bluuebunny/crossref_metadata_2025 huggingface dataset:
Fracture Properties in Dissimilar Metal Weld Junctions: Experimental Methodology of Characterization
Authors: Bourgeois M. , Perez G. , Chapuliot S.
Published: November 2015

Within the framework of European project MULTIMETAL (Structural performance of multi-metal component), several fracture tests on different types of multi-material specimens have been performed. Present fracture toughness standard methods, e.g. ASTM E 1820 are not directly intended for Dissimilar Metal Welds (DMWs). Therefore further investigations are needed in order to define the best practice in fracture mechanical tests and their analysis for DMWs.

Specimens were taken from welded plates: a narrow gap Inconel DMW junction between ferritic and austenitic stainless steels, designed and delivered by AREVA France. The work is focused on the nickel alloy - ferritic steel interface which is the weakest area of such welded pipes regarding ductile tearing. This paper is focusing on the experimental methodology in this particular case of multi-material fracture test specimens.

The first difficulty consists in machining specimens with a location of crack plane at the interface or close to the interface. Physically, the interface between the nickel alloy weld and the ferritic steel is not a straight plane. Some normalized specimen - geometries like CT (Compact Tension specimen), SE(B) (Single Edge Bend specimen), or SE(T) (Single Edge Traction specimen) - have been machined in the DMW junction. Some recommendations are discussed about this first step of work.

The second difficulty is the procedure of fracture test itself. The present fracture toughness standard method uses the method of compliance for the determination of J-Δa curves. The plasticity, in ferritic and stainless steel parts of specimens, has induced unsymmetrical response. Locally the path of the crack has been influenced by the gradient of properties of the multi-material medium (weld, heat affected zone). The J values, determined at crack initiation, are dependent of the location of crack plane. Results between specimens are compared and discussed.

Based on the current standard, this article highlights some shortcomings of this standard when used in heterogeneous specimens. The well-known problem of transferability is also pointed out (different values of J for crack initiation depending of the geometry and size of specimen).

In conclusion further numerical works are needed to assess experimental results and provide intrinsic material data, in terms of fracture properties of the Nickel alloy-ferritic steel interface.
Use of Elastic Follow-Up to Study the Effect of Displacement Controlled Loading on Plastic Collapse Pressures for Circumferentially Cracked Pipes
Authors: Wu Guiyi , Smith David J. , Pavier Martyn J.
Published: November 2015

Structural integrity assessments of pressurised pipes consider plastic collapse as a potential failure mode. This paper uses finite element analysis to explore the effect of the pipe end boundary conditions on the collapse pressure. Two end conditions are considered: a fixed axial load and a fixed axial displacement. The fixed axial displacement condition represents a long-range axial residual stress. In the R6 structural integrity assessment procedure long-range residual stress is associated with elastic follow-up. However, no guidance is given on whether the level of elastic follow-up is sufficient to justify treating long-range residual stress as a primary stress.

In this paper, a method is proposed to estimate elastic follow-up of an internally pressurised pipe containing a fully circumferential crack. It is found that the elastic follow-up is related to the length of the pipe. A short pipe that contains a fully circumferential crack, subjected to a displacement induced axial stress, has a global collapse that is not modified by the fixed displacement condition. The short pipe corresponds to a small elastic follow-up factor, Z. However, as the elastic follow-up factor increases, the presence of long-range residual stress starts to make a contribution to global collapse. When elastic follow-up is significant, a long-range residual stress has the same effect on global collapse as does a mechanical stress.
Further Studies on Predicting Leak Rates Using an Emissions Calculator for Bolted Flanged Connectors
Authors: Rice Dale A. , Waterland A. Fitzgerald (Jerry)
Published: November 2015

Work on the development of a practical tool, the “Fugitive Emissions Calculator” (FEC) has been previously reported. This tool, based in Microsoft® Excel® has been used to help predict anticipated fugitive emissions of various gasket materials with the proposed ASME / PVRC method for estimating leak rates using standard Room Temperature Testing (ROTT) data, the operating pressure, the pipe diameter, gasket stress, and other inputs. To further test the performance of the FEC, a sensitivity analysis has been conducted, focusing on several parameters, including system pressure, assembly efficiency, and gasket stress and their relative degree of significance on the predicted gasket tightness and leak rate. In addition, work has been conducted for developing a method for estimating the stress retention coefficient previously reported as a proposed modification to the PVRC leak rate method. The findings and conclusions of these studies are presented.
Effect of Creep Load on Oxidation Behavior of Main Steam Pipes
Authors: Yang Bo , Huang Yi-chang , Tang Xiao-ying , Huang Yu-hui
Published: November 2015

Main steam pipelines work in the environment of high temperature and pressure steam and withstand double damage between oxidation and creep load for a long time. Creep-oxidation interrupt tests were used in high temperature steam conditions at different stress load to get P92 steel mechanochemical behavior date in the present study. Weight gain method was used to get the oxidation kinetics under different applied loading. Scanning electron microscopy (SEM) micro observation techniques was applied to obtain growth characteristic in the interaction between steam oxidation and creep loading.
Stresses on Aluminum Brazed Plate Fin Heat Exchangers in a Floating Environment
Authors: Hölzl Reinhold , Lehmacher Axel
Published: November 2015

The present paper describes a study for the application of Aluminum Brazed Plate Fin Heat Exchangers (PFHE) in a floating environment. Due to the continuous movements of the ship hull a main focus is given to fatigue considerations because it is well known that aluminum does not have a distinct endurance limit. Therefore it is mandatory to base a fatigue evaluation on a design code as for example the German AD2000 Merkblatt S2 [16] which allows fatigue evaluation of aluminum. There an endurance limit of 5 million cycles is defined. On that basis two plate fin heat exchangers were analyzed focusing on accelerations due to ship motion and thermal fatigue as a secondary consequence of ship movements (liquid sloshing, unsteady flows).

For the acceleration due to ship motions a value out of a concept study was taken. This value of 2.5 m/s2 was used for acceleration in three directions for both exchangers. All calculated stresses were below the endurance limit and therefore no measures have to be taken.

Thermal fatigue as secondary effect of the ship movements was analyzed as a worst case investigation for a block in shell exchanger. The resulting fatigue loads seem not to be a concern in this specific case but it is strongly recommended to carefully check any design for similar or different applications. Furthermore it is recommended generally to carefully ensure stable process conditions.

Summing up all these points the application of PFHE in a floating environment has to be investigated very carefully but seems to be possible.
Machining Test Specimens From Harvested Zion RPV Segments
Authors: Rosseel Thomas M. , Sokolov Mikhail A. , Nanstad Randy K.
Published: November 2015

The decommissioning of the Zion Nuclear Generating Station (NGS) in Zion, Illinois, presents a special and timely opportunity for developing a better understanding of materials degradation and other issues associated with extending the lifetime of existing nuclear power plants (NPPs) beyond 60 years of service. In support of extended service and current operations of the US nuclear reactor fleet, the Oak Ridge National Laboratory (ORNL), through the Department of Energy (DOE), Light Water Reactor Sustainability (LWRS) Program, is coordinating and contracting with Zion Solutions, LLC, a subsidiary of Energy Solutions, an international nuclear services company, the selective procurement of materials, structures, components, and other items of interest from the decommissioned reactors. In this paper, we will discuss the acquisition of segments of the Zion Unit 2 Reactor Pressure Vessel (RPV), cutting these segments into blocks from the beltline and upper vertical welds and plate material and machining those blocks into mechanical (Charpy, compact tension, and tensile) test specimens and coupons for microstructural (TEM, SEM, APT, SANS and nano indention) characterization. Access to service-irradiated RPV welds and plate sections will allow through wall attenuation studies to be performed, which will be used to assess current radiation damage models [1].
Fatigue Monitoring in the Context of Long-Term Operation of the Goesgen Nuclear Power Plant Using AREVA’s FAMOSi
Authors: Wermelinger Thomas , Bruckmüller Florian , Heinz Benedikt
Published: November 2015

In the context of long-term operation or lifetime extension most regulatory bodies demand from utilities and operators of nuclear power plants to monitor and evaluate the fatigue of system, structures and components systematically. As does the Swiss Federal Nuclear Safety Inspectorate ENSI. The nuclear power plant Goesgen started its commercial operation in 1979 and will go into long-term operation in 2019. The increased demand for monitoring and evaluating fatigue due to the pending long-term operation led the Goesgen nuclear power plant to expand the scope of their surveillance and therefore to install AREVA’s fatigue monitoring system FAMOSi in the 2014 outage. The system consists of 39 measurement sections positioned at the primary circuit and the feed-water nozzles of the steam generators. The locations were chosen due to their sensitivity for fatigue. The installed FAMOSi system consists of a total of 173 thermocouples which were mounted in order to get the necessary input data for load evaluation. The advantage of FAMOSi is the possibility to obtain real data of transients near places with highest fatigue usage factors. Examples of steam generator feed-in during heating-up and cooling-down will be given. In addition, spray events before and after the installation of closed loop controlled spray valves will be compared.

The measurements and the results of the load evaluation are not only of interest for internal use e.g. in regard to optimization of operation modes (e.g. load-following), but must also be reported to ENSI annually. In addition, by evaluation of stresses and determination of usage factors combined with an optimization of operation modes an early exchange of components can be avoided.
Calculation of KJ Under Secondary Loads in Isolation for R6
Authors: James Peter
Published: November 2015

A range of methods are currently available within R6 to calculate the inelastic secondary stress intensity factor under secondary loads in isolation, KJS. Each of these methods has different levels of associated conservatism depending on assumptions made, the complexity of the approach and the ability to account for different levels of elastic follow-up. Approaches that include an elastic follow-up factor, Z, for treating the interaction of combined primary and secondary stresses have recently been investigated by Ainsworth and James. However, the maturity of this recent work under combined primary and secondary loading means that one of the most significant aspect of the conservatisms in calculating the combined elastic-plastic stress intensity factor, KJ, is now in the calculation of KJS. This work considers existing approaches in R6 to calculate KJS and proposes a further approach allowing the value of Z to be altered.

For comparison this work considers finite element analyses of a circumferentially cracked cylinder with four thermal distributions and two shallow cracks. These conditions were controlled to manipulate the level of Z. The magnitude of the temperature difference in these profiles has been increased over the analysis time to provide a relationship between the elastic and inelastic secondary stress intensity factors, KIS and KJS, with increasing secondary load to demonstrate any enhancement and subsequent redistribution of the secondary stress. These finite element estimates have been compared to existing methods in R6 to calculate KJS/KIS which reinforce the available advice in R6 for each case. The proposed approach also compares favourably with the finite element results through modification of Z. The proposed approach is also seen to be compatible with the other approaches within R6 as it has been shown to reproduce the Option 2 failure assessment curve for cases where the elastic follow-up is significant (i.e. Z ≫ 5) and conforms to the displacement controlled estimate of KJS in Section III.14.5 of R6.
An Experimental Study of Fluid-Structure Interaction in Basic In-Line Arrangements of Cylinders
Authors: Cardolaccia Jerome , Baj Franck
Published: November 2015

Heat exchangers are very common equipment used in numerous industrial facilities all around the world. Throughout the years, engineers have learned how to build them, how to make them more robust and efficient and how to develop and adapt them for a wide variety of applications. Yet the fact remains that the dynamic motion of a flexible cylinder submitted to a cross flow inside a tube bundle responds to physical principles that are still to be fully understood [1]. More specifically, the prediction of whether or not a tube will exhibit damping-controlled instability (flutter) cannot be achieved better than with an acceptable margin of safety, let alone dealing with unknown geometries or conditions of operation. We offer here to go back to the start and to observe this instability experimentally in even simpler geometries under low-turbulent monophasic flow. For this work, we had a small hydraulic loop at our disposal. It lets water flow at Reynolds numbers from 3000 to 10000 through a working section comprising one to three tubes (or a full 4×5 array), among which only one is flexible. A lot of different patterns have been tested, notably cylinders side-to-side along the flow or transverse to it and cylinders in tandem, vibrating either in the lift or in the drag direction. This experimental setup allowed us to plot the tube frequency, its apparent damping and its amplitude according to the reduced velocity. In the end, we aim to provide the community with some supplementary experimental data and hopefully shed some light on the behavior of these oscillating tubes.
ASME Pressure Vessel Internals and Their Design Code
Authors: Millet Barry , Miller George , Whipple Richard , Kirkpatrick Kenneth , Mosher Bryan
Published: November 2015

It is common for designers to use the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME) when designing vessel internals (i.e. process trays, bed supports, bolted connections, etc). Typically the ASME allowables are directly applied to internals without any regard to the member geometry or failure modes. The ASME code was developed for modes of failures experienced in the pressure boundary and was not intended to be utilized for the design of structural components. ANSI/AISC 360-10 “Specification for Structural Steel Buildings” (AISC) addresses the failure mechanisms experienced in structures based on their geometry and boundary conditions. This paper will provide several examples along with a direct comparison between structural members designed to the AISC and ASME codes. This paper will also provide guidance for using the AISC methodology with material properties at design temperature from ASME Section II Part D for robust design of internal structures.
Revisiting Gasket Selection: A Flowchart Approach — Updates for the 25th Anniversary
Authors: Bausman Anita R. , Waterland A. Fitzgerald (Jerry)
Published: November 2015

25 years ago, Ron Winter presented the seminal paper “Gasket Selection: A Flowchart Approach” to the ASME Pressure Vessel Piping (PVP) community at the June 1990 PVP conference in Nashville, Tennessee [1]. Much has changed since then. New gasket materials have been introduced, and existing materials have been combined in new forms. High temperature vermiculite-based gaskets have come on the market. Further testing has demonstrated failure mechanisms specific to certain gasket materials; new assembly methods have been explored to reduce the effects of bolt elastic interaction and “cross talk”. Grooved profile gaskets, also known as “kammprofiles”, are now listed in ASME B16.20 [2] and widely (and economically) available in the United States. Spiral wound gaskets are obtainable world-wide. A new generation of engineers is responsible for sealing performance in today’s industrial and power plants. Environmental and emissions regulations have evolved. European codes now mandate design methods using gasket leakage while the US and other countries consider it. Much has stayed the same since 1990. New engineers need to learn what is required to seal a bolted flanged joint reliably — this is not typically explored in universities. Many of the steps to select and implement a good gasket seal are the same in 2015 as they were in 1990. This paper reviews and expands the gasket selection process to enable today’s engineers to make informed choices for reliable bolted flanged joints with gasket sealing elements.
Proposed Code Case of Creep Fatigue Evaluation of 9Cr-1Mo-V Steels for High Pressure Vessels in ASME Section VIII Division 2
Authors: Terada Susumu , Yamada Masato , Nakanishi Tomoaki
Published: November 2015

9Cr-1Mo-V steels (Gr. 91), which has an excellent performance at high temperature in mechanical properties and hydrogen resistance, has been used for tubing and piping materials in power industries and it can be a candidate material for high pressure vessels for high temperature processes in refining industries. The current Section VIII Division 2 of ASME code does not permit method A of paragraph 5.5.2.3 to be used for the exemption from fatigue analysis for Gr. 91 steels due to limitation of specified minimum tensile strength (585 MPa > 552 MPa). Method B of paragraph 5.5.2.4 also can’t be used because it requires the use of the fatigue curve which is limited to 371 °C lower than the needed temperature. Therefore new rules for fatigue evaluation of Gr. 91 steels at temperatures greater than 371 °C and less than 500 °C similar to CC 2605 for 2.25Cr-1Mo-0.25V(Gr. 22V) steels are necessary. This paper provides fatigue test results at 500 °C for Gr. 91 steels, the modification of CC 2605, sample inelastic analysis results for nozzles. Then, the new Code Case for Gr. 91 steels is proposed from these results.
Blast Load Inside Enclosure due to Flame Acceleration
Authors: Geng Jihui , Thomas J. Kelly
Published: November 2015

Enclosed chemical processes, laboratory facilities, boilers and reformer furnaces are typical examples of facilities and equipment where an internal VCE may be postulated to occur. The applied blast load history on the enclosure surfaces is required in order to assess the response of the enclosure to the postulated VCE. The internal blast pressure history and associated applied blast loads depend on a number of factors, such as: (1) the maximum flame speed attained in a flammable cloud, (2) the ratio of the cloud volume to the total enclosure volume, (3) the cloud location within the enclosure, and (4) the environment temperature. The purpose of work described in this paper was to investigate the dependence of internal blast pressure history and applied blast loads on the aforementioned factors. It was found that the applied loads on the enclosure surfaces can be roughly classified into two regimes: quasi-static and dynamic, depending on the combination of these factors. It can be important to identify the appropriate blast loading regime in order to properly analyze the structural response of the enclosure.
Identification of Failure Modes Under Design Extension Conditions
Authors: Kasahara Naoto , Nakamura Izumi , Machida Hideo , Nakamura Hitoshi , Okamoto Koji
Published: November 2015

As the important lessons learned from the Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure became essential against severe accident and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premise under design extension conditions such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, best estimation for these failure modes are required for preparing countermeasures and management. Therefore, this study focused on identification of failure modes under design extension conditions. To observe ultimate failure behaviors of structures under extreme loadings, new experimental techniques were adopted with simulation materials such as lead and lead-antimony alloy, which has very small yield stress.

Postulated failure modes of main components under design extension conditions were investigated according three categories of loading modes.

The first loading mode is high temperature and internal pressure. Under this mode, ductile fracture and local failure were investigated. At the structural discontinuities, local failure may become dominant.

The second is high temperature and external pressure loading mode. Buckling and fracture were investigated. Buckling occurs however hardly break without additional loads or constraints.

The last loading is excessive earthquake. Ratchet deformation, collapse, and fatigue were investigated. Among them, low-cycle fatigue is dominant.
A Method of Automatic Defect Recognition for Phased Array Ultrasonic Inspection of Polythene Electro-Fusion Joints
Authors: Hou Dongsheng , Guo Weican , Zheng Jinyang
Published: November 2015

Defect classification is the basis of defect safety assessment because defects of different types can lead to failure in different forms. However, the identification of defect type has long been a critical issue in ultrasonic inspection. Wave acoustic was applied in this study to investigate the sound scattering of metal wires in polyethylene (PE), which provided theoretical support for ultrasonic feature extraction. A method of defect recognition for PE electro-fusion (EF) joints was proposed based on pattern recognition of ultrasonic inspection images. According to location, shape, signal intensity, and cluster conditions, typical defects of EF joints of PE pipes were distinguished and identified in phased array ultrasonic images. Furthermore, an automatic defect recognition software was designed based on the proposed approach; the software was improved and verified through defect inspection and identification experiments. Results showed that accuracy can reach 80% for joints with complex defects and 100% for those with single defects.
Evaluation of Creep Deformation Property of Grade 91 Steels
Authors: Kimura Kazuhiro , Sawada Kota , Kushima Hideaki
Published: November 2015

Creep deformation property of Grade T91 steels over a range of temperatures from 550 to 625°C was analyzed by means of the empirical creep equation reported in the previous study [1]. The creep equation consists of four time dependent terms and one constant and time to rupture is estimated as a time to total strain of 10%. Accuracy of the creep equation to represent creep curve and to predict time to rupture and minimum creep rate was indicated. Times to minimum creep rate, total strain of 1%, initiation of tertiary creep and rupture were evaluated by the creep equation. Stress dependence of strains at minimum creep rate and the initiation of tertiary creep were analyzed. Contribution of four time dependent terms to the strains at minimum creep rate, total strain of 1% and initiation of tertiary creep was investigated. Three parameters to determine a temperature and time-dependent stress intensity limit, St, were compared and a dominant factor of St was examined. Heat-to-heat variation of the creep deformation property was investigated on two heats of T91 steels contain low and high nickel concentrations.
Effects of Dissolved Hydrogen on Crack Growth Rate of Warm-Rolled 316L Austenitic Stainless Steel in Primary Water Condition
Authors: Choi Kyoung Joon , Yoo Seung Chang , Kim Taeho , Hwang Seong Sik , Choi Min Jae , Kim Ji Hyun
Published: November 2015

With the extension of pressurized water reactor’s design life or continued operation, more careful study on the integrity of the internal structures needs to be pursued. In this study, warm-rolling and heat-treatment were applied to 316L stainless steel, in order to simulate the effect of radiation damage such as hardening and radiation-induced grain boundary segregation. And, the crack growth rate testing under constant load condition was performed in the primary water conditions of a pressurized water reactor. Also, in order to investigate the effect of dissolved hydrogen on the crack growth, the dissolved hydrogen concentration was varied between 30 to 50 cc/kg in simulated primary water condition of a pressurized water reactor. The warm-rolled specimens showed the higher crack growth rate than as-received one. Also, the crack growth rate increased as the dissolved hydrogen concentration increases.
A Probabilistic Approach to Fired Heater Tube Remaining Life Assessments
Authors: Leta James V. , Dirham Thomas R. , Dobis Jonathan , Guo Ruohua , Roberts Lionel
Published: November 2015

A case history of a Catalytic Reformer fired heater assessment is used to illustrate an alternative approach to quantify some of the uncertainties associated with fired heater tube remaining life estimates. Such uncertainties include temperature and pressure history, tube wall thickness, and existing creep damage. While it is well understood that fired heater tubes are susceptible to creep and corrosion damage, it can be challenging to quantify the margin of error associated with typical analyses. For example, in order to determine estimates of remaining life, it is not unusual for analysts to use overly conservative input parameters (e.g., minimum measured thicknesses, maximum temperatures and pressures). This often results in a “worst case scenario” or “pass/fail” answer, but it does not necessarily provide insight into the effect of uncertainty. In this paper, an alternative method is utilized to predict heater tube lifetimes. The uncertainty associated with the primary input parameters for the API-579 Part 10 Omega creep procedure is characterized statistically by treating them as random variables and random processes. The probability of tubes failing by a specified time is estimated by performing Monte Carlo simulations. This study is of a practical nature, illustrating how the methodology can be used to aid in decision making.
Effect of Bend Angle on Gross Plastic Deformation of Pipe Bends: A Finite Element Based Study
Authors: Bhattacharya Anindya , Bapat Sachin , Patel Hardik , Patel Shailan
Published: November 2015

Bends are an integral part of a piping system. Because of the ability to ovalize and warp they offer more flexibility when compared to straight pipes. Piping Code ASME B31.3 [1] provides flexibility factors and stress intensification factors for the pipe bends. Like any other piping component, one of the failure mechanisms of a pipe bend is gross plastic deformation. In this paper, plastic collapse load of pipe bends have been analyzed for various bend parameters (bend parameter = tRbrm2) under internal pressure and in-plane bending moment for various bend angles using both small and large deformation theories. FE code ABAQUS version 6.9EF-1 has been used for the analyses.
Fluid-Elastic Instabilities of Clamped-Clamped Aligned and Inclined Cylinders in Turbulent Axial Flow
Authors: De Ridder Jeroen , Degroote Joris , Doaré Olivier
Published: November 2015

Fluid-elastic instabilities arise due to the coupling of structural motion and fluid flow. In the specific case of a clamped-clamped cylinder in axial flow, it will buckle at a sufficiently high flow velocity and start to flutter at even higher flow velocities. This dynamic behavior is of importance to nuclear reactor core design, undersea pipe lines and devices for energy harvesting. In this contribution, the fluid forces and the dynamics of a flexible clamped-clamped cylinder in turbulent axial flow are computed numerically. In contrast to present analytical approaches, this numerical model does not require to tune parameters for each specific case or to obtain coefficients from experiments.

To provide insight in the way viscous fluid forces affect the dynamics of a cylinder in axial flow, fluid forces are computed on rigid inclined cylinders, mimicking the damping force experienced by the same cylinder moving perpendicular to the axial flow. The computations showed the existence of two different flow regimes. Each regime gave rise to a different lift force behavior, which will also influence the damping of the coupled system. Furthermore it is shown that the inlet turbulence has a non-negligible effect on these forces and thus on the dynamics of the cylinder.

Next, the dynamics of a flexible cylinder clamped at both ends in axial water flow are computed by means of a methodology developed earlier. The results are successfully compared with dynamics measured in experiments available in literature. Computationally it was found that the cylinders natural frequency decreases with increasing flow velocity, until it loses stability by buckling. The threshold for buckling is in quantitative agreement with experimental results and weakly nonlinear theory. Above this threshold, the amplitude of the steady deformation increases with increasing flow speed. Eventually, a fluttering motion is predicted, in agreement with experimental results. It is also shown that even a small misalignment (1°–2°) between the flow and the structure can have a significant impact on the coupled dynamics.
Procedure for Plastic Collapse Assessment of a Local Thin Area Near Vessel and Nozzle Intersections Subjected to Internal Pressure and External Loadings
Authors: Konosu Shinji , Ogasawara Kenta , Oyamada Kenji
Published: November 2015

This paper develops a procedure for plastic collapse assessment of vessel (run pipe) - nozzle (branch pipe) intersections with an arbitrarily positioned local thin area (LTA) under different loading conditions, namely internal pressure, external moment on a nozzle applied along various directions with respect to the vessel main axis, and pure bending moment on a vessel. Although simplified procedures for plastic collapse assessment based on the p-M (internal pressure ratio and external bending moment ratio) diagram method have been previously proposed for straight cylindrical vessels and pipe bends with an LTA, very few studies have dealt with the determination of plastic collapse load for an LTA in the critical region of intersecting vessels subjected to internal pressure and external moment loading. This is likely due to the complexity of the stresses caused by the applied loads in the critical region, which arises from geometric discontinuities. In this paper, simple and empirical formulae for predicting conservative plastic collapse loads for an LTA in the critical region of the intersecting vessels are proposed based on the analytical results of stresses at defect-free vessel-nozzle intersections by using linear finite element analysis (FEA). Localized elastic stress retardation factors are taken into account in the evaluation by the results of a non-linear FEA. Consequently, a p-M diagram method is developed for application to vessel-nozzle intersections with an LTA.
Semi-Closed-Form Displacement Equations for Calculating J-R Curves From Pipe Fracture Experiments
Authors: Olson Richard , Thornton Ben
Published: November 2015

The equations to generate a J-R curve from a four-point bend test on circumferentially cracked pipe have been known for many years. Given the experimental pipe load-displacement record and crack growth, the only impediment to routinely calculating pipe J-R curves is the requirement to know the non-cracked pipe elastic and plastic displacements. Traditionally, finite element analyses are used to find these displacements. This paper presents a semi-closed-form solution for the total (elastic plus plastic) non-cracked pipe displacements that eliminates the need to perform finite element analyses to calculate a pipe J-R curve.

Using a Ramberg-Osgood nonlinear representation of the stress-strain curve and the assumption that plane sections remain plane, beam bending equations can be written to find nonlinear beam displacements for pipe bend geometries with a base metal crack. Building on this result, the solution is extended to the dissimilar metal weld (DMW) case with five nonlinear materials.

The non-cracked pipe displacement solutions are presented as well as comparisons using these equations between compact tension specimen J-R toughness curves and J-R curves from pipe experiments.
High Temperature Fatigue of Welded Joints: Experimental Investigation and Local Analysis of Butt Welded Flat and Cruciform Specimens
Authors: Langschwager Kay , Rudolph Jürgen , Scholz Alfred , Oechsner Matthias
Published: November 2015

Austenitic stainless steel of type X6CrNiNb18-10 exhibits advantageous mechanical and chemical properties and is a common material for numerous applications in the nuclear power plant and chemical industries. Besides the mechanical strain induced by high pressure, the fatigue life in welded pipelines is affected by additional thermomechanical strains due to thermal loading. The welding process mainly determines the geometry and metallurgical constitution of the welded joint. Therefore, the butt welds additionally influence the strain gradient along the component and reduce its lifetime.

While the base and weld material are similar, they show different softening and hardening behavior, especially at ambient temperature. Cyclic hardening occurs in the base material, whereas cyclic softening can be observed in the weld material. The hardness distribution along the welded joint reveals no clear differentiation of base material, the heat affected zone and weld material. The attributes of the individual materials cannot be transferred to the welded joint automatically. Thus, the analysis of the interaction between the materials along the welded joint is a main topic of this research. To this end, digital image correlation is used for different kinds of specimens and load conditions. The position along the testing area at which fatigue failure occurs depends on the specimen type and the load condition but not on the temperature. Further, isothermal and anisothermal fatigue tests on welded cruciform specimens are presented. The common practice of the effective strain is discussed for the analyzed conditions.
Application of the Structural Reliability Methods for Justification of Pressure Reduction of Periodic Hydrostatic Test for Primary Circuit of NPP WWER-1000
Authors: Orynyak Igor , Kozlov Volodymyr , Borodii Mykhaylo , Zarazovskii Maksym
Published: November 2015

An analysis is formulated to determine how reductions in test pressures change the effectiveness of hydraulic strength tests (HT). The analysis is applied to Series 1000 Water-Water Energetic Reactor (WWER-1000) nuclear power plants (NPP) operating in countries of the former Soviet Union. During periodic HT for these reactors, the applied pressure exceeds the pressure for the normal operation mode (NOM) by a factor of more than 1.5. These HT pressures are among the highest in the nuclear industry. It is desirable to reduce the HT pressure in order to minimize potential damage to equipment due to pressurization during the tests.

To justify a reduction in the HT pressure, a quantitative, risk-informed assessment of HT effectiveness for changes in HT pressures has been performed. This assessment follows the guidelines of INSAG-25 [1]. A deterministic analysis is used to calculate the HT minimum temperature, based on the estimation of the damage caused by HT and the evaluation of the warm prestressing effect. A probabilistic analysis is used to estimate the change in the probability of equipment fracture caused by a reduction in the HT pressure. The probabilistic analysis assumes that HT is performed as a destructive control method for replaceable components, so that HT combined with replacement or repair of defective components increases their reliability.

A simple probabilistic analysis method, based on an exponent distribution law for defect depth and a lognormal law for the defect aspect ratio, taking into account laws for defect growth, has been proposed. The fracture probability is calculated as the proportion of defects that exceed critical sizes for NOM and HT. Limit load models are used for the determination of the critical size of defects. The variation in reliability is calculated as the difference between fracture probability during NOM after HT at routine and reduced pressures. The calculation results make it possible to analyze the effect of HT pressure reduction for WWER-1000 NPPs.
High Fidelity Simulation of Safety Relief Valve Internal Flows
Authors: Yang Yunchao , Lefebvre Alexis , Zha Ge-Cheng , Liu Qing-Feng , Fan Jun , Chen Dianjing , Wu Yuzhen
Published: November 2015

This paper presents a numerical methodology and simulation for three-dimensional transonic flow in Safety Relief Valves. Simulation of safety relief valve flows is very challenging due to complex flow paths, high pressure variation, supersonic flow with shock and expansion waves, boundary layers, etc. The 3D unsteady Reynolds averaged Navier-Stokes (URANS) equations with one-equation Spalart-Allmaras turbulence model is used. A fifth order WENO scheme for the inviscid flux and a second order central differencing for the viscous terms are employed to discretize the Navier-Stokes equations. The low diffusion E-CUSP scheme used as the approximate Riemann solver suggested by Zha et al. is utilized with the WENO scheme to evaluate the inviscid fluxes. Implicit time marching method with 2nd order temporal accuracy using Gauss-Seidel line relaxation is employed to achieve a fast convergence rate. Parallel computing is implemented to save wall clock simulation time. The valve flows with air under different inlet pressures and temperatures are successfully simulated for the full geometry with all the fine leakage channels. A 3D mesh topology is generated for the complex geometry. Detailed simulations of air flow are accomplished with inlet gauge pressure 0.5MPa and 2.1MPa. The simulated air mass flow rate agrees excellently with the experimental results with an error of 0.26% for the inlet pressure of 0.5Mpa, and an error of 2.5% for the inlet pressure of 2.1MPa. The shock waves and expansion waves downstream of the orifice are very well resolved.
Effect of Hydrogen on Tensile Strength and Ductility of Multi-Pass 304L / 308L Austenitic Stainless Steel Welds
Authors: Balch Dorian K. , San Marchi Chris
Published: November 2015

Austenitic stainless steels such as 304L are frequently used for hydrogen service applications due to their excellent resistance to hydrogen embrittlement. However, welds in austenitic stainless steels often contain microstructures that are more susceptible to the presence of hydrogen. This study examines the tensile strength and ductility of a multi-pass gas tungsten arc weld made on 304L cross-rolled plate using 308L weld filler wire. Sub-sized tensile specimens were used to ensure the entire gage section of each tensile specimen consisted of weld metal. Specimens were extracted in both axial and transverse orientations, and at three different depths within the weld (root, center, and top). Yield strength decreased and ductility increased moving from the root to the top of the weld. A subset of specimens was precharged with hydrogen at 138 MPa (20,000 psi) and 300°C prior to testing, resulting in a uniform hydrogen concentration of 7700 appm. The presence of hydrogen resulted in a slight increase in yield and tensile strength and a roughly 50% decrease in tensile elongation and reduction in area, compared to the hydrogen-free properties.
Experimentation and Adaptive Modeling for Temperature Effect Quantification in PVP Structural Health Monitoring With PWAS
Authors: Kamas Tuncay , Poddar Banibrata , Lin Bin , Yu Lingyu , Giurgiutiu Victor
Published: November 2015

The thermal effects at elevated temperatures mostly exist for pressure vessel and pipe (PVP) applications. The technologies for diagnosis and prognosis of PVP systems need to take the thermal effect into account and compensate it on sensing and monitoring of PVP structures. One of the extensively employed sensor technologies has been permanently installed piezoelectric wafer active sensor (PWAS) for in-situ continuous structural health monitoring (SHM). Using the transduction of ultrasonic elastic waves into voltage and vice versa, PWAS has been emerged as one of the major SHM sensing technologies. However, the dynamic characteristics of PWAS need to be explored prior its installation for in-situ SHM. Electro-mechanical impedance spectroscopy (EMIS) method has been utilized as a dynamic descriptor of PWAS and as a high frequency local modal sensing technique by applying standing waves to indicate the response of the PWAS resonator by determining the resonance and anti-resonance frequencies. Another SHM technology utilizing PWAS is guided wave propagation (GWP) as a far-field transient sensing technique by transducing the traveling guided ultrasonic waves (GUW) into substrate structure. The paper first presents EMIS method that qualifies and quantifies circular PWAS resonators under traction-free boundary condition and in an ambience with increasing temperature. The piezoelectric material degradation was investigated by introducing the temperature effects on the material parameters that are obtained from experimental observations as well as from related work in literature. GWP technique is also presented by inclusion of the thermal effects on the substrate material. The MATLAB GUI under the name of Wave Form Revealer (WFR) was adapted for prediction of the thermal effects on coupled guided waves and dynamic structural change in the substrate material at elevated temperature. The WFR software allows for the analysis of multimodal guided waves in the structure with affected material parameters in an ambience with elevated temperature.
Effect of High Temperature Corrosion on the Service Life of P91 Piping in Biomass Co-Firing
Authors: O’Hagan C. P. , Barrett R. A. , Leen S. B. , Monaghan R. F. D.
Published: November 2015

Co-firing biomass with fossil fuels is increasingly relevant to thermal power plant operators due to new, stricter sanctions relating to carbon footprints. It has been found that the use of biomass results in an altered ash composition, which leads to increased corrosion of the superheater tube walls. This paper presents results for corrosion depth, from initial testing on P91 samples exposed to synthetic salts representative of ash compositions obtained from operational plants. SEM images and EDX element maps are obtained and presented in order to gain an understanding of the complex corrosion mechanism which occurs. A finite element methodology is presented for combined corrosion with creep damage to assess the effect of corrosion tube wall loss on creep rupture life for pressurized tubes.
Building the Technical Case for Long-Term Operation
Authors: Tilley Richard , Dyle Robin
Published: November 2015

United States (US) and International utilities are actively engaged in assessing the economic and societal benefits of operating nuclear plants beyond their initial license periods. Nuclear plant generated electricity is still the largest contributor to non-carbon dioxide emitting generation. In the US, a majority of operating plants has already received approval for an additional 20 years of operation, and soon it is expected that utilities will begin the process to seek a second 20 year renewal. The keys to successful renewal are to maintain safe and reliable operations by building a sound technical case through the following activities:

• Develop comprehensive understanding of aging degradation issues for systems, structures and components (SSCs)

• Implement specific plant aging management programs to address aging degradation

• Confirm behavior of degradation mechanisms for the entire period of operation

This paper will step through the above elements to illustrate how a strong technical case may be created for safe and reliable long-term operation. Examples or case studies will be provided to clearly link the fundamental science of materials degradation to the inspection, testing and evaluation efforts implemented at a plant and to the confirmatory data that is provided by both actual operating experience and the extensive research and development projects pursued by industry, governments, and the academic community.
Temperature Effect on Fiber Optical Sensors for Dry Cast Storage Health Monitoring
Authors: Lin Bin , Yu Lingyu , Giurgiutiu Victor
Published: November 2015

The increasing number, size, and complexity of nuclear facilities deployed worldwide are increasing the need to maintain readiness and develop innovative sensing materials to monitor important to safety structures (ITS). Assessing and supporting next generation nuclear materials management and safeguards for future U.S. fuel cycles with minimum human intervention is of paramount importance. Technologies for the diagnosis and prognosis of a nuclear system, such as dry cast storage system (DCSS), can improve verification of the health of the structure that can eventually reduce the likelihood of inadvertently failure of a component. In the past decades, an extensive sensor technology development has been used for structural health monitoring (SHM). Fiber optical sensors have emerged as one of the major SHM technologies developed particularly for temperature and strain measurements. However, the fiber optical sensors and sensing system has not been developed with adequate solutions and guideline for DCSS applications. This paper presents an experimental study of temperature effect on fiber Bragg grating (FBG) sensors. The reflective spectrum of FBG sensors on the structure was measured with a tunable laser source. The shift of FBG reflective spectrum reflected the thermal expansion on the structure. The shift of the spectrum due to the temperature effect was correlated to the temperature changes. In addition, the FBG sensing methodology including high frequency guided ultrasonic waves (GUW) under different temperatures were also performed to check the performance of high frequency, small strain sensing. The potential of FBG sensors for DCSS applications was explored. The paper ends with conclusions and suggestions for further work.