bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid Inertia Damper Having a Screw Shaped Piston
Authors: Matsuoka Taichi
Published: August 2013

In this paper authors propose a liquid inertia damper that has a screw shaped piston in order to have effect of a series inertia mass. The damper consists of a piston and a cylinder, a screw shaped piston. Water is filled in the cylinder. The peripheral gap of the screw can act as an orifice of a by-pass pipe, and an inertia force is produced by a liquid flow through the gap. In order to confirm the inertia force, a test damper is manufactured, and resisting force characteristics are measured. It is apparent from test results that the damper can have a sum of the inertia force and nonlinear damping force. The series inertia mass is depended on a relation between a diameter of the cylinder and a gap of the screw. To confirm the vibration reduction, harmonic frequency response of one-degree-of-freedom system with the liquid inertia damper is calculated. Finally, the effects of vibration suppression are confirmed numerically.
Non-Destructive Crack Detection by Nanometric Change in Surface Profile Using Digital Holographic Microscope
Authors: Tada Naoya , Uchida Makoto , Uenoyama Yuki
Published: August 2013

When a material is subjected to a small mechanical load, it shows a small elastic deformation of the order of nanometer. If there is a crack on the surface or underneath the surface, small elastic deformation shows non-uniformity around the crack. In this study, a non-destructive crack detection method by nanometric change in material’s surface profile is proposed, and a tensile test of notched plate specimen was carried out. A non-uniform height change by mechanical load appeared near the notch. This fact suggests that the proposed method is available as an NDE method.
Application of Energy Balance Equation to 2 Degree-of-Freedom Model
Authors: Minagawa Keisuke , Fujita Satoshi
Published: August 2013

Generally seismic design of mechanical structures is based on static force in elastic region. However dynamic cyclic load may causes cumulative damage, and such damage induces fatigue failure on the structures. In addition, evaluation method of soundness after a huge earthquake is also required. Therefore quantitative evaluation of cumulative damage by earthquakes is required. Authors have investigated this issue from the viewpoint of the energy balance equation. The energy balance equation expresses cumulative information of response, so that the energy balance equation is adequate for the evaluation of the influence of cumulative load such as seismic response. Authors have already clarified qualitative relationships between input energy and fatigue failure of simple single-degree-of-freedom system. However, in order to apply energy balance equation on actual structure, expansion of it to multi-degree-of-freedom systems is required. This paper proposes extension method of energy balance equation to multi-degree-of-freedom system. This paper investigates 2-degree-of-freedom model as an example of multi-degree-of-freedom model, and relationship between energy and failure is investigated by vibration experiment.
Basic Characteristics of Eddy Current Testing Using Resonant Coupling
Authors: Kobayashi Noriyasu , Ueno Souichi , Nomura Kota , Ochiai Makoto , Kitajima Yuko , Maruyama Shigeki
Published: August 2013

It has been demonstrated that magnetic resonant coupling is effective for improving the characteristics of ECT sensor, especially the lift-off-dependent reduced sensitivity and noise. The lift-off-dependent reduced sensitivity and noise are caused by the decrease of voltage gain from the exciter coil to detector coil. Magnetic resonant coupling is generally usable to increase the voltage gain from the transmitter coil to the receiver coil. Magnetic resonant coupling was applied to ECT in these experiments to investigate the phenomena of magnetic resonant coupling in the ECT. In the ECT setup, the voltage gain G increased more than 6 times by magnetic resonant coupling at a frequency of 105 kHz. The voltage gain ratio (GR/GNR) was rising 1.12 times when the lift-off length increased from 1mm to 2 mm. This result verified that magnetic resonant coupling has the potential for improving the characteristics of ECT. The EDM slit signal and the lift-off noise were calculated from the experimental results, respectively. Using magnetic resonant coupling, the EDM slit signal increased 1.5 times and the lift-off noise was reduced by 34 % at a lift-off length of 2mm. these results confirmed that magnetic resonant coupling is effective for improving the characteristics of ECT. Additional experiments were performed in order to verify the effect of magnetic resonant coupling for the wobbling (lift-off) noise in the tube inspection. In the vibration test of the ECT sensor inside the tube, the lift-off noise decreased by 28 % on average by magnetic resonant coupling. In the scanning test of the ECT sensor inside the tube, the wobbling and other noises were obviously reduced by magnetic resonance coupling.
Prediction of Time to Significant Cracking and Actual Behavior of an Impulsively Loaded Detonation Chamber for Chemical Weapons Destruction
Authors: Asahina Joseph K. , Akasaka Koichi , Nickell Robert E. , Hamada Toshio
Published: August 2013

For repeated operation of a detonation chamber, evaluation of its fatigue damage and estimation of time to crack initiation are of considerable importance from the aspect of safe operation.

This paper proposes the use of a sufficiently conservative operation control fatigue evaluation curve, based upon the ASME Code fatigue design curve and the best fit laboratory air curve upon which the design curve is derived, in order to define operational points for actions to inspect for possible fatigue damage and initiate repairs, as needed. The paper also recommends appropriate actions to verify that any needed repairs maintain structural integrity during subsequent operations.
Small High-Pressure Chamber Shock Tube
Authors: Fukuoka Hiroshi , Yaga Minoru , Takiya Toshio
Published: August 2013

The unsteady supersonic jet formed by the shock tube with small high-pressure section was used as a simple alternative system of pulsed laser ablation. The dynamic of the supersonic jet impinging upon a flat plate are discussed by comparing experimental and calculated results. The experiment and numerical calculation were carried out by schlieren method and by solving the axisymmetric two-dimensional compressible Navier-Stokes equations, respectively. The main parameters are distance between the open end of the shock tube and the flat plate, L/D, and the pressure ratio of the shock tube, Ph/Pb. Where, L, D, Ph and Pb are the distance between the open end of the shock tube and the flat plate, the diameter of the shock tube, pressure of the high and low section of the shock tube, respectively. Collision between the shock wave reflected at the flat plate and the head of supersonic jet takes place. Computational results well predict the experimental dynamic behavior of the shock wave and the supersonic jet. Marked increase in the static pressure on the flat plate under high Ph/Pb and short L/D is observed due to interaction between the shock wave and the unsteady jet flow.
A Special Finite Element for Leak-Before-Break Analysis
Authors: Gill Peter J. , Sharples John , Davey Keith
Published: August 2013

Leak-before-Break is increasingly being used as part of safety justifications, particularly within the nuclear industry. In order to make a Leak-before-Break case for a pressurised component, it is necessary to determine leak rates through cracks under the operating load conditions. The R6 assessment procedure provides equations to calculate leak rates from a known crack opening area. Leak rates evaluated from this calculational route, however, can be subject to safety factors being applied due to various uncertainties. As such there is a strong motivation to better understand the factors affecting leak rates through cracks in pipes, so that there is less conservatism in the leak rate estimation. To perform the investigations into these factors, a special finite element has been developed. This element uses the extended finite element method to model cracks with boundary conditions on the faces due to the leaking fluid. Previous work has shown that leak rates through a crack are affected by closure of the crack, which is due to convective heat transfer from the leaking fluid to the crack faces. Therefore the new 2-D element is used to investigate this and it shows the effect of heat transfer and pressure acting on the crack faces. The first results of leak rate evaluations, using this new element, are presented in the paper.
An Approximate Formula to Calculate the Restoring and Damping Forces of an Air Spring With a Small Tube
Authors: Asami Toshihiko , Yokota Yasutaka , Ise Tomohiko , Honda Itsuro , Sakamoto Hiroya
Published: August 2013

This paper proposes a simple expression for calculating the restoring and damping forces of an air spring equipped with a small tube. Air springs are commonly used in railway vehicles, automobiles, and various vibration isolators. The air spring used in this study consists of two tanks connected by a long tube. Using a tube instead of an orifice enables flexibility in the arrangement of the two tanks. In addition, this makes it possible to manufacture a thin air spring. The oscillating system, which consists of a single mass supported by this type of air spring, is a single-degree-of-freedom (SDOF) system. However, it has two resonance points for a reason that had been unknown for a long period of time. In this paper, we explain why the SDOF system has two resonance points. After that, assuming that the vibration is small and the flow through the tube is laminar, we derive the spring constant and damping coefficient of an air spring subjected to a simple harmonic motion. Then, we calculate the frequency response curves for the system and compare the calculated results with the experimental values. According to the experiment, there is a remarkable amplitude dependency in this type of air spring, so the frequency response curves for the system change with the magnitude of the input amplitude. It becomes clear that the calculation results are in agreement with the limit value when the input amplitude approaches zero.
Modeling of the Effect of Plasticity on the Response of Pipe Systems to Internal Explosions
Authors: Smeulers Jan P. M. , Pape Gersom , Ligterink Norbert E.
Published: August 2013

Pipe systems that are used in the process industry may occasionally be subjected to internal deflagration and detonation waves. In those cases the design of the pipe system should be explosion resistant or even explosion proof. The usual design rule for the analysis of the mechanical response is based on the hoop stress calculated with an equivalent static pressure load, which depends on the magnitude of the detonation pressure. However, it has been found that the response of a pipe to a traveling detonation wave shows a number of effects that lead to much higher stresses. See [1] and [2]. One of these effects is mode coupling, i.e., the excitation of circumferential bending modes, coupled to the initial hoop stress or breathing mode, which may lead to an increase of the local maximum stress by a factor 2.6.

Mode coupling has been investigated theoretically for rings and it has been demonstrated also experimentally, among others by Li c.s. [5]. Using finite element modeling we have investigated under what conditions mode coupling can occur in pipes in which a detonation wave propagates. It appears that a condition for mode coupling in a 3D configuration is that the detonation velocity is larger than the first critical velocity Vc0. For a pipe section of limited length mode coupling will be enhanced by the flanges at both boundaries which reflect flexural waves that propagate in axial direction.

Furthermore, the effect of limited plasticity has been investigated. The results show that mode coupling is being reduced by plasticity. The conclusion is that with plasticity the detonation load can be larger without bursting of the pipe. However, mode coupling will still occur in spite of plastic deformation.

In the paper the modeling of 2D mode coupling is presented and compared with the theoretical analysis. Moreover, the extension of the model to a pipe with a finite length and an “infinite pipe” is discussed and the effect of plasticity is analyzed. The analysis incorporates the influence of the material strain rate sensitivity and it considers the response for regular structural pipe steel as well as high strength steel.
Dynamic Fracture and Anti-Explosion Capacity Investigation of Composite Explosion Containment Vessel
Authors: Hu Yang , Zheng Jinyang , Ma Li
Published: August 2013

Explosion containment vessels (ECVs) have been widely used as they can contain the shock wave and products from high explosions. Recently, there has been an increased interest in composite materials using in ECVs because of their advantages of high specific strength, reduced maintenance costs, and improved corrosion resistance. In this paper, an experiment was carried out using two e-glass/epoxy composite ECVs with an aluminum alloy inner layer to investigate the dynamic fracture and anti-explosion capacity of composite ECVs. The experiment contains two stages. In the first stage, two vessels were tested using 10g and 20g explosive charge, respectively. Dynamic circumferential and axial strain was measured. The vessel under the blast of 10g explosive was in good condition while the other one was failure as a through crack appeared. In the second stage, a large explosive charge of 30g was detonated at the center of vessel and the vessel was damaged seriously. The fracture characteristic is described in detail. The experimental results show that the range of the anti-explosion capacity ζ is between 1.43% and 2.87% which is much higher than that of single layer ECVs and also higher than that mentioned in other literature. A three-dimensional finite element analysis model is established using the ALE method based on ANSYS/LS-DYNA to simulate the experiment results of experimental vessel under the explosive loading. Good agreement between experimental and numerical results can be obtained by comparing the bulging phenomenon and hoop strain around the explosion center. The numerical results also show that the delamination appears and the delamination between the inner metal layer and adjacent composite layer is especially obvious.
Quantification of Creep Cavity Evolution Using a Novel Replica Image Processing Technique
Authors: Yang Haoliang , Davies Catrin M. , Dear John P.
Published: August 2013

In industry, the surface replication technique is employed as a practical method for the lifetime assessment of high temperature components. However, the method is limited as it is a time consuming processes, is susceptible to subjective interpretations and is only sensitive to surface damage, whereas creep damage often initiates sub-surface. A replica of a component’s surface is made by applying a softened plastic foil to it. This foil moulds itself to the alloy’s surface when pressed. After its removal from the alloy, the plastic replica provides an exact copy of the etched surface’s microstructure, which can then be examined.

A new image processing technique has been developed that provides a reliable and repeatable, quantified measure of creep cavitation using images obtained from replica films. A series of interrupted tests have been performed at the same load on 2.25CrMo (P22) ferritic steel at 650 °C. Post testing, samples were prepared and replication performed. A quantitative 2D map of the cavities across the specimens’ surface has been obtained using a novel image processing technique. The results are related to the specimens’ strain measurements using a displacement gauge and a novel potential drop technique. This new image processing technique may provide a valuable tool for industry.
Estimation of Stress Intensity Factors due To Welding Residual Stresses for Circumferentially Cracked Pipes
Authors: Oh Chang-Young , Kim Ji-Soo , Kim Yun-Jae , Oh Young-Jin , Lee Kyoungsoo , Lee Sung-Ho
Published: August 2013

This paper proposes a simple method to estimate stress intensity factors due to welding residual stresses. In this study, finite element analyses for circumferentially cracked pipe are performed to calculate stress intensity factors. Four cracked geometries and two types of weld geometry are considered. KI-solutions for the nonlinear stress distribution on the crack face were determined in accordance with codes and standards. The results are compared with KI-solutions from finite element results. It is found that proposed simple method agrees well with FE results.
Characterizing Austenitic Materials and Nickel Alloys With Electro-Magnetic Imaging
Authors: Kuljis Zoran , Lisowyj Bob
Published: August 2013

Stress Corrosion Cracking (SCC) consists of two stages, an incubation stage followed by a crack propagation stage. The crack propagation stage can be tracked fairly accurately by using Arrhenius energy values. However, the incubation stage can take a long time (20 years is not uncommon), and is far less predictable with no indication of its development. SCC is also localized making it difficult to detect, and is often only found when cracking has gone through-wall and produced a leak. Welds are known to be areas where SCC originates. Any manufacturing repairs to weld locations produce augmented levels of residual stress in the weld area and increase the probability of SCC.

Manufacturing effects also alter the electro-magnetic property of a material, and by monitoring the changes in electro-magnetic property it is possible to characterize material conditions that contribute to the SCC process. Evaluation of these manufacturing effects on several Reactor Vessel nozzles with Dissimilar Metal Butt Welds (DMBWs) has found electro-magnetic property changes, which can characterize, define and produce images of localized repairs, and also show where lack of adequate stress relieving heat treatments exists.

This electro-magnetic property methodology can predict the development of SCC in the incubation process, and can directly confirm where any initial fabrication repairs were performed, or when lack of proper stress relieving exists. A full material characterization history enabling prediction of the future susceptibility to SCC has been achieved. This complete, material characterization history of Alloy 600 components and stainless steel components was the goal of this research. Eddy Current Testing (ECT) was chosen as the NDE technique of choice, because it is sensitive to surface changes and can detect electro-magnetic property changes. Using an imaging process, which detects electro-magnetic property changes, has successfully characterized the complete history of the investigated materials.
Application of an IR Thermography Technique to the Inspection of Local Wall-Thinning Defects in Nuclear Piping Components
Authors: Kim Jin Weon , Yun Kyung Won , Jung Hyun Chul
Published: August 2013

In this study, infrared (IR) thermography was tested on pipe specimens with artificial wall-thinning defects of various dimensions, in order to determine optimal thermal injection conditions and the capability of the procedure for detecting wall-thinning defects in small-bore nuclear piping components. An active IR method was employed in the experiment. The specimen was thermally activated using two halogen lamps, and thermal images were captured via an IR camera. The thermal injection condition that provided the best images of wall-thinning defects was dependent on the pipe geometry; the optimal object distance decreased with decreasing pipe diameter. Under the optimal conditions, IR thermography was able to detect all wall-thinning defects with depth d/t ≥ 0.5, except for a defect that was very short and narrow, in a pipe specimen of length 500 mm at one time. However, the wall-thinning defects with depth of d/t = 0.25 were only detected when they had a suitable length and circumferential angle.
Wavelet Analysis of Flexural Wave Fronts in Water/Slurry Hammer
Authors: Inaba Kazuaki , Takahashi Hiroto , Kurokawa Yu , Kishimoto Kikuo
Published: August 2013

The present study experimentally analyzes flexural wave fronts in water hammer and slurry hammer with polycarbonate tubes by wavelet analysis. The water/slurry hammer was initiated by the impact between the free-falling projectile and the water/slurry in the vertical mounting tube. We measured hoop strain histories of flexural wave fronts at several locations by strain gages and analyzed the histories, using the wavelet transform method. The wavelet power spectrum near the flexural wave fronts and dispersion behaviors in water/slurry hammer were examined. In the water hammer experiments, by tracing the dispersion curve from the time-frequency signal, it is revealed that the water hammer front have a dispersion tendency. Moreover, the measured frequencies indicate a reasonable agreement with the Skalak’s theory [1, 2]. As for slurry, we mixed water and alumina balls or polystyrene (PS) balls. Wave speeds with Alumina or PS balls were compared with theoretical estimations by Han et al. [3, 4]. It is confirmed that the particles enhance slurry hammer’s dispersion and the oscillation frequency of the slurry hammer becomes lower than that of the water hammer. Additionally, the oscillation frequency corresponds to the theoretical value estimated from wave speed assuming particles as rigid-body particles.
Residual Stress Distributions and Guidelines for Crack Inspection in Pipe Bends
Authors: Yetisir Metin , Walker Zane
Published: August 2013

Root cause investigations of feeder pipe cracks detected in one CANDU™ nuclear power plant indicated that the residual stress had a significant role in these failures. As a result, numerous residual stress measurements of pipe bends were obtained and models for predicting the residual stress distributions associated with various bending processes were developed.

This paper provides a comprehensive review of pipe bend residual stress data and provides guidelines for identifying the most susceptible locations for targeted crack inspections. Residual stress data, generated since 1997 as part of the CANDU feeder cracking investigation, was compiled and presented for the quick dissemination of information. This information is summarized in quick lookup tables where likely crack locations are identified for pipe bends manufactured using various fabrication techniques.
Finite Element Simulation of Process Control of Bolt Tightening for Joints With Non-Parallel Contact
Authors: Ganeshmurthy Saravanan , Nassar Sayed A.
Published: August 2013

In this paper, 3-D finite element analysis (FEA) is used for simulating and evaluating the various process control methods that are commonly used in the automated assembly of bolted joints. A joint model with non-parallel contact under the bolt head is used. The FEA model takes into account the thread helix angle of the fastener. Simulation includes the torque-only and the torque-turn process control methods for achieving a desired level of the bolt preload at initial assembly of the joint. The torque-only process control option is simulated by applying a target peak torque value at which the tightening process is stopped. On the other hand, a torque-angle method is simulated by first applying a low level (threshold) torque (to the bolt head) after which the bolt head (or nut) would be rotated by a specified angle of turn, in order to achieve the desired bolt tension. The effect of thread and underhead bearing friction coefficients as well as the hole size are investigated. The FEA simulation provided in this study would be helpful for developing reliable tightening strategies for joints with (as cast) non-parallel bearing surfaces.
New Manufacturing Cycle to Improve the Life of Packing Cups for Hyper-Compressors
Authors: Maggi Carmelo , Tognarelli Leonardo , Capanni Alessio , Wojnar Jan
Published: August 2013

Hyper-compressors are subjected to very high operating pressure, maximum and fluctuating, strongly impacting design and life of all cylinder components. Components subjected to fatigue (both high cycle fatigue and low cycle fatigue) can experience a failure in a very short time that may cause large production losses.

Packing cups proved to be one of the most critical cylinder components and the fatigue behavior of the packing cups subjected to alternating loads, due to the suction and discharge conditions, is their key design factor.

A thorough study has been performed in order to increase the safety factors in all critical regions of the packing cups analyzing a new manufacturing cycle that allows optimizing the compressive pre-stresses on the lube oil parts due to the autofrettage procedure. The approach included a dedicated sensitivity FEM analysis of the autofrettage pressure to determine the correct residual stresses at the lube oil parts in order to keep them under compressive stress in operating conditions and Fracture Mechanics Calculations based on BSI7910 aimed at achieving a design able to survive with a threshold defect larger than the minimum detectable defect.
Bolted Joint Fracture Analysis Study Using Modern Methods
Authors: Griffin David , Reed Gary , Mills Andrew , Brayshaw Russell
Published: August 2013

This paper describes the outcome of a fracture study to ascertain the benefits of using modern three dimensional finite element techniques. The defects considered are postulated to be present at the root of a threaded fastener. The defects are explicitly modelled using three dimensional finite element analysis to extract the relevant fracture parameters.

A large number of thumbnail defects of varying size and aspect ratio have been incorporated into the root of the first engaged thread of studs typically used in pressure vessels. Stress intensity factors at the defect surface and depth locations have been extracted for a number of thermal transient events using a domain integration technique within the general finite element code ANSYS.

The above stress intensity factors were then used to generate fracture calculations using an R6 based procedure [1] for:

• Toughness-based fracture margins for each defect modelled;

• Critical defect size;

• Comparisons with a fully extended defect.
Optical Strain Monitoring Techniques
Authors: Narayanan Aditya , Morris Andy , Davies Catrin M. , Dear John P.
Published: August 2013

The Auto-Reference Creep Management and Control (ARCMAC) system is being developed as a technique to evaluate the remaining life of power plant components. The system consists of a pair of Inconel plates with a configuration of silicon nitride (SiN) spheres on them, and a camera system used to take images of the gauge during the component’s deformation. The purpose of the system is to measure the creep strain accumulated by a component at regular intervals, tracking the relative motion of the spheres in order to measure a point-to-point value of strain. The system is currently used to capture images of gauges already installed on power plants in the UK as part of scheduled maintenance during plant outages.

It is also possible to use the ARCMAC system to capture speckle paint pattern data used in digital image correlation (DIC) in order to visualise the strain field across the heat affected zones (HAZ) in welds and around other strain concentration features. A newer version of the system: the Digital Single Lens Reflex (DSLR) ARCMAC is being developed specifically to capture this kind of data in order to complement the point-to-point strain measurements obtained.

This article presents results of experiments performed at room temperature with the purpose of establishing the basic accuracy of the conventional ARCMAC and the DSLR ARCMAC in order to compare their performance. It also intends to evaluate the performance of the latter when used for digital image correlation. The results showcase the accuracy of the technique at high strains using the DSLR camera, showing its usefulness as a tool to measure creep strain.
Analysis of Ductile Crack Growth in Pipe Test in STYLE Project
Authors: Yin Shengjun , Williams Paul T. , Klasky Hilda B. , Bass B. Richard
Published: August 2013

The Oak Ridge National Laboratory (ORNL) is conducting structural analyses, both deterministic and probabilistic, to simulate a large scale mock-up experiment planned within the European Network for Structural Integrity for Lifetime Management – non-RPV Components (STYLE).

The paper summarizes current ORNL analyses of STYLE’s Mock-Up3 experiment to simulate/evaluate ductile crack growth in a cladded ferritic pipe. Deterministic analyses of the large-scale bending test of a ferritic surge pipe, with an internal circumferential crack, are being simulated with a number of local micromechanical approaches, such as Gurson-Tvergaard-Needleman (GTN) model. Both FEACrack [1] and ABAQUS [2] general purpose finite element programs are being used to predict the failure load and the failure mode, i.e. ductile tearing or net-section collapse, as part of the pre-test phase of the project.

Companion probabilistic analyses of the experiment are utilizing the ORNL developed open-source Structural Integrity Assessment Modular - Probabilistic Fracture Mechanics (SIAM-PFM) framework. SIAM-PFM contains engineering assessment methodologies such as the tearing instability (J-T analysis) module developed for inner surface cracks under bending load. The driving force J-integral estimations are based on the SC.ENG1 or SC.ENG2 models. The J-A2 methodology is used to transfer (constraint-adjust) J-R curve material data from standard test specimens to the Mock-Up3 experiment configuration. The probabilistic results of the Mock-Up3 experiment obtained from SIAM-PFM will be compared to those generated using the deterministic finite element modeling approach. The objective of the probabilistic analysis is to provide uncertainty bounds that will assist in assessing the more detailed 3D finite-element solutions and to also assess the level of confidence that can be placed in the best-estimate finite-element solutions.
Correlation of Piping System Detonation Test Data and System Analyses
Authors: Ligon Thomas C. , Gross David J. , Minichiello John C.
Published: August 2013

This paper describes hydrogen and nitrous oxide detonation experiments that were performed using an approximately 200-ft long 2-inch schedule 40 piping system. The objective of these experiments was to develop an understanding of the loads and forces imposed by internal detonation on piping combinations representative of a typical industrial piping system. The apparatus contained numerous straight pipe lengths with 90° and 45° bends, 90° elbows, and a tee along with rigid foundation supports that were connected to the pipe using typical u-bolt fasteners.

As a detonation wave propagates through a gas-filled piping system, the pipe begins to respond globally once a detonation encounters a change in flow direction, such as a bend, causing a pressure imbalance due to both the internal detonation pressure and change in momentum of the reaction products. The resultant force imparts both axial forces and moments on the pipe exciting both extensional and bending modes.

The test data was used to validate two finite element (FE) models developed using the ANSYS finite-element program: a hybrid model that made use of both shell and beam elements, to determine the interaction between shell and beam modes, and an all beam element model. An additional beam element model was developed using the Bechtel National Inc. software ME101 that was also found to be in agreement with the measured and ANSYS calculated frequencies and support loads. In addition to the detonation testing, the finite-element models were validated against experimental modal analysis data of the piping system that identified the primary modal frequencies and vectors. These data were compared to the modes extracted from finite-element models of the piping system.
A Numerical Study on CMOD Compliance for Single-Edge Bending Specimens
Authors: Wang Enyang , Zhou Wenxing , Shen Guowu , Duan Daming
Published: August 2013

Several well-known equations for estimating the crack length in the SE(B) specimens from the normalized CMOD compliance are evaluated based on two- and three-dimensional finite element analyses. Two-dimensional analyses are carried out first to verify the reported accuracy and applicable ranges for each equation based on the plane strain models with six different crack lengths. Three-dimensional analyses are then carried out to estimate the errors of prediction of the equations that evaluate the crack length from the plane stress- and plane strain-based CMOD compliances. Both plain-sided and side-grooved models are included in the three-dimensional analyses and have seven different thickness-to-width ratios. The error of prediction of a given equation is largely impacted by the thickness-to-width ratio, crack length, presence of side grooves, and use of the plane stress- and plane strain-normalized CMOD compliance. Based on the errors of prediction, the relevance of the plane strain and plane stress conditions to the actual state of stress in the ligament of the SE(B) specimens is inferred. Knowledge of the relevance of the plane stress and plane strain conditions can be used to select either plane stress- or plane strain-based CMOD compliance in the crack length-CMOD equations and improve the accuracy of the prediction.
Experimental Investigation on Seismic Mitigation of Motion Sensitive Equipment Using Multiple Direction Optimized-Friction Pendulum System With Multiple Sliding Interfaces
Authors: Tsai C. S. , Su H. C. , Wang Y. M.
Published: August 2013

Presented in this paper is aimed at experimental evaluation of the efficiencies of the multiple direction-optimized friction pendulum system (MDO-FPS) with multiple sliding interfaces in mitigating the seismic responses of motion sensitive equipment through a series of shaking table tests. Experimental tests of motion sensitive equipment isolated with MDO-FPS isolators and subjected to various types of earthquakes were carried out to investigate the efficiency of the MDO-FPS isolator in reducing the response of equipment during earthquakes. Shaking table test results indicate that the acceleration response of the equipment has been remarkably reduced while compared to that of fixed-base equipment.
Unique Fracture Behaviour of Multi-Perforated Media
Authors: Billon F. , Taborda F. , Lesage J-O.
Published: August 2013

Concerning the risk of fast fracture, multi-perforated tubesheets have a unique behavior. For the fracture analysis, it is assumed that a small ligament is fully cracked from the skin and that failure leads into the two holes on either side of this ligament in a square pitch. This approach is referred to as a “Broken Ligament Approach”, which can be analyzed using four main steps:

(a) Calculation of the elementary stresses in all the tubesheet using a global 3D Finite Element model,

(b) Conversion of the elementary stresses in membrane stresses and bending stresses along the thickness of the tubesheet at the location of the assumed broken ligament,

(c) Creation of a Representative Local Volume (RLV) containing the broken ligament to which boundary loads are applied to obtain the stresses defined in the global model,

(d) Calculation of the Stress Intensity Factor (SIF) along the crack front of the broken ligament with different depth of the crack.

The result is that the SIF passes through a maximum value as the depth of the broken ligament increases through the thickness of the tubesheet. It is thus possible to find an absolute maximum value of the SIF (called SIFam) over the tubesheet for its most severe loadings. Under these conditions, if the toughness of the tubesheet material is greater than SIFam, there is no risk of a fast fracture of the tubesheet. The existence of SIFam is a strong characteristic of the fracture behavior of multi-perforated media.
Improvement of Leak Tightness Analysis of Bolted Closure Systems in Pressure Equipment
Authors: Billon F. , Batmale G. , Drevon B.
Published: August 2013

The aim of this work is to study the Leak Tightness of the closure systems of nuclear pressure equipment during all situations including in-service operating, emergency and accidental conditions. The analysis is performed using a complete 3-dimensional finite element model of the closure system including : the studs, the gasket, the contacts between the gasket and their seating surfaces (contact elements), the nuts, the cover, the part of the shell on which the opening is located and the tightening preload of the studs. It comprises 2 main phases:

(a) Using the 3D model, with non linear internal parameters converted in appropriate linear that allows performing linear analyses, we select, with respect to leaktightness, the most critical thermal and pressure transient among a large amount of transient. This selected transient presents the weakest compressing force between the gasket and its seating surfaces, which is the selection criterion.

(b) Then, using the 3D model we perform a full non-linear analysis of the selected transient, taking into account the non linearity of the contacts as well as the non linearity of the gaskets and the tightening preload of the studs.

Thus for this transient, we obtain the history of the compressive forces on the gasket and particularly the history of the metal-metal contact for the gaskets multi-ring type (metallic-graphite-metallic) and we can check if compressive forces remain effective.

An important consequence is the re-calculation of the tightening preload applied to the studs if the intensity of the metal-metal contact is not sufficient.
The Improved Measurements and Stress Analysis of Cylinder / Pipe With Out-of-Roundness
Authors: Orynyak Igor V. , Lokhman Igor V. , Bohdan Andrii V.
Published: August 2013

The API 579 defines an out-of-roundness as the geometrical imperfection of a shell which is assumed to be constant in the longitudinal direction. In general, there are three types of out-of-roundness imperfections — a) the offset weld misalignment (misalignment of radius in the point of the circumference); b) angular misalignment (misalignment of the first derivative of the radius at some point); c) regular imperfection (radius is the continuous function along the circumference).

The document API 579 [1] contains the procedure (or requirements) of the imperfections measurement as well as their analytical treatment in case of inner pressure loading. Regretfully, at least two principal drawbacks of the document should be pointed out: the formula for regular imperfection description based on the discrete measurements of the surface point is inaccurate. Besides, nothing is said about how to extract the values of the misalignments from them. It should be kept in mind that misalignments cannot exist alone without the continuous deforming of the remaining part of the circumference; notions of the local as well as the global peaking (angular lumps) is confusing. It is practically impossible to discern them physically. Furthermore, the two equal angular misalignments should lead to the same additional stresses irrespective of how we name this misalignment — be it local or global one. In both cases the formulas are incorrect.

The proposed paper gives the solutions for the abovementioned problems. The results of the real measurements of the cross section form of different pipes are presented. The general approach for treating the out-of-roundness is given and an example of measurement of real pipe cross-section is presented. The stress calculation part of the procedure is based on the results presented in work [2].
Pipeline Health Integrity Monitoring (PHIM) Based on Acoustic Emission Technique
Authors: Giunta Giuseppe , Budano Sergio , Lucci Antonio , Prandi Luca
Published: August 2013

The Acoustic Emission (AE) technique allows taking under control the damage as superficial flaws (S-Flaws) occurred during service operation of remarkable zones of steel components, monitoring the initiation and the propagation of critical defects, submitted to static or variable stresses and aggressive environment exposure.

In the framework of the eni gas&power research project oriented to the development of a “AE methodology” for monitoring critical sections of gas transmission pipelines, a study has been carried out jointly with Centro Sviluppo Materiali (CSM), aimed to investigate reliability and applicability of the AE technique to steels used in the Oil&Gas industry.

Steel grades API 5L X65, X80 and X100, representative of traditional and new gas pipelines, have been selected. The project was scheduled investigating the potential of these steels to release elastic waves generated by sources of damage related to ductile or brittle fracture mechanisms.

Hydraulic tests until failure were carried out on single pipes using steel grade API 5L X65 for monitoring the growing of the damage on the tip of artificial surface notches (S-flaw), machined on the wall thickness [1]. Water was used as internal fluid and temperature effect was considered as well. The capability of the AE technique to discriminate ductile and brittle fractures, the essential information to approach an integrity assessment procedure, was achieved. This paper, respect to the previous ones [1], extends the AE methodology for monitoring pipelines supplying both oil and gas. In fact a third burst test was carried out filling the pipe by air and the results on this item are presented.
The Effect of Bi-Axial Stress on Limit Loads of Structures Containing Surface-Breaking Flaws and its Influence on Structural Integrity Assessments
Authors: Wei Liwu , Hadley Isabel
Published: August 2013

Fracture assessment diagram (FAD) based fracture assessment procedures are universally adopted by standards/documents including BS7910, R6, API579-1/ASME FFS-1 and FITNET. In the use of a FAD for structural integrity assessment, one important consideration is to determine the load ratio (Lr) which is defined by two equivalent definitions: Lr is either defined as the ratio of reference stress (σref) to yield strength (σY) as in BS7910, or as the ratio of applied load to plastic limit load as in R6. The solutions of reference stress or limit load are given in the assessment procedures for commonly encountered flawed structures such as a plate containing a surface crack and a cylinder containing an external surface crack. Although the solutions given in the various standards are not all the same, they were invariably derived on the basis of analysis of the force and moment equilibrium with regard to a flawed section and none of them has taken into account the effects of bi-axial stressing on a flawed section, thus leading to the likelihood of an overly conservative assessment.

In this work, finite element analysis (FEA) of various flawed geometries (plate and cylinder containing surface cracks) was performed to compute plastic limit load, with the focus on understanding the effects of bi-axial stressing on plastic limit load. The geometries assessed include a plate with a surface crack subjected to both uni-axial and bi-axial loading, and a cylinder with circumferentially internal and external surface cracks sustaining a combination of axial loading and internal pressure. The investigation of these cases has demonstrated a significant increase in plastic limit load arising from bi-axial stressing. Comparison of the results of plastic limit load obtained from FEA with those derived from BS 7910 reference stress solutions was carried out to assess the extent of conservatism when the standard solutions are used in the applications containing bi-axial stresses. The implication for structural integrity assessment due to bi-axial stressing was also addressed. A comparison between BS 7910 Level 2B (material-specific FAD) and Level 3C (based on a FAD generated with FEA) procedures was also made and it was shown that whether the Level 3C procedure can reduce the conservatism in an assessment is dependent on individual cases.
Novel Impact/Debonding Tolerant Sandwich Panel With Millitubes Grid Stiffened Foam Core
Authors: Li Guoqiang , Ji Gefu , Pang Su-Seng
Published: August 2013

Sandwich construction has been extensively used in various fields. However, sandwich panels have not been fully exploited in critical structural applications due to damage tolerance and safety concern. A major problem of sandwich panels is the debonding at or near the core/face sheet interface, especially under impact loading, which can lead to a sudden loss of structural integrity and cause catastrophic consequences. In order to improve the debonding resistance and energy absorption of sandwich panel under impact loadings, a new foam core is proposed which is a hybrid core consisting of grid stiffened hollow metallic millitubes reinforced polymer matrix. The objective of this study was to characterize its dynamic performances. The core consisted of polymer resin reinforced by grid stiffened continuous metallic millitubes. Low velocity impact test demonstrated that new core panel may be considered a promising option for critical structural applications featured by debonding and multiple impact tolerance.
Residual Stress Measurement of a Ferritic Bead on Plate Benchmark Test Specimen Using the Contour Method
Authors: Hosseinzadeh Foroogh , Bouchard P. John
Published: August 2013

This paper presents new measured residual stress data for a ferritic weld bead on plate benchmark specimen. The contour residual stress measurement method was applied because it could provide an informative map on the plane of interest capable of quantifying local variations in residual stress associated with phase transformations. The quality of the contour cut was optimised by carrying out initial cutting trials to tune the electro-discharge machining cutting parameters. The risk of plasticity during the cutting procedure was minimised by using an “embedded crack” contour cutting configuration, clamping with fitted bolts and a large diameter cutting wire in order to reduce the crack opening and stress concentration at the cut tip. The results of the contour method measurement are in reasonable overall agreement with published stresses measured by neutron diffraction. However, certain features in the results suggest that significant plasticity did occur during the contour cut despite the specific measures taken to minimise this effect.
Beam-Mode Buckling of Buried Pipeline Subjected to Seismic Ground Motion
Authors: Mitsuya Masaki , Sakanoue Takashi , Motohashi Hiroyuki
Published: August 2013

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.