bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear Fatigue Codified Design Rules: Development Status, Margins and Screening Criteria
Authors: Faidy Claude 
Published: October 2018

In the past 10 years, different laboratory test results lead the International Standard Development Organizations (SDO) to review their fatigue design rules in different directions, in particular to consider consequences of environmental effects on existing design rules.
The key document that ask different questions to Code developers is the USNRC NUREG 6909 report: “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials” that confirms some environmental effects on S-N fatigue tests on small specimen. The open question is: how to transfer these results to Fatigue Design Rules of plant components?
This paper will review existing codified rules in major nuclear Codes; in particular USA ASME Boiler and Pressure Vessel Code Section III and French AFCEN RCC-M Code.
The paper will make a first historical background of these Codes and analyze background of these rules by consideration of field experience and existing tests results.
To conclude, the paper will summarize to-day “fatigue road maps” to evaluate margins and screening criteria to assure reliable and safe codified design fatigue life evaluation.
A Seismic Vulnerability Analysis of a Liquefied Natural Gas Subplant
Authors: Pedot Massimiliano , di Filippo Rocco , Bursi Oreste S. 
Published: October 2018

“Special risk” industrial plants can be highly vulnerable when subjected to natural phenomena such as earthquakes, flooding and explosions. In this study we focused our attention on the performance of a liquefied natural gas (LNG) terminal subjected to extreme earthquakes; an LNG terminal consists of a series of process facilities connected by pipelines of various sizes carrying hazardous chemical components. Although tanks, pipes, elbows, bolted flanges have been a major concern in terms of seismic design, generally, they have not been analyzed with modern performance-based procedures. Thus, our work has been devoted to the assessment, within the performance-based earthquake engineering (PBEE) framework, of the seismic performance of tanks, pipes, elbows and bolted flange joints by means of seismic fragility functions. Particular attention was paid to component resistance and to loss of containment (LoC) due to leakage.
A representative case study of an LNG terminal has been selected and tank, support structures and pipework, including elbows and flanges were analyzed with a detailed 3D finite elements model. Preliminary analyses identified elbow and bolted flange joints as critical components. A mechanical model, based on experimental data, defines leakage limit states for bolted flange joints. A significant effort was also devoted to identification of a leakage limit state for piping elbows, and we found the level of the hoop plastic strain to be an indicator.
On a first stage for the probabilistic seismic demand analysis (PSDA) we applied the Cloud method, due to its advantages in terms of consistency in the seismic input and of computational savings. More precisely, we studied the behaviour of critical components using a set of 36 ground motions, selected from a database of historic earthquake accelerations. The results of seismic analysis show that bolted flange joints remain significantly below their leakage threshold while elbows at the top of the LNG tank are likely to show LoC. Fragility functions show that elbows located on the tank platform are relatively unsafe against earthquakes.
On a second stage, in order to detect more complex failure scenarios, we analysed an LNG plant comprising a more complex piping substructure with respect to the original FE model. Moreover, we have treated the LoC of elbows from a probabilistic point of view by means of a Gaussian probability density function associated to a hoop strain limit state. The results provided by the aforementioned refined piping system allow for an improved and more accurate seismic risk assesment of the LNG plant.
Master Curve Testing on Reconstituted Surveillance Charpy Specimens
Authors: Gillemot Ferenc , Horváth Márta , Horváth Ákos , Szenthe Ildikó , Kovács Attila 
Published: October 2018

The original WWER-440 surveillance had 6 sets of specimens and each set had 12 Charpy, 12 COD (crack opening displacement) and 6 tensile specimens made from base material, weldment and HAZ (heat affected zone). The Charpy size precrack TPB (three point bend) COD specimens were located at the end of the chains, where the flux is rapidly decreasing.
During the period of 1970–90, when the WWER-440-V213 units were designed, built and started to operate, the Charpy impact transition curve measurement was the accepted method to evaluate the radiation embrittlement. The technology and the standards to use small size fracture mechanical specimens in surveillance capsules were not developed at the time period when most of the second generation reactors — including the WWER-440 V 213 type — were designed, therefore the fracture toughness specimens were considered less interesting for the utilities and the safety authorities. Fracture toughness curves were elaborated in the laboratories on large size unirradiated specimens and radiation embrittlement adjustments were made according to the Charpy shift. However, during the past 30 years fracture mechanics has rapidly developed, and the testing moved to the direction of using small and mini sized specimens. The development of the Master Curve evaluation method [4,5] allowed the use of small specimens for fracture toughness testing in surveillance programs, and the results obtained on irradiated specimens may be used directly in the lifetime evaluation. The purpose of this work was to develop a specimen production technology and testing procedure to measure these data using the remnants of irradiated surveillance Charpy specimens, and the comparison of the data calculated from CMOD and LLD on irradiated CrMoV type RPV material and weldment.
Importance of Connections in High-Pressure Barricade Design
Authors: Kostecki Jodi , Edel Matthew , Montoya John 
Published: October 2018

High pressure testing and operation of industrial tools and equipment can be hazardous to personnel and property in the event of an accidental mechanical failure or release of contained pressure. Hazard barricades are commonly installed around equipment to protect nearby personnel or property from projectile impacts or overpressure. The ASME Standard PCC-2 “Repair of Pressure Equipment and Piping” allows the use of hazard barricades for this purpose when a safe standoff distance cannot be satisfied, but it currently provides minimal guidance for engineered design. Other references provide guidance for preventing projectile perforation of a barricade. While perforation prevention is a key component of shield design, properly anchoring a shield and inter-connecting the shield components will make the difference between an effective barricade application and a barrier that could potentially compound the consequences of an accidental failure.
This paper investigates the importance of engineered structural connections and consideration of global structural response in the design of protective barricades. The structural models focus on impact loading of steel plates and bolted connections, and the results are directly compared to test results in terms of effective barrier response.
Effects of Non-Normal Input Distributions and Sampling Region on Monte Carlo Results
Authors: Tsembelis Konstantinos , Eom Seyun , Jin John , Cole Christopher 
Published: October 2018

In order to address the risks associated with the operation of ageing pressure boundary components, many assessments incorporate probabilistic analysis tools for alleviating excessive conservatism of deterministic methodologies. In general, deterministic techniques utilize conservative bounding values for all critical parameters. Recently, various Probabilistic Fracture Mechanics (PFM) codes have been employed to identify governing parameters which could affect licensing basis margins of pressure retaining components. Moreover, these codes are used to calculate a probability of failure in order to estimate potential risks under operating and design loading conditions for the pressure retaining components experiencing plausible and active degradation mechanisms.
Probabilistic approaches typically invoke the Monte-Carlo (MC) method where a set of critical input variables are randomly distributed and inserted in deterministic computer models. Estimates of results from probabilistic assessments are then compared against various assessment criteria.
During the PVP-2016 conference, we investigated the assumption of normality of the Monte Carlo results utilizing a non-linear system function. In this paper, we extend the study by employing non-normal input distributions and investigating the effects of sampling region on the system function.
Establishing Fracture Mechanics Based Minimum Allowable Temperatures for Low Temperature Applications of ASME B31.3 Piping
Authors: Kummari Seetha Ramudu , Macejko Brian , Shipley Kraig S. , Prueter Phillip E. , Evans Geoff , Jamal Nijat 
Published: October 2018

Impact test exemption curves in ASME B31.3 [1] were adopted from ASME Section VIII Division 1 (VIII-1) [2] with subtle modifications. The VIII-1 exemption curves were generated based on early fracture mechanics methodologies and limited amount of test data with an assumption on maximum applied stress intended to correspond to the typical VIII-1 allowable stress criteria. The applicability of the exemption curves for low temperature applications of ASME B31.3 piping (such as blowdown events) is open to discussion because of potentially high longitudinal thermal expansion stresses that may exceed the VIII-1 allowable stress criteria. Additionally, unlike in VIII-1 and ASME Section VIII Division 2 (VIII-2) [3], there is no post weld heat treatment (PWHT) credit on Minimum Design Metal Temperature (MDMT) in ASME B31.3. Detailed fracture mechanics analyses have shown that PWHT can significantly reduce the risk of brittle fracture failures due to its relaxation effect on weld residual stresses, a major crack driving force.
In this paper, a fracture mechanics-based methodology for establishing Minimum Allowable Temperatures (MAT) for low temperature applications of ASME B31.3 piping is presented. A state-of-the-art fracture mechanics methodology published in Welding Research Council (WRC) Bulletin 562 [4] is used to develop step-by-step Level 1 and Level 2 procedures for establishing MAT for low temperature applications of ASME B31.3 piping. For the Level 1 methodology, MAT screening curves are developed based on a likely conservative assumption that the stresses in the piping component are at the maximum code allowable stresses in both the hoop and longitudinal directions. For the Level 2 methodology, stress ratio verses temperature reduction curves are developed to consider the effect of lower operating stresses. Similar to VIII-2 [3] toughness exemption curves, the screening curves are generated for both As-Welded and PWHT conditions. The curves can also be used for impact tested materials. The established MAT can be directly coupled to different reference flaw sizes and integrated with an inspection criteria for piping components. Two examples of establishing MAT using both the proposed Level 1 and Level 2 methodologies are presented herein.
Anisotropic Materials Use in the ASME Boiler and Pressure Vessel Code
Authors: Cameron Jay 
Published: October 2018

Very few materials have all their properties behave the same in all orientations of the material. The term for this behavior is anisotropy or anisotropic properties. The properties that are affected and the degree of anisotropy they exhibit, depend on the material family, the alloy, and the processing of the material. This paper will only discuss metals, and limited to those metal specifications adopted in the ASME Boiler & Pressure Vessel Code (B&PVC) Section II, Parts A and B.
The anisotropic properties of plate have been well recognized explicitly and implicitly in the B&PVC for a very long time. At issue, and the specific focus of this paper, is another wrought product form: bars. Bar, specifically round bar — also called rod, is a very useful starting material to manufacture pressure parts. The bar can be stocked at the largest feasible diameter and length, and then cost-effectively machined to whatever diameter and length is desired for the part. Due to the anisotropic properties of bar, there is a need for understanding and setting limitations for the use of such material in the B&PVC. This paper will explore the past history, current status and future directions of the Code requirements for bar.
Determination of Residual Stress Directionality by Instrumented Indentation Testing Using Anisotropic Indenter
Authors: Choi Sungki , Kim Jong Hyoung , Lee Jun Sang , Lee Kyungyul , Choi Min-Jae , Ahn HeeJun , Kwon Dongil 
Published: October 2018

Residual stress is a major factor in failure and fracture in structures or electronic components. Various testing methods are used to measure residual stress: there are saw-cutting, holedrilling, X-ray diffraction and layer-removing methods. In particular, instrumented indentation testing (IIT) has many advantages: it is a simple and non-destructive procedure that can be used for in-field testing.
In previous research, we proposed an algorithm for evaluating the magnitude and directionality of residual stress using an asymmetric Knoop indenter with long and short axes in the ratio 7.11:1. Indenting in different directions with a Knoop indenter creates different indentation load-depth curves depending on the residual stress state. In addition, the directionality of the residual stress can be expressed as a function of the load difference ratio calculated from these load-depth curves.
However, When the Knoop indentation test is performed at small indentation depths, experimental issues such as surface preparation or indentation normality can become significant as the load difference decreases. In order to solve these issues, we introduce a wedge indenter, that makes it possible to select the edge length independent of indentation depth. We can thus decrease indent size when working in a small testing area. The load difference between the stress-free and stressed state is related to the sensitivity of residual stresses, and a wedge indenter can maximize the sensitivity to residual stress. In this study, we suggest a way to use the wedge indenter and verify the model using cruciform bending specimens and finite element analysis.
Stud Bolt Thread Engagement: Implications of Applying New Construction Requirements in Post Construction Scenarios
Authors: Rodery Clay D. 
Published: October 2018

In its 2016 Edition, ASME B31.3 [1] removed its long held provision for thread engagement that deemed the lack of complete engagement acceptable if the lack of engagement is not more than one thread. This change can have implications on existing piping assemblies which prompted some clarifications in ASME PCC-1 [2].
This paper reviews some of the reasons for the change, the issues around determining a specific measurable criterion of an acceptable amount of thread engagement, and proposes alternate criteria for the new construction codes to consider that are easily measurable and enforceable.
Case Studies on the Use of Thermal-Mechanical Finite Element Analysis to Evaluate Weld Ring Gasket and Diaphragm Seal Designs
Authors: Prueter Phillip E. , Davis Robert C. , Rodery Clay D. , McJones Stephen F. , Brodzinski Richard P. , Havekost Josh , Feddeler Daniel E. 
Published: October 2018

Weld ring type gaskets are relatively common in the refining and petrochemical industries. These gasket configurations usually consist of two steel rings, fillet-welded to each of the mating flanges with another seal weld between the lips of the two rings. These seal welds or lip seals are sometimes prone to in-service cracking that can eventually lead to leakage and costly equipment downtime. One particular design feature that can significantly influence the propensity for leakage is the shape of the weld rings; flat-lip weld rings or hollow-lip (Omega-seal) weld rings are the two most commonly used designs. The hollow-lip designs inherently offer more flexibility and can generally accommodate more differential radial thermal expansion between mating flanges.
This paper highlights a case study of a high-pressure heat exchanger where the shell side-to-tube side girth flange joint is fitted with a weld ring gasket configuration. Comparisons are made using detailed finite element analysis (FEA) that include bolt pretension and pressure-temperature loading. Sensitivity to lip seal design, temperature profile, and assumed friction coefficient between seating surfaces is also investigated. Furthermore, general commentary on flat and hollow lip weld ring gasket geometries is provided with design recommendations for different applications. In summary, the flat-lip seal weld experiences high shear stress, even with small amounts of differential temperature between flanges, which makes it prone to cracking. The added compliance of the hollow-lip seal design can minimize stresses in the seal weld, but understanding operating temperature differentials between mating flanges represents a key aspect of ensuring leak-free operation. The design of a diaphragm seal on a flat heat exchanger channel cover is also evaluated using FEA techniques, with sensitivity analysis on the size of the external fillet weld and diaphragm material specification. The analysis techniques presented in this paper offer valuable insight into establishing damage tolerant weld ring gasket and diaphragm seal designs to minimize the potential for leakage and to optimize critical gasket and bolting parameters.
A Thermomechanical PWR Test Facility to Investigate Thermal Shock Loading on a Small Scale Tubular Specimen
Authors: Gill Peter , Platts Norman , Currie Chris , Grieveson Eleanor 
Published: October 2018

Pressurized water reactor environments are known to reduce the fatigue life of austenitic stainless steel components when compared to air environments. Laboratory testing has provided a means of quantifying this, allowing conservative plant assessments to be made. The majority of this testing has been isothermal and carried out on membrane loaded hollow or solid specimens. The geometry and loading of laboratory test specimens is significantly different to that experienced on plant, where complex strain waveforms are generally out of phase with temperature changes, and significant through wall strain gradients may be present. To address the issue of realistic loading, a test facility has been developed which can simulate thermal shock loading on a tubular specimen.
The capability of the test facility was presented at the PVP2016 conference [PVP2016-63161]. Since then the facility has evolved, with modifications made to the rig configuration and specimen geometry in order to maximize the strain amplitude from the thermal shock, including the adoption of an annular flow geometry. These modifications were designed to optimize both the heat transfer coefficient and the speed of cycling between hot and cold water in order to induce a thermal strain that can cause mechanical failure within practicable test durations. In order to calculate the magnitude of the thermal strain, detailed calculations were required both in terms of thermal hydraulics as well as stress analyses. The latest stress analysis has been combined with state of the art life prediction models to estimate the time for crack initiation.
This paper presents the results of the latest stress analysis and life prediction, including the derivation of the heat transfer coefficient for an annular flow region. The life prediction method uses best estimate strain-temperature histories from elastic-plastic finite element analysis (FEA). Heat-specific material properties have been developed during accompanying tests within the same experimental programme, and have been applied to enable cyclic hardening to be taken into account. The comparison of the prediction to an on-going test is also discussed.
Cyclic, Monotonic and Fatigue Performance of Stabilized Stainless Steel in PWR Water and Research Laboratory
Authors: Solin Jussi , Alhainen Jouni , Seppänen Tommi , Karabaki H. Ertugrul , Mayinger Wolfgang 
Published: October 2018

Strain controlled LCF testing extended to 10 million cycles revealed an abrupt endurance limit enforced by secondary hardening. In elevated temperatures the ε-N curve is rotated and endurance limit is lowered, but not vanished. When very low strain rates are applied at 325°C in simulated PWR environment, fatigue life is reduced, but far less than predicted according to NUREG/CR-6909. It is possible, but not probable that the difference is due to different stainless grades studied. We assume that the test method plays a more important role.
We have repeatedly demonstrated in different tests campaigns that interruptions of straining with holds aiming to simulate steady state normal operation between fatigue relevant cycles can notably extend the fatigue endurance. Further proof is again presented in this paper. The suspected explanation is prevention of strain localization within the material microstructure and also in geometric strain concentrations. This actually suggests, that hold effects should be even more pronounced in real components.
Cyclic behavior of austenitic steels is very complex. Transferability of laboratory data to NPP operational conditions depends on test environment, temperature, strain rate and holds in many ways not considered in current fatigue assessment procedures. In addition to penalty factors, also bonus factors are needed to improve transferability. Furthermore, it seems that the load carrying capacity of fatigued stainless steel is not compromised before the crack growth phase. Tensile tests performed after fatigue tests interrupted shortly before end-of-life condition in 325°C (N ≈ 0.85 × N25) showed strength and ductility almost identical to virgin material.
This paper provides new experimental results and discusses previous observations aiming to sum up a state of the art in fatigue performance of German NPP primary loop materials.
Hidden Roles of Time and Temperature in Cyclic Behavior of Stainless Nuclear Piping
Authors: Solin Jussi , Seppänen Tommi , Mayinger Wolfgang , Karabaki H. Ertugrul 
Published: October 2018

Unexpected findings on time and temperature dependent behavior have been recorded during our research on fatigue performance of niobium stabilized stainless steel.
Cyclic straining at 325°C and low strain rates resulted in higher stress responses than in higher rate tests. This effect is particular strong in PWR water environment. Subsurface bulk effect in environment is in contrast to the assumption on similar responses in air and environment, which is the foundation of the ‘companion specimen’ method where the strain in environment is measured from a parallel specimen similarly tested in air.
Our data shows that environmental effects caused by PWR water cannot be isolated as a separate issue. Environment, temperature and strain rate are factors, which interactively affect the cyclic response and fatigue performance of stainless steel in relevant temperatures and loading conditions.
The current ASME Code Section III design curve is based on different translation of the laboratory data than that made by Langer et al. The resulting effect is not as radical as caused by replacement of the original test data to a new highly scattered data base. But also the procedural changes have detectable effects and open a door for a provocative question:
“is the design curve still compatible with the code?”