bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of Uncertainty Sources in Fatigue Usage in Relation to Deterministic Margins, and Sensitivity Analysis
Authors: Garud Y. S. , Steininger David A. 
Published: October 2017

Considerations of environmental effects in fatigue have resulted in proposals to augment the original basis and deterministic methods of fatigue assessment, such as in the ASME Code Subarticles NB-3200 and NB-3600. This process of deterministically combining various elements, each with its own set of safety factors, of the CUF-based assessment has the potential to be overly conservative and restrictive in practice. Furthermore, as in the commonly used deterministic design approaches, fixed safety factors are subjectively assigned; as a result the approach does not provide a logical basis to account for uncertainties or variability, and the resulting level of reliability cannot be assessed quantitatively. Therefore, it is useful and desirable to complement the simplicity of deterministic approach by relating the safety factor to target reliability (or probability of meeting the design criterion) so that an appropriately adequate conservatism can be utilized. The feasibility of such an inter-relation and its underlying probabilistic basis were demonstrated in our recent paper that provided a rational basis to account for the significant uncertainties in assessing the CUF-based fatigue including environmental effects.
The objective of this paper is to provide further assessment of the above basis for uncertainty quantification and its linkage to deterministic safety factor approach, with additional focus on the quantitative sensitivity analysis of varied sources of uncertainty in the CUF estimation. Results of the case studies implementing the proposed approach combining these uncertainties are presented. New expressions for sensitivity assessment are developed. Results of sensitivity analysis are presented with the goal of demonstrating the sensitivity/ranking of significant contributors to the final CUF uncertainty and the resulting deterministic margins in relation to the target (specified) reliability. The overall approach, also summarized in the paper, utilizes the generally accepted concept of propagation of input uncertainties based on the Taylor series method and the framework of the stress-strength interference technique. The utility and limitations of the approach are discussed in defining the acceptable deterministic margins and in quantifying the impact of various elements of conservatism in the current CUF based fatigue evaluations.
Evaluation of ASME Class 3 HDPE Flanged Joints
Authors: Musto Thomas M. , Frazee Glenn R. , Marohl Michael P. H. 
Published: October 2017

In the design of piping systems, there are many options for transitioning between HDPE and metallic piping. One common option is the use of flanged joints. As a result of the visco-elastic nature of HDPE, the use of HDPE-to-metallic flanged joints requires special design considerations. When HDPE-to-metallic flanged joints are used in ASME Class 3 systems, the design is further complicated by the requirements provided in the ASME B&PV Code, Section III for flanged joint analysis.
This paper examines the differences between HDPE piping flanged joints and metallic piping flanged joints, including consideration of industry guidance and available industry testing results. The paper provides a proposed methodology for evaluating ASME Class 3 HDPE-to-metallic flanged joints and HDPE-to-HDPE flanged joints, including the determination of required bolt torque values and the determination of the maximum internal pressure that the joint can resist without experiencing leakage.
Minimizing Visual Effects and Optimizing Routes and Locations for Geothermal Steam Gathering System
Authors: Jonsson Magnus Thor , Magnusdottir Lilja 
Published: October 2017

In geothermal power plants, the steam system is a costly component of the infrastructure in terms of construction requirements. The steam system consists of geothermal wells, well head equipment, pipelines and separators connecting wells to the separators and the separators to the power plant. This paper describes an approach for optimum design of a steam system, with focus on topology and route selection for pipelines transporting two-phase fluid from geothermal wells to a separation station and single-phase pipelines from the separator stations to the power plant.
This article proposes a new approach for selecting the locations of the separators and power plant and routes for both two phase-flow and single-phase flow pipelines in a geothermal steam gathering system. Multiple weighted distance maps calculated by uniform cost Dijkstra’s algorithm are used to find the optimum location of a site for a steam separator based on the flow capacity of geothermal wells. The two-phase flow routes are monotonic and the incline is slight in order to minimize the pressure drop and the slug flow conditions in the pipeline. Once the location of separators has been optimized, the optimum location of the power plant can be determined based on the route selection for both the pipelines transporting steam to the power plant and the pipelines transporting the used geothermal fluid from the power plant to the injection wells. The objective is to minimize both cost and visual effects.
A comparison of this method to traditional methods shows that when the method described in this paper is used, shorter routes and cheaper systems can be designed with less environmental impact.
An Analytical-Based Structural Strain Method for Low Cycle Fatigue Evaluation of Girth-Welded Pipes
Authors: Pei Xianjun , Wang Wei , Dong Pingsha 
Published: October 2017

As a further extension to the structural stress based master S-N curve method adopted by ASME Div 2 since 2007, this paper presents an analytical-based structural strain method for girth-welded piping components. Here, structural strain is defined as outer and inner fiber strains calculated corresponding to a deformation condition in which a pipe section plane before deformation remains as a plane after deformation. The analytical formation takes into account all possible plastic deformation conditions a pipe section subjected to a combined remote cyclic bending and axial tension. A simple numerical procedure is used for solving both outer fiber and inner fiber strains, as well as the corresponding elastic core size. For fatigue evaluation purpose, the outer fiber strain can be used to calculate the corresponding pseudo elastic structural stress range so that the structural stress based master S-N curve can be directly used. Under linear elastic deformation conditions, the structural strain definition becomes exactly the same as that calculated by the structural stress method which is the basis on the ASME Div 2 master S-N was developed.
A set of a recent full scale girth-welded pipe component test data in low-cycle regime was analyzed using the structural strain method. The results showed that all these new test data fall well within the ASME Div 2 master S-N curve scatter band defined by mean+-standard deviations. In addition to its demonstrated effectiveness, the key advantage of this structural strain method is its simplicity for dealing with girth-welded pipe sections, since finite element stress analysis is no longer needed.
Adoption of the Composite Reinforced Pressure Vessels (CRPV) Into the ASME BPV Code
Authors: Biel Richard C. , Cano Gregory 
Published: October 2017

Adoption of composite reinforced pressure vessels (CRPV) into the ASME Boiler and Pressure Vessel Code represented advancement in the technology of pressure vessels. The advantage of this construction technique is that the weight of a CRPV for compressed gas service built may be reduced to about one-half conventional pressure vessel of the same capacity. The concept of hoop wrapping fibers in a plastic composite (>90% fiber fill) makes full utilization of the fiber strength as the fibers share the hoop load with a metal cylinder. With reduced hoop stresses in the metal, a substantial reduction in wall thickness is attainable.
The process of adoption of this technology presented several challenges and some robust administrative hurdles. These included coordination with ASME BPV Code Section X for the composite application and Section VIII for the steel design and overall acceptance of the Case.
The most vexing technical challenge was the inspection of an unfinished weld on the inside of the shell from the outside of the shell. The next challenge was to gain consensus on the testing criteria for the acceptance of finished vessels.
Case 2390 was drafted in the winter of 2000 and spring of 2001 and approved for publication after nine revisions with an approval date of October 9, 2002. The Case was subsequently adopted into the body of ASME BPV Code Section VIII, Division 3 [1] (VIII-3) in the 2010 edition.
Effect of Variable Temperature on the Fatigue Life and Crack Growth Rates of Austenitic Stainless Steels in PWR Coolant Environments
Authors: Platts N. , Gill P. , Cruchley S. , Grieveson E. , Twite M. 
Published: October 2017

The Pressurized Water Reactor (PWR) primary coolant environment is known both to significantly reduce the fatigue life of austenitic stainless steels and to lead to enhanced fatigue crack propagation rates. Relationships for the impact of the PWR coolant environment on fatigue life have been presented in NUREG/CR-6909 using an environmental fatigue correction factor (Fen), which is a function of temperature. Fatigue crack growth behavior has been codified in ASME Code Case N-809 in terms of parameters such as rise time, stress intensity factor, load ratio and temperature. However, plant performance suggests that the application of these predicted environmental effects using current assessment procedures for fatigue for plant transient loading may be unduly pessimistic. One potential reason for this over-conservatism is thought to be that, although the majority of plant design transients result from variations in thermal loading, most available data are derived from isothermal testing.
For the calculation of fatigue initiation life, NUREG/CR-6909 gives guidance on the effective temperature to be used in assessments of thermal transients. Recent results from Thermo-Mechanical Fatigue (TMF) testing on stainless steels in PWR coolant show that this guidance is conservative for out-of-phase cycling of temperature and loading, and potentially non-conservative for in-phase thermal loading. In contrast, code case N-809 gives no guidance on the effective temperature for fatigue crack growth assessments, resulting in maximum temperatures frequently being adopted for assessments of thermal transients. There is therefore a need for a clearer understanding of the impact of variable temperatures during transients on the predicted levels of environmental fatigue.
This paper describes test facilities developed to permit measurements of both thermo-mechanical fatigue life and fatigue crack growth rates in pressurized water reactor environments. Initial test results obtained using these facilities are presented. The fatigue life data have been generated for a range of applied strain amplitudes, 0.45% to 1%, using temperature cycling between 100°C and 300°C. These data, for both in- and out-of-phase temperature and loading, are compared to the predictions of the “weighted Fen” model which is detailed in a separate paper, PVP2017-66030. Similarly, crack growth rate data generated for cycles between 140°C and 280°C are presented and comparisons made against the predictions of the “weighted K rate” (WKR) method detailed in paper PVP2017-65645. In both cases, the test results suggest that the weighted models are able to provide good predictions of an effective temperature to be used in fatigue assessment methods, which offer a significant improvement in the treatment of variable temperatures compared to current assessment practice.
Structural Integrity Assessment of Doel 3 and Tihange 2 RPVs: Fatigue Crack Growth Analysis of Hydrogen Flakes
Authors: Lacroix Valéry , Dulieu Pierre 
Published: October 2017

During the 2012 outages 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 Safety Case 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(a) of ASME B&PV Code Section XI, one of the parts that have to be addressed through the Flaw Acceptability Assessment is the Fatigue Crack Growth (FCG) Analysis of the flaws in the core shells until the end-of-service lifetime of the RPVs. Due to the large number of flaws in the core shells, a specific methodology has been developed in order not to perform the FCG Analysis of each flaw separately.
The paper describes this simplified approach aiming at distributing the flaws according to their inclination and at defining envelope flaws covering the actual flaws to carry out FCG Analysis. Furthermore, the paper highlights and quantifies the conservatisms of this analysis leading finally to demonstrate that the FCG of hydrogen flakes is not a concern in Doel 3 and Tihange 2 RPVs.
Proposal of a New Subsurface-to-Surface Flaw Transformation Rule for Fatigue Crack Growth Analyses
Authors: Lacroix Valéry , Bouydo Afaf , Katsumata Genshichiro , Li Yinsheng , Hasegawa Kunio 
Published: October 2017

When a subsurface flaw is located near the component free surface, the first step consists of characterizing the flaw as surface or subsurface in compliance with subsurface-to-surface flaw proximity rules.
The re-characterization process from subsurface to surface flaw is addressed in all Fitness-for-Service (FFS) Codes. However, the specific criteria for the rules on transforming subsurface flaws to surface flaws are different among the FFS Codes.
This re-characterization concept is essential and important for subsurface flaws in the flaw assessment procedures. It is applied for three stages of the flaw assessment: at service inspection for flaw characterization, at subcritical crack growth calculation, such as fatigue crack growth, and at ductile/brittle fracture assessment. In this frame, fatigue crack growth experiments were recently conducted by the authors and it was highlighted that the subsurface-to-surface transformation is highly sensitive to the aspect ratio a/l of the flaw whereas the proximity factors in the rules are defined by constant values i.e., regardless of the flaw aspect ratios a/l.
The authors have therefore proposed a new subsurface-to-surface flaw proximity rule based on experimental data and equivalent fatigue crack growth rates.
Then, the authors demonstrated through numerous Fatigue Crack Growth (FCG) calculations that the current ASME B&PV Code Section XI surface proximity factor should be updated according to the type of component i.e., piping or vessel.
The paper summarizes all the steps leading to the improvement of the ASME Code Section XI subsurface-to-surface proximity rule, from the fatigue crack growth experiments to the studies of the suitability of the current flaw-to-surface proximity factor.
Furthermore, based on additional fatigue crack growth calculations and more refined investigations, the paper proposes finally a new limit value for the surface proximity factor. As a result, a proposal for modification of the ASME Code Section XI, Appendix C is provided. The paper is used for the technical basis of this proposal.
The Master Curve Fracture Toughness Evaluation of Irradiated Plate Material JRQ Using Miniature-C(T) Specimens
Authors: Yamamoto Masato 
Published: October 2017

The Master Curve approach is a powerful tool to evaluate material-specific fracture toughness of ferritic steels, such as RPV steels, using a limited number of specimens. However, preparing sufficient volume of material for the generally used 25.4mm-thickness fracture toughness specimens is difficult for irradiated reactor pressure vessel (RPV) steels of existing surveillance programs. Utilization of miniature specimens, which can be machined from broken halves of standard Charpy specimens, is a possible solution to address this issue. CRIEPI has been working on the development of test technique utilizing a miniature C(T) (Mini-C(T)) specimens, whose dimensions are 4×10×9.6 mm (0.16 inch thickness specimen). The basic applicability of the Mini-C(T) Master Curve approach on un-irradiated materials had been confirmed for the base metals of typical Japanese RPV steels [1]. International round robin tests [2–4] confirmed the reproducibility of fracture toughness data obtained by Mini-C(T) specimens.
Applicability of the Mini-C(T) specimen on neutron irradiated materials is of another important subject to be ensured. In the present study, the European standard plate material JRQ, which is in irradiated state up to the fluence of 1.85×1019 n/cm2 was subjected to the Master Curve evaluation with Mini-C(T) specimens. Two laboratories, A and B, as well as CRIEPI were involved in this study. Both of the laboratories separately and successfully carried out machining, pre-cracking and fracture toughness testing without excessive technical difficulty even though the material was highly irradiated. Consistent reference temperature, To was estimated as 40°C (Lab. A) or 32°C (Lab. B). The difference between the two laboratories was reasonably small. To was also consistent with that by pre-cracked Charpy V-notch specimens (PCCv), or 1-inch thickness C(T) specimens examined in the former IAEA Coordinated Research Program [5]. As a results of the investigation, the relevance of using Mini-C(T) specimens for irradiated JRQ material was demonstrated.
Prediction of Ductile Material Failure by Using Innovative Damage Mechanics Concepts
Authors: Schaffrath Simon , Feldmann Markus , Brinnel Victoria , Münstermann Sebastian , Novokshanov Denis 
Published: October 2017

Material failure and plastic instability are currently in ASME and EN pressure vessel and piping standards prevented by applying experience-based safety factors. Due to the few existing experimental test results and the inaccuracy of the incorporated design equations, these safety factors are quite high. In particular, modern high strength steels are penalized because of the small yield-to-tensile ratio. Apart from monotonic loading conditions, an economical design of pressurized components to prevent material failure due to ultra-low-cycle fatigue (ULCF) is a big topic.
Experimental tests are in general very expensive and not suitable for the common design. Therefore, a numerical based prediction of the actual burst pressure and the resistance against strong cyclic loading conditions would be favourable. During the last decades innovative damage mechanics concepts have been developed and successfully validated in the scope of structural and plant engineering. Depending on the size of the component and the applied loading condition, several different damage mechanics models are available.
During the studies presented in this paper, a phenomenological damage mechanics model proposed by Bai and Wierzbicki has been utilized. It has been developed to describe the material failure in the upper shelf of the toughness temperature transition curve in case of monotonic loading conditions. Considering an extension based on the effective strain concept proposed by Ohata and Toyoda, the combined model is also able to predict failure in the range of ULCF.
The presented work aims at validating the accurate numerical prediction of failure by using this damage mechanics model. Validation is performed by comparing numerical and experimental results of a burst test of a pressure vessel and cyclic deformation tests of almost constant pressurized bended pipes. The pressure vessel made of HSLA steel P690Q had a length of 3.0 m, a diameter of 1.2 m and a wall thickness of 50 mm. Tests on bended pipes can be separated in two series. A first series made of steel X60 with a diameter of 16 “ and a wall thickness of 9.5 mm as well as a second series made of steel X65 with a diameter of 8.625 “ and a wall thickness of 5.6 mm.
The comparison of experimental and numerical results shows an acutely satisfying prediction of failure. Both, time point and location of failure coincide well. Mesh size dependency must be considered but the approach seems to be promising for further applications.
Experimental Research on Cyclic Response, Hold Effects and Fatigue of Stainless Steel
Authors: Solin Jussi , Alhainen Jouni , Seppänen Tommi , Karabaki H. Ertugrul , Mayinger Wolfgang 
Published: October 2017

Our research on fatigue performance of stainless steel and transferability of laboratory data to nuclear power plant operational conditions continues. The focus is in quantification of time and temperature dependent damage relaxation during holds introduced within strain controlled LCF fatigue tests with niobium stabilized X6CrNiNb1810mod steel. These holds aim to simulate steady state normal operation between fatigue relevant cycles at start-up, shut-down or power changes in PWR primary circuit components, e.g. the pressurizer spray lines and surge line.
Amplified cyclic hardening was observed at strain rates approaching zero at normal operation temperatures (≤325°C). Even more pronounced static hardening is consistently measured during holds in elevated temperatures (≥200°C). Beneficial effects of holds in material endurance were shown five years ago. The latest results suggest another beneficial change in component fatigue performance. In addition to improved material response, de-localization of strain is demonstrated in this paper. Our target is a thermodynamic prediction model for improved assessment of fatigue with normal operation periods. The model should quantify the life extension due to long periods in normal operation at operational temperatures.