Wall Thinning Rate Research Articles

Research On Optimization In NC Bending Process Of Thin-walled Tube Based on Orthogonal Experiment

In the process of research and development of tube bending forming technology, the way of improving the forming quality and establishing the optimization of forming process parameters has become an important problem that should be solved quickly. This text simulated the process of bend forming with the way of finite element, combined with the effects of geometric and physical parameters on the forming quality of bending pipe, taking the important parameters which are measurements of the pipe wall thickness variation as test indexes, made the virtual orthogonal experiment and gained the laws of the bending angle, relative bending radius, relative wall thickness, thrust, pipe friction coefficient between mode have effects on the forming quality of wall thinning rate and wall thickening. Through the comprehensive analysis and additional test, obtained the optimal parameters values, improved the accuracy of simulation and the optimization results of orthogonal test, improved the quality of tube bending forming.

A241 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (5)エルボ管におけるFAC減肉速度の計測と流速依存性(OS2 保全・設備診断技術(6))

A241 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (5)エルボ管におけるFAC減肉速度の計測と流速依存性(OS2 保全・設備診断技術(6))

A243 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (7)LESによる高レイノルズ数エルボ管流れにおける物質移行係数予測(OS2 保全・設備診断技術(6))

A243 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (7)LESによる高レイノルズ数エルボ管流れにおける物質移行係数予測(OS2 保全・設備診断技術(6))

A242 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (6)エルボ管における物質移行係数の直接計測(OS2 保全・設備診断技術(6))

Flow Accelerated Corrosion (FAC) is one of the issues to be noticed considerably in plant piping management. For the integrity and safety of the plant, the wall-thinning and thinning rate due to FAC should be predicted, and we hope to construct the model to predict the wall thinning rate. We have studied FAC from the view point of flow dynamics. The mass transfer coefficient is measured by the electrochemical method with the point electrode. In this study, we evaluate the effect of concentration boundary layer on the point electrode.

Wall thinning in carbon steel pipeline carrying pure water at high temperature

In the boilers of thermal and nuclear power plants, neutral pure water with low electric conductivity is generally used after de‐oxygenation, which is utilized to suppress the corrosiveness of the water. Nevertheless, a relatively high rate of wall thinning occurs on the inside surface of carbon steel pipes, in particular the downstream orifice meters and T‐junctions, sometimes leading to the rupture of the pipe. The generation of wall thinning has been attributed to FAC (flow accelerated corrosion), implying that the water flow must raise the corrosiveness of the boiler water. Contrary to this explanation, the macro‐cell corrosion theory, which was proposed by this author, regards this occurrence as merely localized corrosion. Under such circumstances, a case study was conducted on a burst carbon steel pipe from a high pressure steam line, and the cause was substantially proven to be water‐line corrosion. Because water‐line corrosion is a localized corrosion that can occur without water flow, the wall thinning damage that occurred in the carbon steel pipes must have been brought about by localized corrosion and not FAC.

원전 배관감육 평가를 위한 새로운 기법의 도입 및 타당성

KEPCO EC Revised April 25, 2014; Accepted April 28, 2014)A huge number of carbon steel piping components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the piping components. To manage the wall thinning degradation, most of utilities in the world predict the wall thinning rate based on the computational program such as CHECWORKS, COMSY, and BRT-CICERO, evaluate the UT (Ultrasonic Test) data, and determine next inspection timing, repair or replacement, if needed. There are several evaluation methods, such as band, blanket, and strip methods, commonly used for determining the wear of piping components from single UT inspection data. It has been identified that those single UT evaluation methods not only do not consider the manufacturing features of pipes, but also may exclude the data of the most thinned point when determining the representative wear rate of piping components. This paper describes a newly developed single UT evaluation method, E-Cross method, for solving above problems and introduces application examples for several pipes and elbows. It was identified that the E-Cross method using the length and width of UT data excluded the most thinned points appropriate as the single UT evaluation method for thinned piping components.Keywords: wall thinning, UT inspection, UT data single evaluation method, E-Cross evaluation method, manufacturing tolerance

0807 壁乱流における物質移行係数の計測と電極形状の影響

FAC (flow accelerated corrosion) is a phenomenon that accelerates the wall thinning rate in the flow. Mass transfer coefficient k is one of the important parameters to evaluate pipe wall thinning rate. We measure mass transfer coefficient by electrochemical technique and flow field using stereo PIV in order to observe the relationship between wall thinning and flow field. Based on the previous studies, we can expect that not only flow in the inner layer but also flow in the outer layer affects the mass transfer from the wall surface. Then, we calculate the correlation coefficient of amplitude modulation to observe interaction of inner and outer layer in this study.

A123 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (3) INSSエルボ管における数値計算に基づく物質移行係数の予測(OS2 保全・設備診断技術(1))

A123 エルボ管におけるFAC減肉速度と物質移行係数の評価について : (3) INSSエルボ管における数値計算に基づく物質移行係数の予測(OS2 保全・設備診断技術(1))

Risk Evaluation of Flow-Accelerated Corrosion Based on One-Dimensional FAC Code

The possibility of thousands of flow-accelerated-corrosion (FAC) zones causes long and costly inspection procedures for nuclear, as well as fossil-fuel power plants, even if the number of zones is minimized on the basis of temperature and flow velocity. In order to decrease the number of inspection zones, suitable prediction or estimation procedures for FAC occurrence should be applied, and the resulting computer programs should be tuned with as many inspection data as possible. Such coupling of the estimation and inspection procedures should allow effective and reliable preparation to be made against FAC occurrence and propagation.This paper defines the FAC risk as the mathematical product of the possibility of the occurrence of wall thinning and its hazard scale. The possibility of the occurrence of wall thinning was designated as the time margin for pipe rupture determined by applying a one-dimensional FAC code, which could predict the wall-thinning rate with an accuracy within a factor of 2, while the hazard scale was defined as the volume of effluent steam and water from the ruptured mouth, which was enthalpy of water originally flowing in the pipe multiplied by the square of the pipe inner diameter. High FAC risk zones along entire cooling systems could be evaluated in only one-tenth or one-hundredth of the computer time as for a three-dimensional FAC code to determine the priority for inspection-order importance.

Verification and Validation of One-Dimensional Flow-Accelerated Corrosion Evaluation Code

A six-step procedure based on three-dimensional (3-D) computational fluid dynamics codes and a coupled model of electrochemistry and oxide layer growth models was proposed to estimate local wall thinning due to flow-accelerated corrosion (FAC), and they were applied to evaluate wall-thinning rates, residual lifetimes of the pipes, and applicability of countermeasures against FAC. A verification and validation (V&V) evaluation based on a comparison of calculated and measured wall thinning confirmed that the wall-thinning rate could be predicted with an accuracy within a factor of 2 and that residual wall thicknesses after 1 year of operation could be estimated with an error of <20%.To mitigate one of the disadvantages of the 3-D FAC code, which is the large amount of computational time needed, and to evaluate FAC occurrence probability for entire plant systems, a one-dimensional (1-D) FAC code was developed by applying 1-D mass transfer coefficients and geometrical factors. High-FAC occurrence zones along entire cooling systems and the effects of countermeasures on mitigating the risks could be evaluated within a small amount of computer time. Prior to application of the easy-to-handle FAC code for plant analysis, its accuracy and applicability should be confirmed based on V&V processes. From comparison of maximum wall-thinning rates calculated with the 1-D FAC code, those calculated with the 3-D FAC code, and measured results for experimental loops and secondary piping of an actual pressurized water reactor plant, it was confirmed that the calculated wall-thinning rates agreed with the measured ones within a factor of 2.

Evaluation method for pipe wall thinning due to liquid droplet impingement

In order to evaluate pipe wall thinning due to liquid droplet impingement (LDI), the analysis code system DRAWTHREE-LDI composed of the six steps has been developed. The wall thinning due to LDI is classified into two types which are LDI (corrosion) and LDI (erosion). In LDI (corrosion), the dominant mechanism to dwindle pipe wall thickness is flow-accelerated corrosion which is a chemical process. While in LDI (erosion), it is impact onto wall surfaces due to droplet impingement which is a physical process. The validations on DRAWTHREE-LDI were made through the comparisons of results calculated with those measured in feed water heater vent lines at an actual power plant. Most calculated results agreed with those measured within a factor of two which was the target in the development of DRAWTHREE-LDI. In order to confirm the calculation accuracy, it is strongly required to improve measurement accuracy, since the measured wall thinning rate was obtained by subtraction of the measured wall thickness during the regular inspection period from one during the previous inspection period. The measured wall thickness itself by UT techniques has some measurement errors, and the error increases a lot by the subtraction.

D203 質量移行係数に基づく減肉予測モデル構築の試み(OS6 保全・設備診断技術(4))

Flow Accelerated Corrosion (FAC) is one of the issues to be noticed considerably in plant piping management. For the integrity and safety of the plant, the wall-thinning and thinning rate due to FAC should be predicted, and we hope to construct the model to predict the wall thinning rate. We have studied FAC from the view point of flow dynamics. The mass transfer coefficient is measured by the electrochemical method Based on these knowledge, we summarize the present problems for evaluating the wall-thinning rate.

J057045 質量移行係数に及ぼす濃度境界層の影響の比較(〔J057-04〕乱流における運動量、熱、物質の輸送現象(4))

A method to correct the measurement of the electrochemical experiment using a small electrode is proposed for use in quantitative evaluation of pipe thinning phenomena. In the method, it is assumed that the friction velocity is the only hydraulic behavior to affect wall thinning rate. The method is based on the estimation of the friction velocity and the mass transfer rate from the pipe wall with a fully-developed concentration boundary layer. The applicability of the method was confirmed using the mass transfer coefficients measured at the straight pipe.

D114 高温配管肉厚連続モニタリング装置を用いたPWR二次系水質改善によるFAC抑制効果の検証(OS6 保全・設備診断技術(2))

Flow Accelerated Corrosion (FAC) of carbon steel (CS) piping is one of main issues in secondary system of Pressurized Water Reactor (PWR) nuclear power plant Wall thinning of CS piping due to FAC increases potential risk of pipe rupture, cost for inspection and replacement of damaged pipes In particular, corrosion products generated by FAC of CS piping brought steam generator (SG) tube corrosion and degradation of thermal performance, when it intruded and accumulated in secondary side of PWR. ^(1) Therefore, we estimated an applicability and effectiveness of Oxygenated Water Chemistry (OWC) as a new approach to FAC suppression for PWR secondary system by experiment in laboratory and demonstration test at Tsuruga-2 (1160 MWe PWR, commercial operation started in 1987). ^<(2)(3)> Based on this result, OWC has been applied to condensate system in Tsuruga-2 from Jan 2011 And, to evaluate the FAC mitigation effect of OWC, wall thickness of actual condensate piping in Tsuruga-2 after OWC application was measured by continuous monitoring system, using high-temperature and high-resolution ultrasonic probe In this paper, behavior of actual wall thinning rate of condensate piping in Tsuruga-2 under various pH and DO concentration is discussed

Non-Axisymmetric Mass Transfer Phenomenon behind an Orifice in a Curved Swirling Flow

The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.

원전 탄소강 배관의 액적충돌침식 손상에 대한 B-Scan 검사 및 수치해석적 분석

Liquid droplet impingement erosion (LDIE) known to be generated in aircraft and turbine blades is recently appeared in nuclear piping. UT thickness measurements with both A-scan and B-scan UT inspection equipments were performed for a component estimated as susceptible to LDIE in feedwater heater vent system. The thickness data measured with B-Scan equipment were compared with those of A-Scan. Thermal hydraulic analysis based on ANSYS FLUENT code was performed to analyze the behavior of liquid droplets inside piping. The wall thinning rate and residual lifetime based on both existing Sanchez-Caldera equation and measuring data were also calculated to identify the applicability of the existing equation to the LDIE management of nuclear piping. Because Sanchez-Caldera equation do not consider the feature of magnetite formed inside piping, droplet size, colliding frequency, the development of new evaluation method urgently needs to manage the pipe wall thinning caused by LDIE.

Determination Procedures of High Risk Zones for Local Wall Thinning Due to Flow-Accelerated Corrosion

A modified six-step evaluation procedure has been proposed to evaluate local wall thinning due to flow-accelerated corrosion (FAC). In step 1, the one-dimensional (1-D) distribution of flow turbulence and the temperature along pipes in cooling systems were analyzed with a 1-D system simulation code to obtain approximate mass transfer coefficients at structure surfaces, prior to using a three-dimensional (3-D) computational fluid dynamics (CFD) code for precise flow turbulence analysis of the major parts. In step 2, corrosive conditions were calculated with a N2H4-O2 reaction analysis code. In step 3, high FAC risk zones were determined for further evaluation for wall thinning rates, based on five parameters: temperature, pH, oxygen concentration, mass transfer coefficient, and chromium content. Then, in step 4, the 3-D CFD code was used to calculate precise mass transfer coefficients at the high FAC risk zones. In step 5, the wall thinning rates were calculated using a coupled model of electrochemical analysis and oxide layer growth analysis by applying the corrosive conditions and the mass transfer coefficients. Finally, in step 6, the residual lifetime of the pipes and the applicability of countermeasures against FAC were evaluated.This paper introduces procedures for determining major FAC parameters and evaluation procedures for high FAC risk zones by synthesizing the parameters in step 3. The procedures for determination of high FAC risk zones in a pressurized water reactor secondary cooling system are also demonstrated.

Verification and Validation of Evaluation Procedures for Local Wall Thinning Due to Flow-Accelerated Corrosion and Liquid Droplet Impingement

A six-step evaluation procedures have been proposed to evaluate the local wall thinning due to flow-accelerated corrosion (FAC) and that due to liquid droplet impingement (LDI). Corrosive conditions were calculated with a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with the three-dimensional computational flow dynamics code to obtain mass transfer coefficients at structure surfaces. Then, wall thinning rates were calculated with the coupled model of electrochemical analysis and oxide layer growth analysis by applying the corrosive conditions and the mass transfer coefficients.To apply computer simulation codes for wall thinning due to FAC and LDI to evaluate residual life and the effectiveness of countermeasures, accuracy and applicability of the codes were confirmed based on verification and validation processes. From comparison of the calculated wall thinning rates due to FAC with hundreds of measured results for secondary piping of an actual pressurized water reactor plant, it was confirmed that the calculated wall thinning rates agreed with the measured ones within a factor of 2 and the accuracy of the evaluation model for residual pipe wall thickness after 1 year of operation had an error of <20%. Finally, just the FAC simulation code was applied to evaluate the effects of oxygen injection into the feedwater line.From comparison of the calculated wall thinning rates due to LDI with measured results for vent lines of an actual boiling water reactor plant, it was confirmed that the calculated local wall thinning rates agreed with the measured ones within about a factor of 2, though there were still some outside that region.

Key Parameters to Determine Wall Thinning Due to Flow Accelerated Corrosion

In order to predict occurrence of flow accelerated corrosion (FAC) and to estimate wall thinning rate due to FAC, six step calculation procedures have been proposed. In the procedures, FAC is determined by six parameters, i.e., the flow dynamics parameter, chromium content in materials, temperature, pH, oxygen concentration, and ferrous ion concentration ([Fe2+]) in bulk water. The high FAC risk zones were evaluated by the maximum wall thinning rates, which were determined by a function of 1D FAC parameters. At the indicated high FAC risk zone, 3D distributions of mass transfer coefficients were obtained and then wall thinning rates were calculated with the coupled model of static electrochemical analysis and dynamic oxide layer growth analysis. In the paper, the effects of all parameters except that related to [Fe2+] on FAC occurrence have been discussed and then the effects of [Fe2+] on wall thinning are discussed.

D215 配管減肉予測ソフトウェアFALSETの開発(OS6 保全・設備診断技術)

Pipe wall thinning in power plants has been managed for maintaining plant integrity and safety with great importance. The target thinning phenomena are Flow Accelerated Corrosion (FAC) and Liquid Droplet Impingement Erosion (LDI). At present, the management is based on thinning rate and residual lifetime evaluation using pipe wall thickness measurement results. For the future, more safety and improvement in the management is required, and in this sense, prediction method of wall thinning is willing to be introduced. Therefore, prediction model of FAC and LDI have been constructed in CRIEPI, and to utilize these models to actual plant piping management easily, prediction software "FALSET" is developed. FALSET has equipped with essential function for pipe wall thinning management in power plants, as follows; (1) Information and condition input of plant piping system and its component, (2) Wall thinning rate evaluation with CRIEPI's FAC/LDI prediction model, (3) Loading of wall thickness measurement data files and graphics of data trend, (4) Residual lifetime evaluation considering both measured and predicted thinning rate, (5) Statistical process and graphics of thinning rate and residual lifetime for multi-piping systems. With further verification and improvement of each function, there will be a perspective for this FALSET to be utilized as a management tool in power plants.