bluuebunny/crossref_metadata_2025 huggingface dataset:
Large Engine Aftertreatment in a Pre-Turbine Position: A Path to Compact and Cost-Effective Emissions Reduction
Authors: Downey Markus , Bruestle Claus , Tomazic Dean , Subramaniam Mark , Hayes Christopher
Published: January 2011

With the impending implementation of the Tier 4 emissions standards in the non-road and locomotive sectors, exhaust gas aftertreatment systems will be needed on applications that previously did not require it. Based on the fact that the displacement of these engines is very large, the aftertreatment systems will also be relatively large, heavy and expensive. Additionally, even in these large engine applications, packaging space and systems cost is at a premium. Placing a robust metal aftertreatment system up-stream of the turbo-charger offers an elegant solution to these issues. The higher temperatures and faster temperature rises before the turbine yield faster light-off and better emissions performance. The higher gas density allows the total size of the aftertreatment system in the pre-turbine position to be substantially smaller for a given conversion efficiency, leading to a remarkable packaging and cost benefit of up to 64%. Additionally, by placing the flow-restriction of an aftertreatment system upstream of the turbine, a fuel consumption benefit in the pre-turbine position can be realized as pumping losses of the engine are reduced. The largely steady-state operation of these large engines negates the heat sink effect of the pre-turbine catalytic converters in transient operating conditions. This paper will investigate the benefits of placing an oxidation catalytic converter and partial-flow particulate filter up-stream of the turbo-charger on the fuel consumption of a stationary engine in the 30–35L class by simulation with GT-Power. Different locations for the aftertreatment package as well as optimized sizing for the different locations are investigated to identify the optimum solution for the engine. In addition to the fuel consumption benefits, the cost and weight advantage of the smaller pre-turbine system is emphasized. This view of both the technical and commercial side of the applications, demonstrates a clear advantage for the pre-turbine arrangement of the metal emissions reduction components on large bore engines.
Extracting Cylinder Individual Combustion Data From a High Precision Torque Sensor
Authors: Aulin Hans , Tunestal Per , Johansson Thomas , Johansson Bengt
Published: January 2011

A high precision torque sensor is used for extracting combustion timing information from cylinder individual pressure estimates constructed from the torque measurements. A combination of physics-based and data driven modeling is used where the physical part of the model is based on equations describing contributions of inertial and gas forces while the flexing of the crankshaft, which has rather complex dynamics, is modeled using the data driven approach. The first part of the study shows the derivation of the models and how well the torque at the sensor position can be estimated from the pressures in the four cylinders. The second part demonstrates how it is possible to reconstruct cylinder individual torque and pressure by inverting the pressure to torque model. Going from measured torque to pressure in each cylinder is not trivial since the inverted model is ill conditioned around top dead centre which causes large errors where the precision is the most needed. A parameterized combustion model is therefore introduced to improve the signal to noise ratio in the estimated parameters. The proposed method for detecting combustion demonstrated good results with a coefficient of determination of 0.95 against “true” combustion phasing.
Comparison of Propane and Methane Performance and Emissions in a Turbocharged Direct Injection Dual Fuel Engine
Authors: Gibson C. M. , Polk A. C. , Shoemaker N. T. , Srinivasan K. K. , Krishnan S. R.
Published: January 2011

With increasingly restrictive NOx and PM emissions standards, the recent discovery of new natural gas reserves, and the possibility of producing propane efficiently from biomass sources, dual fueling strategies have become more attractive. This paper presents experimental results from dual-fueling a four-cylinder turbocharged DI diesel engine with propane or methane (a natural gas surrogate) as the primary fuel and diesel as the ignition source. Experiments were performed with the stock ECU at a constant speed of 1800 rev/min, and a wide range of BMEPs (2.7 to 11.6 bar) and percent energy substitutions (PES) of C3H8 and CH4. Brake thermal efficiencies (BTE) and emissions (NOx, smoke, THC, CO, and CO2) were measured. Maximum PES levels of about 80–95 percent with CH4 and 40–92 percent with C3H8 were achieved. Maximum PES was limited by poor combustion efficiencies and engine misfire at low loads for both C3H8 and CH4, and the onset of knock above 9 bar BMEP for C3H8. While dual fueling BTEs were lower than straight diesel BTEs at low loads, they approached diesel BTE values at high loads. With dual fueling, NOx and smoke reductions (from diesel values) were as high as 66–68 percent and 97 percent, respectively, but CO and THC emissions were significantly higher with increasing PES at all engine loads.
Evaluation of Diesel Low Temperature Combustion Fuel-Injection Strategies at Different Engine Loads
Authors: Asad Usman , Zheng Ming
Published: January 2011

High hydrocarbon levels in the exhaust, increased cycle-to-cycle variation and reduced energy-efficiency are typical problems associated with diesel LTC operation. To overcome these challenges, three different fuel injection strategies (late single-injection, early multiple-injections and split-injections) have been investigated on a modified single cylinder common-rail diesel engine. The effects of EGR, boost and injection pressure on the emissions and combustion efficiency have been analyzed. The effect of heavy EGR has been quantified in terms of a trade-off between the combustion phasing and the combustion efficiency. To minimize fuel condensation and wall-wetting with early injections, a criterion for selecting the earliest timing for injection during the compression stroke has also been evaluated. This research is concluded with the formulation of a load management strategy to enable energy-efficient diesel LTC up to 10 bar IMEP.
Effect of Creep on the Residual Stresses in Tube-to-Tubesheet Joints
Authors: Laghzale Nor Eddine , Bouzid Abdel-Hakim
Published: January 2011

Steam generators are the subject of major concern in nuclear power plant safety. Within these generators, in addition to the structural integrity, the gross tightness barrier, which separates the primary and secondary circuits, is primarily ensured by the presence of a residual contact pressure at the tube-to-tubesheet joint interface. Any leakage is unacceptable, and its consequences are very heavy in terms of the human and environmental safety as well as maintenance cost. Some studies have been conducted to understand the main reasons for such a failure. However, no analytical model able to predict the attenuation of the residual contact pressure under the effect of material creep relaxation behavior. The development of a simple analytical model able to predict the change of the residual contact pressure as a function of time is laid out in this paper. The results from the analytical model are checked and compared with those of finite elements.
TRISO Particle and Beryllium Pebble Thermo-Mechanical Response in a Fusion/Fission Engine for Incineration of Weapons Grade Plutonium
Authors: Caro M. , DeMange P. , Marian J. , Caro A.
Published: January 2011

Among the laser inertial fusion-fission energy (LIFE) engine concepts being considered at Lawrence Livermore National Laboratory (LLNL), weapons-grade plutonium (WGPu) LIFE is of particular interest because it is designed to burn excess WGPu material and achieve over 99% fraction of initial metal atoms (FIMAs). At the center of the LIFE concept lies a point source of 14MeV neutrons produced by inertial-confinement fusion (ICF) which drives a sub-critical fuel blanket located behind a neutron multiplier. Current design envisions tristructural isotropic (TRISO) particles embedded in a graphite matrix as fuel and Be as multiplier, both in pebble bed form and flowing in Flibe molten salt coolant. In previous work, neutron lifetime modeling and design of Be pebbles was discussed [10]. Constitutive equations were derived and a design criteria were developed for spherical Be pebbles on the basis of their thermo-mechanical behaviour under continued neutron exposure in the neutron multiplier for the LIFE engine. Utilizing the available material property data, Be pebbles lifetime could be estimated to be a minimum of 6 years. Here, we investigate the thermo-mechanical response of TRISO particles used for incineration of WUPu under LIFE operating conditions of high temperature and high neutron fast fluence. To this purpose, we make use of the thermo-mechanical fuel performance code HUPPCO, which is currently under development. The model accounts for spatial and time dependence of the material elastic properties, temperature, and irradiation swelling and creep mechanisms. Preliminary results show that the lifetime of WGPu TRISO particles is affected by changes in the fuel materials properties in time. At high fuel burnup, retention of fission products relies on the SiC containment boundary behavior as a minute pressure vessel. The discussion underlines the need to develop high-fidelity models of the performance of these new fuel designs, especially in the absence of a fast neutron source to test these fuels under relevant conditions.
Predictions of Creep Crack Initiation Periods
Authors: Davies C. M. , Webster G. A. , Nikbin K. M.
Published: January 2011

Several procedures are available for estimating creep crack initiation (CCI) time periods prior to the onset of creep crack extension from an existing defect in high temperature components. The applicability of a procedure depends on the required material’s data availability. Various methods are described including methods based on the creep fracture mechanics term C*, the crack opening displacement concept and the sigma-d approach. These procedures are applied to, and compared for, an austenitic and ferritic steel of relevance to the electric power generation industry. It is shown that reliable and conservative predictions can be obtained with all methods.
Underwater Impact of Composite Structures
Authors: Owens A. C. , Didoszak J. M. , Kwon A. S. , Kwon Y. W.
Published: January 2011

Fiber reinforced polymer composite structures have very comparable mass densities to that of water. As a result, the effect of the Fluid-Structure-Interaction (FSI) is much greater for those composite structures than for conventional metallic structures. As a result, this study investigates the effects of FSI on composite structures. A series of underwater impact testing has been conducted to understand the dynamic responses of composite structures coupled with the FSI effects. Both air-backed and water-backed underwater impacts are considered and their behaviors are compared to the dry impact test results in order to determine the FSI effects. Furthermore, multiphysics-based computational analyses have been undertaken so as to better understand and interpret the experimental results. The results of this study will provide knowledge necessary to apply composite materials to underwater structural applications.
Parametric Study on the Fluid Elastic Instability Factor of the Fuel Rod for a PWR Plant
Authors: Kim Hyeong Koo , Jeon Sang Youn , Lee Kyou Seok , Kim Jeong Ha , Lee Sang Jong
Published: January 2011

The main objective of this study is to estimate the effects of some considerable fuel design parameters on the fluid elastic instability behavior of the fuel rod. For the estimation, 6 fuel design parameters which seem to have direct relation with fluid elastic instability behavior of the fuel rod have been selected and examined using the PLUS7 fuel rod for OPR1000 PWR plants in Korea. Those are fuel rod creep-down, spacer grid stiffness, spacer grid spring relaxation, inactive spacer grid spring, intermediate flow mixing grid effect and fuel rod damping. As a result, the fluid elastic instability factors are insensitive with spacer grid stiffness, relaxation and intermediate flow mixing grid effect, but the other parameters need to be controlled and evaluated appropriately to maintain stability with proper margins.
Non-Linear Creep-Buckling Analysis: An Approach Based on WRC-443 for Development of Allowable Compressive Stresses in Coke Drums
Authors: Panwala M. Sohel M. , Mehta S. L.
Published: January 2011

Coke Drums are critical equipment in refineries due to variable temperature and pressure. The temperature is also very high and coke drums works in the creep range for some duration of one full cycle. In the present study, a coke drum is subjected to pressure–temperature reversal with each cycle of 48 hours duration. Temperature and pressure varies from 65 to 495 °C and 1.72 to 4.62 bar, respectively. Design temperature of 510 °C and total Operating Weight of coke drum is 2500 tons. The skirt is to be check against the operating weight, operating pressure & wind load/earthquake load at high temperature which causes the compressive stresses in skirt. The phenomenon of creep along with buckling plays a very crucial role in failure of skirt of coke drums. In addition to this, the skirt is provided with slots at specific pitch all around circumference to induce flexibility for fatigue which weakens the skirt for compressive loading. The material of construction is 1.25Cr-0.5Mo. The temperature limit of 1.25Cr-0.5Mo is 482 °C as per external pressure chart & Appendix-3 of ASME Section II, Part D. Design temperature of coke drum is 510 °C & as design temperature is exceeding the temperature limit, allowable compressive stress from ASME Section II, Part D, Subpart 3 can not be used for design. Thus, an allowable compressive stress for 1 Hr and 100,000 Hr has been developed using Non-linear creep-buckling analysis with WRC-443 to check the skirt against induced compressive stresses. The isochronous curve including accumulated creep strain has been developed for 1 Hr & 100,000 Hr using API 579-1/ASME FFS-1 2007. Non-linear creep buckling analysis at 1 Hr & 100,000 Hr has been carried out in ANSYS using isochronous stress-strain curve as material properties. An induced stress in skirt obtained from analysis has been used in WRC-443 for calculation allowable compressive stress in skirt. An allowable compressive stress works out to be 227.8 MPa & 86.8 MPa at 1 Hr and 100,000 Hr, respectively.
A Hierarchical Finite Element Framework for the Assessment of Pressure Vessels to the ASME III Code
Authors: Martin Michael , Rawson Lindsay , Rice David
Published: January 2011

Advances in the design of nuclear power plant pressure vessels require parallel development of associated numerical assessment methods to ensure that the opportunity to optimise plant safety, availability and cost are realised. In the UK, such pressure vessels are generally assessed against Section III, Subsection NB of the ASME Boiler and Pressure Vessel Code. The design by analysis (DBA) concept embedded in ASME III provides a set of design limits that, if achieved, provide assurance against possible pressure vessel failure modes such as ductile burst and ratcheting. The methodology on which DBA is based pre-dates the routine use of FE analysis and as a result can be difficult to apply to the assessment of complex 3D FE stress results. Generally, these traditional methods rely on through-wall stress classification line and stress linearisation techniques, the application of which can be subjective in certain circumstances. This paper describes a hierarchical framework for the assessment of pressure vessels to the ASME III code primary and secondary stress limits using a range of techniques commensurate with 3D FE stress analysis. FE based limit load analysis is used to assess against plastic collapse, in conjunction with automated FE direct shakedown techniques and strain based fatigue post-processing to assess the structural response to complex thermo-mechanical cyclic loading. This approach enables the analyst to obtain expediently the shakedown response and fatigue life of the structure. A demonstration of the hierarchical assessment framework and comparison to a traditional linearisation based assessment is presented in this paper for an example that is representative of nuclear power plant.
Fitness-for-Service of Longitudinal Seam Welds
Authors: Agan Dwight D. , Cohn Marvin J. , Vaillancourt Henry D.
Published: January 2011

A high energy piping (HEP) asset integrity management program is important for the safety of power plant personnel and reliability of the generating units. Hot reheat (HRH) longitudinal seam weld failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The HRH piping system is one of the most critical HEP systems. Since high temperature creep is a typical failure mechanism for longitudinal seam welds, the probability of failure increases with unit operating hours. This paper concludes that some seam welded spools in this specific HRH piping system are more likely to fail earlier than other spools, depending on their actual wall thicknesses and operating temperatures. In this case study, the HRH piping system has operated over 200,000 hours and experienced about 400 starts since commercial operation. There are two separate HRH lines, Lines A and B, for this piping system. The 36-inch OD pipe has a specified minimum wall thickness (MWT) of 1.984 inches. Pipe wall thicknesses were measured in 57 spools. The measured spool MWT values varied from 1.981 to 2.122 inches. On average, Line A operated about 8°F higher than Line B. A comparative risk assessment was performed using the estimated average temperatures and pressures throughout the life of this HRH piping system. Data associated with the reported failures or near failures of seam welded Grade 22 piping systems were plotted as log σHoop versus the Larson Miller Parameter (LMP). The range of log σHoop and LMP values for this unique piping system was also plotted, based on the average operating pressure and the range in the average operating temperatures and the measured spool MWT values. The Line A (with a higher average operating temperature) seamed spool having the lowest measured MWT fell slightly above the threshold line of reported seam weld pipe failures. The Line B (with a lower average operating temperature) seamed spool having the lowest MWT is about 10 operating years from reaching the threshold of reported seam weld pipe failures. The Line A seamed spool having the highest measured MWT is about 8 operating years from reaching the threshold of reported seam weld pipe failures. The Line B seamed spool having the highest measured MWT is more than 18 operating years from reaching the threshold of historical seam weld pipe failures.
Proposal for Inclusion of Torsion in Section XI Flaw Evaluation Procedures for Pipes Containing Surface Crack-Like Flaws
Authors: Bezensek Bostjan , Li Yinsheng , Hasegawa Kunio , Hoang Phuong H.
Published: January 2011

Piping installations in power plant may experience combined bending–torsion loads in the presence of crack-like flaws. ASME Boiler and Pressure Vessel code Section XI non-mandatory Appendix C provides flaw evaluation procedures for pipes with flaws under fully plastic fracture. These are currently limited to straight pipes under pressure and bending loads and no provision is made for torsion loading. The Working Group on Pipe Flaw Evaluation is developing guidance for combining the torsion load within the existing solutions provided in the Appendix C for bending loading on a straight pipe. This paper reports on the finite element analyses performed on the straight pipe containing surface crack-like flaw with pipe diameters ranging from 4″ to 24″ nominal OD and R/t ranging from 6 to 14. Results for pipes with internal pressure are also included. The effect of torsion is notable only for large diameter pipes subject to large torsion loads. For the purpose of non-mandatory Appendix C flaw evaluation the torsion loads can be combined with bending loads using the root of the sum of the squares method as per Section III of the ASME Boiler code for small diameter pipes. For large diameter pipes a weighting factor of 1.2 on torsion moment is recommended.
An Engineering Approach to Characterisation of Twin Flaws in Cleavage
Authors: Bezensek Bostjan , Sharples John , Wilkes Mark
Published: January 2011

Multiple adjacent flaws are aligned and combined into simplified flaws for the purpose of flaw assessment in fitness for service procedures. Adjacent co-planar flaws are characterised by a bounding semi-elliptical flaw in accordance with flaw combination rules. Approximately 10 years ago BS7910 and R6 procedures revised flaw combination rules to allow adjacent co-planar flaws to touch prior to flaw characterisation. An extensive experimental and analytical programme has been underway over the past few years in the UK to examine the conservatism of flaw characterisation for fatigue, ductile tearing and cleavage with the new flaw combination rule. It was found that for fatigue and ductile tearing of flaws in contact the flaw characterisation is conservative, while for cleavage the flaw characterisation was found to be non-conservative when failure is accompanied with only small amounts of crack tip plasticity. In this paper an engineering approach is introduced to identify cases when flaw characterisation becomes non-conservative for cleavage. The approach relies on comparing material’s capacity for plastic deformation with the geometry of the complex flaw. In this manner no detailed analyses or extensive material characterisation are required for every examined case. The procedure is developed on the basis of test data and finite element analyses are used to extend its applicability to other flaws.
Closure Effect on Interaction of Two Surface Cracks Under Cyclic Bending
Authors: Kikuchi Masanori , Wada Yoshitaka , Maitireyimu Maigefeireti , Sano Hirotaka
Published: January 2011

Crack closure effect on interaction of two surface crack growth processes by fatigue is studied. At first, change of C value in Paris’ law along crack front of single surface crack is measured experimentally. It is shown that C value decreases near specimen surface. Crack closure effect is studied numerically for a surface crack by elastic-plastic cyclic analyses. It is found that closure effect appears more strongly near specimen surface than the maximum-depth point. By determining effective stress intensity factor including closure effect, it is shown that change of C value is equal to the change of closure effect along crack front. Using new C value considering closure effect, fatigue crack growth is predicted using S-FEM. It is shown that fatigue life and crack configuration agree well with experimental ones. Finally, interaction of two surface cracks is evaluated numerically, and it is shown that crack closure plays important role on the interaction of two cracks.
Assessment of Lower Regions of Pressure Vessels Subjected to Corrosion Wall Thinning
Authors: Madew Colin , Sharples John , Charles Richard , Smith Godfrey
Published: January 2011

Pressure vessels are common components of plant currently in operation within the nuclear industry and elsewhere. Their assessment and maintenance is of paramount importance to the integrity and safe working of the plant. Often these pressure vessels contain highly corrosive substances, which over time, cause deterioration in the integrity of the vessel. Current codes and standards such as BS7910, API579 and FITNET provide guidance on the assessment of cylinders and pipes with localised and general corrosion, but to date, no such guidance is available for complete vessels, where the corrosion occurs in the lower region of the vessel, e.g. where the base of a vessel is connected to the vessel wall. This paper investigates the resistance to plastic collapse, from internal pressure loading, of flat based cylindrical pressure vessels, where the base and wall thicknesses are considerably different due to corrosion damage. A ‘First Estimate’ or conservative lower bound collapse pressure solution for such vessels is described. The solution has been derived using axi-symmetric finite element models with varying degrees of general corrosion thinning.
Measurement of Residual Stresses in Stainless Steel Cladded Specimens
Authors: Kingston E. , Udagawa M. , Katsuyama J. , Onizawa K. , Smith D. J.
Published: January 2011

Residual stresses were measured in cladded steel specimens using deep hole drilling (DHD) and block removal and surface layering (BRSL) techniques. The samples consisted of a A533B steel substrate and cladded with Type 304 stainless steel using two different welding techniques; electro-slag (ESW) and submerged welding (SAW). Two SAW samples were created; one with a single layer of weld and a second with a double layer of welding. Only a single weld layer of ESW was used on another sample. All three samples were subjected to post-weld heat treatment prior to measurement. The measured residual stress distributions revealed (as expected) tensile stresses in the clad. However, the DHD method measured compressive stresses in the substrate adjacent to the clad for the single layer ESW and SAW welds. In contrast, the BRSL method found that the residual stresses in the substrate were close to zero or approximately tensile. The measurements are compared with results obtained from finite element (FE) simulations of the welding and PWHT treatment. The predicted tensile residual stresses in the clad were found to be larger than the measurements while in the substrate the FE analysis did not predict the measured compressive stresses.
Bolt-Nut Loosening in Bolted Flange Connections Under Repeated Bending Moments
Authors: Ishimura Mitsutoshi , Sawa Toshiyuki , Karami Atsushi , Nagao Takanori
Published: January 2011

Bolted flange connections for wind power generations and chemical plants are subjected to repeated bending moments due to wind and earthquake loads. It is known empirically that the bolts loosening in the bolted connections occur. Thus, it is necessary to examine the bolt loosening in the bolted flange connections under repeated bending moments. The objective of the present paper is to clarify the mechanism of bolt loosening in bolted flange connections subjected to repeated bending moments and to discuss on a solution for preventing the loosening of the bolted flange connections subjected to repeated bending moments, too. The loosening mechanism of the bolted flange connections is examined using the FEM calculations and the experiments. In the loosening experiments using the specified hexagon nuts, it is observed that the loosening of the bolts in the connection occurs due to the permanent-set of the bolts and the movement of the bearing surfaces in the flange due to the external bending moment. In the FEM calculation, it is examined that the bolt loosening in the bolted flange connections qualitatively. In addition, it is found that as the bolt preload increase, the bolt loosening decreases. From the FEM results and the experimental results, it is found that the most effective part for preventing the loosening of the bolted flange connection is the eccentric nut.
Modelling Ductile Tearing From Diffuse Plasticity to Crack Propagation
Authors: Simatos A. , Marie S. , Combescure A. , Cazes F.
Published: January 2011

Continuum models for ductile fracture accurately model onset of ductile tearing thanks to their stress triaxiality dependent formulations. Nevertheless, these models are subject to localization and convergence problems that hinder large crack propagation prediction. This paper presents a method to switch from a continuum mechanics model to a cohesive zone maintaining the mechanical energy. This is obtained thanks to a careful identification of the cohesive law whose computation is based on two points: The thermodynamical definition of the cohesive model and the assumption that, for a given problem, the plastic work during localization must be the same if modelled with a regularized continuum model or with introduction of an equivalent cohesive zone. The cohesive discontinuity is introduced in the framework of the eXtended Finite Element Method developed in CAST3M Finite Element code. This strategy permits to use the continuum model as long as it is the most appropriate and to introduce cohesive zone segments without energy loss. Moreover it solves numerical difficulties associated with the local vision of fracture. The performance of the proposed solution is illustrated on the Rousselier model for which a consistent cohesive law is identified. Results of fracture tests prediction on a CT specimen are compared with those obtained with the conventional Rousselier continuum mechanics formulation.
Multiple Fatigue Crack Growth Prediction Using Standard Stress Intensity Factor Solutions
Authors: Konosu Shinji , Kasahara Kyosuke
Published: January 2011

It is generally believed that multiple fatigue crack growth prediction is difficult with the use of standard stress intensity factor (SIF) solution calculations because of the complicated nature of such issues as magnification and shielding effects. Therefore, almost all the existing FFS rules such as the ASME Section XI Code and JSME Code adopt the procedure whereby multiple cracks grow independently after applying a certain alignment rule based on the initial crack configuration and are combined immediately into an enveloping crack when the crack tips touch. In some cases, the results of the procedures in the existing FFS rules can be unrealistic and may lead to unreliable predictions of the service life of cracked components. This paper describes a new approach to predicting multiple nonaligned fatigue crack growth life by the use of standard SIF solutions. Several examples, as compared with numerical analysis by the body force method for two-dimensional models and experimental results in the literature for three-dimensional models, illustrate the accuracy and effectiveness of the procedure.
The Influence of Switch Temperature on Coke Drum Fatigue Life
Authors: Marangone Fa´bio de Castro , Tinoco Ediberto Bastos , Simo˜es Gomes Carlos Eduardo
Published: January 2011

Coke drums are thin-walled pressure vessels that experience severe thermal cycling condition which consists of heating, filling and rapidly cooling the drum in a short period of time. After some years under operation, cracks at the vessel may occur, especially at high stress concentration areas such as the skirt support to shell attachment. During the filling phase of the cycle, when the empty and cooled coke drum is filled with hot oil, the shell and cone temperatures increase rapidly compared to the skirt temperature and the last is pushed outward, since its bottom is at lower temperature and fixed at a concrete base. During quenching (sudden cooling) phase, the coke drum is filled with water at about 80°C and tends to cool faster than the skirt, which is pulled inward until equilibrium is obtained. The skirt expansion and contraction movement results in bending stresses in axial direction on the top of skirt. As lower the switch temperature is, more severe is the bending effect. One of PETROBRAS delayed coke unit presented some operational problems at pre-heating phase, resulting in lower switch temperatures. This paper presents an analysis showing the influence of the switch temperature on coke drum fatigue life. At first, the transient loading conditions were established from thermocouple measurements at skirt attachment weld (hot box region). Later, a transient thermal analysis was performed with FEA and the temperature gradient at the skirt attachment during entire thermal cycle was obtained. The thermal results were then converted to a structural model which was solved for linear elastic stress including other loads such as pressure. Finally, the maximum stress components for both filling and quenching phases were determined and a complete stress range was calculated as per ASME Section VIII, Div 2. The procedure described above was applied for different switch temperatures scenarios in order to show its influence on the fatigue life of the coke drum.
Fracture Assessment of Austenitic Stainless Steel Piping With Multiple Flaws in Heat-Affected Zone
Authors: Narazaki Chihiro , Saito Toshiyuki , Itatani Masao , Ogawa Takuya , Sasayama Takao
Published: January 2011

Stress corrosion cracking (SCC) has been observed as circumferential multiple flaws in the weld heat-affected zone of primary loop recirculation system piping and core shrouds made of low carbon stainless steel. In the Japan Society of Mechanical Engineers code, Rules on Fitness-for-Service for Nuclear Power Plants, there is no fracture assessment of piping with multiple flaws which are not subject to flaw combination rule criteria. Through fracture testing of piping with two circumferential flaws in the weld heat-affected zone, the limit load estimation method was used for fracture assessment of stainless steel piping.
Discussion on Plastic Collapse Criterion at High Temperatures in FFS Assessment Rules
Authors: Oyamada Kenji , Konosu Shinji , Miyata Hikaru , Ohno Takashi
Published: January 2011

There are several Fitness-For-Service (FFS) standards with evaluation rules in terms of plastic collapse for a pressure vessel or piping component possessing a local metal loss area simultaneously subjected to internal pressure and bending moment. The authors have already reported the results of a comparative study of FFS rules, including the remaining strength factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, which pointed out that there could be significant differences in allowable flaw sizes. This paper describes an additional comparative study on the difference of allowable flaw size for local metal loss assessment between the RSF approach in Part 5 of API 579-1/ASME FFS-1 and the p-M diagram method, focusing on the effect of decreasing yield strength of the material at high temperatures, such as 350 degrees C. The allowable flaw depth at high temperatures derived from API579-1/ASME FFS-1 is larger than that derived by means of the p-M diagram method. However, it is verified by the finite element analysis that the allowable flaw size of the p-M diagram method is set on the stress state of general yielding near a local metal loss area if safety factor is not considered and it is possible to evade ratcheting due to cyclic bending moment in service, such as that caused by earthquake, etc.
Internal Crack Initiation in Low-Cycle Fatigue of Stainless Steel
Authors: Kamaya Masayuki , Kawakubo Masahiro
Published: January 2011

Internal cracks were observed on the fracture surface of Type 316 stainless steel specimens subjected to a low-cycle fatigue test, in which the strain amplitude was more than 1%. In some cases the specimens fractured due to these internal cracks. In this study, the reason and conditions for the internal crack initiation were examined. Fatigue experiments were conducted using Type 316 stainless steel. In order to enhance the internal crack initiation, the specimens were subjected to pre-damaging and surface cracks were removed before the start of the fatigue tests. It was shown that specimens fractured due to internal cracks when the strain amplitude of pre-damaging was more than 1% and hourglass-type specimens were used. The fatigue life was reduced largely due to the internal cracks and the magnitude of reduction was more significant for the smaller strain amplitude of the fatigue tests. Inclusions were observed at the origin of some internal cracks. It was deduced that the hourglass geometry of the specimen enhanced the internal crack initiation. Namely, the multi-axial field was one of the factors promoting the internal crack initiation.
Estimation of CTOD in the Case of Very Thick Plates by Knowing CVN Value at a Given Temperature
Authors: Pillot Sylvain , Corre Ste´phanie , Chauvy Ce´dric , Toussaint Patrick
Published: January 2011

Material properties assessment at given temperature and thickness is of primary importance for steelmakers. Generally, a list of mechanical properties requirements, namely tensile, Charpy V-Notch (CVN), fracture mechanics, as well as chemical or heat treatments limits are furnished by customers. Subsequently, the best compromise has to be found by the steel producer in order to reach these requirements. Concerning tensile and CVN properties, experience is large and metallurgists are used to determine the best product optimizations so as to reach the requirements’ values. However, optimization is generally more complicated regarding fracture mechanics. Tools are therefore needed in order to evaluate these properties with reference to conventional (i.e. tensile and CVN) properties. The objective of the present paper is to present some rules that can be used to extrapolate Crack Tip Opening Displacement (CTOD) values from CVN and tensile properties. Recent example is given to illustrate this methodology. In addition, special attention will be paid to the comparison of estimated and measured CTOD values.
A Proposed Model for Predicting Residual Clamp Load in Gasketed Bolted Joints
Authors: Housari Basil A. , Alkelani Ali A. , Nassar Sayed A.
Published: January 2011

An improved mathematical model is proposed for predicting the residual clamp load in gasketed bolted joints, taking into consideration gasket creep relaxation behavior, bolt stiffness, and joint stiffness. The gasket creep relaxation behavior is represented by a number of parameters which has been obtained experimentally in a previous work. An experimental procedure is developed to verify the proposed model using a single-bolt joint. The bolt is tightened to a target preload and the clamp load loss due to gasket creep relaxation is observed over time under various preload levels. The experimental and analytical results are presented and discussed. The proposed model provides a prediction of the residual clamp load as a function of time, gasket material and thickness, bolt stiffness, and joint stiffness. The improved model can be used to simulate the behavior of creep relaxation in soft joints as the joint stiffness effect is considered. Additionally, a closed form solution is formulated to determine the initial clamp load level necessary to provide the desired level of a steady state residual clamp load in the joint, by taking the gasket creep relaxation into account.
Research Activities in the European Union on Ageing Management for Long Term Operation of Nuclear Power Plants
Authors: Martin Oliver , Ballesteros Antonio , Bruynooghe Christiane , Bie`th Michel
Published: January 2011

The energy supply of the future in the EU will be a mix of renewable, fossil and nuclear. There are 145 nuclear power reactors in operation in 15 out of the 27 EU countries, with installed power ∼132 GWe. The age distribution of current nuclear power plants in EU is such that in 2010 most of them will have passed 20-years and approximately 25% of them 30 years of age. The decrease of energy supply from nuclear generated electricity can not always be compensated in a reliable and economical way within a short time span. For this situation utilities may be keen to upgrade the reactor output and /or to ask their regulatory bodies for longer term operation. Under the research financed in the Euratom part of the Research Directorate (RTD) of the European Commission several projects explicitly address the safe long term operation of nuclear power plants (NULIFE, LONGLIFE) and the topics proposed in the 2010 call explicitly address issues concerning component ageing, in particular non metallic components, i.e. instrumentation and cables (I&C) and concrete ageing. This paper presents an overview of the plans for long term operation (LTO) of nuclear power plants in the EU. Special emphasis is given on research activities on component ageing management and long term operation issues related to safety.
Nondestructive Measurement of Non-Equibiaxial Welding Residual Stresses Using Instrumented Indentation Technique With Knoop Indenter
Authors: Choi Min-Jae , Kim Young-Cheon , Song Won-Seok , Kwon Dongil
Published: January 2011

Welding residual stresses which are generated in almost all welded structures unavoidably can come to be serious cause of fracture and failure of in-service welded structures. Various techniques have been developed to measure and estimate welding residual stresses such as hole-drilling method, saw-cutting method, X-ray/neutron diffraction method and so on. The instrumented indentation technique (IIT) is being attracted to significant alternative as a measurement method of residual stresses because of it’s nondestructive characteristic and usefulness of measurement on local scales. Basic concept of IIT to evaluate residual stresses is to compare two indentation load-depth curves that are measured experimentally between under stress-free state and under stressed state. In case of using Vickers indenter, average surface residual stress can be measured quantitatively from analyzing measured load diffrerence. Each x, y directional residual stresses can be evaluate by using Knoop indenter. Indenting each directions with Knoop indenter, difference load-depth curves are measured under non-equibiaxial stress state. Residual stress directionality can be expressed as the function of the load-difference ratio calculated from the load-depth curves and the conversion factor ratio that is constant regardless of indentation depth. This function was verified with the experimental data and the results of finite element analyses on various biaxial stress states, Knoop indentation model showed good agreement between the experimental data and the simulation results.
Effect of Ovality on Shakedown of Pipe Bends
Authors: Asadkarami Ali , Reinhardt Wolf , Zobeiry Nima
Published: January 2011

This paper investigates the effect of pipe bend ovality on the shakedown boundary utilizing the cyclic elastic-plastic analysis method. The ASME Code, Section III NB-3653.2 recognizes the effect of the bend ovality on the peak stress only. The manufacturing rules of ASME NB-4223.2 limit the maximum bend cross sectional ovality to 8%. The effect of the bend ovality on the ratcheting boundary has not been well established in the literature. The current study compares the effect of primary mean stress (i.e. pressure) combined with expansion (secondary) cyclic bending on the shakedown boundary of a prototypical pipe bend with ovalized and fully circular cross section.
Background on the New ASME PCC-1-2010 Appendix A “Training, Qualification and Certification of Joint Assembly Personnel”
Authors: Brown Warren
Published: January 2011

A revised ASME PCC-1 “Guidelines for Pressure Boundary Bolted Joint Assembly” has recently been published which includes several extensively revised appendices. Among those is Appendix A “Training, Qualification and Certification of Joint Assembly Personnel”, which outlines a training, assessment and certification system for ensuring a minimum level of knowledge for bolted joint assemblers. This paper outlines the background as to why the appendix was written, with commentary on the need and the intended program format.
R6 Weld Modelling Guidelines: Application to Groove Weld Worked Example
Authors: Dennis R. J. , Leggatt N. A. , Smith M. C. , Bouchard P. J.
Published: January 2011

Weld modelling guidelines have recently been developed as part of a new section of the R6 integrity assessment procedure, which is used in the UK nuclear power industry. The intention is to improve the consistency of weld modelling procedures, the accuracy of predicted residual stress profiles and confidence in their use for defect tolerance assessments. The first issue of these guidelines is applicable to austenitic stainless steel joints produced using arc welding processes. The components of interest are mainly thick section nuclear pressure vessels and pipe welds where distortion is not the key issue. Recommendations made in the guidelines are largely based on residual stress analysis methods, validated by measurements on a range of weld mock-ups, developed over several years in support of British Energy projects. The guidelines themselves are divided into two main parts. The procedure itself defines the weld residual stress analysis steps and identifies the key modelling decisions to be made. A much larger section then follows, providing advisory notes on how to make key modelling decisions, with reference to supporting documents and three appendices. The purpose of this paper is to describe the application of the guidelines to a typical weld residual stress assessment. This is in the form of a worked example which details the step-by-step application of the guidelines and describes the key modelling decisions that were made at each step of the procedure. The worked example is for a three bead groove weld specimen. This specimen is an austenitic stainless steel plate with a groove running along the entire length of the plate. The groove is filled with three stringer weld beads.
Benchmark of Computational Fluid Dynamics Simulations Using Temperatures Measured Within Enclosed Vertical and Horizontal Array of Heater Rods
Authors: Chalasani N. R. , Greiner Miles
Published: January 2011

Experiments and computational fluid dynamics/radiation heat transfer simulations of an 8×8 array of heated rods within an aluminum enclosure are performed with nitrogen and helium as backfill gases in both horizontal and vertical orientations. This configuration represents a region inside the channel of a boiling water reactor fuel assembly between two consecutive spacer plates. The rods can be oriented horizontally or vertically to represent transport or storage conditions. The measured and simulated rod temperatures are compared for three different rod heat generation rates to assess the accuracy of the simulation technique. Simulations show that temperature gradients in the air are much steeper near the enclosure walls than they are near the center of the rod array. The measured temperatures of rods at symmetric locations are not identical, and the difference is larger for rods close to the wall than for those far from it. Small but uncontrolled deviations of the rod positions away from the design locations may cause these differences. The simulations reproduce the measured temperature profiles. For nitrogen experiment in horizontal orientation and a total rod heat generation rate of 500 W, the maximum rod-to-enclosure temperature difference is 138°C. The maximum measured heater rod and enclosure wall temperatures 375°C and 280°C, are measured in 2-inch insulated, nitrogen backfill vertical experiment for 1 atm internal pressure. Linear regression shows that the simulations slightly but systematically under predict the hotter rod temperatures but accurately predict the cooler ones. For all rod locations, heat generation rates, nitrogen and helium backfill gases, and apparatus orientations, 95% of the simulated temperatures are within 11°C of the correlation values. These results can be used to assess the accuracy of using simulations to design spent nuclear fuel transport and storage systems.
Proposal of an Internal Burst Pressure Equation Applicable to Planar/Non-Planar Flaw in Wall Thinned Pipes
Authors: Meshii Toshiyuki
Published: January 2011

In this paper, an internal burst pressure equation applicable to all types of planar and non-planar flaw in wall thinned straight pipes was proposed. An idea to rationally classify planar/non-planar flaw in wall thinned pipes was proposed, based on the experimental observation focused on the fracture mode. The results point out the importance to distinguish axially and circumferentially long flaws in wall thinned pipes.