bluuebunny/crossref_metadata_2025 huggingface dataset:
StrainLife: Efficient Fatigue Life Data Generation for an Enhanced Ageing Assessment of Metallic Components
Authors: Heckmann Klaus , Sievers Jürgen , Schopf Tim , Schuler Xaver , de Acosta Ruth , Starke Peter , Boller Christian , Jamrozy Michael , Knyazeva Marina , Walther Frank
Published: October 2018

Pressurized pipes in hot water environment are subject to ageing mechanisms such as fatigue and environmental-assisted fatigue. These ageing effects limit the in-service time of components due to the possibility of crack formation, initiation and growth. Furthermore, uncertainties in life time assessment evolve as a consequence of increased scattering and resulting deviations in material properties. The lack of appropriate information requires safety-oriented design and conservative margins in the acceptable operation time.

In this contribution, investigations on methods for an improved assessment of fatigue life assessment based on microstructural aspects (specifically in the view of piping systems) are presented. The focus is on the metastable austenitic steel AISI 347 (X6CrNiNb18-10) under boiling water reactor operational conditions. In addition to strain-controlled fatigue tests and the hysteresis information, microstructural characterizations of the damage evolution are performed. Fatigue tests are equipped with magnetic and resistometric sensors to measure a different kind of material response correlated with the damage states.

The information obtained is used for an improved derivation of fatigue life evaluations of piping systems. The StrainLife approach and its specific instrumentation is proposed and discussed. In this approach, the number of strain-controlled fatigue tests is basically reduced by an order of magnitude when compared to traditional procedures. A software tool (as a module of the structural analysis code PROST) has been developed to assist users in evaluating and incorporating the respective data and to derive the subsequent fatigue life curves. As an outlook, further development is addressed to transfer the methodology to the assessment of residual fatigue life of components being exposed to ageing in operation.
Advanced High Strength Martensitic Stainless Steels for High Pressure Equipment
Authors: Lardon J. M. , Poulain T.
Published: October 2018

Maraging stainless steels offer a large panel of high strength materials with good ductility and stress corrosion cracking resistance. Their mechanical properties compared to conventional 15-5 PH and 17-4 PH martensitic stainless steels show much better yield strength / toughness compromise for yield strength exceeding 1300 MPa. In the same time, fatigue resistance is significantly increased at high strength stress levels and material keeps good resistance to stress corrosion. These properties make them particularly suitable for ultra-high pressure equipment or high pressure rotating components submitted to high cyclic stresses. Their application for Pascalisation pressure vessels and ultra-high pressure compressors for ethylene gas is briefly presented.
Rapid Thermal Stress Ratcheting Assessment for Pressured Components Based on LMM
Authors: Shen Jun , Chen Haofeng , Liu Yinghua
Published: October 2018

In ASME VIII-2 Code 2004 and previous versions, evaluation procedures for thermal stress ratcheting were provided, which is substantially based on Bree’s diagram. According to VIII-2-2004, the application scope of this method is limited to “in shell” and “general membrane stress due to pressure”. In ASME VIII-2 Code 2007 and later versions, the limitation of “in shell” has been removed and “general membrane stress” was extended to “general or local primary membrane equivalent stress”. However, these methods have their own limitations, and consequently can’t apply to the engineering project widely and rapidly. Rapid thermal stress ratcheting assessment calculations for pressured components with arbitrary geometries and discontinuity effects based on the Linear Matching Method (LMM) were available. Several cases are provided to show how to establish shakedown and ratchet boundaries quickly and easily for components subjected to arbitrary combinations of thermal-mechanical loads. The Bree-like ratchet boundaries for several typical components are obtained, which is useful and valuable for engineering design in Design-by-Analysis (DBA) for pressured components.
Advanced Structural Integrity Assessment Tools for Safe Long Term Operation (ATLAS+)
Authors: Lindqvist Sebastian , Wallin Kim , Moinereau Dominique , Smith Mike , Marie Stéphane , Dillström Peter , Keim Elisabeth , Szavai Szabolcs
Published: October 2018

The main objective and mission of the ATLAS+ project is to develop advanced structural assessment tools to address the remaining technology gaps for the safe and long term operation of nuclear reactor pressure coolant boundary systems. This is achieved by development and validation of:

• innovative quantitative methodologies to transfer laboratory material properties to assess the structural integrity of large components,

• enhanced treatment of weld residual stresses when subjected to long term operation,

• advanced simulation tools based on fracture mechanics methods using physically based mechanistic models,

• improved engineering methods to assess components under long term operation taking into account specific operational demands,

• integrated probabilistic assessment methods to reveal uncertainties and justify safety margins.

Additionally, the objective is to disseminate the findings of the work through special training sessions and links to the NUGENIA association.

The project scope of work focuses on piping systems of the reactor coolant pressure boundary components (RCPB) excluding the reactor pressure vessel (RPV). The project is aimed on an experimental proof of concept and validates the developed methodology both at the laboratory scale and the full scale level.

The ATLAS+ project contains 4 main technical work packages and one training and dissemination package. These are summarised here.
Investigation Into Applications of Local Failure Criterion for X70 Pipeline With Corrosion Defect
Authors: Moon Ji-Hee , Huh Nam-Su , Kim Ki-Seok
Published: October 2018

In this paper, the local failure criterion using stress modified critical strain method based on annex B of API 579 is applied to evaluate the ductile failure of API X70 pipelines with a volumetric corrosion defect. Ductile failure is quantified in terms of strain, representing the tensile strain capacity (TSC) which is commonly used in strain-based assessment for fitness-for-service of pipelines installed in frozen area where large-scale ground movement can arise due to earthquakes, freezing and thawing.

Based on the local failure criterion suggested for API X70 steel material, the TSCs of the corroded pipelines are evaluated by using the detailed finite element (FE) analyses. The effects of internal pressure and defect size (such as longitudinal length, circumferential width and depth in the direction of thickness) on TSC of pipelines subjected to axial displacement are systematically investigated. In addition, TSCs based on local failure criterion are compared with those based on net-section limit load. The TSCs from the present FE analyses for various defect geometries and internal pressure can be used to predict ductile failure of corroded pipelines and to build the framework for a strain-based assessment for in-service pipelines.
Creep Fatigue Damage Assessment of V-Butt Weld Pipe With an Extended Direct Steady Cycle Analysis
Authors: Puliyaneth Manu , Chen Haofeng , Luan Weiling
Published: October 2018

One of the methods to increase the efficiency of power plants is by increasing their operating temperature, this can lead to various damage mechanisms due to creep-cyclic plasticity interactions such as creep ratcheting, cyclically enhanced creep and creep enhanced plasticity. In the presence of welds, their assessments are complicated due to the presence of different material zones, namely parent metal, weld metal and heat affected zone which exhibit different properties. This paper aims at investigating the creep-fatigue damage of a V-butt welded pipe under a constant mechanical load and a cyclic temperature load, considering full interaction between creep and cyclic plasticity using the extended Direct Steady Cycle Analysis (eDSCA) within the Linear Matching Method Framework (LMMF). The impact of applied load level and creep dwell on the failure mechanism and location is investigated. Influence of hoop to axial stress ratio and groove angle is studied comprehensively by choosing ranges covering majority of common pipe configurations. Further validation of results is carried out by using detailed step-by-step inelastic analyses in ABAQUS, thereby demonstrating the accuracy and efficiency of LMM eDSCA in predicating the remaining life of multi-material components such as a welded pipe, combining with appropriate creep and fatigue damage models.
Comparison Between Strain-Based and Energy-Based Creep Failure Simulation
Authors: Kim Seung Jae , Oh Young Ryun , Kim Yun Jae
Published: October 2018

The power plant is required to operate under high temperature and pressure for high efficiency. In order to predict reliable life time of power plant under high temperature, creep-low cycle fatigue life prediction method should be proposed.

In this paper, strain based and energy based failure model are proposed to simulate notch bar creep tensile test. Modification factors considering multiaxial fracture and strain rate effect were proposed in order to simulate notch bar creep tensile test using FE analysis.

Using proposed models, FE result of strain based and energy based damage model are compared with notch bar creep tensile test. As a result, both strain and energy based damage model simulates crack growth well during creep, However, when tertiary creep behavior is considered, energy based failure model simulate rupture time longer than strain based model. It can be inferred that plastic damage accumulation of energy based model is slower than that of strain based model.
Comparison of Various Cyclic Hardening Models for Notched C(T) Specimen Simulation Under Cyclic Loading
Authors: Lee Jong-Min , Kim Hune-Tae , Kim Yun-Jae , Kim Jin-Weon
Published: October 2018

In this paper, simulations using various cyclic hardening models are performed to determine the effect of the hardening model that is used in a finite element analysis. Bi-linear, Armstrong-Frederick kinematic hardening model and Chaboche (third order non-linear) combined hardening model are used in finite element (FE) analysis to simulate material behavior under cyclic loading condition. Hardening parameters included in bilinear and non-linear hardening models are determined from monotonic stress-strain curve obtained from monotonic tensile test and parameters in Chaboche hardening model are determined from hysteresis loop obtained from cyclic tensile test. Simulation of notched C(T) test under cyclic loading is performed using three hardening models. Plastic strain, stress and plastic strain energy at notch tip of specimen are extracted from FE analysis results. Using energy based fatigue analysis, cycle to failure, the cycle at which crack initiation occurs at notch tip, are predicted and compared with experimental results. Through the comparisons, the effect of hardening model on the simulation result under cyclic load is confirmed.
Effects of Socket Weld Field Condition on Vibration Fatigue Behavior of Carbon Steel Piping
Authors: Oh Chang-Young , Kim Dong-Woo , Lee Sang-Hoon , Song Sang-Woo , Kim Nam-Kyu
Published: October 2018

Fatigue failure caused by vibration of socket welds often occurs in a nuclear power plant. The purpose of this study is to evaluate the integrity of the nuclear power plant socket weld under vibration fatigue condition. The vibration fatigue tests were conducted considering the field condition of socket welds. The types of field condition such as the weld quality, slip-on gap condition, weld leg size, eccentricity, pipe diameter were considered. A testing methodology is described, in which the test specimens bolted to the shake table were shaken by adjusting the specimen natural frequency, shake table speed and input acceleration. The results are as follows: There is no tendency to crack originated at the toe and the root. Fatigue strength was greater for 2 × 1 leg length, small diameter and no slip-on gap. Based on these results, the effects of socket weld field condition are discussed for small diameter welded pipe joints in the present study.
Fracture Mechanical Assessment of VVER Reactor Internals
Authors: Pištora Vladislav , Švrček Miroslav , Ferko Peter , Mirzov Ihor
Published: October 2018

Reactor internals of VVER reactors are heavy components made of austenitic steel 08Kh18N10T. As they are close to the reactor core, they receive very high dose during their operation, which causes significant embrittlement. Their brittle fracture initiation has to be excluded during all operating conditions including emergency conditions to maintain its functionality and to avoid mechanical damage of fuel assemblies. During the emergency event the reactor internals are loaded by highly non-uniform temperature field due to thermal shock and also by dynamical loading due to non uniform pressure load. The temperature loading is relatively slow (critical time is about 100 s after beginning of the emergency event), while the mechanical loading is very fast (critical time is about 0.1 s after beginning of emergency event). The worst emergency event for both types of loading is LB LOCA. Due to this fact, both loading types can be assessed separately. This paper deals with the temperature loading. The procedure for fracture mechanical assessment of VVER reactor internals is given in “Guidelines for Integrity and Lifetime Assessment of Components and Piping in VVER Nuclear Power Plants (IAEA-NULIFE-VERLIFE)”, Appendix C “Integrity and Lifetime Assessment Procedure of RPV Internals in VVER NPP’s During Operation”. The procedure prescribes postulated cracks in the components and allowable value of J-integral in dependency on dose and temperature. The assessment of brittle fracture initiation is based on comparison of J-integral calculated for postulated crack for the assessed emergency regime with its allowable value. In the paper, brief description of both the VVER reactor internals design and methodology of the assessment are presented, and also some examples of the results are shown.
A Multidimensional and Multiscale Model for Pressure Analysis in a Reservoir-Pipe-Valve System
Authors: Zheng Feng Jie , Qu Fu Zheng , Song Xue Guan
Published: October 2018

Reservoir-pipe-valve (RPV) systems are widely used in many industrial process. The pressure in an RPV system plays an important role in the safe operation of the system, especially during the sudden operation such as rapid valve opening/closing. To investigate the pressure especially the pressure fluctuation in an RPV system, a multidimensional and multiscale model combining the method of characteristics (MOC) and computational fluid dynamics (CFD) method is proposed. In the model, the reservoir is modeled by a zero-dimensional virtual point, the pipe is modeled by a one-dimensional MOC, and the valve is modeled by a three-dimensional CFD model. An interface model is used to connect the multidimensional and multiscale model. Based on the model, a transient simulation of the turbulent flow in an RPV system is conducted, in which not only the pressure fluctuation in the pipe but also the detailed pressure distribution in the valve are obtained. The results show that the proposed model is in good agreement with the full CFD model in both large-scale and small-scale spaces. Moreover, the proposed model is more computationally efficient than the CFD model, which provides a feasibility in the analysis of complex RPV system within an affordable computational time.
The Thermo-Mechanical Behaviour of Alloy 600 and Alloy 82 Materials
Authors: Akrivos Vasileios , Smith Mike C.
Published: October 2018

Isothermal uniaxial low cycle fatigue tests have been performed at two different total strain ranges (1.5% and 2.5%) and at different temperatures (20, 200, 400 and 600°C) for Alloy 600 and Inconel 82 materials. The materials hardening behaviour has been fitted using the Lemaitre Chaboche formulations using different fitting strategies. Thermo mechanical tests have been performed using a Gleeble machine on both parent material and weld metal. In these tests thermal cycles were applied to a constrained specimen simulating the welding conditions in both the heat affected zone and a weld bead when subsequent beads are deposited alongside. The tests were modelled using two different FE codes, namely Code_Aster and Abaqus. This allowed the validation of the Lemaitre-Chaboche model parameters when the material is subjected to realistic thermo-mechanical cycles. Simulations were conducted using both annealing and/or viscous recovery features to examine their impact on the predicted response.
Fatigue Monitoring of a Dented Piping Specimen Using Infrared Thermography
Authors: Paiva Vitor Eboli L. , Gonzáles G. L. G. , Vieira R. D. , Maneschy J. E. , Vieira R. B. , Freire J. L. F.
Published: October 2018

The present paper combines the fatigue properties rapid assessment approach using uniaxial test specimens proposed by Risitano and co-workers with the nondestructive testing (NDT) inspection approach proposed by Sakagami and co-workers to monitor the onset of fatigue in a reduced scale pipeline test specimen that was previously dented and subsequently subjected to cyclic pressure loading. In addition to the use of the conventional infrared (IR) thermographic method, the present paper uses a self-reference lock-in IR thermography method based on Thermoelastic Stress Analysis (TSA) and its deviation from traditional applications due to the presence of fatigue damage and plastic strains. The paper concludes showing that is possible to predict and monitor and detect fatigue initiation and damage using IR and TSA techniques applied to the thin wall pipe loaded under cyclic hydrostatic pressure.
Tensile Tests for Cast Stainless Steel: Evolution of the RCC-M Code
Authors: Blouin Arnaud , Couvrat Mathieu , Latourte Félix , Soulacroix Julian
Published: October 2018

In the framework of a pressurized water reactor primary loop replacement, elbows of different types were produced in cast austenitic stainless steel grade Z3CN 20-09 M. For that type of component, acceptance tests to check the sufficient mechanical properties include room and hot temperature tensile tests, following the RCC-M CMS – 1040 and EN 10002 specifications. A large test campaign on standard 10mm diameter specimens was performed and exhibited a high scattering in yield stress and ultimate tensile strength values. As a consequence, some acceptance tensile tests failed to meet the required minimal values, especially the ultimate tensile strength. Optical and electronic microscopy revealed that the low values were due to the presence of very large grain compared to the specimen gage diameter. However, tensile tests strongly rely on the hypothesis that the specimen gage part can be considered as a representative volume element containing a number of grains large enough so that their variation in size and orientation gives a homogeneous response. To confirm the origin of the scattering, a huge experimental tensile test campaign with specimens of different diameters was conducted. In parallel, FE calculations were also performed. From all those results, it was concluded that it was necessary to improve the RCC-M code for that type of test for cast stainless steel: to do so, a modification sheet was sent and is being investigated by AFCEN.
Approach for the Dimensioning of Bolted Joint Connections With Threaded Flanges for High Pressure Applications
Authors: Bortz Matthias , Fuenmayor David , Wink Rolf
Published: October 2018

High pressure flange connections for LDPE plants are commonly designed using lens ring gaskets and bolted flange connections. The rules given in the ASME Code Sections B31.3, VIII Div. 2 or VIII Div. 3 for bolted-flange joints offer no guidance for the calculation of threaded flanges.

In this paper, an approach is presented that considers internal pressure and external loads on a flange connection and fulfills the requirements of ASME Section VIII Div.3 and ASME B31.3. Of specific interest is the dimensioning of bolts due to the bending moment with a method that avoids the over-conservatism of the rules given in ASME VIII Div.2 and ASME B31.3. Furthermore, a simplified calculation for threaded flanges considering the stress classification and stress limits given in ASME VIII Div. 3 and using Finite Element Analyses is described.
Presentation of DEFI-PROSAFE Project: Probabilistic Methodology to Assess Margin in Deterministic RPV Integrity Assessment and Proposed Benchmark
Authors: Tiete Ralf , Trewin Richard , Blasset Sebastien , Pistora Vladislav , Posta Miroslav , Niffenegger Markus , Qian Guian
Published: October 2018

In this paper the project DEFI-PROSAFE is presented.

In the frame of Nugenia+ project, a work package was dedicated to the “DEFInition of reference case studies for harmonized PRObabilistic evaluation of SAFEty margins in integrity assessment for long-term operation of reactor pressure vessel” (acronym DEFI-PROSAFE). A methodology is proposed to assess safety margins in RPV integrity accounting for uncertainties propagation, because no commonly accepted European approach exists for probabilistic assessment of RPV fast fracture risk.

The DEFI-PROSAFE methodology, which is based on the comparison between deterministic and probabilistic assessment, will be detailed. The experience gained from the US Screening Criteria (NUREG-1806) and past projects (ICAS, PROSIR), and guideline (IAEA TecDoc 1627) as well as aspects specific to European deterministic integrity approach have been considered. Usually for probabilistic fracture assessment of the RPV, the parameters (describing flaws, material and neutron fluence) are sampled and the RPV cylindrical region is assessed using deterministic thermal hydraulic loading for evaluation of initiation or failure conditional probability. Within DEFI-PROSAFE methodology the uncertainties in thermal-hydraulic input parameters are taken into account and their propagation in the structural assessment is considered. Comparison of RELAP5 thermal hydraulic results and mixing calculation results (KWU-MIX) with experiment relevant to PTS assessment was performed. Furthermore the DEFI-PROSAFE methodology considers RPV discontinuity regions (like RPV nozzle) and specific PIRT analysis has been performed for selection of the TH-parameters.

A new benchmark for probabilistic assessment of RPV was defined within the DEFI-PROSAFE project. The benchmark definition and case studies based on previous R&D project (ICAS, PROSIR) will be presented. The performance of the new benchmark may be submitted as new European project.
Mismatch Effect on the Mode II Type Crack Tip Field in Power-Law Creeping Materials
Authors: Dai Yanwei , Liu Yinghua , Chao Yuh J.
Published: October 2018

The mismatch effect in weldments are widely to be seen in engineering practices. In this paper, the material mismatch effect on the mode II creep crack tip field is investigated and discussed. The effects of material mismatch and heat affected zone (HAZ) width on the C(t)-integral are presented. Both the local mismatch effect and the general mismatch effect are found to play important roles in the variations of C(t)-integral. The mismatch effect on the stress field of the mode II creep crack is also studied. The two-order term solutions are presented to characterize the material mismatch constraint effect on the mode II type creep crack. Some typical cases by considering general mismatch effect and local mismatch effect are given so as to make comparisons between the HRR field, FE solutions and the two-order term solutions. It can be seen that the two-order term solutions can coincide with the FE solutions quite reasonably regardless of creep extent, creep exponent, mismatch factor and HAZ width. This research also reveals the significant effect of the material mismatch on the high order term solutions under various conditions for mode II creep crack.
Weld Residual Stress Activities Within the ATLAS+ Project
Authors: Smith Mike C.
Published: October 2018

Weld residual stresses can have significant effects on the service performance and structural integrity of pressure-retaining components in nuclear power plants. Reliable prediction and measurement of residual stress in plant-representative components can be challenging. The impact of residual stress on structural integrity can also be difficult to predict reliably. This paper describes the residual stress activities taking place within ATLAS+, and covers welded mock-up design and manufacture, residual stress measurements and simulation, the development of residual stress profiles for structural integrity assessment, and their incorporation into assessment procedures.
The Influence of Creep Strain Rate on Creep Damage Formation in Austenitic Stainless Steel
Authors: Hares Edward , Mostafavi Mahmoud , Bradford Richard , Truman Chris
Published: October 2018

Motivated by the need to more accurately account for real, in-service, operating conditions, this paper aims to investigate whether creep strain accumulated at different strain rates is equally damaging. Previous research has suggested that creep strain is more damaging when accumulated more slowly in creep of notched bars. The research presented here seeks to address this question by considering the accumulation of creep strain during stress relaxation of notched bars. Repeat stress relaxation tests with varying dwell lengths were conducted so that the relative damaging effects of the early, rapid accumulation and later, slow accumulation of creep strains could be compared. Another aim was to determine how a lower test temperature affects this creep strain accumulation. In repeat relaxation tests the load is reestablished repeatedly after relaxation dwells of equal duration, until rupture of the specimen occurs. The material used was an ex-service powerplant stainless steel Type 316H. Notched bar specimens were used to introduce stress triaxiality at the notch tip to imitate the multiaxial loads plant components are subjected to during in-service operation. The stresses and strains in the specimens were then assessed using finite element analysis; a user subroutine was implemented so the onset and propagation of creep damage could be simulated throughout the specimens’ creep life. The research found that the material in question had a lower creep ductility at 515°C than at 550°C. The research also showed that creep strain accumulated rapidly at the start of a dwell is significantly less damaging than creep strain accumulated more slowly towards the end of the dwell.
Dynamics of a Free Heaving and Prescribed Pitching Hydrofoil in a Turbulent Flow, With a Fluid-Structure Interaction Approach
Authors: Brousseau P. , Benaouicha M. , Guillou S.
Published: October 2018

This paper deals with the dynamics of an oscillating foil, describing a free heaving (vertical displacement) and prescribed pitching (rotational displacement) movement which is computed from its position in two different ways. A fluid-structure interaction approach is chosen, as the physics of the flow and the structure are strongly coupled. The flow is unsteady, turbulent and incompressible. The pressure/velocity problem is solved using SIMPLEC scheme. First, the pitching movement is considered as a given continuous function of the hydrofoil heaving position. Second, the pitching motion is performed alternately at the end of each heave cycle. For each case, two maximum angles of attack and one heaving amplitudes are studied. Preliminary results showed that a high maximum angle of attack generates more lift hydrodynamics force, but also requires more energy to perform the rotation of pitch.
Fluid-Structure Interaction Approach for Numerical Investigation of a Flexible Hydrofoil Deformations in Turbulent Fluid Flow
Authors: Benaouicha M. , Guillou S. , Santa Cruz A. , Trigui H.
Published: October 2018

The study deals with a 3D Fluid-Structure Interaction (FSI) numerical model of a rectangular cantilevered flexible hydrofoil subjected to a turbulent fluid flow regime. The structural response and dynamic deformations are studied by analyzing the oscillations frequencies and amplitudes, under a hydrodynamics loads. The obtained numerical results are confronted with experimental ones, for validation. The numerical model is performed in the same geometric, physical and material conditions as the experimental set-up carried out in a hydrodynamic tunnel.

A polyacetal (POM) flexible hydrofoil NACA0015 with an angle of attack of 8° is considered to be immersed in a fluid flow at a Reynold number of 3 × 105. The structure is initially at rest and then moved by the action of the fluid flow. The numerical model is based on a strong coupling procedure for solving the Fluid-Structure Interaction problem. The Arbitrary Lagrangian-Eulerian (ALE) formulation of the Navier-Stokes equations is used and an anisotropic diffusion equation is solved to compute the fluid mesh velocity and position at each time step. The finite volume method is used for the numerical resolution of the fluid dynamics equations. The structure deformations are described by the linear elasticity equation which is solved by the finite elements method. The Fluid-Structure coupled problem is solved by using the partitioned FSI implicit algorithm.

A good agreement between numerical and experimental results for the hydrodynamics coefficients and hydrofoil deformations, maximum deflection and frequencies is obtained. The added mass and damping are analyzed and then the FSI effect on the dynamic deformations of the structure is highlighted.
A Comparative Study on Mechanical Behavior of Pipe-Socket Threaded Joints With Taper-Taper Threads and Taper-Parallel Threads Combinations by Finite Element Analysis and Experiments
Authors: Nagata Satoshi , Fujita Shinichi , Sawa Toshiyuki
Published: October 2018

There are two types of combination between external and internal threads used in threaded pipe connections for pressure piping specified in industrial standards like JIS as well as ISO. One is the combination that taper external thread of pipe is engaged with taper internal thread of a fitting. The other is that taper external thread of pipe is engaged with parallel internal thread of a fitting. Taper thread is always used for external thread outside the pipe wall. Both taper thread and parallel one are applicable to internal thread inside the fittings. This paper evaluates the mechanical behaviors of threaded pipe-socket joints (or pipe-coupling joints) and the difference due to the thread type combinations by means of axisymmetric finite element analysis for 3/4” and 3” joints. The analysis shows that the taper-taper threads combination establishes the full-length contact over the engaged threads but the taper-parallel has only a pair of threads in contact at the 1st engaged thread from the end of socket, and the difference results in the different behaviors of the joints. Stress and strain pattern also completely differ due to the difference in the engaged thread length. No significant effect of the size has been found in the present analysis for 3/4”and 3” joints. Experimental tightening tests and pressure leak tests have also been carried out for 3/4” and 3” joints with taper-taper threads combination. The measured experimental stress for 3/4” joints has shown an agreement with the simulated one fairly well. The pressure leak tests have demonstrated that the taper-taper threaded pipe-socket joints can hold internal pressure without leakage without using thread seal tape or jointing compound under low-pressure service condition. The 3/4” joints have started leaking at 1–4MPaG of internal pressure. The 3” joints haven’t shown leakage even at 6MPaG of internal pressure applied.
Creep Modeling of 9-12%Cr Ferritic Steels Accounting for Subgrain Size Evolution
Authors: Esposito Luca , Testa Gabriel , Bertocco Alcide , Bonora Nicola
Published: October 2018

The enhanced performance of new creep-resistant steels is the result of optimized microstructures. Clearly, the microstructure stability at high temperature is essential for the long-term use of this steels generation. In the recent scientific literature, several research addresses the correlation between the microstructure degradation and the creep performance loss. General aim is to introduce state variables able to describe the metallurgy history of the material affecting its current and future response. The possibility to integrate this metallurgical information in predictive modeling is very attractive. In this work, a new creep model for 9-12%Cr ferritic steels, in the framework of the Continuum Damage Mechanics (CDM), is proposed. The damage variable, usually not related to the underlying physics, may have a metallurgical meaning introducing the kinetic law for subgrain evolution. The microstructure of 9-12%Cr steels is designed to produce the 100% martensite during quenching treatment. Since martensite is not a thermodynamic equilibrium phase, the microstructure evolves exhibiting lath widening and subgrains coarsening. The subgrains growth can be ascribed to the creep strain accumulation and consequently the proposed formulation uses the subgrain size evolution to predict the creep rate beyond the minimum creep rate mainly affected by the recovery processes.
Development of an Efficient Stability Analysis Method for a Plate in Uniform Flow by Using Differential Algebraic Equations
Authors: Hara Kensuke
Published: October 2018

This paper addresses an instability problem of a plate in a uniform incompressible and irrotational flow. In particular, this study is aimed at developing a stability analysis method with low computational cost. An analytical dynamics framework for constraint systems is applied to derivation of the fluid force acting on the plate surface. This formulation gives an algebraic relation between the plate displacement and the generalized momentum regarding the velocity potential as a constraint, that is, this relation plays the role of the fluid-structure interaction in the present formulation. Then, the algebraic equation for calculating the fluid force is obtained by a second order time derivative of the constraint. Specifically, the fluid force is given as the Lagrange multiplier, which is introduced for imposing the constraint regarding the fluid-structure interaction mentioned above. The resulting equations are comprised of differential equations regarding the plate displacement and the algebraic equation giving the fluid force. This kind of equations are referred to as the differential algebraic equations. Moreover, derived equations for the fluid-structure interaction are reduced to the eigenvalue problem by employing the generalized Fourier series expansion technique. Then, the stability of this system is evaluated by the eigenvalue analysis. After that, the results are verified by comparing with the results by the previous method.
RSE-M - ASME XI - API 579: Comparison of Failure Assessment Diagrams (FAD)
Authors: Faidy Claude
Published: October 2018

After a short review of the 3 Codes in term of flaw evaluation, this paper will consider the Failure Assessment Diagrams (FAD) proposed in each of them.

The cracked components are evaluated by a dedicated diagram for margin evaluation of ductile tearing resistance of the components: the elastic stress intensity factor of the crack normalized by the toughness of the material on one axis and the applied stresses normalized by a Reference Stress in the other axis.

The 2017 Edition of RSE-M Appendix 5.4 and 5.6, the 2017 Edition of ASME XI Appendix H and the 2016 Edition of API 579 Part 9 will be used in this first comparison.
Acoustic Data Analysis for Detecting Alkali-Silica Reaction Degradation in Concrete
Authors: Dubey Ankit Ramanand , Miele Sarah A. , Agarwal Vivek , Mahadevan Sankaran
Published: October 2018

A primary challenge for the current fleet of light water reactors in the United States is age-related degradation of their passive assets that include concrete, cables, piping, and the reactor pressure vessel. Various nondestructive techniques exist for locally assessing degradation in passive structures in nuclear power plants. This paper presents results from the analysis of acoustic data acquired using the vibro-acoustic modulation (VAM) technique on a medium-sized concrete slab (2 × 2 × 0.5 ft), which has undergone degradation due to alkali-silica reaction (ASR). VAM is a nonlinear vibration technique in which the structure of interest is excited using a combination of specific frequencies and the response is recorded. VAM assumes that an undamaged structure can be represented by a linear system while the representation of a damaged structure must include nonlinearity. Two piezo-stack actuators are used to excite the slab. One stack is dedicated to excite the slab at a low frequency, referred to as pump frequency, and another stack is dedicated to excite the slab at a high frequency, referred to as probe frequency. The concrete slab was cured in an environmental chamber to accelerate ASR-related degradation. In this paper, the measured acoustic signals are analyzed in both the time and frequency domains to understand state of health of the concrete specimen.
A Compendium of Mechanical Testing of Austenitic Stainless Steels in Hydrogen
Authors: Lam Poh-Sang , Duncan Andrew J. , Morgan Michael J. , Sindelar Robert L. , Adams Thad M.
Published: October 2018

Archival materials test data on austenitic stainless steels for service in high pressure hydrogen gas has been reviewed. The bulk of the data were from tests conducted prior to 1983 at the Savannah River Laboratory, the predecessor to the Savannah River National Laboratory, for pressures up to 69 MPa (10,000 psi) and at temperatures within the range from 78 to 400 K (−195 to 127 °C). The data showed several prominent effects and correlations with test conditions:

• There was a significant reduction in tensile ductility as measured by reduction of area or by the total elongation with hydrogen. Hydrogen effects were observed when the specimens were tested in the hydrogen environment, or the specimens were precharged in high pressure hydrogen and tested in air or helium.

• There was a significant reduction in fracture toughness with hydrogen (and sometimes in tearing modulus which is proportional to the slope of the crack resistance curve).

• The effects of hydrogen on ductility can be correlated to the nickel content of the iron-chromium-nickel steels. The optimal nickel content to retain the high tensile ductility in these alloys was 10 to at least 20 wt. %.

• The effects of hydrogen can be correlated to the grain size. Large grain sizes exhibited a greater loss of ductility compared to small grain sizes.

The Savannah River Laboratory test data, especially those not readily available in the open literature, along with the sources of the data, are documented in this paper.
Experimental Assessment of the Dynamic Behavior of Polyolefin Thermoplastic Hot Melt Adhesive
Authors: Ciardiello Raffaele , Tridello Andrea , Goglio Luca , Belingardi Giovanni
Published: October 2018

In the last decades, the use of adhesives has rapidly increased in many industrial fields. Adhesive joints are often preferred to traditional fasteners due to the many advantages that they offer. For instance, adhesive joints show a better stress distribution compared to the traditional fasteners and high mechanical properties under different loading conditions. Furthermore, they are usually preferred for joining components made of different materials.

A wide variety of adhesives is currently available: thermoset adhesives are generally employed for structural joints but recently there has been a significant increment in the use of thermoplastic adhesives, in particular of the hot-melt adhesives (HMAs). HMAs permit to bond a large number of materials, including metal and plastics (e.g., polypropylene, PP), which can be hardly bonded with traditional adhesives. Furthermore, HMAs are characterized by a short open time and, therefore, permit for a quick and easy assembly process since they can be easily spread on the adherend surfaces by means of a hot-melt gun and they offer the opportunity of an ease disassembling process for repair and recycle. For all these reasons, HMAs are employed in many industrial applications and are currently used also for bonding polypropylene and polyolefin piping systems.

In the present paper, the dynamic response of single lap joints (SLJ) obtained by bonding together with a polyolefin HMA two polypropylene substrates was experimentally assessed. Quasi-static tests and dynamic tests were carried out to investigate the strain rate effect: dynamic tests were carried out with a modified instrumented impact pendulum. Relevant changes in the joint performance have been put in evidence. Failure modes were finally analysed and compared. A change in the failure mode is experimentally found: in quasi-static tests SLJ failed due to a cohesive failure of the adhesive, whereas in dynamic tests the SLJ failed due to an interfacial failure, with a low energy absorption.
Hydrogen Compatibility and Suitability of (Ni)-Cr-Mo High-Strength Low-Alloy Seamless Line Pipe Steels for Pressure Vessels for Hydrogen Storage
Authors: Nagao Akihide , Ishikawa Nobuyuki , Takano Toshio
Published: October 2018

Cr-Mo and Ni-Cr-Mo high-strength low-alloy steels are candidate materials for the storage of high-pressure hydrogen gas. Forging materials of these steels have been used for such an environment, while there has been a strong demand for a higher performance material with high resistance to hydrogen embrittlement at lower cost. Thus, mechanical properties of Cr-Mo and Ni-Cr-Mo steels made of quenched and tempered seamless pipes in high-pressure hydrogen gas up to 105 MPa were examined in this study. The mechanical properties were deteriorated in the presence of hydrogen that appeared in reduction in local elongation, decrease in fracture toughness and accelerated fatigue-crack growth rate, although the presence of hydrogen did not affect yield and ultimate tensile strengths and made little difference to the fatigue endurance limit. It is proposed that pressure vessels for the storage of gaseous hydrogen made of these seamless line pipe steels can be designed.
Limitations in the Use of Pressure Scaling for Safety Relief Valve Design
Authors: Dempster William , Taggart Steven , Doyle Christopher
Published: October 2018

A key design method for safety relief valves requires that the forces acting on the valves can be scaled using a simple pressure scaling technique. This allows experimentally determined valve force characteristics to be measured at low pressure conditions and then scaled to the required operational pressures and allows spring characteristics to be specified. Ultimately, this has a direct connection with the opening and closing performance of the valve. In this paper, we question the accuracy of the scaling approach and examine the influence of the effect of built-up pressure in the discharge region of the valve. We investigate the problem theoretically using CFD techniques via the commercial code FLUENT. The influence of the discharge flange size is of particular interest since it can have an effect on the force lift curves by choking at the exit due to a detrimental increase in internal valve pressure. The investigation uses valves conforming to ASME 8 standards as a basis of the investigation. The CFD predictions are compared to experimental results of the force lift behaviour for validation purposes and then used to explore the validity of pressure scaling. The results indicate that when valves are operated with lower pressure ratios pressure scaling is not valid and common scaling approaches are only valid when the discharge flange is choked.
A Nonlinear Least Squares Logistic Fit Approach to Quantifying Uncertainty in Fatigue Stress-Life Models and an Application to Plain Concrete
Authors: Fong Jeffrey T. , Heckert N. Alan , Filliben James J. , Ziehl Paul H.
Published: October 2018

A large number of fatigue life models for engineering materials such as concrete and steel are simply a linear or nonlinear relationship between the cyclic stress amplitude, σa, and the log of the number of cycles to failure, Nf. In the linear case, the relationship is a power-law relation between σa and Nf, with two constants determined by a linear least squares fit algorithm. The disadvantage of this simple linear fit of fatigue test data is that it fails to predict the existence of an endurance limit, which is defined as the cyclic stress amplitude at which the number of cycles is infinity. In this paper, we introduce a nonlinear least square fit based on a 4-parameter logistic function, where the curve of the y vs. x plot will have two horizontal asymptotes, namely, y0, at the left infinity, and y1, at the right infinity with y1 < y0 to simulate a fatigue model with a decreasing y for an increasing x. In addition, we need a third parameter, k, to denote the slope of the curve as it traverses from the left horizontal asymptote to the lower right horizontal asymptote, and a fourth parameter, x0, to denote the center of the curve where it crosses a horizontal line half-way between y0 and y1. In this paper, the 4-parameter logistic function is simplified to a 3-parameter function as we apply it to model a fatigue sress-life relationship, because in a stress-log (life) plot, the left upper horizontal asymptote, y0, can be assumed as a constant equal to the static ultimate strength of the material, U0. This simplification reduces the logistic function to the following form:

y = U0 − (U0 − y1) / (1 + exp(−k (x − x0)),

where y = σa, and x = log(Nf). The fit algorithm allows us to quantify the uncertainty of the model and the estimation of an endurance limit, which is the parameter, y1. An application of this nonlinear modeling technique is applied to fatigue data of plain concrete in the literature with excellent results. Significance and limitations of this new fit algorithm to the interpretation of fatigue stress-life data are presented and discussed.
Uniaxial Fatigue, Creep and Ratcheting Response Simulations of Alloy 617 Using Damage Coupled Viscoplastic Model
Authors: Islam Nazrul , Hassan Tasnim
Published: October 2018

A damage coupled unified constitutive model (UCM-CDM) is developed in this study to predict uniaxial fatigue, fatigue-creep, ratcheting and creep responses of Alloy 617. The experimental data used for validating the UCM-CDM included these responses for different strain rates and strain ranges for temperatures 760–1000°C. Rate dependent modeling features like Norton’s power law, static recovery, and isotropic damage evolution law are incorporated in an existing UCM for improving simulations of short-term stress relaxation and long-term creep responses. A backstress threshold modeling feature is incorporated in the UCM-CDM for improving ratcheting prediction for a wide range of mean and amplitude stresses. Simulations of the creep responses, including the primary, secondary and tertiary creep responses, in addition to the fatigue, fatigue-creep and ratcheting responses using the UCM with one set of model parameter are examined.