bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of PCC-2 in Real World Situations
Authors: Taagepera Jaan , Magyar Chad , Greenfield Matt , Tyson Nathan
Published: May 2012

This paper provides examples of the application of repair procedures described in ASME Post Construction Committee’s PCC-2, Repair of Pressure Equipment and Piping [1] in an oil refinery environment. In one case, the use of a freeze plug is described. This plug was created on a medium diameter water line in order to replace a stuck valve. Another case deals with leaks on a small bore connection off a large high pressure process pipe. This leak was temporarily repaired using a welded sleeve. Another situation involves the patching of a critical water pipe with a through wall leak. This large diameter line is critical to the operation of two refinery units. Thus, its rapid repair was very beneficial to refinery operations. This repair also consisted of a welded sleeve.
CFD Analyses of BWR Steam Plenum to Investigate a Possible Cause for Steam Dryer Outer Hood Visual Examination Anomalies
Authors: Sowah Sandra , Sommerville Daniel V. , Belley Benoit P.
Published: May 2012

A Computational Fluid Dynamics (CFD) model of the steam dome region of a Boiling Water Reactor (BWR) vessel was created to investigate anticipated flow patterns in the outlet plenum. Steady state and transient simulations were performed to investigate the hypothesized existence of stationary vortices at the entrance of each Main Steam Nozzle. These hypothesized stationary vortices are believed to be the cause of wear patterns observed on some BWR steam dryers and to contribute a low frequency (∼15–25 Hz) fluctuating pressure load on the outer hoods of steam dryers. Results of the simulations and available in-vessel visual inspection data support the hypothesis of the presence of the stationary vortices in each Main Steam Nozzle.
Investigation of Differences in the Finite Element Solution of a Sample Fatigue Cumulative Usage Factor Calculation Problem
Authors: Stevens Gary L. , Rathbun Howard J. , Gilman Timothy D.
Published: May 2012

In November 2009, the Electric Power Research Institute (EPRI) assembled an Advisory Panel on Environmental Fatigue, consisting of various industry and vendor participants, whose charter is to provide insight and recommendations to EPRI (including the Pressurized Water Reactor (PWR) Materials Reliability Program (MRP), the Boiling Water Reactor Vessel and Internals Project (BWRVIP), and the Advanced Nuclear Technology (ANT) organizations) on conducting additional work and providing guidance associated with environmental fatigue. The goal of the panel is to identify areas in environmentally assisted fatigue (EAF) formulations, or application of the EAF formulations, contained in regulations and the ASME Code that may cause application difficulties, to determine where new research efforts are necessary to provide guidance or alternatives to application of these formulations, and to investigate industry design problems with a goal of identifying solutions to obtain near- and long-term relief. The Advisory Panel consists of various industry and vendor participants that have been engaged in the environmental fatigue topic over the past several years. As a part of the activities investigated by the Expert Panel, in 2010, a sample problem was defined for use in testing the application of proposed ASME Code Cases for evaluation of EAF using the EAF multiplier (Fen) correction factor methodology. The sample problem was provided to multiple industry organizations and regulators to be solved so that differences in approaches and methods applied to the sample problem could be identified and understood. The intent of this effort was to refine the Fen methodology to clarify issues that have been previously identified and its practical application to typical industry fatigue evaluation problems. NRC staff elected to participate in solving the sample problem and comparing solutions generated by the other participating organizations in order to more fully understand the issues with fatigue calculation methodologies, as well as to provide input and develop consensus on the evaluation approaches. The sample problem represents a simplified form of a traditional reactor pressure vessel-type evaluation for transient thermal stress analysis and fatigue cumulative usage factor (CUF) calculation of a representative piping component evaluated in accordance with ASME Code, Section III, Subarticle NB-3200 methods. This paper describes detailed investigation of differences between two solutions to the Expert Panel sample problem. This investigation involves comparisons of results from the initial finite element solution for thermal and pressure stresses (using different finite element software packages), to the calculation of CUF (both with and without EAF effects). Observations regarding differences in results and the reasons for those differences are identified and discussed. Recommendations for eliminating these differences are also made.
Investigation of Discrete Out-of-Plane Waviness in Composite Wind Turbine Blades Using Ultrasonic Nondestructive Evaluation
Authors: Chakrapani Sunil Kishore , Dayal Vinay , Barnard Daniel , Hsu David
Published: May 2012

With the need for larger and more efficient wind turbine blades, thicker composite sections are manufactured and waviness becomes difficult to control. Thus, there is a need for more effective and field implementable NDE. In this paper we propose a method of detection and quantification of waviness in composite wind turbine blades using ultrasonics. By employing air coupled ultrasonics to facilitate faster and easier scans, we formulated a two step process. Detection was performed with single sided air coupled ultrasonics, and characterization was performed with the help of high frequency contact probes. Severity of the wave was defined with the help of aspect ratio, and several samples with different aspect ratio waves were made. A finite element model for wave propagation in wavy composites was developed, and compared with the experimental results.
Characterisation of the Residual Stress Field and Mechanical Properties of a Narrow-Gap Girth-Welded Stainless Steel Pipe and Subsequent Application to a Numerical Model
Authors: McCluskey Robert J. A. , Sherry Andrew H. , Goldthorpe Martin R.
Published: May 2012

Girth-butt welds are used to join sections of stainless steel pipe in the primary circuit of Pressurised Water Reactors. The welding process creates residual stress fields across the weldment, which can contribute to the crack driving force when a defect is present. Assessment procedures account for such defects, enabling safety justifications to be made for continued operation of nuclear power plant. Such procedures require the size and nature of the residual stress field to be determined in order to make reliable structural integrity assessments. This paper describes the investigation of the residual stress field and fracture behaviour of a recently developed narrow-gap 304-stainless steel girth-butt weld in a primary circuit pipe. Two residual stress measurement techniques, Neutron Diffraction (ND) and incremental Deep Hole Drilling (iDHD), were used to measure the original residual stress field in the pipe weld. A second pipe weld specimen was used to fabricate tensile and fracture toughness specimens from which the mechanical properties of the weld material were determined. The residual stress and mechanical test data were used to develop numerical models of the pipe weld containing a postulated circumferential defect under an applied axial load. The numerical simulation results were applied within a failure assessment diagram, comparing different interaction parameters on the prediction of component failure load.
Creep-Fatigue Behavior in Ferritic-Martensitic Steels
Authors: Li Meimei , Majumdar Saurin , Natesan Ken
Published: May 2012

Ferritic-martensitic steels are the lead structural materials for next-generation nuclear energy systems. Due to increased operating temperatures required in advanced high-temperature reactor concepts, the high temperature performance of structural alloys and reliable high temperature structural design methodology have become increasingly urgent issues. Ferritic-martensitic steels experience significant cyclic softening at high temperatures, and this cyclic softening behavior affects consecutive stress relaxation response during hold time under creep-fatigue loading. It is found that the stress relaxation response during hold of the mod.9Cr-1Mo steel can be accurately described by a stress relaxation model. The creep damage associated with the stress relaxation during hold time can then be accurately calculated using the stress relaxation data and creep rupture data. It is shown that the unit creep damage per cycle in mod.9Cr-1Mo steel decreases considerably with increasing number of cycles due to cyclic softening, and the creep damage is sensitive to the initial stress of stress relaxation. Proper evaluation of the creep-fatigue damage in mod.9Cr-1Mo steel must consider the cyclic softening effect and its associated variations in creep damage from stress relaxation during the hold time.
Flaw Investigation in a Multi-Layer, Multimaterial Composite: Using Air-Coupled Ultrasonics
Authors: Livings Richard A. , Dayal Vinay , Barnard Dan J. , Hsu Dave K.
Published: May 2012

Ceramic tiles are the main ingredient of a multi-layer multi-material composite being considered for the modernization of tank armors. The high stiffness, low attenuation, and precise dimensions of these uniform tiles make them remarkable resonators when driven to vibrate. Defects in the tile, during manufacturing or after usage, are expected to change the resonance modes. The comparison of a pristine tile/lay-up and a defective tile/lay-up will thus be a quantitative damage metric. This study is aimed at examining the vibration modes of the tiles and the composite lay-up and using these vibrations to detect and characterize defects.
Case History Using Advanced Analysis to Evaluate Fitness-for-Service of Cyclic Vessels in the Petrochemical Industry
Authors: Brown Robert G. , Dewees David J.
Published: May 2012

Provided in this paper is a case history that highlights use of advanced numerical analysis techniques to assess the Fitness-for-Service of cyclic pressure vessels using API 579-1/ASME FFS-1 (API 579) [1]. The components were subject to repeated thermal and pressure loadings which resulted in cracking of the base material of these components. A detailed level 3 FFS assessment was performed to assess potential for brittle fracture, determine critical flaw dimensions and evaluate the structural integrity of engineered repairs. The case study demonstrates the value of advanced numerical analysis to substantiate critical run-repair-replace decision making for pressure containing equipment. Detailed simulation of Weld Residual Stress (WRS) and local Post-Weld Heat Treatment (PWHT) showed that the local PWHT performed in the field was ineffective at reducing residual stress and highlights the need for more engineering of PWHT layouts and procedures, particularly for cases where stress corrosion cracking or brittle fracture are limiting design/operating considerations. The results also show how advanced analysis can be used to gain further insight into structural behavior in order to validate more simple methods that support practical decision-making related to fitness-for-service assessments going forward. Fatigue life predictions from a strain-life approach are also compared to ASME Section VIII, Division 2 [2] (S8D2). In addition, a brief comparison of these fatigue analysis methodologies is provided. The results are framed in terms of practical field experience obtained by periodic UT shear wave inspection of 16 identical vessels over a 10 year operating history.
Typical Patterns, Atypical Events, and Uncertainty in Complex Systems
Authors: Amidan Brett G. , Ferryman Thomas A.
Published: May 2012

The power grid is a complex system. Multiple quantities are measured from hundreds of locations, at rates up to 30 Hz. There are both correlated and uncorrelated variables. Powerful methods are needed to examine this large amount of data and better understand the complex system, and in the case of the power grid, identify imminent adverse events, such as blackouts. These methods need to sift through any multicollinearity among the variables, account for the random uncertainty that is present within each variable, and focus on practical differences as defined by domain experts in addition to statistical differences. These methods will then help the user to better understand the complex system by uncovering the hidden gems within the data. These gems include identification of the uncertainty, characterization of the typical patterns, and the discovery of atypical events. This paper will discuss the intricate methods used to explore the data, and the novel displays used to communicate the findings. This paper will also delve into the exploration of other complex systems, like aviation safety, using similar methods.
Case History Fitness-for-Service Assessment of Cyclic Catalytic Reformer Motor Operated Valves in the Petrochemical Industry
Authors: Carr Nick A. , Shipley Kraig S. , Dewees David J.
Published: May 2012

Reactors of cyclic catalytic reformers require catalyst regeneration about every 7 days (∼50 cycles per year). To facilitate the in situ regeneration, large diameter motor operated valves (MOV) are used (typically Class 600 NPS 8 to NPS 16 API 600 gate block valves). Double block-n-bleed arrangements of the MOVs are used to assure isolation of the 350 psig 960°F process and regeneration media. The regeneration MOVs will be closed and in isolation for up to 4 days and can reach temperatures close to ambient depending on their distance from the process flow. Once the MOVs are swung open, the valve body quickly transitions from ambient temperature to 960°F over a matter of minutes. Such an extreme thermal shock has historically led to a number of cracks in the MOV valve bodies. With each unit having over 50 MOVs, it becomes expensive and time consuming to open every MOV at a scheduled turnaround, inspect, and repair any cracking noticed.
Issues Associated With Safe Packaging and Transport of Nanoparticles
Authors: Smith Allen C. , Gupta Narendra
Published: May 2012

Nanoparticles have long been recognized a hazardous substances by personnel working in the field. They are not, however, listed as a separate, distinct category of dangerous goods at present. As dangerous goods or hazardous substances, they require packaging and transportation practices which parallel the established practices for hazardous materials transport. Pending establishment of a distinct category for such materials by the Department of Transportation, existing consensus or industrial protocols must be followed. Action by DOT to establish appropriate packaging and transport requirements is recommended.
Containment Vessel Temperature for Pu-238 Heat Source Container Under Ambient, Free Convection and Low Emissivity Cooling Conditions
Authors: Smith Allen C. , Gupta Narendra
Published: May 2012

The EP-61 primary containment vessel of the 5320 shipping package has been used for storage and transportation of Pu-238 plutonium oxide heat source material. For storage, the material in its convenience canister, called EP-60, is placed in the EP-61 and sealed by two threaded caps with elastomer O-ring seals. When the package is shipped, the outer cap is seal welded to the body. While stored, the EP-61s are placed in a cooling water bath. In preparation for welding, several containers are removed from storage and staged to the welding booth. The significant heat generation of the contents, and resulting rapid rise in component temperature necessitates special handling practices. The test described here was performed to determine the temperature rise with time and peak temperature attained for an EP-61 with 203 watts of internal heat generation, upon its removal from the cooling water bath.
Case Study of Certification of Small Quantities of RAM: Comparison With SGQ Concept
Authors: Abramczyk Glenn , Shuler James , Nathan Steven J. , Smith Allen C.
Published: May 2012

The Small Gram Quantity (SGQ) concept is based on the understanding that small amounts of hazardous materials, in this case radioactive materials, are significantly less hazardous than large amounts of the same materials. The essential functional requirements for RAM packaging are containment of the material, ensuring sub-criticality, and ensuring that the radiation hazard of the package, as represented by the radiation dose for the package, is within the regulatory limits. Knowledge of the composition of the material being shipped is also required. By placing the contents in a containment vessel which is helium leaktight, and limiting the mass so that subcriticality is ensured, the first two requirements are readily met. Some materials emit sufficiently strong photon radiation that a small amount of material can yield a large dose rate. Foreknowledge of the dose rate which will be present for a proposed content is a challenging issue for the SGQ approach. Issues associated with certification for several cases of contents which fall within the SGQ envelop are discussed.
Seismic Analysis Issues in Design Certification Applications for New Reactors
Authors: Morante Richard , Miranda Manuel , Xu Jim
Published: May 2012

The licensing framework established by the U.S. Nuclear Regulatory Commission under Title 10 of the Code of Federal Regulations (10 CFR) Part 52, “Licenses, Certifications, and Approvals for Nuclear Power Plants,” provides requirements for standard design certifications (DCs) and combined license (COL) applications. The intent of this process is the early resolution of safety issues at the DC application stage. Subsequent COL applications may incorporate a DC by reference. Thus, the COL review will not reconsider safety issues resolved during the DC process. However, a COL application that incorporates a DC by reference must demonstrate that relevant site-specific design parameters are within the bounds postulated by the DC, and any departures from the DC need to be justified. This paper provides an overview of several seismic analysis issues encountered during a review of recent DC applications under the 10 CFR Part 52 process, in which the authors have participated as part of the safety review effort.
OSIRHYS IV Project, 700 Bar On-Board Composite Pressure Vessel Mechanical Behaviour Prediction With Uncertainties Knowledge
Authors: Villalonga Ste´phane , Kempeneers Martin , Saffre´ Philippe , Renard Jacques , Halm Damien , Nony Fabien
Published: May 2012

Hydrogen storage remains a key issue for the high scale deployment of fuel cell applications. Gaseous hydrogen storage at high pressure with type IV vessels is the best technology. But it is necessary to reach a significant cost reduction of these storage systems. An optimization of the composite structure can be reached by numerical simulation. The goal of the OSIRHYS IV project is to develop and validate models and methods for composite high pressure design and optimization with behavior uncertainties knowledge. It was decided to limit this study to a particular topology, material and winding process. First burst simulations have been performed and results of linear static computations have been compared to experimental data. The numerical simulation models are compared with regards to vessel component masses, burst pressure, burst mode and local displacements. Results show that linear static analyses using axisymmetric and volume FE models could already predict with a reasonable accuracy the radial behavior of the tank in the case of a safe burst mode. Nevertheless, improvements of partner models are needed to reach better agreement with test data. These improvements need to be based on material and vessel geometry knowledge, behavior modelling and the FE model.
Sensitivity Study of Shakedown Assessments Using Probabilistic Methods
Authors: Vlaicu Dan
Published: May 2012

In this work is presented the development of generic models that emulates the behavior of finite element models under cyclic loads, with the probabilistic representation based on samplings of base-model data for a variety of test cases. The base-model is a pipe with a notch subjected to pressure loading translated into hoop stress and the thermal loading is applied as a cyclic load through the pipe thickness. The probabilistic method takes variations of the nonlinear material properties, loading conditions, and geometrical dimensions, whereas the response variables are defined in terms of stress intensity for the static analyses, and the total accumulated strain as well as the strain ranges translated into the number of allowable load cycles by using the Manson’s common slope method define the response variables for the nonlinear calculations. Bree diagram converted into the Interaction Diagram is used to correlate the results of the nonlinear cyclic analyses and the ASME Code limits for primary and secondary loads from linear elastic analyses, whereas the definition of the shakedown towards of the steady cycle is identified in terms of the local and global components of strain. Furthermore, the Bayesian statistics expands the results of the nonlinear cyclic analysis by combining the interpretations of statistical results to scenarios either not accessible by the frequentist statistics or better served by complex stochastic models.
Proposed ASME Section III Code Case: Reduction of NDE Weld Repairs
Authors: McCracken Steven L. , Swilley Steven M. , Sekinuma Yoshihisa , Hedden Owen , Cowfer Dave , Ranganath Sampath
Published: May 2012

Section III of the ASME Boiler and Pressure Vessel Code requires radiographic testing (RT) of pressure boundary welds. RT is performed to detect flaws that might be created in welds as they are fabricated. Current Section III acceptance standards require rejection and repair of flaw indications characterized as cracks, lack of fusion, or incomplete penetration regardless of the size of the indication or the structural significance of such indications on fitness for service (FFS). The current Section III requirements have been effective in meeting the design objective of preventing pressure boundary failures. However, the rules are sufficiently conservative that not only are structurally significant flaws excluded, but they also exclude more benign indications that have no impact on structural integrity. This approach has resulted in repairs for even minor flaws that have no FFS impact. In addition to the cost of performing these unnecessary repairs, the repairs may have contributed to service induced cracking because of the higher residual stresses from the repair. Clearly, there is a need to revisit the Section III inspection and repair rules so as to distinguish between structurally unacceptable flaws and benign flaws that have no FFS impact. This paper describes the technical basis for the proposed Section III Code Case that uses the FFS approach to eliminate the need for weld repairs for minor flaws that have been shown to have no structural impact. Specifically, the Code Case will provide the option to use qualified volumetric inspection to size the flaw indications accurately and define acceptance criteria to determine flaw sizes that are judged to have little structural significance. In addition to describing the requirements of the proposed Code Case, this paper also describes the technical basis for the flaw acceptance criteria and the results of ultrasonic (UT) qualification testing to demonstrate the capability to detect and characterize fabrication flaw indications.
Development of In Situ Techniques for Torsion and Tension Testing in Hydrogen Environment
Authors: Wang John Jy-An , Ren Fei , Zhang Wei , Feng Zhili , Anovitz Lawrence , Chen Zhe , Xu Hanbing
Published: May 2012

Reliability of hydrogen pipelines and storage tanks is significantly influenced by the mechanical performance of the structural materials exposed to the hydrogen environment. Fracture behavior and fracture toughness are of specific interest since they are relevant to structural integrity. However, many conventional fracture testing techniques are difficult to be realized under the presence of hydrogen. Thus it is desired to develop novel in situ techniques to study the fracture behavior of structural materials in hydrogen environments. In this study, two special testing apparatus were designed to facilitate in situ fracture testing in H2. In addition to a multi-notch tensile fixture, a torsional fixture was developed to utilize an emerging fracture testing technique, Spiral Notch Torsion Test (SNTT). The design concepts will be discussed. Preliminary in situ testing results indicated that the exposure to H2 significantly reduces the fracture toughness of 4340 high strength steels by up to 50 percent. Furthermore, SNTT tests conducted in air demonstrated a significant fracture toughness reduction in samples subject to simulated welding heat treatment using a Gleeble machine, which illustrated the effect of welding on the fracture toughness of this material.
NRC/EPRI Residual Stress Validation Program Phase I: Experimental Specimen Modeling and Measurement
Authors: Broussard J. , Crooker P.
Published: May 2012

The US Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) are working cooperatively under a memorandum of understanding to validate welding residual stress predictions in pressurized water reactor primary cooling loop components containing dissimilar metal welds. These stresses are of interest as DM welds in pressurized water reactors are susceptible to primary water stress corrosion cracking (PWSCC) and tensile weld residual stresses are one of the primary drivers of this stress corrosion cracking mechanism. The NRC/EPRI weld residual stress (WRS) program currently consists of four phases, with each phase increasing in complexity from lab size specimens to component mock-ups and ex-plant material. This paper describes the Phase 1 program, which comprised an initial period of learning and research for both FEA methods and measurement techniques using simple welded specimens. The Phase 1 specimens include a number of plate and cylinder geometries, each designed to provide a controlled configuration for maximum repeatability of measurements and modeling. A spectrum of surface and through-wall residual stress measurement techniques have been explored using the Phase 1 specimens, including incremental hole drilling, ring-core, and x-ray diffraction for surface stresses and neutron diffraction, deep-hole drilling, and contour method for through-wall stresses. The measured residual stresses are compared to the predicted stress results from a number of researchers employing a variety of modeling techniques. Comparisons between the various measurement techniques and among the modeling results have allowed for greater insight into the impact of various parameters on predicted versus measured residual stress. This paper will also discuss the technical challenges and lessons learned as part of the DM weld materials residual stress measurements.
On the Use of Material-Dependent Damping in ANSYS for Mode Superposition Transient Analysis
Authors: Nie Jinsuo , Wei Xing
Published: May 2012

The mode superposition method is often used for dynamic analysis of complex structures, such as the seismic Category I structures in nuclear power plants, in place of the less efficient full method, which uses the full system matrices for calculation of the transient responses. In such applications, specification of material-dependent damping is usually desirable because complex structures can consist of multiple types of materials that may have different energy dissipation capabilities. A recent review of the ANSYS manual for several releases found that the use of material-dependent damping is not clearly explained for performing a mode superposition transient dynamic analysis. This paper includes several mode superposition transient dynamic analyses using different ways to specify damping in ANSYS, in order to determine how material-dependent damping can be specified conveniently in a mode superposition transient dynamic analysis.
Use of LBB Methodology to Support the Transition Break Size Concept
Authors: Nestell James E. , Rackiewicz David W.
Published: May 2012

The design basis for a loss of coolant accident in nuclear power plants has previously been based on the assumption that the largest size coolant pipe instantaneously undergoes a double ended “guillotine” break (DEGB) and the resulting loss of water must be mitigated by an emergency core cooling system (ECCS) to maintain core cooling after shutdown. The U.S. Nuclear Regulatory Commission (NRC) is close to allowing a risk-informed design basis break size, called the Transition Break Size (TBS), to be used for LOCA break size assumptions for ECCS design. The TBS approach will require full safety redundancy for an ECCS system sized to handle a break of the next largest reactor coolant pipe size (rather than the largest reactor coolant pipe size), and it will allow relaxed system redundancy requirements for handling the largest pipe break size. The TBS will thereby reduce the cost of the safety-grade ECCS system in new plant designs and will increase operational flexibility in existing plants. The TBS approach is based on the results of NRC elicitation studies with piping experts regarding historical pipe performance and risk of sudden failure. The approach is non-deterministic and is a conceptual change from the largest-pipe-size break assumption. The conceptual discontinuity between deterministic and elicitation-based break size assumptions could be uncomfortable for those schooled in strictly deterministic accident analyses. In this paper we explore the “leak-before-break” (LBB) methodology as it applies to large pipe break analyses in nuclear piping systems, and show through examples that the elicitation-based TBS approach is indeed conservative when TBS results are compared with deterministic LBB evaluations of similar piping systems. Thus, LBB provides a deterministic means for showing defense in depth against LOCAs greater than the TBS break size.
Grain Structure Refinement in Nickel Alloy Welds by Magnetic Arc Stirring
Authors: McCracken Steven L. , Yu X. , Lim Y. C. , Farson D. F. , Babu S. S.
Published: May 2012

Nickel alloys with high chromium content provide optimum resistant to stress corrosion cracking for service in the reactor coolant system of commercial nuclear power plants. High chromium nickel-base alloys however present many challenges, such as less than ideal weldability and susceptibility to solidification cracking or solid-state cracking depending on welding conditions and dilution effects with dissimilar metals. Moreover, the presence of large solidification grains, typical of nickel alloy weld metals, makes ultrasonic examination of the weldment difficult. Magnetic stirring of the nickel alloy weld pool has the potential to address these challenges and improve joining, overlay welding, cladding, and repair of critical components in commercial nuclear power plants. This study evaluates use of magnetic arc stirring to modify weld pool solidification conditions in order to promote a fine solidification grain structure in nickel alloy welds.
Optimization of Re-Torque and Relaxation Parameters of the GUCP
Authors: Gordon Ali P. , Drilling Brian , Williams Kent , Hebert Scott , Kammerer Catherine C. , Baldwin Frank
Published: May 2012

Self-loosening of bolts in non-permanent connections has been the subject of a myriad of investigations; however, because the vast majority of these studies focused on applications with long-term service conditions involving creep and/or cyclic (working or vibratory) loading, there are no analytical techniques that have been developed to address the load decay behavior of bolted assemblies with gaskets under a primary followed up by a secondary torque. The Ground Umbilical Carrier Plate (GUCP) includes a gasketed ASME-type flange assembly that transfers pressurized, cryogenic hydrogen from the Space Transportation System (STS). Although the threaded stud material is nominally elastic under service conditions, the gasket material, a polytetrafluorethylene (PTFE) matrix filled with 25% chopped glass fibers, undergoes viscous, strain hardening deformation. The consequence of over-torquing the assembly is yielding the stud. Alternatively, the consequence of under-torquing is premature loosening and subsequent fuel leakage. As such, identifying the interactions between assembly configuration, initial torque, etc. to relaxation behavior of the assembly has been identified as a means to reduce the dwell period (the time between initial torque and re-torque). Research is carried out to identify the optimal torque parameters that confer a minimal dwell period. This article documents the Gasket Relaxation and Re-Torque Optimization (GRRO) program used to modify procedures employed when connecting the flanges to the fuel tank of the Space Transportation System prior to a launch.
Identifying Failure Scenarios in Complex Systems by Perturbing Markov Chain Models
Authors: Dabrowski Christopher , Hunt Fern
Published: May 2012

In recent years, substantial research has been devoted to monitoring and predicting performance degradations in real-world complex systems within large entities such as nuclear power plants, electrical grids, and distributed computing systems. Special challenges are posed by the fact that such systems operate in uncertain environments, are highly dynamic, and exhibit emergent behaviors that can lead to catastrophic failure. Discrete Time Markov chains (DTMCs) provide important tools for analysis of such systems, because they represent dynamic behavior succinctly, provide a means to measure uncertainty, and can be used to make quantitative measurements of the potential for change to system performance. Moreover, DTMCs can be extended to be time-inhomogeneous, i.e. to represent behavior that varies over long durations. To date, DTMCs have been proposed for tasks such as fault detection and long-term condition equipment monitoring in real-world complex systems. However, the scope of these models has generally been restricted to describing states and state transitions that directly concern fault conditions or states of degradation. Less work has been done on using DTMCs to represent a more complete range of states a system may enter into during normal operation. Of special interest are sequences of states that involve failure scenarios, in which a system evolves from a normal operating state into undesirable state that leads to widespread performance degradation. Unfortunately, use of large DTMCs often involves large search spaces, a problem which in part motivates our work. This paper describes progress made on developing an approach for using larger, more detailed DTMC models of operational complex systems to uncover potential failure scenarios. The approach uses a combination of methods to perturb a DTMC, simulate alternative system evolutions, and identify scenarios in which a system proceeds from normal operation to failure. Key to the approach is the use of graph theory techniques to reduce the size of the search space involved in exploring alternative behaviors. We show how graph theory techniques can be used to identify critical state transitions which can be perturbed to simulate performance degradation. Using critical transitions, it is also possible to estimate the rate of performance degradation and to understand how this rate is likely to change in response to increased failure incidence. Examples are provided of the use of this approach on a DTMC of significant size to identify failure scenarios in a distributed resource allocation system.
Fracture Resistance and Fatigue Crack Growth of X80 Pipeline Steel in Gaseous Hydrogen
Authors: San Marchi Chris , Somerday Brian P. , Nibur Kevin A. , Stalheim Douglas G. , Boggess Todd , Jansto Steve
Published: May 2012

Gaseous hydrogen is a convenient medium to store and transport energy. As existing petroleum-based platforms are electrified, such as with the growth of fuel cell systems, hydrogen is becoming an attractive fuel which must be distributed, stored and dispensed. Hydrogen is used extensively in refining of petroleum products, and often distributed by pipeline. However, there remains a need to quantify the mechanical properties of low-cost steels in gaseous hydrogen and to relate the measured performance to the variety of microstructures that characterize steels. This study is part of a larger effort to characterize a broad range of steels manufactured for pipelines and to measure their fracture and fatigue resistance in gaseous hydrogen. The fracture resistance and fatigue crack growth rates of two microstructural variations of X80 pipeline steel were measured in gaseous hydrogen at pressure of 21 MPa. The performance of these steels was found to be similar to the performance of other ferritic steels that are currently used to distribute gaseous hydrogen.
CFD Modeling of Blast Loads From a Pressure Vessel Failure
Authors: Edel Matthew , Novia Matthew , Ketchum Donald , Geng Jihui
Published: May 2012

The downhole tool industry commonly conducts tests that require pressurization of a vessel. The most common failure mode is through the launching of end caps, plugs, and fittings as opposed to a catastrophic rupture of the vessel body. This type of vessel failure during high pressure gas testing can produce significant threats to nearby personnel in the form of high energy projectiles and blast waves that must be blocked or dissipated before reaching personnel. Adequately designing a structure to contain this energy depends on how well a worst case scenario event can be modeled. Blast waves ensue from a pneumatic pressure test failure. As a vessel fails, the volume of pressurized gas will expand into the surroundings. A computational fluid dynamics (CFD) model of the pressure vessel and its enclosure will provide an accurate assessment of the blast loads in the environment. This paper describes an experimental test program of a simulated pneumatic pressure vessel failure through the launching of a hypothetical end cap or plug inside an enclosure. The recorded blast loads from three tests at various pressures were compared to simplified two-dimensional CFD model results of the enclosure. Two CFD models were run for each test: the first accounts for the time required for the vessel to open during failure, and the second assumes an instantaneous release of pressurized gas. The CFD results for the first model matched the test results well and provided validation of the modeling approach. The second model indicates the level of conservatism of predicted blast loads when assuming an instantaneous vessel failure. A properly designed pressure testing enclosure can provide a high level of safety in the event of a failure; several types of enclosure designs have proven to be successful, which are discussed in this paper. Equally important is the need to have competent operators with an awareness of the risks involved with pressure testing combined with training and competency programs implemented throughout the industry.
Characterization of a Plate Specimen From Phase I of the NRC/EPRI Weld Residual Stress Program
Authors: Kerr Matthew , Rudland David L. , Prime Michael B. , Swenson Hunter , Buechler Miles A. , Clausen Bjorn
Published: May 2012

Time-of-flight neutron diffraction and contour method residual stress measurements were conducted at Los Alamos National Lab (LANL) on a lab sized plate specimen (P4) from Phase I of the joint U.S. Nuclear Regulatory Commission and Electric Power Research Institute Weld Residual Stress (NRC/EPRI WRS) program. The specimen was fabricated from a 304L stainless steel plate containing a seven pass Alloy 82 groove weld, restrained during welding and removed from the restraint for residual stress characterization. This paper presents neutron diffraction and contour method results, and compares these experimental stress measurements to a WRS Finite Element (FE) model. Finally details are provided on the procedure used to calculate the residual stress distribution in the restrained or as welded condition in order to allow comparison to other residual stress data collected as part of the EPRI lead Phase I WRS program.
Dynamic Structural Analysis of the Model 9979 Type AF Shipping Packaging
Authors: Han Zenghu , Shah Vikram N. , Liu Yung Y.
Published: May 2012

This paper presents the dynamic structural analysis results of Model 9979 Type AF packaging under hypothetical accident conditions. The submitted compliance documentation, Safety Analysis Report for Packaging Model 9979, with the regulatory requirements in 10 CFR 71.73 was based on testing five full-scale prototype units by the Savannah River National Laboratory. According to the test results under accident conditions, the 55-gallon outer drum maintained structural integrity and retained the inner 30-gallon drum, while the 30-gallon drum maintained its confinement of the contents. However, we identified several structural-related issues during our technical evaluation of the report — specifically, whether the structural tests were performed under the worst conditions and/or in the worst test sequence that would yield the most cumulative damage to the packaging. These structural-related issues were evaluated using the finite-element code ABAQUS. The dynamic structural analysis results show that a packaging with the full payload would indeed experience more damage during the drop test than a packaging without the payload. The analysis results also indicate that a corner drop of a fully loaded packaging, followed by a corner crush test, is the worst test sequence and results in highly localized plastic deformation of the 55-gallon outer drum, but no loss of its structural integrity. Both the test results and the dynamic structural analysis results demonstrated that the structural design and performance of the 9979 packaging are acceptable.
Effect of Thread Profile Angle and Geometry Clearance on the Loosening Performance of a Preloaded Bolt-Nut System Under Harmonic Transverse Excitation
Authors: Yang Xianjie , Nassar Sayed A.
Published: May 2012

A mathematical model is proposed for investigating the effect of the thread profile angle, thread and hole clearances on the loosening behavior of a preloaded bolt-nut system that is subjected to cyclic transverse excitation. Experimental verification of the analytical model results is provided for various levels of the initial bolt preload and frictional characteristics. Comparison of the experimental and analytical results on the clamp load decay with the number of cycles verifies that the proposed model predicts the loosening performance with good accuracy.
Effect of Adhesives on the Mechanical Behavior of Thick Composite Joints
Authors: Nassar Sayed A. , Mao Jianghui , Yang Xianjie , Templeton Douglas
Published: May 2012

In this paper, experimental and numerical methods are used to study the deformation and interfacial failure behavior of an adhesively-bonded thick joint made of multi-layer S2 glass/SC-15 epoxy resin composite material. The adhesive material is 3M Scotch-Weld Epoxy Adhesive DP405 Black. Continuum damage mechanics models are used to describe the damage initiation at or near the interface and final failure process. The effect of adhesive overlap length, thickness and plasticity on the interfacial shear stress and normal stress are studied. Experimental and analytical data are used to validate the proposed damage models.
Effect of Residual Stress on Crack Growth Specimens Fabricated From Weld Metal
Authors: Kerr Matthew , Dunn Darrell , Olsen Mitchell D. , Alexandreanu Bogdan , Hill Michael R. , Willis Eric
Published: May 2012

Slitting method residual stress measurements (Hill Engineering and UC Davis) and finite element weld simulation (US Nuclear Regulatory Commission) have been conducted in order to evaluate both the residual stress intensity factor and residual stress profiles for two compact tension coupon blanks. The two compact tension coupon blanks were provided by Argonne National Lab (ANL) and are similar to coupons used in ongoing stress corrosion cracking (SCC) studies in weld metal. The experimental data and finite element results are in reasonable agreement, showing similar trends in calculated residual stress profiles. Results from the work document the effect of specimen size and location on residual stress profiles, and could be used to determine the degree to which residual stresses affect crack growth measurements made in similar coupons.
Effect of Non-Parallel Wedged Surface Contact on Loosening Performance of Preloaded Bolts Under Transverse Excitation
Authors: Yang Xianjie , Nassar Sayed A.
Published: May 2012

An analytical model is proposed for investigating the effect of non-parallel (wedge) contact on the loosening performance of a preloaded bolt-nut connection under transverse cyclic excitation along the wedge direction. From the model, if the wedge angle is sufficiently small, the self-loosening may take place. On the other hand, if the wedge angle is large enough, the self-loosening caused by the back off rotation may be prevented. Experimental and analytical results show that the proposed model accurately predicts both the self-loosening performance, and it also establishes the requirements for preventing the loosening of the preloaded bolt-nut system.
Study of Creep Relaxation Behaviour of 316H Austenitic Steels Under Mechanically Induced Residual Stress
Authors: Nezhad Hamed Yazdani , O’Dowd Noel P. , Davies Catrin M. , Nikbin Kamran M. , Wimpory Robert C.
Published: May 2012

Compact tension 316H austenitic steel specimens, extracted from an as-received ex-service pressure vessel header, have been pre-compressed to different load levels in order to introduce a residual stress field. Finite element (FE) analysis has been performed to predict the load level required to obtain a high magnitude tensile stress field over a significant distance ahead of the notch while preventing a large plastic zone in the specimen. The predicted residual stress profiles along the crack path are compared with those measured using neutron diffraction (ND). Comparisons have also been provided between the ND results of this work with recent work carried out on 316H and 347 stainless steels under different loading levels. The creep relaxation behaviour of the steel has been studied numerically. A proposed method to estimate the steady state creep crack tip parameter, C*, has been examined using the obtained displacement rates for the case of combined loading. Creep relaxation data for combined stresses are compared with the earlier studies.