bluuebunny/crossref_metadata_2025 huggingface dataset:
Design by Analysis of GFRP/CFRP Composite Pressure Vessels
Authors: Muscat Martin , Camilleri Duncan , Ellul Brian
Published: October 2018

The ASME Boiler and pressure vessel code Section VIII Division 2 and the European unfired pressure vessel code EN13445 Part 3 Design by Analysis parts dealing primarily with steel pressure vessels have been around for the last ten to fifteen years. The culmination of work on pressure vessel design by analysis address failure modes directly and are very efficient in order to guarantee that the designed and fabricated steel pressure vessels are fit for their purpose. The ASME Boiler and pressure vessel code Section X and the European codes BS EN13923 and BS EN13121 are some of the existing codes that cover design methods for composite pressure vessels. In these codes various failure criteria and damage mechanics models are possible but as such no comprehensive and robust design by analysis methods have been effectively established to encapsulate all composite pressure vessel failure modes. For instance the design of fibre-reinforced composite pressure vessels is still heavily reliant on experimental testing and prototype verification as opposed to the well-established design by analysis methods applicable to steel pressure vessels. Nonetheless a number of damage mechanics models ranging from mesoscale to microscale models have been established in other research work done on composite materials. This paper reviews the different composite pressure vessel design methods identified in the codes and standards and assesses damage mechanisms that can be used within a design by analysis context to design against possible modes of failure such as the limit load mode of failure, the progressive deformation mode of failure, the fatigue mode of failure and the buckling mode of failure. Damage mechanisms can also be used to develop criteria that allow a stress analyst deduce whether the material has failed, how it has failed and whether it has lost its capability to carry the load actions applied to it. The paper also highlights requirements for design methods based on the finite element method, and the necessary experimental validation required for different damage mechanisms leading to the different modes of failure.
A Simple Calculation Method of the Load Factor and a Bolt Preload Determination Satisfying Allowable Leak Late for Bolted Pipe Flange Connections With Gaskets Subjected to Internal Pressure
Authors: Sawa Toshiyuki , Sato Koji , Mabuchi Toshio
Published: October 2018

In designing bolted pipe flange connections with gaskets under internal pressure, it is important to predict an actual residual contact gasket stress in the connections. For estimating the reduced gasket stress, it is needed how to know the load factor of the connections with gaskets. In the previous paper (2017PVP), for predicting the load factor of the connections with gaskets, a new model was proposed using a circular plate theory. However, the rigidity of the flange hub was assumed and it is necessary to improve the model for calculation. In the present paper, a simple and more accurate calculation method is proposed using a circular plate theory taking into account the reaction force distribution at the gasket interfaces and the effect of flange hub. In addition, the effect of the flange hub is analyzed as a couple problem between a cylindrical shell (hub) and a circular plate. The obtained results of the load factor in the connections are in a fairly good agreement with those obtained from FEM. In the numerical calculations, the values of the load factor for JIS 10K flange connections and ASME flange connections with compressed sheet and spiral wound gaskets (from 2” to 24”) are shown. Using the obtained load factor, the residual contact gasket stress and an amount of gas leakage are predicted. For verification of the simple calculation method for obtaining the load factor and FEM results, experiments to measure the load factor and the amount of the leakage were conducted for 24” connection. The calculated results are compared with the experimental method. In addition, an issue how to determine the bolt preload for satisfying a give allowable real rate is demonstrated.
Proposal of the Local Failure Evaluation Method With Stress Parameters
Authors: Sakaguchi Takashi , Yoshida Mizuki , Sato Takuya , Kasahara Naoto
Published: October 2018

The failure mode known as local failure could occur at structure discontinuities with multiaxial stress conditions. Experiments and analyses of notched bars, which generate multiaxial stress, were conducted. The experiments showed that the tensile strength of a notched bar was stronger than that of a smooth bar. The ratio of the maximum and minimum diameter has become the important factor of this notch strengthening. In addition, the initiation of failure was observed at the inner location from the notch root. According to the analysis results, the Mises-stress became the maximum at the notch root. On the other hand, hydrostatic stress became the maximum at the inner location from the notch root, and this location corresponded to the initiation of fracture. The maximum hydrostatic stress has good correlation with the notch strengthening ratio. These facts reveal that hydrostatic stress must be taken into account for strength evaluation as a dominant factor in addition to the Mises-stress. However, only Mises-stress is considered in the present structural design code of nuclear plants. From above results, the new criterion based on fracture surface, where the coordinate plane consists of hydrostatic stress and Mises-stress, was proposed for local failure. Furthermore, this fracture surface was extended to an isochronous fracture surface in a creep region based on isochronous stress-strain curves.
FEM Stress Analysis and Mechanical Characteristics of Bolted Pipe Connections With Larger Nominal Diameter Inserting PTFE Blended Gasket Under Internal Pressure
Authors: Sato Koji , Sawa Toshiyuki , Zheng Xing
Published: October 2018

The sealing performance prediction of bolted pipe flange connections with gaskets is important factor. However, it is known that the sealing performance of the larger nominal diameter connection is worse than that with smaller nominal diameter connection due to the flange rotation. Furthermore, recently PTFE blended gaskets were developed newly and the excellent sealing performance in the bolted pipe flange connection with smaller nominal diameter is found. So, it is necessary to examine the sealing performance and the mechanical characteristics of pipe flange connections with larger nominal diameter under internal pressure. The objectives of present study are to examine the mechanical characteristics of the pipe flange connection with PTFE blended gasket under internal pressure such as the load factor, the contact gasket stress distribution and the sealing performance using FEM and experiments. Using the obtained contact gasket stress distribution and the fundamental leak rate for smaller PTFE gasket, the leak rate of the connection is predicted under internal pressure. In the FEM calculation, the effects of the nominal diameter of pip flange connections on the mechanical characteristics are shown. In the experiments, ASME class 300 24” pipe flange connections is used and the gasket is chosen as No.GF300 in PTFE blended gaskets. The FEM results of the axial bolt forces are in a fairly good agreement with the experimental results. In addition, the leak rate obtained from the FEM calculations are fairly coincided with the measured results. The mechanical characteristics of pipe flange connection with PTFE blended gasket are compared with those with spiral wound gasket.
Erosion-Corrosion of a Carbon Steel Elbow in a Natural Gas Gathering Pipeline
Authors: Wu Wei , Qiao Qiao , Cheng Guangxu , Pei Tinggang , Li Yun , Yin Hailong , Liu Dongpeng
Published: October 2018

A failed carbon steel elbow from a natural gas gathering pipeline in a gas field in Northeast China was investigated by macroscopic and microscopic examinations, chemical composition analysis, metallographic examination, and numerical simulation methods. The investigation results show that the intrados of the elbow was subject to slight general corrosion, while the extrados suffered from severe localized corrosion. The damage of the elbow resulted from an erosion-corrosion in the natural gas containing a few amount of corrosive impurities, liquid water, and solid particles. The impurities in the natural gas, specifically CO2 and chlorides, would be dissolved into water droplets in the natural gas. These corrosive droplets reacted with the pipe metal, resulting in typical CO2 corrosion of carbon steel pipe. Furthermore, the droplets and solid particles in the gas would destroy the protectiveness of the corrosion product film on the intrados by mechanical erosion, finally leading to the deterioration of the local environment and then the acceleration of corrosion failure. For controlling corrosion, some measures should be given. However, considering the difficulty of the increase in the curvature radius or the internal diameter of the pipeline, increasing wall thickness of the elbow pipe was a relatively feasible measure to mitigate the erosion-corrosion of the pipe.
Proposal of New Upper Limit of Hydrostatic Test Pressure in KT-3 of ASME Section VIII Division 3
Authors: Terada Susumu
Published: October 2018

The current upper limit of hydrostatic test pressure in KT-3 of ASME Sec. VIII Division 3 is determined by general yielding through the thickness obtained by Nadai’s equation with a design factor of 0.866 (= 1.732/2). On the other hand, the upper limit of hydrostatic test pressure in 4.1.6 of the ASME Sec. VIII Division 2 is determined by general yielding through the thickness with a design factor of 0.95. In cases where a ratio of hydrostatic test pressure to design pressure of 1.43 similar to PED (Pressure Equipment Directive) is requested, the upper limit of hydrostatic test pressure may be critical for vessel design when material with a ratio of yield strength to tensile strength less than 0.7 is used. In order to satisfy the requirements in KT-3, it is necessary to decrease design pressure or increase wall thickness. Therefore, it is proposed to change the design factor of intermediate strength materials to obtain the upper limit of hydrostatic test pressure. In this paper, a new design factor to obtain the upper limit of hydrostatic test pressure is proposed and the validity of this proposal was investigated by burst test results and elastic-plastic analysis.
Study on Forming Mechanism of Bimetal-Pipe by External Hydraulic Contraction
Authors: Sun Quanzhao , Yang Guolai , Ge Jianli , Lu Baochun , Song Yanming
Published: October 2018

It is widely known that a bimetal-pipe can be produced by internal hydraulic expansion. An inevitable limitation of which is that the elastic recovery of the outer pipe should be greater than that of the inner pipe when the forming pressure is released. And the existing techniques usually result in plastic deformation of the inner pipe. Considering the circumstance that elastic recovery of the inner pipe is greater than that of the outer pipe, or only elastic deformation in the inner pipe is allowed, an analytical model was developed to investigate the forming process of bimetal-pipes by external hydraulic contraction. The deformation compatibility condition of the bimetal-pipe was obtained according to the deformation rule. The formula relating the applied external hydraulic pressure and the residual contact pressure between the inner and the outer pipes was derived, and the lower and upper limits of the external hydraulic forming pressures were studied. A two-dimensional finite element analysis of the hydraulic contraction forming process of the bimetal-pipe was conducted. The comparison between the theoretical results and the finite element solutions shows that they are in good agreement. The presented methodology can be used in design and manufacturing of bimetal-pipes where the forming pressure should be applied on the outside surface.
Use of UNS N07718 Bolting in ASME Pressure Vessel Applications in Wet Sour Services
Authors: Shargay Cathleen , Tiru Ramakrishnan , Antalffy Leslie , Panchal Anilkumar , Daru Kuntak
Published: October 2018

UNS N07718 (commonly known as Grade 718) is an age-hardenable nickel-chromium alloy which primarily has applications in aircraft components and engine parts, cryogenic tankages, and for downhole and wellhead components in oil and gas. It also has been used primarily as bolting for ASME Section VIII vessels, exchangers and other high strength applications. ASME SB-637, UNS N07718(1) has the highest design allowable stresses of all the bolting materials in ASME Section II, Part D(2), Table 3.

There is a second industry standard which covers UNS N07718 components, namely API 6ACRA(3), which was developed for Oil and Gas equipment. Since this standard is for very different applications compared to the ASME applications, the recommended heat treatments and required mechanical properties of the two standards vary considerably. Bolting to either standard can be specified to meet “NACE hardness limits” for wet sour services, but for the ASME materials, this requires strict controls of the various heat treatment steps as the “box” for meeting all the required properties is tight.

The NACE standards and requirements for wet sour service are discussed in the paper, along with the specified heat treatments and mechanical properties required by the two industry standards. The paper will review the effect of the heat treatments on the expected microstructures and properties. By using testing results of N07718 materials specified to both the materials standards, the heat treatment and properties were optimized for a specific application that was specified to meet NACE hardness limits as well as ASME Code strength requirements.

The paper also makes a recommendation to ASME and ASTM committees to consider incorporating an additional grade of N07718 bolting with lower yield and tensile strength requirements and subsequently slightly lower allowable stresses which will provide lower hardness levels, improved toughness and improved ductility, and make it easier to source a viable N07718 bolting that is endorsed by the Code for wet sour services, and improved for low temperature, cryogenic and other services.
Failure Analysis of Duplex Stainless Steel in an Atmospheric Tower
Authors: Zheng Chengsi , Wang Gang , Wu Xiang , Ai Zhibin
Published: October 2018

An atmospheric tower head, manufactured using a clad plate of carbon steel + 2205 duplex stainless steel (DSS), was reported to show clear cracks in the DSS layer after serving for four years at an atmospheric distillation unit of a refinery. The cracks propagated in a dendritic manner within the heat-affected zone (HAZ) and the weld metal, accompanying locations with a higher hardness than that of locations without cracks. Some nondestructive methods were used to analyze the chemical composition, microstructure, hardness of the base metal, HAZ and weld metal. An analysis based on these results and the statistical data of an HCl-H2S-H2O corrosion environment was proposed to explain the formation of cracks from the viewpoint of physical metallurgy. The analysis showed that there were conditions favorable for the precipitation of the sigma (σ) phase in the DSS layer during the manufacturing process of the head, resulting in the occurrence of stress corrosion cracking (SCC) in the DSS layer under the harsh HCl-H2S-H2O environment. Moreover, some solutions, i.e., the enhancement of anticorrosion measures, the optimized microstructure of the DSS, and modified welding parameters were recommended to avoid a similar failure.
The Fluid Elastic Instability of Concentric Arrays of Tube Bundles Subjected on Cross Flow
Authors: Liu Liyan , Xu Wei , Guo Kai , Jia Zhanbin , Wang Yang , Tan Wei
Published: October 2018

Concentric arrays of tube bundles are applied extensively in heat exchangers at nuclear power plants. Flow induced vibration is one of the main causes of heat exchanger failures. However, there is no corresponding standard and basic parameters in the design code of different countries for concentric arrays of tube bundles. The fluid elastic instability of this type of heat exchangers cannot be calculated, and the design criteria is lacked. In this paper, a circulating water tunnel experimental facility were set up to test the vibration characteristic of concentric arrays subjected to cross flow. A non-contact measurement method based on high-speed photography imaging technology were adopted, which improved the accuracy of the test. Three kinds of tube bundles (0-degree angle, 15-degree angle and 30-degree angle arrangement, radial/circumferential pitch being 33.6/36.4 mm) were studied. The vibration frequency, amplitude and critical velocity of the tube bundle were investigated by changing the flow velocity. Computational fluid dynamics and fluid-structure interaction method were applied to simulate the fluid elastic instability of tube bundles, that were further verified by the experiments. Meanwhile, the numerical simulation supplements the contents of the experimental studies, which is utilizable to investigate and research the fluid elastic instability. The results of this work could provide references for the design of concentric array heat exchangers.
Contribution to Safety Enhancement for BDBE in Structure and Material Fields
Authors: Kasahara Naoto , Sato Takuya , Blahoianu Andrei
Published: October 2018

This paper proposes research issues on contribution to safety enhancement for BDBE in structure and material fields.

There are large difference between DBE and BDBE. Objective of DBE is prevention of accident and conservative approach is adopted such as prevention of all assumed failure modes. As for BDBE, objectives are prevention of safety function loss and mitigation of accident consequences, risk approach is expected. Since DEC is a part of BDBE, approach against DEC is different from DBE. DEC requires best estimate.

Probabilistic Risk Assessment consists of best estimate plus uncertainty.

For stress test, identification of the weakest portions and cliff edges become important.

To realize above approach, prediction of realistic failure modes is essential. Furthermore, relative strength evaluation becomes important to predict order of failure location and their mode, even though absolute strength is not clear.

After Fukushima daiichi nuclear accident, there is a tendency to apply DBE design criteria to BDBE, however, conservative criteria for design are inappropriate for best estimate. Therefore, authors proposes failure mode maps to identify realistic failure mode and its application to mitigation to accident sequences such as fracture control.
Optimization Design of PDC Bit Gauge Using CFD-DPM and Central Composite Design
Authors: Hou Huihui , Liu Zhong , Zhu Hongwu , Zhang Boyu , Wu Tingting
Published: October 2018

Polycrystalline Diamond Compact (PDC) bit has been widely used in natural gas/oil drilling industry for its advantages such as no rotating parts, highly rate of penetration (ROP) and durability. In recent decades, the comprehensive property of PDC bit has been improved rapidly due to the scientists’ efforts. Hydraulic design of PDC bit is very important because the retention of the cuttings may dramatically decrease ROP. Most current researches focus on how blade profile and nozzle parameters affect hydraulic performance of PDC bit, but, the understanding of gauge geometrical parameters (mainly refer to gauge width, gauge length and gauge spiral angle) effects on hydraulic performance of PDC bit is still incomplete.

In this paper, a simulation method and an optimization method were applied to find the best gauge parameter for 8.5 inch PDC bit. In the proposed approach, the approximate range of above three parameters were confirmed first based on previous studies. Then, the central composite design (CCD) was used to design numerical simulation scheme and the discrete particle modeling (DPM) was used to track the cuttings and the velocity of particles and fluid were evaluated to study the hydraulic performance of drill bit under different gauge geometrical parameters. Finally, the optimal geometrical parameter of gauge could be obtained according to the simulation results. Overall, the proposed approach can be used to design PDC bit gauge structure to improve the cuttings’ velocity away from bottomhole, which will result in huge improvement of ROP.
Stress Intensity Factor Coefficients for Circumferential OD Surface Flaws in Cylinders for Appendix A of ASME Section XI
Authors: Lee Darrell R. , Cipolla Russell C. , Liu Michael C.
Published: October 2018

Linear elastic fracture mechanics based flaw evaluation procedures in Section XI of the ASME Boiler and Pressure Vessel Code require calculation of the stress intensity factor (KI). The 2015 Edition of ASME Section XI [1] implemented a number of significant improvements in Article A-3000, including closed-form equations for calculating stress intensity factor influence coefficients (Gi) for circumferential flaws on the inside surface of cylinders. In the 2017 Edition [2], closed-form equations for axial flaws on the inside and outside surfaces of cylinders have been implemented.

In this paper, closed-form equations are developed for circumferential cracks on the OD surface of cylinders, based on tabular data from API 579 (2007 Edition) [3]. The equations presented, represent a complete set of Ri/t, a/t, and a/ℓ ratios. The closed-form equations provide G0 and G1 coefficients while G2 through G4 are obtained using a weight function representation for the KI solutions for a surface crack. These equations permit the calculation of the Gi coefficients without the need to perform tabular interpolation. The equations are complete up to a fourth order polynomial representation of the applied stress. The fourth-order representation for stress will allow for more accurate fitting of highly non-linear stress distributions, such as those depicting high thermal gradients and weld residual stress fields.
Fracture Toughness Behaviour of 316L Stainless Steel Samples Manufactured Through Selective Laser Melting
Authors: Davies Catrin M. , Zhou Ruijan , Withnell Olivia , Williams Richard , Ronneberg Tobias , Hooper Paul A.
Published: October 2018

Selective laser melting (SLM) is a relatively new manufacturing technique which offers many benefits. However the utilisation of SLM manufactured components depends on the assurance of their integrity during operation. Fracture toughness testing (JIC) has been performed on as-built compact tension fracture mechanics samples manufactured in three orthogonal directions. When the crack growth plane was transverse to the interface of the build layers, the fracture toughness values were found to be similar to those manufactured using conventional techniques. However, the fracture toughness is significantly reduced when the crack plane is parallel to the interface of the build layers. Simple heat treatments have been performed on Charpy fracture samples and the resulting impact energy values indicate that the fracture toughness of a component may be improved by heat treatment.
Field Measurement and Numerical Study of the Vibration in the Pipeline of Centrifugal Compressor
Authors: Wu Jia , Zheng Shui Y.
Published: October 2018

In the process of compressor operation, the vibration of the pipeline occurs frequently and has a strong impact on safety. The in-field vibration measurement is carried out on the pipeline of a centrifugal compressor, and the vibration waveform and spectrum characteristics are obtained. Numerical studies are conducted to investigate the relationship between the natural frequency of the pipeline and the fluid excitation frequencies. These numerical results are verified by comparison with the field measurement values, which shows that the method can be useful for engineering applications. Some preliminary conclusions are drawn from the results of the field measurement and the numerical simulation. Pressure fluctuations not only occur in the measuring pipeline, but also spread to the pipeline in the distance. The sensitive frequencies of the pipeline vibration are determined, and the fundamental causes of the vibration revealed. Accordingly, the pipeline structure can be improved, and the method of solving the fluid excitation is discussed to avoid the damage caused by the pipeline vibration and ensure the safety of the equipment and the pipeline.
A Multiple-Loading Single-Sample Exploratory Method of Estimating Damage in Polymer Composite Materials Through Analysis of X-Ray Tomography Images
Authors: Prakash Raghu V. , John Mathew , Carboni Michele
Published: October 2018

This paper presents the results of characterization of damage in polymer composite materials that are in: a) the pristine state, b) subjected to low velocity impact and c) fatigue damaged after impact using x-ray computed tomography (CT) technique. While CT imaging provides excellent details about the presence of the damages, the interpretation of defect size is dependent on setting up of threshold of measurement and intelligent interpretation of data received from the images to ensure proper quantification of damage. It is noted that the selection of pixel intensity (grey value) for thresholding in the quantification of defects through digital image analysis can influence the results in a significant manner. The specimens at different physical conditions in terms of damage or defects imparted by manufacturing method, different loading conditions, etc. were analyzed. The study arrives at the statistical criteria for choosing the right threshold level for image processing for reliable and accurate damage quantification in fiber reinforced polymeric composites. The damage caused to the specimens due to impact as well as post-impact fatigue loading is also estimated.
Fatigue Life Properties of Circumferentially-Notched Bar of Austenitic Stainless Steel With Various Concentration Factors
Authors: Nagaishi Naoaki , Yoshikawa Michio , Okazaki Saburo , Matsunaga Hisao , Yamabe Junichiro , Matsuoka Saburo
Published: October 2018

Fatigue tests were performed using three types of round-bar specimens of Type 304, meta-stable, austenitic stainless steel. The specimens had circumferential notch with stress concentration factors, Kt, of 2, 3 or 6.6. Load controlled fatigue tests were conducted at stress ratio, R, of 0.1 and −1 in ambient air at room temperature. At R of 0.1, fatigue life was decreased with an increase in the stress concentration factor. Conversely, at R of −1, the stress concentration factor had little influence on the fatigue life. To understand the mechanism of the stress ratio effect, local deformation behavior at and beneath the notch root during the fatigue test was computed by means of finite element analysis considering that the plastic constitutive model describes the cyclic stress-strain response.
The Spherical Indentation Approach for Fracture Toughness Evaluation: A Study Based on the Energy Release Rate
Authors: Zhang Tairui , Wang Weiqiang , Li Aiju
Published: October 2018

In this study, we investigated the drawbacks of previous studies regarding the evaluation of fracture toughness from spherical indentation tests (SITs). This was achieved by an examination of the material damage mechanism during indentation tests, uniaxial tensile tests, and Mode I/II fracture tests. A new approach based on the energy release rate was proposed in this study to evaluate the fracture toughness of ductile metals. Scanning electron microscope (SEM) observations revealed that the mechanism for material damage during an indentation test was different with the material damage in uniaxial tensile tests and Mode I fracture tests, but similar to that in Mode II fracture tests. Thus, the energy release rate during SITs should be correlated with JIIC. Compared with previous studies, this new proposed method was more consistent with the actual damage mechanism and did not rely on the specific critical damage values. Experiments on SA508, SA533, 15CrMoR, and S30408 revealed that the maximum error from this energy release rate-based approach was no more than 13% when compared with their conventional counterparts (compact tension tests), and thus can meet the precision requirement of engineering applications.
FEM Stress Analysis of Bolted Flange Joints in Elevated Temperature Service Condition
Authors: Wang Lu , Chen Xuedong , Fan Zhichao , Xue Jilin
Published: October 2018

Performance of a bolted flange joint (BFJ) is characterized mainly by its ‘strength’ and ‘sealing capability’. How to keep the ‘strength’ and ‘sealing capability’ for the BFJ serving at elevated temperature is a difficult problem in engineering applications. The variations of bolt stress and gasket contact stress play an important role on the structural integrity and sealing performance of BFJ in the bolt-up, pressurization and heat-up stages. In this paper, a three-dimensional elastic-plastic finite element model has been developed to investigate the performance of joint under combined internal pressure and elevated temperature. The thermal-structural coupling method has been used to analyze the variations of axial bolt force, maximum blot stress and gasket contact stress under steady-state and transient thermal loadings. The effects of internal pressure, temperature as well as the heating rate on the variations of bolt load, bolt stress and gasket contact stress have been evaluated. The results show that the maximum bolt stress increases while average gasket contact stress decreases with increasing the temperature under steady-state thermal loading. Besides, when the transient thermal loading is considered, heating rate has a significant effect on the maximum bolt stress and gasket contact stress. This research will contribute to the design of BFJ subjected to elevated temperature.
Investigation on Fluid Induced Vibration of Heat Exchanger Beyond Pitch Ratio Range in TEMA Standards and GB/T 151
Authors: Tan Wei , Guo Kai , Jia Zhanbin , Wang Yang , Liu Liyan
Published: October 2018

In new design of heat exchangers with high turbulence intensity and low pressure drop in the shell side, parameters or structures beyond the standards may be adopted and failure risk due to fluid induced vibration can increase. As pitch ratio is related with some significant parameters, the range of pitch ratio determines whether the FIV calculation could be established. In this research, FIV of heat exchangers with pitch ratio beyond the standards was investigated on mechanisms such as vortex shedding, turbulent buffeting and fluid elastic instability. Both theoretical and numerical methods have been applied during the study to get parameters beyond the pitch ratio range. Parameters related to pitch ratio such as additional mass coefficient Cm and damping ratio ζ were extended, and then verified by experiments. Calculating cases on several conditions were accomplished as well as comparation with literatures. The results and methods could be guidelines for the design of new type of heat exchangers and references in the amendment of relevant standards.
Influence of Mean Strain on Fatigue Life of Stainless Steel in PWR Water Environment
Authors: Kamaya Masayuki
Published: October 2018

Change in the fatigue life due to application of the mean strain was investigated for Type 316 stainless steel in simulated pressurized water rector (PWR) primary water environment. The tests were conducted by controlling the strain range to 1.2% for different strain rates of 0.4, 0.004, or 0.001%/s. The applied mean strain was 15% in nominal strain. In addition, cold worked specimens were also subjected to the tests without applying the mean strain. The tests using the cold worked specimens were regarded as the tests with the mean strain without increase in surface roughness due to application of plastic deformation. By inducing the cold working at low temperature, the effect of martensitic phase on the fatigue life was also examined. It was shown that the fatigue life of the stainless steel was reduced in the PWR water environment and the degree of the fatigue life reduction was consistent with the prediction model prescribed in the code issued by the Japan Society of Mechanical Engineers (JSME) and NUREG/CR-6909. Increases in peak stress and stress range due to cold working did not cause any apparent influence on the fatigue life. It was also shown that the 10.5 wt% martensitic phase induced by the low temperature cold working and the increase in the surface roughness caused by application of 15% mean strain did not bring about further fatigue life reduction. It was concluded that the effects of the mean strain, cold working, and martensitic phase were minor on the fatigue life in the PWR water environment. The current JSME and NUREG/CR-6909 models were applicable for predicting the reduction in fatigue due to the PWR water environment even if the mean strain or cold working was applied.
Fatigue Crack Growth in Low Alloy Steels Under Tension-Compression Loading in Air
Authors: Azuma Kisaburo , Yamazaki Yasuhiro
Published: October 2018

Low alloy steels are extensively used in pressure boundary components of nuclear power plants. The structural integrity of the components made of low alloy steels can be evaluated by the procedure of flaw evaluation provided by Section XI of the ASME Boiler and Pressure Vessel Code. According to the Code, the range of stress intensity factor ΔK can be used to determine the fatigue crack growth rates of the material. However, it has been reported that crack closure behavior also strongly influence the fatigue crack growth rate under strong compressive load cycles.

This paper discusses the relation between ΔK and the fatigue crack growth rate for cracks in low alloy steels exposed to air. Compressive-tensile cyclic loadings were applied to center-notched plates to obtain the fatigue crack growth curves. The test data demonstrated that effective SIF range ΔKeff more accurately described the crack growth property due to plasticity induced crack closure. Comparing the test results with the reference crack growth curves in the ASME Code Section XI, it may seem that the crack growth prediction based on the Code underestimates the crack growth rates for compressive-tensile cyclic loadings under high stress level.
Effect of Hydrogen on Fracture Toughness Behavior of 2.25Cr-1Mo-0.25V Steel
Authors: Chai Mengyu , Song Yan , Zhang Zaoxiao , Duan Quan , Cheng Guangxu
Published: October 2018

2.25Cr-1Mo-0.25V steel, which is a high strength low alloy (HSLA) steel, has been widely used for structural material of hydrogenation reactor due to its excellent combination of mechanical properties and resistance to hydrogen embrittlement (HE). However, it still suffers serious hydrogen damage during the aggressive service environment. When sufficient hydrogen concentrates in the reactor steel, the ductility and strength of the steel will be greatly decreased. Such a phenomenon of reduction of toughness is known as HE, and it can significantly weaken the safety and reliability of equipment. Therefore, the aim of this investigation is to focus on the effect of hydrogen on fracture toughness behavior of 2.25Cr-1Mo-0.25V steel. The fracture mechanics specimens in geometry of single edge notch bending were used. The immersion charging method was used to pre-charge hydrogen inside the specimens. Moreover, the fracture toughness of specimens with and without hydrogen pre-charging were measured following the ASTM E1820 standard. Finally, the fracture morphology was observed by scanning electron microscopy (SEM) to identify the HE mechanisms. The results of the present investigation showed that the pre-charged hydrogen resulted in significant reduction of fracture toughness of 2.25Cr-1Mo-0.25V steel, indicating a reduced crack growth resistance of specimens in the presence of hydrogen. Furthermore, the uncharged specimens failed in a ductile manner, whereas the fracture of pre-charged specimens is a mixed ductile and brittle fracture mode. It was believed that the hydrogen-induced decohesion (HEDE) mechanism contributed to the HE in hydrogen pre-charged specimens.
Flamanville EPR RPV’s Heads Carbon Segregation: Vessel Heads Manufacturing
Authors: Lefever Benoit , Marie Stéphane , Berger Thierry , Bobin Vastra Isabelle
Published: October 2018

The FA3 RPV heads segregation has been an important issue for the Flamanville 3 EPR project. A high carbon content of carbon has been measured at the outer central part of the two heads. Manufactured in 2006 according to the RCC-M requirements, these pieces were also submitted to the ESPN (i.e. nuclear pressurized equipment) French order requirements, and in particular the ESPN technical qualification.

This paper presents the manufacturing of these heads to explain the origin of the segregation and place this process in its context, with in particular a clarification of the technical qualification requirements in 2011, which are different to the RCC-M qualification process. This qualification required additional chemical and mechanical characterizations in the segregated area of the representative vessel head. The additional Charpy-V test did not meet the 60 J requirement of the ESPN order and led to the large testing program to characterize the toughness properties of the segregated material.
Study on Promoting Use of Repair, Replacement and Mitigation Techniques in Maintenance Activities of Nuclear Power Plants
Authors: Dozaki Koji , Aoki Takayuki , Koyama Koji , Kanno Masanori , Saeki Ryoichi
Published: October 2018

Maintenance of nuclear power plant facilities involves activities comprising a large system composed of both plant hardware and human subsystems to assure safe and reliable operation. Maintenance activities are composed of inspection, evaluation and corrective measures. Corrective measures are countermeasures for aging degradation, e.g., resetting the inspection period based on the results of inspection and evaluation; mitigation of degradation phenomenon; repair or replacement; preventive maintenance; etc. The corrective measures merit special attention as they are important and valuable actions in order to promote continued efficient and safe plant operations. It is necessary to develop a set of regulatory and industrial technical requirements for a well-structured, documented set of standards, so that corrective measures can be used and applied uniformly and effectively. Currently the code and standard system is less developed in Japan than in the United States.

In this study, the authors considered the relationship between degradation and maintenance and the difference of performance requirements between the plant construction stage and the in-service stage. This effort is intended to clarify the issues of regulation for maintenance activities, with an objective to help develop structured regulatory/industrial requirements with a code and standards consistent with appropriate corrective measures.

The Nuclear Regulation Authority (NRA), the regulatory body in Japan, has reviewed the present Japanese inspection system in response to suggestions from the Integrated Regulatory Review Service (IRRS) mission established by International Atomic Energy Agency (IAEA). The NRA has also been developing a new regulatory inspection system similar to the Reactor Oversight Process (ROP) used in the United States. The expectation for the new Japanese inspection system is to focus regulations on plant issues with higher risk importance, considering both plant hardware and human subsystems. The new Japanese regulatory system addressing maintenance is also expected to enhance electric utilities ability to assure safety is self-motivated and sustained.
SCC Crack Growth Analysis for a Dissimilar Metal Weld Using Advanced FEA
Authors: Ogawa Takuya , Itatani Masao , Hayashi Takahiro , Saito Toshiyuki
Published: October 2018

Management of plant service life is a key issue for improving the safety of light water reactors. Some incidents of primary water stress corrosion cracking (PWSCC) of pressurized water reactor (PWR) components, such as a primary loop piping/nozzle weld, and intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) components, such as a shroud support weld, have been reported in the past. When a crack is detected, crack growth analysis is required as part of the structural integrity assessment of the component with the crack.

In Japan, the “Rules on Fitness-for-Service for Nuclear Power Plants” of the Japan Society of Mechanical Engineers (JSME FFS Code) describes the conventional methodology for analyzing crack growth. The methodology assumes a semi-elliptical crack shape and is based on crack growth calculation at only the deepest and surface points of the crack. However, the actual crack growth behavior is likely to be very different from that analyzed by the conventional methodology due to the complex distribution of residual stress and dependency of crack growth properties on the materials composing the weld joint, particularly in the case of cracks in a dissimilar metal weld. Recently, crack growth analysis techniques using finite element analysis (FEA) have been used to analyze crack growth behavior in more detail.

In this study, a program code was developed for SCC crack growth analysis that consists of fracture mechanics analysis by “ABAQUS”, crack growth calculation and automatic remesh of the FE model by in-house code. Case studies of SCC crack growth analysis for a dissimilar metal weld were performed and the analysis results were compared with those obtained by the conventional methodology. As a result, it was confirmed that the conventional methodology provides a conservative estimation of crack growth behavior. It was also found that the difference in crack growth properties of individual materials composing the weld joint had a significant effect on the crack growth behavior, particularly on a dissimilar metal weld. Furthermore, the effect of the material anisotropy of the SCC crack growth rate for the weld metal on the crack growth behavior was investigated.
Estimation of Stress-Displacement Curve of Multiple Notched Stainless Steel Pipe Under Combined Load of Axial Force and Bending
Authors: Suzuki Ryosuke , Matsubara Masaaki , Arai Kento , Takano Kosuke , Hagiwara Tsukasa
Published: October 2018

Integrity evaluation of stainless steel piping with multiple flaws under combined load is difficult when one flaw is located near other flaw. This is because that the stress state in the piping becomes complicated as a result of the mutual interference of the stress fields occurred by flaws. If the stress-displacement curve of stainless steel piping with two flaws can be estimated by using the curves of single notched stainless steel piping before and after flaw coalescence, the integrity evaluation of stainless steel piping with two flaws becomes easy and simple. In this study, the stress-displacement curves of the single notched pipes with notch angle 37° or 90° subjected to combined tensile and bending loads are obtained experimentally. In addition, the stress-displacement curve of the pipe which has two notches in the same cross section area and both notch angles are 37° and notch interval 16° (total notch angle is 90°) is also obtained experimentally. The stress-displacement curve of the 37°+37° multiple notched pipe is compared with the curves of the 37° single notched pipe and the 90° single notched pipe. In the tensile principal tests, the stress-displacement curve of the 37°+37° notched pipe shows good agreement with the curve of the 37° notched pipe until notch coalescence. In the bending principal test, the error of the stress-displacement curves between the 37° +37° notched pipe and the 37° notched pipe is higher than that of the tensile principal test. The stress-displacement curve of the 37° +37° notched pipe after notch coalescence shows relatively good agreement with the curve of the 90° notched pipe in the bending principal test. After notch coalescence, the error of the stress-displacement curves of the 37° +37° notched pipe and 90° notched pipe for tensile principal test is higher than that for the bending principal test.
Leak Rate Computation: Flow Resistance vs. Thermal-Hydraulic Aspect
Authors: Heckmann Klaus , Sievers Jürgen , Weyermann Fabian
Published: October 2018

The computation of mass flow rates through crack-like defects in piping systems of light water reactors requires typically the description of two-phase flow conditions. The computed discharge rate depends on the crack opening area, the thermal-hydraulic modeling of the flow, and the flow resistance of the crack. Several models have been proposed to characterize the critical flow through crack-like defects. An evaluation of advantages and shortcomings of the different models with regard to the interaction of the three different parts (crack opening area, thermal-hydraulic modeling, flow resistance) has been performed.

In this paper, the flow resistance modeling from several approaches is discussed, and compared with a database from eight different testing programs. Five different flow models are applied to analyze a database of more than 800 leak rate measurements for subcooled water from twelve different experimental programs. It is shown that the correct modeling of the flow resistance is crucial for a best estimate reproduction of the measured data. It turns out that generally, equilibrium models are about as good as non-equilibrium models. The data were processed with the GRS software WinLeck which includes different analytical approaches for the calculation of crack sizes and leak rates in piping components. The most reliable results within the model selection are produced by the CDR model (Critical Discharge Rate) of the ATHLET code (Analysis of Thermal-hydraulics of Leaks and Transients) developed by GRS.

As a conclusion, the accurate modeling of form losses and frictional pressure losses for critical discharge flow rates through crack-like leaks are essential for a reliable prediction of flow rates. Uncertainties in leak rate computations results arise due to the lack of information about the flow geometry and its associated drag. The assumed flow resistance of a through-wall crack influences the computed leak rate as significant as the phase-change- and flow-models. The manifest difference between equilibrium models (Pana, Estorf) and non-equilibrium models (Henry, ATHLET-CDR) seems to be less significant than the pressure loss issue. One can conjecture that, for crack-like through-wall defects, friction effects play a more important role than non-equilibrium effects.
Fracture Toughness Evaluation of Heat-Affected Zone Under Weld Overlay Cladding in Reactor Pressure Vessel Steel
Authors: Ha Yoosung , Tobita Tohru , Takamizawa Hisashi , Hanawa Satoshi , Nishiyama Yutaka
Published: October 2018

An evaluation of the fracture toughness of the heat-affected zone (HAZ), which is located under the weld overlay cladding of a reactor pressure vessel (RPV), was performed. Considering inhomogeneous microstructures of the HAZ, 0.4T-C(T) specimens were manufactured from the cladding strips locations, and Mini-C(T) specimens were fabricated from the distanced location as well as under the cladding. The reference temperature (To) of specimens that were aligned with the middle section of a cladding strip (HAZMCS) was ∼12°C higher than that of specimens that were aligned with cladding strips at the overlap (HAZOCS). To values of partial area in the HAZ were obtained using Mini-C(T) specimen. The To values obtained near the side of the cladding were ∼13°C higher than those away from the cladding. To values of HAZ for both 0.4T-C(T) and Mini-C(T) specimens were significantly lower than that of the base metal at a quarter thickness by 40°C–60°C. Compared to the literature data that indicated fracture toughness at the surface without overlay cladding and base metal of a quarter thickness in a pressure vessel plate, this study concluded that the welding thermal history showed no significant effect on the fracture toughness of the inner surface of RPV steel.