bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Study on Failure Estimation Method for Circumferentially Cracked Pipes Subjected to Multi-Axial Loads
Authors: Li Yinsheng , Hasegawa Kunio , Miura Naoki , Hoshino Katsuaki 
Published: November 2015

When a crack is detected in a piping line during in-service inspections, failure estimation method provided in ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. The failure estimation method in the current codes accounts for the bending moment and axial force due to pressure. The torsion moment is not considered.
Recently, analytical investigations have been carried out by several authors on the limit load of cracked pipes considering multi-axial loads including torsion and two failure estimation methods for multi-axial loads including torsion moment with different ranges of values have been proposed. In this study, to investigate the failure behavior of cracked pipes subjected to multi-axial loads including the torsion moment and to provide experimental support for the failure estimation methods, failure experiments were performed on 20 mm diameter stainless steel pipes with a circumferential surface crack or a through-wall crack under combined axial force and bending and torsion moments. Based on the experimental results, the proposed failure estimation methods were confirmed to be applicable to cracked pipes subjected to multi-axial loads.
Stress Intensification Factors for Non-Concentric Elbow Branches in Old Carbon-Steel Pipelines
Authors: Scano Lorenzo 
Published: November 2015

Unreinforced branch connections manufactured using elbow ducts can be occasionally encountered during the Fitness-For-Service evaluation of very old, low-service, carbon-steel pipelines. For these peculiar components, no Stress Intensification Factors (SIFs) are usually available in the international codes and standards used by practicioners for stress analysis purposes.
In a previous work from the author [1], the SIFs for various elbow branch connections were determined via FEA and a formula was derived through a parametric analysis in order to calculate the SIF for the elbow tees using the codified SIF of the equivalent standard joints. The investigation was restricted to concentric elbow branches, i.e., tees where the elbow duct had the same principal axis of the run pipe.
In this paper the case of non-concentric elbow branches was taken into account, considering the offset between elbow and run pipes and the rotation of the curved duct in the two main meridional planes, thus bringing into focus lateral and non-planar elbow tees. The SIFs were calculated using FEA for different configurations of reducing elbow branches with diameters ranging from 2” to 10” and thicknesses from Piping Schedule 10, 40 and 80. Lateral and non-planar joints were analyzed for one reference geometry and at various offsets and rotation angles. A parametric analysis was then carried out to evaluate the offset effect on the stress intensification both on run and branch side, for in-plane and out-of-plane bending. The results showed a significant impact only on the branch side where an increase in piping offset resulted in a reduction of the dominant out-of-plane bending SIF. The original formula devised for the concentric elbow branch connections was hence modified to include this offset effect. Finally, the combined role of offset and rotation angle was parametrically analyzed for the special geometry investigated. The results demonstrated a significative increment of the SIFs for non-planar tees, both on run and branch pipes, whilst in lateral joints the major SIF increased to a maximum only on the branch side.
Comparison of Plastic Work Curvature Methods for Assessing the Collapse Load of a Structure
Authors: Seal Christopher K. , Han Jae-Jun , Ainsworth Robert A. 
Published: November 2015

Plastic work methods for determining the collapse load of structures present a promising means of analysing complex geometries subjected to combined loading. Recent work has identified the curvature of a plot of plastic work as a function of the applied load as being indicative of the collapse load that is both accurate and physically based.
Several methods by which the curvature plot can be used to identify the plastic collapse load have been proposed by various authors and there is no consensus as to which method should be used. This paper presents an analysis of these and other methods and concludes with a recommendation for a robust approach that could be used in assessment.
Numerical Analysis and Experimental Assessment of the Cylinder Temperature in a Reciprocating Compressor
Authors: Balduzzi Francesco , Tanganelli Andrea , Ferrara Giovanni , Babbini Alberto , Maleci Riccardo 
Published: November 2015

Accurate evaluation of the thermal deformation is important to the analysis of reciprocating compressors since the induced deformations are responsible of the thermal stresses on the cylinder. The cylinder body experiences a non-uniform temperature distribution, with the presence of hot and cold spots, creating a bending strain on the structure. A cylinder cooling system is designed to control the uniformity of the temperature field and to reduce the fresh gas heating due to a hot cylinder body, improving the volumetric efficiency.
Due to the difficulties associated with obtaining detailed data on the heat transfer processes by experimental means, a more and more important role is played by numerical analysis in reciprocating compressor design.
This paper shows the capability of a conjugate heat transfer (CHT) simulation for a double-acting reciprocating compressor cylinder in accurately predicting both the thermal state of the compressor cylinder and the temperature field of the cooling water. The results of the three-dimensional simulations of the water-circuit flow field and the thermal conduction inside the solid metal were compared to temperature measurements collected on a dedicated test bench for both the coolant and the metal structure. Satisfactory agreement was obtained between the experimental data and the numerical computations.
In addition, three different modifications for the CHT model were introduced in order to obtain a better match with the experimental results. The suitability of using the CHT simulation as an efficient tool for replicating the actual condition of the reciprocating compressor was analyzed and discussed.
Effective Outage Planning and Implementation for Nuclear Power Plants in the UK
Authors: Reece-Barkell H. , Vorster W. J. J. 
Published: November 2015

Effective outage planning and implementation is critical to the efficient and safe operation of commercial nuclear power plants in the UK. Statutory outages are necessary for refuelling, for preventive and corrective maintenance when shutdown conditions are required, and for major modification and improvement projects. Outages involve the support of many companies and individuals working together and, as such, require high levels of coordination. Planning of activities before the outage is critical to the overall success of the outage. Establishing the integrity of power plant piping and pressure vessels is a key objective as part of any outage and the methodology and processes involved are the subject of this paper.
Establishing the integrity of piping and pressure vessels requires an understanding of the specific threats, their relationship to the overall condition of the system, and the mitigating measures required to assure safe operation. Understanding the specific threats allows the engineering function of an organisation to advise on pipework and pressure vessel ‘Minimum Acceptable Thicknesses’ which can be used to assure integrity via comparison with thicknesses measured during outage inspections. Minimum Acceptable Thicknesses should be recorded in the outage management documentation so they are accessible during the outage implementation phase.
Historically a variety of different methodologies have been used to advise on Minimum Acceptable Thickness requirements including design drawing specified minimum thicknesses, design code based required thicknesses and thicknesses calculated based on Fitness for Purpose methods. It is important that a robust procedure be applied to promote consistency of approach as regards the calculation of pipework and pressure vessel Minimum Acceptable Thickness requirements across all power station assets. An additional consideration is that of ensuring that the approach adopted is consistent with high level safety case guidance, i.e., the assessment is appropriate for the failure tolerability of the plant item.
This paper provides an overview of the strategy, methodologies and processes employed to determine Minimum Acceptable Thicknesses for pipework components. These ensure that, over a specified inspection interval, were the weld/component to be defect free, it would not fail due to any of the relevant failure mechanisms, which typically are plastic collapse, creep rupture, fatigue, incremental collapse (ratcheting) or buckling.
Readers of this paper will gain a valuable insight into the statutory outage process applicable to nuclear power plants in the UK. A particular focus of this paper is on the structural integrity assessments applied in a non-traditional sense prior to, during and after the statutory outage. As well as sharing a valuable insight into the assessment methodologies this paper highlights best industrial practice.
Temperature and Rise Time Inputs to Fatigue Crack Growth Calculations for Austenitic Stainless Steels in a Pressurised Water Reactor Environment
Authors: Emslie Julian , Watson Chris , Gill Chris , Wright Keith 
Published: November 2015

The draft ASME Code Case N-809 provides a Fatigue Crack Growth (FCG) law for austenitic stainless steel in a Pressurised Water Reactor (PWR) environment. This growth law explicitly considers the effect of the environment through the additional parameters of temperature and rise time applied in conjunction with a standard Paris equation. FCG calculations using this growth law have been shown to have the potential to produce significantly faster growth rates than those predicted using the current ASME XI FCG law for an air environment.
The testing on which this new FCG law is based is predominantly sawtooth loading in isothermal conditions; interpretation of the rise time and temperature variables is not straightforward when applied to PWR thermal transients which exhibit temperature and stress variations simultaneously, and the stress rate is not constant. This paper discusses temperature and rise time assumptions which may be applied with the PWR environment FCG law, and the practical implications of carrying out calculations with these additional parameters.
High Temperature Low Cycle Fatigue Behaviour of MarBN at 600 °C
Authors: Barrett Richard A. , O’Hara Eimear , O’Donoghue Padraic E. , Leen Sean B. 
Published: November 2015

The changing face of fossil fuel power generation is such that next generation plants must be capable of operating under (i) flexible conditions to accommodate renewal sources of energy and (ii) higher steam pressures and temperatures to improve plant efficiency. These changes result in increased creep and fatigue degradation of plant components. The key limiting factor to achieving more efficient, flexible plant operation is the development of advanced materials capable of operating under such conditions. MarBN is a new precipitate strengthened 9Cr martensitic steel, with added boron and tungsten, designed to provide enhanced creep strength and precipitate stability at high temperature. Accurate characterisation of this material is necessary so that it can be used under flexible plant operating conditions with high temperature fatigue.
This paper presents a combined work program of experimental testing and computational modelling on a cast MarBN material. To characterise and assess the fatigue performance of MarBN, an experimental program of high temperature low cycle fatigue (HTLCF) tests is conducted at a temperature of 600 °C. MarBN is found to give an increased stress range compared to previous P91 steel experiments, as well as considerable cyclic softening. To characterise the constitutive behaviour of the cast MarBN material, a recently developed unified cyclic viscoplastic material model is calibrated and validated across a range of strain-rates and strain-ranges, with good correlation achieved with the measured data throughout.
The Effect of Streamwise Tube Motion on the Unsteady Fluid Forces in a Normal Triangle Tube Array
Authors: El Bouzidi Salim , Hassan Marwan 
Published: November 2015

Fluidelastic instability is generally regarded as the most severe type of flow excitation mechanism. When this mechanism prevails, it could cause serious damage to tube arrays in a very short period of time. This mechanism is characterized by a critical flow velocity beyond which the tubes undergo unstable oscillations. Recently, a number of experimental investigations showed that it is possible to have instability in the streamwise direction; previously, it was believed that fluidelastic instability was only a concern in the direction transverse to the flow.
The purpose of this study is to characterize the flow in the channels surrounding a vibrating tube in a normal triangular bundle with P/d = 1.5. The tube is oscillating in the streamwise direction with a constant amplitude. Numerical simulations were conducted by solving the unsteady Reynolds Averaged Navier-Stokes equations (uRANS) cast in Arbitrary Lagrangian-Eulerian (ALE) form. The unsteady flow perturbation is estimated along the flow channel. The pressure perturbation is used to compute the streamwise unsteady force coefficients in the context of Chen’s model. The perturbation phase and decay are extracted and utilized in the framework of the Lever & Weaver model to study the stability of tube bundles due to tube motion in the streamwise direction.
Applying ASME and British Standard Welded Fatigue Methodologies to Thermal Fatigue Case Studies and Investigating Sensitivity to Fatigue Flaw Growth Models
Authors: Prueter Phillip E. , Brown Robert G. 
Published: November 2015

Predicting fatigue cracking at welded locations in fixed process equipment due to cyclic loading is of great interest to the chemical, petrochemical, and nuclear industries. Welded fatigue methodologies have been incorporated into both ASME and international pressure vessel Codes and Standards. These fatigue methodologies are based on welded fatigue tests. Some of the challenges associated with evaluating in-service equipment for susceptibility to fatigue failure are considering the overall scatter associated with the test data that forms the basis of the welded fatigue methodologies and using Code-based fatigue predictions to make practical recommendations relating to establishing inspection intervals and facilitating overall life cycle management. In this study, the Battelle Structural Stress welded fatigue methodology outlined in ASME Section VIII Division 2 is utilized. Additionally, the welded fatigue assessment techniques of British Standard PD 5500 are included for comparison.
In this paper, several case studies are investigated where transient thermal-mechanical finite element analysis (FEA) is used to develop fatigue predictions for several pieces of in-service equipment subjected to cyclic operation that experienced significant cracking in certain regions of the pressure boundary. These case studies focus on the thermal fatigue aspect of the observed cracking. In addition to Code-based fatigue methodologies, fracture mechanics calculations are performed to determine critical flaw sizes, and sub-critical fatigue flaw growth calculations are performed to investigate the propensity for a given initial flaw to propagate to critical dimensions. Furthermore, flaw propagation rate sensitivity to varying fatigue flaw growth models is quantified and discussed. This paper highlights several real-life examples of thermal fatigue cracking and how computational and analytical methods can be used to perform fatigue and flaw growth predictions to understand the root-cause of the observed damage and to determine the likelihood of fatigue crack propagation going forward.
My Pipes Are Corroding! When Should I Repair? Getting the Answers You Need for Maintaining Pipeline Integrity
Authors: Turnquist Michael 
Published: November 2015

This case study exhibits how groundbreaking inspection methodologies combined with innovative computational analysis practices demonstrate the value of conducting fitness-for-service (FFS) assessments on sectional piping. In this instance, a fitness-for-service assessment was performed on two sections of piping experiencing external corrosion at the pipe-to-elbow seam welds.
A full external scan and spot ultrasonic thickness (UT) readings were used to create the corroded geometry and verify accurate measurement of the remaining thicknesses in various corroded locations. This allowed for the actual corroded profiles to be accurately modeled using finite element analysis (FEA).
Complications were present when modeling the observed metal loss. Through the use of innovative finite element mesh generation practices, the actual measured corroded geometry was modeled without the need for over-conservative geometric simplification. A Level 3 FFS assessment was then performed in addition to a remaining life assessment based on observed corrosion rates. The result of this analysis was that the piping could remain in service for at least two additional years before needing repair.
Validation of Friction Model Parameters Identified Using the Inverse Harmonic Balance Method
Authors: Hadji Abdallah , Mureithi Njuki 
Published: November 2015

A hybrid friction model was recently developed by Azizian and Mureithi [1] to simulate the friction behavior of tube-support interaction. However, identification of the model parameters remains unresolved.
In previous work, the friction model parameters were identified using reverse the harmonic method, where the following quantities were indirectly obtained by measuring the vibration response of a beam: friction force, sliding speed of the force of impact and local displacement at the contact point.
In the present work, the simulation by the finite element method (FEM) of a beam clamped at one end and simply supported with the consideration of friction effect at the other is conducted. This beam is used to validate the inverse harmonic balance method and the parameters of the friction models identified previously.
Two static friction models (the Coulomb model and Stribeck model) are tested. The two models produce friction forces of the correct order of magnitude compared to the friction force calculated using the inverse harmonic balance method. However, the models cannot accurately reproduce the beam response; the Stribeck friction model is shown to give the response closer to experiments.
The results demonstrate some of the challenges associated with accurate friction model parameter identification using the inverse harmonic balance method. The present work is an intermediate step toward identification of the hybrid friction model parameters and, longer term, improved analysis of tube-support dynamic behavior under the influence of friction.
Cohesive Zone Modeling of Hydrogen Assisted Cracking in a 15-5 PH Steel and Comparison With Experiments
Authors: Bilotta Giovambattista , Arzaghi Mandana , Hénaff Gilbert , Benoit Guillaume , Moriconi Clara , Halm Damien 
Published: November 2015

Gaseous hydrogen substantially reduces fracture properties such as threshold stress intensity factor and crack growth resistance in the precipitation-hardened martensitic stainless steel investigated in this study. Fatigue crack propagation tests were performed on CT specimens under different atmospheres (hydrogen pressures from 0.09 to 40 MPa) on the Hycomat test bench, at the Pprime Institute in Poitiers, France. A strongly enhanced crack growth regime was identified at high hydrogen pressure and low-frequency loading. Crack growth rates obtained at a constant load under same pressure levels suggest that a combination of tensile stresses above a threshold (KIscc) and fatigue cycles contribute to the hydrogen embrittlement at the crack tip.
These experimental results were compared to the finite element simulation results obtained by a recently developed cohesive zone model at the crack tip. A specifically developed traction-separation law which is suitable to describe the gradual degradation of cohesive stresses under monotonic and cyclic loadings, and which is furthermore sensitive to the hydrogen concentration was used. The effects of the different testing conditions, in terms of loading frequency and hydrogen pressure, on the modeling results are discussed. It was shown that the model qualitatively predicts the detrimental influence of gaseous hydrogen on the crack growth rates.
Fatigue Monitoring and Assessment: Different Approaches Combined for Lifetime Extension Challenges
Authors: Gilman Tim , Gray Mark , Rudolph Jürgen , Heinz Benedikt 
Published: November 2015

For plant lifetime extension programs, several products provide a customized solution for thermal load monitoring and fatigue calculation. Requirements like the consideration of Environmentally Assisted Fatigue (EAF) effects or flexible plant (e.g. load follow) operation have a crucial impact on the engineering practice of a detailed fatigue assessment considering the realistically occurring loads.
Several fatigue monitoring products are available on the market, some with local instrumentation added and some with transfer function approaches using existing plant instrumentation. The regulator in Germany requires thermal loading to be evaluated as realistically as practical, and thus additional instrumentation is typically added to measure the thermal response close to the monitored location. Elsewhere, and specifically in the U.S., the regulator has not required the addition of instrumentation, and thus utilities typically do not choose to add instruments.
It is one purpose of the paper to explain in detail the different engineering approaches and the methodology of fatigue assessment, also under consideration of Environmentally Assisted Fatigue (EAF) and the calculation of the complete six terms stress tensor for given load-time histories. Considering the fatigue analysis of given input data (stress-time-histories) the comparability of fatigue calculations constitutes a challenging item. Recommendations will be given how to harmonize the approaches based on the technical and regulatory requirements.
Finally, the issue of design code based fatigue monitoring guidelines and approaches is discussed. In this context, the German Nuclear Safety Standard KTA 3201.4 is addressed.
Things to Concern for Finite Element Analyses
Authors: Shoji Yasumasa 
Published: November 2015

Recently FEA (Finite Element Analysis) is used in various engineering fields such as for design, verification, validation trouble-shooting and other applications. As the more users are treating FEA, the quality of analyses has become the larger issue.
Finite Element Method (FEM) is just a calculation method to reproduce physical phenomena, and it has functional limitation in nature. As the software becomes more and more user-friendly, the limitation is hidden in the operation. However, as the limitation still exists in principle, users must be aware of it when using the FEA software.
This paper will address about the issues that we are easily trapped in modeling, such as element selection, boundary conditions and other conditions.