The Impact of Flow Accelerated Corrosion (FAC) on Feeder Life Cycle Management

2009 ◽  
Author(s):  
Mahesh D. Pandey ◽  
Mikko I. Jyrkama ◽  
Edward M. Lehockey
Keyword(s):  
Life Cycle ◽  
Wall Thickness ◽  
Safety Concern ◽  
Probabilistic Method ◽  
Life Cycle Management ◽  
Economic Losses ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Flow Accelerated Corrosion ◽  
The Impact

Wall thinning of outlet feeder piping by flow accelerated corrosion (FAC) is a serious form of degradation affecting some CANDU® stations. The general and localized loss of wall thickness is typically highest at or near welds and changes in pipe geometry due to increased velocity or turbulence. While the process is not a high safety concern because catastrophic failure is unlikely, feeder wall thinning may result in significant economic losses as a result of forced shutdowns for repair and replacement. Accurate modelling and prediction of feeder replacements and the probability of feeder failure is not only important for continued fitness-for-service, but essential for feeder life cycle management (LCM). This paper discusses some of the key issues related to feeder FAC, and presents a probabilistic method for modelling the wall thinning process. The wall thickness loss due to FAC is modelled using a random rate model, while the probability of feeder failure is based on an empirical approach. The developed methodology allows the estimation of the remaining life of both inspected and uninspected feeder populations, while methodically accounting for the uncertainties in the problem.

Techniques for Improved Reliability of Wall Thinning Estimation

2006 ◽  
Author(s):  
Yogendra S. Garud
Keyword(s):  
The Other ◽  
Remaining Life ◽  
Data Filtering ◽  
Large Database ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Simplified Method ◽  
Flow Accelerated Corrosion ◽  
The Impact ◽  
Thinning Rate

Wall thinning in pressure retaining components, especially due to the flow-accelerated corrosion, has been a significant factor affecting the safety and unplanned system downtimes. On the other hand, overestimating the impact of possible wall thinning often leads to unnecessary or expensive inspections and replacements. The simplified or quick (short-cut) methods of analysis and prediction often lack the requisite degree of accuracy and confidence. This paper presents a few techniques for better analysis of the wall thinning data to address these issues. These techniques make use of the statistical methods, pattern recognition, and optimization to perform a robust data filtering and thinning rate estimation that accounts for measurement uncertainty. The techniques are discussed with application to a large database and an inspection program. The impact of these analytical improvements is presented in comparison with results of the simplified method of analysis. The results include both the margin on remaining life and the projected wall thinning rates, with implications for inspections.

Numerical Calculation of Shear Stress Distribution on the Inner Wall Surface of CANDU Reactor Feeder Pipe Conveying Two-Phase Coolant

2007 ◽  
Author(s):  
Jong Chull Jo ◽  
Dong Gu Kang ◽  
Kyung Wan Roh
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Wall Thickness ◽  
Shear Stress Distribution ◽  
Cfd Analysis ◽  
Two Phase ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Local Areas ◽  
Flow Accelerated Corrosion

Two-phase flow fields inside feeder pipes of a CANDU reactor have been simulated numerically using a CFD (computational fluid dynamics) code to calculate the shear stress distribution which is the most important factor to be considered in predicting the local areas of feeder pipes highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. The CFD approach with schemes used in this study to simulate the turbulent flow situations inside the CANDU feeder pipes had been verified by showing a good agreement between the investigation results for the failed feedwater pipe at Surry Unit 2 plant in U.S. and the CFD calculation. Sensitivity studies of the three geometrical parameters such as angle of the 1st and 2nd bends, length of the 1st span between the grayloc hub and the 1st bend, and length of the 2nd span between the 1st and the 2nd bends had already been performed. In this study, the effects of void fraction of the primary coolant coming out from the exit of pressure tubes containing nuclear fuels on the fluid shear stress distribution at the inner surface of feeder pipe wall have been investigated to find out the local areas of feeder pipes conveying two-phase coolant, where are highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. As the results of CFD analysis, it is seen that the local regions of feeder pipes of the operating CANDU reactors in Korea, on which the wall thickness measurements have been performed so far, are not coincided with the worst regions predicted by the present CFD analysis where is the connection region of straight & bend pipe near the inlet part of the bend intrados. Finally, based on the results of the present CFD analysis a guide to the selection of the weakest local positions where the measurement of wall thickness should be performed with higher priority has been provided.

Supplementary Technical Basis for ASME Section XI Code Case N-597

2005 ◽  
Author(s):  
Doug Scarth
Keyword(s):  
Wall Thickness ◽  
Structural Integrity ◽  
Computer Code ◽  
Nuclear Regulatory Commission ◽  
Original Design ◽  
Acceptance Criteria ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Technical Basis ◽  
Flow Accelerated Corrosion

Efforts to develop clear and conservative methods to measure and evaluate wall thinning in nuclear piping have been underway since the late 1980’s. The Electric Power Research Institute (EPRI) carried out a successful campaign to address programmatic issues, such as locating and predicting flow-accelerated corrosion (FAC) degradation. This included developing a computer code (CHECWORKS), a users group (CHUG), and a comprehensive program guideline document for the effective prediction, identification and trending of flow-accelerated corrosion degradation. U.S. Nuclear Regulatory Commission (NRC) guidelines are provided in the NRC Inspection Manual Inspection Procedure 49001. At the same time, committees under Section XI of the ASME Boiler and Pressure Vessel Code have addressed evaluation of structural integrity of piping subjected to wall thinning. Code Case N-480 of Section XI provided acceptance criteria that focused on primary piping stresses, with evaluation based on a uniform wall thinning assumption for evaluating the minimum wall thickness of the piping. However, when applying this methodology to low pressure piping systems, Code Case N-480 was very conservative. Code Case N-597 was first published in 1998, and supercedes Code Case N-480. The current version is N-597-2. Code Case N-597-2 provides acceptance criteria and evaluation procedures for piping items, including fittings, subjected to a wall thinning mechanism, such as flow-accelerated corrosion. Code Case N-597-2 is a significant improvement over N-480, containing distinct elements to be satisfied in allowing the licensee to operate with piping degraded by wall thinning. The Code Case considers separately wall thickness requirements and piping stresses, and maintains original design intent margins. The Code Case does not provide requirements for locations of inspection, inspection frequency or method of prediction of rate of wall thinning. As described in the original technical basis document published at the 1999 ASME PVP Conference, the piping stress evaluation follows very closely the Construction Codes for piping. Five conditions related to industry use of Code Case N-597-1 have been published by the NRC in Regulatory Guide 1.147, Revision 13. A number of these issues are related to a need for additional explanation of the technical basis for the Code Case, such as the procedures for evaluation of wall thickness less than the ASME Code Design Pressure-based minimum allowable wall thickness. This presentation addresses these NRC conditions by providing additional description of the technical basis for the Code Case.

The Impact of Probabilistic Modeling in Life-Cycle Management of Nuclear Piping Systems

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
M. D. Pandey ◽  
D. Lu ◽  
D. Komljenovic
Keyword(s):  
Life Cycle ◽  
End Of Life ◽  
Wall Thickness ◽  
Probabilistic Models ◽  
Structural Integrity ◽  
Life Cycle Management ◽  
Limiting Factor ◽  
Piping System ◽  
Practical Case ◽  
The Impact

Flow accelerated corrosion (FAC) is a serious form of degradation in primary heat transport piping system (PHTS) of the nuclear reactor. Pipes transporting hot coolant from the reactor to steam generators are particularly vulnerable to FAC degradation, such as tight radius pipe bends with high flow velocity. FAC is a life limiting factor, as excessive degradation can result in the loss of structural integrity of the pipe. To prevent this, engineering codes and regulations have specified minimum wall thickness requirements to ensure fitness for service of the piping system. Nuclear utilities have implemented periodic wall thickness inspection programs and carried out replacement of pipes prior to reaching an unsafe state. To optimize the life-cycle management of PHTS, accurate prediction of time of replacement or “end of life” of pipe sections is important. Since FAC is a time-dependent process of uncertain nature, this paper presents two probabilistic models for predicting the end of life. This paper illustrates that the modeling assumptions have a significant impact on the predicted number of replacements and life-cycle management of the nuclear piping system. A practical case study is presented using wall thickness inspection data collected from Canadian nuclear plants.

Managing Flow Accelerated Corrosion in Carbon Steel Piping in Nuclear Plants

2004 ◽  
Author(s):  
Z. H. Walker
Keyword(s):  
Carbon Steel ◽  
Steam Generator ◽  
Wall Thickness ◽  
Degradation Mechanism ◽  
Reactor Core ◽  
Operating Conditions ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Flow Accelerated Corrosion ◽  
Steel Piping

In 1996, Flow Accelerated Corrosion (FAC) was identified as a degradation mechanism affecting carbon steel outlet feeder pipes in CANDU® (CANadian Deuterium Uranium) reactors. The maximum rate of FAC was estimated to be <0.120 mm/year. In response, wall thickness inspection programs have been implemented to identify and measure the minimum wall thickness in outlet feeder pipes. These data are necessary to ensure fitness-for-service of the feeder pipe. These data, together with the thermalhydraulic and geometric parameters for the measured feeders, are also very useful for developing empirical wall thickness models. Such models can be used to enhance the understanding of feeder wall thinning leading to an improved capability to predict future wall thickness minima and their locations. The determined dependency of the wall-thinning rate on thermalhydraulic conditions can be used to quantify the potential benefits of maintenance activities, such as steam generator cleaning. Activities such as steam generator cleaning are generally viewed as beneficial in recovering lost thermal efficiency, thereby reducing the severity of the thermalhydraulic conditions by reducing the amount of quality (steam phase) exiting the reactor core. Finally, when wall thickness models are applied to data from different plants, there is the potential of identifying operating conditions that can lead to lower rates of wall loss. This paper addresses the aforementioned important issues associated with FAC of ASME PVP Class 1 carbon steel piping.

Comprehensive Integrity Assessment of Carbon Steel Feeder Pipes/Elbows Subject to Wall Thinning

2009 ◽  
Author(s):  
Xinjian Duan ◽  
Michael J. Kozluk ◽  
Ming Li
Keyword(s):  
Life Cycle ◽  
Life Cycle Management ◽  
Burst Pressure ◽  
Accelerated Corrosion ◽  
Integrity Assessment ◽  
Pressure Tests ◽  
Management Plans ◽  
Service Conditions ◽  
Low Probability ◽  
Flow Accelerated Corrosion

This paper discusses the comprehensive integrity assessment of feeders fabricated from normalized pipe and elbow piping items subject to Flow Accelerated Corrosion (FAC) during in-service conditions. The arguments are based on the improved mechanistic understanding of FAC; review of international piping rupture events; examinations of removed feeders; burst-pressure tests of prototypical and ex-service feeder piping sections, the minimum acceptable wall thickness for feeder piping; and station feeder life cycle management plans. It is concluded that rupture of feeder pipe due to FAC is a very low probability event.

Numerical Evaluation of Wall Thinning Profile in Separation and Union Pipe due to Flow Accelerated Corrosion

2014 ◽  
Author(s):  
Shun Watanabe ◽  
Kimitoshi Yoneda
Keyword(s):  
Wall Thickness ◽  
Power Plants ◽  
Pipe Wall ◽  
Branch Pipe ◽  
Residual Lifetime ◽  
Accelerated Corrosion ◽  
Geometry Factor ◽  
T Tube ◽  
Wall Thinning ◽  
Flow Accelerated Corrosion

Flow Accelerated Corrosion (FAC) is a pipe wall thinning phenomenon to be monitored and managed in power plants with high priority. In Japan, its management has been conducted with conservative evaluation of thinning rate and residual lifetime of the piping based on wall thickness measurements. However, noticeable case of the wall thinning occurred at separation and union pipe. In such pipe system, it is a problem to manage a section beneath reinforcing plate of T-tube pipe and a crotch of T-joint pipe; wall thickness measurement with high accuracy is difficult to conduct in the region by using ordinary ultrasonic testing devices. In this study, numerical analysis for separation and union parts of T-tube and T-joint pipes was conducted, and wall thinning profile by FAC was evaluated by calculating mass transfer coefficient and geometry factor. Based on these results, applicable wall thinning management for T-tube and T-joint pipes was considered. In the case of union flow from main and branch pipe, the wall thinning profile of T-tube showed the tendency of increase at main pipe like semielliptical region. On the other hand, noticeable profile appeared at crotch in T-joint although it was found that geometry factor of T-joint in this flow pattern was half the value of T-tube. An alternative evaluation method to previous one might be needed for such semielliptical region in T-tube and crotch in T-joint.

Probabilistic Estimation of Flow-Accelerated Corrosion Rate at the Welded Joints of the Nuclear Piping System

2012 ◽  
Author(s):  
Dongliang Lu ◽  
M. D. Pandey ◽  
M. I. Jyrkama
Keyword(s):  
Wall Thickness ◽  
Welded Joints ◽  
Probabilistic Method ◽  
Limiting Factors ◽  
Piping System ◽  
Practical Case ◽  
Primary Coolant ◽  
Accelerated Corrosion ◽  
Candu Reactors ◽  
Flow Accelerated Corrosion

Feeder piping is an integral part of the heat transport system (HTS) that supplies the primary coolant from the reactor to the steam generator in CANDU reactors. One of the life limiting factors of the feeder pipes is the highly localized wall thinning caused by the flow-accelerated corrosion (FAC) at the welded joints of the pipes. To ensure the fitness-for-service of the piping system, periodic inspections of the pipe wall thickness and estimation of the FAC thinning rate at the welded joints are needed. A major challenge of FAC rate estimation at the welded joints is that the initial wall thickness is known precisely, since the grinding process before the welding introduces initial thinning in the pipes. Using the nominal wall thickness without considering this initial thinning is likely to overestimate the FAC rate. Another difficult is the sizing error in the wall thickness measurements, which also needs to be properly accounted. This paper develops a sound probabilistic method for the FAC estimation for the welded joints considering both the initial thinning and sizing error. Predictions regarding the lifetime of individual welded joints are also obtained from the proposed method. A practical case study of the problem in a nuclear plant is presented.

Prediction of the Local Areas of CANDU Feeder Pipes Highly Susceptible to Wall Thinning Due to Flow-Accelerated Corrosion

2007 ◽  
Author(s):  
Dong Gu Kang ◽  
Jong Chull Jo
Keyword(s):  
Wall Thickness ◽  
Geometrical Parameters ◽  
Cfd Analysis ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Sensitivity Studies ◽  
Flow Accelerated Corrosion ◽  
Thickness Measurements ◽  
Selection Of ◽  
Good Agreement

Flow fields inside feeder pipes have been simulated numerically using a CFD (computational fluid dynamics) code to calculate the shear stress distribution which is the most important factor to be considered in predicting the local regions of feeder pipes highly susceptible to FAC (flow-accelerated corrosion)-induced wall thinning. The CFD approach with schemes used in this study to simulate the flow situations inside the CANDU feeder pipes has been verified by showing a good agreement between the investigation results for the failed feedwater pipe at Surry Unit 2 plant in U.S. and the CFD calculation. Sensitivity studies of the three geometrical parameters such as angle of the 1st and 2nd bends, length of the 1st span between the grayloc hub and the 1st bend, and length of the 2nd span between the 1st and the 2nd bends have been performed. As the results of CFD analysis, it is seen that the local regions of feeder pipes of Wolsung Unit 1 in Korea, on which the wall thickness measurements have been performed so far, are not coincident with the worst regions predicted by the present CFD analysis where is the connection region of straight & bend pipe near the inlet part of the bend intrados. Finally, based on the results of the present CFD analysis a guide to the selection of the weakest local positions where the measurement of wall thickness should be performed with higher priority has been provided.

Iatan Desuperheater Pipe Failure Caused by FAC: September 28, 2007

2010 ◽  
Author(s):  
Chong Chiu ◽  
Lance B. Gockel
Keyword(s):  
Wall Thickness ◽  
Pipe Wall ◽  
Preliminary Evaluation ◽  
Pipe Failure ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Plant Personnel ◽  
Serious Injury ◽  
Flow Accelerated Corrosion ◽  
Flow Blockage

At approximately 11:40 AM on May 9, 2007, Iatan Unit 1 experienced a catastrophic rupture of a 4 inch superheater (SH) attemperator spray line after nearly 27 years of commercial operations. At the time of the rupture, several plant personnel were in the immediate vicinity performing maintenance on a plugged coal feeder. Plant operators immediately initiated a plant shutdown. This incident resulted in two fatalities and one serious injury. Subsequent examination of the ruptured line indicated significant pipe wall thinning had occurred, leading to the sudden failure of the pipe pressure boundary and the pipe rupture event. The preliminary evaluation of the failed pipe determined that flow accelerated corrosion (FAC) was the likely failure mechanism. To prevent this and similar events, the PII team recommends the following actions be taken to identify other potential areas which may have similar characteristics to the failed pipe: 1. Employ the EPRI method CHECKWORKS (as has been implemented) to identify the susceptible areas. 2. Supplement the EPRI model with connected flow modeling techniques to identify additional inspection areas. 3. If the measured wall thickness is less than 30% of the minimum allowable wall thickness, replace or repair the pipe immediately. 4. If the measured wall thickness is less than the minimum allowable wall thickness (as specified by the B31.1 code), but no less than 30% of the minimum allowable, perform a safety risk assessment. If the risk is determined acceptable, replace or repair the pipe at the next planned plant outage with temporary compensatory actions (such as caution tags, leak flow blockage facilities, etc.). 5. Identify and replace all throttled gate valves and replace them as soon as practical. Until these valves are replaced, utilize NDE techniques to monitor the pipe wall thinning downstream of the valves and replace pipe based on the above criteria in 3 and 4.

Sign in / Sign up

Export Citation Format

Share Document