bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Assessment of SLWR Riser in Brazilian Pre-Salt: The Impact of Slope Changing Point in SN Curve
Authors: F. Senra Stael , Aguiar Ludimar L. , Hippert Eduardo , Garmbis Alexandre G. , Dos Santos Marcelo , D. Martins Marcos André , P. Nunes Luis Manoel
Published: November 2019

One of the main challenges in rigid riser design for Brazilian Pre-salt is the fatigue limit state. At this new production frontier, some key points are imposed as a challenge for riser designers, mainly due to the high level of motions imposed by the FPSO at the riser top in a coupled system with water depth around 2200 meters, and thicker riser’s thermal insulation demanded for flow assurance (which worsens the dynamic response of production risers). Additionally, high contaminant levels in the fluid (CO2 & H2S) demands CRA materials. Within this context, Petrobras has been considering Steel Lazy Wave Riser (SLWR) configuration as a base case scenario for rigid riser projects, since this configuration is able to absorb part of the FPSO motions that would reach the touch down zone (TDZ) and, consequently, making this region much less demanded when compared against Steel Catenary Risers (SCR). In its pioneer deepwater SLWR [1], Petrobras adopted a conservative approach for fatigue assessment that involved degenerated SN curves from DNV-RP-C203, i.e. D curve in cathodic protection with the slope changing point (SCP) shifted to 5 × 106 for external wall and F1 curve in air with SCP at 5 × 107 for internal wall. More recently, both DNVGL and BSI have reviewed their fatigue assessment codes and no longer holds parity between SN curves. BS-7608 Ed. 2014 introduced different SCPs in order to account for a possible non-conservativeness in the assessment of low stresses under variable amplitude in the loading spectra. DNVGL-RP-C203 Ed. 2016 now presents three different bilinear SN curves for the internal wall of pipelines and risers that depends on weld misalignment, while it keeps SCP unchanged. This paper presents a recent case study for a typical SLWR configuration in pre-salt, in order to evaluate the impact of the changes proposed by the new versions of these design codes in the fatigue life of riser girth welds. Results of this work showed that the impact of different positioning of slope changing points in SN curves can have a great importance for riser design, since typical load spectrum lies around this region. Fatigue life could be increased up to twice or three times if one of these codes are adopted instead of the Shifted SN curves. However, the effect of low stresses under variable amplitude loading spectra is still a concern and it should be further investigated.
Viscosity Models for Drilling Fluids: Viscosity Parameters and Their Use
Authors: Saasen Arild , Ytrehus Jan David
Published: November 2019

The most common viscosity models used in the drilling industry are the Bingham, the Power-Law and the Herschel-Bulkley models. The scope of the present paper is to outline how to select the individual models, and how the models need to be re-formulated to be able to have parameters with a physical meaning.

In principle, the Bingham model itself have physical parameters being the yield point and the plastic viscosity. However, the Bingham model very often only very poorly describe the viscosity in complex fluids. This yield stress can be described within a reasonable accuracy by application of the low-shear yield point. A similar problem exists with the Power-Law model resulting from the model’s absence of a yield stress. The compromise model is the Herschel-Bulkley model which contains a yield stress and a power-law term. This model describes the drilling fluid viscosity with reasonable accuracy and includes both the Bingham and Power-Law models as limit formulations.

It is not possible to select fluids based on the Herschel-Bulkley traditional parameters alone. The reason is that the Herschel-Bulkley power-law term’s viscosity parameter has a unit dependent on its power-law exponent. In the present approach the fluid is described using a yield stress, a surplus stress at a characteristic shear rate of the fluid flow and finally a power-law exponent making the fluid applicable in the practical shear rate ranges. The surplus stress is no-longer dependent on other parameters. Hence, we have re-arranged the viscosity model to have independent measurable quantities.
Extended Kalman Filtering for Estimating Drag and Inertia Coefficients for Slender Offshore Structures
Authors: Bhagtani Dhruv , Saha Nilanjan
Published: November 2019

System identification is used in location detection, target tracking, prediction in oil markets and so on. In this paper, the Kalman Filter (extended) technique is explored in monitoring the health of a jacket structure, in a stochastic excited wave environment. Hydrodynamic coefficients drag (CD) and inertia (CM), usually experimentally obtained, are important parameters to assess the force on a structure using the Morison’s equation. Usually these coefficients appearing in the force equation are un-known for majority of the slender offshore structures and are a priori obtained using some set of prototype experiments as these parameters depend on lot of factors (Keulegan-Carpenter number, roughness, dimensions and so on). Therefore, the recourse to parameter identification techniques based on Kalman filtering can be an alternative.

In this paper, the problem is analysed using Airy wave theory where a cylinder is assumed to be fixed at the seabed. Numerical analysis is done to create experimental conditions to observe the dynamic response of the system. These numerical results are then plagued with white noise to represent the observations from experiments. These measurements are subsequently used in identification of the drag and inertia coefficients for the cylinder. This is presently attempted using the Extended Kalman Filter technique.

With the use of this model the Extended Kalman Filter is shown to be able to identify time varying drag and inertia coefficients of the cylinder problem. For the present case, measurement sensors are placed for the measured force, along with the motions: velocity and acceleration. The above method can easily be implemented in jacket structures or similar offshore structures for attention due to increase in forces owing to marine growth.
Effect of LCM Fibers on the Rate of THF-Water Clathrate Hydrate Growth in Water-Based Drilling Fluids
Authors: Nielsen James L. , Nahri Syed Y. , Zhao Wei , Wei Panfeng , Chen Yuanhang
Published: November 2019

This study investigates how different sized fibers used commonly as Lost Circulation Material (LCM) change the time required for induction and agglomeration of natural gas hydrates in drilling fluids using laboratory experimentally obtained data. Three different sizes of LCM fibers, fine, medium and coarse, were studied to observe how the size of each type of fiber affects the rate of hydrates growth. THF-Water clathrate hydrates were used as a model for hydrate growth at standard pressure conditions using a 20:80 molar ratio of THF to water. The concentrations of LCM fibers tested varied between 1–3% by weight. Each type of fiber was tested individually at −6 °C, −3 °C, and 0 °C and monitored for changes in hydrate induction and agglomeration rates. Tests were repeated using water-based drilling fluids using bentonite as the primary viscosifier and barite as a weighting agent to test 10, 12, and 14 ppg fluids. Fibers were tested under static conditions to identify changes in the nucleation and agglomeration rates for each. The rates of hydrate nucleation between samples of THF-Water and LCM fibers and each sample of water-based drilling fluid with LCM fibers was found to be consistent with no statistically significant change in rate being observed due to the fibers present. However, we observed a significant change in the rate of agglomeration that was dependent on the size and concentration of the fiber particles. We identified that fine fibers provided the most significant increase in the rate of agglomeration followed by medium and coarse fibers, respectively, with increasing LCM fiber concentrations. Compared to control samples, using fibers produced initial hydrate agglomeration around the freely suspended fibers. Due to their proximity to other fibers with hydrates developing around them, the hydrates were able to form very large free moving crystals in the solution before completely agglomerating and forming a solid plug. The results and conclusions provide new insights and guidance in drilling fluids and LCM design for offshore deep-water drilling. Gas hydrates can potentially develop and agglomerate along in the BOP and kill/choke lines during a well control event, as what is suspected as what happened in Macondo blowout where a considerable amount LCMs were used during drilling and as a spacer during a negative pressure test.
Cone Penetration Test in Stiff Over Soft Clay in Centrifuge Test
Authors: Xie Qiang , Hu Yuxia , Cassidy Mark , Salehi Alireza
Published: November 2019

This paper describes a numerical study on soil characterization of stiff over soft clays in centrifuge test using cone penetration test (CPT), especially when the top stiff layer is thin relative to the centrifuge cone size. An extensive parametric study was conducted using large deformation finite element (LDFE) analysis, with the cone penetrating continuously from the soil surface. The LDFE model has been validated against existing physical test data with very good agreement. Since the bottom soft clay was normally thick enough to fully mobilise the ultimate cone resistance, its undrained shear strength can be interpreted by the existing approach for cone deep penetration in a uniform clay layer. Thus, the challenge was to interpret the strength of the top stiff layer, where the layer thickness was not thick enough to fully mobilise its ultimate resistance. Both top layer thickness ratios (to the cone diameter) and layer strength ratios were considered in the parametric study. Based on the results from LDFE analyses, the interpretation formula of the undrained shear strength in the top stiff layer was proposed as a set of new bearing factors. The proposed cone bearing factor was a function of the ratio of the measured peak cone resistance in the top layer to the stable/ultimate cone resistance in the bottom layer and the ratio between the top layer thickness to the cone diameter. The formula can be used directly when the top layer thickness was known based on the sample preparation. However, the layer interface can be identified based on the study here, if the top layer thickness was not certain. A design flow chart was provided for interpretations of top clay layer strength and top layer thickness based on the cone resistance profile obtained from CPT test.
On Design and Analysis of a Drivetrain Test Rig for Wind Turbine Health Monitoring
Authors: Balestra Lorenzo , Nejad Amir R. , Naldi Giovanni
Published: November 2019

The reliability of offshore wind turbines is a key factor when estimating maintanence costs, downtime due to component failure and overall efficiency during operational life. Offshore wind turbines have limited accessibility and operate in harsh environments and, as a result, it is difficult to perform frequent checks on electrical and mechanical component. Drivetrain test rigs (DTR) are crucial to the task of: validating the design of new components to avoid early life failure, observe the behaviour of components under load over long periods of time in a controlled environment and produce a maintanence plan that minimize costs and frequency of intervention.

In this paper, after a brief introduction on the state of the art in DTR technology, is described a methodology that can be used to create an effective conceptual design for a drivetrain test rig, focusing also on the possible downscaling.

The paper starts by analyzing the benefits of the drivetrain use in the wind power industry, bringing examples of real test rigs used in industrial and academical world. Once the topic is mastered it is possible to proceed with a description of the various phases needed to obtain the conceptual design, from the definition of layout to the preliminary 3D modeling.

The test rig that is here designed, while inspired from full scale dynamometers used in the industry, is thought as a laboratory tool for academical use that can be used by students to investigate fault detection methods and health monitoring systems of wind turbines. It is also included a section dedicated to the possible techniques for downscaling the test rig, based on simple considerations of the drivetrain mechanical behaviour. Downscaling becomes a key factor when facing the need to test turbine components of ever increasing dimensions in laboratories with limited space and budget. The definition of a procedure to create a scaled version will allow laboratories to build test rigs of smaller dimension but with a damage model for the various components still closely linked to the one in real scale. Downscaling is also a necessity when working with limited power sources, not able to recreate the conditions that the real scale turbine encounters.

The ultimate goal is to define a solid base to allow further development in the detailed design phase.
Time-Domain Diffraction Modelling With Mean Force Effects and Experimental Comparison for Slack-Moored M4 Wave Energy Converter
Authors: Stansby P. K. , Carpintero Moreno E.
Published: November 2019

Linear diffraction modelling of irregular wave structure interaction is standard practice in both the frequency and time domains for fixed and floating bodies. This has been extended for the modular wave energy converter M4 with multiple floats and power take offs. In the time domain second-order forces assuming a stationary body have been added for floating wind energy platforms. This misses second-order, including mean, effects due to radiation damping, drag forces and the mechanical damping of wave energy conversion. If these are linearized they may be included in a frequency domain analysis. However mechanical damping and mooring forces on slack-moored platforms are generally highly nonlinear and time domain analysis is required. In this paper response is first computed with linear analysis and mechanical damping which has been shown to give reasonable prediction of experimental measurement for the response and power output of M4. The response gives the absorbed energy flux due to mechanical and radiation damping which is converted into a mean force through an average wave celerity. The model is extended to include a mooring and these mean forces; the computation is then repeated. The mean forces have negligible effect on response and associated power take off but determine the mooring forces. For a slack mooring zero stiffness is assumed. Comparing with wave basin experiments for the 6-float M4 configuration in operational conditions, mean mooring forces are generally underestimated, markedly for larger periods.
Analysis on Hydrodynamic Responses of a Spar Offshore Wind Turbine With an Innovative Type of Mooring System
Authors: Ma Yuan , Chen Chaohe , Yan Xinkuan , Shen Yijun , Fan Tianhui
Published: November 2019

The mooring system is a key component connecting a floating offshore wind turbine (FOWT) to the seabed. Generally, the traditional mooring systems mainly control the horizontal motions of the floating platform. However, due to the existence of blades, tower structure and the requirement of power generation efficiency, there is a high requirement on the pitching performance when a platform is used for the floating wind turbine. Therefore, an innovative type of mooring system which could improve the pitch performance of the FOWT is really needed.

In this paper, considering the OC3-Hywind Spar floating wind turbine, based on the original type of 3 × 3 mooring system, an innovative type of mooring system which has a better control performance of the pitch of FOWT is designed. Then, the hydrodynamic responses of the floating wind turbine platform are investigated. The influence of two different mooring system types on the hydrodynamic responses of the FOWT are compared and analyzed. The conclusions of this study could serve as a reference for the mooring system design of floating wind turbine systems.
Extreme Response Analysis of an End-Anchored Floating Bridge
Authors: Cheng Zhengshun , Gao Zhen , Moan Torgeir
Published: November 2019

During the design of a floating bridge, extreme structural responses are required to be properly evaluated for ultimate limit state (ULS) design check. This study addresses the estimation of extreme structural responses for an end-anchored curved floating bridge. The floating bridge, about 4600 m, consists of a cable-stayed high bridge part and a pontoon-supported low bridge part. The long-term extreme responses are approximated by using a engineering approach, i.e., the environmental contour method. The sea state with 100-year environmental conditions is considered, and a 90% fractile is used to calculate the short-term extreme responses by using the Gumbel method and the mean up-crossing rate (MUR) method based on 100 1-hour simulations with different seeds.

The extreme responses are expressed as μ + κσ, where μ and σ are the ensemble mean and standard deviation, and κ is a multiplying factor. Numerical results show that structural responses are close to Gaussian distributed. κ of axial force and strong axis bending moment along the bridge girder estimated by both the Gumbel and MUR methods vary in the vicinity of 4. κ estimated by the two method deviates, especially for axial force. Moreover, for both methods the estimated κ deviates more significantly if fewer ensembles are used.
Experimental Study on Hydrodynamic Performance of Mini-AUV in Non-Uniform Flow Field
Authors: Zhuang Jiayuan , Cao Jian , Su Yumin , Zhang Lei , Yu Xianzhao
Published: November 2019

Experimental investigations of hydrodynamic performance of mini-AUV in non-uniform flow field were conducted in the basin of Harbin Engineering University, the revolved body and flat body of mini-AUV model were tested respectively. The three dimensional flow fields were generated by local jet of the underwater pump, and circulated in the basin. The three dimensional velocity distributions at different positions were measured by a Doppler current profiler. The three component balance was used to measure the drag, lateral force and yawing moment acting on the mini-AUV models depending on drift angle in the flow field, and the influence of complex flow field to the hydrodynamic performance of mini-AUV indicated that drag was not sensitive to drift angle and yawing moment was increased obviously. The conducted experiments could supply reference to the maneuverability research of mini-AUV in real marine environments in the future.
Optimization of Valves Packings Through Characterization and Calculation
Authors: Lejeune Hubert , Joulain Frédéric
Published: November 2019

In the valve industry, there is combined demand from the end-users for fugitive emissions reduction and energy efficiency improvement through the reduction of stem/packing friction forces. These two different goals will involve opposite trends on the load to be applied on the packing i.e. high load for good tightness and low load for low friction. Thus, the ability to define optimal ranges of packing tightening is important. Nevertheless, no standardized method for packing calculation nor packing full characterization (mechanical, friction, sealing performance vs. packing load,..) exists in Europe, as for bolted flange joints and associated gasket with EN1591-1 [1] and EN13555 [2].

In collaboration with ESA (European Sealing Association, www.europeansealing.com) and FSA (Fluid Sealing Association, www.fluidsealing.com), the Fluid Equipment Committee of CETIM has developed a tool for the optimization of packing. A set of tests enables to get the packing characteristics needed for the calculation. These tests can also be used for the comparison of packing materials and/or installation procedures performances in defined test conditions.

This paper details the proposed calculation method and describes the associated test rigs and procedures. First test results and a calculation example are also given to show how the method works.
Resource Allocation Model Toward Seismic Water Pipeline Risk Mitigation Measures
Authors: Peyghaleh Elnaz , Alkhrdaji Tarek
Published: November 2019

History of earthquake’s damages have illustrated the high vulnerability and risks associated with failure of water transfer and distribution systems. Adequate mitigation plans to reduce such seismic risks are required for sustainable development. The first step in developing a mitigation plan is prioritizing the limited available budget to address the most critical mitigation measures. This paper presents an optimization model that can be utilized for financial resource allocation towards earthquake risk mitigation measures for water pipelines. It presents a framework that can be used by decision-makers (authorities, stockholders, owners and contractors) to structure budget allocation strategy for seismic risk mitigation measures such as repair, retrofit, and/or replacement of steel and concrete pipelines. A stochastic model is presented to establish optimal mitigation measures based on minimizing repair and retrofit costs, post-earthquake replacement costs, and especially earthquake-induced large losses. To consider the earthquake induced loss on pipelines, the indirect loss due to water shortage and business interruption in the industries which needs water is also considered. The model is applied to a pilot area to demonstrate the practical application aspects of the proposed model. Pipeline exposure database, built environment occupancy type, pipeline vulnerability functions, and regional seismic hazard characteristics are used to calculate a probabilistic seismic risk for the pilot area. The Global Earthquake Model’s (GEM) OpenQuake software is used to run various seismic risk analysis. Event-based seismic hazard and risk analyses are used to develop the hazard curves and maps in terms of peak ground velocity (PGV) for the study area. The results of this study show the variation of seismic losses and mitigation costs for pipelines located within the study area based on their location and the types of repair. Performing seismic risk analysis analyses using the proposed model provides a valuable tool for determining the risk associated with a network of pipelines in a region, and the costs of repair based on acceptable risk level. It can be used for decision making and to establish type and budgets for most critical repairs for a specific region.
Comparison of EN 13555 Gasket Test Data With Predicted Leak Rates Derived From Draft PVRC Equations
Authors: Rice Dale A. , Waterland Jerry
Published: November 2019

In flanged connections, all gaskets have some level of fluid leakage, depending on gasket type and other factors. Using published Room Temperature Tightness (ROTT) test data and draft PVRC (Pressure Vessel Research Council) equations, a simple model to calculate the predicted tightness / leak rates of various gasket materials has been previously documented. The model assumes a set of draft empirical equations previously published by ASME / PVRC but with an incorporated stress loss factor. Tightness at flange assembly as well as following unloading can be estimated with the model. The EN 13555 test standard includes measuring the test gas leak rates for a series of gasket stresses but at a single operating pressure for each test. Correlation of EN 13555 data with PVRC model predicted leak rates over a range of manufactured gasket materials is demonstrated. The leak rate data for specific gasket materials have been found to compare favorably with the leak rates at assembly as determined in using the PVRC model. The application and corresponding limitations of certain EN 13555 gasket parameters are discussed. The end user may wish to consider the use of the PVRC empirical approach to estimate predicted long-term leak rates of competing gasket materials as a key factor in the gasket selection process.
Variable Inertia Damper Using a Flywheel Filled by MR Fluid
Authors: Matsuoka Taichi
Published: November 2019

To get a variable inertia effect for vibration reduction, a semiactive damper using a flywheel filled by MR fluid was developed. The damper comprises a ball screw mechanism and the flywheel, which is able to change a moment of inertia. MR fluid is filled into the flywheel. Particles are clustered at outer circumference edge inside the wheel when the magnetic field is applied to the wheel edge, so the moment of inertia on the flywheel can be changed artificially. The prototype device was manufactured, and the dynamic performance was investigated. Finally the changeable inertia effect was confirmed experimentally.
Using Additive Manufacturing for Making Light Water Reactor Components
Authors: Rebak Raul B. , Lou Xiaoyuan
Published: November 2019

Making light water reactor (LWR) components using additive manufacturing (AM) provides a high degree of design freedom to create complex near net shape geometries, with significant reduction in the deployment time. Since most of the current AM research focus on the refining of the fabrication variables, little information exists on the actual corrosion behavior (including general corrosion, localized corrosion and environmentally assisted cracking - EAC) of AM components. The most frequent operational material failure modes in LWR is EAC and debris fretting of fuel rods, therefore the objective of this work was to evaluate the environmental performance of AM type 316L SS in relation to the traditionally melted and forged wrought material. Stress corrosion cracking results show similar behavior between AM and wrought 316L SS in high temperature water. Ambient temperature electrochemical testing showed that the AM 316L SS was slightly more resistant to localized corrosion than the traditional wrought material and that AM material did not suffer sensitization during fabrication or heat treatment processes.
Improvement of High Temperature Creep Strength of Conventional Grade 91 Steel by Thermomechanical Treatments
Authors: Hernández Rebeca , Serrano Marta , García-Junceda Andrea , Oñorbe Elvira , Vivas Javier
Published: November 2019

The study of the enhanced creep strength of conventional ferritic-martensitic (F/M) grade 91 steel by a thermomechanical treatment (TMT) to increase the precipitation of MX particles in the matrix was performed.

Creep properties were evaluated by tests at constant load at temperatures that varied from 600 °C to 700 °C with different levels of stress for both steels: T91 and T91-TMT. The creep curves and main parameters for both steels in the different conditions were analysed.

Results show a great improvement of creep strength of the T91 after the thermomechanical treatment in comparison with the conventional steel. T91-TMT presents a rupture life significantly higher than T91 and a decrease of the values of the minimum creep rate.

An increase of the density of MX precipitates in the matrix of the T91-TMT due to the thermomechanical treatment in comparison with T91 can be also observed.

A change in the fractography was also detected. T91-TMT specimens showed signs of brittle fracture instead of the ductile fracture, with the common necking effect detected in the T91.
Flaw Acceptance Evaluation for the Final Disposal Canister Under Earthquake Induced Rock Shear
Authors: Chou Hsoung-Wei , Wu Szu-Ying
Published: November 2019

When a canister used for final disposal of spent nuclear fuel is in the deposition hole of deep geological repository, the loading case which would most impact the structure integrity of the canister is to postulate an earthquake induced rock shear through a deposition hole. This paper evaluates the acceptable sizes of defects in the cast iron insert of canister using fracture mechanics analysis. The submodelling technique of finite element analysis was employed to calculate the fracture behavior of the canister with postulated defects subjected to shear loads due to earthquake. At first, the stresses of the global model and the uncracked submodel were compared to check the correctness of the transferred displacements from the global model to the submodel. Then, surface and internal flaws with various shapes and depths were modeled individually in the submodel. A 5 cm shear displacement was applied on buffer and then transmitted to the canister. The calculations of J-integral of each flaw indicate that the surface semi-elliptical defect is more critical and the density of buffer material significantly affects the acceptable size of postulated defects. Present results can provide acceptance criteria of crack detection for canisters during manufacture and examination processes.
Study of the Flow Field in Cylindrical Vessel
Authors: Yang Sha , Dong Qi , Zhang Liucheng , Feng Jiahe , Hu Rongxi
Published: November 2019

A tooth-lock cover is a kind of convenient closure used in explosive containment vessels. But in experiments, it is found that a small amount of explosive exploded in cylindrical vessels could cause severe deformation to the tooth-lock covers. In some situations, the cover would even be blown out of the vessel with severe distortion. The spreading and superposition of the shock waves in the cylindrical vessel is studied in this paper. Impulse is chosen as the evaluation parameter instead of the peak pressure because of the reflection and superposition of the shock waves. The piston method is used to calculate the impulse and the result is verified in 8-tooth cover vessels. This method can evaluate the intensity of the shock wave loaded on the cover. It would be useful in the optimization of the explosion containment vessels.
High Performance Structural Vibration Control by a Preview of the Future Seismic Waveform Generated With a Wave Transmission Network and an AI-Based Estimation System
Authors: Hiramoto Kazuhiko , Matsuoka Taichi , Sunakoda Katsuaki
Published: November 2019

We propose a new active vibration control strategy based on the future seismic waveform information obtained in remote observation sites. The waveform information in the remote site is transmitted by a waveform transmission network to the structure under control. The waveform transmission network is realized by interconnecting multiple controlled structures and observation sites. By using the future waveform information obtained through the network, we propose a control law realizing fairly higher control performance over the conventional structural control methodologies. A preview control law consisting of the state-feedback and feedforward control (preview action) is adopted. For the preview action, future values of the disturbance in some time interval are necessary. However, because the future value of the earthquake waveform is unknown, the preview action contributing the performance improvement is generally impossible. To get over this difficulty, an AI-based wave estimation system to estimate the future earthquake waveform is proposed. The wave estimation system is a multi-layered artificial neural network (ANN). Through a small scale simulation study with a recorded earthquake event in Japan, we show that the proposed control method achieves much higher control performance over the conventional LQ-based active control.
Effective Shank Length of Bolts Under Lateral Loading
Authors: Gao Yong-Jian , Chen Bing-Bing , Zhang Zhai , Zheng San-Long , Yu Qing , Xie Cheng-Chen
Published: November 2019

Additional lateral load tests, with improved techniques, were conducted on M22 stainless bolts to supplement the series of metric system stainless bolt tests which were conducted previously. Using the strain gage-deflection data collected from the entire set, i.e., of different sizes and different lengths, of the bolt tests, the “rigidity coefficient”, which is used in calculating the deflection of the bolts under lateral loads, using the conventionally assumed effective shank length, is derived.

Alternatively, a new analytical effective shank length, which is more accurate than the conventional assumed effective shank length, derived from the test data, is proposed.
Fatigue Analysis for the Lower Assembly of a U-Tube Steam Generator
Authors: Cao Moli J.
Published: November 2019

The lower assembly of a U-tube steam generator consists of a hemispherical primary channel head with a flat bottom, a perforated tubesheet, a partition plate, and a portion of lower shell. The partition plate divides the primary channel head into two halves. Each half contains a primary nozzle and a manway opening. The fatigue analysis of the lower assembly of a U-tube steam generator can be a challenge due to the complexities of the geometry and loading conditions. In this paper, the development of a global finite element model including all important features and several submodels to cover the effects of all these features is described. The tubesheet is simulated using equivalent solid properties with orthotropic material properties. The thermal loads from the inner surfaces of the tubes embedded in the tubesheet are implemented using surface elements. The submodeling technique is utilized to evaluate the local small features, such as tube holes at primary and secondary faces of the tubesheet, with the constraints at the cut-boundaries and the temperature fields of the submodel being extracted from the global model.
On Modeling and Assessment of Bulk Liquid Storage Tanks With Foundation Settlements
Authors: Zhao Mingxin
Published: November 2019

A comprehensive study is conducted on finite element modeling and stress analysis techniques of above ground atmospheric bulk liquid storage tanks with foundation settlements. Both 2-D and 3-D modeling are examined for their applicability and limitations. Simple elastic analysis and 3-step method using a hybrid elastic-plastic procedure are explored and compared. In addition, data processing techniques are proposed to extract effective settlements from tank inspection measurements, which could be used for proper reconstruction of a settled foundation in finite element model. Procedures and practices are proposed and demonstrated to improve the finite element modeling and analysis of storage tanks.
Industry Experience Fabricating Hydroprocessing Reactors Using 2¼ Cr-1 Mo-V Steel
Authors: Shargay Cathleen , Antalffy Leslie , Daru Kuntak
Published: November 2019

Starting in the 1980’s, the process conditions for hydroprocessing reactors became increasingly more severe and started to exceed the economic and technically-feasible ranges for 2¼Cr-1Mo steel. Hence, new grades of reactor steels were developed to meet these demands. Reactor fabricators, steel producers, the Materials Properties Council and some refiners cautiously developed their initial applications of the new materials, with extensive testing of both the materials and fabrication methods, and restrictions to use only the most experienced, highly technical fabrication shops. The data and experience has grown exponentially since then and today, the most commonly-specified material for thick wall reactors is 2¼Cr-1Mo-¼V steel.

The list of qualified fabricators worldwide has also grown, but is still limited. The purpose of this paper is to show how the industry has climbed the “learning curve,” by giving the statistics on the overall numbers of fabricated reactors (which is now over 1150), and the locations of the fabricators by country, that have been produced. Trends on the use of forgings versus plates are also included, along with the major changes over the years in the applicable ASME Codes and API standards affecting these reactors. Some of the lessons learned from past fabrication problems are also discussed along with the subsequent safeguards initiated within the industry standards.
Effect of Pre-Strain and Aging Heat Treatment on the Corrosion Behavior for 2205 Duplex Stainless Steel in 6% FeCl3 Solution
Authors: Zheng Chengsi , Fei Qingnan , Kong Weihai , Ai Zhibin
Published: November 2019

A 2205 duplex stainless steel (DSS) was pre-stretched to 5% and subsequently aged at 850 °C for 0–120 minutes, to explore the effects of pre-strain and aging treatment on the corrosion behavior of the DSS in 6% FeCl3 solution at 50 °C for 72 hours. The microstructure, hardness and corrosion behavior of the pre-strained and aged DSS were investigated based on statistical data and physical metallurgy in comparison with the counterparts without pre-strain. The results showed that the sigma (σ) phase precipitated firstly in δ-ferrite grain boundaries and then in δ-ferrite/γ-austenite (δ/γ) phases boundaries by consuming the volume fraction of δ-ferrite. The volume fraction of σ phase in the DSS with and without pre-strain increased with increasing aging times following a classical Johnson-Mehl-Avrami (JMA) relationship, and the kinetics of the precipitation of σ phase was accelerated by pre-strain throughout the aging time of 60–120 min. The hardness of the non-pre-strained DSS (NP-DSS) was lower than that of pre-strained DSS (P-DSS) throughout 0–120 min at 850 °C. The hardness of NP-DSS increased continuously with increasing aging time, and the hardness of P-DSS decreased firstly and then increased continuously with increasing aging time. The aged NP-DSS displayed a gradually serious pitting with increasing aging time, and the corresponding corrosion behavior of the aged P-DSS exhibited pitting firstly and then mainly cracking, and the pitting occurred in the vicinity of δ/σ and γ/σ boundaries.
Research on the Interference Fit of GV Seat Under the Service Load
Authors: Hu Yifeng , Xu Sihua , Chen Gang
Published: November 2019

The governor valve is a very important component in steam turbine, which can change the power output of the steam turbine by controlling the amount of the inlet steam. The service conditions of governor valve is very complicated, which should suffer high temperatures, high pressure, erosion, water induction and so on. As we all know the fatigue and creep can significantly reduce valve life. However, the damage due to governor valve seat interference fits is also very important for the units’ safety operation. A compromised interference fit can lead to significant valve leakage and possibly catastrophic seat failure. This article bases on a real case from a STP’s SC unit, which is operating in the South Asia market. Simulating the behavior of the valve seat under service conditions by numerical method, to find out the root cause of the interference fit failure and the operational advice for the unit running.
Analysis Approach Examples for Flow-Induced Piping Vibration Mitigation
Authors: Voll Brian J.
Published: November 2019

One of the challenges of analyzing flow-induced vibration in piping systems is determining how to analytically characterize the loading related to the source of the vibration. Simplified methods can be sufficient for evaluating an existing piping configuration through correlation with vibration measurements. However, if vibration mitigation is required a more thoughtful analysis approach should be used so that the anticipated vibration responses of the post-modification piping configuration can be more accurately determined.

Two case histories are presented that illustrate analysis approaches used to evaluate the severity of flow-induced piping vibration and also develop effective vibration mitigation designs. The analysis approaches used in both cases involved the simulation of vibration loading based on limited vibration data. Using the analysis approaches that were developed, vibration restraints were able to be effectively located and designed. The effectiveness of the analytically determined vibration mitigation solutions was confirmed by post-modification testing and observation.
Preparation and Properties of Au/SnO2 Thermocouples for Material Testing Apparatus of Pressure Equipment
Authors: Liu Xiaoliang , Chen Xuedong , Fan Zhichao , Jiang Huifeng
Published: November 2019

Thermocouples are the most common temperature measuring components in petrochemical, metallurgical, aerospace and other fields. However, due to the influence of working environment and its own structural characteristics, the thermocouple is highly susceptible to electromagnetic interference in the environment during its work, which seriously affects its temperature measurement accuracy. In this paper, three different shapes of Au/SnO2 thermocouples were prepared by screen printing technology, and their microstructure, thermoelectric properties and anti-electromagnetic interference were studied. The results show that the Au/SnO2 thermocouples with different shapes can crystallize well after sintering at 750 °C and above. When temperature difference is from 50 to 300 °C, thermocouples with different shapes can produce stable thermoelectric potential, and the shape has no effect on the output thermoelectric potential. The Au/SnO2 thermocouple after 850 °C sintering has the best thermoelectric performance. Au/SnO2 thermocouples can work normally in electromagnetic fields of 3 V/m or less, while standard PtRh10-Pt thermocouples can not work normally in electromagnetic field of 3 V/m. The Au/SnO2 thermocouple obtained in this study has the advantages of simple preparation method, small size, stable output thermoelectric potential and strong anti-electromagnetic interference ability.
Evaluation of Welding Techniques for Stainless Steels Piping Without Use of Backing Gas
Authors: Chiluvuri Siva Kumar , Bliss Kevin , Penso Jorge
Published: November 2019

In the piping fabrication industry Gas Tungsten Arc Welding (GTAW) is used extensively for welding of stainless and high alloy steel pipes, mainly for root pass of single side joints. GTAW process uses an inert gas for both shielding and backing of the weld. Backing gas also known as purge gas, is provided mainly to prevent oxidation of root pass weld from inside the pipe. Typically, Argon or Argon mixture (i.e. Argon with Helium, etc.) are used as backing gas. Argon gas, is colorless, odorless and heavier than air. Many safety incidents have occurred in the Oil and Gas industry (mainly during construction phase) due to asphyxiation. This has typically occurred when a person (usually a welder) goes inside the piping (a confined space) to inspect the root pass weld to ensure it will pass radiography test. Construction industry has failed to fully tackle this issue in a meaningful way and as a result, some significant number of fatalities occur each year. On several occasions, such incidents have resulted in multiple fatalities when coworkers enter the confined space to rescue and become a victim by themselves.

There are a multitude of reasons why people put themselves at risk in this way. Reasons given for a reluctance to use alternative techniques that eliminates backing gas are many and varied. Alternate welding techniques without backing gas were developed many years ago. However, they are still not being used extensively for many reasons and apprehensions. Using these alternate welding techniques with right controls in place, can eliminate the hazard associated with backing gas and improve safety and maintain quality. This paper discusses and evaluates the alternate welding techniques (which do not require backing gas), limitations, welding procedure qualification and inspection requirements.
Probabilistic Fracture Mechanics Analyses Comparison to LBB Assessments
Authors: Kurth Robert , Sallaberry Cedric , Kurth Elizabeth , Brust Frederick
Published: November 2019

Analysis of a generic dissimilar metal weld (DMW) susceptible to primary water stress corrosion cracking (PWSCC) in a pressurized water reactor (PWR) is used to compare the newly developed probabilistic models (xLPR code) to the previously performed deterministic leak before break (LBB) analyses. The objective of this scoping analysis is to develop a generic reactor loop composed of representative welds and to investigate the safety margins in the presence of PWSCC at the Alloy 82/182 locations. These locations have been previously studied and approved for LBB, however not in the presence of active degradation such as PWSCC. The purpose of this study is to investigate potential increase in risk due to this mechanism. Comparisons of the individual weld probabilistic results to the deterministic LBB analysis are made as the first results of this study. Additionally the individual welds are combined into a configuration representative of the primary loop. This configuration is then tested against the criterion recommended by the xLPR acceptance group. This xLPR criterion is then compared to the existing LBB criterion to assess the change, if any, in risk due to PWSCC.
Three-Dimensional Liquid Sloshing Numerical Analysis on a New Designed Tank Container
Authors: Yue Wenjun , Chen Xu
Published: November 2019

Based on the conventional tank container which has a cylindrical vessel, a new structure of tank container was designed to improve the carrying capacity of the tank. Fluid flow inside the new tank container under different operating conditions (liquid filling ratio K, braking deceleration a, filling medium, no baffle and with baffles) was studied. A volume-of-fluid (VOF) method and a k-epsilon (k-ε) turbulence model were used to simulate the fluid flow. Results showed that all the factors studied in this work had an influence on the tank. The maximum impact force increased with the increasing of a and K. A clear linear positive correlation was found between the maximum impact force and braking deceleration. Besides, the maximum impact force had a relationship with the density of medium. Compared with the conventional tank container, the carrying capacity of the new type tank container increases by 11.8%, which means the new type tank container has better economic benefits.
Leak Behavior and Prediction of Metal Ring Joint Gaskets in Simplified Leak Test With Grooved Platen
Authors: Omiya Yuya , Fujii Masahiro
Published: November 2019

Pipe flange connection with metal gasket is used under high temperature and pressure in place required high sealing performance. It has been known that gasket compressive force, which is closely related the leakage decreases by internal pressure action. Since the pressure is very high in metal gaskets, the sealing performance evaluation in internal pressure action is important. However, there is little research that evaluates a little leakage, metal gasket is empirically used up to the present time. Therefore, evaluated sealing performance of metal gasket, it is necessary to clarify the sealing mechanism. In this study, evaluated effect that decreasing of gasket compressive force affects leakage in both octagonal type and oval type in ring joint gasket by simplified leak test using grooved platen and finite element method stress analysis, evaluation method of leakage in metal gasket is proposed. Based on this evaluation method, decision method of initial tightening force that guaranteed one amount of leakage to design internal pressure is shown in pipe flange connection with metal gasket.