bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Numerical Investigations on the Failure Behavior of Pressurized Components Containing Crack Fields
Authors: Gauder Patrick , Schuler Xaver , Seidenfuss Michael 
Published: October 2018

During the 2012 outage of the Belgian nuclear power plants (NPP) Doel 3 and Tihange 2 non-destructive testing (NDT) measurements revealed a high quantity of indications in the upper and lower core shells of the reactor pressure vessels (RPV). A root cause analysis leads to the most likely hypothesis that the indications are hydrogen flakes in segregated zones of the RPV ferritic base material. The laminar and quasi-laminar orientation (0° – 15° inclination to the pressure retaining surface) of the hydrogen flakes, the interaction of several adjacent flakes and the mechanical loading conditions lead to a mixed-mode behavior at the crack tips.
In the framework of an ongoing research project, experimental and numerical investigations are conducted with the aim to describe the failure behavior of such complex crack configurations. The experiments are carried out using two ferritic materials. One is a non-irradiated representative RPV steel (SA 508 Class 2) and the second material is a special lower bound melt of a modified 22NiMoCr3-7 steel (FKS test melt KS 07 C) containing hydrogen flakes. A material characterization is done for both materials including tensile specimens, notched round bars, shear-, torsion- and compact-tension-shear (CTS) - specimens to investigate different stress states. Furthermore, flat tensile specimens with eroded artificial crack fields are used to investigate the interaction between the cracks in different arranged crack fields. Numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure an enhanced Rousselier model is used and an enhanced Beremin model to calculate the probability of cleavage fracture. To account the sensitivity for low stress triaxiality damage by shear loading, the Rousselier model was enhanced with a term to account for damage evolution by shear. The Beremin model will be enhanced with a term to account for different levels of triaxiality. For the numerical simulations in the transition region of ductile-to-brittle failure a coupled damage mechanics model (enhanced Rousselier and Beremin) will be used. In this paper, the current status of the ongoing research project and first results are presented.
Effect of Pre-Heat Treatment on Hydrogen Concentration Behavior of y-Grooved Weld Joint Based on a Coupled Analysis of Heat Transfer-Thermal Stress-Hydrogen Diffusion
Authors: Ozeki Go , Yokobori A. Toshimitsu , Ohmi Toshihito , Kasuya Tadashi , Ishikawa Nobuyuki , Minamoto Satoshi , Enoki Manabu 
Published: October 2018

Hydrogen induced cracking occurs at the welded position of the structure due to concentration of hydrogen during cooling process of welding. In order to prevent the hydrogen induced cracking, Pre-Heat Treatment (PHT) is conducted. However, since PHT takes high cost, it is important to find out the suitable PHT condition based on computational mechanics. One of authors has been proposed α multiplication method which magnifies the hydrogen driving term in the diffusion equation to find out detailed behaviors of hydrogen concentration around a local stress field.
In this study, in order to clarify the effect of PHT on hydrogen diffusion and concentration behaviors, a coupled analysis of heat transfer – thermal stress – hydrogen diffusion combining with α multiplication method was conducted for the model of y-grooved weld joint under various PHT conditions.
This analytical method is as follows. At first, heat transfer analysis was conducted by finite difference method (FDM). And, temperature at each grid obtained by heat transfer analysis was interpolated to each node for thermal stress analysis by the finite element method (FEM). Then, thermal stress was calculated for each node using the interpolated temperature. After that, thermal stress obtained by this analysis was interpolated to each grid point for analysis of hydrogen diffusion by FDM. Using the interpolated thermal stress, stress driven hydrogen diffusion analysis was performed. By conducting sequentially these calculations mentioned above, hydrogen diffusion and concentration behaviors during cooling process were analyzed. The temperature of weld metal was 1500°C. And at initial state, hydrogen was introduced in weld metal. Thermal stress analysis was conducted under plane strain condition.
As a result, hydrogen diffusion and concentration behaviour at weld joint during cooling process was found to be typical at the site of maximum hydrostatic stress and to be affected not only the gradient of hydrostatic stress but also the gradient of diffusion coefficient induced by temperature distribution.
A Normalized Stress of Pull-Out Action on Bolted Joints Under Eccentric Load
Authors: Imura Makoto , Koyama Takayuki , Iizuka Motonobu , Suzuki Takayuki 
Published: October 2018

Our objective is to evaluate precisely a life-cycle of bolted joints under an eccentric load against a bolt axis. Many approaches to achieve the objective based on a lot of theories and practices have been proposed so far [1–12]. As we can refer from their approaches, the opening of the structural interface between clamped plates of bolted joints occurs by the eccentric load, which is over a bolt preload, and then the opening gradually propagates as the eccentric load increases. In the case, nonlinearity appears remarkably on the tensional and bending stress of bolts in the axial direction. In addition to the above, the axial bolt stress larger than expected occurs due to the principle of leverage depending on the load position and the bolted joints layout in the early phase of the pull-out action. Accordingly, the stress evaluation of bolted joints under the eccentric load is very important in order to ensure the safety of industrial machines.
If dimensionless quantities of the bolt stress are found out considering the influence of the structural opening and the load eccentricity, we can have a few advantages as follows. First, bolt stress evaluations can be conducted by easily converting the dimensionless quantities of the bolt stress to the physical dimension quantities in a lot of cases where the bolt preload and the load eccentricity are different. Second, the number of times of verification tests can be reduced.
We are developing a lot of industrial machines which have bolted joints used under eccentric load. In such development [13], bolt stress analyses are usually conducted under the combinations of the following conditions: (i) tapped thread joints, (ii) thin clamped plates than the bolt diameter, (iii) large eccentric loads, (iv) permitting the opening of the structural interface. Therefore, we propose a concept of a normalized bolt stress considering the effect of the structural opening and the load eccentricity. We validated this concept through theoretical studies, finite element analyses, and experiments under the direct load and the centrifugal load.
As a result, the dimensionless quantities of the bolt stress caused by the bolt preload and a lever ratio of bolted joints under combined conditions was determined in this study. We can easily evaluate the bolt stress by simple conversions in a lot of cases in which the bolt preload and the load eccentricity differ.
Formable Duplex Stainless Steel for High Pressure GPHE Applications
Authors: Groth Anders , Sun Chang-Ching , He Hailan , Guan Li , Schedin Erik 
Published: October 2018

The high-pressure applications of traditional Gasket Plate Heat Exchangers (GPHE) are limited by the sheet material, gasket material and the design of the GPHE. The newly developed stainless steel grade UNS S82031 (EN 1.4637) is a duplex stainless steel grade with improved formability compared to other duplex stainless steel grades. It can be used in forming intensive applications, such as in typical chevron corrugated-plate heat exchangers. Compared to the standard austenitic stainless steel grades typically used, the new duplex stainless steel increases the application performance of GPHE applications, such as maintaining higher working pressures.
In this paper, the properties and material behavior of UNS S82031 is compared with the standard austenitic stainless steel UNS S30400 (EN 1.4301) in a pressure test at different working pressures. The pressure test is used to evaluate the performance of the selected material for a GPHE application. The experimental test results are compared with Finite Element (FE) simulation of the same pressure test, to achieve a deeper understanding of the results. The results show that plates made of UNS S82031 can withstand significantly higher working pressures than UNS S30400 for the same PHE-design, proving the new duplex stainless steel UNS S82031 is more suitable for high pressure GPHE applications.
Stress Evaluation Method by Frequency Response Function for Elbow Pipes Under Thermal Stratification
Authors: Alrakan Salman , Kuribayashi Hiroshi , Kasahara Naoto 
Published: October 2018

In nuclear reactors, piping components are susceptible to thermal fatigue damage. This is due to the fluid temperature change along these pipelines that can generate repeated thermal loads. One of these loads is thermal stratification.
Thermal stratification generates an oscillating stratified layer, which induce cyclic thermal stresses leading to fatigue damage. To evaluate thermal fatigue by thermal stratification, a frequency response function for straight pipes was developed. However, this function cannot evaluate elbow pipes under thermal stratification. Here, thermal stress generates due to bending moment that is generated by the horizontal portion unlike straight pipes. Furthermore, the elbow pipe can give rise to stress intensifications which can affect the peak stress values within the elbow.
To understand the stress generation mechanism, Finite element analyses were performed. The study focused on the effect the frequency of the fluid oscillation on the stress generation mechanism. Based on the clarified mechanism, the frequency response function was improved to correspond to the thermal stratification at elbow pipes. Applicability of this function was validated through agreement with finite element simulation.
A Novel Approach for Assessment of Pressurised Equipment for Slow Depressurisation During Fire
Authors: Ebrahimi Kaveh , Mofrad Saeid Rahimi , Millet Barry , Kirkpatrick Kenneth , Miller George 
Published: October 2018

Majority of modern design codes and regulations for pressurised equipment mandate that pressurised equipment are equipped with depressurising facilities so that in the event of an over-pressurising scenario or during emergency shut-downs the equipment can be safely depressurised.
In the process industry, depressurisation calculations are usually done in accordance with the requirements of API 521 standard. For equipment with a wall thickness greater than 25mm, this standard recommends that depressurising facilities are designed to reduce the pressure of a vapour containing system exposed to external pool fire from the initial internal pressure to the final safe pressure within 15 minutes. There are cases where the depressurising time is even further shortened from 15 minutes by design engineers, e.g. for LPG applications or jet fire scenario.
Once depressurisation facilities are sized for the fire-case, depressurising calculations are carried out in order to determine the minimum metal temperatures at coincident pressures reached in the equipment in a non-fire depressurising scenario (called cold-case). This will enable design engineers to analyse equipment for potential brittle fracture of equipment during cold-case depressurisation.
Whilst the above mentioned methodology is usually adequate for majority of applications, there may be occasions that achieving API 521 recommended fire-case depressurisation time would require a large depressurising valve. This can potentially cause:
• Significantly fast depressurising (and subsequent auto-refrigeration) in the cold-case leading to very low metal temperatures and the need for costly materials, particularly in cold climate environments;
• Damage to equipment internals due to high depressurising rate;
• Overloading the existing flare network in a brown field project.
Increasing the depressurising time can alleviate the operational and/or economic issues arising from rapid depressurisations. However, slower-than-usual depressurisation increases the risk of rupture during fire-case, as equipment will be subject to heat for a longer period of time whilst still pressurised.
This paper describes a methodology and identifies the necessary steps for assessment of pressurised equipment for slow depressurisations. The method is based on the provisions in the latest editions of API 521, API 579-1/ASME FFS-1 and Finite Element Analysis (FEA). A sample high pressure vessel is analysed in this paper for both cold and fire depressurisation.
Flange Gasket Behavior Characterization for Service in Arctic Environment
Authors: Lejeune Hubert , Javanaud Stéphane , Richard Kevin 
Published: October 2018

With Oil and Gas exploration and production in low temperature arctic environment, new concerns arise concerning the application of the existing design rules for these conditions. Most codes and standards for bolted flange calculation do not include specific rules concerning application at low temperature. Especially, gasket performances under low temperature are neither tabulated nor easily available from other public sources.
In this context, in collaboration with TOTAL, SCHLUMBERGER and SAIPEM sponsors, the CETIM has performed a program called ARCTICSEAL to characterize the flange gasket behavior in arctic environment. The goal is to check that gasket references, commonly used by these companies, are still usable under low temperature arctic conditions without main performance loss.
The test program involves mechanical and sealing tests performed on 4 gasket types (sheet fiber based, sheet PTFE based, sheet graphite based and graphite spiral wound) with both NPS 8 and NPS 16 gasket sizes. Gasket performances are determined at −60°C, after loading at −25°C. Additional test involving hot/cold thermal cycling ageing (simulation of intermittent hot process fluid in the bolted flange) have also been performed. The result shows the ability of the tested gasket references to maintain good sealing behavior in most cases. Moreover, the hot/cold thermal cycling ageing improves the sealing performances for some of the tested gasket references. Moreover, a dedicated test stand has been developed to study the behavior of NPS 8 flange connection exposed to quick heat-up after exposure to low temperature environment.
Reversing the Chell Model to Predict Using Monte Carlo Simulations the Original Fracture Toughness of Ferritic Steels
Authors: Van Gelderen Derreck , Booker Julian 
Published: October 2018

Warm pre-stress (WPS) is the process of subjecting a pre-cracked component to a load cycle at a temperature higher than subsequent operating temperatures. This process is widely acknowledged as being able to enhance the load to fracture, especially in ferritic steels which exhibit lower shelf cleavage fracture.
Various models exist to predict this type of enhancement, with the Chell model being one of the most widely used within industry. Previous research conducted by Van Gelderen et al. have reformulated the Chell model to create a method of undertaking Monte Carlo Simulations (MCS) to study the effect of WPS on brittle fracture.
Following on from this research, the Chell model could effectively be reversed providing a means of predicting the underlying fracture toughness from experimental WPS data. It also offers the possibility of assessing whether or not a specific specimen has indeed seen an enhancement, solely based on its experimental apparent toughness post WPS.
The reverse Chell model was applied to different experimental data and provided reasonable estimates of the original fracture toughness. In the same way that the traditional Chell model offers conservative estimates, the reverse Chell model also provides “reverse conservative” estimates of the original fracture toughness. It was also used to provide confidence that a typical fatigue pre-cracking procedure performed according to ASTM standard E399 would not be sufficient to induce a WPS benefit on the specimens. This type of check can be of particularly interest when manufacturing small scale specimens (small scale Single Edge Notch Bend (SENB) or miniature sized Compact Tension C(T) specimens); a practice often favoured by industry to maximise the number of tests possible.
Flamanville EPR RPV’s Heads Carbon Segregation: Tests Program Definition to Characterize the Mechanical Properties of the Carbon Segregation
Authors: Marie Stéphane , Demarecaux Jérôme , Fichot Philippe , Keim Elisabeth , May Johannes , Lambrecht Marlies , Chaouadi Rachid , Birkett Peter , Hajjaj Mejido , Miller Cecile 
Published: October 2018

To characterize the mechanical properties of the residual carbon segregation of the Flamanville EPR RPV heads, a testing program have been organized by Framatome and performed in 3 laboratories (Wood, Framatome technical center of Erlangen and SCK Mol).
This paper presents the tests program, how it has been defined and its goals. The main issue was the impact of the carbon content on the toughness properties. A procedure was defined to characterize specifically the toughness distribution in the upper part of the brittle-to-ductile transition. The ductile regime was also investigated. These tests were completed with tensile, Charpy and drop weight tests, representing a final total of approximatively 1700 mechanical tests.
A Proposed Guideline for Applying Waterhammer Predictions Under Transient Cavitation Conditions: Part 1 — Pressures
Authors: Stewart Matthew , Walters Trey W. , Wunderlich Greg , Onat Erin A. 
Published: October 2018

Waterhammer analysis (herein referred to as Hydraulic Transient Analysis or simply “HTA”) becomes more complicated when transient cavitation occurs (also known as liquid column separation). While standard HTA transient cavitation models used with analysis based on the Method of Characteristics show good correlation when compared to known test/field data, the great majority of test/field data are for simple systems experiencing a single transient. Transient cavitation in more complicated systems or from two or more independently initiated transients have not been validated against data.
Part 1 of this paper describes the various safety factors already provided by ASME B31.3 for pressure containment, provides criteria for accepting the results of HTA calculations that show the presence of transient cavitation, and makes recommendations where the user should include additional safety factors based on the transient cavitation results.
Situations are discussed where waterhammer abatement is recommended to reduce hydraulic transient pressures and forces, and for increasing confidence in HTA results in specific cases. The result is a proposed comprehensive and pragmatic guideline which practicing engineers can use to perform waterhammer analysis and apply pressure predictions to pipe stress analysis.
A Proposed Guideline for Applying Waterhammer Predictions Under Transient Cavitation Conditions: Part 2 — Imbalanced Forces
Authors: Stewart Matthew , Walters Trey W. , Wunderlich Greg 
Published: October 2018

Waterhammer analysis (herein referred to as Hydraulic Transient Analysis or simply “HTA”) becomes more complicated when transient cavitation occurs (also known as liquid column separation). This complication is exacerbated when trying to predict imbalanced forces as this often involves comparing pressure times area (“PxA”) forces at two locations (for example at elbow pairs). Whereas the pressure at each elbow location has increased uncertainty because of transient cavitation, the difference in PxA forces at elbow pairs involves subtracting one potentially uncertain pressure from another uncertain pressure. Exacerbating this uncertainty yet further, the existence of vapor in a liquid system can dramatically affect the fluid wavespeed and, hence, the timing of the pressure wave travel between two locations such as elbow pairs; so the pressure calculated at each location would not actually occur at exactly the same time.
This Part 2 discusses methods of accounting for uncertainty in HTA imbalanced force predictions due to cavitation. The criteria in this paper assume that cavitation in the HTA has been assessed and accepted per the criteria in Part 1 of this paper.
A guideline is proposed for accepting and applying such results and, in particular, makes recommendations on safety factors to use in pipe stress analysis for different cases. The specific recommendations depend on numerous factors including:
• Presence or absence of cavitation in hydraulically connected or isolated parts of the system
• If cavitation occurs, whether the peak forces occur before or after cavitation first occurs
• Size of the cavitation vapor volumes with respect to the computing volumes
• Use of point forces as a conservative substitute in place of potentially less certain elbow pair forces or the manual assessment of maximum envelope values for the force.
Situations are discussed where waterhammer abatement is recommended to reduce hydraulic transient forces, and for increasing confidence in HTA results in specific cases. The result is a proposed comprehensive and pragmatic guideline which practicing engineers can use to perform waterhammer analysis and apply imbalanced force predictions to pipe stress analysis.
Demonstrate ASME Section XI Appendix G Margins for Pressurized Water Reactor Inlet and Outlet Nozzle Corner Regions
Authors: Udyawar Anees , Hall J. Brian , Webb Justin , Carolan Alexandria 
Published: October 2018

Since the implementation of pressure-temperature (P-T) limit curves in the 1960s for light water reactors, the P-T limit curves have been based on the limiting locations in the reactor coolant system, which are typically the irradiated reactor pressure vessel (RPV) region adjacent to the core (beltline) and the closure head flange. Recently, it has been questioned as to whether the reactor vessel inlet or outlet nozzle corners could be more limiting due to the stress concentration at these locations. The discussion presented in this paper provides technical justification that the RPV nozzle corner P-T limit curves are bounded by the traditional P-T limit curves for the pressurized water reactors (PWRs).
The current approach in evaluating the Pressurized Water Reactor Inlet and Outlet nozzle corner regions with respect to plant heatup and cooldown Pressure Temperature Limit Curves contains a number of conservatisms. These conservatisms include postulation of a large 1/4T flaw at the nozzle corner region, use of RTNDT (reference nil-ductility temperature), and fracture toughness prediction based on plane strain fracture toughness. The paper herein discusses several factors that can be considered to improve the pressure temperature limit curves for nozzle corners and increase the operating window for nuclear power plant operations.
Prior to the 2013 edition, the ASME Section XI Appendix G did not require the use of a 1/4T flaw for the nozzle corners; furthermore, a smaller postulated flaw size is permissible. Based on inspection capability and experience, a smaller flaw size can easily be justified. The use of a smaller flaw size reduces the stress intensity factors and allows for the benefit of being able to take advantage of increased material toughness due to the loss of constraint at the nozzle corner geometry. The analysis herein considers the calculation of stress intensity factors for small postulated nozzle corner flaws based on a 3D finite element analysis for Westinghouse PWR inlet and outlet nozzle corner regions. The Finite Element Analysis (FEA) stress intensity factors along the crack front are used in the determination of allowable pressures for the cooldown transient Pressure-Temperature limit curves.