bluuebunny/crossref_metadata_2025 huggingface dataset:
Proposal for Update on Evaluation Procedure for Reactor Pressure Vessels Against Pressurized Thermal Shock Events in Japan
Authors: Hirota Takatoshi , Sakamoto Hiroyuki , Ogawa Naoki
Published: November 2014

The evaluation procedure for the reactor pressure vessel integrity of Japanese PWR plants against Pressurized Thermal Shock (PTS) events is prescribed in the Japan Electric Association Code, JEAC 4206, “Method of Verification Tests of the Fracture Toughness for Nuclear Power Plant Components” since 1991. The current procedure was developed based on the PTS verification test program, which was conducted as Japanese national project and the related studies in 1980’s.

Since much progress has been made on fracture mechanics, fracture toughness, in-service inspection techniques/results and so on, it is preferred to advance the current procedure for more credible evaluation by reflecting the latest knowledge.

This paper describes the outline of the studies to update the current procedure.
Numerical Simulation of Laser Shock Peening in Presence of Weld for Fatigue Life Design
Authors: Julan Emricka , Taheri Said , Stolz Claude , Peyre Patrice , Gilles Philippe
Published: November 2014

Laser shock peening (LSP) is a surface mitigation technique that can be applied to improve the life of a metallic component through the generation of a compressive surface stress field induced by high-power laser pulses. Numerical simulation of LSP (produced residual stresses) in presence of an initial stress field similar to those obtained under welding has been carried out in nonlinear dynamic by coupling an explicit code (Europlexus) and an implicit one (Code_Aster). In the first step, an axisymetrical model has been validated by comparison with an analytical solution considering an elastic-perfectly plastic behavior law. Then, comparisons with Abaqus calculations have been carried out in terms of displacements and residual stresses using the Johnson-Cook high strain rate constitutive law to validate multi-impact 3D modeling. High strain rate parameter of Johnson-Cook law has been identified using LSP on thin plates. Validations of the simulations are then performed by comparing with experimental determined deformations caused by LSP on thick plates. For 25 overlapped shots, LSP induced residual stresses calculated with and without initial residual stresses similar to those obtain under welding have been compared to adress the effect of initial stresses on final residual fields.
Achievements of the European Style Project Technical Training Programme
Authors: Toft Adam , Sharples John
Published: November 2014

The STYLE project considers structural integrity for lifetime management of non-reactor pressure vessel components of nuclear power plant. The project is funded under the seventh European Commission framework programme. A broad objective of the project is to assess, optimise and develop application of advanced tools for structural integrity assessment of reactor coolant pressure boundary components other than the reactor pressure vessel. One aspect of the STYLE project is intended to address the issue of succession planning within the European nuclear industry. With many key technical experts now approaching retirement it is essential to progress the technical expertise of those at an earlier stage of their career in the industry.
Crack Growth Prediction and Leakage Potential of Steam Generator Tubes Subjected to Flow Induced Vibrations
Authors: El Bouzidi Salim , Hassan Marwan , Riznic Jovica
Published: November 2014

Nuclear steam generators are critical components of nuclear power plants. Flow-Induced Vibrations (FIV) are a major threat to the operation of nuclear steam generators. The two main manifestations of FIV in heat exchangers are turbulence and fluidelastic instability, which would add mechanical energy to the system resulting in great levels of vibrations. The consequences on the operation of steam generators are premature wear of the tubes, as well as development of cracks that may leak radioactive heavy water.

This paper investigates the effect of tube support clearance on crack propagation. A crack growth model is used to simulate the growth of Surface Flaws and Through-Wall Cracks of various initial sizes due to a wide range of support clearances. Leakage rates are predicted using a two-phase flow leakage model. Non-linear finite element analysis is used to simulate a full U-bend subjected to fluidelastic and turbulence forces. Monte Carlo Simulations are then used to conduct a probabilistic assessment of steam generator life due to crack development.
Numerical Characterization of the Area Perturbation and Timelag for a Vibrating Tube Subjected to Cross-Flow
Authors: El Bouzidi Salim , Hassan Marwan , Fernandes Lais L. , Mohany Atef
Published: November 2014

Fluidelastic instability can have disastrous effects on the integrity of steam generators. Over the last five decades there has been a great deal of research done in an attempt to understand this phenomenon. These efforts have resulted in several theoretical models and design guidelines. The semi-analytical model of fluidelastic instability initially developed by Lever and Weaver is based on a single tube in a channel flow. The mechanism responsible for instability was found to be one of flow redistribution. While previous studies have been able to characterize the pressure and velocity within a tube bundle, the behaviour of the area of the channel has not yet been fully investigated.

The current study aims to characterize the area of the channel surrounding the tube. Reynolds Averaged Navier Stokes (RANS) equations are cast in an Arbitrary Lagrangian Eulerian (ALE) form and are used to compute the flow conditions in a rigid tube bundle due to a single flexible tube vibrating in the transverse direction. The properties of the velocity field are used to determine the channel boundaries. Properties of the channel area such as area perturbation, mean area, and area phase are investigated for various reduced flow velocities. Dynamic simulations are conducted to determine the impact on the stability threshold for transverse fluid force cases using a mass damping parameter range of 10–200.
Void Fraction Effect on Added Mass in Bubbly Flow
Authors: Béguin C. , Pelletier É. , Étienne S.
Published: November 2014

This paper proposes a relation for the added mass coefficient of spherical bubbles depending on void fraction based on results obtained by a semi-analytical method.

This information is essential to completely characterize finely dispersed bubbly flows, where small spherical gas bubbles are present in a continuous liquid phase. Most of the closure relations for Euler-Euler or Euler-Lagrange models are obtained from experiments involving single bubbles. Their applicability to systems with high void fraction is therefore questionable.

This paper uses solid harmonics to solve 3D potential flow around bubbles. Several configurations were calculated for different numbers of particles and spatial arrangements. Our results are compared with previous studies. Depending on the model proposed by previous authors, added mass forces could increase or decrease with the void fraction. This paper solves these discrepancies.

The main purpose of this work is to develop simple formulas fitting our semi-analytical results. These simple formulas are suitable for further use, particularly as added mass models for multiphase flow averaged equations.
Effect of Nonlinearity of Rubber Bearing on a Seismic Isolated Structure Considering Their Layout
Authors: Chirez Sebastien , Fujita Satoshi , Minagawa Keisuke
Published: November 2014

In Japan, in order to ensure seismic safety requirements for buildings such as hospitals, nuclear power plants and communication centers for instance, seismic isolation systems have been developed. The most widely used technologies are rubber bearings and oil dampers, which can enhance the protection of equipment or machinery set up in those buildings. However, the isolation performance may face difficulties in case of huge earthquakes because of the nonlinearity of rubber bearings.

In a former study of our laboratory, an earthquake response analysis based on the Runge-Kutta-Gill’s method had been carried out in order to assess the behavior of the rubber bearings[1]. In this paper, we use the same method but for further accurate and more realistic simulations, the analytical model has been improved in order to assess the response of rubber bearings depending on their layout when we consider the rocking of the building.
Nuclear Power Plants Issues in IAEA Technical Guidelines on Fluid-Structure Interactions
Authors: Takahashi Shiro , Hasegawa Kunio , Nakamura Tomomichi
Published: November 2014

This paper introduces nuclear power plant issues described in International Atomic Energy Agency (IAEA) technical guidelines on fluid-structure interactions (FSIs). The occurrence of FSIs has been recognized for a long time in industry. It is sometimes difficult to predict the FSI phenomena accurately, however, and FSI vibration and water hammer are concerns for structural design or trouble shooting. There have been many problems caused by FSIs in nuclear power plants. In order to avoid FSI problems for newly designed components, it is important to learn from past FSI events that have occurred at actual plants. Four major types of FSI events that have been publicly disclosed are introduced here and the importance of evaluating reactor internals with respect to flow-induced vibration is noted, if the designs of the reactor internals are for prototypes or the operating conditions are changed. The especially significant internals that are susceptible to flow-induced vibration based on past experience are introduced.
Specificities of Welding Activities in RCC M
Authors: Malouines Philippe , Lainez Bernard , de Mathan Nicolas , Wasylyk Andrew
Published: November 2014

The paper will cover the general approach of welding requirements in RCC-M 2012Ad2014[1], from a technical and quality point of view.

It will be clarified how EN standards has been taken in account, mainly due to developments pushed by Pressure Equipment Directive (97/23/EC)[2] in Europe. It will be explained how nuclear activities for welding need to restrain the use of standards developed firstly for the needs of non nuclear industries. New ISO/ EN standards related to welding (ISO 9606-1, ISO 15614-1, ISO 3834) will be considered, and how they may lead to international cohabitation, compatibilities or harmonization, between nuclear codes.
Uncertainties and Margins in Environmental Fatigue Analysis Rules
Authors: Faidy C.
Published: November 2014

During the past 30 years the main rules for fatigue analysis of pressure vessels were based on elastic approaches in order to evaluate cyclic strain amplitude and compare with an S-N fatigue curve for the corresponding material. After review of some rules in different Nuclear and Non-Nuclear Codes, like ASME Boiler & Pressure Vessel Code Section III, French RCC-M and RCC-MRx, European Standards EN 13445, the major conservatisms and uncertainties of different rules are discussed.

All these Codes propose simple rules to evaluate the strain amplitude based on elastic approaches and simplified correction factors (Ke and Kν), transient combination rules and damage cumulating procedure.

In the other hand, the material properties are based on standard fatigue tests done on the material associated to reduction factors to consider some particular effects like scatter, scale, surface roughness, mean stress or environmental effects to transfer them from small specimen to real structures.

Concerned components in this paper are mainly piping systems.

No existing Code covers all the aspects of fatigue with similar conservatisms that can affect the in-service inspection programs and the remaining life assessment of the corresponding components.

After the review of different rules, key factors that affect the results and predictions will be identified. Some proposals will be issued to progress in the near future.

Finally, a first set of recommendation on fatigue analysis will be presented to improve existing codes on harmonized way, associated to material properties needed, as fatigue curves associated to reduction factors.
Residual Stress Investigation in a Stainless Steel Ring Welded Circular Disc by Over-Coring Deep Hole Drilling Simulation and Measurement
Authors: Zheng Gang , Hossain Sayeed , Smith Mike C. , Smith David J.
Published: November 2014

A circular disc containing a partial ring weld has been devised to permit high levels of residual stress to be created in a relatively small specimen. The purpose of this research is to investigate the residual stress within the weld whilst developing a residual stress measurement method called the over-coring deep hole drilling (oDHD) method. The welding simulation, incremental deep hole drilling (iDHD) simulation and measurement and neutron diffraction were previously studied and reported in [1]. In this paper, the welding simulation results were mapped into a 3D model that included the necessary mesh and boundary conditions to simulate the process of residual measurement using the oDHD method. An experimental programme of residual stress measurement using the oDHD method was then conducted on a welded circular disc. The results from the oDHD simulation and measurement matched well with previous iDHD simulations on the original stress field in the ring weld, which also matched earlier neutron diffraction results.
Design, Manufacture and Maintenance of High-Parameter Pressure Vessels in China
Authors: Chen Xuedong , Cui Jun , Fan Zhichao , Zhang Xiaohu , Guan Weihe , Shou Binan , Xie Tiejun
Published: November 2014

With the rapid development of Chinese economy, the pressure vessels are developing towards the direction of high parameters and have at least one of the following characteristics, one is the use of advanced technology and process, diversification and deterioration of raw stock, causing extremalization of service conditions, which is represented by higher pressure, higher or lower temperature, stronger medium corrosiveness; the other is promoting presence of pressure vessels with extreme dimensions in order to improve economic benefit, which is represented by increased diameter, wall thickness, length or height. Service environment and high parameterization of equipment dimensions cause expansion of design boundary, whereas expansion of design boundary will cause changes in failure modes and design criteria. Therefore, a group of Chinese scholars have conducted effective exploration on design, manufacturing and maintenance of high-parameter pressure vessels. This paper describes the expansion of design boundary and changes in failure modes brought by extramalization of service environment and high parameterization of large-sized equipment, reviews technical advancement in design, manufacture and maintenance of Chinese pressure vessels in recent decade, and forecasts recent opportunities and challenges for high-parameter pressure vessel.
Study on Consideration of Size Effects on Design Fatigue Curve
Authors: Hirano Akihiko , Nakane Motoki , Asada Seiji , Sera Takehiko
Published: November 2014

Published works on studying effects of specimen size on fatigue endurance limit and fatigue life were reviewed. Specimen size effect is apparent in many bending fatigue tests. However, axial tension and compression loading fatigue tests showed that the fatigue limit decreased slightly with increasing specimen size. Design margin for the size effect on fatigue limit under axial tension and compression loading condition that is the condition of the data used to construct Design Fatigue Curve (DFC) is not considered to be necessary. If it is considered conservatively, the value less than 1.1 is enough. Axial tension and compression loading fatigue tests using cylindrical specimens having different diameters showed that the fatigue life increased with increasing specimen diameter. This phenomenon is considered to occur due to the crack growth life which is not negligible in relatively large diameter specimens. Based on this, design margin factor on number of cycles is not necessary to be considered in DFC. These design margins based on the axial tension and compression loading fatigue test results are less than the values in current design codes. This indicates that the current design fatigue curves in the codes have large margins. These considerations will be verified after the large scale fatigue tests that are planned in Design Fatigue Curve (DFC) subcommittee in the Atomic Energy Research Committee in the Japan Welding Engineering Society.
Failure Analysis of CO Shift Gas Heat Exchanger Tubes
Authors: Cao Huaixiang , Zhang Hao , Song Mingda , Shen Xiaomin
Published: November 2014

Tubes of a heat exchanger in a chemical plant leaked frequently, and such tubes will be replaced in one or two years. Therefore, it is necessary to find the leak causes and put in place preventive measures. In this paper, analysis methods such as macroscopic examination, the chemical composition test, metallurgical structure analysis, scanning electron microscopy (SEM) observation, energy spectrum (EDS) and X-ray diffraction (XRD) analysis of corrosion products and condensate water analysis are described that were conducted to analyze the leak causes of the heat exchanger tubes. After analyzing operating parameters (temperature, pressure) and the structure of the bottom area of the heat exchanger, it was found that the heat exchanger tubes inlet was operating in the vapor dew point zone. The results indicate that process parameters (temperature, pressure) were not properly selected and there were substantial SO42− in the process of production. As a result of that dew point corrosion in the form of pitting corrosion and stress corrosion cracking (SCC) which caused the leak occurred on heat exchanger tubes. Finally, relevant preventive measures were recommended according to the analysis results.
Response Analysis of a Seismic Isolated Structure Considering a Probabilistic Approach
Authors: Akamatsu Naoki , Fujita Satoshi , Minagawa Keisuke
Published: November 2014

Japan is one of the most advanced countries in earthquake technology. Isolation systems are widely used in large-scale structures such as hospitals and communication centers. For example, an isolated office building has been used as a hub of recovery from accident by Great East Japan Earthquake in Fukushima nuclear power plant. In the meantime, application of probabilistic risk assessment is used for structure of nuclear power plants. In 2006, Regulatory Guide for Reviewing Seismic Design was revised and according to guideline, it is necessary to consider the residual risk1. In addition, seismic isolation systems are expected to be used for nuclear power plants. Recently, the risk of isolation system’s failure needs to be assessed in case of large ground motion. This paper deals with probabilistic approach on seismic response of an isolated structure. Consequently, sensitivity analysis is carried out. Then, as nonlinear behavior in rubber bearings occurs during huge earthquake, it has to be considered in the sensitivity analysis.
Life Extension of Hydrocarbon Equipment in Sour Environment
Authors: Al-Mithin Abdul Wahab , Kumar G. Santhosh , Al-Shaiji Mohammad , Hannan Abdul Sattar A. , Jose Vinod
Published: November 2014

Reliability of equipment is indispensable for the uninterrupted operation of any oil & gas producing facility. Over a period of time, some oil wells producing sour crude were also added to the incoming feed of Gathering centres, which were originally designed for processing sweet crude. Most of the facilities were designed and installed prior to the publication of NACE MR 0175 and NACE TM 0284. As these facilities are still in operation under sour condition, it is prudent to take necessary measures in time for continuing safe operation of these facilities.

In this paper, the authors share their experience in initial detection & online monitoring of service-induced damages to the equipments due to sour service using NDT techniques like Wet Fluorescent Magnetic Particle Inspection, manual ultrasonic testing and time of flight diffraction & Phased Array. The experience gathered during internal coating of the vessels has also been described. Several items of equipment continued in operation to maintain production even after the detection of Hydrogen induced cracking. Periodic monitoring and critical analysis of inspection data provided confidence to continue operation of equipment. This enabled the operating company to extract maximum life of the equipment without compromising on safety.

This Paper focuses on two items of equipment, HP Gas Scrubber from Oil/Gas separation plant and HP Gas Discharge Cooler from CRU. Fitness for Service (FFS) evaluations were carried out for HP Scrubber and the Channel head component of HP Gas Discharge cooler. The analysis was based upon the latest UT scan results and guidelines prescribed in API 579-1/ASME FFS-1. These items of equipment were found not fit for further service. In the interim period, the company procured new scrubber and channel head of the cooler for replacement thus minimizing the shutdown period.
ASME III Fatigue Assessment Plasticity Correction Factors for Austenitic Stainless Steels
Authors: Emslie Julian , Watson Chris , Wright Keith
Published: November 2014

ASME III NB-3200 provides a method for carrying out fatigue calculations using a simplified elastic-plastic analysis procedure. This allows a correction to elastic analysis to be performed in place of a full elastic-plastic analysis. Two mutually exclusive factors are described: the Poisson’s ratio correction accounts for surface stress exceeding the yield strength of the material and the Ke factor accounts for gross section plasticity. The recently released ASME Code Case N-779 provides a more complex but less onerous calculation of the Ke factor. Correction factors from the JSME and RCC-M codes have also been considered in this paper.

The conservatism of different plasticity correction factors has been examined by calculating a ratio between the equivalent strain range from elastic-plastic Finite Element (FE) models and the strain range from elastic FE models and comparing this to calculated plasticity correction factors. Results show the potential for both the current ASME and Code Case Ke corrections to under-predict the strains when compared to those from an elastic-plastic FE assessment.

A preliminary investigation has been carried out into an alternative correction factor based on linearised stress and local thermal stress ranges. This addresses the discontinuity between the two correction methods for surface and sectional plasticity which has been identified as a feature of the ASME correction methodology.
Added-Mass and Viscous-Damping Forces Acting on Various Oscillating 3D Objects
Authors: Onishi Hajime , Kitamoto Tomoya , Maeda Tsuyoshi , Shimohara Hideki , Tanigawa Hirochika , Hirata Katsuya
Published: November 2014

In many fluid-structure-interaction problems, the “added mass”, “inertial mass”, “virtual mass”, “carried mass” or “induced mass” is one of important interests. In the present study, the authors propose a simple and efficient method to specify fluid-force coefficients of an oscillating object in stationary fluid. In this method, the authors consider incompressible-and-viscous fluid under the assumption of an infinitesimal oscillation amplitude of a three-dimensional object, and properly modify the Navier-Stokes equations into linear equations, namely, the Brinkman equations. The solving method is based on a discrete singularity method, one of the boundary methods. Furthermore, the authors conduct experiments, in addition to computations. In order to confirm the method’s effectivity and validity, the authors compute a sphere, comparing our computations to theories and experiments which show good agreement.
Development of Generic Failure Frequency of LNG Plant Equipment Using Offshore Reliability Data
Authors: Kang Seok-Jun , Kim Moon-Ki , Choi Jae-Boong
Published: November 2014

American Petroleum Institute (API) introduced the methodology, which is called Risk-Based Inspection (RBI), for calculating the risk of equipment operated in refinery or petrochemical plants [1]. However, RBI has limitations for applying directly to LNG plants, because API makes the RBI code suitable only to refinery or petrochemical plants. Especially, developing new gff value is needed, because RBI results can be influenced as generic failure frequency (gff) changes [2].

The objective of this paper is recommending new gff only for the main equipment in LNG plant. In order to solve the problem, three gffs will be used. The three are API providing gff value, the gff obtained by OREDA which gathers the data during long period in offshore petrochemical and gas plant, and the gff from real data of Test bed train No.1 working in the present [3]. In this respect, POF values which are calculated by API gff and OREDA gff will be compared. Afterward, the reliability of each cases will be verified by using operating data of Test bed train No.1.
Modeling of Fuel Assemblies in a Boiling Water Reactor for Seismic Analysis
Authors: Koide Yuichi , Goto Yoshihiro , Sato Yuki , Onitsuka Shohei , Ishigaki Hirokuni
Published: November 2014

The purpose of this study is to develop a seismic analysis model of a group of fuel assemblies in a boiling water reactor and to confirm the validity of the developed model. Each fuel assembly was modeled as a beam on the basis of the finite element method. The mass matrix of the model includes an added mass matrix, which represents the coupled inertia effect caused by the coolant water, in order to simulate the coupled vibration of fuel assemblies. The added mass matrix was obtained by calculating the coefficient matrix of the acceleration vector and fluid force vector under the condition that each fuel assembly moves at unit acceleration. The validity of the model was confirmed by comparing the calculated results with experimental ones. The compared specimens for the experiments were full-scale mock-ups. The vibration characteristics of fuel assemblies in each case of 4 bodies and 368 bodies were compared. As a result of the comparison, the calculations of the frequency response were in agreement with the experimental results. Particularly, the calculation results on the resonance frequency were in good agreement, with an error of less than 2 percent, with the experimental ones. Furthermore, the calculated vibration characteristics of 368 fuel assemblies in the case of an earthquake, such as the excited vibration mode and phase characteristics, were in agreement with the experimental ones. We concluded that the developed model of fuel assemblies was applicable to seismic analysis of a boiling water core.
Understanding Damping in Acoustic and Mechanical Systems
Authors: Goyder Hugh
Published: November 2014

A system with damping is much more difficult to model than an undamped system. In particular, the effect of damping on a multi-degree-of-freedom system is not a straightforward extension of the damping found in a single-degree-of-freedom system. The complications of a multi-degree-of-freedom system are first examined by investigating the acoustic modes of a pipe with energy leaking from the boundaries. This system can be modelled exactly and identifies the complexities that need to be understood. Although this is a linear system it is found that in contradistinction to an undamped system it cannot be separated into individual modes of vibration. Modes which bear some similarity to undamped modes can be found but these are always coupled by damping effects which, to add more complications, may involve some modes being active and supplying energy to other modes. The original acoustic system is simplified to systems of finite and eventually two-degrees-of-freedom in an effort to understand the effects of damping. It is found that when damping is added to a system some damping ratios may decrease moving the system into an unfavourable state. Overall some general properties of damping, for example, the constancy of average damping, are deduced.
Material Strength Evaluation for 60 Years Design in Japanese Sodium Fast Reactor
Authors: Nagae Yuji , Onizawa Takashi , Takaya Shigeru , Yamashita Takuya
Published: November 2014

316FR and Mod.9Cr-1Mo steels are candidates as structural materials for Japanese Sodium Fast Reactor (JSFR). The design life and operation temperature of JSFR is 60 years and 550 °C, respectively. Time-dependent allowable stress is essential. The evaluation of allowable stresses to 500,000 h is a considerable item. Long term strength is evaluated from a viewpoint of microstructural evaluation related to fracture mechanism. In addition, degradation after long term operation at elevated temperature is important. Aging is considered as one of the degradation. The effect of aging on short term property is analyzed. Material strength standard is also necessary for very thick tube sheets of forgings and small diameter thin walled seamless pipes, which are made of Mod.9Cr-1Mo steel in steam generators. This paper summarized currently available data and information on the above items, and shows path forward to the development of material strength standard for 60 years design in JSFR.
Investigation of Microstructural Changes due to Thermal Aging in Dissimilar Metal Welds
Authors: Choi Kyoung Joon , Yoo Seung Chang , Bahn Chi Bum , Kim Ji Hyun
Published: November 2014

To investigate the effect of long-term thermal aging on the fusion boundary region between low-alloy steel A533 Gr. B and weld metal Alloy 152, a representative dissimilar weld mockup composed of Alloy 690/Alloy 152/A533 Gr. B was aged in laboratory furnaces under accelerated temperature conditions. The aging time was determined using the diffusion equation. The heat treatment was performed at 450°C for 60-y equivalent time (5,500 h) to simulate thermal aging effects. An additional aging heat treatment was also performed at 400°C for 15- and 30-y equivalent times (6,450 and 12,911 h, respectively) to determine the effects of temperature on aged microstructures. The characterization was mainly conducted in the microstructure of the fusion boundary region in the weld root region using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe tomography. It was determined that the region near the fusion boundary was generally divided into several regions, such as a dilution zone (that included a chemical gradient in the weld side), fusion boundary, and heat-affected zone in the low-alloy steel. The results of this study showed that heat treatment increased Cr content in the dilution zone, but the chemical gradient in the weld side near the fusion boundary persisted. For the microstructure, it was observed that treatment induced the formation and growth of Cr precipitates in the fusion boundary region of the dissimilar metal joints due to the thermodynamic driving force. At two heat treatment conditions (400 and 450°C), although the extent of the results described above differed, the trend in the results appeared to be the same. This microstructure information can improve the understanding of cracking-resistant change when structural changes occur. Furthermore, such data will be important for assessing the effects of aging on structural components and for evaluating the long-term operation of nuclear power plants.
Reciprocating Compressor Cylinder’s Cooling: A Numerical Approach Using CFD With Conjugate Heat Transfer
Authors: Balduzzi Francesco , Ferrara Giovanni , Babbini Alberto , Maleci Riccardo
Published: November 2014

The working cycle of a reciprocating compressor is characterized by heat generation, mainly due to compression transformation and friction phenomena. The main consequences are a reduction of the volumetric efficiency and an increase in the gas discharge temperature. Current regulations such as API618 for reciprocating compressors require a cylinder cooling system. Therefore, a proper design of the cooling circuit is needed in order to achieve the best balance between refrigerating potential and system capacity.

A systematic methodology for the evaluation of the heat transfer process is essential and since experimental characterization of the circuit is complex and case-dependent, the use of a numerical technique is the most favorable and generalizable approach. Within this scenario, 3D analysis shows a great potential although several phenomena must be accounted for in order to accurately model the system.

In this paper, a conjugate heat transfer (CHT) analysis on a double-acting water-cooled reciprocating compressor cylinder is presented, where the three-dimensional flow field of the water circuit and the thermal conduction inside the solid metal are solved simultaneously. The best practice for the imposition of consistent boundary conditions for the metal body is given with special attention to the heat transfer coefficient values for the suction and discharge gas chambers, the compression chamber and the external ambient. The assessment of the numerical methodology is completed with an investigation on the influence of wall roughness and buoyancy effects.
Local Failure Analysis of HPHT Subsea Tree Components due to Triaxial Stress
Authors: Karpanan Kumarswamy , Thomas William
Published: November 2014

Structures can fail prematurely and potentially suddenly when the stress state is in triaxial tension. Triaxial stresses commonly occur in notches, crack tips and thread roots. Yielding criteria such as Tresca and von Mises are based on the difference in the principal stresses and therefore reduce as the three principal stresses become more equal in magnitude. Therefore, structures need to be analyzed for failure due to triaxial stress state when conducting a plastic collapse study. One of the requirements of the ASME Section VIII Divisions 2 and 3, Design by Analysis approach is to check for the local failure of the component due to triaxial stress. Based on the ASME approach, local failure is analyzed by calculating the allowable total equivalent strain and summing the plastic strain history through a damage accumulation function. In this paper, two common HPHT subsea tree components, a gate valve body and a load bearing shoulder are analyzed for ASME local failure criteria.
The Analysis of Acoustic Emission Code and the Research of Acoustic Emission Signal of P355NL1 Under Low Temperature of −40°C
Authors: Biao Xiao , Tang Xiaoying , Liang Nie , Jianping Yao , Jianrong Li
Published: November 2014

The latest content of acoustic emission code GB/T18182-2012 are shown in this paper. The differences of GB/T18182-2012 and GB18182-2000 are summarized. Acoustic emission method was used to inspect the whole process of tensile specimen test under the temperature of 0°C, −20°C and −50°C. Based on the characteristics of the signal of different temperature condition, some difference of these signals was analyzed and discussed. By using the above result, acoustic emission was applied to inspect a drikold storage vessel.
Finite Element Simulation of a Circumferential Through-Thickness Crack in a Cylinder
Authors: Arun Sutham , Sherry Andrew H. , Smith Mike C. , Sheikh Mohammad
Published: November 2014

This paper presents the results of a structural integrity assessment of a large-scale test undertaken as part of the EU programme STYLE on a repair welded pipe containing a circumferential through-thickness crack. The pipe was manufactured from two Esshete 1250 stainless steel pipes joined by a girth weld containing a deep repair. A through-thickness circumferential pre-crack was introduced to the centre of the repair prior to testing in four-point bend. The assessment used a finite element model created in Abaqus, with the weld residual stress introduced by an iterative technique. Linear elastic fracture mechanics was used to evaluate the stress intensity factor KI for the defect and elastic-plastic analyses were performed to characterise the crack driving force J along the crack front. The predicted crack mouth opening displacement as a function of load was compared with the test results and the derived variation in J used to predict crack initiation and growth. The results predicted the global behaviour of the test to within approximately 7% at final load, and the position of maximum crack growth. However, the final extent of crack extension is under-predicted. Reasons for this underprediction are suggested.
Dynamics of the Forced Karman Wake: Comparison of 2D and 3D Models
Authors: Mureithi Njuki W. , Xu Xiaofei , Baranyi Laszlo , Nakamura Tomomichi , Kaneko Shigehiko
Published: November 2014

The interaction between the cylinder motion and the wake is a complex feedback phenomenon in which the symmetry relationship between the wake and the cylinder motion plays a key role. Depending on the frequency of oscillation the symmetry relationship between the unforced von Karman wake and the imposed forced oscillations can induce a series of bifurcations. This detailed bifurcation behavior is the subject of study in the present work. 2D and 3D simulations are carried out for a Reynolds number Re=1000. As the inline cylinder forcing amplitude is increased, the wake undergoes a series of bifurcations and associated changes in the flow structure. Although the 2D analysis is clearly non-physical, it leads to a ‘simpler’ and more tractable model.

Detailed comparison of the 2D and 3D POD modes provides insight into the forced wake dynamics. The 3D spatial mode shapes are significantly similar to those from 2D simulations. The relative modal energy distribution captures well the wake flow complexity. The first mode contains over 90% of the flow energy in the 2D simulations. This ratio drops significantly in the 3D case to around 45%. Clearly 3D effects are very important when it comes to energy distribution between the modes. However, the predominance of the first mode seems high enough to maintain the 2D-like dynamics.

The wake flow is found to undergo two main transitions with increased forcing. The first is periodic shedding to chaotic shedding. The second is chaotic shedding to half-frequency shedding caused by a period-doubling bifurcation. The 2D simulations correctly predict these bifurcations — including the type and the number of bifurcations. The results suggest that the forced wake dynamics are primarily dominated by two-dimensional rather than 3D dynamics. However, 3D effects are important in determining the exact parameter values where bifurcations occur. A previously developed low order analytical model, based on 2D simulations, is also used to predict the wake bifurcation behavior. The relevance of the low order model has interesting implications for VIV control.
Effect of the Type of Stress-Strain Law on the Validity of the Reference Stress Approach in Fracture Mechanics
Authors: Gilles Philippe , Zhang Gongchen , Madou Komlanvi
Published: November 2014

In fracture mechanics, several J-estimation schemes are based on the reference stress approach. This approach has been developed initially in the frame of the R5 rule for creep and R6 rule for elasto-plastic fracture assessments. Later other methods, based on the reference stress concept, where derived like the Js method introduced in the French RSE-M code en 1997 and the Enhanced Reference Stress (ERS) method in Korea around 2001. However these developments are based on the J2 deformation plasticity theory and well established for a pure power hardening law. Even in this latter case, the reference stress depends on the hardening exponent. Js and ERS attempt to minimize this dependence and propose some corrections for recorded behavior laws which cannot be fitted by a power law. However their validation has been established mainly on cases where the material behavior is governed by a Ramberg-Osgood (R0) law. The question may be raised, as for the bilinear hardening law case, of the existence of a reference stress for non RO laws.
Comparisons of Monotonic, Low-Cycle and Ultra-Low-Cycle Fatigue Behaviours of X52, X60 and X65 Piping Steel Grades
Authors: Pereira J. C. R. , de Jesus A. M. P. , Fernandes A. A. , Xavier J. , Martins B.
Published: November 2014

Seismic actions, settlements and landslides, accidental loads, fluctuations in the layers of permafrost and pipelines reeling induce large plastic deformations, with widespread yielding in the pipelines which may lead to failure, either due to monotonic loading or due to cyclic plastic strain fluctuations with high amplitude and short duration (Nf<∼100 cycles). The damage mechanisms from the high intensity cyclic loading show distinct mechanisms from the monotonic and low-cycle fatigue (LCF) (∼100<Nf<∼10000cycles). This fatigue domain is often called ultra-low-cycle fatigue (ULCF) or extreme-low-cycle fatigue (ELCF), in order to distinguish it from LCF. Despite of monotonic ductile fracture and LCF have been subjected to significant research efforts and a satisfactory understanding of these damaging phenomena has been already established, ULCF regime is not sufficiently investigated nor understood. Consequently, further advances should be done since the data available in literature is scarce for this fatigue regime. In addition, the performance of ULCF tests is very challenging and there is no specific help from standards available in literature. In this work, the performance of X52, X60 and X65 API steel grades under monotonic, LCF and ULCF loading conditions are investigated. An experimental program was carried out to derive monotonic, LCF and ULCF data for three piping steel grades. Typical smooth geometries are susceptive to instability under ULCF tests. To overcome or minimize this shortcoming anti-buckling devices may be used in the ULCF tests. The use of notched specimens facilitates the deformation localization and therefore contributes to overcome the instability problems. However, the non-uniform stress/strain states raise difficulties concerning the analysis of the experimental data, requiring the use of multiaxial stress/strain parameters. Optical methods and non-linear finite element models were used to assess the strain and stress histories at critical locations, which are used to assess some damage models.
Additional Guidance for Inelastic Ratcheting Analysis Using the Chaboche Model
Authors: Weitze William F. , Gilman Timothy D.
Published: November 2014

This paper builds on PVP2013-98150 by Kalnins, Rudolph, and Willuweit [1], which documented two calibration processes for determining the parameters of the Chaboche nonlinear kinematic hardening (NLK) material model for stainless steel, and tested the material model using a pressurized cylindrical shell subjected to thermal cycling. The current paper examines (1) whether a Chaboche NLK model with only two terms (rather than four as in PVP-98150) is sufficiently accurate, (2) use of the ANSYS program for material model refinement and finite element analysis, and (3) analysis using temperature-dependent NLK model parameters, again using ANSYS.
An Analytical Solution for Piping Non-Planar Flaws
Authors: Hoang Phuong H. , Mak Chee W.
Published: November 2014

Recent studies on the effect of multi-axis loading on piping non-planar flaws indicate that the ASME Section XI, Appendix C pressure limit load approach for planar axial flaws can be used for evaluation of non-planar flaws provided that the effect of multi axial loading is to be considered. Finite element analysis results presented in this paper also indicate that bending limit load for planar circumferential flaws can be used for evaluation of non-planar flaws subjected multi axial loading. These studies used idealized uniformly thin rectangular flaws whose projected flaw geometry on pipe cross section and on pipe axial section are the same as the circumferential flaw geometry and the axial flaw geometry defined ASME B&PV, Section XI Appendix C. Sample problems with actual pipe wall thinning flaws due to flow accelerated corrosion and pitting in nuclear power plant are utilized for a comparison of the proposed methodology with various methodologies currently used by the industry for locally thinning pipe flaw evaluations.
Development of Residual Stress Profiles for Defect Tolerance Assessments of Thick Section Electron Beam Welds
Authors: Hurrell P. R. , Pellereau B. M. E. , Gill C. M. , Kingston E. , Smith D. , Bouchard P. J.
Published: November 2014

This paper describes the results of weld model analysis and deep hole-drilling measurements undertaken to evaluate residual stress distributions in austenitic and ferritic steel thick section electron beam welds. The work was undertaken in support of a Rolls-Royce and TWI development programme in the UK, for a Reduced Pressure Electron Beam (RPEB, 0.1 to 1mbar) welding process using a mobile local vacuum seal for the manufacture of thick section pressure vessel and pipe welds for nuclear power plant applications. Measurements were undertaken on representative mock-ups including a 160mm thick SA508-3 forging circumferential seam weld, in both the as-welded and furnace post weld heat treated condition. A 316L stainless steel plate butt weld and a 304L pipe girth weld of 80mm and 36mm thickness respectively were also analysed.

There is now considered to be sufficient understanding of the residual stress fields generated by thick Electron Beam (EB) welds, to propose through thickness ‘upper bound’ R6 Level 2 stress profiles for use in defect tolerance assessments. The intention is to incorporate residual stress profiles of this type into the R6 structural integrity assessment procedure, following peer review. This would represent a significant step forward in demonstrating technology readiness for plant applications. It is also anticipated that an ASME Code Case will be drafted and proposed for the RPEB welding process.

EB welding is a relatively low heat input process, compared with a multi-pass arc weld, such that the fusion zone and heat affected zone are narrow. The centre of an EB weld is the last region to solidify and cool-down, so typically there is a high degree of restraint to weld metal contraction, thereby generating a highly tri-axial yield magnitude tensile stress state at the mid-thickness location. The stress components acting in the longitudinal welding direction and through-thickness orientation tend to be large in the centre of EB welds of high aspect ratio (depth / width). By contrast, lower stress levels are produced on the surfaces acting transverse to the weld plane compared to conventional multi-pass metal arc welds. The transverse stress component is most likely to be required for the assessment of any postulated EB welding defects. The residual stress field decays rapidly with distance from the EB joint into the adjacent parent metal. Symmetrical stress distributions are typically generated in a 1-pass EB plate weld and stress fields are characteristically sinusoidal of wavelength between 1 and 4 times the section thickness.
Technical Basis for the Proposed Weld Residual Stress Guidance in API 579-1/ASME FFS-1
Authors: Dewees David J. , Prueter Phillip E. , Kummari Seetha Ramudu
Published: November 2014

Recent progress in the simulation of weld residual stress (WRS), and in its verification and validation (V&V) has provided the opportunity to re-examine existing WRS guidance (Annex E of the Fitness-for-Service (FFS) standard, API 579-1/ASME FFS-1). Comprehensive review of existing guidance and corresponding basis documents, supplemented by validated weld residual stress analysis are utilized to assess the appropriateness of the existing Annex E, and to develop proposals for alternate approaches. The simulation techniques used to support the proposed guidance are described in detail here. The European NeT Program provides an important part of the V&V of all results, and is the focus of this paper. Results using the presented methods show excellent agreement with measurement, therefore providing a sound basis for supplemental analysis to extend available experimental results as necessary. The methods also provide a baseline from which to assess future modeling simplifications for special cases.