bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue Behavior of Nuclear Materials Under Air and Environmental Conditions
Authors: Herter Karl-Heinz , Schuler Xaver , Weissenberg Thomas 
Published: January 2014

The assessment of fatigue and cyclic crack growth behavior of safety relevant components is of importance for ageing management with regard to safety and reliability. For cyclic stress evaluation different codes and standards provide fatigue analysis procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. For the fatigue design curves used as limiting criteria the influence of different factors like e.g. environment, surface finish and temperature must be taken into consideration in an appropriate way.
Fatigue tests were performed in the low cycle fatigue and high cycle fatigue regime with low-alloy steels as well as with Nb- and Ti-stabilized German austenitic stainless steels in an air and high temperature BWR environment to extend the state of knowledge of environmentally assisted fatigue as it can occur in BWR plants.
Using the RPV steel 22NiMoCr3-7 experimental data was developed to verify the influence of BWR coolant environment (high purity water as well as water containing sulphate with 90 ppb SO4 and water containing chloride with 50 ppb Cl at a test temperature of 240 °C and an oxygen content of 400 ppb) on the fatigue life and to extend the basis for a reliable estimation of the remaining service life of reactor components. Corresponding experiments in air were performed to establish reference data to determine the environmental correction factor Fen.
The experimental results are compared with available international mean data curves, the new design curves and on the basis of the environmental factor Fen.
Long Term Fatigue Evaluation in Primary Circuit Components Within Nuclear Power Plants Operated by E.ON
Authors: Reese Sven H. , Klucke Dietmar 
Published: January 2014

Temperature-measuring thermocouples have been applied to various positions on primary circuit piping where most significant thermal loads were expected. Measuring positions were monitored and evaluated, leading to comprehensive information of existing thermal loadings like stratification and thermo shock events.
During design of NPP (nuclear power plant) predicted cumulative fatigue usage factors (CUF) were defined based on specified transients. Conservative assumptions are part of this predicted end of life CUF. In comparison to detailed analysis based on real measured values, these predictions based on specified loads are leading to more conservative results in general. Evaluations underline the conservatism of design predictions in general and result in substantial progress in component integrity assessment knowledge. The range of methods to calculate component specific fatigue usage factors goes from conservative approaches based on the evaluation of the stress range of the specific events up to numerical Finite Element simulations. Based on the level of detail the conservatism decreases while the complexity of the model increases.
An overview of monitoring measures of passive piping components in terms of thermal fatigue assessment is being applied in NPPs operated by E.ON Kernkraft GmbH. Evaluation methods will be discussed in detail and differences between these methods will be presented.
Consideration of Environmentally Assisted Fatigue in Austenitic Stainless Steel — Applicability and Comparison of Existing Numerical Procedures
Authors: Reese Sven H. , Seichter Johannes , Klucke Dietmar 
Published: January 2014

Consideration of environmentally assisted fatigue (EAF) is in discussion internationally. In German KTA Rules the effect is taken into account by means of so called attention thresholds. While the laboratory phenomena themselves are being accepted widely, numerical calculation procedures are revised continuously and transition from laboratory to real plant components is not clarified yet.
Since NUREG/CR-6909, formulas for calculating the Fen factors have been modified several times. For example in ANL-LWRS47-2011 a new set of formulas was published and slightly revised by ANL in 2012. Various calculation procedures like the strain-integrated method and simplified approach have been published while each approach yields to different results.
Beyond this, additional topics like weld factors or plasticity correction factors have to be taken into account. Calculation procedures depending on the level of detail and in the description of loads are yielding to significant variations in the results. Respecting these topics in context of different levels of detail in computational simulations, numerical cumulative usage factor (CUF) evaluation results are likely to differ, depending on the assumptions made.
On the basis of a practical example, methods and approaches will be discussed and recommendations in terms of avoiding over-conservatism and misinterpretation will be presented.
Reliability of Water Jet Peening as Residual Stress Improvement
Authors: Kono Yusuke , Okimura Koji , Toth Rebecca , Sato Tomonobu , Tajima Masakazu , Jardin Cecile , Le-Bec Philippe 
Published: January 2014

As a countermeasure against high residual stress, we have developed some residual stress improvement methods; Water Jet Peening (WJP) [1] [2] for components installed in water, Shot Peening by Ultrasonic-wave vibration (USP) for components installed in air, and outer surface irradiated Laser Stress Improvement Process (L-SIP)[3] for components that can only be accessed from the outer surface.
WJP is applied to Reactor Vessel (RV) outlet/inlet nozzle safe-end joints (Alloy600 weld metal), RV Bottom Mounted Instrument (BMI) inner surface and J-weld. Especially, it is difficult to apply the technology to BMI because BMI inner surface is a very narrow space (inner diameter; approximately 10–15mm) and BMI J-weld configuration is a complicated 3-dimensional form.
On the occasion of actual application, we carry out the verification tests and check that a stress improvement was effective as one of PWSCC mitigations. And the compressive stress induced by the WJP was verified to continue to exist under actual plant operation conditions.
Thus, in addition to replacing the material with Alloy 690, converting the residual stress to compressive one can prevent the occurrence of PWSCC.
Assessment of Slow Crack Growth Test Methodologies Used to Predict Service Life of High Density Polyethylene Piping
Authors: Kalyanam S. , Krishnaswamy P. , Shim D.-J. , Hioe Y. , Kawaguchi S. , Shimura T. , Numata K. 
Published: January 2014

HDPE pipe and piping components have been used successfully and safely for natural gas distribution around the world for several decades. The primary concerns for a 50-year life for buried HDPE piping involves designing against three primary failure modes — ductile fracture, rapid crack propagation (RCP), and slow crack growth (SCG) under sustained pressure loading. Although design methodologies for preventing ductile fracture, and RCP are well established, SCG remains to be a limiting failure mode in determining useful service life of HDPE piping as it may occur under sustained pressure and temperature. Although considerable amount of research has been conducted over the last two decades, SCG still remains less well understood than other failure modes.
A critical evaluation of various test methodologies available to determine the SCG resistance of HDPE resins was conducted using FEA of various widely used laboratory test specimens. While there exist extensive information on the test methodologies and the applicability of each of the SCG testing methods, there is a growing concern as to whether any/all of these SCG tests give the same information akin to the industrial pipe application, particularly so when conflicting messages are obtained from time to failure predictions from two different SCG tests. While notched-pipe test (NPT) proves to be a direct approach to assess SCG resistance of the PE pipe with the use of temperature as a test accelerating factor; in the case of newer grade PE resins, the failure time of NPT can still be considerably large (∼5,000 to 10,000 hours). For this reason, some of the other coupon SCG tests are focus of recent investigations and especially sought after for rapid ranking/assessment of resins and understanding the manufactured HDPE pipe performance.
In this study, FEA was conducted to facilitate a direct comparison of leading SCG test methods, through determination of both the stress intensity factor, KI, and existing constraint factors in various widely used specimen geometries. These results are then compared to pipe specimen with an OD (outer diameter) or ID (inner diameter) surface notch. Since, constraint can have a significant role in SCG initiation, T-stress, and biaxiality ratios (β), these were compared along the crack fronts to arrive at definitive reasons for the smaller failure times observed when testing some of the SCG test specimens, and also reasons for SCG mode of failure observed even under large applied loads (large KI compared to that in a notched pipe) when testing some of the SCG test specimens. The use of stress intensity factor, KI, along with the T-stress and biaxiality ratio (β), is found to provide a complete picture on the broad spectrum of failure times observed from various SCG test specimens and rationale for choosing a SCG test specimen when evaluating HDPE pipe or resins.
Application and Experience Feedback of ASME Code Case N-155-2 for RTR Piping in Nuclear Plants
Authors: d’Udekem Nicolas , Art Philippe , Grisel Jacques 
Published: January 2014

Nowadays, the usefulness of RTR (Reinforced Thermosetting Resin) for pressure retaining equipment does not need further proof: they are lightweight, strong, with low thermal elongation and highly corrosion resistant. The use of RTR piping makes all sense for piping systems circulating raw water such as sea water at moderate pressure and temperature for plants cooling. However, this material is rarely used for safety related cooling systems in nuclear power plants.
In Belgium, Electrabel and Tractebel have chosen to replace the existing carbon steel pipes of the raw water system by GRE (Glassfiber Reinforced Epoxy) pipes, in accordance with the Authorized Inspection Agency, applying the ASME Code Case (CC) N-155-2 defining the specifications and requirements for the use of RTR pipes, fittings and flanges.
After a challenging qualification process, Class 3 GRE pipes are now installed and operating for raw water cooling systems in two Belgian nuclear units and will soon be installed in a third one.
The paper will address the followed qualification processes and the implementation steps applied by Electrabel/Tractebel and relate the overcome obstacles encountered during manufacturing, erection and commissioning of Class 3 GRE piping in order to ensure quality, reliability and traceability required for safety equipment in nuclear power plants.
A Method for Extracting the Time Delay From the Unsteady and Quasi-Steady Fluidelastic Forces in Two-Phase Flow
Authors: Sawadogo Teguewinde , Mureithi Njuki 
Published: January 2014

The time delay is a key parameter for modeling fluidelastic instability, especially the damping controlled mechanism. It can be determined experimentally by measuring directly the time lag between the tube motion and the induced fluid forces. The fluid forces may be obtained by integrating the pressure field around the moving tube. However, this method faces certain difficulties in two-phase flow since the high turbulence and the non-uniformity of the flow may increase the randomness of the measured force. To overcome this difficulty, an innovative method for extracting the time delay inherent to the quasi-steady model for fluidelastic instability is proposed in this study.
Firstly, experimental measurements of unsteady and quasi-static fluid forces (in the lift direction) acting on a tube subject to two-phase flow were conducted. The unsteady fluid forces were measured by exciting the tube using a linear motor. These forces were measured for a wide range of void fraction, flow velocities and excitation frequencies. The experimental results showed that the unsteady fluid forces could be represented as single valued function of the reduced velocity (flow velocity reduced by the excitation frequency and the tube diameter).
The time delay was determined by equating the unsteady fluid forces with the quasi-static forces. The results given by this innovative method of measuring the time delay in two-phase flow were consistent with theoretical expectations. The time delay could be expressed as a linear function of the convection time and the time delay parameter was determined for void fractions ranging from 60% to 90%.
Fluidelastic instability calculations were also performed using the quasi-steady model with the newly measured time delay parameter. Previously conducted stability tests provided the experimental data necessary to validate the theoretical results of the quasi-steady model. The validity of the quasi-steady model for two-phase flow was confirmed by the good agreement between its results and the experimental data. The newly measured time delay parameter has improved significantly the theoretical results, especially for high void fractions (90%). However, the model could not be verified for void fractions lower or equal to 50% due to the limitation of the current experimental setup. Further studies are consequently required to clarify this point. Nevertheless, this model can be used to simulate the flow induced vibrations in steam generators’ tube bundles as their most critical parts operate at high void fractions (≥ 60%).
Application of Stress Intensity Factors for Deep Surface Cracks to Crack Growth Evaluation
Authors: Iwamatsu Fuminori , Miyazaki Katsumasa , Miyata Hajime , Yuya Hideki 
Published: January 2014

Flaw evaluation for nuclear power plants is conducted on the basis of a fitness-for-service code. For instance, the ASME Boiler and Pressure Vessel Code Section XI (ASME Section XI) and the JSME Rules on Fitness-for-Service for Nuclear Power Plants (JSME Code) prescribe a flaw evaluation procedure. In flaw evaluation, an aspect ratio of a detected surface crack is defined by a/l, where a is the crack depth and l is the crack length, and the aspect ratio a/l does not exceed 0.5. Therefore, a deep surface crack, which has an aspect ratio a/l greater than 0.5, is characterized as a semicircle with l = 2a. Meanwhile, deep surface cracks caused by stress corrosion cracking (SCC) have been detected in the Ni based alloy weld metal. Since the limit of the flaw characterization rule which is an aspect ratio a/l ≤ 0.5 seems to conduct to a conservative evaluation result for a deep surface crack, more rational and applicable flaw evaluation is required in order to eliminate surplus conservatism.
In this study, a flaw evaluation procedure based on ASME Section XI or JSME Code is extended to deal with a deep surface crack. To evaluate crack growth behavior for a deep surface crack, coefficients to calculate stress intensity factors were evaluated by finite element analysis (FEA) and shown in tabular form on the basis of equations prescribed in ASME Section XI and JSME Code. To verify the applicability of proposed coefficients to crack growth evaluation, SCC crack growth behavior for a deep initial crack was evaluated by coefficients applied to the ASME Section XI procedure and a detailed FEA method. Applicability of coefficients to crack growth evaluation was verified through comparisons of crack growth behaviors for deep surface crack under various stress fields.
Instrument Nozzles Fatigue Strength Reduction Factor
Authors: Woods Kirby , Thomas Kenneth 
Published: January 2014

Recent industry experience has raised concerns with the NRC regarding the fracture toughness of small partial penetration instrument nozzles. Historically, small-bore instruments have not been evaluated when Pressure-Temperature curves were developed. Typical instrument nozzles have an outside diameter of 3¼ inches or less and a wall thickness of 11/16 inches or less. They were considered to be exempt per ASME XI Appendix G-2223(c), “Fracture toughness analysis to demonstrate protection against non-ductile failure is not required for portions of nozzles and appurtenances having a thickness of 2.5 in. (63 mm) or less, provided the lowest service temperature is not lower than RTNDT plus 60°F (33°C).” Now it appears that the effect of the nozzle discontinuity on the stresses in the beltline region of the shell must be assessed. This paper will show that historical interpretation of the code is correct and a fatigue analysis of the vessel shell adjacent to these instrument nozzles is unnecessary.
The industry experience with instrument nozzle leakages is typically related to the quality of manufacturing as suggested by J.H. Gross. Fabrication and inspection range quality relative to FSRF is ke = 10 for poor and ke < 5 for good quality. This approach appears to correlate well with this consideration and industry experience. This paper will also demonstrate the use of fabrication travelers and/or inspection information that can be used to determine an appropriate FSRF to assess the relative health of these and other components.
Fatigue Performance of Stabilized Austenitic Stainless Steels: Experimental Investigations Respecting Operational Relevant Conditions Like Temperature and Hold Time Effects
Authors: Solin Jussi , Reese Sven , Karabaki H. Ertugrul , Mayinger Wolfgang 
Published: January 2014

Experimental research on fatigue performance of niobium stabilized stainless steel (1.4550, X6CrNiNb1810mod) relevant for German NPP primary piping demonstrated good long life performance.
Fatigue tests periodically interrupted for holds indicated time and temperature dependent hardening during holds at 25°C to 325°C. Notable extension of fatigue life was measured when loading patterns consist of cyclic deformation in lower temperatures than hold annealing. Many NPP piping thermal transients separated by normal operation belong to this category and fatigue assessment based on standard fatigue data seems to underestimate fatigue endurance.
Further results for stabilized stainless steel in air at various temperatures will be provided. A parallel paper will deliver unpublished data in PWR water. The influences of temperature and loading pattern will be discussed aiming to improve fatigue assessment of plant components and to reduce confusion concerning applicability of international design codes.
Asset Integrity Management of High Pressure Piping Systems Subject to Creep
Authors: Cohn Marvin J. 
Published: January 2014

Safety and reliability are the preeminent concerns in the design, operation, and maintenance of power piping. Recent additions to the ASME B31.1 Power Piping Code (Code) have addressed condition assessment of covered piping systems (CPS). Mandatory requirements for the condition assessment of CPS are discussed in Chapter VII of the Code and nonmandatory guidelines are discussed in Appendix V of the Code. These documents discuss design, fabrication, construction, operation, and maintenance issues, and do not provide detailed guidance in the evaluation of high pressure piping systems subject to creep.
An asset integrity management (AIM) program should integrate and consider all attributes that influence the intended function of the original design. In addition to the evaluation of specified design, fabrication, construction, operation, and maintenance issues, an asset integrity management program should also consider and evaluate significant time-dependent anomalies, such as flexible operation modes, malfunctioning supports, and creep redistributed stresses. An AIM program includes the identification of governing drivers that accelerate piping system damage and then develops countermeasures to mitigate or reduce the driving mechanisms.
This paper discusses the large range of piping system stresses and the sensitivity of stress increase to 50% creep life reduction, indicating the need for a robust stress ranking methodology. The process results in an accurate selection of the most critical creep damage weldments for nondestructive examinations.
Stresses in Nozzle Shell Junctions due to External Loads: A Comparative Study
Authors: Chandiramani Dipak K. , Nawandar Suresh K. , Gopalakrishnan Shyam 
Published: January 2014

Various methods have been in use for the determination of stresses at the nozzle-shell junction due to external loads and moments. Some methods evaluate stress in the cylindrical or spherical shell (e.g. WRC 107 now WRC 537) while others evaluate stresses in cylindrical shells and nozzles (e.g. WRC 297). ASME Section VIII Division. 2 specifies use of WRC 107/WRC 297 or Finite Element Analysis (FEA) for determination of stresses at shell-nozzle junctions with external loads and moments on the nozzle.
Each method could yield a different result for the same loading condition and geometry and this has been recognized in comparisons made in WRC 297 with WRC 107 and FEA. Further, customized FEA software are also available for this analysis.
There still seems to be some confusion in users of these methods regarding selection of method for optimization of design. Users not familiar with Finite Element Method prefer to use calculations based on WRC 107/297.
Hang-Sung Lee, et.al. have recently (PVP 2011 – 57407) analyzed nozzle shell junctions using the Finite Element Method, compared their results with calculations to WRC 297 and made recommendations.
The work presented in this paper is not an attempt to compare individual stresses obtained by classical versus analytical methods. Instead, an attempt has been made to consolidate the results obtained by the various methods into charts to enable a user to make a preliminary assessment to ascertain under what geometrical conditions the calculations made by each of the above methods would result in overall Code acceptable stresses without the results being either overly conservative or un-conservative. This is particularly relevant to the geometries which use the graphs and charts which have been extrapolated without rigorous theoretical background in the WRC Bulletin 537. The Finite Element Method has been used as the referee method.