bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficacy of Analysis Techniques in Assessing Broken Wave Loading on a Cylinder Upon a Shoal
Authors: Dassanayake Darshana T. , Antonini Alessandro , Raby Alison
Published: November 2019

Estimation of impulsive wave loading on a cylinder upon a shoal, such as an offshore rock lighthouse constructed on a partially emerged offshore rock with a steep foreshore, poses a unique challenge to marine structural engineers. Large and small scale experimental investigations are the most feasible methods to study this phenomena. However, any experimental investigation with impulsive loading faces challenges in the data analysis, when it is necessary to separate the total impact forces from the force response time series, and to separate the impulsive and quasi-static force components of the total force measurements. This paper is an attempt to re-visit several data analysis techniques with a unique experimental data set to study the advantages and limitations of those techniques, and also to learn how different techniques can be combined into a data analysis methodology to harness maximum information.
Assessment of Variations in the Physico-Mechanical Properties of Fiberglass Tubing Working in Different Environments
Authors: Diniţă Alin , Minescu Mihail , Dumitrescu Andrei , Teodoriu Cătălin , Săraru Codruţ Ştefan
Published: November 2019

This paper presents the results of the experimental investigations carried out by the authors in order to evaluate the changes in the physico-mechanical properties of fiberglass tubing used to transport fluids between different facilities. In the near future, water injection wells will be equipped with fiberglass tubing, as an alternative to the more traditional metal tubing. The mechanical properties of fiberglass material (ultimate tensile strength, impact energy, burst pressure) have been determined for sets of 5 specimens that have been maintained (at a temperature of 80°C) in different environments and with different exposure times (hydrochloric acid: 6/24/48 hours; acetic acid: 6/24/48 hours; hydrochloric acid + hydrofluoric acid: 6/24/48 hours; xylene: 1/2/3 months; condensates: 1/2/3 months).
Numerical Modeling of Radial Fracturing of Cement Sheath Caused by Pressure Tests
Authors: Gheibi Sohrab , Sangesland Sigbjørn , Vrålstad Torbjørn
Published: November 2019

To achieve an acceptable level of zonal isolation, well integrity should be guaranteed in hydrocarbon production and geological CO2 sequestration. Well pressure test can cause different types of failures in the well system leading to leakages through these failures. Laboratory evidences have revealed that occurrence of radial tensile fractures is likely during pressure tests.

In this paper, we use a numerical code call MDEM which was formulated based on discrete element method. The code can model discontinuum feature of fractures. A model of a lab-sized pressure test was built and compared to an experiment previously published. The model was tested under different confinement levels and effect of the tensile strength of rock on the radial fracture was investigated at the same lab-scale. Fracture opening profiles are also presented showing the leakage potential of these fractures under different pressure level.
How Does a Stationary Sand Bed Affect the Flow Dynamics in an Eccentric Annulus?
Authors: Bizhani Majid , Kuru Ergun
Published: November 2019

In the drilling operations, it is common to have a stationary bed of the drilled cuttings in the high angle sections of the wellbore. The bed must be removed in the later stages before running the casing, or when it starts to cause high torque and drag on the drill string. The mere act of circulating drilling fluid, however, may not clean the well (i.e., critical flow rate and shear stress for bed erosion must be reached). In an effort to better understand the underlying mechanisms of bed removal process during hole cleaning, in this paper, we look at how the presence of a stationary sand bed affects the flow field in an eccentric annulus.

Experiments simulating turbulent flow of water in an eccentric annulus with/without the presence of stationary sand bed have been conducted by using a 9m long horizontal flow loop (with an annular configuration of 95 mm ID outer pipe and 38 mm OD inner pipe). The flow loop was equipped with particle image velocimetry (PIV) system, which was used to collect velocity field data. The PIV data were then used to study the characteristics of the turbulent flow of water in the eccentric annulus. The velocity field and Reynolds stress profiles were analyzed in two planes, one perpendicular to the bed interface and off-center of the annulus, and the other along the center-line of the annulus. Experiments were carried out with the presence of two different height stationary sand beds and also without a sand bed as the control case.

The extent to which the presence of the sand bed affects the flow appears to be a strong function of the bed height in the annulus. For a small bed height, deviation of the velocity field from the no bed case was slight. In this case, Reynolds normal and shear stress values were lower near the bed interface comparing to the annulus centerline.

On the other hand, for a flow over a thicker bed, this behavior changed, and the flow became more uniform in the annulus (in terms of turbulence and mean flow properties). The results help in understanding the mechanism of bed erosion under constant pump flow rate. From the practical point of view, data presented here suggest that hole cleaning in an eccentric annulus progressively becomes more difficult as the bed becomes smaller. The results also explain why in long horizontal and extended reach wells often wiper trips are required for proper cleaning of the hole.
Dynamics of an Array of Submersible Mussel Rafts in Waves and Current
Authors: Dewhurst Tobias , Hallowell Spencer T. , Newell Carter
Published: November 2019

A three-by-three grid of submersible mussel rafts was analyzed using an experimentally validated dynamic numerical modeling approach. When submerged, the rafts’ pontoons are flooded, and they are held vertically by lines attached to surface floats and horizontally by a mooring grid. The rafts’ decreased waterplane area and increased inertia reduce the heave and pitch natural frequencies so that they are below the frequencies associated with the greatest wave energy. This has been found to significantly reduce the motion of the rafts compared to the surfaced configuration.

The nine submersible rafts were anchored with 16 anchors and mooring lines. These mooring lines were connected to a grid of adjacent rectangular bays, with each corner (node) supported by a grid float. Each bay contains a raft connected to the submerged nodes of the grid by four bridle lines. The dynamics of the full system were modeled using a combined multibody and Finite Element Analysis (FEA) approach with dynamic loads computed using a modified Morison formulation. This model was implemented in the commercial code OrcaFlex. A similar model for a single submersible raft was previously validated with full-scale field experiments. The full dynamic system was simulated in the maximum expected waves and currents. Mean and maximum tensions in each grid line were quantified. Accelerations and velocities at the mussel rope attachment points were also examined, since these relate to mussel drop-off.
Shape Optimization of a Submerged Pressure Differential Wave Energy Converter for Load Reductions
Authors: Kelly Michael , Alam Mohammad-Reza
Published: November 2019

The ocean is full of untapped energy, however it is a wild place where harsh conditions can occur that can damage wave energy converters (WEC’s). During high load conditions, many WEC’s must go into survival mode to prevent damage or are overdesigned to continue operating in high sea states, which can increase capital costs. The authors propose a different approach, where geometry control is used to change to an absorber shape that experiences minimal hydrodynamic loads during high sea states. This could allow for a decrease in capital costs while increasing the operating range of WEC’s. This paper seeks an optimal geometry of a submerged planar pressure differential WEC that minimizes heave excitation force or motion magnitudes without using the power take-off system. Simple elliptical and circular absorbers as well as optimized absorbers are compared to quantify heave load reductions. Optimized absorbers are generated using a summation of Fourier terms with controllable weights and phases that are optimized with a genetic algorithm for two regular wave conditions. Heave load reductions are found to depend on wave frequency, orientation angle, and elongation. It is shown that peak loads can be reduced by up to 60% when comparing to a circular absorber.
Design of Steel Lazy Wave Riser for External Turret Moored FPSO
Authors: Cheng Jingyun , Cao Peimin
Published: November 2019

The external turret moored Floating Production Storage and Offloading system (FPSO) is one of the preferred solutions for deepwater fields in mild to moderate environments and far away from existing pipeline infrastructures. This paper presents a design of steel lazy wave riser (SLWR) system for an external turret moored FPSO in the water depth of 1,500 meter. The design challenges and feasibility are discussed. Due to the complexity of SLWR geometry, a systematic configuration approach is introduced to achieve the desired riser extreme and fatigue performance target, as well as external turret layout. The study includes the standardized FPSO, the selection of turret configuration, and riser design. The titanium taper stress joints and the interaction with turret structure are also studied. The study provides an optimal solution of the integrated turret, mooring and riser system. It concludes that external turret FPSO with SLWRs can be a feasible and cost effective solution for field development in mild to moderate environments.
Process-Structure-Property Fatigue Characterisation for Welding of X100 Steel Catenary Risers
Authors: Devaney Ronan J. , Connaire Adrian , O’Donoghue Padraic E. , Leen Sean B.
Published: November 2019

Welded connections are a fatigue sensitive location for offshore steel catenary risers. The susceptibility to fatigue is due to the notch effect of the weld and the gradient in microstructure and material properties across the weld which result from welding thermal cycles and differences in the composition of the parent material and weld metal.

In this work, a representative full-scale steel catenary riser girth weld is conducted using X100Q steel. The thermal and strain history in the weld zone are captured using a thermocouple and strain gauge array. A parallel programme of Gleeble thermomechanical simulation is implemented to develop microstructurally uniform heat affected zone (HAZ) test specimens. The parent material, weld metal, simulated HAZ and a cross-weld sample are characterised using a programme of nanoindentation, tensile and fatigue testing.

A softened region with microstructure corresponding to intercritical HAZ (ICHAZ) is identified in the girth weld. Tensile and fatigue failures are shown to occur in a representative microstructural region for simulated HAZ specimens, indicating a susceptibility to failure in the ICHAZ for matched or over-matched X100Q welds.
Lazy Wave Riser Design in High Current and Mild Sour Environment
Authors: Ghosh Rupak , Pellegrini Carlo , Visco Tyler J.
Published: November 2019

This paper presents an innovative design of Lazy Wave Steel Catenary Riser (LWSCR) associated with a major deepwater development in a new frontier and in very high current. The conventional LWSCR design with distributed buoyancy is not found acceptable considering fatigue design acceptance criteria in mild sour environment. The major design requirement is to meet acceptable design life of 20-yrs considering significant damage accumulated due to Vortex-induced-vibration (VIV) and motion fatigue. Further, other development basis including flow assurance requirements and reservoir souring are critical requirements for the design of the riser system.

The paper presents a very useful insight in how several qualified technologies can be leveraged to result in a workable riser design in a very aggressive execution schedule. The results from the analyses of a production LWSCR are presented in the paper.
Standardisation on Measurement and Interpretation of Residual Stress Data
Authors: Mirzaee-Sisan Ali , Bouchard P. John , Hosseinzadeh Foroogh
Published: November 2019

This paper highlights many unanswered questions relating to the characterisation of residual stresses in weldments and their treatment in engineering critical assessment and fitness for service assessment codes and standards. The need for an overarching standardisation framework is identified which goes beyond developing good practice guidelines for numerical prediction or measurement using a specific technique. The framework should cover all uncertainties and possible errors in measuring, simulating and interpreting residual stress in the context of structural integrity assessment.
The Increasing Prevalence of High Frequency Internal Waves in an Arctic Ocean With Declining Sea Ice Cover
Authors: Rippeth Tom , Vlasenko Vasyl , Stashchuk Nataliya , Kozlov Igor E. , Scannell Brian , Green Mattias , Lincoln Ben , Lenn Yueng-Djern
Published: November 2019

Receding seasonal sea ice extent over the Arctic Ocean is increasing access to what was a largely inaccessible region. At lower latitudes the complex vertical current structure associated with large amplitude, high frequency non-linear internal waves, sometimes referred to as solitons, present a significant challenge to the safe engineering design and operation of offshore infrastructure. In this paper we examine the prevalence this type of internal wave in the Arctic Ocean. To do so we will draw on both in situ and remotely sensed oceanographic data. This will be combined with state-of-the-art numerical modelling to demonstrate a link between the geographical occurrence of these waves and the tide. Whilst the link implies that these features are geographically limited, it is also likely that the geographical limits will change with declining sea ice cover. These results will then be used to provide a road map towards a methodology for forecasting the prevalence of these phenomena in a future Arctic Ocean.
Dynamic Response of Metallic Y-Frame Core Sandwich Panels Subjected to Air Blast Loading: Numerical Investigation
Authors: Liu Ting , Cheng Yuansheng , Liu Jun , Chen Ganchao , Chen Changhai , Zhang Pan
Published: November 2019

In this paper, the dynamic response of metallic Y-frame core sandwich plates subjected to air blast loading was investigated by employing the LS-DYNA software. The blast wave was generated by the directly detonation of TNT explosives. The deformation/failure modes and associated structural response were identified and analyzed in detail. Main attention was paid to explore the effects of face sheet thicknesses and core web thickness on the deformation response of Y-frame core sandwich plates. A comparison on the blast performance were drawn among the Y-frame core sandwich panel, corrugated core sandwich panel and solid plate in equal areal mass. Numerical results revealed that the Y-frame core sandwich panel experienced indent deformation in the front face, strut buckling in the core and large bending deformation in the back face under the stand-off distance of 100 mm. Increasing the face sheets and core web thicknesses could improve the blast performance of Y-frame core sandwich panels. The deflections of face sheets were sensitive to the variation of front face sheet and core thicknesses. Moreover, Y-frame sandwich panel has comparable anti-blast capacity with the corrugated counterparts and exhibits superior blast resistance than the solid plate.
Observation of Waves in Naru Strait, Goto, Nagasaki, a Tidal Current Test Site
Authors: Kyozuka Yusaku
Published: November 2019

Waves are primarily important for the tidal current power generation as they relate not only to the wave load acting on the tidal turbine but also to the installation/maintenance cost of the device through the workable day rate at the sea. Generally, the tidal current power site is in a narrow strait, and the wave characteristics are strongly dependent on the place. Also, there are few data itself. So, we conducted the wave observation in Naru Strait, Goto City, Nagasaki, where the tidal current power project by the Ministry of Environment is in progress.

An AWAC (Acoustic Wave and Current Meter) was deployed on the sea bottom of 20m depth in Naru Strait on 18 May and recovered on 12 November, 2017. The wave data obtained for about 6 months were analyzed as wave spectra and mean directions by the records of surface elevation together with tidal current velocity. In particular, the changes of wave amplitude by the tidal current and the storms including typhoon passing are presented.
Combined Wave-Current Induced Instantaneous Liquefaction of a Sandy Seabed
Authors: Yang Li-Jing , Li Chang-Fei , Wang Jun-Qin , Gao Fu-Ping
Published: November 2019

Accurate prediction for the liquefaction depth of a porous seabed is crucial to the design of shallow foundations; nevertheless most previous studies are predominantly limited to wave-only conditions. In this study, the combined wave-current induced instantaneous liquefaction of a sandy seabed is investigated analytically. The explicit expression of liquefaction depth under combined wave-current loading condition is derived, which can converge to that under the linear wave condition when the current velocity approaches zero. Parametric study indicates that the effects of imposing a current onto progressive waves on the distribution of excess pore pressures and the corresponding liquefaction depth are unneglectable, especially for the opposite current conditions.
Nonlinear Wave Loads on Offshore Wind Turbines: Extreme Statistics and Fatigue
Authors: Zhang Yu , Sclavounos Paul D.
Published: November 2019

The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain and frequency-domain nonlinear exciting forces in a seastate with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed.
Numerical Simulation of Fully Nonlinear Interaction Between Regular and Irregular Waves and a 2D Floating Body
Authors: Li Haoran , Bachynski Erin E.
Published: November 2019

A fully nonlinear Navier-Stokes/VOF numerical wave tank, developed within the open-source CFD toolbox OpenFOAM, is used to investigate the response of a moored 2D floating body to nonlinear wave loads. The waveDyMFoam solver, developed by extending the interDyMFoam solver of the OpenFOAM library with the waves2Foam package, is applied. Furthermore, a simple linear spring is implemented to constrain the body motion. An efficient domain decomposition strategy is applied to reduce the computational time of irregular wave cases. The numerical results are compared against the results from potential flow theory. Numerical results highlight the coupling between surge and pitch motion and the presence of nonlinear loads and responses. Some minor numerical disturbance occurs when the maximum body motion response is achieved.
Environmental Assisted Cracking of High Strength Subsea Material due to CP
Authors: Horn Agnes Marie , Østby Erling , Røneid Viggo , Kirkemo Finn
Published: November 2019

Several of the offshore fields in the North Sea are approaching the end of their design life and a cost-effective solution to maximize production is to document that life extension is feasible for an asset. A trend the resent years [1] is that the BOP become larger, hence the required fatigue life increases. One way to meet the increased fatigue life and external loading is to use higher strength steel to meet the design requirements set by the operators. This has motivated research related to the fatigue performance of the base material connector material both for air and under sea water with cathodic protection (CP) [2,3,4] and possible degradation of ductility and toughness in seawater with CP. However, relevant test data for wellheads material that have been in service is not to the authors knowledge, available, nor recommendations in design guidelines related to possible material degradation to be safely applied for life extension of these assets.

To better evaluate life extension of subsea wellheads, a test campaign was initiated by Equinor on a retrieved wellhead in 2015. The wellhead had been in operation since 2000 in the North Sea. The general purpose of the test program was to evaluate if the low alloy steel AISI 8630 modified material had been substantial degraded during 15 years in service compared to design material properties and the materials susceptibility to hydrogen embrittlement.

The test program performed consisted of slow strain rate testing (SSRT) to document possible reduction of strength and ductility, CTOD testing to document possible reduction in toughness and S-N testing to establish the fatigue strength reduction due to seawater with CP.

The outline of the paper is as follows: first a summary of the latest research and trends within wellhead fatigue and materials are discussed. Next, a detailed description of the test program is given: SSRT, toughness testing and fatigue testing are presented. Finally, recommendations and proposal for further research work are given.
Triaxial Testing of Gas Shale Permeability Dependence on Heterogeneous Stress With Respect to Bedding
Authors: Chen Yufei , Jiang Changbao , Yin Guangzhi , Wojtanowicz Andrew K. , Zhang Dongming
Published: November 2019

Shale gas has recently become the most promising source of unconventional hydrocarbon energy. Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but is also controlled by in-situ stresses. Thus, prediction of well’s deliverability requires understanding permeability of a dipping shale with natural bedding under conditions of unequal stresses in-situ. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of Longmaxi shale in the Sichuan Basin, southwest China.

The study involved an analysis of the rock bedding structure, followed with triaxial testing of rock samples and theoretical modeling. We used SEM observation to identify existence of microfractures and numerous inter-particle pores along the shale bedding planes that provide dominant pathways for gas flow depending upon closing stress value. Stress-dependent permeability was tested with a newly-developed multi-functional true triaxial geophysical (TTG) apparatus providing for a steady state gas flow through the rock sample under conditions of normal stress and two unequal tangential stresses. Also simulated were the effects of stress-bedding and load cycling.

The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process for both normal and tangential stress loading cycles. A hysteresis of the permeability response to cyclic loading was the largest when normal stress cycling was dominant. Moreover, permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed — particularly when the tangential stresses were dominant. A theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results.

Assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5% and 14%, respectively, showing dominant effect of normal stress with clear contribution of tangential stresses. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for improvement in computing effective stress in permeability predictions of the Longmaxi shale. It also warrants testing other gas shales to specifically determine the effect.
Numerical Simulation of Ship-Ice Interaction
Authors: Huisman Michael , Erceg Sandro , von Bock und Polach Rüdiger U. Franz , Rung Thomas , Ehlers Sören
Published: November 2019

The increasing activities in arctic sea areas over the last years have led to a rising demand for numerical tools to design and evaluate ice-going ships. Numerical simulation of ship-ice interaction can be a suitable method for engineers to evaluate ship designs in early development phases. We present an efficient method to evaluate local and global loads on ships in level ice at moderate computational effort. The objective of this contribution is the holistic simulation of the icebreaking process along with the hydrodynamic interplay of the broken ice cups with the surrounding level ice and the hull. For this purpose, a free surface flow solver based upon the Lattice Boltzmann method is coupled to an icebreaking model and a contact-dynamic physics engine. Overall, the approach seeks to compute both local loads, acting on the ship hull, as well as the total resistance in ice. The direct simulation approach makes it possible to consider the load contributions of icebreaking and displacement separately and to analyze their contribution to the total resistance more precisely. Simulation results for a tanker in various ice conditions show significant differences in load distribution and can provide valuable information for the designer of ice-going ships.
Cement Bond Strength Measurements
Authors: Opedal Nils , Cerasi Pierre , Vrålstad Torbjørn
Published: November 2019

Cement is an important component to ensure safe and economic sustainable operations of wells. To optimize the performance of cement in a well, and to achieve an adequate level of well integrity, experimental testing of cement under realistic and relevant conditions is vital. This paper reviews three different types of cement bond strengths relevant for the petroleum industry and gives an evaluation of the methodologies used to study these bond strengths. Although the term “Bond strength” should at first be assessed and discussed as an easy-to-understand parameter, the review shows that it is important to understand the fundamental differences between the three-bond strengths. In terms of how they are measured, and in terms of what the information can be used for.
Effects of Cap Bottom Elevation on Wave Loads on the Piles Under the Cap
Authors: Zhou Jifu , Wang Xu
Published: November 2019

High-rise pile cap foundations are generally used to support offshore wind turbines or sea-crossing bridges. They endure complex wave loads due to the interaction of free surface and the cap. An additional pressure increment has been found under the cap when free surface impinges the cap bottom. This additional pressure changes the wave loads on the piles under the cap compared with the case without the cap. In the present paper, we investigate the effects of the cap bottom elevation on the wave loads of the piles under the cap by using fully nonlinear numerical simulations. Based on parameters of waves and the structure used in Donghai Bridge Wind Farm, China, we simulate a number of cases with different cap bottom elevation to explore its influence on wave loads of the piles under the cap. We find that the influence is of significance and requires enough attention.
A Preliminary Study on the Modeling and Analysis of Nonlinear Effects of Ocean Waves and Power-Take-Off Control on Wave Energy Conversion System Dynamics
Authors: Yim S. C. , Adami N. , Bosma B. , Brekken T. , Chen M. , Ghorban Zadeh L. , Glennon D. N. , Lian Y.-S. , Lomonaco P. , Mohtat A. , Ozkan-Haller T. , Thomson J.
Published: November 2019

This article describes the model development and preliminary progress of an on-going research study on the effects of nonlinearities in ocean wave input and power-take-off (PTO) control on wave energy conversion system dynamics and efficiency. The model system employed and progress on recent developments are: (1) nonlinear wave modeling in the ocean, generation and propagation in a wave basin, and (2) nonlinear PTO control algorithm. An overview of the holistic analytical, numerical and experimental research approach/work plan is presented. To provide a simple means for analysis, comparison and performance evaluation, the WEC-Sim numerical platform is used for model implementation and system dynamic simulation. Analytical and numerical predictions of the nonlinear wave fields in a wave basin using the nonlinear Fourier analysis (NLFA) technique and corresponding nonlinear wavemaker theory and a plan for future validation using a comprehensive series of experimental test data as well as ocean wave measurements are described. Efficiency of the nonlinear PTO control and a future evaluation work plan by comparing numerical simulations with results of WEC model test data under corresponding wave conditions of the experimental studies without the presence of the WEC system are also presented.
International Civil Ageing Management and Assessment Methodology of Concrete
Authors: de Haan – de Wilde F. H. E. , de Bont C. G. M.
Published: November 2019

For many nuclear power plants worldwide the operation period will be extended to 60 or 80 years in the coming years. As the operation period increases, the importance of knowledge of ageing mechanisms increases. In the framework of LTO there is limited knowledge about ageing and structural integrity of concrete structures.

Knowledge about the strength of concrete structures and modelling thereof can be improved for a more complete knowledge base on ageing and degradation mechanism in nuclear facilities. Therefore, effort is required to improve the knowledge of concrete, material models and finite element modelling techniques as well as the assessment method.

Recent developments have shown that ageing of civil structures receive more attention internationally (E.g. concrete degradation in bunker building Doel). Traditionally a large part of the research and development is focused on mechanical issues like piping and vessels. In order to increase the knowledge in the field of civil structures, the focus is on investigation of ageing of concrete and determining analysis methods.

This paper focuses on the development of a practical assessment method for ageing of civil structures.

As a first step information from international publications and other sources on civil structures ageing issues and management thereof, will be gathered. Well known international standards taking care of ageing phenomena based on problem areas and good practices are IGALL and GALL.

IGALL and GALL contain information tables based on international experience. This is the starting point of the research in finding an assessment methodology for civil ageing management. It will be shown that IGALL and GALL contain very similar elements. Sorting on the AMPs results in a practical set of datasheets with summarizing information per AMP, including the underlying international experience. The datasheets are of limited size, presenting an helpful overview of the relevant structures or components, materials, environment and mechanisms.

A method for civil ageing management is proposed which will be applied and developed in more detail in future research. Further research is necessary to develop a specific assessment methodology for concrete.
Continued Safe Operation (LTO Research Reactors) High Flux Reactor, Petten
Authors: Stefanini L. , de Haan – de Wilde F. H. E. , Offerein J. F.
Published: November 2019

The HFR is one of the most powerful and versatile Research Reactors in the world. Because of its strategical importance in the medical isotopes production, after 57 years of operating experience a Continued Safe Operations (CSO) mission will take place. The CSO project structure is based on the outline given in the IAEA draft Safety Guide SSG-48. The ageing management for the HFR is evaluated based on the IAEA Specific Safety Guide SSG-10. Moreover, the approach to the contents of the project is supported by the IAEA Draft Guidelines for Peer Review of “Ageing Management of Research Reactors for Continued Safe Operations”. The HFR is the second Research Reactor (RR) in the world to undergo this type of assessment and its experience will be extremely valuable in setting the international standards for CSO of research reactors. This paper describes the phases of the CSO project, the challenges encountered and the experience built during its development.
An Update on the Investigation of Fracture Toughness Properties of the High Flux Reactor Vessel From Surveillance Test Campaign in 2017
Authors: Kolluri M. , de Haan – de Wilde F. H. E. , Nolles H. S. , de Jong A. J. M.
Published: November 2019

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154-O alloy grade with a maximum Mg content of 3.5 wt. %. The vessel experiences large amount of neutron fluences (notably at hot spot), of the order of 1027 n/m2, during its operational life. Substantial damage to the material’s microstructure and mechanical properties can occur at these high fluence conditions. To this end, a dedicated surveillance program: SURP (SURveillance Program) is executed to understand, predict and measure the influence of neutron radiation damage on the mechanical properties of the vessel material. In the SURP program, test specimens fabricated from representative HFR vessel material are continuously irradiated in two specially designed experimental rigs. A number of surveillance specimens are periodically extracted and tested to evaluate the changes in fracture toughness properties of the vessel as function neutron fluence. The surveillance testing results of test campaigns performed until 2015 were published previously in [1, 2]. The current paper presents fracture toughness and SEM results from the recent surveillance campaign performed in 2017. The fracture toughness specimen tested in this campaign received a thermal neutron fluence of 13.56 x1026 n/m2, which is ∼8.9 × 1025 n/m2 more than the thermal fluence received by the specimen tested in SURP 2015 campaign. These results from this campaign have shown no change in the fracture toughness from the values measured in the previous SURP campaign. The SEM observations are performed to study the fracture surface, to measure (by WDS) the transmutation Si formed near crack tip and to investigate various inclusions in the microstructure. SEM fracture surface investigation revealed a tortuous (bumpy) fracture surface constituting micro-scale dimples over majority of the fracture area. Islands of cleavage facets and secondary cracks have been observed as well. EDS analysis of various inclusions in the microstructure revealed presence of Fe rich inclusions and Mg-Si rich precipitates. Additionally, inclusions rich in Al-Mg-Cr-Ti were identified. Finally, changes in mechanical properties of Al 5154-O alloy with an increase in neutron fluence (or transmutation Si) are discussed in correlation with SEM microstructure and fracture morphology observed in SEM. TEM investigation of precipitate microstructure is ongoing and those results will be published in future.
Comparative Risks of Hydrostatic and Pneumatic Pipeline Testing
Authors: Simpson David A.
Published: November 2019

An important step in a pipeline-construction project is confirming that the piping and facilities are adequate for the expected operating pressures. This confirmation is done via a static strength test using a test fluid. All fluids have mass and internal energy. Fluids under pressure have significantly elevated internal energy. All fluids are compressible to some greater or lesser extent, and the fluid added to raise the pressure of the fluid in the bulk volume adds significant energy. The raw mass of a fluid must be considered when evaluating terrain elements and support elements (i.e., pipe stands and pipe racks). The selection process for a test fluid should always endeavor to minimize the total risk of the entire process.

There is guidance in the primary pipeline design/construction codes (e.g., ASME B31 series) for many of the important considerations for managing the risk associated with the tests required to perform this confirmation of fitness for purpose. This code-guidance has historically not shown a clear preference for the selection of one particular test-medium over another. Some jurisdictions have written regulations that step away from ASME guidance and do show a clear preference for hydrostatic testing over pneumatic testing. This preference manifests itself in several ways, but the primary representation is the requirement in statutes and regulations that a pneumatic test have an “exclusion zone” around the test to reduce the risk of injury during the test. These documents tend to not have an exclusion-zone requirement for hydrostatic tests.

This paper is undertakes to demonstrate the relative risks of liquid vs. gaseous test media and presents a background of why pneumatic tests have been singled out by regulators as higher risk and shows why this regulatory preference can result in actually increasing risk rather than decreasing it.
Analysis of the Gasket Damage and Sealing Performance for the Thread Ring Block Heat Exchanger
Authors: Zhuang Fakun , Sui Wen , Xie Guoshan , Shao Shanshan , Han Zhiyuan , Liu Wen
Published: November 2019

The thread ring block heat exchangers, served at the high temperature and pressure, are the key equipment in the petrochemical industry. Due to the severe operational conditions and unsuitable assemble, internal leakage problem commonly occurs, especially for the seal gasket between the tube sheet and shell. Many failed gaskets are collected. Through a series of experiments including chemical composition, metallographic analysis, SEM and fracture analysis, the gasket damage and leakage causes are analyzed. For further interpretation, the gasket stress analysis is completed by the finite element method. It shows that the gasket stress is a main factor that affects the sealing performance for the thread ring block heat exchanger. Under long term operation at high temperature and pressure, the gasket stress between the tube sheet and shell becomes loose and creep. The gasket material also deteriorates with increasing time. Therefore, in order to prevent the internal leakage, the stress should be controlled in an appropriate range. And periodical inspection must be performed.
Comparison and Analysis of Effective Guided Wave Standards Between GB and ASTM
Authors: Ding Ju , Zhang Min , Liu Shu-hong , Tang Chen-huai , Zhu Xu-chen , Tang Deng-chao , Yang Yu-qing
Published: November 2019

This paper discusses four different ultrasonic guided wave standards. Three of them are China’s national standards or industry standards: GB/T 31211-2014 “Nondestructive Testing Ultrasound Guided Wave Detection”, GB/T 28704-2012“Non-destructive testing—Test method for ultrasonic guided wave testing based on magnetostrictive effects”, and DL/T 1452-2015 “Thermal Power Pipeline Ultrasound Guided Wave Detection”. The another one is ASTM E2929:“Standard Practice for Guided Wave Testing of Above Ground Steel Piping with Magnetostrictive Transfusion”. Through six aspects in this article, including testing application scope, preliminary requirements, standard specimen and comparative specimen, distant amplitude curve and time gain curve, the existing difference between China and America is obvious and diversity. It is necessary to explore the underlying reasons for the connection of Chinese code and international code in the field of Non-destructive testing. During the standardization, anyone of the standard should be actually compared on the presentation of chart, and the verification and comparison of results, and lists the similarities and differences of each part based on GB31211.

This paper provides reference for China to integrate with foreign standards in the field of ultrasonic guided wave detection of pressure vessel and pipelines.
An Optimized Heat Treatment Process to Reduce the Weld Residual Stress by Auxiliary Heating
Authors: Luo Yun , Gao Teng , Jiang Wenchun
Published: November 2019

Local post welding heat treatment (PWHT) is a popular method to reduce the residual stress of bigger weld structures. In this paper, the weld residual stresses before and after local PWHT were investigated. The results show that there are larger axial stresses concentration in weld toe and an inconsistent deformation along axial direction during heating stage which may leads to crack. The residual stresses in outer surface are decreased greatly after local PWHT. An optimized local PWHT with auxiliary heating (AH) temperature 800°C and width 800mm were proposed. The axial stress and deformation inconsistent in weld can be reduced by AH, thus leads to the reduction of crack risk in weld toe.
Development of New Design Fatigue Curves in Japan: Discussion of Effect of Surface Finish on Fatigue Strength of Nuclear Component Materials
Authors: Nakane Motoki , Wang Yun , Hatoh Hisamitsu , Yamamoto Masato , Hirano Akihiko , Hayashi Kentaro
Published: November 2019

Based on the world wide fatigue test database, The Design Fatigue Curve (DFC) Phase 1 and 2 subcommittees established in The Japan Welding Engineering Society (JWES) have been developed new design fatigue curves which are applied for the nuclear component materials, in air environment. The effects of the design factor, such as mean stress, size effect and surface finish, etc. on the fatigue curves are also discussed with the fatigue database in order to construct fatigue evaluation method for the new design fatigue curves. The subcommittees also have studied the applicability of newly developed fatigue evaluation method to the nuclear component materials.

This paper reports the fatigue test results of machined finished small-scale test specimens which are used for the verification of proposed fatigue evaluation method. The materials subjected to the fatigue tests are austenitic stainless steel SUS316LTP, low-alloy steels SQV2A and SCM435H, and carbon steel STPT370. Specimens finished with lathe machining are subjected to the tests. The planed maximum height roughness of the specimen are 25 and 100 μm. The fatigue test results show that the surface finish effect on the fatigue strength in the high cycle region of the austenitic stainless steel can be negligible. On the other hand, fatigue strength of the carbon steel and low alloy steel is decreased as increasing the surface roughness of the specimen. Especially, decrease of fatigue strength for the specimens with more than 100 μm maximum height roughness is larger than that of conventional estimation. It is presumed that severe roughness introduced by lathe machining tends to behave as notches and increase the stress concentration at the specimen surface, and resulted in unexpected decrease of fatigue strength.
Load Normalization Method Accounting for Elastic and Elastic-Plastic Crack Growth
Authors: Wallin Kim , Xu Steven
Published: November 2019

A single specimen technique to estimate crack length, standardized in ASTM E1820, is the so called load-normalization technique, also known as the Key-curve technique. The method is based on the separability between deformation and crack length. This means that if the load is normalized by a suitable function of crack length, the result will be a single crack length independent load-displacement curve. If this “Key”-curve is known, then based only on load and displacement information it is possible to estimate the corresponding crack length.

The load normalizing method assumes a plastic response of the specimen during crack growth. If there is crack growth already in the elastic regime, non-linearity in the load-displacement record is not due to plasticity, but due to the crack growth. In this case the standard load-normalization method does not work since it assumes that the non-linearity is due to plasticity or crack tip blunting. Such materials require a modified approach.

Here, a modified load normalization method accounting for possible elastic crack growth is presented. The method is shown to produce realistic crack growth estimates regardless of plasticity level of the specimen. The method applies an improved load normalization equation compared to the one presently used in ASTM E1820.
Dynamics of a Pipe Subjected to Internal and Confined External Flow
Authors: Païdoussis Michael P. , Abdelbaki Ahmed R. , Butt M. Faisal Javed , Moditis Kyriakos , Misra Arun K. , Nahon Meyer
Published: November 2019

We consider a hanging cantilevered pipe conveying water within a water-filled container; the upper portion of the pipe is surrounded by a rigid cylindrical tube of larger diameter, forming an annular fluid-filled region around the pipe. Two flow configurations are investigated : (a) water enters the pipe at its clamped end and flows downwards, discharging at its free end into the container; the fluid exits the container by flowing upwards in the annulus and out; (b) the reverse flow arrangement: water enters the system at the upper end of the annulus and exits by flowing upwards in the pipe. The dynamics of the system is studied theoretically and experimentally for both configurations. The analytical models utilized are outlined and the experiments are described. Theory and experiment find that the system loses stability at sufficiently high flow velocity by flutter or static divergence.
Cyclic Plasticity Analysis of Welded Joint With Welding Residual Stress Using the Direct Method
Authors: Puliyaneth Manu , Chen Haofeng , Luan Weiling
Published: November 2019

To meet the growing energy demands, the power sector continuously strives at enhancing the efficiency of its power plants by increasing the operating temperature. Under cyclic loading conditions, this leads to creep-cyclic plasticity driven damage mechanisms such as cyclically enhanced creep, creep enhanced plasticity and creep ratcheting. A detailed understanding of creep and related damages is therefore essential for predicting any potential failure mechanisms and ensuring confidence in the safe-working of the components. This becomes particularly difficult and challenging in the presence of welds due to two main reason; a) presence of different material zones, namely parent metal, weld metal and heat affected zone; b) introduction of residual stress during welding. An extended Direct Steady Cycle Analysis within the Linear Matching Method (LMM) framework has been previously developed to consider the full interaction between creep and cyclic plasticity. This paper presents the basic theory and an overview behind the LMM framework along with a new application of a welded flange, considering for the first time the effect of residual stress due to welding. A 3D finite element model is adopted for the flange, and it is subjected to a constant pressure and cyclic thermal load of varying dwell. The effects of welding residual stress on the creep-cyclic plastic response of the welded flange are investigated. Additional parametric studies considering different levels of the applied load and dwell period are performed. The results reflect the ease of using LMM over conventional inelastic analysis.