model is based on Henckey deformation theory and the Von Mises yield criteria. The paper shows that reverse yielding that is present in tubes during hydraulic expansion unloading makes the joint less rigid and causes a decrease in the contact pressure depending on the gap clearance and the materials used. A good correlation between the analytical and FEM results is obtained on different treated cases which gives confidence on the developed model.
On a Flaw Shape Idealization of Axial Surface Flaws for Structural Integrity Assessment of Steam Generator Tubes
Authors: Park Seung-Hyun , Choi Jae-Boong , Huh Nam-Su
Published: November 2015

Nowadays, nuclear power plant (NPP) has become one of the most important energy sources to generate electricity in the world. Steam generator (SG) is a heat exchanger included in primary system of NPP.

Alloy 600 MA is widely used for SG tube material and this is well-known as weakness of stress corrosion cracking. In recent year, according to increase the number of long-term operation NPP, many axial surface flaws have been found on SG tube during an in-service inspection. Therefore, many researches have been carried out to maintain structural integrity of SG tube. Commonly, flaw shape needs to be idealized to calculate a burst pressure because detected flaw shape is complicated.

In this paper, validation of EPRI’s weakest sub-crack model, one of the well-known flaw idealization rule, is conducted through finite element (FE) analysis. For this, three actual flaws are assumed and these are idealized by using four flaw shape idealization methods; semi-elliptical crack model, rectangular crack model, maximum length with effective depth crack model and weakest sub-crack model. Burst pressure of each model is calculated and compared with burst pressure of actual shape crack model. As a result, if actual flaw is idealized by weakest sub-crack model, it is expected that conservative and efficient structural integrity assessment will be possible.
Influences of Overall and Local PWHT on Residual Stresses in the Under-Matching Welded Joints
Authors: Qian Yuwen , Zhao Jianping
Published: November 2015

The under-matching welded joint is commonly used in engineering practice and the postweld heat treatment (PWHT) is the common method to reduce the residual stress in the welded joint, while the research on the under-matching welded joint after PWHT is few. The finite element software-ABAQUS is used to simulate the welding process and PWHT process of the under-matching welded joint which is the combination of CF62 (base metal) and 316L (weld) in this paper. The discussion of the influences of both overall and local PWHT on the residual stress in the under-matching welded joint is based on the experimental verification. And the influences of the two methods are compared to propose the better PWHT method to the under-matching welded joint. The results show that both overall and local PWHT can reduce the residual stress in the under-matching welded joint significantly, especially the lower transverse stress than the longitudinal stress. The distribution of the residual stress in the under-matching welded joint after the local PWHT is a little more uniform than that after the overall PWHT. The local PWHT is recommended to the under-matching welded joint in this paper.
Estimation of Elastic Crack Opening Displacement for Thin Elbows With Circumferential Through-Wall Cracks
Authors: Kim Min-Kyu , Surh Han-Bum , Won Min-Gu , Huh Nam-Su , Kim Moon-Ki , Choi Jae-Boong
Published: November 2015

Leak-before-break (LBB) is an important concept that could confirm design and integrity evaluation of nuclear power plant piping. For the LBB analysis, the detective leakage rate should be calculated for a through-wall cracked pipes. For this calculation, the crack opening displacement (COD) calculation is essential.

Recently, sodium faster reactor (SFR) which has thin-walled pipes with Rm/t ranged 30–40 was introduced and then the investigation of these thin walled pipes and elbows has received great attention in the LBB evaluation. In this context, the three-dimensional finite element (FE) analyses for thin elbows with circumferential crack under in-plane bending are carried out to investigate the elastic COD values.

Finally, the solution for elastic COD which can cover sufficiently thin elbow is successfully addressed.
Leakage Rates Through Complex Crack Paths Using an ODE Method
Authors: Gill Peter , Sharples John , Budden Peter
Published: November 2015

The geometry of a crack is a fundamental consideration when calculating leakage rates for Leak-before-Break assessments. Carrying out fluid mechanics calculations does not give any additional benefit if there is not enough information on the crack shape. To address this issue, work is being carried out under the R6 development programme to derive a model that couples fluid mechanics and solid mechanics. The aim is to combine complex crack shapes with relatively simple fluid mechanics models and compare with experimental data. Then, the model can be extended to examine various stress distributions, and give indications as to how conservative are the current models. The model is a development of the one presented in a previous PVP paper (Reference 1), and a special case of isothermal gas flow is considered, where the equations reduce to an Ordinary Differential Equation (ODE). This is solved using a Runge-Kutta integration scheme in MATHCAD. A test case is presented based on the crack geometries considered in experiments, and upon comparison with numerical results; it is clear that choosing the correct crack shape is crucial in obtaining accurate predictions of leak rate. The assumed crack openings are rectangular, diamond or elliptical. In addition to this, weld residual stress profiles are postulated, based on experience of welds in piping components. Comparing the numerical simulations with the simplified DAFTCAT model indicates that the more precise ODE method can reduce conservatism in calculation of leak rates.
Development of Test Guidance for Single Edge Notch Bend Fracture Toughness Specimens Containing Notches Instead of Fatigue Pre-Cracks
Authors: Horn Anthony J. , Budden Peter J.
Published: November 2015

Structural integrity assessment codes such as R6 and BS7910 provide guidance on the assessment of flaws that are assumed to be infinitely sharp. In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. A common feature of these methods is the need to understand how the effective toughness, characterised using the J-integral for a notch, varies with notch acuity. No comprehensive guidance currently exists for obtaining J experimentally from specimens containing notches, hence the typical approach is to use equations intended for pre-cracked specimens to calculate J for notched specimens.

This paper presents a comprehensive set of test guidance for calculating J from Single Edge Notch Bend (SENB) fracture toughness specimens containing notches instead of fatigue pre-cracks. This has been achieved using 3D Finite Element Analyses to quantify the accuracy of formulae intended for pre-cracked specimens in fracture toughness testing standards ASTM E1820, BS7448-1 and ESIS P2-92 when applied to specimens containing notches. The paper quantifies the accuracy of these equations for notched SENB specimens and identifies the conditions under which the equations can lead to inaccurate measurement of J for notched specimens.
Effects of Primary Water Environment on the Thermal Aged Cast Austenitic Stainless Steels
Authors: Fukuta Yuichi , Kanasaki Hiroshi , Yamane Takahisa
Published: November 2015

This report summarizes the results of a scoping fracture toughness tests at high and low temperature for thermally aged cast austenitic stainless steels (CASSs) in a pressurized water reactor (PWR) environment. CF8M (ferrite content = 10.1%, 18.9%) and CF8 (ferrite content = 10.5%) were thermally aged up to 5,000 hours at 465°C. Tensile tests, Charpy impact tests and fracture toughness tests were conducted in air at 325°C and 50°C. Fracture toughness tests were also performed in simulated PWR primary water. Although the effect of 325°C and 50°C in simulated PWR primary water and dissolved hydrogen on the fracture toughness (JIc and J-Δa relationship) were slightly observed, fracture toughness was greater than that predicted by the thermally aged fracture toughness prediction method (Hyperbolic-Time-Temperature-Toughness (H3T) model).
SENT Stable Tearing Crack Path Deviation and its Influence on J
Authors: Hutchison Emily K. , Moore Philippa L. , Bath Warren P.
Published: November 2015

Crack path deviation in Single Edge Notch Tension (SENT) specimens, and its influence on the determination of J, has been investigated as part of the development of a new British Standard for SENT testing, BS 8571 [1]. Crack path deviation by angles up to 50° have been observed during stable tearing in parent material SENT specimens. This paper investigates the effect of crack path deviation on the measured fracture toughness, and offers a correction formula when crack path deviation invalidates the default standard J equations. Mixed mode effects in crack path deviation are also investigated.

A parametric study using finite element analysis has been carried out to compare the value of J calculated using standard equations (which assume a straight crack propagation path) with the value of J calculated using the contour integral method for different levels of crack path deviation. Crack path deviation from the initial crack plane resulted in a non-conservative estimate of fracture toughness using the standard equations. This means that any SENT test exhibiting crack path deviation may need to be discarded, wasting valuable test specimens. Instead, a correction factor has been developed to adjust the calculated value of J if path deviation is observed.
Fatigue Reassessment to Modern Standards for Life Extension of Offshore Pressure Vessels
Authors: Hutchison Emily , Wintle John , O’Connor Alison , Buennagel Emilie , Buhr Clement
Published: November 2015

Life extension of ageing assets is becoming increasingly important for the offshore oil and gas industry. Many pressure vessels in service have reached or are about to reach the end of their design lives, but their continued operation is required until the economic field life is exhausted. Many vessels in-service were designed over 30 years ago, when fatigue assessment was not required by the design standards. Therefore, fatigue reassessment is a critical part of the life extension process.

This paper presents reassessment of a benchmark vessel as a case study for life extension of other similar vessels. Life extension assessments are costly and time consuming, often hindered by a lack of information and a lack of access to the vessels. By determining the commonality between a vessel and the benchmark vessel, it may be possible with suitable on-going in-service inspection to justify life extension of the vessel without the need for a full fatigue life extension reassessment in every case.

The case study considered in this paper is a condensate flash separator vessel constructed in the early 70s which was in operation for 25 years; and is similar to many pressure vessels still in service on offshore platforms. The fatigue lives of key features of the vessel have been calculated and compared using different modern pressure vessel design codes, supported by finite element analysis.
Development of a Method to Assess Impact Hazards
Authors: Gill Peter , Toft Adam
Published: November 2015

The structural integrity of pressure retaining primary circuit components and of the containment boundary is of great significance for the safety justification of all nuclear reactors. In this regard, it is important to understand the vulnerability of safety related components to potential accidents. Whilst the direct consequences of pipe or pressure vessel failure, for example in terms of the extent of loss of coolant, may be tolerable, the indirect consequences of failure may not. A Loss of Coolant Accident (LOCA) may indirectly damage plant safety systems, including the containment boundary, due to the effect of missiles generated by the LOCA. This paper describes a study to develop a modern numerical modelling technique to estimate damage by missiles. Smoothed Particle Hydrodynamics (SPH) has been applied to simulate the acceleration of the missile due to the fluid jet.
Austenitic Cladding and Master Curve
Authors: Brumovsky Milan , Kytka Milos , Kopriva Radim , Falcnik Michal
Published: November 2015

Reactor pressure vessels of PWR/BWR/WWER type reactors are covered by austenitic cladding made by welding on their inner wall. Austenitic materials usually have no transition temperature behavior as they have fcc crystallographic structure. But, austenitic cladding made by welding contain usually up to 8 % of delta-ferrite that results in some transition behavior of fracture properties. This transition can be observed in temperature region below room temperature.

Surprisingly, this transition behavior in static fracture toughness of both cladding layers can be well described by “Master curve” approach.

Results from testing austenitic cladding for WWER type reactors will be shown and discussed, ether in unirradiated as well as irradiated conditions — only small changes in fracture toughness properties in this transition region are observed as a result of irradiation.
Effect of Pipe Restraint on the Conservatism of Leak-Before-Break Design of Nuclear Power Plant
Authors: Kim Yeji , Oh Young-Jin , Park Heung-Bae
Published: November 2015

In light water reactor designs, the concept of leak-before-break (LBB) can be applied for piping systems to exclude the dynamic effects of pipe rupture. The crack opening displacement (COD) and the J integral are important parameters in the LBB design. From preceding researches, it was revealed that when the restraint of pressure induced bending (PIB) is not considered in LBB evaluation, COD can be overestimated, resulting in a decrease in conservatism of the LBB design. If the pipe restraint is not considered, however, applied moment can also be overestimated. Thus, to take the pipe restraint effect into account when conducting the LBB analysis, the decrease of COD and the decrease of the applied moment must be considered simultaneously. In this regard, the authors have developed the restraint coefficient to account for the pipe restraint effect on both COD and the applied moment at the cracked section in earlier research. In this paper, the restraint coefficient was validated by comparing with an elastic-plastic FEA model including restraint boundary conditions. The effects of the restrained COD and the effective applied moment on the LBB evaluation were then investigated using the piping evaluation diagram. As a result, it was confirmed that the decrease in applied moment had greater influence on LBB evaluation than the decrease in COD. Therefore, the current practice of LBB evaluation which assumes the pipe is free to rotate can provide more conservative results than the case in which the pipe restraint is considered.
A Study of the Surface Penetration of High Cycle Thermal Loading in Pressure Retaining Components
Authors: Jones Michael , Carter Keith F.
Published: November 2015

This paper presents an overview of sensitivity studies undertaken by Rolls-Royce into the penetration of High Cycle Thermal Loading (HCTL) in Pressurised Water Reactor (PWR) components.

HCTL is a surface effect which has the potential to impact the fatigue life of pressure retaining components, typically at fluid mixing tees and other regions of turbulent mixing flows at different temperatures. This effect can significantly reduce the fatigue life of components. Understanding the factors that contribute to the penetration depth of HCTL can lead to possible benefits in analysis carried out to inform design decisions and support through-life management.

The sensitivity studies presented herein use governing equations for heat transfer at solid surfaces to assess how component properties and loading conditions such as material type, wall thickness and temperature oscillation frequency affect the penetration depth of HCTL and thus the resultant stresses generated within metal surfaces close to fluid mixing zones.

This paper discusses the potential benefits of improved analysis of HCTL effects to inform component design decisions and support through-life management. This is directly applicable to the selection of Start-of-Life (SoL) defect sizes for defect tolerance studies i.e. the assumed initial defect size, the development of Non-Destructive Examination (NDE) techniques, and the safe estimation of In-Service Inspection (ISI) periods at areas of concern.
Further Tests on Pipe Elements in Commercial Software for Nuclear Power Piping Analysis
Authors: Zeng L. , Börjesson A. , Jansson L. G.
Published: November 2015

The paper reports our further numerical tests on pipe elements in some commercial software for nuclear power piping analysis. Following our earlier tests on pipe elements, numerical tests are conducted using ANSYS, ABAQUS and PIPESTRESS with focus on the accuracy and reliability of key solutions: eigen-frequencies, reaction forces, stresses in pipe bends, deformation and others due to both static and dynamic loads. Benchmark examples are considered: (1) A simple pipe bend with varying wall-thicknesses; (2) A pipe model with two bends; (3) An irregular pipe model. A comparison against computations using elbow and shell elements is reported. The results indicate that analyses using traditional beam elements can go wrong and cautions are necessary, which is of particular importance for cases when extreme flexible piping systems are dealt with. It is concluded that there is a great need for advanced finite element computation for achieving a more reliable and accurate piping analysis.
Analytical Study on Failure Mechanisms by Extreme Loadings Under Design Extension Conditions
Authors: Ogawa Hiroshi , Machida Hideo , Kasahara Naoto
Published: November 2015

As the important lessons learned from Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure were strongly recognized against severe accidents (SA) and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premised under design extension conditions (DEC) such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, the best estimation for these failure modes is required for preparing countermeasures and management. Therefore, this study focused on identification failure modes under design extension conditions. To realize best estimation, it is prerequisite to clarify failure modes with ultimate structural strength under extreme loadings such as very high temperature, pressure and great earthquakes.

The authors attempt to clarify unclear failure mechanisms by extreme loadings under DEC using numerical simulations. In this paper, relations between failure modes and extreme loadings were investigated by the numerical simulation using the cylindrical model which is a typical structure of nuclear reactor structures (for example, Formed Head, Nozzle, Instrument Tube, Guide Tube, Support Skirt, etc.). Moreover, it was shown that failure modes change with an effect of structural discontinuities. Local failure dominates than ductile fracture at locally constraint portions where stress triaxiality becomes high.
A Method to Define the Best Weld Sequence Using a Limited Number of Welding Simulation Analysis
Authors: Asadi Mahyar , Alsoruji Ghazi
Published: November 2015

Weld sequence optimization, which is determining the best (and worst) welding sequence for welding work pieces, is a very common problem in welding design. The solution for such a combinatorial problem is limited by available resources. Although there are fast simulation models that support sequencing design, still it takes long because of many possible combinations, e.g. millions in a welded structure involving 10 passes. It is not feasible to choose the optimal sequence by evaluating all possible combinations, therefore this paper employs surrogate modeling that partially explores the design space and constructs an approximation model from some combinations of solutions of the expensive simulation model to mimic the behavior of the simulation model as closely as possible but at a much lower computational time and cost. This surrogate model, then, could be used to approximate the behavior of the other combinations and to find the best (and worst) sequence in terms of distortion. The technique is developed and tested on a simple panel structure with 4 weld passes, but essentially can be generalized to many weld passes. A comparison between the results of the surrogate model and the full transient FEM analysis all possible combinations shows the accuracy of the algorithm/model.
Effect of Nozzle Dimensions on the Stresses in Compensated Openings in Cylindrical Shells
Authors: Chandiramani Dipak K. , Gopalakrishnan Shyam , Mathkar Ameya
Published: November 2015

Clause 4.5 of ASME Section VIII Div. 2 [1] provides rules for compensation of openings in cylindrical shells having fitted nozzles.

There appears to be no definition of “nozzle” in either ASME Section VIII Div. 2 or ASME Section VIII Div. 1 [2].

The rules provided in Clause 4.5.5 of ASME Section VIII Div. 2 are based on pressure area method which ensures that the reactive force provided by the vessel material is greater than or equal to the load from the pressure.

The key element in applying this method is to determine the dimensions of the reinforcing zone, i.e, the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure.

There appears to be no restriction on the physical dimensions of the nozzle or shell, so long as the required area AT is obtained and the stresses are within allowable limits.

It is therefore possible that all of the required area AT is obtained from the nozzle or from the shell. While both these alternatives would be acceptable, the actual stresses at the shell/nozzle junction may vary considerably.

The work reported in this paper was undertaken with a view to determining if there needs to be any restriction on the proportion of area contributed by shell or nozzle to ensure that actual stresses were within allowable limits.
Re-Evaluation of the Structural Integrity of the Chinese Qinshan 300-MWe Reactor Pressure Vessel Under Pressurized Thermal Shock Using the Master Curve Method
Authors: Cao Yupeng , He Yinbiao , Hui Hu , Li Hui , Xuan Fuzhen
Published: November 2015

Pressurized thermal shock (PTS) is a potential major threat to the structural integrity of the reactor pressure vessel (RPV) in a nuclear power plant. A comprehensive structural integrity analysis of the Chinese Qinshan 300-MWe RPV subjected to PTS events including the small break loss-of-coolant accident (SB-LOCA) and large break loss-of-coolant accident (LB-LOCA) transients was performed by Shanghai nuclear engineering and design institute (SNERDI). The J-integral values at the deepest and the near cladding-base interface points of the crack were calculated with the linear elastic material model. And the RTPTS values were determined by the tangent approach. In the case that the RTNDT at or beyond the RPV design life may exceed the RTPTS according to the previous analysis procedure, the objective of this paper is to apply the Master Curve method to the re-evaluation of the integrity of this RPV, taking account of constraint and crack length effects. The over-conservatism in the previous evaluation is identified by comparing the new calculation with the previous one. The new RTPTS values are increased to varied extents for the different loading transients.
Numerical Study on Fracture Behavior of Complex Cracked Pipes
Authors: Ryu Ho-Wan , Han Jae-Jun , Kim Yun-Jae
Published: November 2015

This study provides the application of damage model to complex cracked pipes which can be found especially in weld overlay region. From the perspective of structural integrity, enough basic and large-scale tests are required to accurately evaluate the components containing a crack-like defect. In this case, damage model using finite element (FE) method can be effectively used for the assessment of full-scale cracked pipes with minimum basic experiments data. The proposed method in this research is based on the stress-modified fracture strain damage model with stress reduction technique.

In this paper, Battelle full-scale complex cracked pipe tests are simulated by the proposed damage model with reasonable procedure. FE simulation is conducted for basic experiments to determine failure criteria with calibrations. Then, crack initiation and maximum loads are predicted to characterize the fracture behavior of full-scale complex cracked pipes. Damage model is applied to both of carbon and stainless steel materials and verification with comparing to test data is conducted.
Improvements and Validation of the Numerical Prediction of the Incipient Cavitation Index
Authors: Rossi Marco Maria Agostino , Messa Gianandrea Vittorio , Ferrarese Giacomo , Malavasi Stefano
Published: November 2015

Cavitation phenomena are harmful and may bring to severe damages to hydraulic devices such as control valves. For this reason, the international standards provide multiple parameters describing the onset and the development of cavitation regimes. These parameters are commonly evaluated through laboratory analysis, however in many cases experimental tests are not affordable, e.g. for large-sized valves. Multiphase CFD models are able to reproduce the physics of the cavitation phenomenon, but do not allow an easy estimation of the incipient cavitation index. Providing effective methodologies for obtaining reliable prediction of this parameter is the objective of our research. Here we present a method for estimating the incipient cavitation index based on single-phase RANS simulations. The considerable robustness of the estimates makes this method even more attractive for engineering purposes compared to similar methodologies that we developed in recent years. The reliability of the method has been proved by comparison with experimental data regarding orifices and control valves.
Subsequent License Renewal in the U.S.
Authors: Young Garry G. , Remer Jason
Published: November 2015

As of January 2015, the NRC has renewed the operating licenses for 75 nuclear units, allowing for up to 60 years of safe operation. In addition, the NRC has license renewal applications under review for 19 units and 5 additional units have announced plans to submit applications over the next few years. This brings the total of renewed licenses and plans for renewal to almost 100% of the operating nuclear units in the U.S. At the end of 2014 there were 38 nuclear plants that had operated for more than 40 years and are eligible to seek a second license renewal (or 38% of the operating units). [1]

Although some nuclear plant owners have shutdown operation recently and others have announced plans to shutdown before reaching 60 years, the majority are keeping the option open for long term operation beyond 60 years. NRC and the U.S. nuclear industry have made significant progress in preparing the way for second license renewal applications. For example, in October 2014, 7 nuclear units were identified as the leading candidates for subsequent license renewal in a New York Times news article. This paper presents the status of the issues being addressed for possible applications for second license renewals for up to 80 years of operation.
Formulae for Plastic ETA Factors Accounting for Strain Hardening in SEB and SET Specimens
Authors: Gilles Philippe , Zhang Gongchen , Wang Xiaobei
Published: November 2015

Elasto-plastic fracture mechanics is commonly used for defect assessments in Nuclear Industry. Most of the approaches are based on the crack driving force J which is compared to a fracture resistance parameter. This fracture resistance parameter cannot be measured directly, but requires either J engineering formulae or Finite Element computations. The η(Eta) factor approach [1] is the most popular method allowing deriving fracture resistance from test records. One of the issue is the dependency of this factor to strain-hardening, namely for the shallow cracks.

This paper analyzes the effect of strain hardening on Eta factor solutions for two types of loading. Detailed Finite Element results are provided for Single Edge Cracked specimens under bending or tension. The results are compared to other formulae from the literature and new formulae are proposed.
Assessment of Bend Fatigue Tests Using RSE-M Stress Analysis Techniques and the ASME Section III Fatigue Design Rules
Authors: Booth Steven E. , Vorster Willem J. J.
Published: November 2015

Preparing the scope and extent of components requiring inspections in industrial plant demands careful consideration given the commercial implications. Stress analysis can usefully be employed to ascertain whether pipework components should be inspected. This can be achieved by interpreting pipework loads whilst giving consideration to all relevant failure mechanisms. Moreover, due to the size of the components the use of stress analysis can provide a means of targeted inspections by identifying areas of high stress where material damage is most likely to be observed. This paper compares the findings of fatigue tests reported by MPA Stuttgart in the mid 1990s of pipework bends subjected to combined pressure and moment loading with calculated fatigue damage using an analytical approach which combines the RSE-M stress analysis methods with the ASME Division I Section III NB fatigue design rules. The comparison is of interest as it has been found that the combined use of RSE-M and the ASME Division I Section III NB fatigue damage rules provides good agreement of calculated stresses with the locations and orientation of crack initiation observed in the fatigue tests. The calculated ASME Division I Section III NB fatigue endurance was found to bound that determined for the tests by a reasonable margin. Therefore, this approach provides a powerful means of assessing the fatigue life of in-service bends and confirms that the use of these tools is appropriate.
Suppression of Acoustic Resonance in Rectangular Cavities Using Spanwise Control Cylinder
Authors: Omer Ahmed , Mohany Atef
Published: November 2015

Flow over cavities can be a significant source of noise in many engineering applications when a coupling occurs between the flow instabilities at the cavity mouth and one of the acoustic cross-modes in the accommodating enclosure. In this paper, a passive noise control technique using a spanwise cylinder located at the cavity upstream edge is investigated experimentally for two different cavities with aspect ratios of L/D = 1.0 and 1.67, where L is the cavity length and D is the cavity depth. The effect of both the location of the cylinder and its diameter on the flow-excited acoustic resonance is investigated in air flow with Mach number up to 0.45. This passive control technique is found to be effective in suppressing the acoustic resonance excitation when compared to the base case where no cylinder is attached. It is observed that using the optimum cylinder location and diameter reduces the acoustic pressure to less than 140 Pa, compared to the base case with values exceeding 2000 Pa. Moreover, a shift in the onset of acoustic resonance to higher velocities is observed. Localized hot-wire measurements of the free shear layer at the cavity mouth during the off-resonance conditions reveal that attaching a spanwise cylinder at the cavity upstream edge reduces the spanwise correlation of the free shear layer which, in turns, reduces its susceptibility to acoustic excitation. To further understand the interaction between the cylinder’s vortex shedding and the free shear layer at the cavity mouth, a numerical simulation of the flow field using a detached eddy simulation (DES) model has been carried out. The simulation shows that the suppression occurs due to a disturbance of the cavity shear layer by the vortex shedding from the cylinder which results in altering the impingement point at the downstream edge of the cavity, and thereby weakening the feedback cycle that controls the acoustic resonance excitation.
Phase 2b Weld Residual Stress Round Robin: Mockup Design and Comparisons of Measurement and Simulation Results
Authors: Benson Michael L. , Tran Minh N. , Hill Michael R.
Published: November 2015

The U. S. Nuclear Regulatory Commission and the Electric Power Research Institute, cooperating under the auspices of a memorandum of understanding, conducted a double-blind round robin study for prediction of weld residual stress in a full-scale pressurizer surge line mockup. This work is the latest in a series of studies aimed at understanding and reducing uncertainty in the numerical prediction of weld residual stress. The round robin study involved both measurements and modeling. The measurements included deep hole drilling and contour method. Ten international participants submitted finite element modeling results to the study. This paper summarizes the mockup design, the modeling problem statement, and the measurement and modeling results.