Power Plant Piping Research Articles

Evaluation of stress relaxation cracking susceptibility in Alloy 617 for advanced USC boilers

In this study, the stress relaxation cracking susceptibility of Alloy 617, which is a candidate material for advanced ultra-supercritical (A-USC) power plant pipe work, was evaluated. In order to evaluate the effect of aging and grain size on stress relaxation cracking susceptibility, materials aged at 700 °C and coarse grain materials heat treated at 1200 °C for 1 h, 1225 °C for 2 h, 1250 °C for 3 h were tested in addition to as-solution-annealed materials. A three-point bending test with notch placed at the center of each specimen was used for the examination. The test results showed that only the aged material suffered stress relaxation cracking. The time-to-crack tends to be shortened when initial strain in the test is increased. This suggests that higher residual stress in the weldment would increase the risk of stress relaxation cracking. It was proposed that the larger magnitude of creep strain occurs via stress relaxation during the three-point bending test due to higher yield strength caused by γ' phase strengthening, and low ductility due to grain boundary carbides in aged materials promoted stress relaxation cracking. The critical conditions to cause crack could be estimated from the stress relaxation cracking boundary in the map of the relationship between the initial strain and the creep strain during the three-point bending test.

Seismic fragility evaluation of the base-isolated nuclear power plant piping system using the failure criterion based on stress-strain

Abstract In the design criterion for the nuclear power plant piping system, the limit state of the piping against an earthquake is assumed to be plastic collapse. The failure of a common piping system, however, means the leakage caused by the cracks. Therefore, for the seismic fragility analysis of a nuclear power plant, a method capable of quantitatively expressing the failure of an actual piping system is required. In this study, it was conducted to propose a quantitative failure criterion for piping system, which is required for the seismic fragility analysis of nuclear power plants against critical accidents. The in-plane cyclic loading test was conducted to propose a quantitative failure criterion for steel pipe elbows in the nuclear power plant piping system. Nonlinear analysis was conducted using a finite element model, and the results were compared with the test results to verify the effectiveness of the finite element model. The collapse load point derived from the experiment and analysis results and the damage index based on the stress-strain relationship were defined as failure criteria, and seismic fragility analysis was conducted for the piping system of the BNL (Brookhaven National Laboratory) - NRC (Nuclear Regulatory Commission) benchmark model.

Experimental study and multiscale modelling of the high temperature deformation of tempered martensite under multiaxial loading

The microstructural deformation of ex-service 9Cr-1Mo steel, with a tempered martensitic microstructure, has been examined in this study, through the combined use of electron backscatter diffraction (EBSD) and multiscale modelling techniques. Both the experimental and predicted deformation of the material at a notch root on a range of scales from the specimen level down to the microstructural block level are compared. A tension loaded notch specimen of the material which was extracted from an ex-service power plant pipe was used for this analysis. The deformation at the specimen level was quantified by analysis of the load displacement curves and notch opening displacement, which showed excellent agreement with the predicted results from the experimentally calibrated elastic-plastic finite-element model of the specimen geometry. The microstructural deformation was experimentally measured through the use of EBSD carried out at the notch root before and after high temperature mechanical testing. The initial orientation of the microstructure as well as the displacement around the boundary of the area of interest in the macroscale model were applied to a representative volume element (RVE) and a slip based crystal plasticity modelling framework was implemented to model the in-elastic deformation of the material under high temperature loading.

Prediction of grain orientation in dissimilar metal weld using ultrasonic response of numerical simulation from deliberated scatterers

Ultrasonic nondestructive testing plays an important role in structural integrity monitoring of dissimilar metal weld (DMW) structures in pressure vessels and piping of nuclear power plants. Inspection of DMW components is too complicated due to its anisotropic behavior to ultrasonic beam propagation. Many researchers are working rigorously to model the grain orientation and ultrasonic beam skewing in DMW structures but still not completely resolved yet. This paper is intended to estimate the grain orientation with the help of numerical simulation for a given asymmetric DMW component with specified scatterers. The DMW is fabricated from austenite stainless steel and carbon steel base metals with austenite stainless steel filler metal using Gas Tungsten-Arc Welding. To study this research a finite element method (FEM) based numerical simulation has been used to exactly evaluate the grain structure. This model mainly depends on the elasticity matrix which is a function of the grain orientation and attenuation of ultrasonic energy of the weld. Iterative measurement of grain orientation using macrograph of the etched weldment with 5 × 5mm mesh size was carried out then the attenuated elasticity matrix was fed into the FEM COMSOL software model as input parameter. Result obtained from numerical simulation (time of flight and amplitude) are validated with the experimental result and good agreement (above 0.8 correlation coefficient) have been observed at higher iterations. This macro-graphic information based numerical model shows the potential to predict the grain orientation of DMW.

원전 매설배관 및 탱크 규제현황

원전 매설배관 및 탱크 규제현황

Enhancement of radiation on hydromagnetic Casson fluid flow towards a stretched cylinder with suspension of liquid-particles

The presence of dust particles is involved in many engineering and industrial processes like transport of petroleum, emission of smoke from vehicles, piping of power plants, treatment of wastewater, and corrosive particles in mining. Because of the importance of this phenomenon, we considered the Casson liquid flow past a stretching hollow cylinder with fluid–particle suspension and convective boundary condition aspects. Numerical solution is obtained via shooting techniques after the applying of similarity variables to the governing partial equations. Key parameters of the problem are discussed through graphs. It is noticed that the clean fluid temperature is always higher value than the dust fluid and also the presence of radiation enhanced the temperature at the surface.

Experimental Investigation for Effects of Steam Wetness and Static Pressure on Acoustic Resonance Frequency at Side Branch Piping under Wet Steam Flow

Flow-induced acoustic resonances in steam piping with closed side branches cause severe structural vibration and fatigue damage of piping and components in many industrial applications such as power plants. The steam state in the steam piping of power plants is not only dry steam but also wet steam. From our previous experiments under low-pressure wet steam flow, the resonance frequencies, which is important parameter to predict acoustic resonance, under wet steam obtained by the theoretical equation and assuming a saturated sound speed were within ±6% of the measured values. However, the static pressure in practical steam piping is often higher than that in our previous experiments. In this study, we conducted experiments on acoustic resonance in a single side branch under a high-quality wet steam flow with the static pressure as parameters to investigate the effects of the static pressure on acoustic resonance frequency under wet steam flow.

Influence of stress level on uniaxial ratcheting effect and ratcheting strain rate in austenitic stainless steel Z2CND18.12N

Uniaxial ratcheting behavior of Z2CND18.12N austenitic stainless steel used nuclear power plant piping material was studied. The results indicated that ratcheting strain increased with increasing of stress amplitude under the same mean stress and different stress amplitude, ratcheting strain increased with increasing of mean stress under the same stress amplitude and different mean stress. Based on least square method, a suitable method to arrest ratcheting by loading the materials was proposed, namely determined method of zero ratcheting strain rate. Zero ratcheting strain rate occur under specified mean stress and stress amplitudes. Moreover, three dimensional ratcheting boundary surface graph was established with stress amplitude, mean stress and ratcheting strain rate. This represents a graphical surface zone to study the ratcheting strain rates for various mean stress and stress amplitude combinations. The graph showed the ratcheting behavior under various combinations of mean and amplitude stresses. The graph was also expressed with the help of experimental results of certain sets of mean and stress amplitude conditions. Further, experimentation cost and time can be saved.

Modeling the cyclic softening and lifetime of ferritic-martensitic steels under creep-fatigue loading

Ferritic-martensitic (F/M) steels are a common choice for high-pressure, high-temperature boilers and steam piping in power plants, but cyclic softening without saturation is a major degradation mechanism of F/M steels. This degradation mechanism is more pronounced and complex under creep-fatigue loadings. For reliable, but not overly conservative design a better understanding of this phenomenon is necessary. The intent of this work is to characterize and model the softening and lifetime behavior under creep-fatigue conditions at high temperature. Therefore, low-cycle fatigue (LCF) tests with hold time were performed at 550 °C.A distinct dependence of the softening behavior on hold time was found. Additionally, detrimental effect of compressive hold time on lifetime was also observed in this study. All effects of hold time were more pronounced for small strain amplitudes. Based on these experimental observations, a unified viscoplastic deformation and damage model is further developed to describe the high-temperature cyclic softening and lifetime behavior of F/M steels under creep-fatigue loading. An optimized parameter set for the extended model is determined based on experimental results. Good agreement of experimental results and model descriptions is achieved both under pure fatigue as well as under creep-fatigue conditions. The detrimental effect of compressive hold times on lifetime of ferritic-martensitic steels is well represented.

Failure analysis of AISI 321 stainless steel welded pipes in solar thermal power plants

Abstract AISI 321 stainless steels (SS) pipes are commonly used in solar thermal power plants for transport of thermic fluid containing chloride ions at ~ 400 °C. Several of these SS pipes have failed while in service after very short exposure to service conditions leading to leakage of the thermic fluid. The present study aims to understand the root cause of failure of these pipes which were seam welded together with spot welds on the surface. The seam welding had been done either by a) laser beam welding (LBW) or by metal inert gas welding (MIG). Dye penetrant tests were applied to the pipes followed by microstructural analysis of the pipes using optical microscopy, and field emission scanning electron microscopy (FESEM). Subsequently, phase determination was carried out by X-ray diffraction. Stress corrosion cracking (SCC) susceptibility of the laser beam welded, MIG welded and spot welded joints were tested as per ASTM G36 in boiling MgCl2. Detailed investigation revealed that leakage in each case occurred near spot welded joints due to chloride-induced SCC of AISI 321 SS. SCC susceptibility tests of the welds showed that both the seam welds and the spot welds had residual stresses beyond the threshold limit which resulted in early nucleation of cracks in presence of chloride ions. Improper post-weld heat treatment (for LBW, MIG and spot weld) was identified to be the root cause of failure of the pipes.

Mathematical modeling of orifice downstream flow under flow-accelerated corrosion

The main objective of this paper is to establish an analytical model to evaluate the rate of corrosion in a horizontal pipe downstream of an orifice under flow-accelerated corrosion (FAC). FAC is a major issue causing the wall thinning of carbon steel piping in power plants. In this work, the dimensional analysis was employed using the method of repeating variables and the Buckingham Pi Theorem. It was found that the Sherwood number and the relative distance from orifice are the main dimensionless parameters influencing FAC downstream of an orifice. Concerning the available experimental data, two different cases considered; orifice ratio (OR) of 0.25 and 0.5. The result of mathematical modeling agreed with the experimental data. The maximum value of the FAC rate could be well-predicted for the OR of 0.25, while the location of the maximum FAC rate could be well predicted for the OR of 0.5. It was found that the maximum value of FAC rate increases with decreasing orifice ratio and also the maximum value will be located between 1 and 4dp downstream of the orifice in both cases. This work could be useful for professionals in industry and researchers in the field and could be the starting point for a new way of evaluating the FAC rate downstream of a flow’s singularity.

Effect of Ferrite on the Precipitation of σ Phase in Cast Austenitic Stainless Steel Used for Primary Coolant Pipes of Nuclear Power Plants

Effect of Ferrite on the Precipitation of σ Phase in Cast Austenitic Stainless Steel Used for Primary Coolant Pipes of Nuclear Power Plants

Fracture Toughness of Z3CN20.09M Cast Stainless Steel with Long-Term Thermal Aging

Accelerated thermal aging tests were performed at 400 °C for nearly 18,000 h on Z3CN20.09M cast stainless steel which was used for primary coolant pipes of nuclear power plants. A series of Charpy impact tests were conducted on Z3CN20.09M after different long-term thermal aging time. The test results indicated that the Charpy impact energy of Z3CN20.09M cast stainless steel decreased rapidly at an early stage and then almost saturated after thermal aging of 10,000 h. Furthermore, J-resistance curves were measured for CT specimens of longitudinal and circumferential pipe orientations. It showed that there was no obvious difference in the fracture characteristics of Z3CN20.09M in different sampling directions. In addition, the observed stretch zone width (SZW) revealed that the value of initiation fracture toughness J SZW was significantly lower than that of fracture toughness J IC, indicating a low actual crack initiation energy due to long-term thermal aging.

Circumferential current field testing system with TMR sensor array for non-contact detection and estimation of cracks on power plant piping

Piping is a critical component in power plant, which is subject to surface thermal fatigue cracks. Due to the high temperature and the presence of coatings, conventional non-destructive testing methods are unsuitable to detect the thermal fatigue cracks on power plant piping. This paper presents a novel circumferential current field testing system for the non-contact detection and estimation of cracks on power plant piping. A 3D dynamic finite element method model is developed to obtain the characteristic signals and optimize the inducing frequency. The circumferential uniform current field testing system with tunnel magneto resistance (TMR) sensor array is set up and the crack detection experiments are carried out. The results show that the circumferential current field testing system with TMR sensor array can achieve non-contact, visual and efficient detection of cracks on power plant piping in a one pass scan. The depth and length of cracks can be estimated by the proposed calibration method.

Simulation of water hammer phenomena using the system code ATHLET

Abstract Water Hammer Phenomena can endanger the integrity of structures leading to a possible failure of pipes in nuclear power plants as well as in many industrial applications. These phenomena can arise in nuclear power plants in the course of transients and accidents induced by the start-up of auxiliary feed water systems or emergency core cooling systems in combination with rapid acting valves and pumps. To contribute to further development and validation of the code ATHLET (Analysis of Thermalhydraulics of Leaks and Transients), an experiment performed in the test facility Pilot Plant Pipework (PPP) at Fraunhofer UMSICHT is simulated using the code version ATHLET 3.0A.

Gašenje individualnih kotlovskih postrojenja i povezivanje na toplovodnu mrežu sistema daljinskog grejanja

U radu je opisano je unapređivanje kvaliteta daljinskog grejanja i smanjenje zagađenja i povećanje efikasnosti celog sistema. Na grejnom području Karaburma JKP „Beograske elektrane“ postoji trinaest kotlovskih postrojenja koja rade na ugalj i mazut, koriste se za proizvodnju toplotne energije. Tokom 2016. godine izveden je novi predizolovani toplovod od toplane Dunav do Karaburme gde se nalaze pet kotlovskih postrojenja koja su ugašena tako da su svi korisnici toplotne energije priključeni na novi toplotni izvor. U radu su prikazani problemi koji su se javljali prilikom izvođenja radova pri gašenju individualnih kotlovskih postrojenja, pri izgradnji novog predizolovanog toplovoda i pri izgradnji toplotnih podstanica. Cilj ovog rada je unapređivanje kvaliteta daljinskog grejanja i smanjenje zagađenja i povećanje efikasnosti celog sistema.

Pitting corrosion of thermally aged cast duplex stainless steel for primary coolant pipes of nuclear power plants

ABSTRACTThe pitting corrosion of thermally aged Z3CN20.09M cast duplex stainless steel (CDSS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy. Both pitting potential and charge transfer resistance values of thermally aged specimens became less positive with aging time, while passive current density increased, indicating that thermal aging causes degradation in pitting corrosion resistance. The pitting potential of thermally aged specimens after annealed is higher than that of thermally aged specimens revealing that the pitting corrosion resistance of annealed specimens has been improved. The α’ phase precipitation during thermal aging in ferrite brings the Cr-enriched and Cr-depleted zone microstructures which mainly induced the degradation of pitting corrosion resistance. The microsegregation of Cr element or Cr enriched and Cr-depleted zones will be alleviated or even removed due to the Cr-rich α’ phases dissolution during the process of annealing. So, the pitting corrosion resistance of annealed specimens is improved.

Direct simulation of conjugate heat transfer of jet in channel crossflow

We present a DNS study of a hot, low momentum laminar water jet discharged into a cold turbulent channel stream through a circular orifice in one of the steel channel walls. The channel wall has a finite thickness and its outer side is cooled under Robin type thermal boundary conditions for a realistic external environment, leading to a conjugate heat transfer system. Nusselt number and r.m.s temperature fluctuations on the wall are compared with our earlier DNS results for the simpler iso-thermal and adiabatic conditions at the channel inner surface. Temperature fluctuations inside the channel wall are resolved to provide data for a conjugate heat transfer (CHT) thermal fatigue test case related to the ageing of pipe walls and welds studies, as found, for example, in power plant piping T-junctions. The crossflow Reynolds number is Re=3333, jet-to-crossflow velocity ratio is R=1/6 and fluid-to-solid conductivity ratio is 1/64.The near-wall mean flow structures, a horseshoe vortex ahead and on the sides of the jet orifice, a shallow recirculation behind the discharge and a counter-rotating vortex pair drawing in a blanket of cooler cross-flow, lead to a complex convective and turbulent wall heat transfer pattern around the orifice. The main findings are:(i)Wall maps of Nusselt number and r.m.s temperature, θr.m.s, for conjugate heat transfer are only qualitatively similar to the iso-thermal and adiabatic wall cases.(ii)Inside the solid θr.m.s and its dissipation, analysed from RANS modelling perspective, show that predicted thermal spot length scales are discontinuous on the interface, at variance with the 2-point spectrum-derived scales.(iii)At the high wavenumber range, the spanwise temperature spectra decrease according to exponential-decay spectral models for the fluid turbulence in the Kolmogorov range, but with large exponential coefficients increasing with depth inside the solid.

Dynamics of large-diameter water pipes in hydroelectric power plants

An outline is made of physical behaviour of water - filled large pipes. The fluid-wall coupling, the key factor governing the pipe dynamics, is discussed in some detail. Different circumferential pipe modes and the associated cut-on frequencies are addressed from a theoretical as well as practical point of view. Major attention is paid to the breathing mode in view of its importance regarding main dynamic phenomena, such as water hammer. Selected measurement results done at EDF are presented to demonstrate how an external, non-intrusive sensor can detect pressure pulsations of the breathing mode in a pressure pipe. Differences in the pressure measurement using intrusive and non-intrusive sensors reveal the full complexity of large-diameter pipe dynamics.

Thickness reconstruction of nuclear power plant pipes with flow-accelerated corrosion damage using laser ultrasonic wavenumber imaging

The pipeline is an essential part of nuclear and other power plants. Designed to operate for decades, the pipeline is susceptible to multiple types of damage due to working in a high pressure, high temperature, and highly corrosive environment. Therefore, it requires regular inspection. The issue of many current nondestructive testing systems for pipelines is the use of a one-dimensional scan mechanism along the longitudinal direction of the pipe, which is incompatible with the two-dimensional curvature of elbow pipes, yet it is at these places in which the flow changes directions inside the elbow pipes that a common type of damage occurs: flow-accelerated corrosion damage. In this article, flow-accelerated corrosion damage is visualized using the Ultrasonic Wavenumber Imaging algorithm, which maps the dominant local spectroscopic wavenumber of the wavefield at a particular mode and a particular frequency. In previous studies, the mode and frequency were chosen empirically. In this article, a novel theoretical study is presented to optimize the two input parameters of Ultrasonic Wavenumber Imaging based on a sensitivity analysis of the spectroscopic wavenumber with respect to the change in thickness of the structural base. Additionally, an inverse method is proposed to estimate the thickness of the structure based on the Ultrasonic Wavenumber Imaging map.