bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic Phased Array Evaluations of Implanted and In-Situ Grown Flaws in Cast Austenitic Stainless Steel Pressurizer Surge Line Piping
Authors: Crawford Susan L. , Cinson Anthony D. , Moran Traci L. , Prowant Matthew S. , Diaz Aaron A. , Anderson Michael T.
Published: May 2012

A set of circumferentially oriented thermal fatigue cracks (TFCs) were implanted into three cast austenitic stainless steel (CASS) pressurizer (PZR) surge-line specimen welds (pipe-to-elbow configuration) that were salvaged from a U.S. commercial nuclear power plant that had not been operated. Thus, these welds were fabricated using vintage CASS materials that were formed in the 1970s. Additionally, in-situ grown TFCs were placed in the adjacent CASS base material of one of these specimens. Ultrasonic phased-array responses from both types of flaws (implanted and in-situ grown) were analyzed for detection and characterization based on sizing and signal-to-noise determination. Multiple probes were employed covering the 0.8 to 2.0 MHz frequency range. To further validate the Pacific Northwest National Laboratory (PNNL) findings, an independent in-service inspection (ISI) supplier evaluated the flaws with their American Society of Mechanical Engineers (ASME) Code, Section XI, Appendix VIII-qualified procedure. The results obtained by PNNL personnel compared favorably to the ISI supplier results. All examined flaws were detected and sized within the ASME Code-allowable limits.
Technical Basis for Proposed Weight Function Method for Calculation of Stress Intensity Factor for Surface Flaws in ASME Section XI Appendix A
Authors: Xu Steven X. , Scarth Douglas A. , Cipolla Russell C.
Published: May 2012

Analytical evaluation procedures for determining the acceptability of flaws detected during in-service inspection of nuclear power plant components are provided in Section XI of the ASME Boiler and Pressure Vessel Code. Linear elastic fracture mechanics based evaluation procedures in ASME Section XI require calculation of the stress intensity factor. A method for calculating the stress intensity factor is provided in Appendix A of ASME Section XI. This method consists of a two-step process. In the first step, the stress distribution, as calculated in the absence of the flaw, is obtained at the flaw location. For a surface flaw, the stress distribution at the flaw location is then fitted to a third-order polynomial equation. In the second step, the fitted polynomial representation of the stress distribution is used with standardized influence coefficients to calculate the stress intensity factor. An alternate method for calculation of the stress intensity factor for a surface flaw that makes explicit use of the Universal Weight Function Method and does not require a polynomial fit to the actual stress distribution is proposed in this paper for implementation into Appendix A of ASME Section XI. Universal Weight Function coefficients are determined from standardized influence coefficients through closed-form equations. Closed-form equations for calculation of the stress intensity factor are provided. The technical basis and verification for this alternate method for calculation of the stress intensity factor are described in this paper.
Detection of Stress Corrosion Cracking by Direct-Current Potential Difference Method
Authors: Tada Naoya , Uchida Makoto , Maeda Hiroki , Hozuki Atsushi
Published: May 2012

Stress corrosion cracking (SCC) is one of serious damages occurred in power generating plants, petrochemical plants, and gas pipelines. However, it is not easy to detect and evaluate SCCs because their shapes are complex and they are usually initiated in the weldment composed of base metal, weld metal, and heat-affected zone. In this study, the direct-current potential difference method (DC-PDM) was applied to SCCs artificially introduced in plate specimens and the applicability of DC-PDM to their detection was discussed. It was found from the measurement results that the potential differences near SCC were higher than those away from SCC. This fact suggests that SCC is detectable by DC-PDM.
A Simple Method to Estimate the Vibration Characteristics of a PWR Fuel Assembly
Authors: Kim Hyeong Koo , Lee Kyou Seok , Kim Jeong Ha , Jeon Sang Youn , Hwang Sun Tack
Published: May 2012

The main objective of this study is to establish a simple method making it possible to analyze the dynamic characteristics of the nuclear fuel assembly considering the geometrical configuration and the supporting condition of reactor internals etc. without any prototype test or FE models. In this study, a general frequency expression has been suggested for Bernoulli-Euler beams with generally restrained boundary conditions using Fourier series as a mode function. And using the frequency expression, the natural frequencies and mode shapes of a conventional fuel assembly for OPR1000 plants with reactor end conditions are calculated and compared with the test results in order to figure out its applicability to estimation on vibration characteristics of the fuel assembly. As a result, since the method suggested in present study gives quite a similar one with test result, present method will be useful to perform design evaluation preliminarily on the vibration characteristic of developing new fuel assembly.
Stress Redistribution Locus of Perforated Plate Under Displacement-Controlled Loading, Force-Controlled Loading and Thermal Loading
Authors: Watanabe Osamu , Matsuda Akihiro
Published: May 2012

Stress and strain locus in inelastic deformation is important to evaluate the fatigue strength and creep-fatigue strength. The stress redistribution locus (SRL) of perforated plate under displacement-controlled condition has been studied so far by the present authors. The SRL curve under displacement-controlled loading is almost independent of the employed constitutive equation, and the SRL takes the similar curve as Neuber’s one, if the inelastic stress/strain is non-dimensionalized by elastic solutions. However, the SRL under force-controlled loading is not studied yet, which is closely related to collapse load and fatigue strength. The response under thermal loading is also important for fatigue strength and creep-fatigue strength. Based on the 3D FE solutions under force-controlled loading or thermal loading for the perforated plate, the nonlinear feature will be discussed.
A Framework for Designer-Driven Exploration of Computational Weld Mechanics Design Space
Authors: Asadi Mahyar , Goldak John A.
Published: May 2012

This paper demonstrates a framework for analyzing multiple analyses of welds and welded structures as a single run. For each point in the design space a 3D transient thermal-stress analyses is solved for the weld and/or a welded structure. This enables the designer to explore the design state space for the design points specified in a Design of Experiments (DOE) matrix. This makes it simpler and quicker for a human to set up tens or hundreds of analyses. Also the CPU time to solve each analysis must be sufficiently short. Examples of DOE matrices created for Computational Weld Mechanics (CWM) optimization analyses are presented; i) a discontinuous combinatorial optimization of the weld sequence to minimize distortion in a girth weld, ii) a continuous optimization to mitigate distortion of an edge welded bar using side heaters, pre-bending with prescribed deflections at isolated points and pre-bending with a smooth prescribed displacement function.
Demonstrating Leak Tight Joints During Piping Design
Authors: Mair David
Published: May 2012

Pipe stressing programs will often show that the selected class of flange is not capable of accommodating the applied piping moments. In this case, unless a higher class of flange is chosen or the piping layout changed to reduce the flange moments, the pipe stressing program will indicate that the piping does not meet all of the requirements of the piping code. If the moments acting on the flange cannot be reduced, must a higher class of flange be chosen or are there other flange analysis techniques that can be used to show that the moments are not excessive? This paper compares a range of flange analysis techniques to investigate the bending moments that may be accommodated; both from a flange stress and from a flange leakage point of view. The objective of the work is to illustrate the variations in computed results and to help the piping designer choose an appropriate method for assessing flange moments. There is a multitude of different flange configurations considering combinations of flange type, size, class, schedule, gasket and the results of any comparison will be affected by many other parameters such as pressure, temperature and bolt pretension. The comparisons have thus been limited to a range of commonly used flange configurations in sizes up to 12 inch in an attempt to draw some general conclusions about the various assessment methods.
A Study of Fluid-Structure Coupled Analysis for Large LNG Storage Tanks in Consideration of Uplift
Authors: Hayashi Shoichiro , Taniguchi Tomoyo , Umeda Akira , Yamada Hisayuki , Kawasaki Takumi , Nagahara Hitoshi
Published: May 2012

With the rising demand for LNG in recent years, expansion of existing LNG terminals and construction of new ones are planned in many places around the world, and some of such projects are already in progress. Sites selected for these projects may not necessarily have favorable soil conditions from the viewpoint of seismic protection. Seismic demand tends to be higher for LNG storage tanks to be built on such sites. Severe seismic deign conditions require precise estimation of the uplift at the annular part during the earthquake. Depending on the estimation results, either of the following measures needs to be taken: increase of the plate thickness; installation of anchors or seismic isolators; and, occasionally, modification of the tank proportion. Uplift estimation is usually based on conventional design methods in which seismic load is converted into static load, because dynamic behavior of uplift is hardly taken into account in the design process due to its complexity. Some previous fundamental studies revealed that tank uplift and other dynamically induced responses would tend to be smaller than those simulated by static loads. This indicates a possibility of optimizing tank structure based on these research results. As a step toward introducing the uplift response in tank design properly, a time-history FEM analysis with fluid-structure coupling was carried out to understand the tank uplift behavior. This paper reports the findings from the analysis, including comparison with conventional analysis and previous fundamental studies. Since the rocking response may reduce overturning moment and base shear of tanks, structural design may have benefits if such mechanisms are properly taken into account.
Failure Probability Analysis Based on FRI Model for SCC Growth Introducing Stress Intensity Factor Distribution as Function of Crack Depth
Authors: Maeda Noriyoshi , Shoji Tetsuo
Published: May 2012

Failure probability of welds by stress corrosion cracking (SCC) in austenitic stainless steel piping is analyzed by probabilistic fracture mechanics (PFM) approach based on an electro-chemical crack growth model named FRI model[1] through which a basic equation is derived. Introducing the relation among dK/dt, da/dt and dK/da (K: stress intensity factor, a: crack depth and t: time) into the basic equation, modified basic equation is derived which can give da/dt in explicit form in contrast to the fact that the basic equation is transcendental and can be solved only numerically by iterative method. From numerical evaluation of K distribution at a crack tip under bending stress, it is realized that there exists a relation between a and K and it can be expressed approximately by quadratic function, i.e. K=Km{1−(a−am)2/am2}. By examining K as function of a, am is proved to be a linear function of membrane stress to bending stress ratio. These findings are incorporated into the modified basic equation which is shown to be able to calculate da/dt without instability and needs no iteration. Stratified Monte-Carlo method is introduced which defines two dimensional sampling space composed of a/c (c is crack length at surface) ranging from 0 to 1 and K from 0 to Kw which has to be defined referring to KSCC. Log-normal distributions are anticipated for a/c and K probability distributions. The median of K is decided referring to median of a in Bru¨ckner model. Parameter surveys for cumulative failure probability (CFP) performed with the basic equation and the modified basic equation give very close results. In this study, the residual stress distribution generated by residual stress at welding is anticipated to be tensile on inner surface and compressive on outer surface like bending stress distribution. Therefore the simulation is performed under bending dominative condition. The modified basic equation is proved to need about 1/2 calculation time of needed by the original basic equation in the CFP simulation.
Irradiation Performance Update on Advanced Nuclear Fuel of PLUS7™
Authors: Jang Young Ki , Jeon Kyeong Lak , Kim Jae Ik , Shin Jung Cheol , Kim Yong Hwan , Hwang Sun Tack , Kim Man Soo , Lee Tae Hyoung , Yoon Yong Bae , Kim Tae Wan
Published: May 2012

An advanced nuclear fuel of PLUS7™ for OPR1000s and APR1400s in Korea has been developed and irradiated in PWR nuclear power reactors. It has high performance characteristics from the safety and economy points of view comparing to the current fuel. Zirconium-based nuclear fuel structural components are grown and/or deformed under the circumstances of high temperature and irradiation. Excessive growth or deformation should be prevented not to interfere with adjacent fuels or reactor internals. After development for three (3) years from 1999, this fuel was verified successfully using four (4) LTAs in Ulchin unit 3. After each cycle, irradiation-related performance items were measured using the precise measurement systems in poolside and evaluated. After three (3) cycle irradiations, one discharged fuel assembly was disassembled and examined in detail. Finally, ten (10) rods including skeleton were sent to PIE test facility for further detailed examination. After in-reactor verification using LTAs, eight (8) OPR1000s were replaced with this advanced fuel. In the mean while, the surveillance program using the commercially supplied fuels was launched to reconfirm irradiation-related parameters such as growth, creep, corrosion and deformation, etc. Four (4) fuel assemblies which consist of two (2) assemblies to be discharged after two (2) cycle irradiations and the other two (2) to be discharged after three (3) cycle irradiations were selected for this surveillance program. In this paper, irradiation-induced parameters such as fuel assembly width and length growth, assembly bow and twist etc. are updated.
Prediction of Fracture Toughness Transition From Tensile Test Data Applying Neural Networks
Authors: Dlouhy´ Ivo , Hadraba Hynek , Chlup Zdeneˇk , Va´lka Libor , Zˇa´k Libor
Published: May 2012

Reference temperature localizing the fracture toughness temperature diagram on temperature axis was predicted based on tensile test data. Regularization artificial neural network (ANN) was adjusted to solve the interrelation of these properties. For analyses, 29 data sets from low-alloy steels were applied. The fracture toughness transition dependence was quantified by means of master curve concept enabling to represent it using one parameter — reference temperature. Different strength and deformation characteristics from standard tensile specimens and notched specimens, instrumented ball indentation test etc. have been applied. A very promising correlation of predicted and experimentally determined values of reference temperature was found.
Evaluation of the Sliding Behavior of the Rack Using CAV Concept
Authors: Iwasaki Akihisa , Nekomoto Yoshitsugu , Morita Hideyuki , Nishida Shingo , Nagaya Mitsuru , Okuno Daisaku , Chigusa Naoki
Published: May 2012

The spent fuel taken out of a nuclear plant reactor is temporarily stored in spent fuel racks. This fuel will often have to be stored in the long periods before it can be moved to a reprocessing facility. Therefore, the spent fuel rack must have a large capacity with a high tolerance against big seismic loads. So, the free standing rack is developed as the optimal equipment meeting these requirements. The free standing fuel rack is installed on the floor in the spent fuel pool and it can have the simple structure, as it needs no supports on the floor or the wall of the spent fuel pool. The free standing spent fuel rack structure actively incorporates the effects of the friction force generated on the spent fuel pool floor, and the fluid effect. So, seismic analysis is performed by nonlinear dynamic time history analysis. In this study, we applied CAV concept (CAV: Cumulative Absolute Velocity) to evaluate of nonlinear rack response. And it was confirmed that the CAV concept using the low-pass filter is useful to evaluate the sliding and rocking behavior of the rack by simulation analysis.
Modeling Crack Growth in Weld Residual Stress Fields Using the Finite Element Alternating Method
Authors: Brust F. W. , Zhang T. , Shim D.-J. , Wilkowski G. , Rudland D.
Published: May 2012

Flaw indications have been found in some nozzle to stainless steel piping dissimilar metal (DM) welds and reactor pressure vessel heads (RPVH) in pressurized water reactors (PWR) throughout the world. The nozzle welds usually involve welding ferritic (often A508) nozzles to 304/316 stainless steel pipe) using Alloy 182/82 weld metal. The welds may become susceptible to a form of corrosion cracking referred to as primary water stress corrosion cracking (PWSCC). It can occur if the temperature is high enough (usually >300C) and the water chemistry in the PWR is typical of operating plants. The weld residual stresses (WRS) induced by the welds are a main driver of PWSCC. Modeling the growth of these cracks in these WRS fields until leakage occurs is important for safety assessments. Currently, the prediction of PWSCC crack growth is based on the stress intensity factors at the crack tips. Several methods for modeling the crack growth through these WRS fields are possible, including using analytical, natural crack growth using finite element methods, and using the finite element alternating method. In this paper, finite element alternating method (FEAM) is used for calculating stress intensity factors and modeling the growth. First the FEAM method for growing cracks is presented. Next, several examples of modeling growth through control rod drive mechanism (CRDM) heads are presented. Finally, a short example examining multiple cracks in CRDM heads is presented. For many problems the FEAM approach for rapidly modeling crack growth is quite convenient, especially for difficult to mesh crack geometries.
Measurement of Fugitive Emissions of Industrial Valves
Authors: Schaaf Manfred , Schoeckle Friedrich
Published: May 2012

Against the background of the reduction of fugitive emissions, the demands on industry are increasing, steadily. In Europe the Integrated Pollution Prevention and Control (IPPC) directive [1] determines emission levels for different industrial facilities. Member countries must adopt these specifications into national guidelines like in Germany the TA-Luft (“Technical Instructions on Air Quality Control”) [2]. In addition, the German VDI guideline 2440 (“Emission control - Mineral oil refineries”) [3] gives more detailed procedures to meet the requirements. Apart from this qualification test in VDI 2440 in Germany, some other (more comprehensive) test procedures are established worldwide to examine the mechanical and tightness behavior of the packing material in valves. These test procedures are e. g. API 622 [4] or ISO 15848-1 [5]. The different test parameters of these test standards are compared in this paper with the ones of the VDI guideline 2440. Also, some typical test results of the VDI 2440 testing shall be illustrated and discussed in respect on the transferability to the other standards. Because the test procedures in the standards are different, it is not possible to perform the test on the same testing device. Especially the added requirement in ISO 15848-1 to measure the tightness of the body joint, leads to additional requirements on the testing equipment. In addition to the well-established test rig for the characterization of the mechanical and tightness properties of the packing material, a new testing device for valves is introduced. With this equipment, the stuffing box packing and the body seal of valves can be tested. The measurement of the friction forces during the stem cycles and the determination of the tightness characteristics (with Helium or Methane) are in the focus of the investigations of this test bench.
Strategies for Treating Weld Residual Stresses in Probabilistic Fracture Mechanics Codes
Authors: Brust Frederick W. , Kurth R. E. , Shim D. J. , Rudland David
Published: May 2012

Risk based treatment of degradation and fracture in nuclear power plants has emerged as an important topic in recent years. One degradation mechanism of concern is stress corrosion cracking. Stress corrosion cracking is strongly driven by the weld residual stresses (WRS) which develop in nozzles and piping from the welding process. The weld residual stresses can have a large uncertainty associated with them. This uncertainty is caused by many sources including material property variations of base and welds metal, weld sequencing, weld repairs, weld process method, and heat inputs. Moreover, often mitigation procedures are used to correct a problem in an existing plant, which also leads to uncertainty in the WRS fields. The WRS fields are often input to probabilistic codes from weld modeling analyses. Thus another source of uncertainty is represented by the accuracy of the predictions compared with a limited set of measurements. Within the framework of a probabilistic degradation and fracture mechanics code these uncertainties must all be accounted for properly. Here we summarize several possibilities for properly accounting for the uncertainty inherent in the WRS fields. Several examples are shown which illustrate ranges where these treatments work well and ranges where improvement is needed. In addition, we propose a new method for consideration. This method consists of including the uncertainty sources within the WRS fields and tabulating them within tables which are then sampled during the probabilistic realization. Several variations of this process are also discussed. Several examples illustrating the procedures are presented.
Lessons Learned for Nuclear Piping Integrity in New Reactors
Authors: Wilkowski G. , Brust F. , Krishnaswamy P. , Wichman K. , Shim D.-J.
Published: May 2012

From the early 1980’s to the present time, there has been a significant amount of research and development on the structural integrity of nuclear power plant piping. From those efforts, there are a number of lessons that could be applied to design and fabrication of new nuclear power plant piping systems. In this paper, the various aspects evaluated in NRC-funded efforts for understanding degraded piping were reviewed and implications on how to avoid detrimental aspects were discussed, as well as some more recent efforts. Some of these aspects include; (1) materials aspects (variability of wrought stainless steel base metal toughness with composition, dynamic strain aging effects on toughness of ferritic steels, fracture toughness in HAZ/fusion lines, material anisotropy effects on toughness, effects of static versus dynamic loading on material toughness, cyclic loading effects during seismic loading on toughness, thermal aging effects on strength and toughness), (2) designing weld sequencing to avoid SCC cracking; (3) crack morphology effects on leak-rate evaluations, (4) system effects that can significantly affect the structural integrity analysis of the piping system (secondary stresses, restraint of pressure induced bending, system displacement and rotation constraints, and margins associated from full dynamic analyses).
Long Life Fatigue Performance of Stainless Steel
Authors: Solin Jussi , Reese Sven , Mayinger Wolfgang
Published: May 2012

Fatigue of Niobium stabilized austenitic stainless steel (X6CrNiNb1810 mod) was studied using specimens extracted from a solution annealed and quenched primary piping material sample. This paper reports and discusses results of non-standard experiments to complement previously published test data. The NPP primary piping components spend long times in operation temperature between fatigue cycles originating from thermal transients. This was roughly simulated by fatigue tests periodically interrupted for intermediate annealing in elevated temperature. Fatigue endurance was notably increased when low strain amplitudes were used. The life extension is explained by the cyclic stress strain response. Hardening followed by slow cyclic softening was consistently observed after annealing. It is generally assumed that cumulative accumulation of fatigue damage occurs at a wide range of loading amplitudes. We performed two level and spectrum straining tests combining amplitudes above and below the (Nf > 107) endurance limit. The endurance limit seems to be effective also in variable amplitude loading. In terms of modified Miner rule, even “negative damage” was obtained in two level tests below and above the constant amplitude endurance limit. This behavior is linked to prominent secondary hardening of the steel.
Discussion on Fatigue Design Curves for Stainless Steels
Authors: Solin Jussi , Reese Sven , Mayinger Wolfgang
Published: May 2012

The new stainless steel air curve endorsed in NRC RG 1.207 for new US designs only was recently adopted into ASME III without restrictions on applicability. We assume that the new (2009b) ASME curve may be applicable to some grades of stainless steel, but not to all. This paper reports contradictory data for stabilized austenitic stainless steels extending up to 10 million cycles in room temperature at air environment. Niobium and titanium stabilized stainless steel specimens were sampled from 100% relevant material batches fabricated for NPP primary piping. Additional research and more recent data for titanium stabilized steel suggest that our PVP 2009-78138 conclusions are not limited to one material grade. Therefore, the revised ASME design curve cannot be considered universally applicable.
Finite Element Modelling of a Tube to Vessel Attachment Weld and Local Post-Weld Heat Treatment
Authors: Pellereau Benjamin M. E. , Hurrell Paul R. , Gill Christopher M. , Allen Sarah L.
Published: May 2012

This paper describes Finite Element (FE) modelling of a weld between a tube and a machined feature on a curved pressure vessel surface. The components were manufactured from a ferritic steel with a matched weld metal deposited by a mechanised TIG process. The weld region then underwent a local Post-Weld Heat Treatment (PWHT) which used heating bands and cooling air flows to control the temperature distribution. The PWHT’s aim was to provide stress relief and HAZ tempering, while minimising the stresses due to thermal gradients in the component. Trial welds on representative test pieces had predicted significant welding-induced distortions. Therefore, during the weld and PWHT, restraints were applied to the tube to prevent excessive deformation. The material behaviour was represented using Abaqus’ built-in material options, with the same properties for both the base metal and the filler. Isotropic hardening was assumed and the stress relaxation during the PWHT was modelled by applying a Norton creep law only during the hold time. Phase transformation effects in the ferritic material were not included. Initial modelling used a 2D axisymmetric model to allow sensitivity studies to inform the development of the PWHT process. These showed that the degree of stress relief was much more sensitive to the soak temperature than the hold time. Subsequent runs analysed a 3D model using a segmented block-dumping technique, with the deposition modelled by introducing the weld elements in 90° segments. The 3D modelling was undertaken in order to more accurately model potentially asymmetric welding distortions and residual stresses. The torch was represented by a body flux into each segment after its introduction. This model was also run without restraint to provide validation by comparing the predicted distortion with measurements from the welding trials; a good match was demonstrated. Further comparisons were made between the predicted stresses and results of Incremental Centre Hole-Drilling (ICHD) stress measurements made on the trial specimens both in the as-welded condition and after PWHT. The measured stresses were close to those predicted by the FE analysis and the key features of the predicted stress field were apparent in the measurement data. Due to the location of the tube’s attachment to the pressure vessel, thermal expansion of the vessel during the PWHT caused the tube to bend. The induced bending stresses were then relaxed during the soak and re-introduced in the opposite sense as the system cooled. This effect was captured by running the analysis as a submodel of a global FE model with displacements read across at nodes in the pressure vessel shell immediately below the weld.
Analysis of Acoustic Fatigue in Safety Relief Systems
Authors: Smeulers Jan P. M. , van Beek Pieter J. G. , Golliard Joachim
Published: May 2012

To protect installations in the gas and oil industry and process industries against overpressure the installation of relief systems is common practice. However, there have been incidents where such systems fail as a result of high dynamic loads caused by: the generation of shock waves when the relief valve is opened very instantly; the occurrence of two-phase flow in the relief line and the corresponding formation of slugs; instability of the relief valve and acoustic fatigue. This paper focuses on acoustic fatigue, which occasionally has been the cause of incidents like at Krechba – In Salah Gas Project Algeria where a breakdown of a relief system occurred. The extremely high sound levels caused by the expanding flow through a relief line finally caused fatigue failure of the system. Such incidents are the reason for the requirement to analyze the possibility of acoustic fatigue of relief systems and other systems with a strong acoustic source already during the design. In the paper we present the method that TNO applied for acoustic fatigue analysis. So far a calculation of the internal sound power levels was made and evaluated against the allowable levels presented by Carucci and Mueller [1]. However, this method does not allow computing the cyclic stresses of the piping. Due to the large dimensions and the high frequencies involved, it is not possible to compute accurately the sound field in the piping and to use a deterministic method to evaluate the cyclic stresses of the piping. In this paper we present work recently done where the Statistical Energy Analysis (SEA) method is applied to evaluate the cyclic stresses in the piping material. Due to the statistical nature of the method, it is not possible to determine with deterministic certainty the stress levels in every point of the piping. Yet, this method gives a range of cyclic stress for each pipe section or element. This leads to a more reliable criterion for acoustic fatigue studies than the earlier method, which is based on maximum allowable pressure fluctuations.
Cohesive Zone Modeling of Ductile Crack Growth in Circumferential Through-Wall-Cracked Pipe Tests
Authors: Shim Do-Jun , Uddin Mohammed , Brust Frederick , Wilkowski Gery
Published: May 2012

Cohesive zone modeling has been shown to be a convenient and effective method to simulate and analyze the ductile crack growth behavior in fracture specimens and structures. However, the cohesive zone modeling has not been applied to simulate the ductile crack growth behavior of a circumferential through-wall cracked pipe. In this paper, cohesive zone modeling has been applied to simulate the ductile crack growth of a past through-wall-cracked pipe test that was conducted during Degraded Piping Program. The ABAQUS code was used for the three-dimensional finite element analysis. The bending moment at crack initiation, maximum bending moment, crack extension, and J-integral values were calculated from the finite element analysis. These results were compared with the experimental results. In addition, results obtained from an existing J-estimation scheme (LBB.ENG2) were provided for comparison. All results showed reasonable agreement. The results of the present study demonstrate that the cohesive zone modeling can be applied to simulate the ductile crack growth behavior of a through-wall cracked pipe.
Recent Developments in ARCMAC and Related Creep Strain Monitoring Techniques
Authors: Narayanan Aditya , Morris Andy , Davies Catrin Mair , Dear John
Published: May 2012

Developments have been made to E.ON’s Auto-Reference Creep Management and Control (ARCMAC) system to measure strain at high temperature using both Digital Image Correlation (DIC) and conventional ARCMAC techniques. These techniques are aimed at measuring creep strain rate in power plant steam pipes and associated weldments operating at high temperatures and pressures for the purposes of estimation of remaining life of such components. The ARCMAC optical strain measurement system is used to measure point to point strain through the capture and analysis of images of a pair of Inconel gauges, with Silicon Nitride spheres, welded to steam pipe and other components. A modified ARCMAC image capture system has been developed using a DSLR camera, with higher resolution offering the potential to capture DIC images suitable for measuring strain accurately. Development of the system to measure strain using both ARCMAC gauges and DIC at high temperature offers the potential to obtain full-field strain measurement across features such as welds, giving a useful improved research tool for creep evaluation. The recently developed DSLR-ARCMAC camera system has been optimised to measure strain using a number of optical strain measurement techniques, including the ARCMAC strain measurement procedure and DIC. These techniques have been used to measure strain during room temperature tensile tests prior to their use at high temperatures. Following these experiments, creep testing of CMV steel specimens is planned paying particular attention to the evaluation of the ARCMAC system at high temperatures.
Inelastic Behavior of Threaded Piping Connections: Reconciliation of Experimental and Analytic Results
Authors: Ryu Yonghee , Behrouzi Anahid , Melesse Tsega , Matzen Vernon C.
Published: May 2012

Modeling the behavior of piping systems with threaded joints is difficult because the joints do not act as rigid connections. At one level of approximation the connection can be modeled as a semi-rigid connection using a rotational spring. This study modeled a straight pipe using either Euler-Bernoulli beam elements [4] or Finite Element Analysis (FEA) shell elements and a support condition using the rotational spring. Laboratory tests were conducted on 1 in. diameter specimens of black iron Schedule 40 pipe in a cantilever configuration. The specimen was loaded monotonically into the inelastic region. A Ramberg-Osgood model [5] was used to represent the rotational spring and the correlation between test results and analytical predictions was quite good.
Size Effects on Fracture in Uncontained Plasticity Conditions in 304(L) Stainless Steel
Authors: Wasylyk Andrew P. , Sherry Andrew H.
Published: May 2012

In the structural integrity assessment of structures containing defects, ductile tearing and plastic collapse are treated as competing failure mechanisms. The validity of fracture toughness measurements in test specimens is limited by the development of plasticity ahead of the crack tip. Compact Tension (CT) specimens are commonly used to characterise the ductile fracture toughness. Three sizes of CT specimens (thickness 25, 15 and 10mm) were tested using the unloading compliance technique and the J-Resistance curve characterised. Concurrently, the development of the plastic zone was monitored on the surface of specimens using digital image correlation. This enabled the plastic zone size to be correlated with the evolution of crack growth. It was found that in all specimens no crack growth occurred prior to plastic yielding of the un-cracked ligament on the specimen surface. Furthermore, a reduction in initiation and tearing toughness was observed with reduction in specimen size. The Rice and Tracey local approach was developed to predict the specimen size effect.
PWSCC Crack Growth Mitigation With Inlay
Authors: Rudland David , Brust Frederick W. , Shim D. J. , Wilkowski G.
Published: May 2012

Primary water stress corrosion cracking (PWSCC) is an issue of concern in the dissimilar metal welds (DMW) connecting vessel nozzles and stainless steel piping in PWR nuclear power plants. PWSCC occurs due to the synergistic interaction of several factors including tensile weld residual stresses, a corrosion sensitive weld metal (usually Alloy 82/182 weld metal) and a corrosive environment. Several mechanical mitigation methods to control PWSCC have been developed in order to alter the weld residual stresses on the nozzle. These methods consist of applying a weld overlay repair (WOR), using a method called mechanical stress improvement process (MSIP), and applying an inlay to the nozzle ID, the latter of which is the subject of this paper. An inlay consists of machining the pipe ID at the region of the DMW and applying a PWSCC resistant weld material at the machined region. The PWSCC resistant material is mainly Alloy 52/152, which has a higher chromium content compared with Alloy 82/182. The inlay is a corrosion resistant material, and the proposed application thickness (after final machining) is 3 mm. Therefore, once the crack grows through the inlay, the growth in the underlying A82/182 material is much faster. This leads to a complicated crack shape which is small at the nozzle ID and becomes larger in the original weld material and approaches a balloon shape. Here the weld residual stress state caused by the inlay is first discussed. Next, the effect of crack growth through the inlay and into the underlying Alloy 82/182 material is discussed. Finally, implications of inlay for mitigation and consideration of alternatives is discussed.
Mitigation of Distortion in an Edge-Welded Bar by Clamping Parameters
Authors: Asadi Mahyar , Goldak John A.
Published: May 2012

The objective is to demonstrate a capability developed to explore a design space to minimize distortion and evaluate the sensitivity of the distortion of an edge weld on a 152 × 1220 × 12.5 mm bar of Aluminum 5052-H32 wrt clamping. For each point in the design space, a full computational model that includes transient 3D thermal and stress analysis is solved using VrWeld software [1]. The bar has no displacement constraints other than rigid body constraints and the resulting camber from welding bends the bar. The minimum distortion in this discrete design space is assumed to be the optimal design to minimize the final distortion, i.e., objective function. The design space parameters chosen are clamping parameters, i.e., prescribed displacements, and the release time value in the design space. The bar is fixed at both ends and subjected to a range of prescribed displacements opposite to the direction of the camber. In the first set of tests the prescribed displacement is applied directly in the middle of the bar and in the second set of tests the displacement field is prescribed as a parabolic displacement along the full length of the bottom of the bar. In addition to the effect of the prescribed displacement on final distortion is shown to be highly correlated with the delay time at which the prescribed displacement is released after the weld is finished. The best pair of the prescribed value and the release time value in the design space. The distortion and residual stress fields in the mitigated bar with a nodal prescribed displacement in the middle of the bar and the mitigated bar with a parabolic prescribed displacement along the bottom surface of the bar are compared.
The Evolution of Stress and Strain Tensors in Welds With Mitigation of Residual Stress and Distortion
Authors: Goldak John A. , Asadi Mahyar
Published: May 2012

By getting the data from an ordered set of Gauss points on the flow line of a material point that passes near the weld pool, the evolution of the stress/strain tensor fields is visualized. The principal plastic strain tensor, principal deviatoric stress tensor, hydrostatic stress and temperature are visualized. This is done for three weld distortion mitigation strategies: i) pre-bending by applying a prescribed displacement, ii) applying a tensile load to the weld and iii) applying side heaters to the weld. Visualizing the evolution of the principal stress and strain vectors gives interesting insight into the mechanics of plastic deformation near a weld pool.
Fragility Analysis of Threaded T-Joint Connections in Hospital Piping Systems
Authors: Ju Bu Seog , Tadinada Sashi Kath , Gupta Abhinav
Published: May 2012

The cost of damage to the non-structural systems in critical facilities like nuclear power plants and hospitals can exceed 80% of the total cost of damage during an earthquake. Studies assessing damage from the 1974 San Fernando and 1994 Northridge earthquakes reported a widespread failure of non-structural components like sprinkler piping systems (Ayer and Phillips, 1998). The failure of piping systems led to leakage of water and subsequent shut-down of hospitals immediately after the event. Consequently, probabilistic seismic fragility studies for these types of structural configurations have become necessary to mitigate the risk and to achieve reliable designs. This paper proposes a methodology to evaluate seismic fragility of threaded T-joint connections found in typical hospital floor piping systems. Numerous experiments on threaded T-joints of various sizes subjected to monotonic and cyclic loading conducted at University of Buffalo indicate that the “First Leak” damage state is observed predominantly due to excessive flexural deformations at the T-joint section. The results of the monotonic and cyclic loading tests help us evaluate the following characteristics for a given pipe size and material: (i) Maximum allowable value of rotational deformation at the T-joint section to prevent “First Leak” damage state; (ii) The force-displacement and moment-rotation relationships at the T-joint section. A non-linear finite element model for the T-joint system is formulated and validated with the experimental results. It is shown that the T-joint section can be satisfactorily modeled using non-linear rotational springs. The system-level fragility of the complete piping system corresponding to the “First Leak” damage state is determined from multiple time-history analyses using a Monte-Carlo simulation accounting for uncertainties in demand.
Weld Residual Stress in Large Diameter Nuclear Nozzles
Authors: Zhang Tao , Brust F. W. , Wilkowski Gery
Published: May 2012

Weld residual stresses in nuclear power plant can lead to cracking concerns caused by stress corrosion. These are large diameter thick wall pipe and nozzles. Many factors can lead to the development of the weld residual stresses and the distributions of the stress through the wall thickness can vary markedly. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe and nozzle joints with welds. This paper represents an examination of the weld residual stress distributions which occur in various different size nozzles. The detailed weld residual stress predictions for these nozzles are summarized. Many such weld residual stress solutions have been developed by the authors in the last five years. These distributions will be categorized and organized in this paper and general trends for the causes of the distributions will be established. The residual stress field can therefore feed into a crack growth analysis. The solutions are made using several different constitutive models such as kinematic hardening, isotropic hardening, and mixed hardening model. Necessary fabrication procedures such as repair, overlay and post weld heat treatment are also considered. Some general discussions and comments will conclude the paper.
A Direct-Search Computational Weld Mechanics Optimization Using Least-Square Approximation
Authors: Asadi Mahyar , Goldak John A.
Published: May 2012

Using a frame-work for exploring a design space in Computational Weld Mechanics (CWM), a recent direct-search algorithm from Kolda, Lewis and Torczon is modified to use a least-square approximation to improve the method of following a path to the minimum in the algorithm. To compare the original and modified algorithms, a CWM optimization problem on a 152 × 1220 × 12.5 mm bar of Aluminum 5052-H32 is solved to minimize the weld distortion mitigated by a side heating technique. The CWM optimization problem is to find the best point in the space of side heater design parameters: power, heated area, longitudinal and transverse distance from the weld such that the final distortion is as low as possible (minimized). This CWM optimization problem is constrained to keep the stress level generated by the side heaters, in the elastic region to avoid adding an additional permanent plastic strain to the bar. The number of iterations, size of DOE matrix required and CPU time to find the minimum for the two algorithms are compared.