bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Combustion Recession After End-of-Injection at Diesel Engine Conditions
Authors: Jarrahbashi Dorrin , Kim Sayop , Genzale Caroline L.
Published: December 2016

Recent experimental observations show that lifted diesel flames tend to propagate back towards the injector after the end of injection under conventional high-temperature combustion conditions. Earlier studies have referred to this phenomenon as “flashback,” but more recently the term “combustion recession” has been adopted to reflect findings that the process appears dominated by “auto-ignition” reactions upstream of the lifted flame after the end of injection. Since this process is only initiated after the end of injection, it is also closely linked to the end-of-injection entrainment wave and its impact on the transient mixture-chemistry evolution upstream of the lift-off length. A few recent studies have explored the physics of combustion recession with experimental and simplified modeling approaches, but the details of the chemical kinetics and convective-diffusive transport of reactive scalars in this phenomenon are still largely unexplored. There are also uncertainties in the capability of engine computational fluid dynamics (CFD) simulations to accurately capture entrainment wave and combustion recession phenomena.

In this study, highly-resolved numerical simulations have been employed to explore the mixing and combustion of a diesel spray after the end of injection and the influence of modeling choices on the prediction of these phenomena. The simulations are centered on a temperature sweep around the Engine Combustion Network (ECN) Spray-A conditions, from 800–1000 K, where different combustion recession behaviors are observed experimentally. Reacting spray simulations are performed in the open-source CFD software OpenFOAM, using a Reynolds-Averaged Navier-Stokes (RANS) approach with a traditional Lagrangian-Eulerian coupled formulation for two-phase mixture transport. Two reduced chemical kinetics models for n-dodecane by Yao et al. and Cai et al. are used to evaluate the impact of low-temperature chemistry and mechanism formulation on predictions of combustion recession behavior. Observations from the numerical simulations are consistent with recent findings that a two-stage auto-ignition sequence drives the combustion recession process; self-sustained reacting mixtures arise in distinct regions that are spatially separated from the lifted flame. Simulations with two different chemical mechanisms indicate that low-temperature chemistry reactions drive the likelihood for second-stage ignition and combustion recession that in turn strongly influence local entrainment in these mixtures and likelihood of combustion recession.
Numerical Studies of Glow Plug Shield on Natural Gas Ignition Characteristics in a CI Engine
Authors: Pan Kang , Wallace James S.
Published: December 2016

This paper presents a numerical study on fuel injection, ignition and combustion in a direct-injection natural gas (DING) engine with ignition assisted by a shielded glow plug (GP). The shield geometry is investigated by employing different sizes of elliptical shield opening and changing the position of the shield opening. The results simulated by KIVA-3V indicated that fuel ignition and combustion is very sensitive to the relative angle between the fuel injection and the shield opening, and the use of an elliptical opening for the glow plug shield can reduce ignition delay by 0.1∼0.2ms for several specific combinations of the injection angle and shield opening size, compared to a circular shield opening. In addition, the numerical results also revealed that the natural gas ignition and flame propagation will be delayed by lowering a circular shield opening from the fuel jet center plane, due to the blocking effect of the shield to the fuel mixture, and hence it will reduce the DING performance by causing a longer ignition delay.
Analysis of Engine Air Handling Systems for Light-Duty Compression Ignition Engines Using 1-D Cycle Simulation: Achieving High Dilution Levels for Advanced Combustion
Authors: Gowda Kodebyle Raju Nandini , Dempsey Adam , Curran Scott
Published: December 2016

Previous research studies have shown that low temperature combustion (LTC) strategies are capable of achieving very low NOx and soot emissions while maintaining high thermal efficiency. To achieve LTC, there has to be sufficient mixing time between the fuel and air in a dilute, yet overall lean, environment. Dilution with a combination of fresh air and exhaust gas recirculation (EGR) is typically used to achieve longer mixing times and reduce the peak combustion temperatures. However, there are challenges associated with today’s engine air handling systems’ ability to move large combinations of EGR and air simultaneously. As the EGR demand is increased to reduce NOx emissions or retard combustion phasing, the global equivalence ratio tends to increase because of the boosting systems’ limited ability to supply fresh air. In this study, a one-dimensional engine modeling approach was used to analyze the behavior of a production light duty diesel engine equipped with a variable geometry turbocharger and a high-pressure loop EGR system under LTC conditions. The model is used to predict the global equivalence ratio as a function of the EGR level at a variety of operating conditions. The EGR level was varied from 0 to 50% at speeds ranging from 1,500 to 2,500 rpm and loads from 2 to 10 bar brake mean effective pressure. The objective of this study is to evaluate the air handling system’s capability of driving high amounts of EGR and air simultaneously for light duty engines to successfully achieve LTC operation over a large portion of the operating space. The results of the simulations show that at light loads, large amounts of EGR can be used while maintaining globally lean operation. However, as the engine load increases, a globally stoichiometric condition is reached relatively quickly, and high engine loads with greater than 30% EGR and overall lean conditions were achievable.
Numerical Study on Spray and Flame Lift-Off Length of Acetone-Butanol-Ethanol and Diesel Blends in a Constant Volume Chamber
Authors: Zhang Saifei , Xu Zhengxin , Wu Wei , Lee Chia-Fon F.
Published: December 2016

Acetone-butanol-ethanol mixture (ABE) is being studied as an alternative fuel because it not only preserves the advantages of oxygenated fuels, but also lowers the cost of fuel recovery for butanol during fermentation. The previous experimental study on spray and flame lift-off length for diesel with 20% addition of ABE mixture, shows a shorter and narrower spray and a much longer flame lift-off length compared to those of neat diesel, which leads to considerably less soot emission level of ABE20.

In this study, a detailed mechanism capable of predicting the ignition delay for ABE as well as ABE-diesel blends is implemented to the KIVA-3V program to simulate the spray dynamics and lift-off length inside the constant volume chamber. The presented model is able to capture the trends with regard to ignition delay, combustion duration and peak pressure. The overall predictivity for ABE20 is better than that of D100. Spray penetration and the lift-off length for both fuels are simulated and the numerical definition for lift-off length is discussed. It is found that the threshold temperature to define lift-off length can be uniform under different ambient temperatures, but varies with respect to oxygen concentration. The simulations also agree with the measurements in predicting the lift-off length decreases as temperature and oxygen concentration increases. Finally, the simulation sooting tendency is presented to show that, due to the improved spray and combustion process of ABE-diesel blend, the soot emission level is much less than conventional diesel fuel.
Rapidly Pulsed Reductants for Diesel NOx Reduction With Lean NOx Traps: Comparison of Alkanes and Alkenes as the Reducing Agent
Authors: Reihani Amin , Patterson Brent , Hoard John , Fisher Galen B. , Theis Joseph R. , Lambert Christine K. , Smirnov Evgeny , Roemer Dirk
Published: December 2016

Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in order to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air (Diesel NOx aftertreatment by Adsorbed Intermediate Reductants) [1].

There is a vast parameter space that needs to be explored in order to maximize the NOx conversion at high temperatures and flow rates while minimizing the fuel penalty associated with the hydrocarbon injections. Four parameters were identified as important for RPR operation: (1) the flow field and reductant mixing uniformity; (2) the pulsing parameters including the pulse frequency, duty cycle, and rich magnitude; (3) the reductant type; and (4) the catalyst composition, including the type and loading of precious metal, the type and loading of NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. A novel injection and mixer system was designed that allowed for the investigation of previously unexplored areas of high frequency injections up to f = 100Hz.

Under RPR conditions, H2, CO, dodecane, and C2H4 provided approximately 80% NOx conversion at 500°C, but at 600°C the conversions were significantly lower, ranging from 40 to 55%. The NOx conversion with C3H8 was low across the entire temperature range, with a maximum conversion of 25% near 300°C and essentially no conversion at 600°C. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of temperature between 280°C and 630°C. Among the hydrocarbons, this suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.
Development of Design Methods for Piping Systems in a Seismically Base Isolated Nuclear Plant
Authors: Adams Timothy M. , Ahn Eun Woo , Kim Sungjune , Kim Sookyum , Kim Deasoo
Published: December 2016

KEPCO Engineering and Construction is developing a Nuclear Power Plant Design that places the Nuclear Island on a base isolation system while the remaining plant structures are on standard structural foundations. When subjected to seismic (earthquake) loading, this will result in large differential displacements between the nuclear island and the adjacent buildings. Critical piping systems, which must remain functional during and after the seismic event, must withstand the large displacements. This paper summarizes the studies conducted to develop design methods for such piping systems. Also presented are the recommended approaches to be used in the design of such piping systems.
Considerations in the Capacity Uprating of an EOR HRSG
Authors: Aumuller John J. , Lange Carlos F. , Humphries Michael J.
Published: December 2016

In enhanced oil recovery operations, the steaming capacity of a heat recovery steam generating unit is limited by the available energy provided from the gas turbine generator, however, there are a number of other component parameters that limit the thermal and mechanical performance of any specific heat recovery steam generator. These additional parameters reside on both the flue gas side and water / steam side of the heat recovery steam generator.

Repetitive failures of steam generator components are evidence of damage mechanisms that are active during operation. Some of these damage mechanisms are explored to determine the immediate impact in up-rating the steam generators to higher capacity throughput and also, on longer term reliability. A resulting finding of this study examines the efficacy of using P22 low alloy piping in lieu of carbon steel piping to address flow accelerated corrosion.
Redesign of LDPE Secondary Compressor Valves to Better Tolerate Polyethylene Wax Fouling
Authors: Simpson Karl , Sanford Joel , Finnefrock Lavon
Published: December 2016

This paper discusses the redesign of valves in high-pressure reciprocating compressors used in the manufacture of Low Density Polyethylene (LDPE) resin. The compressors have Multi-poppet (MPV) style valves which are affected by LDPE wax fouling. This fouling causes the poppets to stick open leading to gas recirculation (valve leakage) and associated process fluid heating. This heating can cause the compressors to shut down on high discharge temperatures requiring operations personnel to push process gas through the valves to try to clear the waxes, or to have maintenance personnel replace the valves. Poppets sticking due to wax fouling can also result in compressor gas discharge temperatures increasing high enough to cause Ethylene decomposition (Decomp) which can cause the production line to vent to atmosphere. This paper describes analysis and testing to change the valve design from MPV, to Single-poppet (SPV) style valves to reduce the effects of wax fouling.
Validation of a CFD Analysis Model for the Thermal-Hydraulic Response of PWR Steam Generator to a Steam Line Break
Authors: Jo Jong Chull , Min Bok Ki , Jeong Jae Jun
Published: December 2016

This paper presents a validation of a computational fluid dynamics (CFD) analysis method for a numerical simulation of the transient thermal-hydraulic responses of steam generator (SG) secondary side to blowdown following a main steam line break (MSLB) at a pressurized water reactor (PWR).

To do this, the CFD analysis method was applied to simulate the same blowdown situation as in an experimental work which was conducted for a simplified SG blowdown model, and the CFD calculation results were compared with the experimental results.

As the result, both are in reasonably good agreement with each other. Consequently, the present CFD analysis model has been validated to be applicable for numerical simulations of the transient phase change heat transfer and flow situations in PWR SGs during blowdown.
Study on Metallography Test of the Steel SPV490 for Atmospheric Storage Tank After Fire
Authors: Fang Zhou , Hu Weiwei , Liu Deyu , Li Guanghai , Wang Zhe
Published: December 2016

The fire process was simulated by the heat treatment to the Steel SPV490 of atmospheric storage tank, thereby obtaining the metal specimens in different fire temperature, holding time, and cooling modes. And as the temperature increases, the microscopic structure of Steel SPV490 changes under different working conditions, which could be shown in optical microstructure pictures after doing the interception, inlay, polishing, finishing to the specimens. The result shows that, the mechanical properties of the Steel SPV490 for storage tank changes as the temperature rising from the microscopic view. Nodulizing of the cementite in pearlite occurs, and the strength decreases when the high strength steel SPV490 of large atmospheric storage tanks under air cooling condition below 700 °C, however, it equivalents to the normalizing process, as the sorbite occurs in the steel, and the strength increases a bit when the temperature is above 900 °C. The water-cooling of steel SPV490 above 900 °C equivalents to the process of quenching. The occurrence of martensitic substantially increases the strength and the brittleness, and the elongation decreases rapidly.
Influence of Lode Angle on the ASME Local Strain Failure Criterion
Authors: Karpanan Kumarswamy , Thomas William
Published: December 2016

Failure strain at any point on a structure is not a constant but is a function of several factors, such as stress state, strain rate, and temperature. Failure strain predicted from the uniaxial tensile testing cannot be applied to the bi-axial or tri-axial stress state. ASME Sec VIII-Div-2, and −3 codes give methods to predict the failure strain for multi-axial stress state by considering the triaxiality factor, which is defined as the ratio of mean stress to the equivalent stress. Failure strain predicted by the ASME method (based on the Rice-Tracey ductile failure model) is an exponential curve that relates the failure strain to the triaxiality factor. The ASME VIII-3 method also gives procedures to calculate failure strain for various material types: ferritic, stainless steel, nickel alloy, aluminum, etc.

Experimental results of failure strain at various stress states show that the failure strain is not only a function of the triaxiality factor, but also a function of the Lode angle. The Lode angle takes on the value of 1, 0, and −1 for tension, pure shear, and compression stress state, respectively. Experimental data shows that the failure strain is a 3D surface which has an exponential relation with triaxiality and a parabolic relation with the Lode angle. To validate the ASME failure strain prediction, this paper compares experimental failure strain test data from literature with the ASME predictions. The ASME predictions are non-conservative especially for moderately ductile materials such as aluminum and high strength carbon steel. A reduction factor on failure strain for low ductile material is presented using the relation between the R (yield/ultimate) and the stress ratio (shear/tensile stress).

The ASME method does not account for the environmental effects while calculating the failure strain. High pressure, high temperature (HPHT) subsea components designed using ASME VIII-3 code are subjected to various environments in subsea, such as seawater, seawater with cathodic protection (CP) and production fluid (crude oil). Experimental data shows that the Elongation (EL) and/or Reduction in Area (RA) from tensile testing decrease in these environments. Therefore, to account for any environment effect on the failure strain, reduced EL and RA can be used to predict the failure strain.
A Practical Approach to Mitigate the Excessive Vibration of a Piping System Subjected to Flow-Induced Excitation
Authors: Azizian Reza , Torrado Paolo
Published: December 2016

Vibration is a common problem in industrial facilities which may lead to the propagation of undesired high stress levels induced by the deflection of a component as well as the interaction between different metallic components. In a piping system, a long term excessive vibration may cause fatigue and fretting-wear which may result in system failure. In the present work, excessive vibration problems in a piping system were explored in greater detail. Different sources of vibration, as well as proper approaches to evaluate and assess the integrity of the system, were investigated. A case study of a piping system subjected to flow-induced excitation was assessed. This assessment was established based upon both numerical modeling of the system utilizing CAESAR II software and vibration readings of the piping system while operating in an industrial facility. Furthermore, an experimental modal analysis was implemented using ME’scope software to calibrate the numerical model. Theoretical and operational modal analyses were performed in order to adopt proper modifications to mitigate the excessive vibration.
Evaluation of Reactor Cavity Structure for Ex-Vessel Steam Explosion Loading
Authors: Kwon Gunup , Davieau Michael R. , Hoang Phuong , McLean John B. , Hooks Robert W.
Published: December 2016

This paper documents the analytical evaluation of a reactor cavity structure subjected to ex-vessel steam explosion loading. The ex-vessel steam explosion may occur during a severe accident scenario after beyond-design-basis earthquake event when the molten core of the failed vessel begins to drop into a flooded reactor cavity area. This causes an impulse load on the reactor cavity that can impose greater demand on the structural components. The structural integrity and leak-tightness of the reactor cavity structure were evaluated using a detailed finite element analysis model. For selected critical loading cases, local damage in close proximity to the explosion locations was visible in the reactor cavity structure. While localized damage was present, the explosion loading cases did not affect the overall stability of the structure and the strain at the liner location was low enough to prevent any tearing of the liner or leakage.
Investigation of Preparation Processes and Corrosion Resistance of NiCrBSi Coatings Fabricated by Laser-High Frequency Induction Hybrid Cladding
Authors: Lu Shuhua , Ling Xiang , Zhang Jinchun
Published: December 2016

The surface of many key components used in petrochemical industry may be damaged by corrosion, wear and overheat during service. This damage can make a significant impact on the safe and reliable operation process of the device. Low alloy steel is widely used to manufacture pressure vessels and pipes because of the higher strength and good processing properties, but has poor corrosion resistance and wear resistance. Laser cladding is an advanced and effective surface modification technology. It can improve the surface properties of the matrix material at lower cost. But these claddings crack easily due to the high temperature gradient in the laser molten pool and physical properties differences between the cladding material and matrix. This problem has affected the development of laser cladding. Laser-high frequency induction hybrid cladding is a novel technology which combines laser beam heat source and induction power. It can decrease the cracks in the claddings effectively and has been received significant attentions in recent years.

Nickel base alloy powders have good corrosion resistance, wettability and high temperature lubricity. In this research, NiCrBSi composite claddings were fabricated on the surface of low alloy steel by the way of laser-high frequency induction hybrid cladding and coaxial powder feeding. The optimum cladding technology parameters to obtain the cladding layers that with good metallurgical combination, reasonable dilution rate and without cracks and defects were developed by optimizing the processing parameters such as laser power, powder feeding rate, laser scanning speed and induction heating temperature. The hardness distribution, microstructure, element distribution and phase of the cladding layers fabricated by the optimum parameters were systematically investigated by means of micro-hardness tester, optical microscopy (OM). Compared with the untreated material, experiment results show that the micro-hardness from substrate to NiCrBSi cladding layer exhibits step distribution, and the hardness of the NiCrBSi cladding layer is higher than that of the base metal. The microstructure showed good metallurgical bonding between NiCrBSi cladding and substrate had been achieved. In addition, directionally solidified microstructures were deposited. From the top to bottom of the cladding layer, the microstructures are, in order, equiaxed crystal, dendrite crystal, cellular crystal, columnar crystal and plane crystals. The corrosion resistance of the base metal and specimens manufactured by laser-high frequency induction hybrid cladding were evaluated in 3.5% NaCl solution by electrochemical testing. The experimental results demonstrate that the corrosion resistance of the NiCrBSi cladding layer fabricated by laser-high frequency induction hybrid cladding technology is better than the base metal.
Strength and Fatigue Analysis of Tube-Sheet Subjected to Thermal Shock
Authors: Shen Jun , Tang Yanfang , Xu Juncheng , Liu Yinghua
Published: December 2016

A calculation model for a tube-sheet under thermal shock loading with the finite element code ANSYS is established in this paper. A three-dimensional finite element model is established to simulate thermal shock process in order to obtain temperature and stress distributions of the structure. The duration time of the thermal shock is taken as about ten seconds and thermal cycling numbers are more than 1000 times for the whole service life of the structure. In order to capture accurate temperature and stress profile of this structure, thermo-mechanical coupling approach and transient thermal analysis is used. Temperature and stress distribution are obtained under the given thermal boundary conditions at different time points and it is also easy to get the stress amplitude of the other points in this structure between any two time points. According to the numerical results, the stress induced by thermal shock changes with time and its magnitude and amplitude cannot be ignored. Strength and fatigue evaluations are also performed according to ASME VIII-2 to ensure its safety.
Thermo-Mechanical Fatigue Life of Coke Drum Skirt Attachment Designs
Authors: Kagita Gurumurthy , Srinivasan Balaji , Pottem Penchala Sai Krishna , Achary Gudimella G. S. , Sripada Subramanyam V. R.
Published: December 2016

Skirt to bottom head attachments of coke drums experience severe thermo-mechanical cyclic stresses, causing failures due to low cycle fatigue. Accordingly, many skirt attachment designs have evolved over a period of time starting with simple conventional weld build up design, improved weld build up design, integral forged attachment design and others. The objective of this paper is to compare thermo-mechanical fatigue life of three different skirt attachment designs using elastic-plastic fatigue assessment methods of ASME Section VIII, Division 2. A transient thermal analysis model is first developed incorporating appropriate boundary conditions. The time-dependent variable heat transfer coefficients at the inner surface of the coke drum, which change with the operation stages and the levels of oil filling and water quenching, are determined based on the field measured thermocouple temperature data on the outer surface of the coke drum. Sequentially coupled elastic-plastic transient thermo-mechanical stress analyses of coke drum skirt attachments are carried out using both Twice Yield and cycle-by-cycle methods. The effective strain ranges and the fatigue life of three different skirt attachment designs are calculated and compared.
Fatigue Performance of Stainless Steels (304L, 347) in Experiments Simulating NPP Operation With Hold Times
Authors: Karabaki Ertugrul , Twite Marius , Solin Jussi , Herbst Matthias , Mann Jonathan , Burke M. Grace
Published: December 2016

Advanced Fatigue Methodologies (AdFaM), a joint project of European research laboratories, vendors and plant operators, was launched in 2014 to build on the results from recent laboratory studies of fatigue behavior of austenitic stainless steels under NPP-relevant conditions that showed improved lifetimes compared to the best fit to test data presented in NUREG/CR-6909, and to further investigate transferability between specimen test results and the fatigue behavior of NPP components during plant operation.

In particular, AdFaM has focused on an empirical and mechanistic investigation of the effects of hold times on fatigue life. A small number of previous test results suggest an increase in fatigue life for stabilized grades of austenitic stainless steel when hold times (ranging from several hours to days) are introduced into a test between periods of strain-controlled cyclic loading. Tests incorporating hold times may be more representative of material behavior in NPPs, where temperature transients due to start-ups, shutdowns and major power changes may be separated by long periods of steady state operation.

Under AdFaM, fatigue endurance tests incorporating hold times have been completed on stabilized and non-stabilized stainless steel grades (Types 304L and 347) and the mechanisms responsible for the observed variations in fatigue life have been investigated using a range of microscopy techniques.

Results confirm a significant extension of fatigue life due to hold times in both stabilized and non-stabilized grades. Life extension appears to be linked to hold hardening observed in cyclic behavior, and this link has been investigated through microstructural characterization of fatigue specimens examined before and after holding at elevated temperature.

This project helps to improve the understanding of transferability of results from small specimen tests (without hold times) to analysis of NPP components and provides insights that will contribute towards continuing development of fatigue design curves and analysis methods in Design Codes such as ASME Code Section III and KTA 3201/3211.

The AdFaM project is now complete. The valuable results and insights gained from this work demonstrate the significant benefits of collaborative research between various industrial and academic partners in the area of fatigue of NPP materials.
Equivalent Explosion Source for PVB Blast Wave Infiltration
Authors: Geng Jihui , Thomas Kelly
Published: December 2016

Pressure vessel burst (PVB) explosions are credible explosion hazards at a number of chemical processing and petroleum refining facilities. PVBs can present both blast and fragment hazards. Blast prediction methods specific to spherical PVBs were first developed in the 1970s and revised blast curves were subsequently published. The directional effects from non-spherical PVBs were recently investigated by the authors, resulting in correlations for blast overpressure and impulse for a range of vessel geometries and burst conditions. The existing blast charts coupled with these correlations provide a well-defined blast prediction method for PVBs. When a PVB blast wave propagates through an enclosure opening (e.g., window or door), the result is an infiltrated blast wave which will propagate downstream into the enclosure. This paper addresses the infiltration of a PVB blast wave through an opening on a wall. The properties of an infiltrated blast wave depend primarily on the incident blast wave peak pressure, positive phase duration and the opening size. The purpose of the work described in this paper is to introduce an equivalent explosion source, characterized by these three parameters, so that the infiltrated PVB blast loads can be evaluated based on the equivalent source and existing blast curves.
Statistical Methods and Database Splitting for HCF Data Analysis
Authors: Blatman Géraud , Le Roux Jean-Christophe , Wallin Kim , Solin Jussi , Métais Thomas , Karabaki Ertugrul , Mayinger Wolfgang
Published: December 2016

Fatigue curves are receiving nowadays an increased level of attention in the wake of experimental campaigns showing that the original ASME III mean air curve, also known as the Langer curve [1], does not represent accurately part of the recently obtained laboratory data.

EDF, VTT and E.ON have been working towards a relevant fatigue assessment strategy. The three organizations recently exchanged HCF databases, providing a common benchmark to test and compare the various analysis methods. Following the 2014 PVP paper [2], several statistical approaches are being investigated. A special focus is given to methods able to properly account for run-out data points, which do not have the same statistical significance as failed data points.

Besides, it has to be noted that only a limited number of material grades are used in NPP primary loop components and in each case, the material batches are identified and specified in detail. Therefore, a more accurate and relevant fatigue assessment might be obtained by splitting large datasets that generally mix various testing conditions and material grades. A comparison is made between a “mixed” approach and a “separated” one, in which the fatigue assessment is performed successively for two or more subsets, e.g. associated with two testing temperature ranges and/or steel grades. Both “mixed” and “separated” strategies are applied to the EDF and the E.ON databases containing fatigue data in different temperatures for non-stabilized and stabilized austenitic stainless steels. The resulting data scatters are compared and the significance of these statistical approaches to fatigue assessment is discussed.
Development of a Quick and Easy-to-Install Strain Measurement Tool for Both Bending and Torsional Piping Stress Assessment
Authors: Takahama Tsunemichi , Nishimura Kazuma , Ninomiya Seiichiro , Matsumoto Yoshihiro , Harada Yutaka
Published: December 2016

To assess the stresses on small-bore piping, we have developed a new tool that can be easily installed on a piping surface without adhesive bonding and that measures strains on piping quickly and accurately. This tool, which we call a “strain gauge holder,” is patented in Japan.

As the tool can contain four strain gauge rosettes, with each rosette comprising three elements, the longitudinal strains and sheer strains can be measured synchronously at any four points precisely 90 degrees apart, with one point in each quadrant.

By mockup testing, we confirmed that the measured bending and torsional strains by the holder were almost equivalent to the measured strains by the bonded gauges with adhesive, and that the holder made it possible to synchronously measure all of the strains resulting from the moment of force acting in three axes on the piping by measuring the bending and torsional strains in each quadrant.

The strain gauge holder is expected to significantly reduce the pre- and post-working time required for strain measurement and stress assessment of piping in real plants.
Use of the Extended Finite Element Method in the Assessment of Delayed Hydride Cracking
Authors: Booth Martin , Martin Michael
Published: December 2016

Zirconium alloys, as used in water-cooled nuclear reactors, are susceptible to a time-dependent failure mechanism known as Delayed Hydride Cracking, or DHC. Corrosion of zirconium alloy in the presence of water generates hydrogen that subsequently diffuses through the metallic structure in response to concentration, temperature and hydrostatic stress gradients. As such, regions of increased hydrogen concentration develop at stress concentrating features, leading to zirconium hydride precipitation. Regions containing zirconium hydride are brittle and prone to failure if plant transient loads are sufficient.

This paper demonstrates the application of the Extended Finite Element Method, or XFEM, to the assessment of the DHC susceptibility of stress concentrating features, typical of those considered in the structural integrity assessment of heavy water pressure tube reactors. The method enables the calculation of a DHC threshold load. This paper builds on the process-zone approach that is currently used to provide the industry-standard DHC assessment of zirconium alloy pressure tubes and also recent developments that have extended the application of the process-zone approach to arbitrary geometries by the use of finite element cohesive-zone analysis. In the standard cohesive-zone approach, regions of cohesive elements are situated in discrete locations where the formation of zirconium hydride is anticipated. In contrast, the use of XFEM based cohesive formulations removes the requirement to define cohesive zones a priori, thereby allowing the assessment of geometries in which the location of hydride material is not known.
Dimensional Accommodation of Bolt Coating and its Impact on Bolt/Thread Loading Capability
Authors: Cheta Ayman , Bett B. J. (John)
Published: December 2016

Coated bolting has been widely used on flanged joints of pressure vessels and piping whenever there is a potential for atmospheric corrosion. The applied bolt coating has to be dimensionally accommodated, typically by over tapping the nut or less frequently, under sizing the bolt threads. A recently published technical paper by MacMoy, Ian [7], alleged that this practice is not in compliance with relevant industry standards and potentially compromises the sealing integrity of the flange joint. MacMoy’s paper recommended that any coating that requires over tapping in order to apply a coating’s optimal thickness should be avoided.

In this paper, the authors investigated relevant industry practices, and performed proof testing of some sample bolt sizes. The outcome of this investigation and the details and results of the proof-testing are shared in this paper.
An Approach to Modification of Compact Tension J-R Curves for Analysis of Surface Cracked Pipe Stability
Authors: Olson Richard
Published: December 2016

It is well known that J-R curves from C(T) specimens do not have the correct constraint for surface cracked (SC) pipes. More appropriately, fracture toughness for surface cracked pipes is better characterized by two-parameter models where toughness is not a single value like J, but rather is a curve that defines a critical locus of fracture toughness and constraint values. Unfortunately, for the vast majority of situations, toughness property data for pipe fracture analyses using elastic-plastic fracture mechanics (EPFM) J-estimation scheme techniques to assess the load carrying capacity of the cracked pipe section, consist only of C(T) specimen J-R curves. The alternatives, when analyzing a surface crack, are to simply use the C(T) data and live with the consequences or else perform the analysis using some sort of “correction” applied to the C(T) specimen data to get better predictions of surface crack stability.

This paper examines the feasibility of using a correction to a C(T) specimen J-R curve to yield better predictions of the load carrying capacity of surface cracked pipe. The analyses discussed herein are constrained by: a) The availability and limitations of analytical models of the relevant phenomenon, and b) The availability of experimental pipe fracture data to test hypotheses about the form of a “correction”. Within these constraints, an initial estimate of a “correction” has been developed and is tested against some surface crack pipe experimental data.
License Renewal Experience in the U.S.: Continue to Seek Long Term Operation or Shutdown?
Authors: Young Garry G.
Published: December 2016

As of January 2016, there were 99 operating nuclear units in the U.S. and the NRC had renewed the operating licenses for 81 of those nuclear units allowing for up to 60 years of safe operation (83 renewed licenses had been issued, but 2 of those units are now shutdown). In addition, the NRC has license renewal applications under review for 11 more units and 5 units have announced plans to submit applications in the next few years. This brings the total of renewed licenses and plans for renewal to almost 100% of the 99 operating units in the U.S. At the end of 2015, there were about 40 nuclear units that had operated for more than 40 years and most of those units are eligible to seek a second license renewal for up to 80 years of operation. [1]

Unfortunately, in the past few years, 5 nuclear units have been prematurely shutdown and 3 additional units with licenses to operate for 60 years are scheduled to be prematurely shutdown between 2016 and 2019 for economic reasons. However, the majority of the nuclear plant owners are keeping the option open for long term operation beyond 60 years. NRC and the U.S. nuclear industry have made significant progress in preparing the way for a second round of license renewal applications. For example, the NRC published draft regulatory guidance on the second (or subsequent) license renewal process in December 2015. This paper presents the status of the efforts underway for possible applications for second license renewals for up to 80 years of operation and the issues that may result in additional premature plant shutdowns in the U.S.
Inner Pressure/Bending Creep Test on Circumferentially Welded Large Diameter Pipe of Grade 91 Steel: Creep Damage Mechanism and Applicability of NDE
Authors: Nishinoiri Satoshi , Takahashi Yukio , Fukutomi Hiroyuki , Yaguchi Masatsugu
Published: December 2016

In this study, an inner pressure/bending creep test on a circumferentially welded large diameter 9Cr steel pipe was conducted at a temperature of 650°C to investigate the creep damage mechanism and applicability of nondestructive evaluation techniques to the detection of creep damage. The test was interrupted before steam leakage based on a change in axial strain at the surface of the welded joint. Surface cracks were observed at the lower part of the specimen along the circumferentially welded joint where axial tensile stress was applied. As a result of phased array ultrasonic inspection, indications of internal defects were first detected along welded joints where the failure life ratio was 54% with the range of indication increasing with test time. The indications of internal defects were in good agreement with observations of sectional views in welded joints.
Effect of Bend Angle on Plastic Limit Loads of Pipe Bends Under In-Plane Bending Moment
Authors: Li Shunjie , Zhou Changyu , Li Jian , Miao Xinting
Published: December 2016

The effect of bend angle on plastic limit loads of pipe bends (elbows) under in-plane opening and closing bending moment is presented using three-dimensional large strain nonlinear finite element analyses. The results show that the presence of ovality significantly leads to the stress concentration in the middle cross section, which is the critical section of pipe bends. Meanwhile the state of stress concentration is also associated with the loading modes including the in-plane opening bending moment and the closing bending moment. Then plastic limit loads of pipe bends are further studied. It is found that plastic limit loads are decreasing with the increase of bend angles. Especially the variation of plastic limit loads of small angle pipe bends (bend angle from the 0 degree to 90 degree) is larger than that of large angle pipe bends (bend angle greater than 90 degree). Based on the finite element results, the present plastic limit load solutions are not fit for the large angle pipe bends (bend angle greater than 90 degree).
Residual Stress Mapping for an Excavate and Weld Repair Mockup
Authors: Olson Mitchell D. , DeWald Adrian T. , Hill Michael R. , McCracken Steven L.
Published: December 2016

This paper describes a sequence of residual stress measurements made to determine a two-dimensional map of biaxial residual stress (weld direction and transverse to the weld direction) in a mockup with a partial arc excavation and weld repair (EWR), as well as three additional maps of one component of residual stress. The mockup joins two dissimilar metal plates (SA-508 low alloy steel and Type 316L stainless steel) with a nickel alloy weld metal (Alloy 82/182). A partial groove is then excavated and filled in with SCC resistant Alloy 52M weld metal. The mockup was fabricated to investigate the effectiveness of the EWR mitigation methodology being investigated through the development of ASME Code Case N-847 to address stress corrosion cracking problems in reactor coolant system butt welds. The biaxial stress map is determined using a newly developed technique called primary slice removal (PSR) mapping, which uses both contour method and slitting measurements. In this case, the technique requires measuring the longitudinal stress along a plane and the long transverse stress remaining in a slice removed adjacent to that plane. This paper includes descriptions of the experiments and data analysis. The measured residual stresses follow expected trends and compare favorably to the results of computational weld residual stress modeling.
Assessing the Condition and Estimating the Remaining Lives of Pressure Components in a Methanol Plant Reformer: Part 1 — NDE
Authors: Shannon Brian E. , Jaske Carl E. , Miranda Gustavo
Published: December 2016

Statoil Tjelbergodden operates a 2,400 ton/day methanol plant in Norway. In order to assess the condition and reliability of high temperature components within the reformer, a series of advanced non-destructive examination (NDE) technologies were applied to radiant catalyst tubes, outlet pigtails, and outlet collection headers. The inspection techniques were selected and developed to provide data that could easily be used in the engineering assessment of the high-temperature components. Special focus was given to detecting and quantifying high-temperature creep damage. This paper describes the NDE techniques that were employed and provides examples of typical data obtained by using the techniques. Catalyst tubes were inspected using the H SCAN® (Figure 1) multiple sensor technology. This technique utilizes two types of ultrasonic sensors, eddy current sensors, laser measurements, and elevation location sensors in scanning each catalyst tube. The H SCAN® P-CAT™ (Figure 2) technique is applied to outlet pigtails, while the H SCAN® H-CAT™ (Figure 3) technique is applied to outlet headers.
Application of the Modified Ritchie–Knott–Rice Criterion to Predict Fracture of Miniaturized Charpy Type SE(B) Specimens From Full Sized Specimens
Authors: Yamaguchi Teruhiro , Higashino Yuma , Meshii Toshiyuki
Published: December 2016

This paper introduces our experience of using miniaturized Charpy type SE(B) specimen in obtaining fracture toughness Jc of a material in the ductile to brittle transition temperature (DBTT) region. 0.55% carbon steel JIS S55C, whose tensile to yield stress ratio σTS/σYS was equal to 1.8 was chosen as a material to simulate a degraded (embrittled) material in the DBTT region.

Focus was placed on whether the modified Ritchie–Knott–Rice (RKR) failure criterion which predicts the onset of cleavage fracture when the crack opening stress measured at 4 times the crack-tip opening displacement σ22d exceeds this σ22c can be applied to miniaturized specimen that does not meet the ASTM E1921 requirement of M = (W-a)σYS/Jc ≥ 30. In concrete, the points 1) whether it could predict whether cleavage fracture will occur or not and 2) whether the σ22c in the case cleavage occurs is identical with that of full sized specimens, were focused. Charpy type SE(B) specimens of Width W × thickness B of 2 × 2 mm, 3 × 3 mm and 10 × 10 mm, whose M were predicted to be smaller than 30, were chosen as miniaturized specimens and 25 × 25 mm were chosen as full sized specimen. Results showed that the modified RKR criterion could appropriately predict cleavage fracture naturally for 25 × 25 mm specimens and 10 × 10 mm specimens, though M < 30 for this type specimen. The modified RKR criterion could also predict that cleavage fracture will not occur for 2 × 2 mm specimens. σ22c obtained from 25 × 25 and 10 × 10 mm specimens showed small difference, indicating that Jc obtained from 10 × 10 mm specimens can be used to transfer Jc obtained by 25 × 25 mm specimens.
Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Stoichiometric CH4/O2/N2-Mixtures and CH4/O2-Mixtures in Long Pipes
Authors: Schildberg Hans-Peter
Published: December 2016

In the recent past (PVP2013-97677, PVP2014-28197, PVP2015-45286) we had started to determine the static equivalent pressures pstat of the eight detonative pressure scenarios in long and short pipes for different detonable gas mixtures. The pstat-values are of vital importance for process design: by assigning static equivalent pressures to the highly dynamic detonative pressure peaks it is possible to apply the established pressure vessel guidelines, which can only cope with static loads, for the design of detonation pressure resistant pipes. One important finding was that the ratio R between pstat at the location where transition from deflagration to detonation occurs and pstat in the region of the stable detonation strongly depends on the reactivity of the gas mixture. In this paper we present experimental data showing the variation of R over the entire explosive range of Methane/O2/N2 mixtures. Qualitatively, the results should be representative for all other combustible/O2/N2-mixtures. Furthermore, recommendations for estimating pstat values of short pipe scenarios on basis of the long pipe scenarios are given.