Research Papers: Design and Analysis

J. Pressure Vessel Technol. 2016;139(3):031201-031201-8. doi:10.1115/1.4034407.

A novel method is developed for the design of pressure vessels with tooth-locked quick-actuating closures by considering the contact between the teeth and utilizing the surface-to-surface contact model with contact element and coulomb friction. Elastic and elastic–plastic analyses via the finite element method were employed. It is shown that these pressure vessels can meet the requirements of strength and fatigue.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031202-031202-10. doi:10.1115/1.4034584.

In this paper, we present an exploratory study on the evaluation of reliability levels associated with the piping design equations specified by ASME Boiler and Pressure Vessel (BPV) Code, Section III. Probabilistic analyses are conducted to evaluate reliability levels in straight pipe segments with respect to performance functions that characterize the different failure criteria using advanced first-order reliability method (AFORM). One important failure criterion considered in this study relates to the plastic instability which forms the basis of piping design equations for emergency and faulted load level conditions as defined in the ASME code. The code-specified definition of plastic instability is based on the evaluation of a collapse moment which is defined using the moment–curvature curve for a particular component. In this study, we use elastic-perfectly plastic, bilinear kinematic hardening, and multilinear kinematic hardening stress–strain curves to develop closed-form expressions for the moment–curvature relationship in a straight unpressurized pipe. Both the pressurized and the unpressurized loading conditions are considered. The closed-form reliability is evaluated using Monte Carlo simulation because of the complex nature of the closed-form expression. The reliability values are calculated with respect to the maximum allowable moment specified by the code design equations that use deterministic safety factors.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031203-031203-13. doi:10.1115/1.4035038.

A high-temperature design and an integrity evaluation for a finned-tube sodium-to-air heat exchanger (FHX) in a sodium test facility were conducted based on full 3D finite-element analyses, and comparisons of the design codes were made. A model FHX has been installed in a sodium test facility of sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger (SELFA) for simulating the thermal hydraulic behavior of the FHX unit in the prototype Gen IV sodium-cooled fast reactor (PGSFR). For the design evaluations, ASME Section VIII Div. 2 has been applied for the FHX as a whole. For parts of the FHX operating in the creep regime, nuclear grade elevated temperature design (ETD) codes of ASME Section III Subsection NH and RCC-MRx were additionally applied to evaluate the integrity against creep-fatigue damage. For parts of the FHX operating at low temperature, ASME Section III Subsection NB was applied additionally to evaluate the integrity upon load-controlled stresses and fatigue. The integrity of the FHX was confirmed based on the design evaluations as per the design codes. Code comparisons were made in terms of the chemical compositions, material properties, and conservatism. The conservatism was quantified and compared at the critical low temperature location between ASME Section VIII Div. 2 and ASME-NB, and at the critical high-temperature location between ASME-NH and RCC-MRx.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031204-031204-9. doi:10.1115/1.4035131.

A zero curvature method to estimate the limit load is introduced in detail, and a uniform computing process for computerization of the zero curvature method is presented. A new protection criterion against plastic collapse is proposed. A lot of examples are performed and discussed. The zero curvature load determined by the zero curvature method is a preferable definition of the limit load for perfectly plastic materials or the plastic load for strain strengthening materials. Both advantages of the ASME VIII-2 code and the EN-13445 standard are absorbed in the new protection criterion.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031205-031205-8. doi:10.1115/1.4034675.

The smoothed inverse eigenstrain method is revisited for the reconstruction of residual fields and eigenstrains from limited strain measurements within axially symmetric tubes. The application of the present approach is successfully demonstrated for two cases of analytical solution and experimental measurements. The well-known advantage of the smoothed inverse eigenstrain approach is that it not only minimizes the deviation of measurements from the model predictions but also will result in an inverse solution satisfying all of the continuum mechanics requirements. As a result, less number of experimental measurements is required to reconstruct the complete residual fields. Consequently, the distribution of residual stresses is obtained without requiring the details of the hardening behavior of the material. Furthermore, the eigenstrain field is inversely determined satisfying the total strain compatibility equations, and a closed form analytical solution is presented for the distribution of eigenstrains.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031206-031206-12. doi:10.1115/1.4035082.

In this study, an engineering approach for estimations of fracture mechanics parameters, i.e., J-integral and crack opening displacement (COD), for complex-cracked pipes was suggested based on reference stress concept, where stress-strain data of the material was used to assess structural integrity of complex-cracked pipes. In the present study, new reference loads that can reduce the dependency on strain hardening of the material have been suggested for complex-cracked pipes under each loading mode. By using the proposed optimized reference load for complex-cracked pipes, J-integral and COD estimation procedures have been proposed based on the reference stress concept together with the elastic solutions for complex-cracked pipes. The predicted J-integrals and CODs based on the proposed method have been validated against published experimental data and FE results using actual stress–strain data. Moreover, the predictions using the proposed methods are also compared with those using the existing solutions for simple through-wall cracks (TWCs) based on reduced thickness analogy concept.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031207-031207-11. doi:10.1115/1.4035507.

Design of the top wind stiffeners of aboveground storage tanks designed to the requirements of API 650 is investigated. The current design methodology is based on intuition and experience without a sound technical justification. This paper investigates a diameter limit to be used in the design of the top stiffener ring by using finite-element analysis (FEA) in a parametric study. Linear bifurcation analysis (LBA) and geometrically nonlinear analysis including imperfections (GNIA) were performed on cylindrical storage tanks. By modeling tanks with different diameters and limiting the design of top stiffener ring for a diameter of 170-ft (52-m), the buckling loads are investigated. It was found that the 170-ft (52-m) diameter is a suitable upper limit to design the top stiffener rings for larger diameters.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031208-031208-9. doi:10.1115/1.4035414.

A physically and statistically based method for steam generator (SG) heat exchanger tubes (HET) integrity assessment is proposed. The method based is on the stochastic laws of crack dimensions distribution with taking into account its growth, limit load-model of cracked tube, and SG plugging statistics. Based on the history of the tubes, plugging of the specific SG three statistical parameters has to be found: initial number of defects, stochastic parameter of defect depth, and the defect growth rate. The developed method was used for the prediction of HET failure for all Ukrainian SG. It is also used for the justification of pressure reduction of hydrostatic test (HT) for primary circuit of WWER NPPs. It is shown that the pressure reduction from 24.5 to 19.6 MPa for WWER-1000 s and from 19.1 to 15.7 MPa for the WWER-440 s does not practically increase the HET failure probability during operation.

Commentary by Dr. Valentin Fuster

Research Papers: Fluid-Structure Interaction

J. Pressure Vessel Technol. 2016;139(3):031301-031301-15. doi:10.1115/1.4034467.

Experimental measurements of the steady forces on a central cluster of tubes in a rotated triangular array (P/D=1.5) subjected to two-phase air–water cross-flow have been conducted. The tests were done for a series of void fractions and a Reynolds number (based on the pitch velocity), Re=7.2×104. The forces obtained and their derivatives with respect to the static streamwise displacement of the central tube in the cluster were then used to perform a quasi-steady fluidelastic instability analysis. The predicted instability velocities were found to be in good agreement with the dynamic stability tests. Since the effect of the time delay was ignored, the analysis confirmed the predominance of the stiffness-controlled mechanism in causing streamwise fluidelastic instability. The effect of frequency detuning on the streamwise fluidelastic instability threshold was also explored. It was found that frequency detuning has, in general, a stabilizing effect. However, for a large initial variance in a population of frequencies (e.g., σ2=7.84), a smaller sample drawn from the larger population may have lower or higher variance resulting in a large scatter in possible values of the stability constant, K, some even lower than the average (tuned) case. Frequency detuning clearly has important implications for streamwise fluidelastic instability in the steam generator U-bend region where in-plane boundary conditions, due to preload and contact friction variance, are poorly defined. The present analysis has, in particular, demonstrated the potential of the quasi-steady model in predicting streamwise fluidelastic instability threshold in tube arrays subjected to two-phase cross-flows.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031302-031302-9. doi:10.1115/1.4034468.

In this study, a computational fluid dynamics (CFD) analysis of the transient flow field inside the secondary side of a nuclear reactor steam generator (SG) during blowdown following a feedwater line break (FWLB) accident is performed to evaluate the transient hydraulic loading (pressure) on the SG internals and tubes. The nonflashing liquid flow is assumed for a conservative prediction of the transient blowdown loading. The CFD analysis results are illustrated in terms of the transient velocity and pressure disturbances at some selected monitoring points inside the SG secondary side and compared with those predictions obtained from the existing simple analytical model to examine the physical validity of the CFD analysis model. As a result, the existing simple analytical model cannot yield the transient velocity and pressure disturbances and results in underestimation during blowdown as compared to the CFD calculations. Based on the present CFD analysis results, it is seen that an FWLB may result in excessive disastrous transient hydraulic loading on the SG internal structures and tubes near the feedwater inlet nozzle due to the significant pressure changes (pressure wave with very high amplitude) and abruptly increased velocity of water near the feedwater nozzle.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031303-031303-8. doi:10.1115/1.4034405.

This paper presents a numerical study of the dynamic response and stability of a partially confined cantilever pipe under simultaneous internal and external axial flows in opposite directions. The onset of flow-induced vibrations is predicted by the developed numerical model, and moreover, limit-cycle motion occurs as the flow speed becomes larger than a critical value. The numerical results are in good agreement with existing experimental results. The simulation gives control over many physical parameters and provides a better insight into the dynamics of the pipe. A parametric study regarding the stability of the system for varying confinement length is performed. The current results show that there is an increase in the susceptibility of the system to instability as the extent of confinement is increased.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031304-031304-9. doi:10.1115/1.4034587.

A series of experimental tests were conducted for low-velocity impact on a composite box containing water in order to study the fluid–structure interaction (FSI). Then, baffles were inserted in the box to examine their effect on the structural response of the composite box. Finally, a computational study was conducted to supplement the experimental study. The water level inside the composite box was varied incrementally from 0% (i.e., no water) to 100% (full water). The impact velocity was also changed. In the experimental study, strain gauges and the load cell were used to measure the strain responses at the front, side, and back surfaces as well as the impact force. The results showed that the FSI effect was significant to the structural responses depending on the water level. The effect of the baffle was different among the front, side, and back surfaces. Both experimental and numerical results agreed well.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):031305-031305-7. doi:10.1115/1.4035130.

This paper presents an evaluation of the applicability of a numerical analysis model to the transient thermal-hydraulic response of steam generator (SG) secondary side to blowdown following a steam line break (SLB) at a pressurized water reactor (PWR). To do this, the numerical analysis model was applied to simulate the same blowdown situation as in an available experiment which was conducted for a simplified SG blowdown model, and the numerical results were compared with the measurements. As a result, both are in reasonably good agreement with each other. Consequently, the present numerical analysis model is evaluated to have the applicability for numerical simulations of the transient phase change heat transfer and flow situations in PWR SGs during blowdown following a SLB.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031306-031306-11. doi:10.1115/1.4035271.

Flow-induced acoustic resonances in piping with closed side branches cause severe structural vibration and fatigue damage of piping and components in power plants. Practical piping systems of power plants often have a steam flow, and moreover, the steam state can be not only dry (i.e., gas single-phase flow with superheated steam) but also wet (i.e., high-quality two-phase flow with mixture of saturated steam and saturated water). Although many researchers have investigated acoustic resonances at side branches, acoustic resonances under a wet steam flow have not yet been clarified since previous studies were mainly conducted under an air flow. Moreover, there have been few previous experiments performed under a steam flow, particularly a wet steam flow. The objective of this study is to investigate acoustic resonances in a closed side branch under a wet steam flow. Experiments on dry and wet steam flows under low pressure and also on an air flow were conducted and the results were compared. Moreover, the applicability of a theoretical equation for the resonance frequency, calculated as the first acoustic mode frequency using the branch piping depth with end correction and the sound speed in dry and wet steam, was evaluated. For our experimental conditions, it was confirmed that the effects of dry steam and air on acoustic resonances were similar. However, higher acoustical damping was confirmed under wet steam than under dry steam, which is considered to be caused by the existing liquid phase (i.e., droplets and/or liquid film). The resonance frequencies under wet steam obtained by the theoretical equation and assuming a saturated sound speed were within ±6% of the measured values, and the critical Strouhal numbers under wet steam were similar to those under dry steam and air when the resonance frequencies were evaluated by the proposed method.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031307-031307-8. doi:10.1115/1.4035318.

Fluid excitation forces acting on stationary cylinders with cross-flow are the coupling of vortex shedding and turbulence buffeting. Those forces are significant in the analytical framework of fluid-induced vibration in heat exchangers. A bench-scale experimental setup with an instrumented test bundle is constructed to measure fluid excitation forces acting on cylinders in the normal triangular tube arrays (P/D = 1.28) with water cross-flow. The lift and drag forces on stationary cylinders are measured directly as a function of Reynolds number with a developed piezoelectric transducer. The results show that the properties of fluid excitation forces, to a great extent, largely depend upon the locations of cylinders within bundle by comparison to the inflow variation. A quasi-periodic mathematical model of fluid excitation forces acting on a circular cylinder is presented for a tightly packed tube bundle subjected to cross-flow, and the bounded noise theory is applied between fR = 0.01 and fR = 1. The developed model is illustrated with lots of identification results based on the dominant frequency, the intensity of random frequency, and the amplitude of fluid excitation forces. A second model has been developed for fluid excitation forces between fR = 1 and fR = 6 with the spectrum index introduced. Although still preliminary, each model can predict the corresponding forces relatively well.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031308-031308-9. doi:10.1115/1.4035376.

A theoretical model for wave propagation across solid–fluid interfaces with fluid–structure interaction (FSI) was explored by conducting experiments. Although many studies have been conducted on solid–solid and fluid–fluid interfaces, the mechanism of wave propagation across solid–fluid interfaces has not been well examined. Consequently, our aim is to clarify the mechanism of wave propagation across a solid–fluid interface with the movement of the interface and develop a theoretical model to explain this phenomenon. In the experiments conducted, a free-falling steel projectile was used to impact a solid buffer placed immediately above the surface of water within a polycarbonate (PC) tube. Two different buffers (aluminum and polycarbonate) were used to examine the relation between wave propagation across the interface of the buffer and water and the interface movement. With the experimental results, we confirmed that the peak value of the interface pressure can be predicted via acoustic theory based on the assumption that projectile and buffer behave as an elastic body with local deformation by wave propagation. On the other hand, it was revealed that the average profile of the interface pressure can be predicted with the momentum conservation between the projectile and the buffer assumed to be rigid and momentum increase of fluid. The momentum transmitted to the fluid gradually increases as the wave propagates and causes a gradual decrease in the interface pressure. The amount of momentum was estimated via the wave speed in the fluid-filled tube by taking into account the coupling of the fluid and the tube.

Commentary by Dr. Valentin Fuster

Research Papers: Materials and Fabrication

J. Pressure Vessel Technol. 2016;139(3):031401-031401-10. doi:10.1115/1.4034676.

Through-thickness distributions of the welding residual stresses were studied in the range of 50–100 mm thick plates by using finite-element modeling (FEM) and neutron diffraction measurements. In order to simulate the residual stresses through the thickness of the thick weld joints, this paper proposes a two-dimensional generalized plane strain (GPS) finite-element model coupled with the mixed work hardening model. The residual stress distributions show mostly asymmetric parabola profiles through the thickness of the welds and it is in good correlation with the neutron diffraction results. Both the heat input and plate thickness have little influence on the residual stress distributions due to the relatively large constraints of the thick specimen applied for each welding pass. A general formula has been suggested to evaluate the distributions of the through-thickness residual stresses in thick welds based on FEM and neutron diffraction experimental results.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031402-031402-8. doi:10.1115/1.4035727.

This study evaluates the plastic responses of thick cylinders made of transversely isotropic materials under mechanical cyclic loads, using the kinematic hardening theory of plasticity. The Hill yield criterion is adapted to the kinematic hardening theory of plasticity. The constitutive equations of plastic strains are obtained using the adapted yield criterion. The flow rule based on the kinematic hardening theory of plasticity associated with the Hill yield criterion is represented to evaluate the cyclic behavior of transversely isotropic cylindrical vessels. A numerical method is proposed to calculate the stresses and plastic strains in this structure due to the cycling of pressure at its inside surface. The numerical solution is validated simplifying the results with those of isotropic materials. Using the proposed method, the effect of anisotropy on ratcheting and shakedown response of the vessel is evaluated. It has been shown that the ratcheting or shakedown response of the vessel and the rate of ratcheting are highly affected by the anisotropy ratio. The numerical results of this paper show that the yield strength ratio, which is affected by initial work hardening of the metal, may control the ratcheting behavior of the cylindrical vessels.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031403-031403-6. doi:10.1115/1.4035272.

A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15 °C using B × B specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm, where the crack reached around the intercritical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15 °C or room temperature. The difference in test results, for the same material, is associated with the different constraint levels in the two loading modes, taking into account that pop-ins were triggered in high-constraint SE(B) tests, while it was not the case for low-constraint SE(T) tests.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031404-031404-4. doi:10.1115/1.4035789.

Four-point bend tests were performed on Cr-coated steel specimens that were pulsed laser heated (PLH) with two pulses per area from a millisecond pulse duration laser. Cracks were observed in the PLH specimens extending to the substrate. Specimens subjected to PLH exhibited reduced cycles to failure under all the loadings. This indicates that the PLH process replaces the crack initiation process, and the PLH-formed cracks give the expected crack propagation behavior. This approach provides a method to separately study the effects of crack formation and crack propagation in fatigue life tests. It is especially applicable to situations in which the cracks to be propagated are induced by thermomechanical processes.

Commentary by Dr. Valentin Fuster

Research Papers: Operations, Applications and Components

J. Pressure Vessel Technol. 2016;139(3):031601-031601-10. doi:10.1115/1.4034677.

An important safety factor to be considered when designing a plant is the prevention of overpressure-induced explosions, to which many plants are vulnerable because of pressurized fluids in plant components. A pilot-operated pressure relief valve is a core device for venting off overpressure formed inside vessels and pipelines. The pilot-operated pressure relief valve has a highly complicated structure, and its design and production should be thoroughly studied. In this study, a simplified structure for the pilot-operated pressure relief valve was proposed to facilitate the design and production processes, and the effective ranges of its design variables were determined to enable the prediction of the impact of the design variables in the design and production processes. The ranges determined were validated by a numerical flow analysis and experiment as follows. We calculated the maximum orifice diameter at which the main valve does not open and examined the minimum orifice diameter that can resist the impact of strong shock waves. Additionally, we defined the orifice diameter range that ensures the stable opening and closing of the main valve under various pressure conditions. The effective ranges of the design variables determined in this study can be used to ensure safe operation of a pilot-operated pressure relief valve under various pressure conditions with the design of the proposed simplified structure.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031602-031602-8. doi:10.1115/1.4035788.

Extended dry storage of spent nuclear fuel makes it desirable to assess the structural integrity of the storage canisters. Stress corrosion cracking of the stainless steel canister is a potential degradation mode especially in marine environments. Sensing technologies are being developed with the aim of detecting the presence of chloride-bearing salts on the surface of the canister as well as whether cracks exist. Laser-induced breakdown spectroscopy (LIBS) methods for the detection of Chlorine are presented. In addition, ultrasonic-guided wave detection of crack-like notches oriented either parallel or perpendicular to the shear horizontal wave vector is demonstrated using the pulse-echo mode, which greatly simplifies the robotic delivery of the noncontact electromagnetic acoustic transducers (EMATs). Robotic delivery of both EMATs and the LIBS system is necessary due to the high temperature and radiation environment inside the cask where the measurements need to be made. Furthermore, the space to make the measurements is very constrained and maneuverability is confined by the geometry of the storage cask. In fact, a large portion of the canister surface is inaccessible due to the presence of guide channels on the inside of the cask's overpack, which is strong motivation for using guided waves for crack detection. Among the design requirements for the robotic system are to localize and track where sensor measurements are made to enable return to those locations, to avoid wedging or jamming of the robot, and to tolerate high temperatures and radiation levels.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031603-031603-8. doi:10.1115/1.4035790.

The maximum upsurge (MU) and the maximum air chamber pressure (MACP) are critical parameters for the design of air cushion surge chamber (ACSC) in hydropower stations. In this paper, the existence of the MU and the MACP are proved under compound conditions. The theoretical formula predicting the most dangerous superposition moment of the MU and the MACP under compound condition is derived, and the influence factors are analyzed as well. To verify the accuracy of the formula, the rigid model based on Runge-Kutta method (RKM) and the elastic model based on the method of characteristics (MOC) are established, respectively, according to the parameters of the ACSC system in the practical hydropower station. The numerical results agree well with the theoretical predictions. In addition, the MU and the MACP under three control conditions are simulated, respectively, and the results show that when the cross-sectional area of throttled orifice is small, the MU and the MACP occur under the successive load rejection condition (SLR); when the cross-sectional area is large, the MU and the MACP occur under the load rejection after load acceptance condition (LRLA).

Commentary by Dr. Valentin Fuster

Research Papers: Pipeline Systems

J. Pressure Vessel Technol. 2016;139(3):031701-031701-11. doi:10.1115/1.4034409.

Recently published analytical solutions for the remaining strength of a pipeline with narrow axial and axisymmetric volumetric flaws are described in this paper, and their experimental and numerical validation are reviewed. Next, the domains of applicability of each solution are studied, some simplifications suitable to steel pipelines are introduced, and an analytical model for the remaining strength of corroded steel pipelines is presented. This analytical solution is compared with the standards most widely used in the industry for assessment of corroded pipelines: ASME B31G, modified ASME, and DNV RP-F101. The empirical and analytical solutions are compared with respect to their most relevant parameters: critical (or flow) stress, flaw geometry parameterization, and Folias or bulging factor formulation. Finally, two common pipeline steels, API 5L grades X42 and X100, are selected to compare the different corrosion assessment methodologies. Corrosion defects of 75%, 50%, and 25% thickness reduction are evaluated. None of the experimental equations take into account the strain-hardening behavior of the pipe material, and therefore, they cannot properly model materials with very dissimilar plastic behavior. The comparison indicates that the empirical methods underestimate the remaining strength of shallow defects, which might lead to unnecessary repair recommendations. Furthermore, it was found that the use of a parameter employed by some of the empirical equations to model the assumed flaw shape leads to excessively optimistic and nonconservative results of remaining strength for long and deep flaws. Finally, the flaw width is not considered in the experimental criteria, and the comparative results suggest that the empirical solutions are somewhat imprecise to model the burst of wide flaws.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2017;139(3):031702-031702-12. doi:10.1115/1.4035463.

A statistical predictive model to estimate the time dependence of metal loss (ML) for buried pipelines has been developed considering the physical and chemical properties of soil. The parameters for this model include pH, chloride content, caliphate content (SO), sulfide content, organic content (ORG), resistivity (RE), moisture content (WC), clay content (CC), plasticity index (PI), and particle size distribution. The power law-based time dependence of the ML was modeled as P = ktv, where t is the time exposure, k is the metal loss coefficient, and v is the corrosion growth pattern. The results were analyzed using statistical methods such as exploratory data analysis (EDA), single linear regression (SLR), principal component analysis (PCA), and multiple linear regression (MLR). The model revealed that chloride (CL), resistivity (RE), organic content (ORG), moisture content (WC), and pH were the most influential variables on k, while caliphate content (SO), plasticity index (PI), and clay content (CC) appear to be influential toward v. The predictive corrosion model based on data from a real site has yielded a reasonable prediction of metal mass loss, with an R2 score of 0.89. This research has introduced innovative ways to model the corrosion growth for an underground pipeline environment using measured metal loss from multiple pipeline installation sites. The model enables predictions of potential metal mass loss and hence the level of soil corrosivity for Malaysia.

Commentary by Dr. Valentin Fuster

Research Papers: Seismic Engineering

J. Pressure Vessel Technol. 2016;139(3):031801-031801-10. doi:10.1115/1.4034406.

Many recent studies have emphasized the need for improving seismic performance of nonstructural systems in critical facilities in order to reduce the damage as well as to maintain continued operation of the facility after an earthquake. This paper is focused on evaluating system-level seismic fragility of the piping in a representative high-rise building. Piping fragilities are evaluated by incorporating the nonlinear finite-element model of a threaded Tee-joint that is validated using experimental results. The emphasis in this study is on evaluating the effects of building performance on the piping fragility. The differences in piping fragility due to the nonlinearities in building are evaluated by comparing the fragility curves for linear frame and nonlinear fiber models. It is observed that as nonlinearity in the building increases with increasing value of peak ground acceleration, the floor accelerations exhibit a reduction due to degradation/softening. Consequently, the probabilities of failure increase at a slower rate relative to that in a linear frame. It is also observed that a piping located at higher floor does not necessarily exhibits high fragilities, i.e., the fundamental building mode is not always the governing mode. Higher order building modes with frequencies closest to critical piping modes of interest contribute more significantly to the piping fragility. Within a particular building mode of interest, a good indicator of the amplification at different floor levels can be obtained by the product of mode shape ordinate and modal participation factor. Piping fragilities are likely to be higher at floor levels at which this product has a higher value.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Pressure Vessel Technol. 2016;139(3):034501-034501-5. doi:10.1115/1.4034586.

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN versus Kmax. It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1, and −2. In addition, the da/dN increases with decreasing R ratio for R < −2. This paper converts from da/dN versus Kmax to da/dN versus ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN versus ΔKI is better equation than da/dN versus Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2016;139(3):034502-034502-5. doi:10.1115/1.4034674.

An experimental setup was designed and fabricated for the channel driven cavity flow in order to provide benchmark data for validation of any numerical analysis program for solving fluid–structure interaction (FSI) problems. The channel driven cavity flow is a modification from the lid-driven cavity flow. To provide the fluid–structure interaction, the bottom face of the cavity is a deformable flat plate. All other boundaries are rigid. The fluid motion inside the cavity is driven by the flow through a narrow channel topside of the cavity. To establish suitable boundary conditions for numerical analyses of the experiment, the inlet of the channel has a given fluid velocity, while its outlet has a known pressure. Water is used as the fluid in this study. Multiple strain gages and laser displacement sensors were used to measure dynamic responses of the plate attached at the bottom of the cavity.

Commentary by Dr. Valentin Fuster

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