bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Slow Crack Growth Test Methodologies Used to Predict Service Life of High Density Polyethylene Piping
Authors: Kalyanam S. , Krishnaswamy P. , Shim D.-J. , Hioe Y. , Kawaguchi S. , Shimura T. , Numata K.
Published: January 2014

HDPE pipe and piping components have been used successfully and safely for natural gas distribution around the world for several decades. The primary concerns for a 50-year life for buried HDPE piping involves designing against three primary failure modes — ductile fracture, rapid crack propagation (RCP), and slow crack growth (SCG) under sustained pressure loading. Although design methodologies for preventing ductile fracture, and RCP are well established, SCG remains to be a limiting failure mode in determining useful service life of HDPE piping as it may occur under sustained pressure and temperature. Although considerable amount of research has been conducted over the last two decades, SCG still remains less well understood than other failure modes.

A critical evaluation of various test methodologies available to determine the SCG resistance of HDPE resins was conducted using FEA of various widely used laboratory test specimens. While there exist extensive information on the test methodologies and the applicability of each of the SCG testing methods, there is a growing concern as to whether any/all of these SCG tests give the same information akin to the industrial pipe application, particularly so when conflicting messages are obtained from time to failure predictions from two different SCG tests. While notched-pipe test (NPT) proves to be a direct approach to assess SCG resistance of the PE pipe with the use of temperature as a test accelerating factor; in the case of newer grade PE resins, the failure time of NPT can still be considerably large (∼5,000 to 10,000 hours). For this reason, some of the other coupon SCG tests are focus of recent investigations and especially sought after for rapid ranking/assessment of resins and understanding the manufactured HDPE pipe performance.

In this study, FEA was conducted to facilitate a direct comparison of leading SCG test methods, through determination of both the stress intensity factor, KI, and existing constraint factors in various widely used specimen geometries. These results are then compared to pipe specimen with an OD (outer diameter) or ID (inner diameter) surface notch. Since, constraint can have a significant role in SCG initiation, T-stress, and biaxiality ratios (β), these were compared along the crack fronts to arrive at definitive reasons for the smaller failure times observed when testing some of the SCG test specimens, and also reasons for SCG mode of failure observed even under large applied loads (large KI compared to that in a notched pipe) when testing some of the SCG test specimens. The use of stress intensity factor, KI, along with the T-stress and biaxiality ratio (β), is found to provide a complete picture on the broad spectrum of failure times observed from various SCG test specimens and rationale for choosing a SCG test specimen when evaluating HDPE pipe or resins.
Towards the Development of Filament Wound Composite Structures Submitted to Very High Internal Pressure, Based on Complex Geometry Shapes
Authors: Vargas Rojas Erik , Chapelle David , Perreux Dominique
Published: January 2014

Industrial applications, especially composite structures bearing high internal pressure, and fabricated using the filament winding process face certain difficulties like the reinforcement of complex shapes, as well as the correct placement of fibers over the surface of a mandrel. In some cases the definition of the manufacturing parameters respond more to cost or time criteria rather than engineering standards, reducing largely the advantages of the said manufacturing process. In order to overcome these obstacles, this research aims to propose a solution that permits to fabricate complex shapes with the desired winding angles at a certain region of complex-shaped mandrels. A numerical tool that simulates the placement of fiber tows over the surface of complex geometries is developed and validated by means of the fabrication of convex and concave composite structures using detachable mandrels. Previous results show that it is feasible to wind complex geometries with good accuracy.
A Study of Dynamic Response Behavior During Earthquake for Large LNG Storage Tanks in Consideration of Uplift
Authors: Hayashi Shoichiro , Taniguchi Tomoyo
Published: January 2014

Under severe seismic design conditions for LNG storage tanks in recent years, detail verification of soundness of structure including uplift behavior of bottom plate has been required. The design state is used to be analyzed statically as if the maximum dynamic pressure represents reciprocal processes during the earthquake. However, the previous studies reveals that the static analysis fails to calculate dynamic response behavior including uplift of bottom plate. In this paper, fluid-structure coupled 3-dimensional time-history FE analysis was performed for study of dynamic response including uplift of bottom plate. The time history FE analysis reveals undulating deformation at top of sidewall, which had not been observed under static conditions. This deformation is affected by stiffness of stiffener rings installed at the sidewall and effect of that on tank response was investigated. The FE analysis also proves that uplift height of bottom plate under reciprocal pressure is significantly smaller than that due to static conditions. This study makes clear the dynamical behavior of tank during earthquake and magnitude of influence of dynamic loading on that. In addition, the concept of introducing such dynamic effect to static analysis is proposed.
Application and Experience Feedback of ASME Code Case N-155-2 for RTR Piping in Nuclear Plants
Authors: d’Udekem Nicolas , Art Philippe , Grisel Jacques
Published: January 2014

Nowadays, the usefulness of RTR (Reinforced Thermosetting Resin) for pressure retaining equipment does not need further proof: they are lightweight, strong, with low thermal elongation and highly corrosion resistant. The use of RTR piping makes all sense for piping systems circulating raw water such as sea water at moderate pressure and temperature for plants cooling. However, this material is rarely used for safety related cooling systems in nuclear power plants.

In Belgium, Electrabel and Tractebel have chosen to replace the existing carbon steel pipes of the raw water system by GRE (Glassfiber Reinforced Epoxy) pipes, in accordance with the Authorized Inspection Agency, applying the ASME Code Case (CC) N-155-2 defining the specifications and requirements for the use of RTR pipes, fittings and flanges.

After a challenging qualification process, Class 3 GRE pipes are now installed and operating for raw water cooling systems in two Belgian nuclear units and will soon be installed in a third one.

The paper will address the followed qualification processes and the implementation steps applied by Electrabel/Tractebel and relate the overcome obstacles encountered during manufacturing, erection and commissioning of Class 3 GRE piping in order to ensure quality, reliability and traceability required for safety equipment in nuclear power plants.
Experimental and Numerical Investigations on Nozzle Reinforcements
Authors: Wieschollek Matthias , Hoffmeister Benno , Feldmann Markus
Published: January 2014

Pipes and nozzles attached to large liquid storage tanks can be susceptible to earthquake induced damages. Adequate design and detailing of shell nozzle reinforcements significantly improves their seismic performance. Damages to nozzles, often combined with elephant-foot-buckling, belong to the most frequent failure modes of large liquid storage tanks caused by earthquakes. The failure consequences depend very much on the liquid contents which may be hazardous; prevention of leakage is a crucial design and verification criteria. European and American standards provide detailed recommendations for structural dimensioning and detailing of shell nozzle reinforcements, however no reliable statements can be made to their seismic behaviour. This paper describes the results of six experimental tests on three typical types of shell nozzle reinforcements. These full scale tests were carried out in the range of ultra-low cycle fatigue for longitudinal and transverse load directions as they can be expected under seismic actions. Based on the evaluation of the test results appropriate FE-models were derived by which parametrical numerical investigations were conducted. Through these studies the influence of different parameters (e.g. thickness of shell plate, reinforcing plate, bottom plate etc.) on the seismic behaviour has been investigated. Finally recommendations for the dimensioning of nozzles reinforcements with particular attention to seismic resistance were developed.
A Numerical and Experimental Study of the Disk Pressure Test
Authors: Ardon Kevin , Charles Yann , Gaspérini Monique , Furtado Jader
Published: January 2014

The Disk Pressure Test is used to select metallic materials for hydrogen storage and transportation and consists of a thin metallic disk bulged out until fracture by applying a gas pressure on its lower face. The ratio of the fracture pressures obtained with a neutral gas and with hydrogen gas defines a phenomenological index for material hydrogen sensitivity. In order to use the Disk Pressure Test for the selection of materials exposed at high pressure (50–70 MPa), a thorough study of this method has been carried out. Experimental investigations of damage mechanisms at different scales and finite element computations of the test have been carried out to exhibit the main features of hydrogen embrittlement in low alloy Fe-Cr-Mo tempered steels during the disk rupture test. Finite Element computations of the test permitted to predict the global response and to understand the effect of boundary conditions and of material behavior on stress gradients and plastic strain distribution throughout the disk. Using hydrogen sensitive cohesive elements to model the global crack path, good agreement with experiment was obtained on the effect of disk thickness and of hydrogen pressure rate on the failure pressure. The relative influence of loading conditions and material behavior on the hydrogen embrittlement during the disk rupture test are discussed.
Guidelines for Seismic Design and Analysis of Pressure Vessels
Authors: Wieschollek Matthias , Diamanti Kalliopi , Pinkawa Marius , Hoffmeister Benno , Feldmann Markus
Published: January 2014

An adequate design of pressure vessels, also for seismic actions, is crucial in particular if due to hazardous content the consequences of failure may become very severe. While very detailed and specific seismic design rules for structural buildings are provided by several codes, such rules are missing for pressure vessels. This paper describes the results of a study on seismic performance and applicability of existing European and American codes to pressure vessels with cylindrical and spherical shapes and provides a comparison of design outcomes according to these codes. The investigations were performed for different case studies of existing pressure vessels which were selected to be representative for the current practice. The studies comprised numerical investigations as well as simplified models for the estimation of the dynamic properties of the vessel structures. The applicability of behaviour factors was discussed based on proposals made by European and American codes, so that finally recommendations for the behaviour factor of pressure vessels with different shapes and types of supports have been developed based on pushover analyses and non-linear incremental dynamic analyses.
A Method for Extracting the Time Delay From the Unsteady and Quasi-Steady Fluidelastic Forces in Two-Phase Flow
Authors: Sawadogo Teguewinde , Mureithi Njuki
Published: January 2014

The time delay is a key parameter for modeling fluidelastic instability, especially the damping controlled mechanism. It can be determined experimentally by measuring directly the time lag between the tube motion and the induced fluid forces. The fluid forces may be obtained by integrating the pressure field around the moving tube. However, this method faces certain difficulties in two-phase flow since the high turbulence and the non-uniformity of the flow may increase the randomness of the measured force. To overcome this difficulty, an innovative method for extracting the time delay inherent to the quasi-steady model for fluidelastic instability is proposed in this study.

Firstly, experimental measurements of unsteady and quasi-static fluid forces (in the lift direction) acting on a tube subject to two-phase flow were conducted. The unsteady fluid forces were measured by exciting the tube using a linear motor. These forces were measured for a wide range of void fraction, flow velocities and excitation frequencies. The experimental results showed that the unsteady fluid forces could be represented as single valued function of the reduced velocity (flow velocity reduced by the excitation frequency and the tube diameter).

The time delay was determined by equating the unsteady fluid forces with the quasi-static forces. The results given by this innovative method of measuring the time delay in two-phase flow were consistent with theoretical expectations. The time delay could be expressed as a linear function of the convection time and the time delay parameter was determined for void fractions ranging from 60% to 90%.

Fluidelastic instability calculations were also performed using the quasi-steady model with the newly measured time delay parameter. Previously conducted stability tests provided the experimental data necessary to validate the theoretical results of the quasi-steady model. The validity of the quasi-steady model for two-phase flow was confirmed by the good agreement between its results and the experimental data. The newly measured time delay parameter has improved significantly the theoretical results, especially for high void fractions (90%). However, the model could not be verified for void fractions lower or equal to 50% due to the limitation of the current experimental setup. Further studies are consequently required to clarify this point. Nevertheless, this model can be used to simulate the flow induced vibrations in steam generators’ tube bundles as their most critical parts operate at high void fractions (≥ 60%).
Comparison of Design Requirements for Nuclear Steam Generators in the ASME and RCC-M Codes
Authors: Cao Junjie , Caple Peter
Published: January 2014

As two major international codes for class 1 nuclear power plant components, both ASME BPVC Section III and RCC-M Code have been applied to the design of steam generators for nuclear power plants. With respect to the design requirements for steam generators, there are many similarities between the ASME and RCC-M rules as a result of the historic development of the RCC-M Code which evolved from a foundation based on the ASME Code. However, differences do exist in the two codes. In this paper, detailed requirements related to steam generator pressure boundary design in ASME Subsection NB are compared with corresponding requirements in RCC-M Subsection B to identify the differences between the two codes. Supplemental requirements to the ASME Code requirements are proposed for steam generator pressure boundary design to meet the design criteria in both codes. This approach may be also applied to other Class 1 components.
Study on Temperature Distribution of Pebble-Bed HTR Fuel Element by Using Boundary Element Method
Authors: Wang Haitao , Wang Xin
Published: January 2014

Spherical fuel elements with a diameter of 60mm are basic units of the nuclear fuel for the pebble-bed high temperature gas-cooled reactor (HTR). Each fuel element is treated as a graphite matrix containing around 10,000 randomly distributed fuel particles. The essential safety concept of the pebble-bed HTR is based on the objective that maximum temperature of the fuel particles does not exceed the design value. In this paper, a microstructure-based boundary element model is proposed for the large-scale thermal analysis of a spherical fuel element. This model presents detailed structural information of a large number of coated fuel particles dispersed in a spherical graphite matrix in order that temperature distributions at the level of fuel particles can be evaluated. The model is meshed with boundary elements in conjunction with the fast multipole method (FMM) in order that such large-scale computation is performed only in a personal desktop computer. Taking advantage of the fact that fuel particles are of the same shape, a similar sub-domain approach is used to establish the temperature translation mechanism between various layers of each fuel particle and to simplify the associated boundary element formulation. The numerical results demonstrate large-scale capacity of the proposed method for the multi-level temperature evaluation of the pebble-bed HTR fuel elements.
Measurement of Fatigue Crack Growth Rates for SA-372 Gr. J Steel in 100 MPa Hydrogen Gas Following Article KD-10
Authors: Somerday Brian , San Marchi Chris , Nibur Kevin
Published: January 2014

The objective of this work is to enable the safe design of hydrogen pressure vessels by measuring the fatigue crack growth rates of ASME code-qualified steels in high-pressure hydrogen gas. While a design-life calculation framework has recently been established for high-pressure hydrogen vessels, a material property database does not exist to support the analysis. This study addresses such voids in the database by measuring the fatigue crack growth rates for three heats of ASME SA-372 Grade J steel in 100 MPa hydrogen gas at two different load ratios (R). Results show that fatigue crack growth rates are similar for all three steel heats and are only a mild function of R. Hydrogen accelerates the fatigue crack growth rates of the steels by at least an order of magnitude relative to crack growth rates in inert environments. Despite such dramatic effects of hydrogen on the fatigue crack growth rates, measurement of these properties enables reliable definition of the design life of steel hydrogen containment vessels.
Estimation of Weld Induced Residual Stresses of Thick Welded Sections Using Numerical Welding Simulation
Authors: Gooroochurn Yogendra (San) , Thibaux Philippe , Cooreman Steven , Antonissen Joachim
Published: January 2014

Welding processes are quite complex in nature as they involve the interaction of multiple physical phenomena. The thermal history developed during the process causes the material to undergo complex phase transformations. Non-uniform contraction and expansion of heat affected, softer, areas constrained by cooler, harder, areas of the material induce residual stresses and the weldment undergoes permanent deformation. When thick sections are welded, the formation of phases and the distribution of residual stresses are even more complex. These could lead to failure of the welded components during service. For the design of pressure vessel applications understanding the phase formation and residual stress distribution in thick weldments is critical. Numerical simulation was used to understand the influence of multiple variables on the residual stresses induced by a welding process The challenges involved in performing welding simulation of thick sections are described. Furthermore numerical and experimental results are compared and discussed.
Elastic-Route Estimates of Strain Range for Notched Components Under Thermal Loading Without Performing Linearization of Stresses
Authors: Fujioka Terutaka
Published: January 2014

This paper describes simplified methods for estimating the strain range produced in notched components under thermal loading for the purpose of fatigue, creep, and creep-fatigue damage assessment. The methods presented are based on the previously proposed stress relaxation locus and the elastic follow-up factor combined with a newly proposed method for evaluating primary-plus-secondary stress limit. The procedures contained in the methods do not need the linearization of stresses. The proposals are validated by performing elastic-plastic finite element analysis of notched components subjected to cyclic thermal loading.
Treatment of Defects Found in Inspection for Threaded Locking Ring Heat Exchanger
Authors: Li Xufeng , Yang Jingbiao , Zheng Jiong , Luo Weijian , Wu Xilai
Published: January 2014

The process characteristics and failure mechanisms of threaded locking ring heat exchanger in medium pressure hydrogenation plant in refinery was analyzed, and the weak part of the threaded locking ring heat exchanger was identified. Inspection strategy has been determined based on the analysis of the process characteristics and failure mechanisms, and the full inspection was implemented using effective techniques. Defects found in the inspection for the threaded locking ring heat exchanger was treated well based on the failure mechanisms analysis. The safety situation of the threaded locking ring heat exchanger was in good conditions and in controllable state after full inspection.
Application of Stress Intensity Factors for Deep Surface Cracks to Crack Growth Evaluation
Authors: Iwamatsu Fuminori , Miyazaki Katsumasa , Miyata Hajime , Yuya Hideki
Published: January 2014

Flaw evaluation for nuclear power plants is conducted on the basis of a fitness-for-service code. For instance, the ASME Boiler and Pressure Vessel Code Section XI (ASME Section XI) and the JSME Rules on Fitness-for-Service for Nuclear Power Plants (JSME Code) prescribe a flaw evaluation procedure. In flaw evaluation, an aspect ratio of a detected surface crack is defined by a/l, where a is the crack depth and l is the crack length, and the aspect ratio a/l does not exceed 0.5. Therefore, a deep surface crack, which has an aspect ratio a/l greater than 0.5, is characterized as a semicircle with l = 2a. Meanwhile, deep surface cracks caused by stress corrosion cracking (SCC) have been detected in the Ni based alloy weld metal. Since the limit of the flaw characterization rule which is an aspect ratio a/l ≤ 0.5 seems to conduct to a conservative evaluation result for a deep surface crack, more rational and applicable flaw evaluation is required in order to eliminate surplus conservatism.

In this study, a flaw evaluation procedure based on ASME Section XI or JSME Code is extended to deal with a deep surface crack. To evaluate crack growth behavior for a deep surface crack, coefficients to calculate stress intensity factors were evaluated by finite element analysis (FEA) and shown in tabular form on the basis of equations prescribed in ASME Section XI and JSME Code. To verify the applicability of proposed coefficients to crack growth evaluation, SCC crack growth behavior for a deep initial crack was evaluated by coefficients applied to the ASME Section XI procedure and a detailed FEA method. Applicability of coefficients to crack growth evaluation was verified through comparisons of crack growth behaviors for deep surface crack under various stress fields.
Instrument Nozzles Fatigue Strength Reduction Factor
Authors: Woods Kirby , Thomas Kenneth
Published: January 2014

Recent industry experience has raised concerns with the NRC regarding the fracture toughness of small partial penetration instrument nozzles. Historically, small-bore instruments have not been evaluated when Pressure-Temperature curves were developed. Typical instrument nozzles have an outside diameter of 3¼ inches or less and a wall thickness of 11/16 inches or less. They were considered to be exempt per ASME XI Appendix G-2223(c), “Fracture toughness analysis to demonstrate protection against non-ductile failure is not required for portions of nozzles and appurtenances having a thickness of 2.5 in. (63 mm) or less, provided the lowest service temperature is not lower than RTNDT plus 60°F (33°C).” Now it appears that the effect of the nozzle discontinuity on the stresses in the beltline region of the shell must be assessed. This paper will show that historical interpretation of the code is correct and a fatigue analysis of the vessel shell adjacent to these instrument nozzles is unnecessary.

The industry experience with instrument nozzle leakages is typically related to the quality of manufacturing as suggested by J.H. Gross. Fabrication and inspection range quality relative to FSRF is ke = 10 for poor and ke < 5 for good quality. This approach appears to correlate well with this consideration and industry experience. This paper will also demonstrate the use of fabrication travelers and/or inspection information that can be used to determine an appropriate FSRF to assess the relative health of these and other components.
Effectiveness of Weld Buttering Repair of Externally Loaded Pressure Vessels With Corrosion Damage
Authors: Swanek Doug S. , MacKay John R. , Farrell Shannon P. , Link Rick , Timms Chris M. J.
Published: January 2014

General corrosion damage can significantly reduce the collapse resistance of externally loaded pressure vessels. This is a consequence of the loss of wall thickness and the associated development of high bending and membrane stresses in the corroded area. A common method used to recover wall thickness is weld buttering, whereby weld material is applied to the affected area. This method is convenient and cost-effective compared to other repair options; however, the extent to which weld-induced distortions and residual stresses counteract the reclamation of wall thickness has not been studied. In the current work, the influence of weld buttering on collapse resistance was explored through collapse tests. Three ring-stiffened cylinders were fabricated by cold rolling and welding high-strength steel plates. Corrosion damage was simulated in two of the cylinders by removing approximately 20% of the wall thickness in a square patch extending between two ring-stiffeners. The simulated damage on one cylinder was repaired using weld buttering. A third baseline cylinder had no simulated corrosion damage. With respect to the baseline cylinder, the simulated corrosion damage reduced the collapse capacity by 5.9%; weld buttering recovered 4.8% of that capacity. It is concluded that weld buttering can be an effective corrosion repair technique, despite the introduction of weld distortions and residual stresses in the vessel.
Flammability Analysis for Actinide Oxides Packaged in 9975 Shipping Containers
Authors: Laurinat James E. , Askew Neal M. , Hensel Steve J.
Published: January 2014

Packaging options are evaluated for compliance with safety requirements for shipment of mixed actinide oxides packaged in a 9975 Primary Containment Vessel (PCV). Radiolytic gas generation rates, PCV internal gas pressures, and shipping windows (times to reach unacceptable gas compositions or pressures after closure of the PCV) are calculated for shipment of a 9975 PCV containing a plastic bottle filled with plutonium and uranium oxides with a selected isotopic composition. G-values for radiolytic hydrogen generation from adsorbed moisture are estimated from the results of gas generation tests for plutonium oxide and uranium oxide doped with curium-244. The radiolytic generation of hydrogen from the plastic bottle is calculated using a geometric model for alpha particle deposition in the bottle wall. The temperature of the PCV during shipment is estimated from the results of finite element heat transfer analyses.
Benchmarking of Improved DPAC Transient Deflagration Analysis Code
Authors: Laurinat James E. , Hensel Steve J.
Published: January 2014

The transient deflagration code DPAC (Deflagration Pressure Analysis Code) has been upgraded for use in modeling hydrogen deflagration transients. The upgraded code is benchmarked using data from vented hydrogen deflagration tests conducted at the HYDRO-SC Test Facility at the University of Pisa. DPAC originally was written to calculate peak deflagration pressures for deflagrations in radioactive waste storage tanks and process facilities at the Savannah River Site. Upgrades include the addition of a laminar flame speed correlation for hydrogen deflagrations and a mechanistic model for turbulent flame propagation, incorporation of inertial effects during venting, and inclusion of the effect of water vapor condensation on vessel walls. In addition, DPAC has been coupled with CEA, a NASA combustion chemistry code. The deflagration tests are modeled as end-to-end deflagrations. The improved DPAC code successfully predicts both the peak pressures during the deflagration tests and the times at which the pressure peaks.
Effect of Cycle Frequency on Fatigue Crack Propagation Behavior for Steels in Hydrogen Storage
Authors: Wada Yoru
Published: January 2014

This paper addresses the characteristics of the fatigue crack propagation behavior of high-strength low-alloy steels in a high-pressure hydrogen gas environment, especially in terms of the role of cycle frequency. Several heats of the steels, with different steel strengths and microstructures, were tested in high-pressure gaseous hydrogen utilizing fracture mechanics specimens. When the cycle frequency decreases, they showed higher crack propagation rates (da/dN) at or above a certain K (= KmaxT) on a Kmax-da/dN diagram, while no cycle frequency dependencies were observed on da/dN below KmaxT. This KmaxT and observed da/dN were different among the various steels, and resulted from the difference in hydrogen gas embrittlement susceptibility caused by metallurgical variables (e.g. hardness, microstructure, impurity segregations). It is shown that the values of KmaxT observed in the steels were almost equivalent to KIH-R (the threshold stress intensity factor for hydrogen-assisted crack growth) of the steels tested which were obtained with slow rising load tests (K̇ = <0.08MPa-m1/2/s) in high-pressure gaseous hydrogen. Therefore, the increase in da/dN above KmaxT is attributed to the occurrence of hydrogen-assisted crack growth (da/dt), which is well explained by the KIH-R parameter.
Effect of Multi-Axial Stress on Creep Damage Behavior for Notched Specimen of P92 Steel
Authors: Shigeyama Haruhisa , Sugiura Ryuji , Yokobori A. Toshimitsu , Matsuzaki Takashi
Published: January 2014

In this study, interrupted creep crack growth tests were conducted using C(T) specimen with side-grooves and circular notched round bar specimen of P92 steel. After the interrupted tests, to investigate the creep crack growth and damage progression behaviors of P92 steel under the multi-axial stress field, cross-sectional observations around the notch and crack tip were conducted. From the measurement results of the change of micro Vickers hardness and void area fraction with creep time, it was indicated that the region of low hardness and high void area fraction were existed near the notch or crack tip. Then, three-dimensional elastic-plastic creep analyses were conducted for each specimen. From the results of finite element analyses, the regions of high hydrostatic stress and high tri-axiality factor were in good agreement with the region of high void area fraction for each specimen. This result indicated that the multi-axial stress field contributes to the void formation. Furthermore, the effects of the absolute value and gradient of tri-axiality factor on void formation were discussed.
Risk Evaluation Method of Acoustically Induced Vibration (AIV) Based on Random Vibration Theory
Authors: Nishiguchi Masato , Izuchi Hisao , Minorikawa Gaku
Published: January 2014

The widely recognized design criteria for Acoustically Induced Vibration (AIV) is basically based on the past failure examples reported by Carucci and Muller. However, the validity of these AIV criteria has not been fully investigated theoretically. The authors had developed the evaluation method for the Flow Induced Vibration (FIV) caused by turbulence in the pipe downstream of the combining tee. In this study, this FIV evaluation method developed by the authors was applied to evaluate AIV risk since both AIV and FIV cause random vibrations of the piping shell mode and the difference between AIV and FIV is just the source of the excitation force. The results of this AIV evaluation method indicates that the AIV risk increases as the pipe diameter decreases and this tendency agrees with the experiment result and conventional acoustic calculation. This AIV evaluation method can introduce the allowable power level limit which has no contradiction with the past failure examples reported by Carucci and Mueller. From the considerations mentioned above, the proposed method would be useful as one of the risk screening of AIV.
Nondestructive Monitoring of Variations of Residual Stresses in Steel Weldments by Magnetic Barkhausen Noise Method
Authors: Gür C. Hakan , Erian Gökhan , Batıgün Caner , Çam İbrahim
Published: January 2014

Variations of surface residual stresses as a function of weld runs in API 5L X70 steel plates were non-destructively monitored by Magnetic Barkhausen Noise (MBN) method. After each weld run, MBN signal and hardness distributions were recorded. MBN signals were converted into stress values by using a specific calibration procedure. The results were analyzed by considering microstructure investigations and hardness measurements, and then, they were compared with the results of X-ray diffraction measurements. MBN method seems to be a good candidate for monitoring the variation of surface residual stresses. It may also provide critical data for computer simulation and process design of welding processes.
Fatigue Performance of Stabilized Austenitic Stainless Steels: Experimental Investigations Respecting Operational Relevant Conditions Like Temperature and Hold Time Effects
Authors: Solin Jussi , Reese Sven , Karabaki H. Ertugrul , Mayinger Wolfgang
Published: January 2014

Experimental research on fatigue performance of niobium stabilized stainless steel (1.4550, X6CrNiNb1810mod) relevant for German NPP primary piping demonstrated good long life performance.

Fatigue tests periodically interrupted for holds indicated time and temperature dependent hardening during holds at 25°C to 325°C. Notable extension of fatigue life was measured when loading patterns consist of cyclic deformation in lower temperatures than hold annealing. Many NPP piping thermal transients separated by normal operation belong to this category and fatigue assessment based on standard fatigue data seems to underestimate fatigue endurance.

Further results for stabilized stainless steel in air at various temperatures will be provided. A parallel paper will deliver unpublished data in PWR water. The influences of temperature and loading pattern will be discussed aiming to improve fatigue assessment of plant components and to reduce confusion concerning applicability of international design codes.
Modeling of a Mainframe Server Frame Subjected to Seismic Loadings
Authors: Notohardjono Budy , Canfield Shawn , Ecker Richard
Published: January 2014

This paper describes the finite element modeling of a mainframe server frame. The frame consists of a server rack or frame with its add-on stiffening brackets. The frame is anchored directly to the floor with bolts at each of the four corners. The Telcordia Zone 4 earthquake test profile represents a severe dynamic load input and will be used herein to analyze the mainframe server frame. The main objective of this modeling is to validate the frame design prior to actual seismic testing, which ultimately ensures the structural integrity of a functional mainframe system during a seismic event. The server frame finite element (FE) model is derived from a three dimensional CAD model of a standard sheet metal frame weldment assembly which is then simplified and meshed with finite elements. This FE model represents the server frame, welded connections, and stiffening brackets, which are specifically designed to withstand seismic test profiles. To represent the components that populate the server frame, point masses are tied to the frame at the same attachment points that exist in the real assembly. The validation of the FE model involves the use of a horizontal shaker test to assess the server frame’s stiffness. The goal of this paper is to show a good correlation between FE model and test results using two separate FE solver technologies: implicit and explicit. For an implicit solver, linear material properties were used to obtain modal behavior that approximates the actual server frame’s behavior. Once these outputs were achieved, further response refinement was attempted by porting the model to an explicit dynamic solver. An explicit solver allowed non-linear material properties and body to body contact behavior to be included in the FE model while applying the seismic test profile to the server frame using a time domain input. The explicit dynamic model outputs used to correlate to actual test results were the modal dynamics, the displacement of the top of the server frame, and the maximum reaction force at the anchored corners. Finally, a functional system was subjected to the Telcordia Zone 4 seismic test profile. The system was functional during and after the seismic test with no significant structural damage having occurred.
Creep Crack Growth Prediction of Very Long Term P91 Steel Using Extrapolated Short-Term Uniaxial Creep Data
Authors: Maleki S. , Mehmanparast A. , Nikbin K. M.
Published: January 2014

Practical time frames in newly developed steels, and technical and financial restrictions in test durations means that extrapolation of short-term laboratory test results to predict long-term high temperature service component failure is an area of concern when conducting a fitness for service or remaining life assessment. Recent literature presenting uniaxial creep and crack growth tests indicate that some materials show lower failure strains during longer term laboratory tests. The constraint based remaining failure ductility based NSW model crack prediction model has been shown to be capable of predicting upper/lower bounds of creep crack growth in a range of steels when data are obtained from relatively short to medium-term laboratory experiments (< 10,000 hours). This paper compares and analyses the response of the NSW model to predict long term creep crack propagation rates using a wide database of modified 9Cr material over s range of temperatures. The paper employs extrapolation methods of available uniaxial data to make viable conservative predictions of crack growth at high temperatures where at present no data is available.
Prediction of SENB Fracture Toughness From Charpy Data Using the Beremin Model in the Lower Transition Region
Authors: Smith Robin J. , Sherry Andrew H. , Bannister Adam C. , Horn Anthony J.
Published: January 2014

This work focuses on the application of a mechanistic local approach model to describe the statistical distribution of experimental Charpy (CVN) impact test data obtained at several temperatures in the ductile to brittle transition temperature range. The current objective is to develop a correlation in the lower transition regime between quasi-static CVN absorbed energy (CVE) and the J-integral fracture toughness (Jc) obtained from deeply pre-cracked Charpy (PCCVN) specimens tested quasi-statically to laboratory test standards. The Beremin model for cleavage fracture has been applied to a ferritic steel which has been comprehensively tested using standard CVN, shallow U-notched and PCCVN specimen types in the lower ductile to brittle transition. This has enabled a prediction to be made of the absorbed CVE at cleavage fracture initiation for a Charpy specimen tested quasi-statically in the lower part of the CVN transition curve. By applying the Beremin model to PCCVN single edge notch bend specimens at quasi-static rates it was possible to use the Weibull stress, to achieve a reliable correlation between CVE and Jc in the lower ductile to brittle transition region. The results from this work indicate that the Beremin model can provide a theoretically based correlation for CVE to Jc fracture toughness for a ferritic steel under quasi-static loading conditions. The overall objective of the project remains to predict dynamic CVN absorbed energy using micromechanical modelling and which is valid for all ferritic steels.
Asset Integrity Management of High Pressure Piping Systems Subject to Creep
Authors: Cohn Marvin J.
Published: January 2014

Safety and reliability are the preeminent concerns in the design, operation, and maintenance of power piping. Recent additions to the ASME B31.1 Power Piping Code (Code) have addressed condition assessment of covered piping systems (CPS). Mandatory requirements for the condition assessment of CPS are discussed in Chapter VII of the Code and nonmandatory guidelines are discussed in Appendix V of the Code. These documents discuss design, fabrication, construction, operation, and maintenance issues, and do not provide detailed guidance in the evaluation of high pressure piping systems subject to creep.

An asset integrity management (AIM) program should integrate and consider all attributes that influence the intended function of the original design. In addition to the evaluation of specified design, fabrication, construction, operation, and maintenance issues, an asset integrity management program should also consider and evaluate significant time-dependent anomalies, such as flexible operation modes, malfunctioning supports, and creep redistributed stresses. An AIM program includes the identification of governing drivers that accelerate piping system damage and then develops countermeasures to mitigate or reduce the driving mechanisms.

This paper discusses the large range of piping system stresses and the sensitivity of stress increase to 50% creep life reduction, indicating the need for a robust stress ranking methodology. The process results in an accurate selection of the most critical creep damage weldments for nondestructive examinations.
Stability Analysis of Rectangular Plates in Incompressible Flow With Fourier Multiplier Operators
Authors: Hara Kensuke , Watanabe Masahiro
Published: January 2014

This paper describes a development of a method which improves the computational efficiency for a linear stability analysis of a plate in an uniform incompressible and irrotational flow. We introduce the Fourier multiplier operator to formulate the fluid and plate interaction problem with the mixed boundary condition. In previous typical approaches, a singular integral equation often appears in the formulation of a pressure distribution on the plate. The computation time for solving the integral equation is one of the problem encountered in the stability analysis. Applying the Fourier multiplier operator to this system, the equation of the plate-fluid interaction problem can be formulated with a pair of the Fourier and the inverse Fourier transforms. Moreover, the integration to derive the equations of motion can be efficiently carried out by using the discrete Fourier transform.
Numerical Computation of Modal Characteristics of a Clamped-Clamped Cylinder in Turbulent Axial Pipe Flow
Authors: De Ridder Jeroen , Degroote Joris , Vierendeels Jan , Van Tichelen Katrien , Schuurmans Paul
Published: January 2014

In this paper the modal characteristics of a flexible cylinder in turbulent axial flow are investigated with partitioned fluid-structure interaction simulations. In these simulations a computational fluid dynamics calculation to resolve the flow field is coupled with a computational structure mechanics calculation to compute the structural behavior. The cylinder is initially deformed according to an eigenmode in vacuo and then released. From this free vibration decay of the cylinder in the turbulent axial flow, modal characteristics are determined. To assess the accuracy of these calculations, the same configuration is computed as in an experiment with a solid brass cylinder mounted in a water-conveying pipe. The natural frequency appears to be relatively insensitive to an increase in flow velocity in this case. Both experiments and computations show the same trend of slightly decreasing natural frequency with increasing flow velocity. The damping, on the other hand, is very sensitive to the flow velocity. A change in flow velocity from 10m/s to 30 m/s results in a modal damping increase from 1.4% to 3.0%. Changes in molecular viscosity due to temperature differences had only a small effect on modal damping.
Stresses in Nozzle Shell Junctions due to External Loads: A Comparative Study
Authors: Chandiramani Dipak K. , Nawandar Suresh K. , Gopalakrishnan Shyam
Published: January 2014

Various methods have been in use for the determination of stresses at the nozzle-shell junction due to external loads and moments. Some methods evaluate stress in the cylindrical or spherical shell (e.g. WRC 107 now WRC 537) while others evaluate stresses in cylindrical shells and nozzles (e.g. WRC 297). ASME Section VIII Division. 2 specifies use of WRC 107/WRC 297 or Finite Element Analysis (FEA) for determination of stresses at shell-nozzle junctions with external loads and moments on the nozzle.

Each method could yield a different result for the same loading condition and geometry and this has been recognized in comparisons made in WRC 297 with WRC 107 and FEA. Further, customized FEA software are also available for this analysis.

There still seems to be some confusion in users of these methods regarding selection of method for optimization of design. Users not familiar with Finite Element Method prefer to use calculations based on WRC 107/297.

Hang-Sung Lee, et.al. have recently (PVP 2011 – 57407) analyzed nozzle shell junctions using the Finite Element Method, compared their results with calculations to WRC 297 and made recommendations.

The work presented in this paper is not an attempt to compare individual stresses obtained by classical versus analytical methods. Instead, an attempt has been made to consolidate the results obtained by the various methods into charts to enable a user to make a preliminary assessment to ascertain under what geometrical conditions the calculations made by each of the above methods would result in overall Code acceptable stresses without the results being either overly conservative or un-conservative. This is particularly relevant to the geometries which use the graphs and charts which have been extrapolated without rigorous theoretical background in the WRC Bulletin 537. The Finite Element Method has been used as the referee method.
Hydrogen-Assisted Fracture of Type 316L Tubing and Orbital Welds
Authors: San Marchi C. , Hughes L. A. , Somerday B. P. , Tang X.
Published: January 2014

Austenitic stainless steels have been extensively tested in hydrogen environments. These studies have identified the relative effects of numerous materials and environmental variables on hydrogen-assisted fracture. While there is concern that welds are more sensitive to environmental effects than the non-welded base material, in general, there have been relatively few studies of the effects of gaseous hydrogen on the fracture and fatigue resistance of welded microstructures. The majority of published studies have considered welds with geometries significantly different from the welds produced in assembling pressure manifolds. In this study, conventional, uniaxial tensile testing was used to characterize tubing of type 316L austenitic stainless steel with an outside diameter of 6.35 mm. Additionally, orbital tube welds were produced and tested to compare to the non-welded tubing. The effects of internal hydrogen were studied after saturating the tubes and orbital welds with hydrogen by exposure to high-pressure gaseous hydrogen at elevated temperature. The effects of hydrogen on the ductility of the tubing and the orbital tube welds were found to be similar to the effects observed in previous studies of type 316L austenitic stainless steels.