bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhanced Creep Life Evaluations for Grade 91 Circumferential Weldments
Authors: Cohn Marvin J. 
Published: October 2017

The basic power piping creep life calculations consider the important variables of time, temperature and stress for the creep rupture properties of the unique material. Some engineering evaluations of remaining life estimate the applied stress as the design stress obtained from a conventional piping stress analysis. Other remaining life evaluations may assume that a conservative estimate of the applied stress is no greater than the hoop stress due to pressure. The creep rupture properties of the unique material are usually obtained from the base material creep rupture properties. The typical methodologies to estimate remaining life do not consider the actual applied stress due to malfunctioning supports, multiaxial stress effects, axial and through-wall creep redistribution, time-dependent material-specific weldment creep rupture properties, residual welding stresses, and actual operating temperatures and pressures.
It has been determined that the initiation and propagation of Grade 91 creep damage is a function of stress to about the power of 9 at higher applied stresses. There have been many examples of malfunctioning piping supports creating unintended high stresses. When the axial stress is nearly as high as the hoop stress, the applicable corresponding uniaxial stress for creep rupture life is increased about 30%. Multiaxial stress effects in circumferential weldments (e.g., when the axial stress is nearly as high as the hoop stress) can reduce the weldment creep life to less than 1/6th of the predicted life assuming a uniaxial stress or hoop stress due to pressure only.
Since 2012, the ASME B31.1 Code has required that significant piping displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity [1]. This paper discusses a strategy for an enhanced creep life evaluation of power piping circumferential weldments. Piping stresses can vary by a factor greater than 2.0. Consequently, the range of circumferential weldment creep rupture lives for a single piping system may vary by a factor as high as 40.
Although there is uncertainty in the operating times at temperatures and pressures, all of the weldments within the piping system have the same time, temperatures, and pressures, so the corresponding uncertainties for these three attributes are normalized within the same piping system. Since the applied stresses are the most important weld-to-weld variable within a piping system, it is necessary to have an accurate evaluation of the applied stresses to properly rank the creep rupture lives of the circumferential weldments. This methodology has been successfully used to select the lead-the-fleet creep damage in circumferential weldments over the past 15 years.
Hydrogen Isotope Permeation and Trapping in Additively Manufactured Steels
Authors: Karnesky Richard A. , Chao Paul , Buchenauer Dean A. 
Published: October 2017

Additively manufactured (AM) austenitic stainless steels are intriguing candidates for the storage of gaseous hydrogen isotopes because complex vessel geometries can be built more easily than by using conventional machining options. Parts built with AM stainless steel tend to have excellent mechanical properties (with tensile strength, ductility, fatigue crack growth, and fracture toughness comparable to or exceeding that of wrought austenitic stainless steel). However, the solidification microstructures produced by AM processing differ substantially from the microstructures of wrought material. Some features may affect permeability, including some amount of porosity and a greater amount of ferrite. Because the diffusivity of hydrogen in ferrite is greater than in austenite (six orders of magnitude at ambient temperature), care must be taken to retain the performance that is taken for granted due to the base alloy chemistry. Furthermore, AM parts tend to have greater dislocation densities and greater amounts of carbon, nitrogen, and oxygen. These features, along with the austenite/ferrite interfaces, may contribute to greater hydrogen trapping.
We report the results of our studies of deuterium transport in various austenitic (304L, 316, and 316L) steels produced by AM. Manufacturing by Powder Bed Fusion (PBF) and two different blown powder methods are considered here (Laser Engineered Net Shaping® (LENS®) and a Direct Laser Powder Deposition (DLPD) method with a higher laser power)). The hydrogen permeability (an equilibrium property) changes negligibly (less than a factor of 2), regardless of chemistry and processing method, when tested between 150 and 500 °C. This is despite increases in ferrite content up to FN = 2.7. However, AM materials exhibit greater hydrogen isotope trapping, as measured by permeation transients, thermal desorption spectra, and inert gas fusion measurement. The trapping energies are likely modest (<10 kJ/mol), but may indicate a larger population of trap sites than in conventional 300-series stainless steels.
Commentary on Recent Changes in ASME B31.3 Post Weld Heat Treatment Requirements and the Effectiveness of Weld Preheat
Authors: Prueter Phillip E. , Smith Katelyn J. , Macejko Brian , Shipley Kraig S. 
Published: October 2017

The 2014 Edition of ASME B31.3, Process Piping [1], introduced significant changes to the post weld heat treatment (PWHT) requirements for P-No. 1 carbon steel materials. In particular, PWHT is no longer a mandatory requirement for any wall thickness provided that multi-pass welding is employed for wall thicknesses greater than 5 mm (3/16 of an inch) and a minimum preheat of 95°C (200°F) is implemented for wall thicknesses greater than 25 mm (1 inch). Detailed fracture mechanics analyses have shown that the lack of a mandatory PWHT requirement for thicker P-No. 1 components may result in a significant increase in risk for brittle fracture failures due to near-yield level weld residual stresses. Given the concern throughout the pressure vessel and piping community regarding potential brittle fracture failures, this updated PWHT guidance is examined.
Impact testing requirements and exemption curves were introduced in the 1987 Addenda [2] of ASME Section VIII Division 1 (VIII-1) [3] in Paragraph UCS-66 and extended into ASME Section VIII Division 2 (VIII-2) [4]. During the VIII-2 rewrite in 2007 [5], the available technical and historical basis for the UCS-66 exemption curves was examined and improved to reflect modern fracture mechanics standards. The result of that effort was a systematic approach that can be modified for particular geometries and assumed flaws, if desired. The method used the most modern, fracture mechanics approach for welds in API 579-1/ASME FFS-1, Fitness-For-Service, (API 579) [6] based on the failure assessment diagram (FAD). As a result of explicitly accounting for weld residual stress, two separate sets of exemption curves are provided in VIII-2 [4]; one set for as-welded components and another set for PWHT components. In this paper, a similar approach is summarized to generate exemption curves by establishing newer as-welded and PWHT curves using the Fracture Toughness Master Curve (Master Curve) as documented in upcoming Welding Research Council (WRC) Bulletin 562 [7]. The increased propensity for brittle fracture in as-welded components versus PWHT components is clearly highlighted using this approach. The Master Curve, in conjunction with the elastic-plastic fracture mechanics employed in API 579 [6] provides a means to develop exemptions curves anchored in state-of-the-art fracture toughness technology that can be directly tied to different reference flaw sizes. Additionally, commentary on the appropriateness of the current ASME B31.3 [1] PWHT requirements is offered and the effectiveness of using weld preheat in lieu of PWHT as permitted in the National Board Inspection Code (NBIC) [8] is examined using simplified computational weld analysis.
Crack Growth Rates for Evaluating PWSCC of Thick-Wall Alloy 690 Material and Alloy 52, 152, and Variant Welds
Authors: Jenks Amanda R. , White Glenn A. , Crooker Paul 
Published: October 2017

Due to the widespread use of thick-wall Alloy 690 and its corresponding weld metals Alloys 52 and 152 in various replacement, repair, mitigation, and new plant pressurized water reactor (PWR) applications, there is a need in the industry for an equation or methodology for predicting crack growth rates (CGRs) for primary water stress corrosion cracking (PWSCC) of these materials. Although there have been no indications of PWSCC reported in these materials in PWRs to date, there is the possibility that such an indication could be reported in the future or the possibility that a manufacturing defect could be conservatively interpreted as PWSCC. Crack growth rates are thus needed to support leaving such an indication in service for a justified period of time. In addition, safety assessments of hypothetical PWSCC flaws require prediction of PWSCC crack growth rates for these materials, so as to set appropriate inspection intervals. Current inspection intervals were selected to be conservative pending a consensus CGR model.
Example applications for which PWSCC CGRs are needed to determine appropriate reexamination intervals include Alloy 690 penetration nozzles attached to the inside of the reactor pressure vessel top head with Alloy 52/152/variant welds, and Alloy 52/152/variant weld inlays and onlays used to mitigate Alloy 82/182 piping butt welds.
An international PWSCC CGR Expert Panel was organized by EPRI, with the participation of national laboratories sponsored by the US Nuclear Regulatory Commission (NRC),1 to support the development of such PWSCC CGR equations. A database of over 500 Alloy 690 CGR data points and over 130 Alloy 52/152 CGR data points using thick-wall compact tension specimens from seven research laboratories was compiled, scored for data quality, and assessed to determine the effects of numerous parameters such as temperature, crack-tip stress intensity factor, yield strength, and crack orientation. The methodology and results of these statistical analyses are presented in this paper. It should be noted that this paper provides a status of the ongoing work, which is planned for completion in late 2017.
A Detailed Proposal for an Oxidation Test for Flexible Graphite
Authors: Bond Stephen 
Published: October 2017

While the oxidation of graphite in gaskets is a well known phenomenon it is often poorly quantified and the factors affecting it not always well known. There are some standard tests that can be used to determine graphite quality. While many of these material standards concentrate on the compositional impurities (sulfur, chlorides etc.) and the ash content; these are indicative of other properties and they are no real indication of oxidation performance. Recently, some test methods have been published that suggest a method for measuring oxidation performance; however, they have some shortcomings or constraints.
Using modern, standard TGA (ThermoGravimetric Analysis), the work presented in this paper aims to provide a more detailed standard test that can be used to measure the oxidation rate of graphite in flowing air for a given set of time and temperature conditions. The paper will show what other conditions are critical and which are less significant in specifying a standard test. This will lead to the presentation of a suggestion for an improved standard test that builds on and further codifies the tests currently published.
Finally, this paper will show the oxidation rates of a variety of different commercial graphite grades to illustrate the vast range of oxidation rates that are possible from the various grades of graphite.
Additive Manufacturing of Pressure Vessels (With Plating)
Authors: McNelly Brendan P. , Hooks Richard L. , Setzler William R. , Hughes Craig S. 
Published: October 2017

Additive manufacturing (AM) allows for product development with light weight, fewer machining constraints, and reduced costs depending on the application. While AM is an emerging field, there is limited research on the use of AM for pressure vessels or implementation in high stress environments. Depending on the design approach and limitations of traditional material-removal fabrication techniques, AM parts can achieve high strength-to-weight ratios with reduced manufacturing efforts. Coupling AM with alternative metal and composite materials allows for unique designs that have high strength-to-weight ratios for pressure-based applications. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has conducted research on a number of these composite designs, focusing on the use of carbon fiber or metal plating with the AM materials.
Before implementing AM in field tested prototypes, JHU/APL performed strength limitation tests on AM pressure vessels (PVs) in the laboratory to prove their effectiveness. PVs constructed with varying thicknesses and coating techniques were divided into three groups, each with a uniform wall thickness that provided a congruent surface area to withstand higher pressures. These PVs were then paired with one of three coating/plating technologies, forming a trade matrix of varying AM thicknesses and plating techniques. Once fabricated and plated, these test PVs were hydro-statically tested at increasing pressure levels. This pressure testing demonstrates that the use of AM to create PVs, when paired with specific plating techniques, can result in structures with significant strength capabilities at lighter than normal PV weights.
Furthermore, JHU/APL has begun to test the AM PVs in a number of research projects. Such testing is desired because these unique parts can be easily manufactured in shapes and volumes that were previously unattainable through common manufacturing techniques. AM parts are now commonly used in air-frames; however, in higher pressure underwater scenarios AM’s capabilities are unproven. JHU/APL has begun to apply this new and emergent field to the effective design of AM PVs, which can play a significant role in the field of underwater vehicles and similar projects.
Simulation of the Interaction Between a Slender Flexible Cylinder and an Axial High-Speed Air Flow
Authors: Degroote Joris , Hertens Ine , Osman Akil , Vierendeels Jan 
Published: October 2017

This research analyzes the interaction between fibers and the air jets that are used to accelerate them in fiber processing industries. Typically, supersonic flow is used to achieve sufficiently high thread speeds. However, this flow contains shocks and expansions, resulting in large longitudinal variations in force on the thin and flexible thread. Consequently, a complex fluid-structure interaction (FSI) occurs between the supersonic air flow and the thread.
In this research, the fluid-structure interaction between a supersonic air flow and a thread is studied numerically using three-dimensional simulations. The thread is represented by a smooth and flexible cylindrical body. The displacement of the thread is calculated for a given traction on its surface using a finite element structural dynamics code. The compressible flow around the thread is calculated using a finite volume computational fluid dynamics (CFD) code, using the arbitrary Lagrangian-Eulerian (ALE) framework to account for the thread deformation.
In these partitioned simulations, the kinematic and dynamic equilibrium conditions on the fluid-structure interface are satisfied using a coupling algorithm. Two coupling algorithms are compared and the influence of numerical parameters is investigated. The fluid-structure interaction simulations reveal transversal running waves in the thread. By comparing the speed of these waves with the propagation speed of the shock waves in the tube, it can be concluded that these phenomena are not related.
An Investigation Into the Lifetimes of Solid and Hollow Fatigue Endurance Specimens Using Cyclic Hardening Material Models in Finite Element Analysis
Authors: Gill Peter , James Peter , Currie Chris , Madew Colin , Morley Andrew 
Published: October 2017

This paper considers finite element analyses that have been performed to support a fatigue endurance testing programme. This programme is aimed at understanding the influence of Light Water Reactor (LWR) environment on the fatigue life of austenitic steels under thermo-mechanical loading. Testing has typically been performed on membrane loaded fatigue specimens under isothermal conditions. However, a new test facility at Amec Foster Wheeler has been developed to enable hollow specimens to be subjected to thermal and mechanical loading for a range of thermal cycles.
This work has provided a theoretical underpinning of the observed difference in lifetimes between pressurised and unpressurised specimens, and therefore provides a means of mapping data from hollow specimen testing back to solid specimen data. The parameter used to quantify these differences was the Von Mises equivalent strain. This accounts for the additional contributions from radial and hoop strains (which come about due to the internal pressure) and therefore gives enhanced strain amplitude which is fed into the S–N curve. By comparing unpressurised and pressurised lifetimes this way, a direct comparison could be made with test results. This serves two purposes; one is to provide mechanistic understanding of the difference in lifetimes. Secondly the approach will develop an assessment methodology to treat hollow specimens so a direct comparison can be made to bar specimen S–N curves. To provide further confidence in this mechanism being the dominant factor behind this difference, an independent calculation was carried out using multi-axial fatigue life models, namely Brown-Miller and Fatemi-Soci. Good agreement was observed with these models indicating that the Von Mises strain parameter was a valid parameter to characterise the multi-axial strain behaviour at the initiation site.
The increase in Von Mises strain between pressurised and unpressurised specimens was found to be a factor of 1.20 on average. This was slightly less than the experimentally derived strain differences of about 1.25. However, there was another aspect of the test results that required investigation. It has been observed from tests that the hollow specimens had a tendency to fail at a region just after the shoulder, which is where the specimen increases in thickness. Upon inspection of the plastic strains from FEA, it became clear that there was a small increase in strain on the inside surface due to this geometric feature of the specimen. The strain at the high strain region was a factor of 1.025 higher than the centre of the specimen after shakedown. Therefore, when the two effects of geometry and incremental plasticity are combined, the agreement between experiment and FEA is better. There is still a slight difference between the observed factor and the predicted factor, and reasons for this discrepancy are discussed in the paper.
Thermal Stress Ratchet Check in Piping Analysis
Authors: Adibi-Asl R. , Noban M. , Chen E. 
Published: October 2017

The ASME B&PV Code, Section III NB-3600 provides a requirement to avoid thermal stress ratcheting under thermal transient conditions. The ratchet check in this code is based on calculating the range of temperature difference between the outside and inside surfaces of the pipe for pairs of load sets. The calculated temperature ranges are then compared with a code equation which is a function of pressure, geometry and material properties.
This paper reviews the thermal stress ratchet requirements in ASME Section III Subsection NB with respect to piping analysis. A simplified formula is proposed for thermal stress ratchet check which eliminates the difficulties and ambiguities associate with the formulation provided in the NB-3600 code. The paper also investigates temperature distributions for various components (including flat plate and pipe) by performing heat transfer analysis. The results are compared with the ratchet limit. Using plate solutions to estimate the temperature range of pipe could sometimes give non-conservative results.
Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs: ASME B&PV Code Section III Primary Stress Re-Evaluation Accounting for the Presence of Hydrogen Flakes
Authors: Dulieu Pierre , Lacroix Valéry 
Published: October 2017

During the 2012 outage at Doel 3 and Tihange 2 Nuclear Power Plants, a large number of quasi-laminar indications were detected, mainly in the lower and upper core shells of the Reactor Pressure Vessels (RPVs). The observed indications could subsequently be attributed to hydrogen flaking induced during the component manufacturing process. As a consequence, both units remained core unloaded pending the elaboration of an extensive evaluation demonstrating that they can be safely operated.
The Structural Integrity Assessment of the RPVs, through the Flaw Acceptability Assessment, aimed at demonstrating that the identified indications do not jeopardize the integrity of the reactor vessel in all operating modes, transients and accident conditions. This demonstration has been done on the basis of a specific methodology inspired by the ASME B&PV Code Section XI procedure but adapted to the nature and the number of indications found in the Doel 3 and Tihange 2 RPVs.
As requested by Article IWB-3610(d)(2) of ASME B&PV Code Section XI, one of the parts that have to be addressed through the Flaw Acceptability Assessment is the Primary Stress Re-Evaluation assuming local area reductions of the pressure retaining membrane i.e., of the core shells, due to presence of the flaws. This is performed using the limit analysis provided by Article NB-3228.1 of the ASME B&PV Code Section III. Results are compared to those using the plastic analysis of Article NB-3228.3. The acceptance criterion that needs to be verified is that the calculated collapse pressure should be more than 1.5 times the design pressure.
The paper presents the 2D conservative approach developed in order to carry out this analysis dealing with large number and high density of flaws. Furthermore, the paper validates this 2D conservative methodology through detailed 3D XFEM elastic-plastic calculations.
Investigations of In-Plane Fluidelastic Instability in a Multi-Span U-Bend Tube Bundle: Tests in Air Flow
Authors: Feenstra Paul , Sawadogo Teguewinde , Smith Bruce , Janzen Victor , Cothron Helen 
Published: October 2017

The tubes in the U-bend region of a recirculating type of nuclear steam generator are subjected to cross-flow of a two-phase mixture of steam and water. There is a concern that these tubes may experience flow-induced vibration, including the damaging effects of fluidelastic instability.
This paper presents an update and results from a series of flow-induced vibration experiments performed by Canadian Nuclear Laboratories for the Electric Power Research Institute (EPRI) using the Multi-Span U-Bend test rig. In the present experiments, the main focus was to investigate fluidelastic instability of the U-tubes subjected to a cross-flow of air. The tube bundle is made of 22 U-tubes of 0.5 in (12.7 mm) diameter, arranged in a rotated triangular configuration with a pitch-over-diameter ratio of 1.5. The test rig could be equipped with variable clearance flat bar supports at two different locations to investigate a variety of tube and support configurations.
The primary purpose of the overall project is to study the effect of flat bar supports on ‘in plane’ (‘streamwise’) instability in a U-tube bundle with realistic tube-to-support clearances or preloads, and eventually in two-phase flow conditions. Initially, the test rig was designed for tests in air-flow using an industrial air blower. Tests with two-phase Freon refrigerant (R-134a) will follow.
This paper describes the test rig, experimental setup, and the challenges presented by simulating an accurate representation of current steam generator designs. Results from the first series of tests in air flow are described.