Showing papers in "Journal of Pressure Vessel Technology-transactions of The Asme in 2020"

Weld Metal Chemistry of Mineral Waste Added SiO2-CaO-CaF2-TiO2 Electrode Coatings for Offshore Welds

Abstract: Offshore structures in recent time are witnessing the increased application of dissimilar metal welds for enhanced structural integrity. Offshore structures are complex systems. Fabrication, maintenance, and repair of these structures require conventional and advanced welding technologies along with suitably chosen welding consumables. The present work aims at the design and development of shielded metal arc welding (SMAW) electrode coating using extreme vertices design methodology. This work also attempts to study weld metal chemistry along with microstructure and microhardness. Red ochre, a mineral waste from iron ore is added in the coating composition. Multi response optimization has been carried out to obtain optimum flux composition and to study the effect of individual constituents and their interactions on the weld chemistry and microhardness.

Computational Fluid Dynamics Analysis of the Flow Force Exerted on the Disk of a Direct-Operated Pressure Safety Valve in Energy System

Abstract: The flow force acting on a valve disk plays an important role in the overall performance of pressure safety valves (PSVs). To quantify the disk force, computational fluid dynamics (CFD) methods have been widely implemented. In this paper, the capability of CFD models, and the identification of the most suitable turbulence models' geometry modeling and mesh requirements have been assessed to establish the accuracy of CFD models for disk force prediction. For validation purposes, a PSV disk force measuring rig was designed and constructed to obtain the steady-state flow forces exerted on the valve disk at different valve openings. The CFD model assessment is achieved by comparing the simulation results to experimental measurements; this is achieved in two stages. Stage 1 investigates the use of Reynolds averaged Navier–Stokes (RANS)-based turbulence models where two-dimensional (2D) simulations are performed with five turbulence models. The results indicate that a variety of force results are produced by different turbulence models, among which the shear stress transport (SST) k–ω was found to have the best performance. Stage 2 investigates meshing and the use of symmetry and geometry simplifications; 2D, 1/8 three-dimensional (3D) and 1/2 3D mesh models are examined. The results indicate that the 1/8 3D mesh model is the optimal choice, owing to its higher accuracy and reasonable grid scale. The studies performed in this paper extend the knowledge of compressible flow force prediction, and should facilitate the design or optimization of PSVs.

Damage Localization in Pressure Vessel by Guided Waves Based on Convolution Neural Network Approach

Abstract: This paper investigates the damage localization in a pressure vessel using guided wave-based structural health monitoring (SHM) technology. An online SHM system was developed to automatically select the guided wave propagating path and collect the generated signals during the monitoring process. Deep learning approach was employed to train the convolutional neural network (CNN) model by the guided wave datasets. Two piezo-electric ceramic transducers (PZT) arrays were designed to verify the anti-interference ability and robustness of the CNN model. Results indicate that the CNN model with seven convolution layers, three pooling layers, one fully connected layer, and one Softmax layer could locate the damage with 100% accuracy rate without overfitting. This method has good anti-interference ability in vibration or PZTs failure condition, and the anti-interference ability increases with increasing of PZT numbers. The trained CNN model can locate damage with high accuracy, and it has great potential to be applied in damage localization of pressure vessels.

Mechanical Buckling Analysis of Saturated Porous Functionally Graded Elliptical Plates Subjected to In-Plane Force Resting on Two Parameters Elastic Foundation Based on HSDT

Abstract: In this paper, mechanical buckling analysis of a functionally graded (FG) elliptical plate, which is made up of saturated porous materials and is resting on two parameters elastic foundation, is investigated. The plate is subjected to in-plane force and mechanical properties of the plate assumed to be varied through the thickness of it according to three different functions, which are called porosity distributions. Since it is assumed that the plate to be thick, the higher order shear deformation theory (HSDT) is employed to analyze the plate. Using the total potential energy function and using the Ritz method, the critical buckling load of the plate is obtained and the results are verified with the simpler states in the literature. The effect of different parameters, such as different models of porosity distribution, porosity variations, pores compressibility variations, boundary conditions, and aspect ratio of the plate, is considered and has been discussed in details. It is seen that increasing the porosity coefficient decreases the stiffness of the plate and consequently the critical buckling load will be reduced. Also, by increasing the pores' compressibility, the critical buckling load will be increased. Adding the elastic foundation to the structure will increase the critical buckling load. The results of this study can be used to design more efficient structures in the future.

Determination of Folias Factor for Failure Pressure of Corroded Pipeline

Abstract: Corrosion assessment and burst pressure prediction of line pipes with corrosion defects are essential for the integrity assessment of steel transmission pipelines. The failure assessment methods proposed in codes or handbooks may be overly conservative or exhibit significant scatter in their predictions. In this paper, the effects of two key parameters—the flow stress and Folias bulging factor, on predicting the failure pressure of pipelines with defects are studied. The Folias bulging factor is suggested by fitting the results from finite element (FE) analysis. Then, a new prediction method for the failure pressure of pipelines with defects is proposed. The failure pressures predicted by the proposed method are in better agreement with the experimental results than the results by the other methods such as B31G, MB31G, Det Norske Veritas (DNV), and rectangular parabolic area (RPA).

Performance Evaluation of Alternating Current Square Waveform Submerged Arc Welding as a Candidate for Fabrication of Thick Welds in 2.25Cr-1Mo Heat-Resistant Steel

Abstract: The paper evaluates the performance of alternating current (AC) square waveform submerged arc welding (SAW) as a candidate technology for manufacturing thick welds for high-pressure vessels. A new mathematical formulation for calculating melting efficiency in square waveform arc welding is presented. The melting efficiency and the heat consumption are presented as a mathematical model of welding parameters, namely welding current, welding speed, current frequency, and electrode negativity (EN) ratio. The proposed approach is demonstrated through the welding of 2.25Cr-1Mo heat-resistant steel performed over a wide range of welding parameters. The investigation provides deeper insights into the interplay between process parameter, total heat consumption, and melting efficiency. The effect on flux consumption is also explained. The melting efficiency is inversely proportional to flux consumption. The welding heat does not necessarily promote the plate melting. Improper use of welding heat may lead to decreased melting efficiency and increased unwanted melting and consumption of welding flux. Compared to the conventional direct current (DC) power sources, the AC square waveform welding achieves almost the same order of melting efficiency with added advantages of better weld bead shape and flux consumption in a desirable range. The two additional parameters (frequency and EN ratio) of the AC square waveform power source provide more freedom to fine-tune the process and thereby efficiently use welding heat. The results of this investigation will be advantageous to the designers and fabricators of high-pressure vessels using AC square waveform welding.

Metamodeling Time-Temperature Creep Parameters

Abstract: There exist many time-temperature parameter (TTP) models for creep rupture prediction of components including the Larson–Miller (LM), Manson–Haferd (MH), Manson–Brown (MB), Orr–Sherby–Dorn (OSD), Manson–Succop (MS), Graham–Walles (GW), Chitty–Duval (CD), Goldhoff–Sherby (GS) models. It remains a challenge to determine which model is “best”, capable of accurate interpolation and physically realistic extrapolation of creep rupture data for a given material. In this study, metamodeling is applied to create a unified TTP metamodel that combines and regresses into twelve TTP models (eight existing and four newly derived). An analysis of the mathematical problems that exist in TTP models is provided. A matlab code is written that can: (1) calibrate the material constants of any of the twelve TTP models (using the metamodel); (2) determine the most suitable stress-parameter function; (3) and report the normalized mean square error (NMSE) of rupture predictions for a given material database. Using the metamodel, and code, a design engineer can make an intelligent selection of the “best” TTP model for creep resistant design. This process is demonstrated using four isotherms of alloy P91 creep rupture data. To assess the influence of material, further validation is performed on alloys Hastelloy X, 304SS, and 316SS. It is determined that the “best” model is dependent on material type and the quality and quantity of available data.

Investigation of Fluid-Elastic Instability in Tube Arrays at Low Mass Damping Parameters in Cross-Flow

Abstract: Fluid-elastic instability (FEI) is the most dangerous vibration mechanism in tube arrays. As the research shows in the recent years, the mechanism of FEI turns to be clear, but threshold prediction in low mass damping parameter (MDP) tube arrays is still not accurate because of the complexity of the instability mechanism. In this work, computational fluid dynamics (CFD) simulation is first validated by comparison with the water tunnel experiments in four kinds of tube arrangements and then extended to two-phase flow to get more data in low MDP range. Using fluid force coefficients calculated by CFD simulation, unsteady modeling of the tube model is established and the critical velocities match well with experiment and CFD simulation results. The effect of tube arrangement and Reynolds number on the fluid force coefficients and the predicted critical velocity is studied according to the unsteady flow theory. The results show that instability critical velocity of the normal triangular array can be underestimated at MDP lower than 1. When the frequency ratio (streamwise direction to transverse direction) decreases to below 0.8 in the rotated triangular array, the streamwise instability occurs earlier than transverse instability. The methods and conclusions in this paper can be used in FEI analysis in both streamwise direction and transverse direction.

Experimental and Numerical Analysis of Ratcheting Behavior of SS 316 L Thin-Walled Pipes Subjected to Cyclic Internal Pressure

Abstract: This paper investigates ratcheting behavior of SS316 L thin-walled steel pipes subjected to cyclic internal pressure experimentally and numerically. Numerical simulations were performed using abaqus software, and nonlinear isotropic/kinematic hardening model. According to experimentations, it was found that the ratcheting strain is only significant in the hoop direction of a pipe subjected to cyclic internal pressure. The effects of pressure amplitude and mean pressure on ratcheting behavior of thin walled pipe in hoop direction were studied experimentally and numerically, and it was observed that increasing the pressure amplitude and mean pressure increased the percentage of ratcheting strain. Another important point about the results was the dominance of pressure amplitude on mean pressure. The results showed that at higher mean pressures the effect of pressure amplitude on increasing the percentage of ratcheting strain was greater. Finally, the experimental and numerical results were in good agreement.

Development of a Tensile Strain Capacity Predictive Model for American Petroleum Institute 5L X42 Welded Vintage Pipelines

Abstract: Pipelines can be exposed to a wide variety of loads, depending on the environments and the area of application. These loads may impose large longitudinal plastic strain on pipelines, which could constitute a significant threat to the structural capacity of the pipeline. Reliable calibration of the strain capacity of pipelines plays an important role in the strain-based design (SBD) method. In this paper, a tensile strain capacity (TSC) predictive model (an equation) for welded X42 vintage pipes has been developed by conducting nonlinear parametric analysis followed by nonlinear regression analysis. First, our previously validated extended finite element method (XFEM) model was used to demonstrate the applicability of the XFEM in simulating full-scale ductile fracture response of pipelines subjected to biaxial loading, using pressurized American Petroleum Institute (API) 5L X42 vintage pipes subjected to four-point bending. Second, a parametric study investigating the effects of pipe and defect geometries as well as loading on the pipe TSC is presented. The nonlinear parameterization using XFEM was conducted in abaqus/standard. The TSC trends obtained for the various parameters considered were examined to derive appropriate individual variable functions for each parameter while taking any significant interactions between the parameters into consideration. Also, a nonlinear regression analysis is employed to develop a nonlinear semi-empirical model for predicting the TSC. The results obtained from the developed TSC predictive model (TSCvin.) was compared with those evaluated using the validated XFEM models. The results showed good agreement. Finally, statistical analysis was conducted to ensure the model is unbiased and predicts conservative TSCs by modifying the model using probabilistic error analysis. The modified model is capable of increasing the confidence level in the predicted TSC hence becoming a practical tool for reliable prediction of TSC of X42 vintage pipes needed for conducting pipeline integrity assessment. This modified predictive model is useful in practical applications because it provides a quantifiable degree of conservatism and reliability to the predicted TSCs.

A grain size-dependent equation for creep rupture life of grade 91 steel verified up to 233,000 hours

Abstract: Grade 91 steel is widely used as steam pipes in ultrasupercritical (USC) steam boilers. In residual creep life assessment of the pipes by calculation, one needs creep rupture life of the steel as a function of stress and temperature in a time range longer than 105 h. Four regions with different creep rupture characteristics appear in a stress versus creep rupture life diagram of the steel. Main steam pipes made of the steel are used in a long-term region with low values of stress exponent and activation energy for creep rupture life (referred to as region G in this paper). Creep rupture lives of the steel in this region vary from heat to heat depending on their prior austenite grain size. This paper proposes a grain size-dependent equation representing creep rupture life of the steel in region G. The equation is verified with creep rupture data up to 232,833 h at 600 °C. Region G is absent in some heats with a large grain size. The equation can rationalize the absence in the heats. In a stress versus creep rupture life diagram of grade 92 steel, there is the same long-term region G. In the region, a creep rupture life of each heat is dependent on its grain size as is the case in grade 91 steel. The proposed equation accords well with the creep rupture lives of the grade 92 steel in region G.

Local Constitutive Behavior of Undermatched Welded Joints in Pipeline Steel Using Digital Image Correlation Technology

Abstract: Although the identification of local constitutive behaviors is possible based on digital image correlation (DIC), few studies have been reported that characterize the properties of the girth-welded joints of pipeline steel. The DIC technique was used to measure the strain fields of undermatched girth-welded joints of X80 pipeline steel under uniaxial tension in this paper. First, microstructure optical observations and micrometer hardness measurements were used to test the size and hardness of the subregions in the specimens. Second, the local strain data in different regions of the girth-welded joint were obtained via DIC technology, and the stress data were obtained via uniaxial tensile tests. Then, the stress–strain relationships of the weld metal (WM), base metal (BM), and subregions of the heat-affected zone (HAZ) of the girth-welded joints of pipeline steel were obtained. Finally, the constitutive parameters of the Ramberg–Osgood model in the different regions were determined by curve fitting of the strain and stress data. The local yield strength, elastic modulus, and hardening exponent of the welded joints were obtained. The yield stresses of the different subregions of the welded steel joint followed the sequence BM > WM > HAZ, which was consistent with the results of the hardness measurements. The hardening exponents of the different subregions of the welded steel joint followed the sequence HAZ > WM> BM.

Design of a Metamaterial-Based Foundation for Fuel Storage Tanks and Experimental Evaluation of Its Effect on a Connected Pipeline System

Abstract: The recent advance of seismic metamaterials has led to various concepts for the attenuation of seismic waves, one of them being the locally resonant metamaterial. Based on this concept, the so-called metafoundation has been designed. It can effectively protect a fuel storage tank from ground motions at various fluid levels. In order to show the effectiveness of the proposed design, the response of the metafoundation is compared to the response of a tank on a traditional concrete foundation. The design process of conceiving the metafoundation, optimizing it for a specific tank, and its seismic response are described herein. Furthermore, the response of a tank during a seismic event can cause severe damages to pipelines connected to the tank. This phenomenon can be of critical importance for the design of a seismic tank protection system and must be treated with care. Since the coupled structure (tank + foundation + pipeline) exerts highly nonlinear behavior, due to the complexity of the piping system, a laboratory experiment has been conducted. More precisely, a hybrid simulation (HS) that uses the metafoundation and a tank as a numerical substructure (NS) and a piping system as a physical substructure (PS) was employed. To make the results relatable to the current state of the art, additional experiments were performed with concave sliding bearings (CSBs) as an isolation system in the NS. The metafoundation offered a clear attenuation of tank stresses and, in some cases, also reduced the stresses in the piping system.

Burst Pressure Prediction of Pipes With Internal Corrosion Defects

Abstract: Corrosion in pipeline walls can lead to severe loss of material to a point which will cause complete loss of pipeline integrity. The contemporary approach of corrosion prevention is to use internal lining system to isolate the corrosive medium from the inner surface of the host pipe. The objective of this study is to assess the burst pressure of pipelines with internal corrosion defects. The mechanical response of carbon steel API X42, X52, and X70 pipe grades are empirically estimated and implemented in a finite element model. The geometry of an internal corrosion defect is defined through its depth, width, and length, and a parametric study is undertaken to investigate the influence of the corrosion defect parameters to the overall burst pressure of the pipe. Based on the results from the parametric study, the Buckingham π-theorem is used to derive an analytical closed-form expression to predict the burst pressure of internally corroded pipes, which is found to agree markedly well with the experimental results.

Numerical and analytical studies of low cycle fatigue behavior of 316 LN austenitic stainless steel

Abstract: Mechanical components are frequently subjected to severe cyclic pressure and/or temperature loadings. Therefore, numerical and analytical low cycle fatigue methods become widely used in the field of engineering to estimate the design fatigue lives. The primary aim of this work is to evaluate the accuracy of the most commonly used numerical and analytical low cycle fatigue life methods for specimens made of 316 LN austenitic stainless steel and subjected to fully reversed uniaxial tension-compression loading, in the room temperature condition. It was found that both Maximum shear strain and Brown-Miller criterions result in a very conservative estimation for uniaxially loaded specimens, however, Maximum shear strain criteria provides better results compared to the Brown-Miller criteria. The total strain energy density approach was also used, and both the Masing and non-Masing analysis were adopted in this study. It is found that the Masing model provides conservative fatigue lives, and non-Masing model results in a more realistic fatigue life prediction for 316 LN stainless steel for both low and high strain amplitude. The fatigue design curves obtained from the commonly used analytical low cycle fatigue equations were reexamined for 316 LN SS. The obtained design curves from Langer model and its modified versions are non-conservative for this type of material. Consequently, the authors suggest new optimized parameters to fit the given test data. The obtained curve using the currently suggested parameters is in better agreement with the experimental data for 316 LN SS.

Creep Deformation Property and Creep Life Evaluation of Super304H

Abstract: Creep deformation behavior, creep strength property and microstructural evolution during creep exposure were investigated on Super 304H steel for boiler tube. In the high stress and lower temperature regime, creep rupture strength of Super 304H steel is higher than that of SUS304H steel. The slope of stress vs. time to rupture curve of Super 304H steel, however, becomes steeper with increases in creep exposure time and temperature, and the creep rupture strength of Super 304H steel becomes closer to that of SUS304H steel after the tens of thousands of hours at 700°C (1292°F) and above. In the short-term, at 600°C (1112°F), creep rupture ductility increases with increase in creep rupture life. However, it tends to decrease after showing this maximum value and the creep rupture ductility decreases with increase in temperature. The complex shape of creep rate vs. time curves, with two minima in creep rate, was observed at 600°C (1112°F). Several type precipitates of niobium carbonitride (Nb(C,N)), Z phase (NbCrN), and copper were observed in Super 304H steel, as well as M23C6 carbide and sigma phase observed in SUS304H steel. The change in slope of stress vs. time to rupture curve is caused by disappearance of precipitation strengthening effect during creep exposure. Accuracy of creep rupture life evaluation was improved by stress range splitting method which takes into account the change in slope of stress vs. time to rupture curves was demonstrated.

An Innovative Yield Criterion Considering Strain Rates Based on Von Mises Stress

Abstract: An innovative yield criterion based on von Mises stress is proposed to represent the strain rate-dependent behavior under dynamic load. Considering the strain rate in the constitutive model, the distortional strain energy density is derived and the yield criterion is established. A plot of yield strength for a range of strain rate reveals that despite the differences in material properties and test methods, the yield strength rise can be represented by a unified criterion. The overall yield behavior of the material under dynamic load can be explained by introducing the strain rate into the constitutive model and threshold distortional strain energy density. This criterion is in a simple form that may be widely applied.

Study of Various International Codes and Standards for Flanged and Flued Type Expansion Bellows Design

Abstract: Differential longitudinal thermal expansion between the shell and the tube bundle is a well-known problem in fixed tubesheet heat exchanger design. An expansion bellows provide flexibility for thermal expansion and also function as a pressure retaining part. In this paper, guidelines for design of flanged and flued type (thick wall) expansion bellows available in international codes and standards including ASME VIII-1 and 2, EN-13445, and TEMA and EJMA codes are presented. These codes and standards are compared in terms of information available for thick wall expansion bellows design with regard to condition of applicability of design formula, spring rate determination, parameter to define the initial geometry, stress determination, and fatigue evaluation. Inherent limitations of these codes with respect to expansion bellows design, research gape, and recommendations for effective design are also presented in this paper. Brief history and information provided in various codes and standards related to unreinforced thin wall expansion bellows (bellows expansion joints) are also presented to understand evaluation of expansion bellows design.

Constraint Effects in Slow Crack Growth Test Methods for Service Life Prediction of High Density Polyethylene Piping

Abstract: High-density polyethylene (HDPE) pipe and piping components have been used successfully and safely for natural gas distribution around the world for several decades. The primary concerns for a 50-year life for buried HDPE piping involves designing against three primary failure modes—ductile fracture, rapid crack propagation (RCP), and slow crack growth (SCG) under sustained pressure loading. Although, design methodologies for preventing ductile fracture and RCP are well established, SCG remains to be a limiting failure mode in determining useful service life of HDPE piping as it may occur under sustained pressure and temperature. Although considerable amount of research has been conducted over the last two decades, SCG still remains less well understood than other failure modes. A critical evaluation of various test methodologies available to determine the SCG resistance of HDPE resins was conducted using finite element analysis (FEA) of various widely used laboratory test specimens. While there exist extensive information on the test methodologies and the applicability of each of the SCG testing methods, there is a growing concern as to whether any/all of these SCG tests give the same information akin to the industrial pipe application, particularly so when conflicting messages are obtained from time to failure predictions from two different SCG tests. While notched-pipe test (NPT) proves to be a direct approach to assess SCG resistance of the polyethylene (PE) pipe with the use of temperature as a test accelerating factor; in the case of newer grade PE resins, the failure time of NPT can still be considerably large (∼5000 to 10,000 h). For this reason, some of the other coupon SCG tests are focus of recent investigations and especially sought after for rapid ranking/assessment of resins and understanding the manufactured HDPE pipe performance. In this study, FEA was conducted to facilitate a direct comparison of leading SCG test methods, through determination of both the stress intensity factor, KI, and existing constraint factors in various widely used specimen geometries. These results are then compared to pipe specimen with an outer diameter (OD) or inner diameter (ID) surface notch. Since, constraint can have a significant role in SCG initiation, transverse/constraint stress (T-stress), and biaxiality ratios (β), these were compared along the crack fronts to arrive at definitive reasons for the smaller failure times observed when testing some of the SCG test specimens, and also reasons for SCG mode of failure observed even under large applied loads (large KI compared to that in a notched pipe) when testing some of the SCG test specimens. The use of stress intensity factor, KI, along with the T-stress and biaxiality ratio (β), was found to provide a complete picture on the broad spectrum of failure times observed from various SCG test specimens, and rationale for choosing a SCG test specimen when evaluating HDPE pipe or resins.

Improvements on Evaluation Functions of a Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessels

Abstract: In Japan, a probabilistic fracture mechanics (PFM) analysis code PASCAL was developed for structural integrity assessment of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. By reflecting the latest knowledge and findings, the evaluation functions are continuously improved and have been incorporated into PASCAL4 which is the most recent version of the PASCAL code. In this paper, the improvements made in PASCAL4 are explained in detail, such as the evaluation model of warm prestressing (WPS) effect, evaluation function of confidence levels for PFM analysis results by considering the epistemic and aleatory uncertainties in probabilistic variables, the recent stress intensity factor (KI) solutions, and improved methods for KI calculations when considering complicated stress distributions. Moreover, using PASCAL4, PFM analysis examples considering these improvements are presented.

Water Hammer Causes Water Main Breaks

Abstract: Most underground water main breaks can be stopped, since the technology is now available to evaluate water system piping failures and determine corrective actions. The problem is defined in terms of several variables: (1) Water hammer is the initiator of nearly all underground water main breaks. (2) In nonacidic soils, fatigue directly causes piping cracks. (3) In acidic soils, water hammer cracks the pipes, and crevice corrosion is accelerated at those crack sites. Additionally, those cracks serve as moisture sources to induce piping surface corrosion due to galvanic corrosion between the soil and the metallic pipe wall. Even so, some failures are solely due to corrosion. (4) Dynamic pipe stresses are significantly larger than stresses caused by static loading, i.e., hoop stresses and strains may be as much as four times the calculated static stress due to water hammer. (5) If dynamic stresses are not considered, calculations incorrectly conclude that water mains will not be damaged. (6) That is, water hammer calculations determine pressure surge magnitudes that are multiples of the operating pressures, where dynamic effects cause fatigue cracks due to the applied pressures and the number of cycles for those pressures to break water mains.

Plasticity Correction on Stress Intensity Factor Evaluation for Underclad Cracks in Reactor Pressure Vessels

Abstract: Structural integrity assessment of reactor pressure vessels (RPVs) is essential for the safe operation of nuclear power plants. For RPVs in pressurized water reactors (PWRs), the assessment should be performed by considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. To assess the structural integrity of an RPV, a traditional method is usually employed by comparing fracture toughness of the RPV material with the stress intensity factor (KI) of a crack postulated near the RPV inner surface. When an underclad crack (i.e., a crack beneath the cladding of an RPV) is postulated, KI of this crack can be increased owing to the plasticity effect of cladding. This is because the yield stress of cladding is lower than that of base metal and the cladding may yield earlier than base metal. In this paper, detailed three-dimensional (3D) finite element analyses (FEAs) were performed in consideration of the plasticity effect of cladding for underclad cracks postulated in Japanese RPVs. Based on the 3D FEA results, a plasticity correction method was proposed on KI calculations of underclad cracks. In addition, the effects of RPV geometries and loading conditions were investigated using the proposed plasticity correction method. Moreover, the applicability of the proposed method to the case which considers the hardening effect of materials after neutron irradiation was also investigated. All of these results indicate that the proposed plasticity correction method can be used for KI calculations of underclad cracks and is applicable to structural integrity assessment of Japanese RPVs containing underclad cracks.

A JSME Code Case on Piping Seismic Design Based on Inelastic Response Analysis and Strain-Based Fatigue Criteria

Abstract: A Code Case in the framework of the Nuclear Codes and Standards of Japan Society of Mechanical Engineers (JSME) has been published to incorporate seismic design evaluation methodologies for piping systems by detailed inelastic response analysis and strain-based fatigue criteria as an alternative design rule to the current rule, in order to provide a more rational seismic design evaluation by taking directly the response reduction due to plasticity energy absorption into account. The Code Case provides two strain-based criteria: one is a limit to maximum amplitude of equivalent strain amplitude derived from detailed analysis and the other is a limit to the fatigue usage factor also based on the equivalent strain amplitude. Some discussions are provided on the adequacy of additional damping in the simplified inelastic analysis and the safety margin and reliability of fatigue evaluation by the detailed inelastic response analysis provided in the Code Case.

Study on Fatigue of Tubing Joint Thread Induced by Vibration in HTHP Ultradeep Wells

Abstract: According to the tubing string failure statistics in the oilfield, fatigue crack of tubing joint thread in high temperature high pressure (HTHP) ultradeep gas wells remains a problem because it can cause tubing strength degradation, tubing fracture failure, well workover, and even well abandonment. In order to obtain a better understanding of tubing thread fatigue and quantify the fatigue life of tubing joint thread in HTHP ultradeep wells, experimental study, elastic–plastic mechanical simulation, and multi-axial fatigue calculation are carried out in this paper. Based on the similarity theory, the vibration mechanical testing device of the tubing string is designed, and the multi-axial load of the tubing joint thread in the actual working condition is obtained. Meanwhile, tubing joint BX1 thread model is established with ansys software, and the stress distribution of tubing joint thread is analyzed on the boundary condition acquired from experiments of vibration test of tubing string. Finally, according to the multi-axial fatigue theory, the fatigue life prediction value of the tubing thread made of Super 13Cr110 and Super 15Cr125 is compared and analyzed. The work presented in this paper can provide theoretical method and technological basis for the study on the frequent failure mechanism of tubing joint thread in HTHP ultradeep gas wells.

Experimental and Numerical Investigation on Ductile Fracture of Steel Pipelines

Abstract: Rupture of steel pipelines leads to the loss-of-containment that may be accompanied with loss of life or damage to property and environment. Therefore, the understanding of the fracture characteristics of steel grades used in the pipelines is essential for a safe and reliable design. In this study, a set of small-scale fracture tests was designed and conducted in order to characterize the fracture of X65 steel grade. The experimental results show that not only is the fracture strain dependent on the triaxial stress condition but also the three-dimensional nature of the stress field considerably affects the ductile fracture toughness. Moreover, parallel finite element (FE) simulation of experiments were conducted and a hybrid experimental–numerical approach was used to calibrate the Mohr–Coulomb fracture criterion and obtain the equivalent plastic strain to fracture of X65 steel as a three-dimensional function of stress triaxiality and Lode angle. An engineering application friendly ductile fracture model is proposed for X65 steel pipelines.

Limit and Shakedown Analysis of 45-Degree Piping Elbows Under Internal Pressure and In-Plane Bending

Abstract: This paper carries out the limit and shakedown analysis of 45 deg piping elbows made up of elastic–perfectly plastic materials by means of the recently proposed stress compensation method (SCM). The elbows are subjected to steady internal pressure and cyclic in-plane closing, opening, and reversed bending moments. Different geometries of the piping elbows and various combinations of these applied loads are investigated to generate various plastic limit and shakedown limit load interaction curves. The plastic limit bending moment and plastic limit internal pressure calculated with the SCM are compared to those determined by the twice-elastic-slope approach. Full step-by-step (SBS) elastic–plastic incremental finite element analysis (FEA) is utilized to verify the structural cyclic responses on both sides of the curves obtained and further to confirm the correct shakedown limit loads and boundaries. It is shown that the SCM calculates the shakedown limit load accurately and possesses about 40 times the computation efficiency of the SBS elastic–plastic incremental method. The effects of the ratios of mean radius to wall thickness and bending radius to mean radius of the piping elbow as well as the loading conditions on the plastic limit and shakedown limit load interaction curves are presented. The results presented in this work give a comprehensive understanding of long-term response behaviors of the piping elbow subjected to cyclic loadings and provide some guidance for the design and integrity assessment of piping systems.

Experimental Study on Damping Acoustic Pressure Pulsations in Pipeline Systems Using Helmholtz Resonators

Abstract: Acoustic pressure pulsations can be problematic in industrial pipelines, especially when the excitation frequency matches an acoustic resonance frequency of the pipeline. The objective of this paper is to investigate the effectiveness of Helmholtz resonators (HRs) in multiple arrangements on the attenuation of acoustic pressure pulsations in piping systems. In a resonant pipeline (i.e., an acoustic standing wave scenario), maximal attenuation is achieved when the HR is inserted at the acoustic pressure antinode. The insertion loss (IL) in an off-resonant system is found to be relatively consistent, unless there is a coupling between the HR and the downstream end termination in which case there is a decrease in attenuation. Multiple, small-volume HRs in various configurations can achieve the same level of damping as that of a single HR with the same total volume. Moreover, it is shown that the use of multiple HRs placed at strategic spacing intervals along the length of a pipeline can yield significant acoustic damping, without the need for characterizing the acoustic waves in the pipeline system. An axial spacing of a quarter wavelength of the frequency of interest between multiple HRs is shown to increase the peak attenuation, which is indicative of a favorable coupling between HRs. The effect of flow velocity and its directionality with respect to the sound source is also investigated. The results presented in this paper provide practical techniques that can be used for the implementation of HR in pipeline systems.

Two-Dimensional Electro-Elastic Analysis of FG-CNTRC Cylindrical Laminated Pressure Vessels With Piezoelectric Layers Based on Third-Order Shear Deformation Theory

Abstract: The purpose of this paper is to show the electro-elastic static behavior of cylindrical sandwich pressure vessels integrated with piezoelectric layers. The core is made of functionally graded carbon nanotube-reinforced composite (FG-CNTRC). The cylinder is embedded between two piezoelectric layers made of PZT-4. The effective material properties of reinforced core with carbon nanotubes (CNTs) are calculated based on rule of mixture. The constitutive relations are developed in cylindrical coordinate system based on a higher-order shear deformation theory for both core and piezoelectric layers. The employed higher-order theory is based on third-order variation of deformations along the thickness direction to improve the accuracy of numerical results. The method of eigenvalue–eigenvector is used for solution of system of governing equations along the longitudinal direction. The numerical results are provided along the longitudinal and radial directions in terms of significant parameters such as various patterns of CNTs, various volume fractions of CNTs, various elastic foundation coefficients, and various applied electrical potentials.

Assessment on Strain-Based and Stress-Based Design Strategies for Components at Elevated Temperatures: A Comparative Study

Abstract: Geometrical discontinuities (such as holes and grooves) widely exist in many components, which operate at elevated temperatures. Creep assessment of the geometrical discontinuities is essential for the safe operation of the system. In general, creep evaluations are conducted from the stress-based and strain-based strategies, but comparative studies on the extent of conservatism of these two design strategies are rarely included. In this work, creep test data of the notched components made of 9–12% Cr steel conducted by authors and that of 9Cr–1Mo steel collected from published works are employed for comparative evaluations. Results indicate that strain-based and stress-based strategies are both relatively conservative for notches in metal materials, and the conservatism of the assessment strategies increases with the notch acuity ratio of the component. The differences of the conservatism for strain-based and stress-based strategies are dependent on the notch acuity ratio and the ductility of the materials. For a blunt notch, the strain-based strategy is more conservative than the stress-based strategy for materials mentioned, while the dominant assessment strategy is dependent on stress redistribution performances of components with a sharp notch.

On Piping Vibration Screening Criteria

Abstract: Vibration-related issues are common in the engineering practice. Piping vibrations can range from those barely noticeable to the ones which result in total system failure in a very short time . This paper presents a synthesis of the criteria which should be used to estimate the severity of vibrations based on both exhaustive literature research and the authors' experience accumulated over the years of engineering practice.