bluuebunny/crossref_metadata_2025 huggingface dataset:
Modal Analysis of a Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow
Authors: Deri Enrico
Published: October 2017

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. EDF has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy.

The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was presented in previous PVP conferences with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions.

This paper presents some extended physical analysis applied to some selected points of the aforementioned experiment series: the response modes are identified by means of operational modal analysis (i.e. under unmeasured flow excitation) and presented in terms of frequency, damping and mode shapes.

Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluidelastic instability.
Prediction of the Temperature Dependence on Fracture Toughness by New Stress Distribution Scaling Method
Authors: Ishihara Kenichi , Hamada Takeshi , Meshii Toshiyuki
Published: October 2017

In this paper, a new method for scaling the crack tip stress distribution under small scale yielding condition was proposed and named as T-scaling method. This method enables to identify the different stress distributions for materials with different tensile properties but identical load in terms of stress intensity factor (K) or J-integral (J). Then, a method to predict the fracture load at an arbitrary temperature from the already known fracture load at a reference temperature was proposed by assuming that the temperature dependence of a material is represented as the stress-strain relationship temperature dependence. This method was combined with the T-scaling method and the knowledge “fracture stress for slip induced cleavage fracture is temperature independent.” Once the fracture load is predicted, fracture toughness Jc at the temperature under consideration can be evaluated by running elastic-plastic finite element analysis. Finally, the above-mentioned framework to predict the Jc temperature dependency of a material in the ductile-to-brittle temperature region was validated for 0.55 % carbon steel JIS S55C. The proposed framework seems to have a possibility to solve the problem the master curve is facing in the relatively higher temperature region, by requiring only tensile tests.
Simplified Assessment of Studs Allowing for Low Constraint Conditions
Authors: James P. , Madew C. , Jackson M.
Published: October 2017

Defect tolerance assessments are carried out to support the demonstration of structural integrity for high integrity components such as nuclear reactor pressure vessels. These assessments often consider surface-breaking defects and assess Stress Intensity Factors (SIFs) at both the surface and deepest points. This can be problematic when there is a high stress at the surface, for example due to the stress concentration at the root of a screw thread. In the past this has led to the development of complex and costly 3D finite element analyses to calculate more accurate SIFs, and still resulting in small apparent limiting defect sizes based on initiation at the surface point.

Analysis has been carried out along with supporting materials testing, to demonstrate that the increased SIF at the surface point is offset by a reduction in crack-tip constraint, such that the material exhibits a higher apparent fracture toughness. This enables a more simplistic assessment which reduces the effective SIF at the surface such that only the SIF at the deepest point needs to be considered for many defects. This then leads to larger calculated limiting defect sizes. This in turn leads to a more robust demonstration of structural integrity, as the limiting defect sizes are consistent with the capability of non-destructive examination techniques.

An overview of the supporting materials testing is provided in an accompanying paper. The accompanying paper details how it was not possible to demonstrate the required material response with conventional tests, such as those using shallow-notched bend specimens. Instead it was necessary to develop modified specimens in which semi-elliptical defects were introduced into a geometry which replicated the notch acuity at the root of a screw thread. These tests were used to quantify the stud materials sensitivity to constraint. Conventional three-point bend tests were also seen to confirm these values.

A series of R6 constraint modified assessments have been considered to understand the benefit from including a loss of constraint, particularly when assessing the surface breaking SIF. This has necessitated a series of complex finite element analyses to define the elastic SIF as well as the elastic constraint parameter, T-Stress, T. Further verification analyses have also been performed to determine the equivalent elastic-plastic J and Q parameters. These have been used to provide guidance on how best to assess surface breaking defects within studs. This has shown that the increased perceived toughness at the surface location means that under the majority of conditions, the assessment can simply be based upon the SIF at the depth location using high constraint fracture toughness.

This paper provides an overview of the process undertaken to provide simplified guidance on assessing defects within studs that allows benefit from constraint loss.
ASME Code-Case Proposal to Explicitly Quantify the Interaction Between the PWR Environment and Component Surface Finish
Authors: Métais Thomas , Courtin Stéphan , De Baglion Laurent , Gourdin Cédric , Le Roux Jean-Christophe
Published: October 2017

Fatigue rules from ASME have undergone a significant change over the past decade, especially with the inclusion of the effects of BWR and PWR environments on the fatigue life of components. The incorporation of the environmental effects into the calculations is performed via an environmental factor, Fen, which is introduced in ASME BPV code-case N-792 [5], and depends on factors such as the temperature, dissolved oxygen and strain rate.

Nevertheless, a wide range of factors, such as surface finish, have a deleterious impact on fatigue life, but their contribution to fatigue life is typically taken through the transition factors to build the fatigue design curve [2] and not in an explicit way, such as the Fen factor. The testing supporting the rules pertaining to Environmental Fatigue Correction Factor (Fen) Method in ASME BPV was performed on specimens with a polished surface finish and on the basis that the Fen factor was applicable without alteration of the historical practice of building the design curve through transition factors. The extensive amount of testing conducted and reported in References [2] and [7] (technical basis for ASME BPV current EAF rules) was used to propose a set of transition coefficients from the mean air curve to the design curve on one hand, and on the other hand to build a Fen factor expression, defined as the difference between the life in air and in PWR environments.

The work initiated by AREVA in 2005 [9] [10] [11] demonstrated that there is a clear interaction between the two aggravating effects of surface finish and PWR environment for fatigue damage, which was not experimentally tested in the References [2] and [7]. These results have clearly been supported by testing carried out independently in the UK by Rolls-Royce and AMEC FW [12]. These results are all the more relevant as most NPP components do not have a polished surface finish. Most surfaces are either industrially polished or installed as-manufactured.

It was concluded that this proposal could potentially be applicable to a wide range of components and could be of interest to a wider community. EDF/Areva/CEA have therefore authored a code-case introducing the Fen-threshold, a factor which explicitly quantifies the interaction between PWR environment and surface finish. This paper summarizes this proposal and provides the technical background and experimental work to justify this proposal.
Fracture Toughness Testing of a Low Alloy Structural Steel Using Non-Standard Bend Specimens and an Exploratory Application to Determine the Reference Temperature, T0
Authors: Scarabeli Barbosa Vitor , Ruggieri Claudio
Published: October 2017

This work addresses an experimental investigation on the cleavage fracture behavior of an ASTM A572 high strength, low alloy structural steel using standard and non-standard SE(B) specimens, including a non-standard PCVN configuration. One purpose of this study is to develop a fracture toughness test procedure applicable to bend geometries with varying specimen span over width ratio (a/W) and loaded under 3-point and 4-point flexural configuration. We provide a new set of plastic η-factors applicable to these non-standard bend geometries which serve to estimate the experimentally measured toughness values in terms of load-displacement records. Another purpose is to investigate the effects of geometry and loading mode in fracture tests using non-standard bend specimens. Fracture toughness testing conducted on various bend specimen geometries extracted from an A572 Grade 50 steel plate provides the cleavage fracture resistance data in terms of the J-integral at cleavage instability, Jc. The experimental results show a potential effect of specimen geometry and loading mode on Jc-values which can help mitigating the effects of constraint loss often observed in smaller fracture specimens. An exploratory application to determine the reference temperature, T0, derived from the Master Curve methodology also provides additional support for using non-standard bend specimens in routine fracture applications.
EDS Containment Vessel TNT Equivalence Testing
Authors: Crocker Robert W. , Haroldsen Brent L. , Stofleth Jerome H.
Published: October 2017

The V26 containment vessel was procured by the Project Manager, Non-Stockpile Chemical Materiel (PMNSCM) for use on the Phase-2 Explosive Destruction Systems. It was fabricated under Code Case 2564 of the ASME Boiler and Pressure Vessel Code, which provides rules for the design of impulsively loaded vessels [1]. The explosive rating for the vessel, based on the Code Case, is nine (9) pounds TNT-equivalent for up to 637 detonations. This report documents the results of tests that were performed on the vessel at Sandia National Laboratories to qualify the vessel for explosive use [2]. Three of these explosive tests consisted of: (1) 9lbs bare charge of Composition C-4 (equivalent to 11.25lbs TNT); (2) a 7.2lbs bare charge of Composition C-4 (equivalent to 9lbs TNT); (3) a bare charge of 9lbs cast TNT. The results of these tests are compared in order to provide an understanding of how varying charge size affects vessel response when the ratio of free volume to charge volume is small, and in making direct comparisons between TNT and Composition C-4 for TNT equivalency calculations. In a previous paper [3], the 7.2lbs bare charge of Composition C-4, (2) above, was compared to 7.2lbs of Composition C-4 distributed into 6 charges.
European Standard on Small Punch Testing of Metallic Materials
Authors: Bruchhausen Matthias , Austin Tim , Holmström Stefan , Altstadt Eberhard , Dymacek Petr , Jeffs Spencer , Lancaster Robert , Lacalle Roberto , Matocha Karel , Petzová Jana
Published: October 2017

Life extension of aging nuclear power plant components requires knowledge of the properties of the service-exposed materials. For instance, in long term service the tensile and creep properties might decline and the ductile-to-brittle transition temperature (DBTT) might shift towards higher temperatures. Monitoring of structural components in nuclear power plants receives much attention — in particular in the context of lifetime extension of current plants, where the amount of material available for destructive testing is limited.

Much effort has therefore been invested in the development of miniature testing techniques that allow characterizing structural materials with small amounts of material. The small punch (SP) test is one of the most widely used of these techniques. It has been developed for nuclear applications but its use is spreading to other industries.

Although the SP technique has been used for more than 30 years, there is currently no standard covering its most widely used applications. Within the auspices of ECISS TC 101 “Test methods for steel (other than chemical analysis)” WG 1 is currently developing an EN standard on the “Small Punch Test Method for Metallic Materials”. The standard will address small punch testing for the determination of tensile/fracture properties as well as small punch creep testing.

This paper gives an overview of the state-of-the art of the SP tests and describes the scope of the standard under development.
Surface Roughness 3D Modelling and its Association With Leak Tightness for a Metal-to-Metal Contacting Surface
Authors: Anwar Ali A. , Dempster William , Gorash Yevgen , Nash David
Published: October 2017

This paper presents an overview of a numerical method developed to allow one-way structure-fluid interaction of a scanned representative surface of a Pressure Relief Valve (PRV) measuring 100 μm by 100 μm to be incorporated into a coupled finite element and computational fluid dynamics model to investigate gas leak rates through micro-gaps in full size metal-to-metal contacting components. The virtual representative surface is created via a real scan using a 3D micro coordinate and surface roughness measurement system. The scan of the physical surface is converted to a CAD format and a finite element model generated which is deformed for a given loading condition. The micro-gaps of the deformed FEA model are extracted and imported into the CFD solver to find the resulting volumetric/mass flow rate for the same set of pressure conditions. This coupled approach allows the leakage rate to be found based on only the surface roughness of metal-to-metal sealing surfaces. This methodology can now be expanded to understand the behaviour and response of metal-to-metal deformable contacting surface components under pressure. Thereafter, the design objective is to minimise or eliminate component leakage.
Deformation and Fracture Behaviour of 316L Stainless Steel Manufactured Through Selective Laser Melting
Authors: Davies C. M. , Garg P. , Hooper P. A.
Published: October 2017

Selective Laser Melting (SLM) is a relatively new manufacturing technique that offers many benefits. However the utilisation of SLM manufactured components depends on the assurance of their integrity during operation. The influence of processing parameters and build orientation on the tensile deformation and Charpy impact energy has been examined. In addition, the influence of processing parameters on the resultant microstructure has been determined. The processing parameters have been found to have a significant effect on both the tensile and Charpy impact energies. It was found that a layer thickness of 25 μm, scan speed of 800 mm s−1 and hatch spacing of 60 μm resulted in the best properties determined, with tensile properties comparable to that of cold drawn material but impact energies around 25% lower. Significant porosity was observed in the samples especially for high scan speeds and hatch spacing which is considered to be the main cause of poor material properties in most samples examined.
Assessment of the Influence of the Use of Weld Overlay As a Repair Method on the Stress Level of Bulged Sections of Coke Drums
Authors: Vivas Gabriel A. , Moret Armando J. , Bello Roberto E. , Melian Luis M. , Araque Egler D.
Published: October 2017

Several studies recognized that cracks in delayed coke drums resulted from low cycle fatigue induced by cyclic thermal stress [1], [2], [3]. According to a coke drum survey coordinated by API in 1996 [1], there are two different areas where cracks are produced. The first zone is located at the shell to skirt weld, and the second at the bulged areas found in the cylindrical section. In the second case, from 145 coke drums 57% reported that had shell bulging problems. Of the drums that bulged, 87 % also showed cracks.

Recently, it has been reported the use of a novel weld repair procedure on bulged sections of a drum. In this repair, the bulge is overlaid with weld metal on the inside or outside on the bulge depending on the bulge shape. It has been reported that this repair procedure can stop further bulging on the shell, but detailed information about its influence has not yet been published.

Finite element analysis of several bulged patterns that were identified from some laser mappings are used to compare the level of the stress after a weld overlay repair is made. The study was carried out running a sequentially-coupled thermo-mechanical analysis. The assessment shows the influence of the thickness and the extent of the weld overlay on the level of stress on bulged coke drums. The results indicated that depending on the initial bulged shape this repair method either reduces or increases the level of the stress. When an inward deformation pattern is observed, an external reinforcement is recommended; however, when an outward deformation pattern is developed in a coke drum, an external weld overlay repair is not recommended.
Fracture Toughness Variation With Flaw Depth in Various Specimen Geometries and Role of Constraint in Material Fracture Resistance
Authors: Hioe Y. , Kalyanam S. , Wilkowski G. , Pothana S. , Martin J.
Published: October 2017

A series of pipe tests with circumferential surface cracks has been conducted along with fracture toughness tests using single-edge notch tension (SENT) specimens having similar crack depths and crack orientations as the surface-cracked pipes. This paper presents observation of measured fracture toughness variation due to the crack depth and discusses the effect of constraint on the material resistance to fracture.

Crack-tip-opening displacement (CTOD) measurements were obtained with the use of a dual clip-gauge mounted on both the SENT specimens and center of the surface-cracks in the pipes. CTOD was obtained at both the crack initiation and during the crack growth through the ligament. CTOD is a direct measure of the material toughness in the pipe and SENT tests. CTOD at crack initiation and during crack growth can also be related to the material J-Resistance (J-R) curve. Commonly, the material resistance is assumed to be the same for all circumferential surface-crack geometries in a surface-cracked pipe fracture mechanics analyses. However, based on experimental observations on a series of recently conducted surface-cracked pipe tests, the CTOD at the center of the surface crack at the start of ductile tearing and maximum moment changed with the depth of the surface crack. This is believed to be a constraint effect on plasticity in the ligament which depends on crack depth. The CTOD values at crack initiation were decreasing linearly with crack depth. This linear decrease in CTOD trend with flaw depth was also observed in SENT tests.

More importantly, the decrease in CTOD with surface crack depth was significant enough that the failure mode changed from being limit-load to elastic-plastic fracture even in relatively small-diameter TP304 stainless steel pipe tests. This toughness drop explains why the Net-Section-Collapse (limit-load) analysis overpredicted the maximum moment for some crack geometries, and why the deeper surface cracks tore through the pipe thickness at moments below that predicted by the NSC analysis for a through-wall crack of the same circumferential length. An “Apparent NSC Analysis” was developed in a companion paper to account for the changing toughness with crack depth [1].

Finally, this same trend in decreasing toughness with flaw depth is apparent in surface-cracked flat plates [2] and axial surface flaws in pipes [3]. The leak-before-break behavior for axial surface cracks is also not explained by numerical calculations of the crack-driving force when assuming the toughness is constant for all surface cracks and the through-wall cracks, but the change in toughness with surface flaw depth explains this behavior. Previously, axial flaw empirical limit-load solution was developed by Maxey and Kiefner [4], and is consistent with the observations from this paper.
Fatigue Life Properties of Circumferentially-Notched, Type 304 Austenitic Stainless Steel in Hydrogen Gas
Authors: Nagaishi Naoaki , Yoshikawa Michio , Okazaki Saburo , Matsunaga Hisao , Yamabe Junichiro , Matsuoka Saburo
Published: October 2017

Fatigue tests were performed using circumferentially-notched, round-bar specimens with a stress concentration factor, Kt, of 6.6 for Type 304, meta-stable, austenitic stainless steel. The tests were carried out in ambient air and in hydrogen gas at a pressure of 0.7 MPa at room temperature. In the relatively short fatigue life regime, the specimen showed a marked decrease in fatigue life. In contrast, in the longer-life regime, the specimen showed no degradation in fatigue life in hydrogen gas. The fatigue life curve and fatigue limit were predicted by assuming that the notch was equivalent to a circumferential crack, with the predicted values subsequently compared with the experimental results. With regard to the low-alloy steel, JIS-SCM435, it has been reported that the predictions were in good agreement with the experimental data [1]. However, there is a disparity between what was predicted and the actual experimental results in the case of Type 304. The reasons for this divergence are also discussed in relation to the yielding condition, as well as to the cyclic-plastic deformation behavior at the notch root.
Pressurized Creep-Fatigue Testing of Alloy 617 Using Simplified Model Test Method
Authors: Wang Yanli , Jetter Robert I. , Sham T.-L.
Published: October 2017

The Simplified Model Test (SMT) is an alternative approach to determine cyclic life at elevated temperature and avoids parsing the damage into creep and fatigue components. The Elastic-Perfectly Plastic (EPP) combined integrated creep-fatigue damage evaluation approach incorporates the SMT data based approach for creep-fatigue damage evaluation into the EPP methodology to avoid the separate evaluation of creep and fatigue damage and to eliminate the requirement for stress classification as in current methods; thus greatly simplifying evaluation of elevated temperature cyclic service. The conceptual basis of the SMT approach is that if the effects of plasticity, creep and strain redistribution in the SMT specimen result in a stress-strain hysteresis loop that envelopes the hysteresis loop at the peak strain location in the component, then the SMT results can be used to assess the cyclic damage in the component.

The original SMT concept (Jetter, 1998) considered that the effects of sustained primary stress loading could be safely neglected because the allowable local stress and strain levels were much higher than the allowable sustained primary stress levels. This key assumption requires experimental verification. The influence of the internal pressure on SMT creep-fatigue life is demonstrated and the effect of primary load on the SMT design approach is discussed.
Embedded Capacitance Sensor Array for Structural Health Monitoring of Pipeline Systems
Authors: Weber Jarod , Shi Jianfeng , Zhang Chuck
Published: October 2017

Embedded capacitance sensor arrays for Structural Health Monitoring (SHM) of piping is explored. Using a capacitive electrode layer system embedded within Fiber Reinforced Polymer (FRP) layers, to detect potential damage and loading conditions. The sensors are comprised of an electrode array, and allow changes in system capacitance to be monitored. Combined with baseline data points, subsequent measurements can provide indication of applied force changes within composite patched or composite reinforced piping, allowing for repair or reinforcement health status monitoring. Unlike traditional sensors which only measure a single point, the proposed approach incorporates an electrode array technique, while capacitive sensing affords the ability to detect minuscule changes in force on the whole pipe surface. Thus, providing detection and monitoring capabilities beyond those currently employed by industry such as optical fiber or strain gauge.
Application of Model-Based Condition Monitoring to the Human Cardiovascular System
Authors: Reich Alton , Heym Jason
Published: October 2017

The techniques applied by mechanical engineers to problems of machinery condition monitoring can also be applied in other fields. This paper discusses applying techniques that are regularly applied to machinery and system condition monitoring to the human cardiovascular system. Techniques such as physics-based system modeling coupled with limited measurements can be used to infer the condition of a system or specific component. In this case, a mathematical model of the flow through the cardiovascular system was implemented and can be used independently to simulate system performance. Given basic system parameters including heart rate and vascular resistances, the model generates time varying flows and pressures in different portions of the system. The model can be used to interpret a measurement performed on the system to obtain additional information about the state of the system. In this case pulse waveform information is used to make a system flow measurement. This paper will provide an overview of the technique used, the structure of the model, and the initial validation with patient data.
Acceptable Levels of Corrosion for Pressure Boundary Bolted Joints
Authors: Brown Warren , Long Stewart
Published: October 2017

This paper outlines recent work in the field of pressure boundary bolted joint integrity and the effect of corrosion on bolted joint components. It summarizes recent analysis and testing which determined the risk to joint integrity or catastrophic failure associated with corrosion of the joint components; bolts, nuts and flanges.

The paper details, at a high level, the work performed and outlines the limits to corrosion that can be applied in the field for each component as an inspection limit to trigger planned replacement or emergency shut down.
Reproducing Fluid-Elastic Coupling Forces on a U-Tube With a Hybrid Testing Approach
Authors: Lhuillier Vincent
Published: October 2017

In the nuclear industry, flow-induced vibrations of Steam Generator (SG) tubes are extensively studied for safety justifications and for optimizing the maintenance policies of these components. This paper presents a hybrid testing approach that reproduces the coupled fluid-elastic forces acting on the SG-tubes, by means of an active control system. By modal control strategy and precise pole placement, it is possible to recreate in dry conditions the dynamics of the tube in the turbulent secondary flow. Since the quality of pole placement strongly depends on the model accuracy, this paper also presents the identification method of the instrumented tube.
Evaluation and Extension of Allowable Stress Values for GR.91
Authors: Kimura Kazuhiro
Published: October 2017

Evaluation and extension of allowable stress values of Grade 91 steel have been investigated with the updated creep database. Creep database has been updated and 2,046 of time to rupture data, 523 of time to initiation of tertiary creep data and 388 of time to 1% total strain data have been compiled. Accuracy of evaluation and extrapolation was examined on several type data analysis procedures. Larson-Miller and Orr-Sherby-Dorn parameters were used. Lot-centering method, data-censoring by 1,000 h, and region-splitting method by half-yield were investigated. Precise and conservative evaluation was obtained by region-splitting analysis with 3rd and 2nd order polynomials for high- and low-stress regimes, respectively. According to the data analysis, Minimum Stress-to-Rupture, Sr, and Allowable Stress Intensity Values of St and Smt have been evaluated and extended to 500,000 hours.
Heat Transfer Enhancement in Three-Dimensional Flow Past a Hydrophobic Cylinder for Heat Exchanger Applications
Authors: Mastrokalos M. E. , Kaiktsis L.
Published: October 2017

Hydrophobic surfaces, enabling flow slip past a solid boundary, can be effective for suppressing flow unsteadiness, as well as for heat transfer enhancement; both are important for heat exchanger applications. In the present work, a computational investigation of forced convection heat transfer in cross-flow past a hydrophobic circular cylinder is performed at a Reynolds number value of 300, for which flow past a non-hydrophobic cylinder is three-dimensional. Here, the cylinder surface is maintained at a constant temperature, whereas a Prandtl number of unity is considered. Surface hydrophobicity is modelled based on the Navier model. In a first step, slip conditions are implemented on the entire cylinder surface (full slip), for a nondimensional slip length b* = b/D = 0.20, b being the slip length and D the cylinder diameter. This results in a suppression of flow unsteadiness, as well as in a simultaneous heat transfer enhancement; the latter is quantified by the increase of the mean Nusselt number. Next, in order to reduce the extent of the hydrophobic region, and thus the associated cost, a partial slip setup is considered. This setup consists of alternating hydrophobic and non-hydrophobic strips along the spanwise direction, the width of which is selected considering the spanwise wavelength, λz, of three-dimensional flow. Further, following recent studies of the authors on two-dimensional flow, a non-hydrophobic region is considered around the average rear stagnation point (in the circumferential direction), for all hydrophobic strips. It is shown that the present setup can result in values of mean Nusselt number comparable to those attained with full slip. Overall, the present results illustrate that a proper implementation of partial hydrophobicity on the cylinder surface, along the circumferential and the spanwise direction, results in a suppression of wake unsteadiness and fluctuating forces, as well as in a simultaneous enhancement of heat transfer rates.
Development of Fit-for-Purpose Austenitic Stainless Steels With High Polythionic Acid Stress Corrosion Resistance
Authors: Osuki Takahiro , Seto Masahiro , Okada Hirokazu , Sagara Masayuki , Matsumoto Satoshi , Ono Toshihide
Published: October 2017

In the process units with Polythionic Acid Stress Corrosion Cracking (PTA-SCC) such as hydrotreater or hydrocracker, the neutralization treatment like soda ash washing and/or PWHT, Post Weld Heat Treatment, are conducted for stabilized austenitic stainless steels of TP321H or TP347H to mitigate the potential of PTA-SCC. 347AP, the proprietary version of Type 347LN, is remarkable for the possibility to save the fabrication and turnaround cost by the elimination of the neutralization treatment and/or PWHT and its reliability to PTA-SCC resistance without PWHT and neutralization was proven by the long-term service experience. However it has not been investigated the difference between 347AP and TP347H for the Stress Relaxation (SR) cracking resistance of welded joint required for the long term operation at elevated temperature.

On the other hand, in atmospheric distillation units and vacuum distillation units using the crude containing high Total Acid Number (TAN), the resistances to both Naphthenic Acid Corrosion (NAC) and PTA-SCC are required by elevating the design temperature. Therefore, Fit-for-purpose austenitic stainless steels with high PTA-SCC resistance without stabilization treatment are required for the complicated environment with the variation of temperature, pressure and fluid in petroleum refinery process using the crude containing high S content.

In this study, SR cracking susceptibility of 347AP is investigated and it is found that 347AP has lower SR cracking susceptibility than TP347H without stabilization treatment.

Next, in order to improve NAC resistance compared with 347AP, the effect of Mo, Cu and W contents to NAC are investigated based on 347AP, and it is clarified that the increase of Mo content greater than 3% is the most effective to improve NAC resistance. Moreover, the conventional welding filler with the similar NAC and PTA-SCC resistances to base metal is investigated, and it is reported that ER NiCrCoMo-1 filler was recommended for the welding fabrication of Fit-for-purpose austenitic stainless steels with high PTA-SCC resistance.
Weldability Evaluation of P87 and 230W Filler Metals in Alloy 230 to Grade P91 Steel Dissimilar Metal Weld
Authors: Sarich Conner , Alexandrov Boian , Benatar Avraham , Penso Jorge , Kovacich Jerry
Published: October 2017

The objective of this study was to perform comparative weldability evaluation of weld filler metals for an Alloy 230 / P91 steel dissimilar metal weld (DMW) that will be used in once through steam generator (OTSG) on an offshore oil platform. The weldability characteristics of filler metals EPRI P87 and Haynes 230W were evaluated using the cast pin tear test (CPTT) and a stress relaxation cracking (SRC) test in combination with metallurgical characterization using light optical and scanning electron microscopy.

Solidification cracking susceptibility rankings generated with the CPTT showed that undiluted P87 filler metal had better resistance to solidification cracking than undiluted Alloy 230W. The SRC testing preformed in the Gleeble 3800™ thermo-mechanical simulator showed that none of the tested welds failed in stress relaxation cracking mode during simulated service at 600°C under constant displacement and tensile load at 90% of the high temperature yield strength. During the SRC testing, filler metal 230W exhibited some level of stress relaxation, while no evidence of stress relaxation was found in filler metal P87.
An Improved Continuum Damage Constitutive Model for Creep Deformation of Cast 20Cr32Ni1Nb Steel
Authors: Guo Xiaofeng , Gong Jianming , Geng Luyang
Published: October 2017

An improved continuum damage constitutive model is presented to describe the creep behavior of centrifugally cast 20Cr32Ni1Nb stainless steel. In order to determine the internal softening mechanisms of the steel, microstructural observations of damage in 20Cr32Ni1Nb steel are made using the long-term iso-thermal aging treatment. Based on the physics of microstructural processes, a two state variable theory which represents two damage mechanisms related to particle coarsening and microcrack is employed to account for tertiary creep. The kinetic equation which describes the coarsening of the precipitates with time is coupled with Liu-Murakami creep damage constitutive model. Good agreement between predicted and experimental data proves the validity of the proposed model. Compared with the failure times predicted by power law based models, such as Kachanov-Robotnov and Liu-Murakami model, life predictions based on the proposed model are found to be more reasonable over a wide stress range. Additionally, the proposed model is also applied to analyze the accumulation and development of damage in 20Cr32Ni1Nb manifold components.
Evaluation Method for Seismic Fatigue Damage of Plant Pipeline
Authors: Inada Fumio , Sakai Michiya , Morita Ryo , Tamura Ichiro , Matsuura Shin-ichi , Saito Kiyoshi , Ohtori Yasuki
Published: October 2017

Although acceleration and cumulative absolute velocity (CAV) are used as seismic indexes, their relationship with the damage mechanism is not yet understood. In this paper, a simplified evaluation method for seismic fatigue damage, which can be used as a seismic index for screening, is derived from the stress amplitude obtained from CAV for one cycle in accordance with the velocity criterion in ASME Operation and Maintenance of Nuclear Power Plants 2012, and the linear cumulative damage due to fatigue can be obtained from the linear cumulative damage rule. To verify the performance of the method, the vibration response of a cantilever pipe is calculated for four earthquake waves, and the cumulative fatigue damage is evaluated using the rain flow method. The result is in good agreement with the value obtained by the method based on the relative response. When the response spectrum obtained by the evaluation method is considered, the value obtained by the evaluation method has a peak at the peak frequency of the ground motion, and the value decreases with increasing natural frequency above the peak frequency. A higher peak frequency of the base leads to a higher value obtained by the evaluation method.
Effect of Mechanical Model on Limit Load Analysis of High Pressure Heater Tubesheet
Authors: Du Yan-Nan , Tang Xiao-Ying , Wang Jia-huan , Yang Zhi-Gang , Ren Yi-Feng , Wang Zhen-Bang , Wang Shao-jun
Published: October 2017

Tubesheet is the main part of high pressure heater, which is very thick based on chinese code GB151 for the design of heat exchangers. Increased tubesheet with large thermal stress are not conducive to manufacture, heat transmission and detection. The stress and structure of tubesheet are so complex that the time costs too large during the analysis design, and stress classification exists uncertainty. Limit load method contributes to tubesheet lightweight. 3-D finite element model used for analysis design should be simplified reasonably. In this paper, the effect of mechanical model on limit load analysis of high pressure heater tubesheet conforming to the design-by-analysis code is researched. It is found that the tubesheet could pass the plastic collapse assessment, and the thickness of tubesheet could be decreased. The difference between the equivalent sold tubesheet model and the whole tubesheet model exists during plastic collapse assessment. Though the local stress distribution is different, the limit load results occurred plastic collapse by the equivalent sold tubesheet model is close to that by the whole tubesheet model. The limit load occurred plastic collapse is influenced by max circular diameter of tube layout little. The reason is attributed to original tubesheet owning enough rigidity related to thickness, and high stress appeares on the inner wall of jointing of tubesheet with head. The equivalent sold tubesheet model could be used for primary evaluation of limit load, and the whole tubesheet model is suited for partial analysis. The results provide some reference for the design-by-analysis of high pressure heater tubesheet.
Corrosion Behavior of X70 Pipeline Steel and Corrosion Rate Prediction Under the Combination of Corrosive Medium and Applied Pressure
Authors: Li Kaikai , Wu Wei , Cheng Guangxu , Li Yun , Hu Haijun , Zhang Hao
Published: October 2017

Natural gas transmission pipeline is prone to internal corrosion due to the combination of corrosive impurities in the pipe (such as CO2, H2S and chlorides) and applied pressure of the pipeline, which seriously affects the safe operation of the pipeline. In this work, the corrosion behavior of a typical X70 pipeline steel was investigated by using potentiodynamic polarization and electrochemical impendence spectroscopy (EIS). The polarization and EIS data under different CO2 partial pressures (0–1 atm), H2S concentrations (0–150 ppm), chloride concentrations (0–3.5 wt%) and tensile stress (0–400 MPa) were obtained. The results show that corrosion rate increases with the increase of CO2 partial pressure and chloride concentration, respectively, while first increases and then decreases with the increase H2S concentrations. The corrosion rate is less affected by elastic tensile stress. In addition, a quantitative prediction model for corrosion rate of natural gas pipeline based on adaptive neuro-fuzzy inference system (ANFIS) was established by fitting the experimental data which maps the relationship between the key influencing factors (i.e. CO2 partial pressure, H2S concentration, chloride concentration and tensile stress) and the corrosion rate. The prediction results show that the relative percentage errors of the predicted and experimental values are relatively small. The prediction accuracy of the model satisfies the engineering application requirement.
Elasto-Plastic Finite Element Analysis of Long-Lived Seismic Ties for Thermal Power Boiler Structure
Authors: Aida Kiyoshi , Morikawa Shoji , Shimono Masaki , Kato Motoki , Morishita Kunihiro , Amano Tatsuya
Published: October 2017

This paper deals with the modification of recently developed steel seismic ties, which are energy absorbing devices installed between a boiler and its support structure. To enhance the aseismic reliability of the boiler and its support structure for recently increased specified earthquake loads, the useful live of the seismic ties must be prolonged. To achieve this, changes to the sectional shapes of the seismic ties have been analyzed and designed with the help of elasto-plastic finite element analysis.
Technical Basis for the Exemptions to Mandatory Post Weld Heat Treatment (PWHT) of SA-738 Grade B for Sec. III Div. 1 Subsection NE Application
Authors: Hayashi Takahiro , Kim Charles C. , Kumagai Kohki , Goto Mitsuhiro , Otake Shiro
Published: October 2017

With the current practice in steel making and welding process control, thick and large structural components fabricated from the widely used steel materials such as SA-738 Grade B have good material properties sufficient enough to meet the increasing demand of avoiding a large amount of Post Weld Heat Treatment (PWHT) applications at both shop and site. The original rule in the ASME Boiler and Pressure Vessel Code (the Code), however, allows the exemption to mandatory PWHT for SA-738 Grade B by limiting the applicable material thickness equal to or less than 1 3/4 in. (44 mm) for Section III, Division 1, Subsection NE application.

A Code Case was proposed with the purpose to increase the maximum thickness for the exemption of mandatory PWHT from 1 3/4 in. (44 mm) in the original rule to 2 3/8 in. (60 mm). In order to demonstrate the applicability of the PWHT exemption for material with increased thickness, material tests have been performed mainly for the test data required in the ASME Sec. III Div. 1 Subsection NE for three different heats of the plates. The tests performed also include additional data to those required by the Code, such as fracture toughness (KJc) test, microstructural observation, hardness test and oblique Y-groove test for SMAW process.

All the tests results for the base materials and weld joints have shown sufficient rationale to increase the exemption thickness to mandatory PWHT to 2 3/8 in. (60 mm).
Numerical Simulation of Local Post Weld Heat Treatment by Electric Heating Method of Pressure Equipment
Authors: Sun Liang , Ji Fang , Wang Xiaomei , Deng Guide , Cheng Lei
Published: October 2017

The local post weld heat treatment by electric heating method is widely used to eliminate welding residual stress in processes of manufacture and maintenance of pressure equipment. The key point of local post weld heat treatment is to choose a reasonable heated band width and insulated band width. But the criterions to determine the minimum heated band width and insulated band width are different according to Chinese, European and American standards, which are GB/T 30583-2014, EN 13445-4: 2009 and AWS D10.10/D10.10M :1999, respectively. Taking the local post weld heat treatment for the circumferential butt weld between two thick cylinders both with a 115 mm thickness as an example, numerical simulation is used to compare the wall temperature distribution of the cylinders during the heat preservation stage when the heated band width and insulated band width are chose according to the above three standards, and the numerical simulation was verified by the tested temperature from one field experiment. The results show that the numerical calculation method can accurately predict the wall temperature of the cylinders during the local heat treatment, and the wall temperature of the surfaces on which the heaters are arranged according to the three standards all well meets the requirement of the heat treatment, but the wall temperature of the surfaces without the heaters cannot meet the temperature requirement. So double-side heating and double-side insulating are suggested to be adopted during local post weld heat treatment.
Introduction of Gasket Testing Protocols in the New RCC-M® F7000 Revision Proposal
Authors: Lejeune Hubert , Boulben Cédric
Published: October 2017

AFCEN, publisher of the French Nuclear code RCC-M® [1] (Design and Construction Rules for Mechanical Components of PWR Nuclear Islands) has launched an action for the revision of the Annex ZV and F7000 respectively concerning the design and installation of the Bolted Flange connections (BFC). This paper focuses on the gasket testing procedures defined in the proposed project for revision of F7000.

First, the general strategy of gasket testing protocols detailed in the F7000 revision project is introduced. Then the new specific gasket characterization procedures for the determination of the relevant mechanical and sealing parameters required in the calculation following the new proposed RCC-M® Annex ZV are detailed. A focus is done on the introduction of a systematic analysis procedure to determine the required force to reach the Metal-to-Metal Contact (MMC) between the compression flanges (for grooved gaskets) or between the compression flanges and the gasket limiter ring. The results of these specific test protocols on a selected set of gasket types are also presented. Finally the test protocols defined for gasket production acceptance are shortly introduced.
Study on the Rocking Vibration Induced in Three-Dimensional Seismic Isolation System
Authors: Tomita Noriaki , Fujita Satoshi
Published: October 2017

Many earthquakes have occurred in Japan, and Japanese design seismic wave for several plants have became more severe after strong earthquakes. Especially, since vertical seismic conditions have became more severe, it is difficult to ensure the safety margin of the seismic evaluations in industrial facilities. As a way to ensure the margin of seismic evaluations, it is effective to adopt the vertical seismic isolation system. When the vertical frequency with the vertical isolation system becomes low frequency range, the rocking vibration will occur.

By using the seismic isolation system of approximately 3 [Hz] in vertical frequency, the response in vertical direction is reduced without large rocking vibration.

However, variations of a specification in seismic isolation system may occur in actual isolation device. Therefore, in this paper, the vibration characteristic including the rocking vibration is discussed, and also an analysis method is evaluated in consideration of the variation of vertical stiffness. Then, using the proposed analytical method, the tendencies of the vertical frequency variation and the rocking vibration response are confirmed. The rocking vibration occurs because of the deviation between the center of gravity and center of stiffness. Therefore, it is necessary to control the decentering between the center of gravity and rigidity. However, assuming the number of actual seismic isolation devices applying the structure, eccentricity ratio is expected to be approximately under 0.05. Therefore, the effect of eccentricity ratio on the rocking vibration is considered to be small.