bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation on Parametrically Excited Motions of Point Absorbers in Regular Waves
Authors: Tarrant Kevin R. , Meskell Craig
Published: November 2014

Free floating objects, such as a self reacting wave energy converter (WEC), may experience a condition known as parametric resonance. In this situation, at least two degrees of freedom become coupled when the incident wave train has a frequency approximately twice the pitch or roll natural frequency. This can result in very large amplitude motion in pitch and/or roll. While classic linear theory has proven sufficient for describing small motions due to small amplitude waves, a point absorber WEC is often designed to operate in resonant conditions, and so exhibits significant non-linear responses. In this paper, a time-domain non-linear numerical model is presented for describing the dynamic stability of point absorbers. The pressure of the incident wave train is integrated over the instantaneous wetted surface to obtain the non-linear Froude-Krylov excitation force and the non-linear hydrostatic restoring forces, while first order diffraction-radiation forces are computed by a linear potential flow formulation. The model was applied to a scale model of a specific WEC design, the Wavebob. Comparison with limited data from scale model wave tank tests provided further confidence in the model.
STYLE: Modelling of the Extraction of Bend Specimens From Repair Weld and the Influence of Residual Stress on Fracture Testing
Authors: James Peter , Ford Mike
Published: November 2014

Within the EU 7th framework programme, STYLE, a number of large-scale tests have been performed. One of these tests, Mock-Up 2 (MU-2), was performed on a through wall crack located at a repair weld adjacent to a multi-pass narrow-gap weld. The aim of MU-2 was to investigate ductile crack growth under conditions with significant levels of residual stress. As part of the materials testing programme, low-constraint fracture specimens (three-point bend specimens with a/t=0.1) were extracted from the weld to test the weld materials fracture toughness. An overview of these tests is provided here.

However, these low constraint tests demonstrated somewhat unusual fatigue crack growth on inserting the crack, leading to the crack depth being shorter in the centre of the specimens to the outside. Subsequently, although it has not been possible to use these specimens to determine the materials J-R curve, it does provide a features test for ductile modelling with the Gurson-Tvergaard-Needleman (GTN) local approach model for ductile crack growth. This paper provides an overview of the modelling associated to understand these observations, including an estimate of the retained residual stress, fatigue growth estimates and subsequent ductile modelling.

An overview of the calibration of the GTN model is also provided using the weld material’s tensile tests, high constraint compact-tension tests and MU-2.
Braiding: A New Production Method Approach for Composite Pressure Vessels in Automotive Applications
Authors: Lengersdorf Michael , Multhoff Jörg , Gries Thomas
Published: November 2014

With the first serial production of a hydrogen fuel cell car announced to enter the market in 2015, there is a prospective mass market for mobile pressure vessel applications. In automotive applications three factors are mainly decisive for a successful integration: low weight, a competitive price range and a safe operation implementation. Composite vessels can fulfill these demands. State-of-the art for the production of the composite structure is wet-filament winding. It is well established for smaller production volumes. However the potential of rise in output is limited. In filament winding only a limited number of usually 1–10 fibres is layed onto a mandrel at once. Braiding in comparison allows the simultaneously deposition of a multitude of fibres, standard machinery allow braiding of more than 200 fibres. A filament wound composite structure lacks fracture resistance under certain load cases. Composite structures known to have better fracture resistance are interlaced fibre architectures, such as braid. This applies especially for impact performance [7].

The braiding process strongly depends on the desired product. The machinery has to be chosen accordingly to application regarding e.g. the number of fibre carriers and their quantities. In automotive applications the dimensions are limited to a certain range due to available build space in the car. This paper will show which parameters have to be considered when setting up a production line for braided pressure vessels. This is done against the background of typical pressure vessel dimensions in automotive applications.
Performance-Based NDE Personnel Qualifications
Authors: Stephens Henry M.
Published: November 2014

This paper establishes an alternative approach for nondestructive examination (NDE) personnel qualification for the boiler and pressure vessel (B&PV) industry. This is the “white paper” developed by the Section XI, Division 2, Task Team, Performance-based NDE Personnel Qualifications. It is anticipated to be the basis for the NDE personnel qualification criteria for the revised Section XI, Division 2, REQUIREMENTS FOR RELIABILITY AND INTEGRITY MANAGEMENT (RIM) PROGRAM FOR NUCLEAR POWER PLANTS that is currently being developed.

Based on review of a number of quantitative NDE reliability studies conducted to-date the current deterministic approach to NDE personnel qualification based on such schemes as ASNT SNT-TC-1A, ANSI/ASNT CP-189, EN-473, ISO-9712 and other similar approaches are not as effective as desired. The goal of this document is to present an alternative approach to the deterministic NDE personnel qualification schemes.

This paper presents a systematic approach to training together with performance-based tests, psychometrically validated evaluation of knowledge and skills that will improve a NDE candidate’s performance. A majority of traditional employer-based written examinations are not developed or validated psychometrically. The use of third-party psychometrically validated examinations would replace the current practice of employer developed and administered examinations. It improves upon traditional ASNT SNT-TC-1A, ASNT/ANSI CP-189, ISO-9712, etc., requirements by including more comprehensive hands-on practical examinations on a statistically valid set of samples containing flaws representative of those expected to be encounter in shop and field conditions. The sample sets will be designed for either a “general” NDE method, or “limited” technique(s) of a method, or for industry specific sector needs, as applicable.
In-Plane Vibration Damping of a U-Tube With Wet and Dry Flat-Bar Supports
Authors: Feenstra Paul A. , Janzen Victor P. , Smith Bruce A. W.
Published: November 2014

Tests are being planned which will use AECL’s MR-3 Freon test facility and a Multi-Span U-Bend (MSUB) test rig to investigate the dynamics of tube vibration in two-phase flow, in particular those mechanisms that can cause excessive damage to steam-generator tubes. In preparation for the tests, free- and forced-vibration tests were conducted to measure the vibration energy dissipation (damping) of a single U-bend tube in air, with dry and wet anti-vibration bars, under a variety of tube-support conditions. This paper presents the relevant damping mechanisms and documents methods used to conduct the tests and to analyze the energy dissipated at the supports. Results indicate that for in-plane motion without tube-to-support contact, viscous damping related to wet AV B supports is much smaller than guidelines based on other types of supports suggest. To begin to examine the effects of the tube coming into contact with its supports, such as friction-related energy dissipation, the results of tests with light tube-to-support preloads are also presented.
Critical Flaw Size Evaluation in Butt-Fusion Joints of HDPE Pipes
Authors: Kalyanam S. , Krishnaswamy P. , Focht E. M. , Shim D.-J. , Brust F. W. , Hioe Y.
Published: November 2014

The integrity of high density polyethylene (HDPE) piping and fusion joints are a topic of interest to the nuclear industry, regulators, ASME code, and the plastics pipe industry. The ASME Code Case N-755-1 has been approved and addresses the use of HDPE in safety related applications. Over the last few years some of the concerns identified with the parent HDPE pipe material and the fusion joints have been addressed while others are still being resolved. One such unresolved concern is the effect of the fusion process on the integrity of the joint, specifically, the introduction of flaws during the fusion process. The potential impact of flaws in the fusion joint on the service life of the HDPE piping is being evaluated.

The current study calculates stress intensity factors (SIF) for circumferential flaws and uses them to evaluate the potential structural integrity of HDPE fusion joints in pipes. The recent API 579-1/ASME FFS-1 standard provides SIF (KI) solutions to various semi-elliptical and full-circumferential (360°) surface cracks/flaws on the outer surface (OD) and the inner surface (ID). The API 579-1/ASME FFS-1 standard SIF tables and finite element analysis (FEA) of selected cases were used to develop simplified SIF relations for full-circumferential surface flaws that can be used for plastic pipes with diameters ranging from 101.6 mm (4 inch) through 914.4 mm (36 inch) and dimensional ratios (DRs) from 7 through 13. Further, the SIF of embedded flaws akin to lack-of-fusion regions was evaluated. The results from this study serve as precursors to understanding and advancing experimental methods to address important issues related to the critical tolerable flaw size in the butt-fusion joint material and were utilized to select the specimen tests and hydrostatic pipe tests used to evaluate various joining processes. Further, they will help with understanding the essential variables that control the long-term component integrity and structural performance of HDPE pipe joints in ASME Class 3 nuclear piping.
Buckling and Lateral Pressure in Spiral Wound Gaskets
Authors: Attoui Hocine , Bouzid Abdel-Hakim , Waterland Jerry A.
Published: November 2014

The buckling of spiral wound gaskets (SWGs) causes turbulence of the fluid flow inside flanges and may result in leakage failure over time due to the unwinding of the spirals. A few limited studies on the lateral forces generated by axial compression of the gasket sealing element which cause this phenomenon are available in the literature. The lateral forces are generated during initial tightening and are not distributed uniformly in the circumferential direction. Hence there is an introduction of concentrated forces in small areas.

The non-uniform gasket contact stress caused by the tightening sequence makes the problem more complex. It is suggested to study experimentally the buckling of spiral wound gaskets by developing a special test bench designed for this purpose. This test bench is able to measure the lateral loads and winding inward displacement during the tightening process. The experimental results are to be compared to those obtained by numerical FE simulation for the purpose of extrapolating for other size gaskets.
Two-Phase Damping in Vertical Pipe Flows: Effect of Void Fraction, Flow Rate and External Excitation
Authors: Charreton C. , Béguin C. , Ross A. , Etienne S. , Pettigrew M. J.
Published: November 2014

Predicting vibration effects in steam generators requires good knowledge of two-phase damping ζ2φ. The purpose of this work is to correlate two-phase damping in axial flow with tube transversal excitation frequency and magnitude. The test section consists of a stiff square tube subjected to internal axial flow of air-water mixture. The hydraulic diameter is 3 inches. The tube is supported with linear bearings and fitted with flexible tubing on both ends to allow motion in the transverse direction. Compression springs allow setting the natural frequency of the tube oscillation. A motor provides transverse sinusoidal excitation to the tube assembly. ζ2φ is determined from the frequency response function. As a result of this study, ζ2φ is represented as a function of excitation frequency and amplitude, void fraction and flow rate. Specific information is gained through high frame rate videos of the oscillating tube, including bubble transverse velocity and size for low void fraction, and flow pattern transitions. Indeed, it is suspected that two-phase damping is partly caused by the work rate of virtual mass forces of the gas phase. Better knowledge of the physical process involved in two-phase damping will allow better modeling and prediction of tube behavior.
Stainless Steel Tank Failure Analysis and Nondestructive Evaluation
Authors: Song Mingda , Cao Huaixiang , Shen Xiaomin , Song Xue , Zhang Hao
Published: November 2014

Penetrating cracks were found in the head straight section of a stainless steel tank before it was put into use. Penetrant testing, chemical analysis, metallographic analysis, X-ray residual stress test, crack surface scanning electron microscopy analysis and energy spectrum analysis was applied to study the cause of the cracks. The results showed that, chloride ion stress corrosion cracking was the reason of the failure. Metal magnetic memory detection and hardness testing were also used to evaluate the stress distribution of the head. The extreme points of the magnetic field gradient, hardness and tensile stress showed high coherence to the positions of the cracks. These results indicated that the metal magnetic memory method has good application prospects for the assessment of stainless steel deformation and stress state.
The Weld Depth and Angle Acuity Effects on the Crack Growth Behaviour of P91 Feature Test Specimens
Authors: Yatomi M. , Mehmanparast A. , Maleki S. , Nikbin K. M.
Published: November 2014

In this paper the creep crack initiation and growth path through the type IV region of large feature sized SEN(T) specimens of Mod. 9Cr-1Mo steel at 650 °C are investigated. The large SENT specimens contained 100mm long welds were tested with an initial EDM starter crack of 2mm placed at the surface. One specimen had a 10mm and the second had a 30mm weld at the centre depth tapering down to the surface shaped as an approximate semi oval. A third specimen with similar weld dimensions but of substantially smaller size was tested to identify the effect of size on crack path. The results suggest that despite the sharp angular direction of the welds, the crack path still went through the type IV region reaching an angle parallel to the load line direction and finally failing by net section rupture. The smaller specimen exhibited a faster deviation from the weld path compared to the thicker specimens. The approximated data for crack growth rates were correlated with the C* parameter and compared satisfactorily with standard compact tension weld test data. Metallographic observations were also performed to identify the region of the cracking and the damage associated with it. Specimen crack path showed clear indications that cracking follows the type IV region.
PIV Measurements of Aeroacoustic Sources of a Shallow Cavity in a Pipeline
Authors: Mohamed S. , Ziada S.
Published: November 2014

The aeroacoustic sources generated by flow over a cylindrical shallow cavity in a pipeline are examined in the presence of plane sound waves at various Strouhal numbers and sound intensities. The cavity is exposed to high Reynolds number fully developed turbulent flow. Extensive PIV flow measurements are performed to characterize the unsteady velocity and vorticity fields at various time instants within the sound cycle. Finite element analysis is used to obtain the particle velocity field of the sound field. The results of the PIV flow measurements and those of the finite element simulations are combined into Howe’s aeroacoustic integrand to compute the spatial and temporal distributions of the aeroacoustic sources resulting from the cavity shear layer interaction with the sound field. The results are compared with the measured aeroacoustic source strength obtained by means of the Sound Wave Method (SWM) [1]. The advantages and disadvantages of both techniques are discussed.
Failure Analysis of Shift Gas Tubes
Authors: Shi Jin , Wang Yian , Liu Wen , Jing Weike , Zhou Yufeng , Shao Shanshan , Zhang Kai , Chen Qiuping , Li Wurong
Published: November 2014

In a scheduled maintenance inspection of a fertilizer power station, a series of circumferential cracks were found in shift gas heat transfer tubes. In order to get an understanding of the failure mechanism, a failure analysis was performed on the leak-off shift gas tubes in this paper. The tubes were observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The fractography and metallurgical examination results showed that the crack initiated along grain boundaries and propagated through grain boundaries and the crack tips were oxide filled and not branched. Typical fatigue striations were observed on the fracture surfaces. The surface intergranular corrosion cracks caused by sensitization resulted in stress concentration. Fatigue cracks propagated along slip plane of grains under varying load. Moreover, the oxides on the surface of slip planes reduced the cohesive strength of steel substrate on both sides of slip planes. The synergistic effect of corrosion and fatigue, herein referred to as corrosion-fatigue, was the dominant mechanism of the failure. The vibration analysis of the tubes was carried out, and the results indicated that the vibration was induced by Karman vortex shedding and wobbling turbulent flow. In addition, prevention methods have been proposed to avoid corrosion-fatigue of the tubes.
Singing Mitigation in an Export Riser via Liquid Injection: A Field Case Study
Authors: Belfroid S. P. C. , Korst H. J. C. , van Beek P. , Lunde K. , Eidsvik I. G. , Hansen F. , Olsen B.
Published: November 2014

Flexible Risers are prone to the generation of high amplitude tonal noise, i.e. a so-called singing riser. Recently, severe vibrations and high noise levels were encountered on the turret of an FPSO in the Norwegian Sea, resulting in significantly reduced production. The vibrations could be attributed to pulsations generated either by a flexible jumper (connecting topside to turret), the gas lift riser or the gas export riser. Field measurements showed that the most likely source was the 10 inch gas export riser. Due to the vibrations, a reduced production limit was set. A field measurement campaign was started to inject liquid into the export risers to provisionally increase production, while in the meantime permanent solutions were evaluated and installed.

Liquid was injected batch wise and continuously. The main field trial was initiated by a batch of MEG (mono ethylene glycol) (2 times 500 liters) followed by continuous injection of small amounts of MEG. Between settling periods, the gas export rate was increased in steps until vibrations were detected. At detection, the MEG injection rate was increased until vibrations/pulsations disappeared, after which gas export was increased again. This process was repeated to maximum gas flow rate, after which the liquid injection and gas export were similarly stepwise decreased.

During this test, the gas export could be increased tenfold with moderate liquid injection rates (up to a maximum of 25 l/hr). Similar tests were done with TEG as injected fluid. However, TEG was far less efficient in suppressing the singing. This is attributed to the higher viscosity of the TEG at the injection temperatures and the method of injection.
Assessment of Fracture Toughness Models for Ferritic Steels Used in Section XI of the ASME Code Relative to Current Data-Based Models
Authors: Kirk Mark , Erickson Marjorie , Server William , Stevens Gary , Cipolla Russell
Published: November 2014

Section XI of the ASME Code provides models of the fracture toughness of ferritic steel. Recent efforts have been made to incorporate new information, such as the Code Cases that use the Master Curve, but the fracture toughness models in Section XI have, for the most part, remained unchanged since the KIc and KIa curves were first developed in Welding Research Council Bulletin 175 in 1972. Since 1972, considerable advancements to the state of knowledge, both theoretical and practical have occurred, particularly with regard to the amount of available data. For example, as part of the U.S. Nuclear Regulatory Commission’s (NRC’s) pressurized thermal shock (PTS) re-evaluation efforts the NRC and the industry jointly developed an integrated model that predicts the mean trends and scatter of the fracture toughness of ferritic steels throughout the temperature range from the lower shelf to the upper shelf. This collection of models was used by the NRC to establish the index temperature screening limits adopted in the Alternate PTS Rule documented in Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50.61a (10CFR50.61a). In this paper the predictions of the toughness models used by the ASME Code are compared with these newer models (that are based on considerably more data) to identify areas where the ASME Code could be improved. Such improvements include the following:

• On the lower shelf, the low-temperature asymptote of the KIc curve does not represent a lower bound to all available data.

• On the upper shelf, the de facto KIc limit of applicability of 220 MPa√m exceeds available data, especially after consideration of irradiation effects.

• The separation between the KIc and KIa curves depends on the amount of irradiation embrittlement, a functionality not captured by the ASME Section XI equations.

• The temperature above which upper shelf behavior can be expected depends on the amount of irradiation embrittlement, a functionality not captured in the ASME Section XI equations.
Fracture Toughness After Long-Term Aging in 9Cr-1Mo-V Steel for Pressure Vessels
Authors: Miyamura Takeo , Nanba Shigenobu , Nakanishi Tomoaki , Yamada Masato
Published: November 2014

9Cr-1Mo-V steel with excellent high temperature strength is one of candidate materials for advanced pressure vessels in oil-refining plants, whose process temperature is expected to be around 500°C. Although 9Cr-1Mo-V steel has been applied as boiler tube material in power generation for a few decades, it was reported that embrittlement occurred after long-term aging around 600°C which is accelerated condition for pressure vessel operation. Since pressure vessels are more sensitive in stress-concentration around crack tip than boiler tube because of its large wall thickness, fracture toughness is an important property of concern when 9Cr-1Mo-V steel is applied to pressure vessels. In this research, 9Cr-1Mo-V steel with tempered-martensitic microstructure was aged up to max. 10000 hr at 500, 550 and 600°C, and fracture toughness was evaluated after the aging by Charpy impact test.

The influence of heat treatment conditions such as austenitizing, tempering and PWHT were also investigated, because the heat treatment conditions used in pressure vessels are different from those of boiler tube. In case of samples treated under the conditions for pressure vessels, Charpy impact values at 0°C were sufficient around 200J before aging, and decreased after aging depending on its conditions, and longer time and higher temperature led to more severe degradation. When the aging time at 550°C and 600°C was converted to the equivalent aging time at 500°C by Larson-Miller-equation, the impact value was estimated to keep over 50J after several decades at the operating temperature for pressure vessels. In contrast to the conditions for pressure vessels, the heat treatment conditions used in boiler tube made initial impact value decreased significantly, because tempering and PWHT were shorter than those of pressure vessels. Therefore, the samples heat treated under boiler tube conditions showed lower impact values around 50J in the earlier stage of aging. Considering all obtained results, it was suggested that the serious degradation of fracture toughness in 9Cr-1Mo-V after long term aging would not occur in actual service time for pressure vessels.
Estimation of Through-Wall Cracking Frequency of RPV Under PTS Events Using PFM Analysis Method for Identifying Conservatism Included in Current Japanese Code
Authors: Osakabe Kazuya , Masaki Koichi , Katsuyama Jinya , Katsumata Genshichiro , Onizawa Kunio
Published: November 2014

To assess the structural integrity of reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events, the deterministic fracture mechanics approach prescribed in Japanese code JEAC 4206-2007 [1] has been used in Japan. The structural integrity is judged to be maintained if the stress intensity factor (SIF) at the crack tip during PTS events is smaller than fracture toughness KIc. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of pressure components has become attractive recently because uncertainties related to influence parameters can be incorporated rationally. A probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. According to the PFM analysis method in the U.S., through-wall cracking frequencies (TWCFs) are estimated taking frequencies of event occurrence and crack arrest after crack initiation into consideration.

In this study, in order to identify the conservatism in the current RPV integrity assessment procedure in the code, probabilistic analyses on TWCF have been performed for certain model of RPVs. The result shows that the current assumption in JEAC 4206-2007, that a semi-elliptic axial crack is postulated on the inside surface of RPV wall, is conservative as compared with realistic conditions. Effects of variation of PTS transients on crack initiation frequency and TWCF have been also discussed.
Overpressure Fragility Evaluation of a Mark I Drywell Using Thermal-Mechanical Finite Element Analysis
Authors: Talaat Mohamed M. , Nakaki David K. , Douglas Kyle S. , Hashimoto Philip S. , Bayraktarli Yahya Y.
Published: November 2014

The overpressure fragility of a Mark I boiling water reactor drywell was performed by detailed finite element (FE) analysis. The drywell overpressure capacity is controlled by the onset of leakage in the bolted head flange connection once separation exceeds the capacity of the silicone rubber O-ring seals.

The FE analysis was conducted at 6 discrete accident temperatures, ranging from 150 to 425°C. The overpressure evaluation used an axisymmetric model of the drywell head region for computational efficiency, and verified it by comparing to results from one FE model which used 3D solid elements. The mechanical properties of the steel materials were defined as temperature-dependent linear-elastic.

The median overpressure capacity at each temperature was determined using a 2-step thermal-stress analysis procedure. First, a steady-state heat transfer analysis was conducted to map out the temperature distribution in the drywell wall, which is exposed to the accident temperature on the inside and ambient temperature on the outside. Second, a quasi-static multi-step stress analysis was performed. The vertical differential movement between the flange surfaces was monitored and compared to the O-ring rebound capacity to define the pressure at the onset of leakage. After leakage occurred, the relationship between leakage area and increased pressure was recorded.

The evaluation predicted the median overpressure capacity and the lognormal standard deviation for uncertainty in O-ring rebound capacities, bolt preload, and model sophistication, in addition to the median pressure-leak area relationship.
SSRT and Fatigue Crack Growth Properties of High-Strength Austenitic Stainless Steels in High-Pressure Hydrogen Gas
Authors: Itoga Hisatake , Matsuo Takashi , Orita Akihiro , Matsunaga Hisao , Matsuoka Saburo , Hirotani Ryuichi
Published: November 2014

Slow strain rate tests (SSRTs) were performed with two types of high-strength austenitic stainless steels, Types AH and BX, as well as with two types of conventional austenitic stainless steels, Types 304 and 316L. The tests used the following combinations of specimen types and test atmospheres: (i) non-charged specimens tested in air, (ii) hydrogen-charged specimens tested in air (tests for internal hydrogen), and (iii) non-charged specimens tested in hydrogen gas at pressures of 78 ∼ 115 MPa (tests for external hydrogen). Type 304 exhibited a marked reduction of ductility in the tests for both internal hydrogen and external hydrogen, whereas Types AH, BX and 316L exhibited little or no degradation. In addition, fatigue crack growth (FCG) tests for the four types of steels were also carried out in air and hydrogen gas at pressures of 100 ∼ 115 MPa. In Type 304, FCG in hydrogen gas was more than 10 times as fast as that in air, whereas the acceleration rate remained within 1.5 ∼ 3 times in Types AH, BX and 316L. It was presumed that, in Types AH and BX, a small amount of additive elements, e.g. nitrogen and niobium, increased the strength as well as the stability of the austenitic phase, which thereby led to the excellent resistance against hydrogen.
Trend Prognosis and Online Diagnostics of Thick Walled Boiler Components for a Flexible Mode of Operation
Authors: Wagner Joël , Deeskow Peter
Published: November 2014

In a scenario of an increasing use of renewable energy, conventional power plants will be more and more forced to compensate for the volatility of the natural resources. Even huge coal-fired units which have been designed for baseload operation will face an increased number of start-up/shutdown cycles and the requirement for faster load changes.

For the power plant operator that means a challenge as well as a chance: a challenge because the plant experiences higher alternating stresses which may reduce the lifetime. A chance because usually there are incentives for contributions to the grid stability which may give him additional profits. Coping with the challenges and making the best of the chances will require a detailed and quantitative assessment of the lifetime consumption in various modes of operation.

In this paper, an online software solution is presented that provides this kind of information right at the fingertips of the plant engineers. The innovative approach integrates the most recent European standards concerning the calculation of lifetime consumption from load cycling with state-of-the-art methods of predictive analytics and cutting-edge FEM technologies: the recent standards supported by FEM calculations allow an estimation of lifetime consumption which is unchained from unnecessary allowances. The predictive analytics easily correlate plant operation and lifetime consumption and allow for a reliable prediction of fatigue. This in turn gives the necessary information to make the best of the chances of load flexibilization while mitigating the risks of increased lifetime consumption. If the expected fatigue in a given period is exceeded due to the current mode of operation one can react with a more moderate mode of operation — or the other way round, if the expected fatigue is not reached.

Examples from German coal-fired power plants which have been put under economic pressure by the ongoing “Energiewende” (energy turnaround) are presented to demonstrate this approach.
Predicting Creep Rupture Using Damage Mechanics
Authors: Bonora Nicola , Esposito Luca , Dichiaro Simone
Published: November 2014

Creep rupture strength values are basis for design in many high temperature applications. The application of new heat resistant steel in power plants is a typical example where long rupture time data are required. Different assessment methods are available to get the material creep rupture strength in service condition. Mainly these methods are phenomenological in nature or mere procedures of data fitting. The main challenging issue using these methods concerns their reliability of extrapolation from short term creep data. Numerical methods based on continuum damage mechanics (CDM) are largely used to predict creep strain accumulation and creep rupture. Most of the proposed CDM models are based on the Kachanov’s definition of effective stress. Damage accumulates with time (time-fraction) or strain (strain-fraction rule) as a result of void nucleation and growth, and rupture time is predicted to occur when damage reaches a critical value, characteristic for the material. The authors discussed elsewhere the influence of the damage evolution law on the strain accumulation in the tertiary creep stage [1–3]. For a given model formulation, damage model parameters can be identified to reproduce accurately the creep rupture time or the creep rate but usually poor results are obtained in predicting both the strain accumulation in the tertiary stage and the time to rupture. Often a very high value of the critical damage (close to 1) is required to match experimental data, which is not consistent with physical evidences of creep damage. However for time-limited applications a simple linear damage law can be used and a creep rupture formulation can be derived. In this paper the CDM has been used to formulate an engineering approach for creep rupture assessment of metals and alloys.
Comparison of Different Analysis Design Methods in the Calculation of Hydrogenation Reactor Skirt Structure
Authors: Pan Jianhua , Chen Xuedong , Jun Cui
Published: November 2014

The skirt support structure of hydrogenation reactor works in the conditions of high temperature and high pressure. There is not only high mechanical stress but also high temperature difference stress in this zone. The service environment of the structure is in poor conditions. In this paper, temperature field analysis on the local structure of skirt hot box is carried out. The stress classification method and direct route method are used to calculate the skirt support structure of hydrogenation reactor. The calculation results are compared. Results of these two analysis and design methods are both meet with the requirements of relevant standards. The results obtained by two methods are discussed. Some meaningful conclusions are obtained.
Local and Global Reference Stress for Circumferential Irregular-Shaped Defects in Pipes
Authors: Ageiev Sergii , Orynyak Igor , Radchenko Sergii
Published: November 2014

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects, based on simulation of global and local ultimate plastic states are proposed. There are some peculiarities of proposed procedures.

First, the schematic analysis of the deformation process of pipe with surface defects is suggested, based on which two critical cases have been specified: global (the Net-Section-Collapse (NSC) criterion) and local, which are applicable for a very wide surface defect and for a sharp crack, respectively. The global solution also describes behaviour of through wall defects.

Second, within the framework of the available Net-Section-Collapse criterion the unified algorithm for determination of reference stresses (global solution) for irregular-shaped circumferential defects under multifactor loading (internal pressure, axial force, bending moment) is proposed.

Third, according to the local modelling, the restricted capability to resist plastic deformations is takes into account by inserting of artificial symmetrical defect. The unified procedure for calculation of reference stresses (local solution) for pipe with irregular-shaped circumferential defects under multifactor loading is developed.

Forth, an analysis of proposed procedure by comparing with results of full-scale burst tests.
Study on Piping Response Under Multiple Excitation Validation for Elastic-Plastic Analysis of Piping
Authors: Kai Satoru , Watakabe Tomoyoshi , Kaneko Naoaki , Tochiki Kunihiro , Moriizumi Makoto , Tsukimori Kazuyuki
Published: November 2014

Piping in a nuclear power plant is usually laid across several floors of a single building or adjacent buildings, and is supported at many points. As the piping is excited by a large earthquake through multiple supporting points, seismic response analysis by multiple excitations within the range of plastic deformation of piping material is necessary to obtain the precise seismic response of the piping. The verification of the dynamic analysis method of piping under an elastic domain, which is excited by multiple seismic inputs, was performed in our study last year and the correspondence of a piping response between an analysis and an experiment have been confirmed [17][18]. However, few experiments under plastic deformation conditions have been performed to verify the validity of multiple excitation analysis under a plastic deformation range. To obtain better understanding of the behavior of piping under a large seismic input, it is important to investigate the seismic response by multiple excitations and to verify the validity of the analytical method by multiple excitation experiments.

This paper reports the validation results of the seismic elastic-plastic time history analysis of piping compared with the results of the shaking test of a 3-dimensional piping model under a plastic deformation range using triple uni-axial shake table. Three directional strains from the analysis and the experiments were compared in order to validate the analysis method. As a result, it is confirmed that the elastic-plastic analysis by time history excitation shows good agreement with the test results.
Influence of Local Wall Thinning and Support Stiffness in Piping Systems on Safety Assessments for Dynamic Loading
Authors: Kerkhof Klaus , Dwenger Fabian , Hinz Gereon , Schmauder Siegfried
Published: November 2014

The load bearing behavior of piping systems depends considerably on support distances and stiffness as well as cross section characteristics.

Stiffness of supports can often be defined only with difficulty by applying simplified procedures or guidelines based on assumptions. Load cases can be estimated quite well, but the safety assessment of a piping system can only be as reliable as the system model can realistically describe the present support stiffness or imperfections e.g. local wall thinning. As a consequence, the prediction of the system response may be poor. It is likely that calculated frequencies differ from natural frequencies determined experimentally. These frequency shifts lead to unrealistic predictions of stress analysis.

Examples for overestimations and underestimations of stress analysis are given regarding the load case earthquake, depending on whether the frequency shift runs into or out of the plateau of the applied floor response spectrum.

The influence of local wall thinning on modal characteristics is investigated. Conservative estimations of the influence on the load bearing behavior regarding severe local wall thinning are given. For fatigue checks the linear response of an experimental piping system is calculated and safety margins are demonstrated by comparing calculated with experimental results.
Fatigue Assessment of NPP Piping and Components Using Realistic Thermal-Mechanical Load Histories
Authors: Rudolph Jürgen , Maneschy José Eduardo , Cisternas Miguel , Freire José Luiz F. , Costa Felippe M. S. , Silva Bruno
Published: November 2014

Modern state-of-the-art fatigue monitoring approaches gain in importance as part of the ageing management of conventional and nuclear power plant components (NPP) and particularly in the context of lifetime extension projects and new plants. A key feature of qualified fatigue monitoring is the measurement of realistic loads based on plant instrumentation and/or local temperature measurement. The major prerequisites for any subsequent fatigue assessment are the accurate component stress analysis and the identification of relevant cycles, using highly qualified and efficient cycle counting methods.

In the framework of the paper the pertinent cycle counting methods such as rain flow and peak-valley, are evaluated and allocated to the relevant design codes. The peculiarities of a nuclear power plant typical one year operational thermal load time history is discussed in terms of the resulting stress-time history. The peak-valley and the rain flow methods are applied to that typical power plant operational load sequence and compared to the reference methods. Both idealized model transients without knowledge of the exact sequence in time and the processing of real load time histories are compared and considered.

Design data and actual data for a given annual cycle of a Brazilian nuclear power plant (NPP) constitute the basis for a design code conforming (ASME Section III) fatigue assessment (calculation of partial usage factors for a reference piping component). Conventional and more advanced methodologies are subsequently applied for comparison purpose. The influence of the cycle counting method applied on the resulting partial fatigue usage factors are elaborated based on the given realistic plant data.
Circular Braiding Process Simulation for a Pressure Vessel
Authors: van Ravenhorst Johan H. , Akkerman Remko
Published: November 2014

Pressure vessel manufacturing is currently dominated by the filament winding process. When higher production rates are required, circular braiding can be considered as an alternative because hundreds of yarns are deposited simultaneously from interlacing spools. The process has a high repeatability and is suited for automated series production, as is currently shown with the production of a-pillars and rockers in the automotive industry. Important manufacturing constraints related to the overbraiding of cylindrical pressure vessels are to avoid excessive jamming of the braid, typically occurring at a small mandrel radius, and to achieve a 100% cover factor at the largest mandrel diameter. In this paper, design guidelines for braiding of cylindrical pressure vessels are proposed. It is shown that a proper choice of the yarn cross-sectional area size and of yarn width-to-thickness aspect ratio can improve the design feasibility, but an adjustment of the braid angle can be required as well.
Fatigue Performance Analysis of Hoop-Wrapped Composite Cylinders With Pit Defects on Liner Based on Element Birth and Death Method
Authors: Deng Guide , Li Qingwan , Sun Liang , Wang Jingxian , Ling Xiang
Published: November 2014

Pit defects due to corrosion may occur in the inner surfaces of metal liners of fiber wrapped composite cylinders during working process, which may affect their anti-fatigue performance. Finite element method was used to analyze the stress of hoop-wrapped composite cylinders with pit defects of different sizes based on element birth and death method to take the pre-stress resulted from autofrettage process into consideration. Numeral results show that stress concentration appears in the pit defects, but the portion of the liner far away from pit defects keeps the same stress level with the defect-free composite cylinder. Pit defects on liner reduce the fatigue performance of the composite cylinder. Goodman equation was utilized to calculate the equivalent alternating stress amplitude to evaluate the variation of the fatigue performance with the dimensional change of the pit defects in the inner surfaces of metal liners of hoop-wrapped composite cylinders.
TUEV NORD Concept Loop: Lifetime Optimisation of Pipelines
Authors: Trieglaff Ralf , Schrandt Christian , Schulz Axel , Schulz Mayk
Published: November 2014

LOOP is a concept to evaluate corroded or damaged pipelines based on detailed data from UT-pigging. The procedure of LOOP delivers a 3D-model generated from the data of a commercial in-line inspection tools (ultrasonic, magnetic flux). This makes it possible to use the full functionalities of the relevant finite element software like evaluation of wall-thinning (LOOP 1) and fracture mechanics analysis to evaluate cracks in the wall (LOOP 2). In this paper is given the basic ideas of the LOOP concept, where the main focus is directed to the LOOP 1 assessment procedure.

Based on a real example of a corroded pipeline is demonstrated the assessment procedure, which is based on an elastic-plastic analysis of a real inner contour of the corroded surface transferred in the finite element geometry model. The unique element is that the surface data of the UT-pigging is used directly to generate the geometry model in the FE-software ANSYS. The assessment procedure is validated by a burst pressure test of a corroded pipeline. The result of the burst pressure test is compared with the calculated limit load from an elastic-plastic analysis based on measured material properties.

Additionally, the assessment procedure is compared with the results of a limit load analysis based on DIN EN 13445-3 and with the results of the standard assessment procedure. At the end the assessment procedure is compared with the procedure given in API 579-1 standard.
Fluid-Structure Interaction and Co-Simulation: Analysis of a Beam-Supported Sphere for VIV Application
Authors: Ardito Raffaele , Perotti Federico , Mandelli Simone , Novarina Davide , Malavasi Stefano
Published: November 2014

The recent developments in numerical tools and computing resources seem to provide a suitable environment to perform numerical analyses of Fluid-Structure Interaction problems. The Co-Simulation technique, in particular, develops the idea of coupling a CFD software with a structural one in order to simulate complex FSI phenomena with a partitioned approach, stressing the concept of software modularity. In this way, it is possible to adopt software tools at the cutting edge of technology. Nonetheless, several difficulties may arise in the choice of the partitioning scheme and of the algorithmic details for the step-by-step time integration.

This paper deals with the application of the Co-Simulation technique to a benchmark case experimentally investigated in previous works: the vortex-induced vibrations (VIV) of a beam supported sphere (that is, a sphere fixed to the end of a slender cantilever beam) in a free surface flow. This problem is challenging although apparently simple and it seems quite absent from literature so far. In this paper, the computational issues are thoroughly investigated and the model is validated by comparison with the experimental data. In this way, a robust framework is created in order to deal with VIV problems.
Gasket Testing Regimen for Transportation Intermediate Bulk Containers
Authors: Grant Kenneth R. , Lokey Tom
Published: November 2014

Comprehensive testing using various different gasket types and materials was performed in order to determine the best overall performance in gasket suitability and leakage reliability on an IBC (Intermediate Bulk Container), provided by a tank manufacturer. Prior to testing, the tank was filled with water just below the elevation of the manway, and the remaining space was charged with air. Testing was performed in two phases. Phase 1 was conducted as a simple pressure test with the container in a static state. For Phase 2, a test procedure was developed to include temperature and pressure variations, soak and dwell times, torque value calculations, leakage rates, sustainability, and a simulation of artificial vibration effects on bolted flange connections. Utilizing the Phase 2 procedure gives the ability to compare the various gasket materials under real world conditions, which will reveal the optimum gasket that provides the safest and most reliable connections for the transportation industry. Four corrosion resistant polytetrafluoroethylene (PTFE) based gasket materials were selected to be tested on the IBC. The gasket materials included virgin PTFE, glass-filled PTFE, tanged 316 stainless steel reinforced expanded PTFE (ePTFE), and corrugated 316 stainless steel reinforced expanded PTFE. All testing was performed indoors in a controlled environment. Testing on each gasket type was performed using the same equipment, while following the same test procedures.