Load Factor for Evaluating Non-Planar Flaws in Carbon Steel Piping Using Limit Load Methodology

2016 ◽  
Author(s):  
Phuong H. Hoang
Keyword(s):  
Carbon Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Local Strain ◽  
Limit Load ◽  
Evaluation Methodology ◽  
Load Factor ◽  
Wall Thinning ◽  
Steel Piping

Non-planar flaw such as local wall thinning flaw is a major piping degradation in nuclear power plants. Hundreds of piping components are inspected and evaluated for pipe wall loss due to flow accelerated corrosion and microbiological corrosion during a typical scheduled refueling outage. The evaluation is typically based on the original code rules for design and construction, and so often that uniformly thin pipe cross section is conservatively assumed. Code Case N-597-2 of ASME B&PV, Section XI Code provides a simplified methodology for local pipe wall thinning evaluation to meet the construction Code requirements for pressure and moment loading. However, it is desirable to develop a methodology for evaluating non-planar flaws that consistent with the Section XI flaw evaluation methodology for operating plants. From the results of recent studies and experimental data, it is reasonable to suggest that the Section XI, Appendix C net section collapse load approach can be used for non-planar flaws in carbon steel piping with an appropriate load multiplier factor. Local strain at non-planar flaws in carbon steel piping may reach a strain instability prior to net section collapse. As load increase, necking starting at onset strain instability leads to crack initiation, coalescence and fracture. Thus, by limiting local strain to material onset strain instability, a load multiplier factor can be developed for evaluating non-planar flaws in carbon steel piping using limit load methodology. In this paper, onset strain instability, which is material strain at the ultimate stress from available tensile test data, is correlated with the material minimum specified elongation for developing a load factor of non-planar flaws in various carbon steel piping subjected to multiaxial loading.

Limit Analysis of a Pipe Section With Non-Uniform Wall Thinning

2002 ◽  
Author(s):  
Keshab K. Dwivedy
Keyword(s):  
Limit Analysis ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Structural Integrity ◽  
Pipe Wall ◽  
Limit Load ◽  
Pipe Section ◽  
Wall Thinning ◽  
Uniform Wall

Certain process piping in nuclear and non-nuclear power plants undergo pipe wall thinning due to flow assisted corrosion (FAC). This localized mechanism of corrosion combined with erosion is complex. The potential degradation of the pipe wall depends upon the water chemistry, operating temperature and pressure, flow velocity, piping material and piping configuration. The management of FAC in a power plant is performed in the following basic steps: Identification of potential locations, UT inspection of locations and characterization of pipe wall thinning, and evaluation of wall thinning to establish structural integrity and/or repair/replacement. The section of the pipe is repaired or replaced if the structural integrity cannot be established until next scheduled inspection. In the past 15 years, FAC programs have been established in nuclear power plants. Structural integrity evaluation is a part of the program. Simplified methods and rules are established in ASME Section XI code and in several code cases for verifying structural integrity. Pressure design methods are formalized for uniform and non-uniform wall thinning. However, the limit analysis methods for moment loading in the code rules are formulated for uniform thinning of the wall for simplicity. FAC related wall thinning is truly non-uniform, and treating it as non-uniform in the analysis can show additional structural margin compared to analysis conservatively assuming a uniformly thinned wall. This paper has developed simple analytical formulation of limit load carrying capability of a pipe section with non-uniform thinning. The method of analysis is illustrated with examples of actual plant situations. The formulation developed here can be used with the ASME code method to extend remaining life of FAC degraded components until the plant can plan for repair or replacement. Thus the analytical tool can help the plant owners to save resources by performing repair and replacement in a planned manner.

Effect of Circumferential Location of Local Wall Thinning Defect on the Collapse Moment of Elbow

2006 ◽  
Author(s):  
Jin Weon Kim ◽  
Yeon Soo Na ◽  
Chi Yong Park
Keyword(s):  
Carbon Steel ◽  
Internal Pressure ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Piping System ◽  
Main Concern ◽  
Wall Thinning ◽  
Bending Load ◽  
Local Wall Thinning ◽  
Steel Piping

Local wall-thinning due to flow-accelerated corrosion is one of the degradation mechanisms of carbon steel piping in nuclear power plant (NPP). It is a main concern in carbon steel piping systems in terms of the safety and operability of the NPP. Recently, the integrity of piping components containing local wall-thinning has become more important for maintaining the reliability of a nuclear piping system, and has been the subject of several studies. However, although wall-thinning in pipe bends and elbows has been frequently reported, its effect on the integrity of pipe bends and elbows has not yet been systematically investigated. Thus, the purpose of this study was to investigate the effect of the circumferential location of a local wall-thinning defect on the collapse behavior of an elbow. For this purpose, the present study used three-dimensional finite element analyses on a 90-degree elbow containing local wall-thinning at the crown of the bend region and evaluated the collapse moment of the wall-thinned elbow under various thinning geometries and loading conditions. The combined internal pressure and bending loads were considered as an applied load. Internal pressure of 0∼20 MPa and both closing-and opening-mode bending were applied. The results of the analyses showed that a reduction in the collapse moment of the elbow due to local wall-thinning was more significant when a defect was located at the crown than when a defect was located at the intrados and extrados. Also, the effect of the internal pressure on the collapse moment depended on the circumferential location of the thinning defect and mode of the bending load.

Failure Probability Assessment of Piping Systems Affected by SCC and Pipe Wall Thinning for LBB Analysis

2011 ◽  
Author(s):  
Hiromasa Chitose ◽  
Hideo Machida ◽  
Itaru Saito
Keyword(s):  
Failure Probability ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Probability Assessment ◽  
Wall Thinning ◽  
Piping Systems ◽  
Leak Before Break ◽  
Thinning Rate ◽  
Service Inspection

This paper provides failure probability assessment results for piping systems affected by stress corrosion cracking (SCC) and pipe wall thinning in nuclear power plants. On the basis of the results, considerations for applying the leak-before-break (LBB) concept in actual plants are presented. The failure probability for SCC satisfies the target failure probability even if conservative conditions are assumed. Moreover, for pipe wall thinning analysis, pre-service inspection is important for satisfying the target failure probability because the initial wall thickness affects the accuracy of the wall thinning rate. The pipe wall thinning analysis revealed that the failure probability is higher than the target probability if the bending stress in the pipe is large.

Effects of Flow Accelerated Corrosion on Piping Steady-State Vibration Evaluations

2003 ◽  
Author(s):  
Brian J. Voll
Keyword(s):  
Steady State ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Vibration Monitoring ◽  
Accelerated Corrosion ◽  
Monitoring Programs ◽  
Wall Thinning ◽  
Piping Systems ◽  
Flow Accelerated Corrosion

Piping steady-state vibration monitoring programs were implemented during preoperational testing and initial plant startup at most nuclear power plants. Evaluations of piping steady-state vibrations are also performed as piping and component failures attributable to excessive vibration are detected or other potential vibration problems are detected during plant operation. Additionally, as a result of increased flow rates in some piping systems due to extended power uprate (EPU) programs at several plants, new piping steady-state vibration monitoring programs are in various stages of implementation. As plants have aged, pipe wall thinning resulting from flow accelerated corrosion (FAC) has become a recognized industry problem and programs have been established to detect, evaluate and monitor pipe wall thinning. Typically, the piping vibration monitoring and FAC programs have existed separately without interaction. Thus, the potential impact of wall thinning due to FAC on piping vibration evaluations may not be recognized. The potential effects of wall thinning due to FAC on piping vibration evaluations are reviewed. Piping susceptible to FAC and piping susceptible to significant steady-state vibrations, based on industry experience, are identified and compared. Possible methods for establishing links between the FAC and vibration monitoring programs and for accounting for the effects of FAC on both historical and future piping vibration evaluations are discussed.

Application of Laser-Generated Ultrasound for Evaluation of Thickness Reduction in Carbon Steel Pipes

2006 ◽  
Vol 321-323 ◽  
pp. 743-746 ◽  
Author(s):  
Jong Ho Park ◽  
Joon Hyun Lee ◽  
Gyeong Chul Seo ◽  
Sang Woo Choi
Keyword(s):  
Carbon Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Guided Wave ◽  
Thickness Reduction ◽  
Steel Pipes ◽  
Time Frequency ◽  
Wall Thinning ◽  
Local Wall Thinning

In carbon steel pipes of nuclear power plants, local wall thinning may result from erosion-corrosion or flow-accelerated corrosion(FAC) damage. Local wall thinning is one of the major causes for the structural fracture of these pipes. Therefore, assessment of local wall thinning due to corrosion is an important issue in nondestructive evaluation for the integrity of nuclear power plants. In this study, laser-generated ultrasound technique was employed to evaluate local wall thinning due to corrosion. Guided waves were generated in the thermoelastic regime using a Q-switched pulsed Nd:YAG laser with a linear slit array. . In this paper, time-frequency analysis of ultrasonic waveforms using wavelet transform allowed the identification of generated guided wave modes by comparison with the theoretical dispersion curves. Modes conversion and group velocity were employed to detect thickness reduction.

Fracture Assessment of Austenitic Stainless Steel Piping With Multiple Flaws in Heat-Affected Zone

2010 ◽  
Author(s):  
Chihiro Narazaki ◽  
Toshiyuki Saito ◽  
Masao Itatani ◽  
Takuya Ogawa ◽  
Takao Sasayama
Keyword(s):  
Stainless Steel ◽  
Heat Affected Zone ◽  
Nuclear Power ◽  
Power Plants ◽  
Estimation Method ◽  
Limit Load ◽  
Low Carbon ◽  
Fracture Assessment ◽  
Steel Piping ◽  
Weld Heat

Stress corrosion cracking (SCC) has been observed as circumferential multiple flaws in the weld heat-affected zone of primary loop recirculation system piping and core shrouds made of low carbon stainless steel. In the Japan Society of Mechanical Engineers code, Rules on Fitness-for-Service for Nuclear Power Plants, there is no fracture assessment of piping with multiple flaws which are not subject to flaw combination rule criteria. Through fracture testing of piping with two circumferential flaws in the weld heat-affected zone, the limit load estimation method was used for fracture assessment of stainless steel piping.

A Feasibility Study of Noncontact Ultrasonic Sensor for Nuclear Power Plant Inspection

2017 ◽  
Vol 3 (2) ◽  
Author(s):  
Akinori Tamura ◽  
Chenghuan Zhong ◽  
Anthony J. Croxford ◽  
Paul D. Wilcox
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
Thickness Measurement ◽  
Piping System ◽  
Wall Thinning ◽  
Plant Inspection ◽  
Ultrasonic Thickness

A pipe-wall thinning measurement is a key inspection to ensure the integrity of the piping system in nuclear power plants. To monitor the integrity of the piping system, a number of ultrasonic thickness measurements are manually performed during the outage of the nuclear power plant. Since most of the pipes are covered with an insulator, removing the insulator is necessary for the ultrasonic thickness measurement. Noncontact ultrasonic sensors enable ultrasonic thickness inspection without removing the insulator. This leads to reduction of the inspection time and reduced radiation exposure of the inspector. The inductively-coupled transducer system (ICTS) is a noncontact ultrasonic sensor system which uses electromagnetic induction between coils to drive an installed transducer. In this study, we investigated the applicability of an innovative ICTS developed at the University of Bristol to nuclear power plant inspection, particularly pipe-wall thinning inspection. The following experiments were performed using ICTS: thickness measurement performance, the effect of the coil separation, the effect of the insulator, the effect of different inspection materials, the radiation tolerance, and the measurement accuracy of wastage defects. These initial experimental results showed that the ICTS has the possibility to enable wall-thinning inspection in nuclear power plants without removing the insulator. Future work will address the issue of measuring wall-thinning in more complex pipework geometries and at elevated temperatures.

309 High Temperature Impact-Fretting Wear Experiments for Evaluation of Pipe Wall Thinning Phenomena in Nuclear Power Plants

2013 ◽  
Vol 2013.49 (0) ◽  
pp. 87-88
Author(s):  
Yoshiki SATO ◽  
Akira IWABUCHI ◽  
Michimasa UCHIDATE ◽  
Hitoshi YASHIRO ◽  
Akito OYAKAMA ◽  
...  
Keyword(s):  
High Temperature ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Pipe Wall ◽  
Fretting Wear ◽  
Wall Thinning ◽  
Temperature Impact

FSI-Based Assessment of FAC-Caused Wall Thinned Piping

2009 ◽  
Author(s):  
Sun-Hye Kim ◽  
Yoon-Suk Chang ◽  
Young-Jin Kim
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Structural Integrity ◽  
Flow Characteristics ◽  
Limit Load ◽  
Bend Angle ◽  
Piping System ◽  
Integrity Assessment ◽  
Wall Thinning ◽  
Analysis Scheme

Lots of investigations on failures of wall thinned piping have been carried out since the accident of Surry unit 2 in USA. From these preceding efforts, flow accelerated corrosion (FAC) which is a kind of wall thinning phenomenon is revealed main factor of failure of pipes in nuclear power plants. However, there are a few researches which directly take into account of flow characteristics and geometric changes for stress assessment of FAC-caused wall thinned piping. In this paper, structural integrity assessment employing a fluid-structure interaction (FSI) analysis scheme is performed on pipes representing secondary piping system of PWR which consists of straight pipes and elbows of various bend angles. Prior to the assessment, CFD analyses are conducted to predict plausible wall thinning location by considering flow and geometric parameters such as bend angle and radius of elbow. Then, for typical pipe geometry, detailed limit load analyses are performed to calculate maximum stress caused by turbulence and velocity of flow near the wall thinned part. Through these kinds of detailed parametric analyses, effects of FSI were observed, which should be considered for assessment of FAC-caused wall thinned piping.

Review of Pipe Wall Thinning Mechanism Study and its National Project in Japan

2011 ◽  
Author(s):  
Hiroshi Miyano ◽  
Naoto Sekimura ◽  
Masayuki Takizawa ◽  
Masaaki Matsumoto
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Pipe Wall ◽  
High Reliability ◽  
Safety Margin ◽  
Fiscal Year ◽  
Mechanism Study ◽  
Wall Thinning ◽  
Piping Systems ◽  
The Government

For nuclear power plants, the four major requirements are 1) high safety, 2) high reliability, 3) economical competitiveness, and 4) minimum environmental impact. However, it is still difficult to completely avoid problems concerning structural materials caused by stress corrosion cracking (SCC) and for piping systems caused by flow accelerated corrosion (FAC) and liquid drop impingement (LDI). Since especially FAC and LDI are uncertain phenomena as pipe wall thinning, there are the piping rupture accident risks on all piping systems under the specific conditions. In Japan, after August 2004, the accident of the secondary pipe rupture in Mihama Power Plant Unit 3, The Kansai Electric Power Co., Inc. (KEPCO), R&D projects on pipe wall thinning phenomena and mechanism have been employed by many organizations. On the other hand, evaluation of the safety and reliability of piping systems of long term operating plants and with the special attention to seismic condition have been requested. It was requested to enable evaluation of pipe wall thinning and its reliability with more accuracy. This project was programmed under the government budget from 2006 to 2010 fiscal year according to the Strategy Load-Map for Ageing Management generated by the society of industry, government and academia [1]. As the milestone for the first half decade of the load-map, the project had these achievements: 1) Establish computer program for FAC simulation, 2) Clarify droplet behavior for LDI prediction, 3) Simplified calculation model of pipe wall thinning for seismic evaluation, 4) Evaluate safety margin of thinned piping by FAC or LDI.

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