bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the Design Pressure and Failure Modes for the API 12F Shop Welded Flat Bottom Tanks for Oil Storage
Authors: Rondon Andres , Guzey Sukru
Published: December 2016

This study aims to determine the failure modes of the eleven API 12F shop welded tanks plus two proposed new sizes through finite element and stress analysis of more than 350 different models. Four separate analysis where carried out throughout this investigation. An elastic stress analysis considering non-linear deformations was performed to determine the yielding pressure of the tanks and maximum design pressure. An elastic buckling mode analysis evaluated the potential buckling pressure as a failure mode of the tanks. The redistribution of stresses due to inelastic deformations and plastic collapse were evaluated through an elastic-plastic stress analysis. Finally, a wind load analysis was developed to study the stress levels and uplift deformation of the API 12F tank with greatest aspect ratio (H/D). The presented research provides meaningful engineering calculations to evaluate the current design and capacity of the API 12F flat bottom tanks guaranteeing a safe performance of the equipments.
Damage Detection in Thick Steel Plates Using Guided Ultrasonic Waves and Non-Contact Laser Vibrometry
Authors: Tian Zhenhua , Howden Stephen , Ma Linlin , Lin Bin , Yu Lingyu
Published: December 2016

This paper presents damage detection in thick steel plates by using guided ultrasonic waves and non-contact laser vibrometry. Guided waves are generated by piezoelectric transducers (PZT). A scanning laser Doppler vibrometer is used to measure the full velocity wavefield of guided waves in the plate, based on the Doppler Effect. The measured full wavefield in terms of time and space contains a wealth of information regarding guided wave propagation in the plate as well as guided wave interaction with damage. Through wavefield analysis, the cumulative energy map of damage induced waves is derived for damage detection and quantification. For the proof of concept, an experiment is performed on a ¼ inch steel plate with three surface defects of different sizes and shapes. The detection result shows that the locations and sizes of high energy areas in the cumulative energy map agree well with those of the actual defects. Overall the method presented in this paper using guided waves and non-contact laser vibrometry is effective to detect and quantify location, size and shape of damage in thick steel plates.
Wave Propagation Across the Interface of Fluid-Structure Interaction With Various Surface Conditions of Solid Medium
Authors: Kojima Tomohisa , Inaba Kazuaki , Takahashi Kosuke
Published: December 2016

This study aims to clarify the effect of surface conditions of solid on wave propagation at solid-fluid interface with fluid-structure interaction. Although many studies have been done to develop the theoretical models of fluid-structure interaction caused by wave propagation, they do not take into account the surface conditions of the solid medium on the solid-fluid interface where interaction occurs. In this study, we experimentally investigated the wave propagation across the solid-fluid interface with several value of surface wettabilities and roughnesses of solid. We conducted an impact experiment with a free-falling projectile which hit the cylindrical solid buffer placed on top of the water surface within the elastic tube standing on the ground. During the experiments, cavitation bubbles were generated from the interface of the buffer and water. That generation was inhibited according to the decrease of the value of the contact angle (improve of the wettability) of the buffer surface. The amplitude of transmitted pressure wave from the buffer to water become smaller than the theoretical value according to the decrease of the value of the contact angle on the buffer surface (the smallest value was 55% of the theoretical value). Concerning the surface roughness, the amplitude of transmitted pressure wave becomes smaller than the theoretical value according to the shape of the buffer surface become more different from flat surface (the smallest value was 75% of the theoretical value). These experimental results indicate that by taking into account the surface condition of the solid on the interface, more accurate model of fluid-structure interaction or ways to reduce the damage of structures by fluid-structure interaction would be proposed.
Evaluation of Groove Radius Assessment Criteria Based on Brittle and Ductile Local Failure Models
Authors: Brown Gregory W. , Parietti Lucie , Rose Brian , Anderson Ted L.
Published: December 2016

API 579-1/ASME FFS-1[1] Part 5 (2007 edition) contains procedures for assessing local metal loss based on failure by plastic collapse. Equation (5.10) defines “acceptable” tip radii for grooves to ensure a plastic collapse failure mode. Grooves failing the radius check must be treated as a crack-like flaws. The validity of Equation (5.10) is questionable, and it may be excessively conservative. This paper presents new rules for groove assessment based on brittle and ductile failure models. Computation of the Weibull stress using finite element analysis (FEA) was employed to determine the minimum groove radius required to eliminate the possibility of cleavage fracture. The Bao-Wierzbicki ductile failure model was used with FEA to evaluate burst pressure and to determine a new groove radius criterion defining the plastic collapse regime, allowing categorization as metal loss. Groove-like flaws categorized as neither sharp cracks nor as metal loss are evaluated using an effective toughness concept. This concept quantifies the difference in fracture response between a sharp crack and a notch with a finite tip radius. The upcoming 2016 API 579-1/ASME FFS-1 rules remove the excessive conservatism found in Part 5 of the 2007 edition and avoid the abrupt transition between crack and metal loss assessment types based on groove radius.
Ratcheting With No Thermal Bending and Membrane Stress
Authors: Adibi-Asl R. , Reinhardt W.
Published: December 2016

The ASME B&PV Code provides design by analysis rules that address failure mechanisms under cyclic loading. One of these potential failure mechanisms is incremental plastic collapse, or ratcheting. Miller presented the technical basis for the present Code requirements in a technical paper in 1959. Miller’s equations for the ratchet boundary address a beam under a cyclic through-thickness thermal gradient acting together with a steady axial mechanical load. This ratchet boundary applies approximately to a pressurized cylinder with through-thickness thermal bending stress. Conditions arise sometimes in practice where cooling or heating is applied simultaneously to the inner and outer surface of pressure boundary. The extreme case of such a scenario arises when both surfaces experience the same thermal condition such that there is a cyclic thermal stress but both zero membrane thermal stress and zero thermal bending stress The question is, could ratcheting occur in this case?

This paper derives the ratchet boundary for cases when the maximum temperature occurs mid-way through the thickness. The linearized stress due to thermal loading is zero. The solution is obtained using FE analysis and the Non-Cyclic Method (NCM) that has been proposed previously by the authors. The NCM is a generalization of the static shakedown theorem and allows the ratchet boundary to be calculated for both elastic and elastic-plastic cyclic stress states.
Experimental Study on the Ultimate Limit State of a Lead-Rubber Bearing
Authors: Kim Jung Han , Kim Min Kyu , Choi In-Kil
Published: December 2016

Recently, a base isolation system used to be introduced for the seismic safety of nuclear power plants. The isolation system should keep its function over the design level earthquake with a high confidence like any other equipment in nuclear power plants. The seismic response of isolators by the extended design level earthquakes should be controlled not to exceed the ultimate limit state of it. In this study, lead-rubber bearings (LRBs) were tested. The small scale test specimen of a LRB had 550 mm diameter and the full scale was 1,500 mm diameter. The displacement controlled horizontal displacements were applied to the specimens with a constant vertical load in a test. The small scale model was tested under the various vertical load conditions to define the failure mode when the compressive force is excessive. In this test, the shear fracture by a large horizontal displacement with a relatively low axial load around the design axial load and the buckling fracture by a high axial load with a small effective area resisting the axial force were compared. The full scale model was tested to understand various characteristics such as the dependency of strain rate, the function of excitation displacement and the bidirectional behavior on the two-dimensional horizontal plane. As an experimental result, the behaviors of isolators under the ultimate limit state were investigated and the considerations for the prototype test of isolation devices were discussed.
Interacting Threats Mitigated: Carbon Composite System’s Ability to Restore/Increase Pipeline Strength
Authors: Meyer Nico
Published: December 2016

Fiber Reinforced Polymers (FRPs), a qualified structural building material for several industries, have recently demonstrated additional validation in pressure pipeline applications. With validated durability’s of their own, glass and carbon fiber reinforced polymers (GFRP and CFRP) have demonstrated significant ability to prevent and arrest corrosion in steel and concrete applications while increasing/renewing structural capacities of corroding elements. Although other coatings prevent deterioration of ferrous materials, CFRP and GRFP applications can reinforce and/or effectively replace the pipeline using the existing pipe as a composite form. GFRP and CFRP applications have proven ability in external applications of dented and artificially corroded pressure pipelines with interacting threats of girth and seam welds. The repair systems received cyclic loading up to 72% of the specified minimum yield strength and tested beyond 100,000 and 370,000 pressure cycles without failure for dents and simulated corrosion, respectively. This paper will provide a quick overview of relevant testing on GFRP and CFRP application for corrosion mitigation/rehabilitation with more detail on the recent validation of FRP applications for dented and corroded pressure pipes.
Anchor Bolt Failures in Coke Drums
Authors: Samman Mahmod
Published: December 2016

Anchor bolt failures that are commonly experienced by coke drums typically show signs of axial and/or shear overload. Temperature measurements and thermographic images have demonstrated that side-to-side temperature differences in coke drums can be more than 400 degrees Fahrenheit. In this paper, finite element models are used to examine the displacement of skirt base plates. Various combinations of circumferential thermal gradients, support deck slopes, and friction coefficients between drums and support structures are used. The study shows that observed thermal gradients can result in significant longitudinal, circumferential, and radial displacements and explains observed overload failures of anchor bolts. In addition, the study demonstrates the roles of deck slope and friction coefficient on base plate displacements.
EDS Containment Vessel Explosive Test and Analysis
Authors: Crocker Robert W. , Haroldsen Brent L. , Stofleth Jerome H. , Yip Mien
Published: December 2016

This report documents the results of two of tests that were performed on an explosive containment vessel at Sandia National Laboratories in Albuquerque, New Mexico in July 2013 to provide some deeper understanding of the effects of charge geometry on the vessel response [1]. The vessel was fabricated under Code Case 2564 of the ASME Boiler and Pressure Vessel Code, which provides rules for the design of impulsively loaded vessels [2]. The explosive rating for the vessel, based on the Code Case, is nine (9) pounds TNT-equivalent. One explosive test consisted of a single, centrally located, 7.2 pound bare charge of Composition C-4 (equivalent to 9 pounds TNT). The other test used six each 1.2 pound charges of Composition C-4 (7.2 pounds total) distributed in two bays of three.
Effect of Adjacent Tube Expansion on the Residual Contact Pressure of Tube-to-Tubesheet Joints
Authors: Bouzid Abdel-Hakim , Zhu Linbo
Published: December 2016

The tubular heat exchangers of nuclear, oil and gas industries often experience shutdowns due to failures of the tube-to-tubesheet joints. They are the very weak link between the heat transfer process thermos-fluids and separation boundary. The complex elasto-plastic behavior of the expanded joint and the lack of a proper design procedure of the expansion process are the two main factors contributing to the low quality and low performance of this kind of assembly. The inadequacy of a proper evaluation of the residual contact pressure achieved by the expansion process make the joint vulnerable and prone to leakage failure. Among the multiple parameters that effect the residual contact pressure is the adjacent tube-to-tubesheet expansion.

It is proposed to study the elasto-plastic behavior of tube-tube to tubesheet joints during the expansion process using numerical FEM. The numerical FE model will be validated analytically prior to study the influence of adjacent expansion. Particular emphasis will be put on the effect of adjacent tube expansion and the expansion order sequence on the residual contact pressure. The effect of ligament size and the adjacent tube expansion sequence are also investigated. Such a study would provide general guidelines on how to control the expansion process and help the design engineer to predict accurately the residual stresses that are the major source of stress corrosion cracking and leakage failure.
Towards Detailed Material Deformation Patterns in the Hypervelocity Impacts of Laminated Plates With Smoothed Particle Hydrodynamics
Authors: Zisis Iason , van der Linden Bas , Giannopapa Christina , Koren Barry , Dam Jacques
Published: December 2016

Hypervelocity impacts onto the outer structure of spacecraft induce shock waves, which in case of multimaterial structures interact with the material interfaces. This interaction is expected to produce different deformation patterns for laminates compared to the patterns appearing for materials with homogeneous density. In order to exhibit these different features and to show that the Smoothed Particle Hydrodynamics computational method is capable of describing them, a numerical hypervelocity impact experiment is performed for three plates. The first one is a laminate, with discontinuous density and material parameters, the second is a simple homogenized version of the laminate and the last is a monolithic metal plate.
Pressurizer Safety Valve Data Collection, Analysis, and Performance
Authors: Esselman T. , Zysk G. , Streeter P. , Elaidi B. , Garcia H. , Khatri S. , Kewalramani M. , Brackeen E. , Mortorff A.
Published: December 2016

The Pressurizer Safety Valves (PSVs) at Diablo Canyon Power Plant were manufactured by Crosby and are model 6M6 HB-86-BP valves. The valves have intermittingly experienced leakage as the units are heated up and pressurized to normal operating conditions. When leakage occurs, a time-consuming de-pressurization and re-pressurization process is implemented that causes significant delays in the return to power after an outage. Following the elimination of the upstream water seal, leakage has occurred on individual valves during all but one start-up.

After recent PSV leakage, instrumentation was installed to obtain information during the subsequent unit heat up and pressurization. The instruments included thermocouples on the inlet pipe, the discharge pipe, and the valve. Data was collected during a unit start-up in which two of the three installed valves leaked.

Piping and valve analyses were performed using the data to modify the valve installation procedures, to modify the process for accommodating piping thermal growth, and to modify the pressurization rate during start-up. Upon implementation of these changes, none of the PSVs leaked during the subsequent unit heat up and pressurization, saving more than 24 critical path hours.

The data, analyses, and modifications will be described along with the analyses used to support an increase in the pressurization rate for unit start-up.
Ultrasonic Inspection of Hydrogen Flakes in Large Forgings: From Qualification to Site Inspection
Authors: Moussebois Dominique , Ancrenaz Patrick
Published: December 2016

During 2012 RPVs inspections, nearly-laminar indications were detected in the lower and upper core shells of Doel 3 and Tihange 2 RPVs. As a consequence, the Doel 3 and Tihange 2 NPPs have to stay in cold shutdown until it was proved that they can be safely operated. The performance and capability of the applied UT technique to detect and characterize hydrogen flakes had to be confirmed. To achieve this objective, extensive investigations were launched on blocks extracted from a steam generator shell known for containing hydrogen flakes.

The paper describes the UT validation performed and the results of the destructive tests which enable to demonstrate the capability of a straight ultrasonic beam to detect and size nearly laminar indications and to correctly identify ligaments between two adjacent indications. It addresses the formal extension of qualification performed by correlating UT measurements acquired on a large numbers of real hydrogen flakes, simulations of UT responses and destructive examinations.

Lessons learned from the experiments are finally described.
Overview of the Doel 3 and Tihange 2 Reactor Pressure Vessel Safety Cases
Authors: De Smet Michel , Van Vyve Jean
Published: December 2016

During the summer outages of 2012, large numbers of indications were found inside the shell material of the Doel 3 and Tihange 2 reactor pressure vessels (RPV). Therefore both plants remained in cold shutdown with their core unloaded. A series of examinations, tests and inspections were performed leading to the conclusion that the indications are hydrogen flakes and that they do not affect the structural integrity of the RPVs, regardless the operating mode, transient or accident condition. All this was documented in the Safety Case Reports issued in December 2012 and the Safety Case Addenda issued in April 2013.

Based on those reports, the Belgian Federal Agency for Nuclear Control (FANC) authorized the restart of both units that went back on-line in June 2013. In parallel, a number of requirements from the FANC were addressed such as the qualification of the applied Ultrasonic Testing (UT) procedure, and mechanical testing of irradiated specimens containing hydrogen flakes. The preliminary tests showed unexpected results regarding the shift in RTNDT (Reference Temperature for Nil Ductility Transition) under irradiation that could not confirm the hypotheses considered in the initial Safety Case Reports. Therefore, the Licensee Electrabel decided to shut down both plants immediately.

In order to fully address this concern, the material test programme was extended including several RPV materials and covering additional irradiation campaigns. This led to a modification of the irradiation embrittlement trend curves considered in the structural integrity analysis. In addition, the qualification of the UT procedure led to an updated cartography of the flakes. The structural integrity assessments of both RPVs were revised accordingly. The final Safety Case Reports, confirming the fitness-for-continued operation of both RPVs, were submitted to the FANC in October 2015. FANC allowed restart of both units on November 17th, 2015.

The paper gives a historical overview of the Doel 3 and Tihange 2 RPV Safety Cases and explains how the roadmap was built in order to demonstrate the RPV’s structural integrity in the presence of hydrogen flakes.
Measurements of Residual Stresses Using Mechanical Strain Relaxation Methods and Mapping in a Thin-Walled Girth Welded Pipe Mock-Up
Authors: Serasli Karim , Romac Remi , Cave Douglas
Published: December 2016

Girth welded pipes such as those located offshore on platforms in the North Sea are subjected to highly corrosive environment. The need to consider welding residual stresses in the assessment of the fitness for service and damages to these pipes when investigating local corrosion damages across a welded region is therefore important for the operators of the platforms and the manufacturers of the pipes.

This paper presents a review of work carried out to ascertain the welding residual stresses present within a thin-walled girth welded pipe mock-up made from steel API 5LX Grade 52. The mock-up was manufactured to replicate typical pipes used to convey gas, oil and water through the platforms. The mock-up was of diameter 762mm and of thickness 19mm. The incremental deep hole drilling (iDHD) technique and the contour method were applied to characterize the residual stresses in the weld and heat affected zone of the specimen. The results of these measurements are presented and compared to highlight agreements and discrepancies in the measured residual stress distributions using these different techniques.

Most residual stress measurement methods are limited in terms of their stress and spatial resolution, the number of measurable stress tensor components and their quantifiable measurement uncertainty. In contrast, finite element simulations of welding processes provide full field distributions of residual stresses, with results dependent on the quality of the input conditions available. As measurements and predictions are not often the same, the true residual stress state is therefore difficult to determine. In this paper, through-thickness residual stress measurements are made using the contour and iDHD methods and these residual stresses measured using the iDHD technique are then used as input to a residual stress mapping technique provided within a finite element analysis to reconstruct the residual stress field in the whole specimen. The technique is applied iteratively to converge to a balanced solution which is not necessarily unique. The solution can then be reused for further simulations and residual stress analyses, such as corrosion simulation. Results of the reconstruction are presented here.
Chloride-Induced Stress Corrosion Crack Growth Under Dry Salt Conditions: Application to Evaluate Growth Rates in Multipurpose Canisters
Authors: Sindelar Robert L. , Carter Joe T. , Duncan Andrew J. , Garcia-Diaz Brenda L. , Lam Poh-Sang , Wiersma Bruce J.
Published: December 2016

The conditions of continued dry storage of the spent nuclear fuel in multipurpose canisters render the canisters, a component for confinement in dry storage cask systems, susceptible to chloride-induced stress corrosion cracking (SCC). The requisite conditions involve deposits of chloride-bearing marine salts and/or dust that deliquesce on the external surface of the cooling canister to create brine at weld residual stress regions. The subcritical crack growth rate at this “dry salt” condition, investigated by several researchers, has shown a relatively slow growth rate compared to chloride-cracking under aqueous conditions. A new SCC growth rate test specimen configuration has been developed to enable an initially dried salt assemblage to deliquesce under temperature and humidity conditions to load the fatigue pre-cracked, wedge-opening-loaded (WOL) specimen with the brine and enable measurements of crack growth rate (da/dt) under falling stress intensity factor, KJ, conditions. The application of the results to a canister weldment with a residual stress profile to predict crack extension in time is described. The results are evaluated in terms of development of acceptance standards for this type of flaw, should SCC be identified and characterized through inservice inspection (ISI).
Fatigue Life Estimation of Pitted Specimens by Means of an Integrated Fracture Mechanics Approach
Authors: Larrosa Nicolas O. , Chapetti Mirco D. , Ainsworth Robert A.
Published: December 2016

The synergistic nature of corrosion and fatigue is one of the main reasons for the premature failure of engineering structures and components. The decrease in fatigue life of specimens subjected to aggressive environments is likely to be attributed to local, pit-induced, stress concentrations that cause premature initiation of fatigue cracks. In this work, we have developed a predictive approach to assess the life of specimens containing pits assuming the pit both as a crack and as a smooth notch. The proposed approach assumes that even though the critical place for crack initiation seems to be the pit mouth, once the crack initiates, during propagation, the location of the hot spot shifts according to the location of the crack tip and due to the redistribution of stresses and strains. An integrated fracture mechanics approach that compares the driving force of the crack emanating from the pit and the evolution of the material threshold to crack propagation with crack length is proposed. The material threshold is estimated from the plain fatigue endurance limit, the position d of the strongest microstructural barrier and the SIF threshold for long cracks. The effective driving force is assessed by means of parametric FEA. This approach considers the influence of the pit geometry on the stress field surrounding the crack providing a more realistic estimate of the applied driving force. The maximum applied stress range as a function of number of cycles (S-N curves) have been estimated for different configurations (stress level, initial crack length, location at the crack front) assuming that failure of the component will be given when the critical crack length is reached. The procedure has been first developed and used to assess deep pits, as these are the most detrimental and common configuration encountered in real Oil and Gas applications.
Characteristic Values of Fracture Toughness Test Data
Authors: Li Yuebing , Jin Weiya , Gao Zengliang , Ding Zhenyu , Lei Yuebao
Published: December 2016

Fracture toughness of reactor pressure vessel materials appears obvious scatter. It is desirable in assessment codes to characterize fracture toughness by a low fractile of its distribution. This low fractile is known as a characteristic value. However, the real distribution type is unknown, and usually assumed to be normal, lognormal or Weibull. In this paper, the characteristic values with given confidence level and probability are obtained by one-sided tolerance factors for normal, lognormal and Weibull distribution. These characteristic values are compared with that obtained with minimum of three equivalent.
Contribution of the Bending Stiffness of the Tank Bottom Plate and Out-of-Round Deformation of Cylindrical Shell to the Tank Rocking Motion
Authors: Taniguchi Tomoyo , Nakashima Teruhiro , Yoshida Yuuichi
Published: December 2016

Effects of bending stiffness of the tank bottom plate and out-of-round deformation of cylindrical shell on uplift of the un-anchored flat-bottom cylindrical shell tanks are investigated. Numerical tank models whose bottom plate has different bending stiffness reveal that changes in bending stiffness of the tank bottom plate may have little influence on uplift of the tanks. Contrary, numerical tank models whose cylindrical shell is stiffed differently reveal that out-of-round deformation of the cylindrical shell may have significant influence on uplift of the tanks. In addition, uplift of the tanks may have little influence on development of waves on the fluid surface like sloshing.
Statistical and Probabilistic Analysis of Fatigue Life Data With Two- and Three-Parameter Weibull Distribution Functions
Authors: Wei Zhigang , Luo Limin , Gao Litang , Nikbin Kamran
Published: December 2016

Product durability and reliability validation requires fatigue testing of limited samples and the corresponding statistical and probabilistic analyses of the test data. The uncertainties introduced into the tests with limited sample size and the assumptions made about the underlying probabilistic distribution function will significantly impact the analysis results and the result interpretation. In this paper, a large amount of fatigue life data collected from several programs are analyzed. The values of the parameters estimated from the two-parameter and three-parameter probabilistic distribution functions, Weibull in particular, are compared. Finally, the observations are summarized and some recommendations are provided.
Historical Rates of Soil Side Corrosion for Use in Fitness-for-Service Evaluations of Buried Metallic Pipe
Authors: Munson Douglas , Pandey Mahesh , Jyrkama Mikko , Angell Peter
Published: December 2016

Nuclear power plants and many other industries are required to periodically inspect their buried piping to determine its fitness-for-continued service (FFS). The FFS process requires that both the general corrosion rate and the rate of maximum penetration for localized corrosion (e.g., pitting) be estimated so that the remaining lifetime and/or time until the next inspection can be determined. Revision 1 to ASME Code Case N-806, “Evaluation of Metal Loss in Class 2 and 3 Metallic Piping Buried in a Back-Filled Trench” [1] provides 4 options for estimating the corrosion rates:

a. Wall thickness measurements from the current examination and from one or more previous examinations of the same metal loss region.

b. Repeat measurements at two or more times from another location that has a predicted metal loss rate greater than or equal to the rate of the metal loss region under evaluation.

c. Repeat measurements using corrosion coupons, linear polarization probes, or electrical resistance probes

d. Generic historical data

Each of these methods has its uses and limitations, and it is generally preferable to consider results from 2 or more of the methods.

This paper examines historical data gathered by the National Bureau of Standards (NBS, renamed in 1988 as the National Institute of Standards & Technology - NIST) at ∼ 70 locations around the US in the 1930s – 1950s. Maximum penetration and weight loss (general corrosion) data from each site were placed in one of four soil texture groups for both carbon steel and cast iron. A regression analysis was performed to determine the median rates and 80% and 95% probabilistic values. It was found that results within each soil texture group were relatively similar and that the corrosion rates in the first 3 years after burial tended to be much higher than rates in years 5–18. The coefficients of determination were determined to quantify differences within each soil texture group.

It is proposed that the steady state rates provided herein are an option to be used as the Historical Rates for FFS evaluations as described in [1].
Evaluation of the Susceptibility of Duplex Stainless Steel 2205 to Hydrogen Assisted Cracking in REAC Systems
Authors: He Mei , Lippold John , Alexandrov Boian , Penso Jorge
Published: December 2016

Duplex stainless steel (DSS) is one material choice to fabricate the reactor effluent air cooler (REAC) of hydrocracker units in order to improve the performance and service lifetime of these units. Unfortunately, several failures from around the world have been reported in REAC units constructed of DSS, some within five years of service. Based on failure analysis reports, the failures were generally associated with welded joints and were caused by crevice/pitting corrosion and stress corrosion cracking. Given the condition of hydrogen-rich environment, high-pressure process fluid, and service temperature, this type of cracking is most likely a form of hydrogen assisted cracking (HAC). It is highly influenced by phase balance (ferrite/austenite) after welding and welding procedures, with high levels of ferrite in the weld metal or HAZ increasing the susceptibility to HAC. In this study, different weld metal phase balances were prepared by autogenous gas tungsten arc welding (GTAW). The delayed hydrogen cracking test (DHCT) was used to evaluate the effects of the weld phase balance on the susceptibility to HAC in DSS 2205 welds. Using this approach, weld metal ferrite levels on the order of 90 vol% ferrite led to very rapid failure, while reducing the ferrite level to approximately 60 vol% greatly increased resistance to HAC.
A Proposal to Consider Cycle Counting Methods for Fatigue Analysis of Nuclear and Conventional Power Plant Components
Authors: Costa Felippe M. S. , Freire José Luiz F. , Rudolph Jürgen , Maneschy José Eduardo
Published: December 2016

This paper points out some relevant aspects of the simplified elasto-plastic fatigue analysis as addressed in the ASME Code Section III Subsection NB and its application to two structural components that are subjected to a slow or to a fast thermal transient. The structural components considered are a thick-walled pipe and a nozzle-to-vessel junction. For the case of the thick-walled pipe, a closed form analytical solution proposed by Albrecht for pipes subjected transient temperature loading was implemented and its results were compared to coupled thermal and mechanical finite element analyses using a commercial finite element software. The application of the analytical solution allows for an optimization of the time consumed to obtain the stresses that occur across the thickness of the pipe as a function of time, i.e. the membrane plus bending plus peak stress range, Sp. The analytical solution equally allows for the linearization of the stress components actuating along the pipe thickness for all time steps considered within the thermal stress solution. This yields the membrane plus bending stress range, Sn, and allows for a design code conforming plasticity correction by means of Ke factors. In the considered case of the nozzle-to-vessel junction, a finite element solution was used. It was one aim of the study to point out, that under fast transients loading situations the relevant stresses Sp and Sn do not necessarily coincide with each other.

In the ASME Code the alternating stress Sa is a function of the factor Ke and of the range of Sp, with Ke being a function of the range of Sn and of the material properties. Consequently, a non-conservative fatigue analysis may result in the case of performing cycle counting only based on the time history of the critical Sp values and simply assigning the corresponding Sn and Ke values. This paper exemplifies one of those cases and proposes a method to overcome this problem.
Crack Opening for Steam Generator Tubes With Realistic Boundary Conditions
Authors: Reinhardt Wolf , Kizhatil Revi
Published: December 2016

Steam generator tubes are subject to operational loads in the presence of aggressive environmental conditions. This combination of conditions can sometimes result in through-wall cracks. Since the tube material has high ductility, detectable leaks may occur long before the structural integrity of the tubes is challenged. Although operation with confirmed cracks is typically not permitted, the presence of cracks cannot be ruled out when an initiation mechanism is active.

There are two scenarios dealing with through-wall cracks, namely leak-before-break that deals with the integrity of through-wall cracks with leakage below the operational shutdown limit, and an accident pop-through scenario where an accident overload causes a part-through-wall crack to penetrate the wall and leak. Both leak-before break and accident pop-through scenarios involve the calculation of leakage rate through the crack, which in turn needs the opening of the crack under the applied loads to be determined. The opening displacement is affected by the size of the crack and by the stiffness of the tube with its supports. Ignoring the effect of the tube on crack opening can severely overestimate the crack opening. The present paper discusses a method to include the tube stiffness in calculating crack opening with the objective of determining leakage. The method addresses both elastic and plastic conditions at the crack and in the surrounding tube.
Residual Stresses in Thick-Section Electron Beam Welds in RPV Steels
Authors: Vasileiou Anastasia N. , Smith Mike C. , Gandy David , Ferhati Arben , Romac Remi , Paddea Sanjooram
Published: December 2016

Low pressure electron beam welding offers the prospect of large increases in productivity for thick section welds in RPV steels. However, it is important to understand how this welding process affects the structural performance of the completed weld. This paper reviews and presents key results from a programme of weldment manufacture, materials characterisation, residual stress measurements, and finite element modelling of EB welds made in plate of three thicknesses, 30mm, 130mm, and 200mm, and in three steels: SA508 Gr 2, SA508 Gr 3 C1 1, and SA516 Gr 70.
Case Study of the Surface Cracking of Austenite Stainless Steel Weld Overlay Cladding in Hydrogen Environment
Authors: Li Xufeng , Ou Kesheng , Wang Lei , Zheng Jiong , Luo Weijian , Hu Huasheng , Fu Ruwen , Zhu Junjun , Zhu Pengan
Published: December 2016

Austenite stainless steel weld overlay cladding is widely used for the equipments working in pressurized hydrogen environment such as hydrogenation reactors. Surface cracking is a basic failure mode of the weld overlay cladding, and also a quite difficult problem for safety assessment and defect elimination. In this paper, two cases of surface cracking of austenite stainless steel weld overlay cladding are introduced. Firstly, the inspection results and cracking causes are analyzed in detail. Secondly, two kinds of treatment methods for the defects are introduced. Finally, some suggestions for inspection and assessment of surface cracking of weld overlay cladding are proposed.
Research on Phased Array Ultrasonic Technique for Testing Tube to Tube-Sheet Welds of Heat Exchanger
Authors: Guo Weican , Qian Shengjie , Ling Zhangwei , Hou Dongsheng
Published: December 2016

The tube to tube-sheet weld is the main connection structure of heat exchanger. This paper presents the phased array ultrasonic technique for testing the tube to tube-sheet welds of heat exchanger. The optimization analysis of phased array parameters and the simulation on the acoustic field with CIVA software were completed. The mentioned phased array parameters included array elements, array element size, deflection angle, ultrasonic frequency and so on. An ultrasonic testing system was designed and fabricated in accordance with the structure of heat exchange tube and fillet welds position. The ultrasonic C-scan was carried out by the ultrasonic testing system with its circumferential scanning by a mechanical scanning device while the axial electronic linear scanning by the phased array probe. At last, tests on samples with the porosity and incomplete fusion flaws were performed by the ultrasonic testing system. Experimental results showed that the phased array ultrasonic technique could effectively detect the porosity flaws and the incomplete fusion flaws in the tube to tube-sheet welds of heat exchanger.
Load Factor for Evaluating Non-Planar Flaws in Carbon Steel Piping Using Limit Load Methodology
Authors: Hoang Phuong H.
Published: December 2016

Non-planar flaw such as local wall thinning flaw is a major piping degradation in nuclear power plants. Hundreds of piping components are inspected and evaluated for pipe wall loss due to flow accelerated corrosion and microbiological corrosion during a typical scheduled refueling outage. The evaluation is typically based on the original code rules for design and construction, and so often that uniformly thin pipe cross section is conservatively assumed. Code Case N-597-2 of ASME B&PV, Section XI Code provides a simplified methodology for local pipe wall thinning evaluation to meet the construction Code requirements for pressure and moment loading. However, it is desirable to develop a methodology for evaluating non-planar flaws that consistent with the Section XI flaw evaluation methodology for operating plants. From the results of recent studies and experimental data, it is reasonable to suggest that the Section XI, Appendix C net section collapse load approach can be used for non-planar flaws in carbon steel piping with an appropriate load multiplier factor. Local strain at non-planar flaws in carbon steel piping may reach a strain instability prior to net section collapse. As load increase, necking starting at onset strain instability leads to crack initiation, coalescence and fracture. Thus, by limiting local strain to material onset strain instability, a load multiplier factor can be developed for evaluating non-planar flaws in carbon steel piping using limit load methodology. In this paper, onset strain instability, which is material strain at the ultimate stress from available tensile test data, is correlated with the material minimum specified elongation for developing a load factor of non-planar flaws in various carbon steel piping subjected to multiaxial loading.
Complexities of In-Service Failures in Dissimilar Metal Welds Between Grade 91 and Austenitic Stainless Steels
Authors: Siefert John , Parker Jonathan , Totemeier Terry
Published: December 2016

The efficiency of thermal power plants is related to operating steam pressure and temperature. The desire to maximize performance, while minimizing emissions, provides a large incentive to introduce new power generating plants with higher temperature and pressure. Improvements to design can offer important benefits, but, a key enabling technology to greater thermal efficiency is the development and acceptance of engineering materials with superior properties.

Next generation heat recovery steam generators (HRSGs) are expected to require the use of thick-section dissimilar metal welds (DMWs) due a competitive market that is rapidly pushing increases in efficiency (and therefore an increase in steam temperature). There is an increasing concern that the current, “conventional practice” for fabricating DMWs is ill-established and not optimized for applications where the ferritic material is Grade 91 steel. To address the complexity of issues associated with the performance of DMWs, a series of research studies are underway with the Electric Power Research Institute. This paper reviews a number of in-service failures arising from DMWs between Grade 22 and austenitic stainless steels and Grade 91 and austenitic stainless steels.
Assessment of Analysis Methods for Dynamic Loading of Skirt Supported Vessels
Authors: Gjinolli Agron E. , Bremigan Cary D. , Dorgan Jason E.
Published: December 2016

Reciprocating engines and turbines continue to provide fuel efficient, clean and flexible motive power for many gas compression and power generation applications. Compression and/or power generation stations that were originally built in isolated areas are now in or near neighborhoods, requiring greater focus on acoustic performance. New emission regulations now require catalyst systems on most all gas engines. These new requirements have increased the complexity for a modern reciprocating engine exhaust system including both new installations and retrofit. While these engines are durable and flexible, they create many challenges for the exhaust system designer. The exhaust vessels are commonly installed on top of structural steel supports, self-supported directly on the foundation or skid via a shell skirt, (Figure 1).

This paper will discuss the analytical methods used to address these challenges. A combination of static, vibration-pulsation and dynamic structural analysis with specific attention to the seismic analysis of the skirt supported vessels, as well as acoustical design and flow modeling techniques are used to evaluate the design options. The overall objective of the system design will be discussed relative to the typical free standing vertical vessel/stack systems used at many compression and power generation stations.
Shakedown Analysis of Post-Weld Residual Stress in a Pressurizer Surge Nozzle Full-Scale Mockup
Authors: Tran Minh N. , Hill Michael R.
Published: December 2016

Computational weld residual stress analyses are commonly evaluated at room temperature in order to validate against weld residual stress measurements, which are conducted at room temperature. However, in addition to weld residual stress produced in the course of manufacturing, plant components are subject to internal water pressure and elevated temperature during operation. The current work explores the changes in weld residual stress state due to the presence of internal pressure and temperature at operating conditions. This paper is a follow-up to earlier work, which presented a numerical finite element simulation of the weld residual stress in a pressurizer surge nozzle full-scale mockup as a part of a broader program of cooperative work on weld residual stress organized by the U.S. Nuclear Regulatory Commission and the Electric Power Research Institute. The analysis is performed using two different constitutive hardening models (isotropic and nonlinear kinematic). Two main effects on the weld residual stress field result from the application of internal pressure and temperature: one is elastic, and reversible, and the other is plastic, which is irreversible. The results indicate that the majority of the change in plasticity, and hence the change in stress, occurs during the initial increase in internal pressure and temperature. Furthermore, the results demonstrate that the additional stress due to operating conditions is largely due to the thermal expansion between the ferritic steel, stainless steel, and nickel-based alloy weld.
Occlusion effect on compensatory formant production and voice amplitude in response to real-time perturbation
Authors: Mitsuya Takashi , Purcell David W.
Published: December 2016

The importance of auditory feedback for controlling speech articulation has been substantiated by the use of the real-time auditory perturbation paradigm. With this paradigm, speakers receive their own manipulated voice signal in real-time while they produce a simple speech segment. In response, they spontaneously compensate for the manipulation. In the case of vowel formant control, various studies have reported behavioral and neural mechanisms of how auditory feedback is processed for compensatory behavior. However, due to technical limitations such as avoiding an electromagnetic artifact or metal transducers near a scanner, some studies require foam tip insert earphones. These earphones occlude the ear canal, and may cause more energy of the unmanipulated first formant to reach the cochlea through bone conduction and thus confound the effect of formant manipulation. Moreover, amplification of lower frequencies due to occluded ear canals may influence speakers' voice amplitude. The current study examined whether using circumaural headphones and insert earphones would elicit different compensatory speech production when speakers' first formant was manipulated in real-time. The results of the current study showed that different headphones did not elicit different compensatory formant production. Voice amplitude results were varied across different vowels examined; however, voice amplitude tended to decrease with the introduction of F1 perturbation.
Energy pulses reveal possible new state of memory
Authors: Boddy Jessica
Published: December 2016

Transcranial magnetic stimulation brings latent working memories back to direct consciousness.
Bringing legends to life
Authors: McLaughlin Kathleen
Published: December 2016

Geneticist Li Hui believes a DNA database can authenticate mythical figures from before the dawn of China.
Molecular gas in the halo fuels the growth of a massive cluster galaxy at high redshift
Authors: Emonts B. H. C. , Lehnert M. D. , Villar-Martín M. , Norris R. P. , Ekers R. D. , van Moorsel G. A. , Dannerbauer H. , Pentericci L. , Miley G. K. , Allison J. R. , Sadler E. M. , Guillard P. , Carilli C. L. , Mao M. Y. , Röttgering H. J. A. , De Breuck C. , Seymour N. , Gullberg B. , Ceverino D. , Jagannathan P. , Vernet J. , Indermuehle B. T.
Published: December 2016

The massive Spiderweb galaxy is surrounded by molecular gas as it goes through its formation process.