bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intense X-Ray Measurement of Transient Hydraulic Phenomena in Molten Pool During Laser Welding Process
Authors: Yamada Tomonori , Shobu Takahisa , Yamashita Susumu , Ogawa Takemitsu , Sugihara Kenta , Nishimura Akihiko , Muramatsu Toshiharu 
Published: August 2013

Spatial temperature distribution during the laser welding process has a huge effect on any residual stress distribution. Therefore, understanding of the transient hydraulic phenomena which affect the temperature distribution in the molten pool is very important.
In this work, intense X-ray measurement at the Super Photon ring-8 GeV (SPring-8) facility well carried out to document the transient hydraulic phenomena in the molten pool during the laser welding process. Based on in-situ observation of inside material, the experimental results confirmed that the molten pool shapes, hydraulic condition such as flow velocity, etc.. In the case of laser power is 330W and spot diameter is 1mm, we observed the steady flow which consisted of downward flow and upward flow. The flow velocities were about 19.5 mm/s and 9.0 mm/s, respectively. Moreover, the rate of phase change was obtained from molten pool shape during laser welding. The rate of phase change was not constant during laser welding. Thus the interface shape might change at all time. Therefore, to evaluate the temperature distribution, it is necessary to consider not only convection but also the interface shape.
These results indicate that the intense X-ray measurement during laser welding is very effective for the understanding the molten pool phenomena.
Advances in Hypercompressor Valve and Valve Spring Design
Authors: Bagagli Riccardo , Capanni Alessio , Maggi Carmelo , Tognarelli Leonardo 
Published: August 2013

The life of valves is extremely important for the availability of hyper-compressors in LDPE plants.
The valves operate due to the action of the differential pressure across a moving element, typically with a poppet shape, and close due to the action of dedicated counteracting springs housed into the same valves. A proper design of the spring is a balance between ensuring the “on time” opening/closure of the valve, a low impact velocity of the poppet and low fluttering.
Particular attention shall be paid to the dynamic behavior avoiding to excite the spring and poppet-spring system close to themselves resonance frequencies. Different factors such unexpected transient conditions or vortex shedding phenomena could shorten the life of valves springs and valves bodies, since the valve spring is forced to operate out of the design conditions.
A compressor application presenting evidence of spring surge phenomena (resonance of spring itself) is presented. Frequencies exciting spring natural modes frequencies can be introduced in the process gas by vortex shedding generated along the gas outflow through the valve during the transient conditions or in regime conditions.
Since the vortex shedding frequency predictability is affected by some bias inaccuracy level coming from process variability and model approximation, then a robust design approach is to employ progressive spring that is insensitive to surge phenomena.
This paper gives an overview of progressive and non-linear springs and the benefits they offer compared to linear springs and how progressive springs has to be designed for hyper-compressor valves application. Several spring designs are analyzed with a simplified prediction model, the results (load deflection, stiffness, natural frequencies, fatigue lives) are then compared with finite element analysis and bench tests results using a specifically developed test bench allowing to measure spring natural frequencies and to conduct accelerated fatigue testing.
Error Analysis for FEM Analysis of Cracks Using Submodels
Authors: Gloger Daniel , Enderlein Marco , Kuna Meinhard 
Published: August 2013

In order to assess the safety against fracture of nuclear shipping casks, drop tests are simulated using the finite element method. The simulations are based on a global model without defects. From the results positions are derived at which a crack initiation from a defect would be most likely. At each of these positions a submodel with a crack is inserted. The insertion of the crack changes the stiffness and therefore the stress of this region. Depending on the submodel size the calculated fracture mechanics parameters deviate from the reference value found without using the submodel technique.
The objective is to determine this deviation only from one submodel. A practicable method for the determination of the required submodel size is developed calculating the difference of the traction vector between the submodel with opened and with closed crack. Its scalar product with the weight function results in the contribution of the submodel boundary to the deviation. Integrated over the boundary it yields the deviation of the submodel. The shape of the submodel can be optimized by expanding sections of the submodel boundary with a high contribution.
Finite Element Modelling of Reduced Pressure Electron Beam Stainless Steel Plate and Pipe Welds
Authors: Pellereau Benjamin M. E. , Hurrell Paul R. , Gill Christopher M. , Ayres Kevin 
Published: August 2013

Rolls-Royce plc is conducting work to investigate the feasibility of using Reduced Pressure Electron Beam Welding (RPEB) for thick section welded joints in power plant construction. As part of the work, simple specimens have been manufactured at TWI ltd in order to develop welding parameters and conditions and to examine the achievable weld quality. Previous work in this project has shown good correlations between measured and predicted stresses in RPEB welds in ferritic components [5,6].
This paper describes Finite Element (FE) modelling that was carried out to try to predict the residual stress field generated by the welding process in three of the specimens. The first specimen that was modelled was a full penetration butt weld in 80 mm thick Type 316L plate (W17). The other two models were of circumferential butt welds in 14 inch nominal diameter Type 304L pipe. The first pipe model (W20) was a single pass, 360° weld, while the second (W22) featured a slope-up and slope-down each lasting for 16° either side of a 360° full penetration weld, giving a total weld of 392°. The modelling was carried out in Abaqus [1] using a DFLUX user subroutine to model the welding heat input as a cylindrical heat source, due to the reduced pressure during specimen manufacture, only radiation heat losses were considered. The built-in Chaboche mixed hardening model was used for both materials during the structural analysis.
The residual stresses predicted by the FE modelling have been compared with the results of Deep Hole Drilling (DHD) that was carried out on the equivalent specimens. Full details of the measurements are reported in [4].
Code Aspects Related to Combination of Stresses due to Hydrogen Detonation: Beam and Combined Effects
Authors: Minichiello John C. , Ligon Thomas C. , Gross David J. 
Published: August 2013

Stresses in piping systems subject to hydrogen detonation loading are complex. There are high-frequency localized shell-type stresses, such as hoop membrane, longitudinal through-wall bending and hoop through-wall bending due to asymmetric modes. There are low-frequency gross beam-type stresses, similar to those from a waterhammer, as the unbalanced forces excite the beam bending and bar wave modes in the piping system. From a code compliance standpoint, all the stresses need to be considered and categorized in terms of the type of failure that they can cause.
Part 1 developed a method to estimate the local shell stresses due to the detonation wave. This paper, Part 2, discusses an investigation into the global beam bending effects. It proposes a methodology for combining the beam and local shell effects, and evaluating the results in terms of complying with a typical piping code.
The gross stresses due to the propagating detonation wave can be evaluated using beam-finite element models and time-history analysis, similar to analyses for waterhammer. As with waterhammer, these stresses are typically considered “occasional” loads. However, the beam stresses can coincide with very high hoop or radial shell stresses, due to the high peak pressures involved, so that the simple comparison of using longitudinal stresses may not be an adequate design check. This paper recommends a combination of shell-equivalent stresses and beam-stress intensities that result in a conservative comparison, when compared to a full time-history analysis, but one which is not overly conservative.
With the exception of ASME Section III, Class 1, most U.S. piping codes do not provide rules for fatigue evaluation for loads other than displacement controlled loads. ASME B31.3 Appendix P provides guidance for pressure fluctuations, but the focus is primarily gross stress effects. The local effects from a detonation wave include both a “skin” stress effect on the inside surface and a through-wall bending effect due to the dynamic nature of the effects of the propagating wave. Both of these must be considered if the number of occurrences is significant. This paper proposes a method to consider these localized stresses that is patterned after the guidance in ASME Section III, NB-3600.
Effect of Ageing on Residual Stresses in Welded Stainless Steel Cylinders
Authors: Do Son , Smith David , Smith Mike 
Published: August 2013

Operation of components at high temperature in power stations leads to the relaxation of residual stresses created in welded stainless steel cylinders. In this work a number of Esshete 1250 stainless steel cylinders containing girth welds and repair welds were manufactured. Two cylinders were then put to a furnace for 10,000hrs and 20,000hrs at 650°C. These conditions simulated the effects of aging.
The residual stresses in the girth welds and repair welds before and after aging were measured using a number of methods based around the Deep Hole Drilling method. This paper describes the experiments carried out to obtain the through-wall distribution of stresses.
It is evident that there was significant relaxation of the residual stresses due to aging. The peak tensile residual stress in girth welds was relaxed from 500MPa to 110MPa and the peak compressive residual stress in girth welds was relaxed from −301MPa to −135MPa after 10,000 hours at 650°C. The repair weld residual stresses were not only relaxed at the peak stresses but relaxed average levels from 220MPa to 140MPa for hoop stresses and from 180MPa to 145MPa for axial stresses. The implications of these findings are discussed in the context of future fracture tests.
High-Temperature Constitutive Behavior of Austenitic Stainless Steel for Weld Residual Stress Modeling
Authors: Qiao Dongxiao , Zhang Wei , Feng Zhili 
Published: August 2013

Weld residual stress is a major driving force for initiation and growth of primary water stress corrosion cracking (PWSCC), which is a critical challenge for weld integrity of reactor pressure vessel nozzles in nuclear industry. Predicting weld residual stresses for the purpose of understanding and mitigating PWSCC requires the knowledge of material constitutive rule especially strain hardening behavior over a wide range of temperatures. Though it is adequate for describing deformation at low temperature, the conventional, rate-independent, elastic-plastic constitutive rule falls short in predicting the strong microstructure-mechanical interaction such as the softening due to recovery (dislocation annihilation and realignment) and recrystallization at elevated temperature in welding.
To quantify the extent of softening under temperature and strain conditions relevant to welding, a framework has been developed by combining advanced experimental techniques and finite element modeling. First, physical simulation in a Gleeble testing machine is used to simulate the temperature transients typical of dissimilar metal weld by subjecting round tensile bar shaped specimens to rapid heating and cooling. Second, the digital image correlation (DIC) technique is used to map the non-uniform strain field and extract local strain history needed for accurately determining the true stress vs. true strain curve of softened material. Third, the thermally-mechanically processed specimens are characterized metallographically to correlate the microstructure changes to the measured stress-strain behavior. Finally, a thermal-stress finite element model of three-bar frame is used to study the effect of softening on the predicted weld residual stresses. As a first step toward developing the much-needed, comprehensive material constitutive relation database for dissimilar metal weld, the framework has been applied to study AISI 304L austenitic stainless steel. The extent of softening due to different duration of high-temperature exposure is studied and its influence on final residual stresses is discussed.
Empirical Estimation of the Abrasion Endurance Life of Epoxy Coatings for Applications on Transmission Pipelines
Authors: Mally Timothy S. , Walker Roger H. , French Jesse J. 
Published: August 2013

Internal and external pipeline erosion due to suspended particulate matter, wax and sand content, and geoseismic motion can rapidly reduce pipeline wall thicknesses to critically low values. Due to low shrinkage rates on curing, epoxy polymer coatings are well suited for slowing the rate at which pipe wall thickness is lost. The abrasion resistance of an epoxy coating is a function of the hardness of the coating, the abrasive particle velocity, angle of impact, and particle size. This paper describes the authors’ attempts to estimate longevity of certain Bisphenol-A based epoxy coatings against particulate abrasion.
Details are presented for the abrasion resistance testing of four different commercial epoxy coatings. Experimental methodology is detailed consisting of two different methods of accelerated erosion testing: water-jet droplet erosion and fixed frequency mechanical abrasion. The methods are used to calculate abrasion endurance lifetime for a variety of pipeline installation environments.
Test samples are exposed to abrasive wear for a given period of time and material loss is measured. Loaded and unloaded abrasion testing is used to represent forces proportional to buried and non-buried piping. Erosion volume and time to the specified erosion depth are compared with control data on uncoated carbon steel substrates. This accelerated erosion data is transposed to reflect in-situ life expectancies.
Industrial Application of Small Punch Testing for In-Service Component Condition Assessment: An Overview
Authors: Dogan Bilal , Hyde Thomas 
Published: August 2013

The Sampling and Small Punch testing (SPT) is a powerful technique based on tests using miniaturized specimens machined out small sampled material of components in service. At present, it is the only existing method capable of providing experimental characterization of service exposed materials of components and materials of new built plants. Small sampling is non-invasive and SPT provides direct measured material properties. It provides a significant technology capability that facilitates assessing power plant operating equipment for structural integrity and operational condition. The new method provides utility members an attractive option to interrogate equipment for making run/inspect/repair/replace decisions. The SPT technique supported by assessment software, NDE and Metallography, used to define guidelines for components life assessment cross the power generation and petro-chemical sectors, serving both utilities, and constructors. It addresses the industrial need for personalized material and welds data required for a) lifing of plant; consumed life and residual life of components, b) convenience of repairing, replacing, life of the new welds on old components, c) cost of component deterioration, cost of normal service, d) characterizations and qualifications of blade repairs, of coating materials-methods.
The first international SPT workshop was organized in June 27–28, 2011 in Nottingham, UK in order to discuss the state-of-the art SPT Creep and Fracture, and the draft CEN Cope of Practice (COP). The International SPT Experts Group serves as international forum for discussion and collaboration of industrial application of SPT methodology for in-service component life assessment. It is noted the draft CEN COP needs to be revised. Presently, European, Japanese and Indian national SPT project groups are running SPT tests and working on analysis programs.
The present paper reports on a) the use of SPT in materials and component characterization, and b) drafted technical program by the international experts group to harmonize international efforts on SPT testing and analysis for efficiency and cost effectiveness. The draft program to bring the SPT methodology to standardization and develop an engineering component condition assessment tool for industrial application.
Fire Testing of High Density Polyethylene Piping Systems
Authors: Munson Douglas , Decker Dana 
Published: August 2013

Degradation of raw water piping systems is a major issue facing nuclear power plant owners. High density polyethylene (HDPE) is a cost-effective alternative to corrosion resistant alloys and has been found to perform well in power plant applications for over 10 years. When used above ground, fire resistance may be an issue. HDPE starts to melt at ∼235°F (115°C) and has an auto-ignition temperature of ∼662°F (350°C). Additionally, toxic gasses are released when it burns.
The paper summarizes the development of a method that can be used to protect HDPE piping from postulated fire events is situations where the system must remain operable or not contribute to the fire load. The method was demonstrated using a proof-of-concept fire test of four piping subassemblies that contained many of the fittings that are commonly found in HDPE piping systems. The assemblies were subject to a 3-hour fire test following the guidance of ASTM E119 followed by a hose stream test following the guidance of ASTM E2226. All four specimens survived the test, with each retaining its overall geometry, cross section, and structural and pressure boundary integrity.
Detailed Finite Element Analysis of Darlington NGS Feeder Pipes With Locally Thinned Regions Below Pressure Minimum Thickness
Authors: Haq Irfan , Stojakovic Mike , Fabbri Sandy 
Published: August 2013

Feeder Pipes in CANDU nuclear stations are experiencing wall thinning due to flow accelerated corrosion (FAC) resulting in locally thinned regions in addition to general thinning. In Darlington NGS these locally thinned regions can be below pressure based minimum thickness (tmin) in the straight pipe region (STR1) between Grayloc and Bend 1. The (tmin) is required as per ASME Code Section III NB-3600 Equation (1). A methodology is presented to qualify the locally thinned regions under NB-3200 (NB-3213 & NB-3221) using internal pressure loading only. Detailed finite element models are used for internal pressure analysis using ANSYS v11.0. All other loadings such as deadweight, thermal and seismic loadings are separately qualified under NB-3600 using a general purpose piping stress analysis software. The piping stress analysis is based on average thickness equal to tmin along with maximum values of ASME Code stress indices (Table NB-3681(a)-1). The requirement for the use of this methodology is that the average thickness of each cross-section with the locally thinned region shall be at least tmin. In contrast, the finite element analysis models are thinned to 0.75 tmin (in increments of 0.05 tmin) all-around the circumference in the straight section region allowing for flexible inspection requirements. In Darlington NGS there are 22 different types of feeder pipes which have been grouped into 6 types based on similarities in pipe size, straight section length, bend angle and orientation. Thickness versus the allowable axial extent curves were developed for 6 representative feeder types. The stress analysis results show that all Darlington NGS outlet feeder pipes are fit for service with locally thinned regions in STR1 with down to 75% of the pressure based minimum thickness.
This paper demonstrates the methodology and effectiveness of finite element analysis in extending the useful life of degraded piping components.
Status of French Road Map to Improve Environmental Fatigue Rules
Authors: Faidy Claude 
Published: August 2013

During the past 30 years many fatigue tests and fatigue analysis improvements have been developed in France in order to improve Codified Fatigue Rules of RCC-M and ASME Codes [1, 2].
This paper will present the major technical improvements to obtain reasonable evaluation of potential fatigue damage through EDF road map. Recently new results [3] confirm possible un-conservative fatigue material data:
- High cycle fatigue in air for stainless steel,
- Environmental effects on fatigue S-N curve for all materials
- Fatigue Crack Growth law under PWR environment for stainless steel.
In front of these new results, EDF has developed a “Fatigue Road Map” to improve the different steps of Codified fatigue rules.
A periodic up-dating of proposed rules in the different French Codes: RCC-M, RCC-MRx and RSE-M with research of harmonization with other Code rules developed in USA, Japan and Germany in particular, will be done on a yearly basis. During the past 15 years, many results have been obtained through fatigue tests of stainless steel materials:
- mean and design fatigue curve in air,
- environmental effects on fatigue curves,
- plasticity effects,
- bi-axial load effects,
- mean stress effects,
- stress indices,
- transferability from small to large specimen,
- weld versus base metal.
In parallel, many new developments have been made in non-nuclear pressure equipment industry: like the reference stress of ASME Section VIII or the structural stress of EN 13445. These methods are mainly well adapted to fatigue pressure cycling.
In front of that situation, the French nuclear code organization needs to propose reliable rules for new design and for operating plants. Different proposals are under discussion and the status of the EDF proposals are presented in the paper.
The consequences could be important for the utilities because a large part of the in-service inspection program is connected to some fatigue usage factor level between 0.5 and 1.