bluuebunny/crossref_metadata_2025 huggingface dataset:
Significance of Ms and Validation of Reference Stress Solutions for Crack Like Flaws: Part 2
Authors: Ishizaki Yoichi , Thorwald Greg , Yonekawa Futoshi
Published: October 2020

This is Part 2 of two papers discussing the significance of two key factors of crack like flaw assessment in the Fitness for Service assessment.

While FEM analysis technology has been advancing amazingly in recent years, and FEM based fitness-for-service assessment of a damaged components, such as crack like flaws and local metal loss assessment, has become mainstream in assessments, it is still important to understand the reference stress solution based on a limit load analysis and the role of each factor in the failure mode to control the damaged component safely until the end of its life.

In API 579-1/ASME FFS-1[1], Part 9, Assessment of Crack like Flaws, those reference stress solutions were developed based on the limit load analysis using Folias factor Mt and surface correction factor Ms. Folias factor Mt and surface correction factor Ms, are factors that account for the bulging effect around flaws. Those factors enable prediction of a maximum allowable pressure of a damaged cylindrical shell from a simple flat plate model that contain same size of a damaged area.

As for Folias factor, Mt, it is well known to express the relationship between the reference stress of a through-wall crack flat plate and a through-wall crack cylinder. The application of Mt is clearly defined in ASME/API 579 FFS-1 part 9C, as well as papers by Folias et al. The the significance of the surface correction factor for surface flaw, Ms, has not been commonly understood well enough in general. Unfortunately, API 579-1/ASME FFS-1 also does not clearly mention its significance and how Ms is to be applied in the stress analysis. At a glance, Ms looks like a similar factor to Mt, and it is tempting to simply apply Ms to primary membrane stress term like Mt, but that is not correct. Eventually, an incorrect application of Ms would lead to an incorrect discussion of a flaw characterization. Often, there is a question about ASME/API 579 FFS-1 Part 9C reference stress solutions, especially for ASME/API 579 FFS-1 eq. 9C.76, from the misunderstanding meaning of the Ms factor. Addressing this issue is important to maintain the integrity of the Fitness-For-Service technology.

In this Part 2 of two papers, validation of equations obtained in Part 1 are discussed and proven based on FEM analysis.
Structural Evaluation With Elastic and Inelastic Analysis Methods on a High Temperature Storage Tank Subjected to Static and Dynamic Loadings
Authors: Wang Wen , Zhang Xiaochun , Wang Xiaoyan , Cai Maoyuan
Published: October 2020

The structural integrity of reactor components is very essential for the reliable operation of all types of power plants, especially for components operating at elevated temperature where creep effects are significant and where components are subjected to high-temperature alteration and seismic transient loading conditions. In this article, a molten salt storage tank in high temperature thorium molten salt reactor (TMSR) is evaluated according to ASME-III-5-HBB high temperature reactor code. The evaluation based on 3D finite element analyses includes the load-controlled stress, the effects of ratcheting, and the interaction of creep and fatigue. The thermal and structural analysis and the application procedures of ASME-HBB rules are described in detail. Some structural modifications have been made on this molten salt storage tank to enhance the strength and reduce thermal stress. The effects of ratcheting and creep-fatigue damage under elevated temperature are investigated using elastic analysis and inelastic analysis methods for a defined representative load cycle. In addition, the strain range and the stress relaxation history calculated by elastic and inelastic methods are compared and discussed. The numerical results indicate that the elastic analysis is conservative for design and a full inelastic analysis method for estimating input for creep-fatigue damage evaluation need to be developed.
Characterization of Anisotropic Mechanical Properties of X70 Spiral Welded Steel Pipes
Authors: Park Dong-Yeob , Liang Jie , Gravel Jean-Philippe
Published: October 2020

Anisotropic tensile and compressive properties of base metals and girth welds of two API X70 spiral welded pipes have been investigated in this study. Spiral welded pipes exhibit different characteristics of anisotropy with respect to pipe axis in comparison with UOE pipes, as the anisotropic property is determined by the thermo-mechanical rolling process of plates and coils produced for pipes. Yield strengths measured from respective tensile and compressive tests are quite comparable at a given material and orientation, although tensile yield strengths are somewhat greater. The results of compressive tests also indicate an anisotropy in the through-thickness direction as well as in the longitudinal direction; high yield strengths are observed at the through-thickness direction or nearby for both base metals and girth welds of the two pipes.
Life Assessment of a Coke Drum by Using the Thermal-Mechanical Fatigue Properties and Laser Scanning Approach
Authors: Han Zhiyuan , Xie Guoshan , Wang Zengchao , Yin Jianzhong , Shi Jin
Published: October 2020

Coke drums are critical equipments in delayed coking plants, which are operated under severe thermal-mechanical conditions by cyclic heating and quenching processes. Cracks are usually developed during service because of severe plastic deformation and low-cycle fatigue. Thus, the assessment of the deformation severity and remaining life is important for safety operating of the coke drums. This study investigated the bulging damage and fatigue life of 6 coke drums after 16 years and 22 years of service in China. A thermal-mechanical fatigue test were first performed to simulate complex loading condition experienced by the coke drum. The thermal-mechanical fatigue life curve of the fabrication material was obtained. Then, a internal laser scanning was employed to measure the deformation and bulges of drum shells. The finite element analysis was developed to calculate the cyclic stress and strain and bulging severity based on the laser mapping and operating conditions. The fatigue life of the coke drum was assessed by the Coffin-Manson-Basquin’s relationship. The life evaluation results of different methods were compared and analyzed. The results showed that a reasonable life of the coke drum can be obtained by using the thermal-mechanical fatigue properties and laser scanning approach.
Tensile and Fatigue Failure of 17-4 PH Martensitic Stainless Steels in Presence of Hydrogen Depending on Frequency and Heat Treatment
Authors: Sezgin Jean-Gabriel , Yamabe Junichiro
Published: October 2020

Slow-strain-rate tensile (SSRT) and fatigue-life tests were carried out on 17-4PH martensitic stainless steel with an ultimate tensile strength (UTS) of ∼ 1 GPa. The specimens were precharged by exposure to hydrogen gas at pressures of 35 MPa or 100 MPa at 270°C for 200 h. The SSRT tests used smooth axisymmetric specimens made of two grades of 17-4PH (H1150 and H900) differing by the UTS due to their thermal history. No degradation of the UTS was observed for both H1150 and H900 grades. However, the relative reduction in area (RRA) was 0.31 for H1150 or 0.11 for H900, translating a difference in their hydrogen sensitivity. Both grades presented different fracture-surface morphologies: a mixture of quasi-cleavage (QC) and intergranular (IG) facets for H1150 and cleavage (C) facets for H900. Circumferentially-notched axisymmetric specimens made of H1150 were used for the fatigue-life tests in the [10−3 Hz;10 Hz] frequency range. Our previous study on low-alloy steels with UTS of around 950 MPa demonstrates that the fatigue life of a circumferentially-notched specimen with a sharp notch can be successfully predicted from the fatigue crack growth (FCG) property following the Paris law. This study used the same specimen geometry and a BCC steel with a similar UTS value; hence, the FCG behavior was investigated from the fatigue-life test of the notched specimen. As a result, the degradation of fatigue lives attributed to the FCG acceleration was observed in presence of hydrogen. A FCG acceleration ratio bounded to 30 was observed in the high-cycle regime, accompanied by QC facets. A FCG acceleration ratio bounded to ∼100 was observed in the low-cycle regime, accompanied by QC and IG facets. A FCG model accounting for the interaction of elementary mechanisms was proposed and succeeded in predicting the FCG acceleration ratio observed on H1150. This model was also successfully applied to a low-alloy steel with a comparable UTS (1002 MPa) tested in gaseous hydrogen.
Estimating Stable Mean Responses for Linear Structural Systems by Using a Limited Number of Acceleration Time Histories
Authors: Nie Jinsuo R. , Xu Jim , Graizer Vladimir , Seber Dogan
Published: October 2020

For seismic analyses of linear structural systems including soil-structure systems, the current practice (e.g., the U.S. Nuclear Regulatory Commission (NRC) Standard Review Plan (SRP) (NUREG-0800 [1], “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition”) and American Society of Civil Engineers (ASCE)/Structural Engineering Institute (SEI) Standard 4-16 [2], “Seismic Analysis of Safety-Related Nuclear Structures”) allows for estimating mean seismic responses by using as few as four or five input time histories. This paper examined whether this practice can achieve a stable mean response by explicitly considering the uncertainty in the Fourier phase spectra of the input time histories and exploring how this uncertainty can affect the coefficient of variation (CV) of the in-structure response spectra (ISRS). ISRS are the response spectra of the seismic response time history at a location in the structure subjected to an input seismic time history. We found that the maximum CVISRS across all frequencies is around 40% purely due to the uncertainty in the Fourier phase spectra for a typical range of design earthquakes for U.S. nuclear power plants. To estimate a mean ISRS within ±10% of the true mean ISRS, our analyses showed that this level of CVISRS may require a minimum of 16 input time histories for a confidence level (CL) of 68% and 61 for a CL of 95% for soil-structure systems of low fundamental frequencies. For stiffer systems (for example, with a fundamental frequency of 5 hertz (Hz)), the maximum CVISRS is about 30%, and thus, the minimum required number of input time histories may be reduced to 9 for a CL of 68% and 35 for a CL of 95%. In summary, the four or five time histories in the current practice may not be sufficient for estimating stable mean responses, especially for soil-structure systems with very low frequencies.
Investigation and Resolution of the Fluid Structure Interaction of High Rate HVGO Pumps
Authors: Kaye Alwyn
Published: October 2020

A suite of High Rate Heavy Vacuum Gas Oil (HVGO) pumps in an operating Upgrader Plant experienced repeated failures; typically, less than 7 weeks. The need for online measuring tools arose that could measure pump and piping system strain changes with dynamic thermal gradients. The challenge was to record the effect on the entirety of pump component alignment and vibration. In current industrial practices no such tools and techniques are directly and comprehensively available for rotary equipment. Strain gauges are not accurate, and cannot provide broader real time strain mapping.

Optical metrology can analyze the mechanical properties and behavior of all kinds of materials in various test scenarios. To date such methods are experimental and principally found in advanced application environments. At the time the method was unknown and especially in such a difficult industrial plant. In such a complex and extreme hot and cold operating service warm-up, cooling, with variations in flow and temperature, can directly and dynamically affect strain measurements.

It was not certain whether optical meorology measurement techniques would be able to identify and correlate dynamic operating scenarios with the source of the pump and pipe hardware issues experienced in these Heavy Vacuum Gas Oil (HVGO) pump systems.

The influence of the casing thickness and stiffness on the resulting vibration characteristics was investigated by using FEA and operational testing and dynamic analysis. Increasing the interface web thickness results in notable reduction in deformation. Comparison of the results of the live testing against the initial design was performed and studied for remedial action. Materials and heat treatment options were also evaluated and reported. The three-dimensional turbulent flow was modelled and analyzed.

The application of those tools for this type of problem are described along with the other rigorous techniques employed. The range of tools included modal and vibration analysis, thermography, rotor and shaft dynamics, baseplate, frame, metallurgical analysis and ultimately compared with FEA, pipe stress modelling and strain analysis.

This paper should be read in conjunction with PVP 2020-21204; Piping & Equipment Dynamics of High Rate HVGO Pumps.
A New Method for Preventing Plastic Collapse of Ellipsoidal Head Under Internal Pressure
Authors: Li Keming , Zheng Jinyang , Zhang Zekun , Gu Chaohua , Xu Ping
Published: October 2020

Ellipsoidal head is a common end closure of pressure vessel. Plastic collapse is a crucial failure mode considered in the design of ellipsoidal head subjected to internal pressure. Internally pressurized ellipsoidal head tends to be hemisphere (geometric strengthening) due to the effect of material hardening before plastic collapse occurs, which enhances load carrying capacity of ellipsoidal head. However, in the current pressure vessel codes such as ASME BPVC.VIII.1 and BPVC.VIII.2, EN 13445-3, and Chinese codes GB/T 150.3 and JB 4732, design methods based on linear elastic or perfectly-plastic theory are used to prevent plastic collapse of ellipsoidal head, leading to conservative design. Therefore, we developed a new method for preventing plastic collapse of ellipsoidal head under internal pressure, considering the effects of material hardening and geometric strengthening. The new method was developed on basis of our previous extensive work on finite element analysis and experiments for plastic collapse of internally pressurized ellipsoidal heads. The new method provides sufficient margin of safety by checking against the experimental bursting results of full-scale ellipsoidal heads with various geometries, various material types and various manufacturing methods. Compared with the design methods in the current pressure vessel codes, the new method shows an advantage of economy. This new method had been approved by China Standardization Committee on Boilers and Pressure Vessels, and at present it has been introduced into the Chinese pressure vessel code.
INCEFA-PLUS: Increasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment
Authors: Mottershead Kevin , Bruchhausen Matthias , Cicero Sergio , Cuvilliez Sam
Published: October 2020

INCEFA-PLUS is a five year project supported by the European Commission HORIZON2020 programme. The project concludes in June 2020. 16 organisations from across Europe have combined forces to deliver new experimental data which is being used to develop improved guidelines for assessment of environmental fatigue damage to ensure safe operation of nuclear power plants. Within INCEFA-PLUS, the effects of mean strain and stress, hold time, strain amplitude and surface finish on fatigue endurance of austenitic stainless steels in light water reactor environments have been studied experimentally, these being issues of common interest to all participants. The data obtained has been collected and standardised in an online environmental fatigue database, implemented with the assistance of an INCEFA-PLUS led CEN workshop on this aspect. As the end of the project approaches, INCEFA-PLUS is developing and disseminating methods for including the new data into assessment approaches for environmental fatigue degradation.

This paper provides an overall update to project developments since it was last presented at PVP2019 (PVP2019-93276), and provides provisional project conclusions (which will be finalised for presentation at the conference). As well as being a standalone paper, the paper will also serve as an introduction to other papers being submitted covering specific aspects of the project. In particular this paper summarises:

• The results of 3 years of testing (nearly concluded at the time of paper submission)

• A summary of revealed sensitivities to, and inter-dependencies between:

○ Mean strain and stress, surface finish, strain amplitude and hold time.

○ Environment

○ Material

○ Laboratory (including specimen size and form)

• The latest thoughts on how the project results will be used to advance development of improved assessment guidelines.

• Progress developing an International EAF database.

• A summary of dissemination achieved and planned.

• The status of INCEFA-SCALE plans for work after the end of INCEFA-PLUS.
Research and Development of Viscous Fluid Dampers for Improvement of Seismic Resistance of Thermal Power Plants: Part 9 — Investigation Regarding Damage Between Furnace and Cage
Authors: Aida Kiyoshi , Minagawa Keisuke , Fujita Satoshi
Published: October 2020

Boilers in coal-fired thermal power plants were often damaged by earthquakes such as the Great East Japan Earthquake in 2011. Since the coal-fired thermal power generation has been one of the main power generation methods after the Great East Japan Earthquake, mitigation of damage of boilers in thermal power plants by earthquakes is the very important subject in order to recover our daily life immediately after strong earthquakes. Meanwhile, a boiler in a coal-fired thermal power plant was damaged by Hokkaido Eastern Iburi Earthquake in 2018, and this damage was one of the causes of Hokkaido’s prefecture-wide blackout. According to a report by an electric power company, a damage occurred between a furnace and a cage of the boiler. In general, lengths, shapes, weights and so on of a furnace are different from a cage, so vibration characteristics and seismic response are different as well. Thus the connecting part between the furnace and the cage is a weak point in the boiler, and the damages often occurred there. Therefore this paper investigates seismic response of a boiler by a numerical analysis using a frame model from the viewpoint of the damage of the furnace and the cage. Various seismic waves were used as input waves in order to investigate the influence of the input wave. A result of a modal analysis was also provided in this paper.
Non-Destructive Examination of Diffusion-Bonded Compact Heat Exchangers
Authors: Selby Greg , Aakre Shaun , Fan Zhaoyan
Published: October 2020

Compact heat exchangers (CHX) fabricated using the diffusion bonding process will be useful in the design and operation of Generation IV nuclear power plants. The NDE challenges posed by diffusion-bonded compact heat exchangers (DBHE) are quite different from those of their more familiar shell-and-tube cousins. The examination scope encompasses three parts: the welds joining the headers to the CHX body; the body’s solid perimeter, serving as the pressure boundary; and the channeled interior. Current investigations are in support of a Section III Code Case including CHX fabrication rules and post-fabrication nondestructive evaluation (NDE) requirements to ensure adequate initial quality. In-service examination methodologies are also considered to inform code developers, regulators, and vendors exploring use of CHX in advanced reactor designs.

The welds joining the headers to the CHX body likely will be full-penetration set-on welds of conventional design. Standard fabrication examinations, namely visual, dye penetrant and hydrostatic examinations will likely suffice. Additional methods should be specified for the purpose of ensuring that the weld stresses have not caused degradation or separation of individual layers within the adjacent diffusion-bonded core. The channeled core of the CHX is geometrically complex and does not allow application of traditional NDE methods from the outside. Radiography permits imaging of small demonstration scale components. Meanwhile, identifying bond failures within larger components may require embedded strain sensors. A theory for employing strain sensors to detect failures within the core is introduced here along with early experimental results. The diffusion-bonded solid perimeter should be examined to ensure that any presence of bonding failures is allowable. Ultrasonic examination results are presented, obtained from test blocks containing simulated bond failures and from high-pressure CHX used during lab studies.
Guidelines for Storage Tank Level 3 Fitness-for-Service Assessments
Authors: Huang John , Subramanian Kannan
Published: October 2020

This paper explores the application of the required loads while performing fitness-for-service (FFS) assessments on an in-service storage tank. Specifically, API 579 – 1, Level 3 FFS assessments involving finite element analyses are studied. In the authors’ experience, due to the absence of specific details about the application of loads within the design codes and post construction standards such as API 579 - 1, the chosen load application is purely at the discretion of the analyst. Often times, choosing one methodology over the other can result in non-conservative assessments. For example, in order to apply wind load pressure distributions on tanks and vessels for plastic collapse and buckling behavior, API 579 – 1 directs the user to ASCE 7 – 16 for wind load calculations. However, previous versions of ASCE 7 did not specify a circumferential pressure distribution for cylindrical structures which can significantly vary around the circumference of a large diameter storage tank. In addition, a few changes in ASCE in the recent edition affect the assessment of in-service tanks for seismic loads. The authors assessed various load cases on tanks of varying diameter to thickness (D/t) ratios and diameter to height ratios. The results show that the choice of loading can have a significant impact on the buckling characteristics of the tanks in-service. This is an attempt to develop some assessment guidelines to support the proposed Tank Assessment Section in a future Edition of API 579 – 1 Standard.
Extrapolation of Creep Rupture Data Using Parametric Numerical Isothermal Datum (P-NID) Method for Inconel 617
Authors: Haque Mohammad Shafinul
Published: October 2020

The development of advanced power plants requires alloys to operate at elevated temperature and pressure for an extended period of time. It is critical to consider creep during the design process to avoid catastrophic failure. Creep rupture data are often not available for desired operating conditions. Accurate extrapolation of creep life is necessary. One of the earliest and most widely used life prediction model is the classic Larson-Miller Parametric (LM) model. Over time numerous time-temperature parametric (TTP) models have been proposed such as Manson-Haferd, Orr-Sherby-Dorn, Manson-Succop, Graham-Walles, Goldhoff-Sherby parametric models. Non-TTP models such as the Wilshire equation is available. The prediction models vary in mathematical form, and number of material constants but shares a common calibration approach. Each model is calibrated against data for every available isotherm. A recently proposed model calibration approach is the parametric numerical isothermal datum (P-NID) method that can be applied to an existing model for improved long-term extrapolation. The P-NID approach is different than the traditional approach as the data are transferred to a datum temperature followed by model calibration against the transferred data at the datum temperature. The calibrated model is then transferred back to the original temperatures.

In this study, the P-NID method is applied to the LM model to perform extrapolation for Inconel 617 alloy. Creep rupture data for five isotherms ranging from 800 to 1000°C and stress levels from 9MPa to 170 MPa are used. A detail step by step procedure is provided for the application of the P-NID method to calibrate the LM model (LM-NID). The extrapolation performance of the classic LM and LM-NID models are compared. Normalized Mean Squared Error (NMSE) is used to analyze prediction accuracy. It is observed that the LM-NID model provides a realistic inflection free prediction compared to the LM model. A 10% data-cull from the lowest stress data is performed to assess the reliability of extrapolation. Based on the comparison a recommendation is provided.
CFD Simulation for Ball Valve Erosion of Natural Gas Pipelines Under Gas-Sand Two-Phase Flow
Authors: Peng Donghua , Dong Shaohua , Zhang Laibin
Published: October 2020

This paper examined the erosion characteristics of the curved core surface of the ball valve when subjected to the two-phase flow of sand-carrying high-pressure gas. The Computational Fluid Dynamics (CFD) method for joint analysis was used to establish the erosion simulation model, the critical factors, such as the ball opening degree, ball diameter affecting the flow field and erosion distribution of the gas-solid two-phase flow were analyzed. The flow field simulation results show that the gas velocity changed violently after entering the ball valve due to the reduction of the cross-sectional area, and the maximum velocity at the turning position increased gradually in conjunction with the decrease in opening degree, while remain unchanged with the increase of ball diameter. Moreover, the particle trajectory show that particles flowing in from the right straight pipe section mainly colliding with three areas including outer wall surface (zone 1), upstream wall surface (zone 2) and the outlet pipe section near the lower wall of the ball valve (zone 3), which were consistent with the location of that particle wall collision happens. The comparative analysis of the maximum erosion rate under different influencing factors shows that decreases with the increase of the ball diameters the opening degree and ball diameter. This research provided theoretical guidance to the erosion analysis of the ball valve core by the two-phase flow of high-pressure sand-carrying gas subjected to the changes in a variety of crucial parameters. This paper also presented a field application value for the design and maintenance of the ball valve in the natural gas pipeline.
The Effect of Cyclic Hardening Model on Deformation Behavior of Cracked Body Under Creep-Fatigue Loading Condition
Authors: Jung Hyun-Woo , Kim Yun-Jae , Takahashi Yukio , Nikbin Kamran , Davies Catrin M. , Ainsworth Robert A.
Published: October 2020

In this study, to determine appropriate cyclic hardening model for simulating creep-fatigue crack growth, sensitivity of hardening model on global/local deformation behavior during creep-fatigue crack growth is studied using finite element (FE) debonding analysis method. Three hardening models derived from tensile stress-strain curve to treat large strain near crack are considered in this study: isotropic hardening model, kinematic hardening model and combined hardening model. Simulation results indicate that cyclic hardening model does not make large difference in global deformation behavior but make difference in local deformation behavior. The effect of hardening model on inelastic strain and stress near crack are discussed in detail.
Estimation of Charpy Index Temperature of SA 508 Mn-Mo-Ni Low Alloy Steels at 41J Using Small Punch Tests
Authors: Kim Jongmin , Hong Seokmin , Lee Taekyoung , Kim Minchul
Published: October 2020

Small Punch (SP) test is one of the miniature test methods, which is a quasi-destructive testing method that evaluates the mechanical properties from limited volumes of materials. Structural materials in nuclear power plants experience degradation in the neutron irradiation environment during the operation, and this aging is assessed by measuring the Charpy index temperature shift of materials at 41J (T41J). However, there are many difficulties in deriving T41J or the fracture toughness from the SP test due to the difference in the failure mode between the SP tests and the conventional Charpy impact and fracture toughness tests. In this study, a method to predict the index temperature at 41J by using the key parameters obtained from SP load-displacement curve was proposed. T41J prediction methods using the fracture energy and displacement after the maximum load in SP test were proposed, and an analysis of the correlation between the key parameters of SP test and the fracture toughness values was performed. As a result of applying displacement after the maximum load parameter of SP curve, it showed better prediction than the fracture energy parameter, and the fracture mode in transition curve of SP was consistent with that of Charpy impact test.
Shakedown and Limit Analysis of Kinematic Hardening Piping Elbows Under Inner Pressure and Bending Moments
Authors: Peng Heng , Liu Yinghua
Published: October 2020

The stress compensation method (SCM) for shakedown and limit analysis was previously proposed and applied to elastic-perfectly plastic (EPP) piping elbows. In this paper, the SCM is extended to account for limited kinematic hardening (KH) material model based on the extended Melan’s static shakedown theorem using a two-surface model defined by two hardening parameters: initial yield strength and ultimate yield strength. To validate the extended SCM, a numerical test on a cylinder pipe is performed. The results agree well with ones from literature. Then the extended SCM is applied to the shakedown and limit analysis of KH piping elbows subjected to inner pressure and cyclic bending moments. Various loading combinations are investigated to create the shakedown limit and plastic limit load interaction curves. The effects of the material hardening, angle of the elbow and loading conditions on the shakedown limit and plastic limit load interaction curves are presented and analysed. The present method is incorporated in the commercial software of Abaqus and can be considered as a general computational tool for shakedown analysis of KH engineering structures. The obtained results provide a useful information for the structural design and integrity assessment of practical piping elbows.
Investigation of Chloride-Induced Stress Corrosion Cracking for AISI 304/304L Stainless Steel Using Notched Bar Specimens
Authors: Jeong Jae-Yoon , Kim Yun-Jae , Lam Poh-Sang , Duncan Andrew , Lee Myeong-Woo
Published: October 2020

Spent nuclear fuels are stored in dry storage canisters made of austenitic stainless steels. Canisters have a sensitivity to chloride-induced stress corrosion cracking since some storage facilities are located in coastal regions, and this environment could have a higher risk for pits and cracks to form on the surface of canisters. Hence, this paper suggests an experimental method of evaluating crack initiation for austenitic stainless steels. Notched bar specimens fabricated using AISI 304 and 304L stainless steels are designed to simulate loads corresponding to welding residual stresses on the surface of canisters. For testing to be conducted in chloride environments, the developed tester for evaluating CISCC is designed such that the notched bar specimens are immersed into the brine of 5% salinity and are loaded by tightening a spring to provide a constant load condition at 50 °C temperature. Also, initial load applied to each notched specimen is verified using finite element analysis as in the same experimental condition. As a result, the areas by pitting corrosion on notches are 1measured using the Image Analyzer program and the stress parameters obtained from the finite element analysis are used to correlate the effect of the pit formation.
The Effect of Thermal Cycling and Packing Stress on Stem Friction and Sealability
Authors: Girão Carlos D. , Veiga José C. , Cristello Josmar B.
Published: October 2020

Control valves are widely used in modern plants in order to keep process variables within a required operating range and ensure both a quality product and efficient operation. Nonlinearities, such as deadband and high static friction (stiction), are the most common cause of oscillations in process variables. Since plants usually consist of various interacting control loops, even small oscillations propagate and disrupt the process parameters out of their operating range, risking accidents, increasing product rejection rates, and decreasing profitability. Packing friction is the primary source of nonlinearities for rotating and sliding-stem valves, and while it is often tested and defined in room temperature, it is common for packings to undergo one or more thermal cycles during their life cycle. A particular packing style may have low stem friction with little to no stiction in room temperature, but present a completely different behavior either in elevated temperatures or after cycling. Failure to ensure correct packing tightness and select proper packing material can disrupt an otherwise well-designed control loop. This study correlates the resulting valve stem friction for different packing styles when subjected to multiple assembly stresses and temperatures. Finally, those same styles undergo standardized fugitive emissions testing, where packing behavior is studied while undergoing thermal and mechanical cycles.
Numerical Simulation of Thermal-Mechanical Stress Field of Coke Drum Considering Deformation
Authors: Yin Jianzhong , Wang Zengchao , Xu Junchen , Han Zhiyuan , Xie Guoshan
Published: October 2020

The coke drum is subjected to a combination of thermal-mechanical loads during operation, so its safety and reliability must be considered in actual production. In each production cycle, the thermal stress generated by temperature fluctuations in the coke drum is the main cause of structural failure. Based on this, a long-term service carbon steel coke drum was used as the research object and a method was proposed to evaluate the universality of the bulged coke drums in this paper. The details are as follows: firstly, the deformed coke drum was processed into a finite element geometric model by internal laser scanning detection. Then, the thermal mechanical coupled finite element analysis was performed on the two regions with large deformation based on the dynamic thermal boundary method. Next, the stresses and strains of the perfect geometry were analyzed and compared. Finally, the stress and strain distribution levels of different bulging patterns are obtained. These results indicate that the maximum stress and the maximum strain of the deformed region were increased by 35% and 77%, respectively, compared with the perfect geometry. Therefore, when evaluating the remaining life of the coke drums, bulges must be taken into account. Furthermore, this method proposed in this paper can provide guidance and reference for the life assessment of coke drums.
Case Study of the Effect of Combined Axial and Lateral Loadings on the Critical Buckling Capacity of Piping Supports
Authors: Wiseman Phillip , Mayes Alex , Karnik Shreeya
Published: October 2020

Snubbers are used in industry to restrain piping in dynamic events which can see significant axial loading as well as lateral acceleration. Snubbers are often employed with an extension when required to bridge gaps between the piping and building structure. As a result, they are susceptible to buckling instability issues. The pipe support and restraint design by analysis buckling criteria for supports given within the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 1, Subsection NF is investigated to determine the behavior of snubber assemblies under combined axial and lateral loadings. Four types of analyses are performed on the assemblies under the action of axial loading to demonstrate finite element and closed form solutions. These include the following: linear Eigen buckling, nonlinear second order large deformation method, energy method and Euler Bernoulli beam theory. In addition, a variety of snubber assembly sizes are subjected to combined axial and lateral loading in the form of multiple magnitudes of lateral acceleration. The behavior was analyzed by the Euler Bernoulli beam theory and nonlinear second order large deformation method. The techniques of each method are compared providing explanations of the assumptions taken, relevant limitations and recommended applications.
Materials Degradation and Strength Reduction Factors of CFRP and Their Applications in Repair of Nuclear Safety Related Piping
Authors: Uddin M. F. , Pothana S. , Krishnaswamy P. , Smith L. , Basavaraju C.
Published: October 2020

Carbon Fiber Reinforced Polymer (CFRP) composites have been used for decades in various industries such as aerospace, oil and gas, mainly due to their high strength-to-weight-ratio and excellent corrosion resistance. However, the use of CFRP in nuclear industry is very limited. Recently, a new ASME Boiler and Pressure Vessel (BPV) Code Case N-871 has been accepted for internal repair of buried Class 2 and 3 nuclear safety related piping using CFRP for Service Levels A, B, C and D. The ASME BPV Code Case N-871 allows the use of both Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD) methods to design the CFRP repair system. The USNRC has not yet accepted this code case. In 2016, a relief request was submitted to US Nuclear Regulatory Commission (US-NRC) by Surry Power Station, Virginia Electric and Power Company to perform internal repair of degraded ASME Class 2 and 3 safety related circulating and service water buried piping using LRFD method and CFRP, which was approved by US Nuclear Regulatory Commission (NRC).

It is documented in the literature that CFRP materials experience property degradation when exposed to certain environments and creep behavior under sustained loading. From a limited number of tests, it has also been found that the overall strength of CFRP repair decreases with an increase in the number of plies, however, the extent of the strength reduction is not well-supported with test data. The statistical values of CFRP strength can be determined in three ways. The ASME BPV Code Case N-871 recommends using the characteristic value of CFRP strength at a 5th percentile value with 80% confidence, whereas the A-basis (1st percentile with 95% confidence) and B-basis (10th percentile with 95% confidence) values of strength are used in other industries such as in aerospace applications. For a safety related nuclear application, it is therefore important to evaluate how these values compare to one another. The property degradation due to environmental exposure, creep behavior, multi-ply laminate as well as difference in various statistical analysis can be given a general term as strength reduction factor and These factors will have a direct effect on the safety margin of any CFRP repair using the ASD method and hence, it is essential to confirm these factors with an adequate number of experiments.

In this work, mechanical testing and statistical analyses have been conducted to identify specific degradation mechanisms in CFRP as well as other design considerations that may affect the effective factor of safety of the repair system. These include the effect of multi-ply laminates, misalignment angle, width of the specimen as well as the characteristic values of the ultimate strength. Finally, the strength reduction factors are determined from test results followed by a discussion of how these factors affect the overall effective factor of safety of the repair system.
Review of Life Assessment and Repair Strategies for Hydrogen Reformer Furnace Outlet Header Castings
Authors: Nelson Jeremy , Silfies Trace , Crandall Brian , Penso Jorge
Published: October 2020

Steam methane reforming is the most common method of hydrogen production relevant for plants in the petroleum upgrading, downstream refining, methanol, and ammonia industries. Owner-operators of steam methane reformer furnaces continue to make repair and replacement decisions that involve the cast outlet manifold fittings. One key part of these plans is assessment of the weldability and remaining life of the cast components. The 20Cr-32Ni-1Nb alloy casting materials typically used in the outlet manifolds are usually operated in the low end of their creep temperature range but are subject to metallurgical aging mechanisms which reduce their ductility, weldability, homogeneity, and fracture toughness. This paper covers the practices employed by several owner-users to optimize the lifecycle costs of the outlet manifold castings. These practices include but are not limited to controlled materials specifications, in-situ weldability tests, non-destructive testing in-situ and destructive testing post service, and repair practices such as annealing heat treatments.

This paper also includes a limited survey of several owner-users and their fleets of reformer heaters. The details in the survey include the population of affected cast manifold components, alloy grades for the castings and welds, operating temperature ranges, number of startup and shutdown cycles, ranges of time in service, generic design details, and repair case studies.

Also discussed are recent improvements in the state of the art for high temperature materials property data-gathering, as well as the structural modeling via Finite Element Methods. These new technologies are opportunities for future work to develop better strategies in the areas of condition assessment, repair planning, and remaining life prediction, taking into account the relevant parameters of installed manifold components, including: specific aging behavior of the casting chemistry, component mechanical design details, as well as the welding and heat treatment parameters during initial fabrication and subsequent maintenance activities.
On the Study of Packed Catalyst Bed Stresses for Outward Radial Flow Reactors
Authors: Zhao David , Zhao Mingxin
Published: October 2020

Pressure drop in a radial flow reactor occurs when process flow crosses the packed catalyst bed installed between the two concentric perforated screens during operation. This pressure drop generates the lateral bed stress against the reactor’s perforated screens to shift. The pressure drop will further grow as catalyst attrition increases in production. For an outward radial flow, the pressure drop may exert higher stresses to the outer screen as the packed bed is pushed toward it. An extreme case is when the entire catalyst bed could be pinned to the outer screen of the reactor by enough pressure drop. This could cause the internal components to be overly stressed on the excessive bed load, for which the components might not have been designed adequately. Predicting how radial pressure drop impacts the bed stress and shifts the load distribution is important in preventing mechanical failure during operation. In this study, an analytical model is derived based on Janssen’s theory, a classical semi-empirical granular solid material model, to examine a generic packed catalyst bed in an outward radical flow reactor. A modification to Janssen’s theory is introduced to include pressure drop in order to explore its effects on bed stress and load. The critical condition is derived.
Fabrication and Assembly of the First Accident Tolerant Fuel Concept for TREAT Testing
Authors: Woolum Connor , Imholte D. Devin , Fleming Austin , Kamerman David , Tritthart Korbin
Published: October 2020

Following the tragic events at the Fukushima Daiichi power plant in 2011, priority was given to increasing the accident tolerance of fuel systems for the current fleet of nuclear reactors. These enhanced Accident Tolerant Fuel (ATF) concepts include a wide variety of fuel and cladding materials, both as variants of the current Zircaloy-UO2 system and also as novel fuel and cladding concepts. In addition to testing at steady-state, prototypic, conditions within a nuclear reactor, performance of these ATF concepts in off-normal and transient conditions must be evaluated. The Transient Reactor Test (TREAT) facility at Idaho National Laboratory’s (INLs) Materials and Fuels Complex (MFC) was restarted in the Fall of 2017 and is well-suited to serve this purpose. September of 2018 marked the first fueled specimen to be tested in TREAT since its restart; testing of fuel specimens has been ongoing since then. Initial fuel tests focused on the traditional Zircaloy-UO2 fuel system in order to gain a more thorough understanding of operating characteristics of both the test vehicle system and also the interactions between the reactor and the experiment itself. These tests also served to commission new test vehicles using the well-characterized Zircaloy-UO2 system.

The Separate Effects Test Holder, SETH Capsule, is a modular capsule designed such that it can support a wide variety of specimen geometries ranging from prototypic pressurized water reactor (PWR) fuel samples, heat sink based experiments, and more. The capsule itself is an additively manufactured titanium capsule, within which the experimental specimen is loaded. The SETH Phase I series of tests included five individual SETH capsules, each with a single fuel rodlet and instrumentation to measure temperature during irradiation in TREAT. Each fuel rodlet is representative of a fuel rod in a PWR, with UO2 in Zircaloy-4 cladding.

In August of 2019, TREAT irradiated the first ATF candidate fuel, U3Si2. This marked the first transient test of an ATF concept and is part of a larger campaign that will irradiate a total of four capsules containing ATF concepts. This test campaign, SETH Phase II, built upon the previous SETH Phase I campaign with a nearly identical design except for the fuel rodlet itself. Two of the four SETH capsules contained U3Si2 fuel within Zircaloy-4 cladding, and the other two capsules contained U3Si2 fuel within SiC cladding.

This paper reviews the design, fabrication, and assembly efforts resulting in the four qualified SETH capsules for TREAT irradiation of these ATF concepts.
Case Study on Beam-Mode Flow Induced Vibration Against Random Force Fluctuation due to Turbulent Flow at Bend
Authors: Kataoka Shunji , Matsuura Kota
Published: October 2020

The flow induced vibration is the important phenomena when designing piping system and rigorous analysis method without excessive conservatism is highly demanded. Recently guidelines published by Energy Institute is often applied in design phase of piping system to consider the vibration risk in design; however, the safety factor for the method is not fully investigated, especially, for example, the effect of the piping layout, flexibility factor of bend, extrapolation to large bore headers, etc ....

In previous paper, Authors investigated the forcing function due to turbulence flow at the bend by using LES-CFD analysis and quantified the random force fluctuation at the 90 degrees miter bend and two smooth bends and showed that random vibration analysis with these forcing functions can be used to assess the risk of piping vibration.

In this paper, the authors conducted a series of random vibration analysis on the beam mode vibration of typical piping systems. The design variable, such as piping diameter, diameter to thickness ratio, number of flow direction change in each span, and support span were varied as a parameter of the design and evaluated the magnitude of stress and vibration level. The results were compared with the LOF score provided by Energy Institute Guidelines and clarified the difference in design margin of the methods. In conclusions, provides some guidance to reasonably apply the screening method in the design phase of the piping system.