TOFD Automatic Ultrasonic Testing for Condition Monitoring of Coke Drums

Cracking and bulging in welded and internally lined pressure vessels that work in thermal-mechanical cycling service have been well known problems in the petrochemical, power and nuclear industries. In spite of this problem has been studied during the last fifty years, published literature and industry surveys show that similar problems still occur nowadays. Typical examples of this problem are the coke drums in the delayed coking units refinery process. Delayed coking units are among the refinery units that have higher economical yields. To shut down these units represents a high negative economical impact in refinery operations. Also, the maintenance costs associated with repairs are commonly very high. Cracking and bulging occurrences in the coke drums, most often at the weld areas, characterize the history of the operation of delayed coking units. To anticipate through wall cracking in these coke drums, AUT (automatic ultrasonic testing); Dual TOFD (time of flight diffraction) and the Phased Array technique simultaneous inspection system was selected among other inspection techniques as a condition monitoring tool during an unit turnaround. The inspection methodology in combination with fracture mechanics was used to classify discontinuities as acceptable and non-acceptable. This indicated approach helped to optimize the workscope during the turnaround and establish guidelines for inspection and repair of the delayed coker unit. This work presents the different steps followed during the inspection and fitness for service evaluation. Also, this study shows advantages and disadvantages of the AUT-Phased Array technique.

French RPV PTS Assessment: An Overview of EDF Research and Development in Progress on Thermalhydraulic, Materials and Mechanical Aspects

A significant extensive Research & Development work is conducted by Electricite´ de France (EDF) related to the structural integrity re-assessment of the French 900 and 1300 MWe reactor pressure vessels in order to increase their lifetime. Within the framework of this programme, numerous developments have been implemented or are in progress related to the methodology to assess flaws during a pressurized thermal shock (PTS) event. The paper contains three aspects: a short description of the specific French approach for RPV PTS assessment, a presentation of recent improvements on thermalhydraulic, materials and mechanical aspects, and finally an overview of the present R&D programme on thermalhydraulic, materials and mechanical aspects. Regarding the last aspect on present R&D programme, several projects in progress will be shortly described. This overview includes the redefinition of some significant thermalhydraulic transients based on some new three-dimensional CFD computations (focused at the present time on small break LOCA transient), the assessment of vessel materials properties, and the improvement of the RPV PTS structural integrity assessment including several themes such as warm pre-stress (WPS), crack arrest, constraint effect ....

Mechanical Stress Improvement Process (MSIP) Used to Prevent and Mitigate Primary Water Stress Corrosion Cracking (PWSCC) in Reactor Vessel Piping at V.C. Summer

During the October 2000 refueling outage at the V.C. Summer Nuclear Station, a leak was discovered in one of the three reactor vessel hot leg nozzle to pipe weld connections. The root cause of this leak was determined to be extensive weld repairs causing high tensile stresses throughout the pipe weld; leading to primary water stress corrosion cracking (PWSCC) of the Alloy 82/182 (Inconel). This nozzle was repaired and V.C. Summer began investigating other mitigative or repair techniques on the other nozzles. During the next refueling outage V.C. Summer took mitigative actions by applying the patented Mechanical Stress Improvement Process (MSIP) to the other hot legs. MSIP contracts the pipe on one side of the weldment, placing the inner region of the weld into compression. This is an effective means to prevent and mitigate PWSCC. Analyses were performed to determine the redistribution of residual stresses, amount of strain in the region of application, reactor coolant piping loads and stresses, and effect on equipment supports. In May 2002, using a newly designed 34-inch clamp, MSIP was successfully applied to the two hot-leg nozzle weldments. The pre- and post-MSIP NDE results were highly favorable. MSIP has been used extensively on piping in boiling water reactor (BWR) plants to successfully prevent and mitigate SCC. This includes Reactor Vessel nozzle piping over 30-inch diameter with 2.3-inch wall thickness similar in both size and materials to piping in pressurized water reactor (PWR) plants such as V.C. Summer. The application of MSIP at V.C. Summer was successfully completed and showed the process to be predictable with no significant changes in the overall operation of the plant. The pre- and post-nondestructive examination of the reactor vessel nozzle weldment showed no detrimental effects on the weldment due to the MSIP.

Managing the Aging of Critical Components of Nuclear Power Plants

Managing the aging of critical components within a nuclear power plant is a challenging task that ultimately determines the value and revenue generation of the plant. This paper will provide an overview of a process for determining the critical components of the power plant and describe a long term equipment reliability and aging management program for these components. This program determines the potential failure modes and rates for each critical component part and identifies the effective repair, replacement, inspection, diagnostic, and maintenance activities. It also describes a tool for determining the optimal timing of these activities to produce the most value for the power plant. This program is currently being implemented at several power plants. As nuclear plants strive to reduce costs, extend life and maximize revenue, the aging management program and the supporting tools summarized in this paper can enable development of a long term, cost efficient plan to manage the aging of the plant’s critical components and systems.

Finite Element Modeling of Blade-Rotor System in Turbomachinery

Modal analysis of Blade-Disk system under the effect of bearing flexibility is investigated. The present study has considered soft to hard bearing flexibility. The main objective here is to read from the modal analysis results the frequencies that are carrying out some information on blade vibration. The modal analysis shows that that there are few frequencies that are changing with the change of bearing flexibility. These are shaft mode only, shaft-blade nature, disk mode only, disk-blade nature, and blade mode only. The shaft-blade modes are the ones of concern here.

Data Analysis for RPV Life Management Studies of Temperature Measurements From Monitoring of Safety Injection Fluid in Spent Fuel Pit Cooling and Treatment System Storage Tank

In Electricite´ de France (EDF) probabilistic analyses for Reactor Pressure Vessel (RPV) life management, it’s used to take the temperature of the Reactor Spent fuel Pit cooling and treatment System storage tank as a constant. The aim of our study is to evaluate the stability of this temperature. Since 1999, we collected for several sites, and several nuclear plant units, the temperature of the Reactor Spent fuel Pit cooling and treatment System storage tank. Our results illustrate that this temperature depends on the season and the site. We first proposed to give a modelisation of this temperature dependent of the external temperature; even if this modelisation leads to a good R2, it’s not optimum. We also proposed to explain the temperature using the temperature of the essential service water or for lack the temperature of the river. In the case of extreme quantile study (meaning low temperature), we proposed to use the normal approximation, which seems to be conservative.

Integrated Plant Life Cycle Management: The IAEA Contribution

For the past couple of decades there has been a change of emphasis in the world nuclear power from that of building new Nuclear Power Plants (NPP) to that of taking measures to optimize the life cycle of operational plants. National approaches in many countries showed an increase of interest in Plant Life Management (PLIM), both in terms of plant service life assurance and in optimizing the service or operational life of NPP. A strong convergence of views is emerging from different National approaches, particularly in the area of the economic aspects of NPP operation and in the evolution in the scope of NPP PLIM. The latter can directly affect the cost of electricity from NPP in an increasingly competitive environment. The safety considerations of a NPP are paramount and those requirements have to be met to obtain and to extend/renew the operating license. To achieve the goal of the long term safe, economic and reliable operation of the plant an Integrated Life Cycle Management Programme (ILCMP) is necessary. Some countries already have advanced PLIM Programmes while others still have none. The ILCMP objective is to identify all that factors and requirements for the overall plant life cycle. The optimization of these requirements would allow for the minimum period of the investment return and maximum of the revenue from the sell of the produced electricity. Recognizing the importance of this issue and in response to the requests of the Member States the IAEA Division of Nuclear Power implements the Sub-programme on “Engineering and Management Support for Competitive Nuclear Power”. Four projects within this sub-programme deal with different aspects of the NPP life cycle management with the aim to increase the capabilities of interested Member States in implementing and maintenance of the competitive and sustainable nuclear power. Although all four projects contain certain issues of PLIM there is one specific project on guidance on engineering and management practices for optimization of NPP service life including decommissioning. This particular project deals with different specific issues of NPP life management including aspects of ageing phenomena and their monitoring, issues of control and instrumentation, maintenance and operation issues, economic evaluation of NPP life cycle management including guidance on its earlier shut down and decommissioning. The paper describes in detail the full scope IAEA activities on different issues of NPP life management and some of its achievements in this field during the nearest past as well as plans for the future.

French Procedure for Ageing Management Program of Safety Components

Managing ageing and remaining lifetime of an industrial facility is a concern that must be taken in account by utility as soon as possible in daily activities. The corresponding actions engaged in France are based on 3 major step that are described in the paper: • routine maintenance, • exceptional maintenance, • systematic and periodic review of safety important components and structures sensitive to ageing to assure the effectiveness of the maintenance actions and maintain a high safety level of the plant with a good competitiveness. Following different on-going programs on ageing management of different components, EDF developed its own approach, based on IAEA guidelines, in order to systematically review all the ageing management programs implemented on its 3-loop plants. The methodology is done in 3 steps: • selection of components and justification, • degradation mechanism analysis, • synthesis and consequences on maintenance programs. After a presentation of each step of the procedure a quick overview of the status of application in France is done. Comparison of the methodology with similar methodology used in different other countries is done to close the paper.

Study and Application of Health Monitoring by Fiber Optic Sensors in Civil Engineering

In civil engineering, the smart health monitoring method by use of fiber optic sensor is a new approach that evaluates the structural health situation. The current status in applications of fibre optic structural health monitoring in civil engineering structures with a brief introduction of the advantages, basic principles of fibre optic sensors is described in this paper. Leakage detection and potential damage to pipelines are emphasized. Finally, existing problems for packing and implementing fibre optic sensors in structures are discussed.

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

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.