bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Stoichiometric H2/O2/N2-Mixtures in Long and Short Pipes
Authors: Schildberg Hans-Peter 
Published: November 2015

As continuation of recently published experimental work [1,2], the static equivalent pressures (“pstat“) of the different detonative pressure scenarios occurring in stoichiometric H2/O2/N2 mixtures were determined in long and short pipes at ambient initial temperatures (20 °C) and initial pressures ranging from 4 bar abs to 35 bar abs. The pipes used for the tests were about 10 m long and had radial dimensions of 48.3×2.6 and 114.3×3.6 (outer diameter [mm] × wall thickness [mm]). The O2 content was varied from about 10 vol.-% to the highest value possible in stoichiometric mixtures (33.3 vol.-%).
For the tests in the long pipes the focus was on the variation of the ratio between the static equivalent pressure at the point where transition from deflagration to detonation occurred and the static equivalent pressure in the region of the stable detonation (pstat_DDT_long / pstat_stable). The ratio attained a maximum of about 5 at 14.78 vol.-% O2 (stoichiometric H2/air) and decays to 1 when increasing the O2 content to 24 vol.-%. This drop indicates that with increasing O2 content ever less precompression is required to cause auto ignition in the precompressed gas directly ahead of the deflagrative flame front. For mixtures of H2 with N2-diluted air the ratio exhibits a slight decrease which is in contrast to what would be expected and is not yet understood. The results obtained for the ratio between pstat of scenarios 3 and 4 (stable detonation and reflected stable detonation) and the Chapman-Jouguet pressure of the investigated gas mixtures confirmed the findings presented in PVP2013-97677 for ethylene/air-mixtures.
For mixtures of H2 and slightly diluted air the load for the reflected instable detonation was found to be about 7 · pstat_stable, the load at the DDT in the short pipe is 6.6 · pstat_stable and the load for coalescence of DDT and reflection is about 14 · pstat_stable.
Optimization of the Existing Screening Method by Introducing Fen Correlations
Authors: Métais T. , Gilman T. , Genette P. , Chinthapalli A. 
Published: November 2015

In the wake of numerous experimental tests carried out in air and also in a PWR environment, both abroad and in France, an update of the current fatigue codification is underway. Proposals are currently being formulated in France [1] [2] and discussions are taking place in the frame of a French working group involving EDF, AREVA and CEA.
In parallel with these worldwide modification efforts, it is necessary to evaluate their impact on the NSSS components. In the USA, many such evaluations have already been implemented for license renewal to operate power plants beyond their initial 40 years of operation. In order to reduce the scope of the calculations to perform, a preliminary screening was carried out on the various areas of the primary loop: this screening is detailed in an EPRI report [3]. The output of this screening process is a list of locations that are most prone to EAF degradation process and it is on these zones only that detailed EAF calculations are carried out.
In France, with the approaching fourth decennial inspection of the 900 MWe (VD4 900 MWe) power plants, EDF needs also to map out the impact of these updates to the RCC-M code before initiating detailed calculation efforts.
The EPRI report was not applicable as such to the French plants due to domestic specificities and more particularly, a need for a more detailed Fen estimation. A method was therefore developed by EDF, peer-reviewed by SI with the main innovation being the introduction of correlations enabling the calculation of Fen on the basis of the geometrical dimensions and the information available in the transient document.
This paper presents how these correlations were built and proposes to benchmark them with some existing sample case problems.
Options for Defining the Upper Shelf Transition Temperature (Tc) for Ferritic Pressure Vessel Steels
Authors: Kirk Mark , Stevens Gary , Erickson Marjorie , Server William , Gustin Hal 
Published: November 2015

This paper evaluates current guidance concerning conditions under which the analyst is advised to transition from a linear-elastic fracture mechanics (LEFM) based analysis to an elastic-plastic fracture mechanics (EPFM) based analysis of pressure vessel steels. Current guidance concerning the upper-temperature (T>c) for LEFM-based analysis can be found in ASME Section XI Code Case N-749. Also, while not explicitly stated, an upper-limit on the KIc value that may be used in LEFM-based evaluations is sometimes taken to be 220 MPa√m (a value herein referred to as KLIM). Evaluations of Tc and KLIM were performed using a recently compiled collection of toughness models that are being considered for incorporation into a revision to ASME Section XI Code Case N-830; those models provide a complete definition of all toughness metrics needed to characterize ferritic steel behavior from lower shelf to upper shelf. Based on these evaluations, new definitions of Tc and KLIM are proposed that are fully consistent with the proposed revisions to Code Case N-830 and, thereby, with the underlying fracture toughness data. Formulas that quantify the following values over the ranges of RTTo and RTNDT characteristic of ferritic RPV steels are proposed:
• For Tc, two values, Tc(LOWER) and Tc(UPPER), are defined that bound the temperature range over which the fracture behavior of ferritic RPV steels transitions from brittle to ductile. Below Tc(LOWER), LEFM analysis is acceptable while above Tc(UPPER) EPFM analysis is recommended. Between Tc(LOWER) and Tc(UPPER), the analyst is encouraged to consider EPFM analysis because within this temperature range the competition of the fracture mode combined with the details of a particular analysis suggest that the decision concerning the type of analysis is best made on a case-by-case basis.
• For KLIM, two values, KLIM(LOWER) and KLIM(UPPER), are defined that bound the range of applied-K over which ductile tearing will begin to occur. At applied-K values below KLIM(LOWER), ductile tearing is highly unlikely, so the use of the KIc curve is appropriate. At applied-K values above KLIM(UPPER), considerable ductile tearing is expected, so the use of the KIc curve is not appropriate. At applied-K values in between KLIM(LOWER) and KLIM(UPPER), some ductile tearing can be expected, so it is recommended to give consideration to the possible effects of ductile tearing as they may impact the situation being analyzed.
These definitions of Tc and KLIM better communicate important information concerning the underlying material and structural behavior to the analyst than do current definitions.
Repercussion of Autofrettage on the Fatigue Crack Growth in the Vicinity of Catalyst Entry Opening for Polyethylene Autoclave Reactor
Authors: Haeri Navid , Cornah Brian A. 
Published: November 2015

Background. The authors conducted a study to analyse the impact of autofrettage practice on the fatigue crack growth in the vicinity of the catalyst entry nozzle in a MK.15 ICI LDPE autoclave reactor.
Methods. The authors created 3-D finite element models of the quadrant of the opening. Elastic-plastic analysis was carried out to evaluate the residual stresses from the autofrettage which were then used as an input to the fracture mechanics analysis. Linear Elastic Fracture Mechanics (LEFM) methodology was then deployed associating a Radial Direction, Quarter-Circular Corner Crack pattern as per API 579/ASME VIII Div.3 for the purpose of calculating the crack tip stress intensity. A number of hypothetical pressure cycles were considered in order to calculate the crack growth rate as per ASME Div.3 (Paris’ Law) both with and without residual stresses from autofrettage analysis.
Results. The study results showed the change in the crack behaviour as a result of adding the autofrettage residual stresses onto the model and discussed the implications of such a practice on the design life for autoclave reactors.
System Stiffness and Restraint Effects on Circumferential Crack Opening Displacements: A Rotational Stiffness Approach
Authors: Young Bruce A. , Olson Richard J. 
Published: November 2015

Current crack opening displacement (COD) solutions for leak-before-break (LBB) analyses assume the ends of the cracked pipe, which is subjected to remote bending and internal pressure, are free to rotate. However, in plant piping systems, the pressure induced bending and imposed rotations are restrained, because the ends of the pipe are constrained by the rest of the piping system and other components. Hence, existing evaluation procedures, theoretically overestimate the COD values of a circumferential through-wall crack (TWC) in a piping system. These overestimations comprise one of the uncertainties in an LBB analysis, as it leads to an under-prediction of the leakage-size-crack length of a postulated leaking TWC for a prescribed leakage detection limit in a plant, and thus, results in a non-conservative estimation of the crack stability from an LBB perspective.
Historical efforts on the effects of restraint on COD have focused on a restraint distance from the crack to restrain the rotation of the pipe. This study provides a fundamentally different approach in that the underlying theory develops a relationship between the apparent rotational stiffness of a pipe with unrestrained ends and the material modulus as a function of crack length and pipe geometry. Thus, the local system stiffness from a plant structural model can be used to modify the unrestrained value of COD.
Effect of Reverse Yielding on the Residual Contact Stresses of Tube-to-Tubesheet Joints Subjected to Hydraulic Expansion
Authors: Bouzid Abdel-Hakim , Kazeminia Mehdi 
Published: November 2015

The analytical prediction of the contact stress in tube-to-tubesheet joints subjected to hydraulic expansion is conducted without any consideration to reverse yielding that can occur inside the tube. Most existing models consider the tube and tubesheet to unload elastically when the expansion pressure is released. These models are therefore less conservative as the overestimate the contact pressure.
An analytical model that considers strain-hardening material behavior of the tube and tubesheet and accounts for reverse yielding has been developed. The model is based on Henckey deformation theory and the Von Mises yield criteria. The paper shows that reverse yielding that is present in tubes during hydraulic expansion unloading makes the joint less rigid and causes a decrease in the contact pressure depending on the gap clearance and the materials used. A good correlation between the analytical and FEM results is obtained on different treated cases which gives confidence on the developed model.
On a Flaw Shape Idealization of Axial Surface Flaws for Structural Integrity Assessment of Steam Generator Tubes
Authors: Park Seung-Hyun , Choi Jae-Boong , Huh Nam-Su 
Published: November 2015

Nowadays, nuclear power plant (NPP) has become one of the most important energy sources to generate electricity in the world. Steam generator (SG) is a heat exchanger included in primary system of NPP.
Alloy 600 MA is widely used for SG tube material and this is well-known as weakness of stress corrosion cracking. In recent year, according to increase the number of long-term operation NPP, many axial surface flaws have been found on SG tube during an in-service inspection. Therefore, many researches have been carried out to maintain structural integrity of SG tube. Commonly, flaw shape needs to be idealized to calculate a burst pressure because detected flaw shape is complicated.
In this paper, validation of EPRI’s weakest sub-crack model, one of the well-known flaw idealization rule, is conducted through finite element (FE) analysis. For this, three actual flaws are assumed and these are idealized by using four flaw shape idealization methods; semi-elliptical crack model, rectangular crack model, maximum length with effective depth crack model and weakest sub-crack model. Burst pressure of each model is calculated and compared with burst pressure of actual shape crack model. As a result, if actual flaw is idealized by weakest sub-crack model, it is expected that conservative and efficient structural integrity assessment will be possible.
Estimation of Elastic Crack Opening Displacement for Thin Elbows With Circumferential Through-Wall Cracks
Authors: Kim Min-Kyu , Surh Han-Bum , Won Min-Gu , Huh Nam-Su , Kim Moon-Ki , Choi Jae-Boong 
Published: November 2015

Leak-before-break (LBB) is an important concept that could confirm design and integrity evaluation of nuclear power plant piping. For the LBB analysis, the detective leakage rate should be calculated for a through-wall cracked pipes. For this calculation, the crack opening displacement (COD) calculation is essential.
Recently, sodium faster reactor (SFR) which has thin-walled pipes with Rm/t ranged 30–40 was introduced and then the investigation of these thin walled pipes and elbows has received great attention in the LBB evaluation. In this context, the three-dimensional finite element (FE) analyses for thin elbows with circumferential crack under in-plane bending are carried out to investigate the elastic COD values.
Finally, the solution for elastic COD which can cover sufficiently thin elbow is successfully addressed.
Development of Test Guidance for Single Edge Notch Bend Fracture Toughness Specimens Containing Notches Instead of Fatigue Pre-Cracks
Authors: Horn Anthony J. , Budden Peter J. 
Published: November 2015

Structural integrity assessment codes such as R6 and BS7910 provide guidance on the assessment of flaws that are assumed to be infinitely sharp. In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. A common feature of these methods is the need to understand how the effective toughness, characterised using the J-integral for a notch, varies with notch acuity. No comprehensive guidance currently exists for obtaining J experimentally from specimens containing notches, hence the typical approach is to use equations intended for pre-cracked specimens to calculate J for notched specimens.
This paper presents a comprehensive set of test guidance for calculating J from Single Edge Notch Bend (SENB) fracture toughness specimens containing notches instead of fatigue pre-cracks. This has been achieved using 3D Finite Element Analyses to quantify the accuracy of formulae intended for pre-cracked specimens in fracture toughness testing standards ASTM E1820, BS7448-1 and ESIS P2-92 when applied to specimens containing notches. The paper quantifies the accuracy of these equations for notched SENB specimens and identifies the conditions under which the equations can lead to inaccurate measurement of J for notched specimens.
SENT Stable Tearing Crack Path Deviation and its Influence on J
Authors: Hutchison Emily K. , Moore Philippa L. , Bath Warren P. 
Published: November 2015

Crack path deviation in Single Edge Notch Tension (SENT) specimens, and its influence on the determination of J, has been investigated as part of the development of a new British Standard for SENT testing, BS 8571 [1]. Crack path deviation by angles up to 50° have been observed during stable tearing in parent material SENT specimens. This paper investigates the effect of crack path deviation on the measured fracture toughness, and offers a correction formula when crack path deviation invalidates the default standard J equations. Mixed mode effects in crack path deviation are also investigated.
A parametric study using finite element analysis has been carried out to compare the value of J calculated using standard equations (which assume a straight crack propagation path) with the value of J calculated using the contour integral method for different levels of crack path deviation. Crack path deviation from the initial crack plane resulted in a non-conservative estimate of fracture toughness using the standard equations. This means that any SENT test exhibiting crack path deviation may need to be discarded, wasting valuable test specimens. Instead, a correction factor has been developed to adjust the calculated value of J if path deviation is observed.
Fatigue Reassessment to Modern Standards for Life Extension of Offshore Pressure Vessels
Authors: Hutchison Emily , Wintle John , O’Connor Alison , Buennagel Emilie , Buhr Clement 
Published: November 2015

Life extension of ageing assets is becoming increasingly important for the offshore oil and gas industry. Many pressure vessels in service have reached or are about to reach the end of their design lives, but their continued operation is required until the economic field life is exhausted. Many vessels in-service were designed over 30 years ago, when fatigue assessment was not required by the design standards. Therefore, fatigue reassessment is a critical part of the life extension process.
This paper presents reassessment of a benchmark vessel as a case study for life extension of other similar vessels. Life extension assessments are costly and time consuming, often hindered by a lack of information and a lack of access to the vessels. By determining the commonality between a vessel and the benchmark vessel, it may be possible with suitable on-going in-service inspection to justify life extension of the vessel without the need for a full fatigue life extension reassessment in every case.
The case study considered in this paper is a condensate flash separator vessel constructed in the early 70s which was in operation for 25 years; and is similar to many pressure vessels still in service on offshore platforms. The fatigue lives of key features of the vessel have been calculated and compared using different modern pressure vessel design codes, supported by finite element analysis.
Austenitic Cladding and Master Curve
Authors: Brumovsky Milan , Kytka Milos , Kopriva Radim , Falcnik Michal 
Published: November 2015

Reactor pressure vessels of PWR/BWR/WWER type reactors are covered by austenitic cladding made by welding on their inner wall. Austenitic materials usually have no transition temperature behavior as they have fcc crystallographic structure. But, austenitic cladding made by welding contain usually up to 8 % of delta-ferrite that results in some transition behavior of fracture properties. This transition can be observed in temperature region below room temperature.
Surprisingly, this transition behavior in static fracture toughness of both cladding layers can be well described by “Master curve” approach.
Results from testing austenitic cladding for WWER type reactors will be shown and discussed, ether in unirradiated as well as irradiated conditions — only small changes in fracture toughness properties in this transition region are observed as a result of irradiation.
A Study of the Surface Penetration of High Cycle Thermal Loading in Pressure Retaining Components
Authors: Jones Michael , Carter Keith F. 
Published: November 2015

This paper presents an overview of sensitivity studies undertaken by Rolls-Royce into the penetration of High Cycle Thermal Loading (HCTL) in Pressurised Water Reactor (PWR) components.
HCTL is a surface effect which has the potential to impact the fatigue life of pressure retaining components, typically at fluid mixing tees and other regions of turbulent mixing flows at different temperatures. This effect can significantly reduce the fatigue life of components. Understanding the factors that contribute to the penetration depth of HCTL can lead to possible benefits in analysis carried out to inform design decisions and support through-life management.
The sensitivity studies presented herein use governing equations for heat transfer at solid surfaces to assess how component properties and loading conditions such as material type, wall thickness and temperature oscillation frequency affect the penetration depth of HCTL and thus the resultant stresses generated within metal surfaces close to fluid mixing zones.
This paper discusses the potential benefits of improved analysis of HCTL effects to inform component design decisions and support through-life management. This is directly applicable to the selection of Start-of-Life (SoL) defect sizes for defect tolerance studies i.e. the assumed initial defect size, the development of Non-Destructive Examination (NDE) techniques, and the safe estimation of In-Service Inspection (ISI) periods at areas of concern.
Analytical Study on Failure Mechanisms by Extreme Loadings Under Design Extension Conditions
Authors: Ogawa Hiroshi , Machida Hideo , Kasahara Naoto 
Published: November 2015

As the important lessons learned from Fukushima-nuclear power plant accident, mitigation of failure consequences and prevention of catastrophic failure were strongly recognized against severe accidents (SA) and excessive earthquake conditions. To improve mitigation measures and accident management, clarification of failure behaviors with locations is premised under design extension conditions (DEC) such as severe accidents and earthquakes. Design extension conditions induce some different failure modes from design conditions. Furthermore, the best estimation for these failure modes is required for preparing countermeasures and management. Therefore, this study focused on identification failure modes under design extension conditions. To realize best estimation, it is prerequisite to clarify failure modes with ultimate structural strength under extreme loadings such as very high temperature, pressure and great earthquakes.
The authors attempt to clarify unclear failure mechanisms by extreme loadings under DEC using numerical simulations. In this paper, relations between failure modes and extreme loadings were investigated by the numerical simulation using the cylindrical model which is a typical structure of nuclear reactor structures (for example, Formed Head, Nozzle, Instrument Tube, Guide Tube, Support Skirt, etc.). Moreover, it was shown that failure modes change with an effect of structural discontinuities. Local failure dominates than ductile fracture at locally constraint portions where stress triaxiality becomes high.
Effect of Nozzle Dimensions on the Stresses in Compensated Openings in Cylindrical Shells
Authors: Chandiramani Dipak K. , Gopalakrishnan Shyam , Mathkar Ameya 
Published: November 2015

Clause 4.5 of ASME Section VIII Div. 2 [1] provides rules for compensation of openings in cylindrical shells having fitted nozzles.
There appears to be no definition of “nozzle” in either ASME Section VIII Div. 2 or ASME Section VIII Div. 1 [2].
The rules provided in Clause 4.5.5 of ASME Section VIII Div. 2 are based on pressure area method which ensures that the reactive force provided by the vessel material is greater than or equal to the load from the pressure.
The key element in applying this method is to determine the dimensions of the reinforcing zone, i.e, the length of the shell, height of the nozzle and reinforcing pad dimensions (if reinforcing pad is provided), that resist the applied pressure.
There appears to be no restriction on the physical dimensions of the nozzle or shell, so long as the required area AT is obtained and the stresses are within allowable limits.
It is therefore possible that all of the required area AT is obtained from the nozzle or from the shell. While both these alternatives would be acceptable, the actual stresses at the shell/nozzle junction may vary considerably.
The work reported in this paper was undertaken with a view to determining if there needs to be any restriction on the proportion of area contributed by shell or nozzle to ensure that actual stresses were within allowable limits.