bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Pre-Strain on Mechanical Properties of Pressure Vessel Grades: Assessment of Stress Relieving/Post Weld Heat Treatments Efficiency at Regenerating Properties
Authors: Heritier Deborah , Pillot Sylvain , Corre Stéphanie , Chauvy Cédric , Toussaint Patrick
Published: August 2013

During fabrication of large pressure vessels, thick plates are submitted to numerous process phases that may affect the initial (i.e. as delivered) properties of the material. Regarding the advantages (both technical and economical) of cold forming process, this technique is largely preferred and widely spread.

Modern forming presses and rollers are now sufficiently powerful to roll very thick plates (typically up to 250mm thick) devoted to ultra-heavy pressure equipments. As force does not really constitute a limitation anymore, current limitations are now focusing on maximum admissible strain in materials. This particular limit is linked to:

- Intrinsic maximum deformation admissible by the material (given by tensile tests),

- Regulation rules coming from construction codes.

From a practical point of view, the actual limitation comes from the construction codes that are very severe.

Main codes (ASME Boilers and Pressure Vessels Construction Code from American side and EN 13445 Unfired Pressure Vessels Construction Code from European side) both give a limit equal to 5% strain for using material in “as-strained” condition without any heat treatment. Above this limit, the philosophy differs from one code to another.

While European Code requires a full quality treatment of the strained material (Normalisation or Austenitization / Tempering), American code only requires Tempering, allowing fabricators the possibility of using the mandatory Post Weld Heat Treatment (PWHT) (needed by welded zones) as a tempering treatment to improve welded zone toughness and to regenerate material properties.

The purpose of this contribution is to review the effect of pre-strain on mechanical properties (Hardness, Tensile and Toughness transition curves) for different strain levels and to evaluate the ability of typical PWHT to regenerate material properties. Results presented in this paper are based on both recent studies on the most common up-to-date materials as well as on historical data collected in the last decades.

This study clearly demonstrates that the required PWHT is efficient enough to regenerate all material properties and that there is no need to apply a full quality heat treatment, even for the highest level of strain. This benefits both the fabricator and the end user as it implies reducing costs and risks of components deformation while maintaining the necessary level of service properties.
CMOD Compliance of B×B Single Edge Bend Specimens
Authors: Shen Guowu , Tyson William R. , Gianetto James A.
Published: August 2013

In ASTM standard E1820, the single edge bend (SE(B)) geometry is one of those recommended for fracture toughness testing. The width to thickness (W/B) ratio recommended in E1820 for this specimen is 2. However, in certain cases, it is desirable to use specimens having alternative W/B ratios; the range of W/B suggested in E1820 is 1 to 4. In E1820, the crack size a may be evaluated during J-integral or CTOD resistance testing using the crack mouth opening displacement (CMOD) elastic unloading compliance C. The equation given to relate a to C using a dimensionless compliance BCE incorporates Young’s modulus E. For the three-dimensional (3-D) SE(B) specimens that are in neither plane stress nor plane strain condition, this parameter E may be considered as a normalizing parameter varying between extremes E (plane stress) and E/(1−ν2) (plane strain) depending on crack depth (a/W) and specimen W/B ratio.

In the present study, 3-D finite element analysis (FEA) was used to evaluate the CMOD compliance of B×B SE(B) specimens with shallow and deep cracks and compared with that from Tada’s plane stress equation. Crack sizes evaluated using plane stress and plane strain assumptions with the 3-D CMOD compliance obtained from FEA were compared with the actual crack size of the specimens used in FEA. It was found that the errors in crack size using plane strain or plane stress assumptions can be larger than 5%, especially for shallow-cracked specimens. In the present study, an effective modulus with values between plane stress and plane strain is proposed and evaluated by FEA for the 3-D B×B SE(B) specimens. The values were fitted to a polynomial equation as a function of u = 1/(√(BCE)+1) for use in estimating the dimensionless compliance for crack size evaluation for B×B SE(B) specimens. It is shown that the errors in crack size evaluation can be significantly reduced using this effective modulus.
Proposal of Revised Flaw Acceptance Criteria for Ultrasonic Examination of Welds in Section VIII Division 3: Part 1
Authors: Terada Susumu , Yoshida Toshio
Published: August 2013

The current flaw acceptance criteria for ultrasonic examination of welds in Table KE-301-1 and KE-301-2 of ASME Section VIII Division 3 (hereinafter Div.3) are almost similar to Code Case 2235 on ultrasonic examination of welds in lieu of radiography. This code case is based on general membrane stress and Charpy impact values of Section VIII Division 2 (hereinafter Div.2). The stress levels of Div.3 are higher due to lower design margin and larger stress gradient through the thickness due to large wall ratio than those of Div.2, and Charpy impact values requirements of Div.3 are also different from those of Div.2. Therefore, the flaw acceptance criteria on ultrasonic examination of welds for Div.3 should be reviewed. This paper is the first part of a two part paper. It describes the basic idea for review of flaw acceptance criteria in Div.3 and the proposed revised surface flaw acceptance criteria for welds based on fracture mechanics evaluation.
Electrochemical Properties of 304 Stainless Steel Under Proportional and Non-Proportional Multiaxial Loading Condition
Authors: Huang Yuhui , Xuan Fu-Zhen , Itoh Takamoto , Tu Shan-Tung
Published: August 2013

Corrosion fatigue tests and electrochemical tests under proportional and non-proportional loading conditions were conducted on 304 stainless steel in 0.63 mol/L sodium chloride solution at the room temperature. Two biaxial loading paths were applied to study the effect of proportional and nonproportional loadings on polarization properties as well as the formation potential of pits. Surface observations of multiaxial corrosion fatigue specimens were carried out by SEM. It was shown that the proportional loading had a more significant effect on corrosion rate compared with non-proportional loading. The continuous rotation of principal stress plane when applied nonproportional loading inhibits the pit formation.
Degradation of Moderator Graphite in Gas Cooled Reactors
Authors: Moskovic Robert
Published: August 2013

Magnox reactors employ pile grade A (PGA) graphite as moderator. Reactor cores are typically constructed of twelve to thirteen layers of interlocking graphite bricks. Their temperature varies from 250°C at the bottom to 360°C at the top of the core. It serves a dual role as both the moderator and encasing the fuel in the channels. These are through the middle of the bricks and continuous through the core. The bricks are either octagonal or square in shape. A unit of eight brick of equal numbers of each shape has a single interstitial channel at the point where the corners of two octagonal and two square bricks meet. The interstitial channels are used for control rods, absorbers and canisters of graphite samples installed to replicate the service exposure of reactor bricks and to be used for measurements. The graphite loses mass during service due to radiolytic oxidation, by CO2 caused by energy deposition, mainly γ radiation. Neutron irradiation brings about hardening and dimensional change which decrease with the increasing distance from the bore to the outer surface of the brick. The gradient in the dimensional changes as well as thermal transients generate internal strains and in turn stresses. This paper reviews changes of some physical and mechanical properties of graphite during service and describes the cracking and fracture behavior of graphite. Statistical analysis of density showed that it decreases during the service with increasing neutron dose and decreasing reactor core height/temperature. Crack initiation involves a prior formation of a process zone.
Seismic Response Reduction in Piping Systems Using Plastic Deformation of Pipe Support Structures
Authors: Takahashi Tsuneo , Maekawa Akira
Published: August 2013

This study describes inelastic seismic design of piping systems considering the effect of plastic deformation of a pipe support structure. The damping coefficient of a piping system is focused on, and the relation between seismic response of the piping system and elastic-plastic behavior of the support structure was studied using nonlinear time history analysis and complex eigenvalue analysis. The analysis results showed that the maximum seismic response acceleration of the piping system decreased largely in the area surrounded by pipe elbows including the support structure which allowed plastic deformation. Furthermore, modal damping coefficient increased a maximum of about seven-fold. The increase ratio of the modal damping coefficient was proportional to the size of the effective mass ratio, when a relatively large increase was seen in the increase ratio of the modal damping coefficient. On the other hand, the amount of the initial stiffness of the support structure made a difference in the increasing tendency of the modal damping ratio. In the case of relatively small initial stiffness, the modal damping ratio of only one vibration mode increased. The increment of the modal damping ratio was proportional to the effective mass ratio in the case of large initial stiffness. In the viewpoint of the inelastic seismic design, the seismic response of the piping system was little affected by the plastic deformation of the support structure with 10% variation of the secondary stiffness to the initial stiffness. The result suggested that the seismic response of the piping system with the support structure can be estimated by using only the support model which has the elastic perfectly plastic property even if there are various shapes of steel type of support structures.
Pressurization of Containment Vessels From Plutonium Oxide Contents
Authors: Askew Neal M. , Hensel Steve J. , Laurinat James E. , Skidmore T. Eric
Published: August 2013

Transportation and storage of plutonium oxide is typically done using a convenience container to hold the oxide powder which is then placed inside a containment vessel. Intermediate containers which act as uncredited confinement barriers may also be used. The containment vessel is subject to an internal pressure due to several sources including; (1) plutonium oxide provides a heat source which raises the temperature of the gas space, (2) helium generation due to alpha decay of the plutonium, (3) hydrogen generation due to radiolysis of the water which has been adsorbed onto the plutonium oxide, and (4) degradation of plastic bags which may be used to bag out the convenience can from a glove box. The contributions of these sources are evaluated in a reasonably conservative manner.
Predicting Post-Weld Residual Stresses in Ferritic Steel Weldments
Authors: Hamelin Cory J. , Muránsky Ondrej , Bendeich Philip J. , Edwards Lyndon
Published: August 2013

The implementation of a semi-empirical solid-state phase transformation subroutine in the ABAQUS finite element package is presented to predict the influence of transformation strain on the post-weld residual stress field in ferritic steels. The phase transformation subroutine has been outlined in a previous study (PVP2011-57426), where it was proven accurate in predicting the phase compositions in the fusion and heat affected zone (HAZ) of an autogenous TIG beam weld in SA508 Gr.3 Cl.1 steel.

While previous work focused on predictions of the steady-state material response using a 2D thermal model, the present analyses are 3D and capture the varying phase composition at weld start- and stop-ends. Predicted cooling rates at either end of the specimen are significantly higher, leading to a variation in the predicted microstructure along the weld line.

To better understand the structural changes that occur in ferritic steels during a conventional welding process, a representative model of SA508 Gr.3 Cl.1 steel is discussed. The contribution of thermal, metallurgical, and transformation-induced plastic strain is highlighted in this example, providing insight to the key simulation variables necessary for accurate weld models of ferritic steels. Preliminary coupled thermo-mechanical analyses are presented that compare predicted residual stress distributions with those measured in SA508 Gr.3 Cl.1 beam welds via neutron diffraction; good agreement is observed.
Further Predictions of Fracture Experiments of a Pre-Cracked Pressurised Thermal Shock Disk (PTS-D) Specimen Under Warm Prestressing Loading Cycles
Authors: Teng H. , Sharples J. K. , Budden P. J.
Published: August 2013

Finite element analyses have been performed to investigate the effects of warm prestressing (WPS) of a pre-cracked PTS-D (Pressurized Thermal Shock Disk) specimen. Three basic types of WPS loading cycles were used in the analyses: LUCF (Load-Unload-Cool-Fracture) cycle; LCF (Load-Cool-Fracture) cycle; and LCTF (Load-Cool-Transient-Fracture) cycle. The analyses aimed to predict the fracture toughness enhancements due to WPS using different analysis methods and to make comparisons with the experimental work conducted by the Belgium SCK-CEN organisation under the European NESC VII project.

The finite element results were used to derive the enhanced fracture toughness by three different engineering methods: (1) Chell’s displacement superposition method; (2) the local stress matching method; and (3) Wallin’s empirical formula. The enhanced fracture toughness was evaluated at the deepest point of the semi-elliptical crack based on three different levels of as-received fracture toughness of 43.96, 65.94, and 86.23 MPam1/2, which correspond to probabilities of failure of 5%, 50% and 95%, respectively.

The predicted fracture loads were compared with the experimental fracture loads for the three WPS loadings cycles. The results show good agreement.
Structures and Properties of X80 Pipeline Girth Welds for Different Welding Procedures
Authors: He Xiaodong , Liu Yangqin , Zhu Lixia , Tong Ke , Shao Xiaodong
Published: August 2013

The X80 girth welds were produced by solid-wire gas metal arc welding (GMAW) and shield metal arc welding (SMAW) using two welding consumables respectively, which contained different mass fraction of C, Mo and Ni. The tensile properties, notch toughness, hardness, and microstructures of welded joints were evaluated. The results indicate that high strength and good toughness of welded joints can be achieved. But the tensile properties of all weld metal of GMAW and SMAW process were evidently different because of the difference of mass fraction of C, Mo, Ni. The strength reduced slightly in softening zone of HAZ. Using welding consumable which contain higher Mo additions, the microstructure in weld seam and fusion zones were IAF+GB and GB+M respectively. Furthermore, the mechanical properties of X80 pipeline welded by single wire welding and double wire welding respectively have been compared. The double wire welds exhibited lower yield strength but higher toughness compared to the corresponding single wire welds.
Low Cycle Fatigue Behavior of Welded Components: A New Approach — Experiments and Numerical Simulation
Authors: Lang Eliane , Rudolph Jürgen , Beier Thomas , Vormwald Michael
Published: August 2013

Nuclear power plant components are often subjected to local plastic deformations due to low cycle operational thermal loading conditions. The fatigue behavior of weld seams is of particular interest in this context. Applicable design codes for fatigue life assessment use factors (e.g. Fatigue strength reduction factors – FSRF) within the simplified elastic-plastic or general elastic-plastic analysis in connection with the design fatigue curves for non-welded components. This way, the influence of the weld seam on the fatigue behavior is approximately considered. Emanating from this status quo ideas for a new approach considering the particularities of the fatigue behavior of the weld seam in more detail are developed. The proposed approach is based on material mechanics and constitutes a combination of experimental findings and numerical calculations in order to determine the local strains and the fatigue relevant influence of geometrical and metallurgical notches induced by the weld seam. Experiments on welded specimens provide the fatigue life as well as the stabilized cyclic stress-strain curve as relevant input parameters for the finite element analyses. The proposed model is capable of considering the exact geometry of the weld seam obtained by 3D scanning with very high resolution and the different material strengths due to the weld. The consideration of the principal influences on the fatigue behavior of weld seams paves the way to the application of established damage parameters such as PJ with the future objective to transfer the results also on arbitrary proportional and non-proportional loadings with variable amplitudes.
Constructing a Validated Deformation Mechanisms Map Using Low Temperature Creep Strain Accommodation Processes for Nickel-Base Alloy 718
Authors: Asadi Mahyar , Guillot Dominic , Weck Arnaud , Hegde Subray R. , Koul Ashok K. , Sawatzky Trevor , Saari Henry
Published: August 2013

A creep Deformation Mechanism Map (DMM) of an engineering alloy can be an effective tool for developing physics-based prognostics systems. Many classical diffusion based rate equations have been developed for time dependent plastic flow where dislocation glide, dislocation glide-plus-climb and vacancy diffusion driven grain boundary migration (diffusion creep) are rate controlling. These creep rate equations have been proven experimentally for simple metals and alloys and form the basis of constructing an Ashby’s DMM. Long term creep testing and analysis of complex engineering alloys has shown that power law breakdown phenomenon is related to the dominance of Grain Boundary Sliding (GBS) as opposed to diffusion creep. Rate equations are now available for GBS in complex alloys and, in this paper, a DMM is constructed for a fine grained Alloy 718 and this is validated by comparison with a collection of experimental data obtained from the literature. The GBS accommodated by wedge type cracking is considered dominant at low homologous temperatures (0.3 to 0.5Tm i. e. melting temperature in Kelvin) whereas GBS accommodated by power-law or cavitation creep dominates above 0.55Tm.
Experimental Study on a Multiple-Use Spherical Containment Vessel
Authors: Hu B. Y. , Dong Q. , Gu Y.
Published: August 2013

In this paper, we present experimental results of three explosion tests performed on a multiple-use spherical containment vessel, which has been employed to withstand internal blast loading from 25 kg TNT high explosive in the past ten years. The experimental observations of the blast loading and the vessel response histories are compared, and it can be found that the remarkable strain increase occurs in the second response cycle of the strain-time history may be caused by the effect of the reflected shock wave. The occurrence of strain growth at different locations of the vessel are specially concerned, and details on the vibration modes and frequency spectra of the spherical vessel are investigated. Based on the present experimental results and the previous theories, three possible mechanisms of strain growth are discussed, which leads to a conclusion that the effect of reflected shock waves, modal superposition and nonlinear modal coupling may all contribute to strain growth.
Evaluation of Mass Transfer Coefficient Under Swirl Flow Generated by the Combination of Pipe Elements
Authors: Suzuki Shota , Nakamura Takao
Published: August 2013

Flow accelerated corrosion (FAC) is the major pipe wall thinning phenomena in power plants. The management of pipe wall thinning has been carried out for pipe elements such as elbow, orifice, etc. of the piping system in power plants. It is usually applied to thinning estimation methods with a combination of analytical code and measurement of pipe wall thinning. In piping system, it is known that several pipe elements which are connected in series may generate swirl flow. Therefore the arrangement of pipe elements is considered to be one of the major reasons to affect thinning phenomena. In Mihama Unit3 pipe failure accident of 2004, it was pointed out the swirl flow caused by piping layout might influence thinning rate after orifice. This paper focuses on the conditions and parameters (combination, distance, etc. of pipe elements) that affect the generation of swirl flow and analyzes the effect of such parameters in mass transfer coefficient after the pipe elements. The results of this research can be utilized for taking account for the effect of swirl flow in the calculation of geometry factor to improve the accuracy of simulation codes.
Use of Limit Load Analysis for Design of Pressure Vessel Cover
Authors: Jain Rahul
Published: August 2013

This paper explores the use of limit load analysis methods for the design of a pressure vessel manway cover as per the ASME boiler and pressure vessel code guidelines. The results of elastic and limit load finite element analysis are discussed for the design. The concept of reference volume consideration along with linear elastic finite element analysis to determine the lower bound limit load has been explored and the results are compared with the non-linear elastic-plastic limit load analysis.
Flow Loads on the Shroud in a Boiling Water Reactor due to a Recirculation Outlet Line Break: A Comparative Study Between Potential Flow and Computational Fluid Dynamics Methodologies
Authors: Ananth Raju , Sowah Sandra , Gillis Jay
Published: August 2013

This paper compares two methodologies for estimating the flow loads on the shroud of a typical BWR caused by a Recirculation Outlet Line Break. First, assuming an ideal and irrotational flow field, the complex potential methodology is used to calculate a two dimensional approximation of the flow field by ignoring variations along the radial direction. As a simplification for the comparative study the annulus will be assumed to be devoid of any structural components such as the jet pumps. The flow field derived from the potential flow approach will be used to compute the total lateral and moment loads acting on the shroud. These load values will be compared against similar values derived from a three dimensional and more realistic flow field computed by Computational Fluid Dynamics (CFD).

The potential flow based method is computationally simpler as compared to the more time consuming CFD approach.
Component Tests of Huge Scale All-Steel Multi-Curve Buckling Restrained Braces
Authors: Tsai C. S. , Su H. C. , Chiang T. C. , Lin Y. C.
Published: August 2013

Many countries have gradually adopted the buckling-restrained brace (BRB) for preventing structural damage during earthquakes since its introduction in the 1970s. In this study, we propose an all-steel BRB called the multi-curve buckling-restrained brace (MC-BRB) to overcome the shortcomings of traditional BRBs that use mortar encased in a steel tube. This new BRB consists of double core plates, each with multiple neck portions that form multiple energy dissipation segments, enlarged segments, lateral support elements, and constraining elements that are designed to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be connected to the lateral support and constraining elements to increase buckling strength and prevent the lateral support and constraining elements from sliding during earthquakes. The lateral support elements can be windowed to allow quality control checks to be performed and the condition of the core plate to be monitored after an earthquake. In this study, a huge-scale component test with an axial load of 14000 KN in the core plates was carried out to investigate the behavior of the new BRB and its capabilities for seismic mitigation. A comparison of the experimental results and theoretical calculations indicate that the all-steel MC-BRB possesses a stable and predictable mechanical behavior under cyclic loadings.
A New Analytical Solution for Optimum Design of Shrink-Fit Multi-Layer Compound Cylinders
Authors: Sharifi Mojtaba , Hematiyan M. R. , Banan Roshanak
Published: August 2013

In this paper, by using an analytical optimization method, formulas for general optimum design of multi-layer compound cylinders are presented. For this purpose, considering the Tresca’s yield criterion, the maximum shear stresses occurred simultaneously in inner radiuses of all layers, are minimized. The formulas for obtaining optimum values of layers radiuses, contact pressures, and radial interferences are derived. A technique for shrink-fitting of cylinders is also described and relationships for radial interferences and required temperature differences between cylinders for each step of the shrink-fitting process are derived using an analytical method. It is indicated that compound cylinders with more layers have higher internal pressure capacity for a specified weight. Three different examples are presented to show the effectiveness of the method.
Scanning Electron Microscope of Fatigue and Creep-Fatigue From Stress Concentrations in Plates
Authors: Watanabe Osamu , Kikuchi Marina , Matsuda Akihiro
Published: August 2013

Fatigue crack propagation forms a distinctive pattern which is observable on the fracture surfaces of materials. Purpose of this study is to analyze the fracture process of the materials received under cyclic distortion loading using scanning electron microscope. The test piece made of type 304 stainless steel with the hole of a different size is examined on the conditions of the high temperature fatigue and creep-fatigue. This study first takes a picture of the fracture with SEM, and measures the intervals of striation on fracture surfaces. Next, this study calculates the number of the crack propagation cycles and compares with the original experimental data defined by the load decrease condition or the crack length.

Consequently, there is not so much differences at striation intervals regardless of the size of the root notch radius in the present tests. However, the striation spacing in the creep fatigue test has grown about twice of striation intervals in the high temperature fatigue-test.
Study on the Frequency Response Characteristics of Thermal Stress Induced by Multidimensional Fluid Temperature Fluctuation
Authors: Perez T. Cristian Santiago , Kasahara Naoto
Published: August 2013

A simplified one dimensional approach for predicting the thermal stress in structures subject to near wall fluid temperature fluctuations has been previously developed and published by the author Kasahara. The method predicted the thermal stress by calculating the frequency response, formulated by the product of the effective heat transfer and the effective thermal stress related to one-dimensional temperature gradient developed through the wall thickness of the structure. Although, currently adopted by the Japanese Society of Mechanical Engineers (JSME) guideline for calculating the thermal fatigue damage in structures, recent studies have highlighted the limitations of the one dimensional approach by showing the presences of multidimensional fluid temperature fluctuation in plane direction, increasing the need to extend the current analysis to more detailed multidimensional guideline.

The aim of this research is to advance the theoretical knowledge and understanding of complex multidimensional phenomenon related to local thermal fluctuations within small localized area at the surface of the structure, referred to as “Hot Spot” which is observed to have important effects on the thermal stress phenomenon. Furthermore, the understanding of heat transfer processes in the structure, especially heat diffusion that is known to produce a thermal gradient and, therefore, thermal stress. Understanding the behavior of each heat transfer process in the Hot Spot and the relationship to the response in frequency has formed the bases for extending the current one-dimensional model.

This paper presents the analytical results of the study and proposes an extended multidimensional model to understand the thermal stress in tee-junction due to fluid temperature fluctuation and the close relation with the frequency. The model is derived from the understanding of the phenomenon which has leaded to quantify the effect by introducing certain multidimensional factors to explain the impact of the multidimensional fluid temperature fluctuation.
The Influence of Long-Range Residual Stress on Plastic Collapse and Local Yielding of Internally Pressurized Pipes
Authors: Wu Gui-yi , Smith D. J. , Pavier M. J.
Published: August 2013

The determination of plastic collapse for cracked pipes is important in structural engineering design and component integrity assessment. Long-range residual stresses are usually treated as primary stresses which contribute to plastic collapse of pipes subjected to internal pressure. This paper explores the differences between load and displacement controlled conditions applied to the ends of thin- and thick-walled pipes. Both load and displacement control can represent long range or fit-up residual stresses if they are considered as primary or secondary stresses respectively. Both global collapse and local yielding for pipes containing partially and fully circumferential cracks are examined. Detailed three-dimensional (3D) finite element (FE) analyses are used to simulate the pipe and crack geometry and the boundary conditions. The cracked pipes are assumed to be open ended. For a defect free pipe the FE results for global collapse agree with analytical solutions for both load and displacement controlled end conditions. For high tensile end loads and displacements lower collapse pressures are found for displacement conditions, while it is the converse for high compressive end loading. However, when a crack is introduced it becomes evident that tensile or compressive displacement control has little impact on global collapse and therefore longrange displacement controlled (or residual) stresses do not contribute to collapse. On the other hand local net section yielding is strongly affected by either load or displacement controlled end conditions.
Experimental Incompressible Forces Applied in a Safety Valve
Authors: Chabane Saïd , Corbin François , Couzinet Anthony , Pierrat Daniel , Bayart Martin
Published: August 2013

Safety valves are crucial devices in the industry. Indeed, these valves are simple and robust in their design. Safety valves are the ultimate overpressure device protection when all other devices are insufficient or failed. The poor design of these devices can be disastrous.

A conventional safety relief valve is mainly composed of a disk maintained pressed against a nozzle by a spring. When the pressure forces on the upstream face of the disk are below the force applied to the spring, the valve is closed. If an accidental overpressure event occurs in the process under protection, the pressure forces become high compared to spring elastic forces and the safety valve opens to relief pressure. Thus, the pressure in the process under protection is reduced to an acceptable value.

The force exerted by the pressure on a disk of a safety valve is essential for a correct design of the spring and the inner ring. To understand the forces, a safety relief valve was modified and the spring removed; a force measurement tool was mounted in order to measure the forces exerted at different inlet pressure and lift. These tests were made for several ring settings.

These measurements were made in incompressible fluid on a water test loop.

Finally, inlet and outlet conditions of the safety valves were modeled respectively by thermodynamic 1D-model. The safety valve is described by dynamic 1D-model where the hydrodynamics forces applied to the moving disk are provided by measurements in water.
Mechanical Behavior of Steel Pipes With Local Wall Distortions Under Cyclic Loading
Authors: Pournara Aglaia E. , Karamanos Spyros A.
Published: August 2013

Evaluating the severity of pipe wall distortions is a crucial step towards safeguarding the structural integrity of aging hydrocarbon pipeline infrastructure. The present research refers to the remaining life of oil and gas transmission steel pipelines with local wall distortions (i.e. dents and buckles) under repeated loading. The research described in this paper constitutes the first part of a large numerical/experimental research project, aimed at developing methodologies and relevant design guidelines towards assessing and repairing structural pipeline damages in the form of local wall distortions. The paper describes numerical research aimed at investigating the residual structural integrity of smooth dented and buckled steel pipes, with respect to repeated loading that causes fatigue, with the purpose of designing large-scale experiments. Finite element models are developed to simulate the formation of dents and buckles on the pipe wall at various sizes (depths). The deformed steel pipes are further subjected to cyclic pressure or cyclic bending loading in order to estimate the remaining fatigue life of the deformed pipe. The local stress and strain variations due to cyclic loading application are calculated numerically at the deformed area of the pipe wall. In addition, the local strain variations are expressed in terms of strain concentration factors (SNCF) at the critical region of the pipe.
Assessment of Fatigue Crack Growth in Imperfect Lap Joint: Part 1 — Analysis of Stress Distribution on Virtual Crack Plane
Authors: Wakasa Masaru , Igi Satoshi , Yoshida Shoichi , Sekine Kazuyoshi , Tsuchida Tomohiko , Iwata Katsuki
Published: August 2013

The deck plates of a single-deck-type floating roof for large oil storage tanks are joined by single-welded full-fillet lap joints. In areas with frequent strong winds, fatigue cracks sometimes occur in the welds of the deck plates. The aim of the present study is to investigate the effect of the gap imperfection of the lap joint on the fatigue life. Generally, weld imperfections significantly reduce the fatigue crack propagation life of the welded joints. A stress analysis using the finite element method was performed to provide the basic data for the fatigue crack growth analysis.
Simulation and Measurement of Residual Stresses in a Stainless Steel Ring Welded Circular Disc
Authors: Zheng Gang , Hossain Sayeed , Smith Mike , Smith David
Published: August 2013

Residual stresses were predicted and measured in a circular disc containing a partial ring weld. This study first created an axisymmetric finite element model so that the process of introducing the ring weld was simulated using thermal and mechanical modelling. The resulting residual stresses were then mapped onto a 3D model which included the necessary mesh and boundary conditions to simulate the process of residual stress measurement using the deep hole drilling method. Then an experimental programme of residual stress measurement using the deep hole drilling method and the neutron diffraction technique was conducted on the welded circular disc. The results from the deep hole drilling measurements matched well with the neutron diffraction results on the original stress field in the ring weld. While comparison between measurements and predicted residual stresses show that predicted hoop stresses are slightly higher than measured, there is in general a fair comparison between measured and predicted residual stress.
Dealing With Heavy Loads in Large Diameter Piping
Authors: Rojas Hector , Gutkovsky Andrey
Published: August 2013

It is common in a refinery that some piping systems have to handle several flow conditions. However, when a new proposed condition implies the filling of an existing 68″ (1727 mm) line with molten Sulfur, which was initially designed for gas operation, a well thought engineering case study is required to guarantee that no damage will occur under the new operating conditions.

This paper covers the procedures employed to qualify the integrity of a 68″ (1727 mm) piping system, initially designed to carry Sulfur vapors and required to handle occasional filling with molten Sulfur due to operational demands.

The procedures of reviewing the initial configuration, design of modifications and reinforcements to the piping system and the use of Finite Element Analysis (FEA) in order to qualify several unique support configurations are explained in this paper.
Mitigation of Distortion in an Edge-Welded Bar by Optimization Control of the Welding Current and Speed Profile During Welding
Authors: Asadi Mahyar , Goldak John A. , Bayley Christopher
Published: August 2013

Welding distortion is usually controlled by clamping techniques that can be tack welds, pre-bending, and tension loading. Side heating or fast cooling can also mitigate the distortion in some applications. In addition to the clamping techniques, process parameters affect the distortion so that if one can control the welding process parameters, an optimized profile of such parameters could alleviate the distortion. It is shown in this paper that the distortion can be mitigated by using an optimized profile of welding current and travelling speed. These profiles keep the power per unit length of welding constant. It is shown that an increasing welding current at the beginning and the end of the welding path on an edge welded bar of Aluminum could result in a bar that is closer to flat compared to the constant welding current. Developing an optimized weld process parameter profile requires a trustable computational model to implement a control problem using a predictive model for distortion in front of the weld pool in order to adjust the welding current and speed. Unlike using a constant welding current for the full path of weld, the path length is divided into several sub-paths. For each of weld sub-path the control problem learns from the previous sub-path and tries to find the new value for the welding current and speed that minimize the distortion using predictive Computational Weld Mechanics (CWM). Final deflections of the bar are also compared between a constant welding current and optimized profile of welding current.
A Pipe Bend Subject to a Uniformly Distributed Radial Force
Authors: Mazzeo Joseph M.
Published: August 2013

The effects of a distributed radial load on an elbow or bend within a piping system, caused by large changes in momentum due to fluid flow, are often represented by a single force. The method presented here will result in more accurate results. In this paper, equations are derived to predict deformations of a pipe bend or curved beam cantilever at its free end due to a uniformly distributed radial force. Assuming isotropic, linearly elastic materials of uniform cross section, uniform bend radius, and small deformations, equations are derived using Castigliano’s theorem. Deformation due to shear and axial stresses is also considered. Derived equations are validated through a case example which compares them to a model consisting of a number of straight beam elements assembled to model a curved beam. The example demonstrates that free end deformations can be integrated into a piping analysis program by using the direct stiffness method in order to obtain the resulting displacements, forces, and moments that result from restraint of the bend due to the stiffness of the attached pipe.
Alternative Tracing Gas Mixtures for Valve Fugitive Emission Measurements
Authors: Lejeune Hubert , Cougnon Laurent
Published: August 2013

Helium is commonly used as a tracer gas for leakage measurements across the world. This gas is easy to use without safety issues and enables to measure a very wide magnitude of leakage rates with well proven detectors (Mass Spectrometers). Nevertheless, shortage and price increase of helium in several world areas, encourage industry users to look for alternative tracing gases for leakage measurement.

The Valve Commission of CETIM has decided to investigate the use of two alternative tracer gas mixtures in the field of packing fugitive emissions testing according to ISO 15848-1. This standard allows the use of Helium and Methane as tracer gases. The leakage measurements based on Hydrogen tracer gas has been developed in the recent years, with the use of Hydrogen (5%)-Nitrogen (95%) mixture for safety concerns.

The test programme involves comparative fugitive emission measurements on graphite packing, following ISO 15848-1 test procedure with Helium, Hydrogen (5%)-Nitrogen (95%) and Methane (10%)-Nitrogen (90%) mix tracer gases. Several measuring methods are investigated as sniffing, accumulation, flushing and global vacuum using the relevant detectors for the different gases and measurement methods.

Whereas the measurements did not appear to be sensitive enough with the Methane (10%)-Nitrogen (90%) for some measurements methods, the Hydrogen (5%)-Nitrogen (95%) mixture has shown a good potential for fugitive emission measurements according to ISO 15848-1.
Cleavage Crack Propagation and Arrest in a Nuclear Pressure Vessel Steel
Authors: Bousquet Amaury , Marie Stéphane , Bompard Philippe
Published: August 2013

The integrity assessment of Reactor Pressure Vessels, mainly based on crack initiation, can be completed by studying crack propagation and arrest. Whereas engineering approaches do not take into account dynamic effects, these effects are important in unstable cleavage crack propagation, arrest and possible propagation re-initiation events. This study deals with physical mechanisms of cleavage crack propagation and numerical computations related to brittle fracture in the framework of local approach to fracture.

Experiments were carried out on thin CT 25 specimens made of 16MND5 PWR vessel steel at five temperatures (−150°C, −125°C, −100°C, −75°C, −50°C). Two kinds of crack path, straight or branching path, were observed. Branching cracks appear for the highest critical loadings at initiation, that increase the elastic stored energy and the effect of plasticity. The elastic-viscoplastic behavior of the ferritic steel was studied up to a strain rate of 104 s−1 and taken into account in the numerical simulations. The eXtended Finite Element Method (X-FEM) was used in CAST3M FE software to model crack propagation. Numerical computations combine a local non linear dynamic approach with a RKR type fracture stress criterion. The different physical micro-mechanisms, involved in cleavage fracture, were examined by the means of SEM fracture surface analyses at different temperatures and strain rates for the two kinds of crack path.

The links of the critical fracture stress with both temperature and strain rate for straight crack path as well as analyses of branching crack phenomena were considered by the means of Scanning Electron Microscopy (SEM) fracture surface analyses, 3D quantitative optical microscopy and FE computations in order to aim at a robust physical justification of the propagation model which has already been developed at CEA in the frame of the B. Prabel PhD.
Comparative Study of Leak-Tightness Performance of Wafer Type and Lug-Wafer Type Valves During a Fire
Authors: Cheta Ayman M. , Jung Gonghyun
Published: August 2013

Many companies do not allow the use of wafer type valves in flammable and/or toxic services. During a fire, the long bolts expand faster than the valve body, causing the joint to lose tightness and making the fire bigger. However, there is no consensus with regard to wafer-lug type valves. Some companies believe that since the bolts are protected inside the lugs the problem is solved. Others believe than the long bolts will always be a problem. In this paper, the authors used finite element analysis to compare the leak-tightness performance of both types during a fire.
The Importance of a Strong Training Element Within the European STYLE Project
Authors: Toft Adam , Sharples John
Published: August 2013

With many key technical experts within the European nuclear industry now approaching retirement, the continued training and professional development of less experienced people is vital for the future viability of the industry. Consequently, European framework programme projects are including a strong training element within their work packages. 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. The 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.
Basic Study on Pressure Vessel for Vaporization of Cryogenic Fluids by Direct Contacting Normal Temperature Fluids
Authors: Watanabe Toshiaki , Maehara Hironori , Itoh Shigeru
Published: August 2013

In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of consciousness for environmental agreement. On the other hand, as for fisheries as well, the use of a source of energy that environment load is small has been being a pressing need. We paid attention to the effective use of cold heat of the liquid fuel which is a cryogenic fluid. That method is to use a cold heat which an cryogenic fluid has, without a heat exchanger. The mixture of the extreme low temperature fluid and the normal temperature fluid becomes the cause which causes pressure vessel and piping system crush due to explosive boiling and rapid freezing. Therefore, we carried out the experiments related to promotion of evaporating cryogenic fluids, in the contact directly of the room temperature fluids and cryogenic fluids.
Basic Study on Vessel to Make Ice Ball and Coolant for Keeping Freshness of Marine Products
Authors: Watanabe Toshiaki , Maehara Hironori , Itoh Shigeru
Published: August 2013

The mixture of the extreme low temperature fluid and the normal temperature fluid becomes the cause which causes pressure vessel and piping system crush due to explosive boiling and rapid freezing. In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of consciousness for environmental agreement. On the other hand, as for fisheries as well, the use of a source of energy that environment load is small has been being a pressing need. Therefore, we carried out the experiments related to promotion of evaporating cryogenic fluids, in the contact directly of the water and liquid nitrogen.
Basic Study on Optimal Design of System Supporting Structures Subjected to Random Inputs Using the Probabilistic Vibration Theory
Authors: Shintani Atsuhiko , Nagami Tadashi , Ito Tomohiro , Nakagawa Chihiro
Published: August 2013

In this paper, we investigate the optimal design of the piping system supported by elasto-plastic damper subjected to the random input based on the random vibration theory. Using proposed optimal design, the structural integrity of both the piping systems and the elasto-plastic supporting devices are considered and the optimal conditions such as the supporting location, the capacity of the supporting devices are searched. Numerical simulations are performed using a simple piping system model for the white Gaussian noise input based on the random vibration theory.