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Check valve analysis and prioritization (CVAP) methodology and wear prediction

This thesis emphasizes on plant reliability and safety hinges on the proper functioning of several check valves. Over the Past decade, the Nuclear Industry Check Valve Group (NIC), industry organizations, non-Intrusive diagnostic equipment vendors and engineering consulting firms have proactively developed solutions to address generic problems that result in unplanned maintenance and avoidable plant unavailability. Several utilities have performed reevaluations of safety- and reliability-significant check valve installations, and have instituted programs that employ a combination of testing, inspection, and maintenance to improve plant reliability. There is a wide variance in tools and techniques used to address check valve reliability. These tools range from those based principally on qualitative information to others that apply a combination of qualitative and quantitative methods to assess valve condition.
The Project describes the need for and benefits of applying quantitative wear and fatigue predictions to screen and prioritize safety-related, economically significant, and/or production- critical, “mega-watt robber” check valves. This technique has been used successfully at several U.S. nuclear units to identify misapplied check valves and to prioritize inspection and maintenance activities based on each valve’s propensity for accelerated internal wear. The population of valves recommended for inspection and/or modification can be reduced, allowing effort to be focused on those valves that are more likely to degrade prematurely. This Check Valve Analysis and Prioritization (CVAP) methodology results in an analytical framework for check valve condition monitoring and condition based maintenance. The methodology can provide a benefit to check valve applications regardless of whether they fall under the IST, INPO-SOER 86-03, and/or Condition Monitoring programs.

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3 CHAPTER 1 INTRODUCTION Alternatives to Quantitative Predictive Analysis The alternatives to quantitative screening, prioritization, and optimization are either extensive disassembly and visual inspection or trending qualitative data. Disassembly and inspection is the most conclusive means of determining the internal condition of a check valve wear; however, cumulative fatigue usage cannot be detected by inspection unless it has progressed to a level of a visible crack. Disassembly and inspection is resource-intensive and introduces the risk of future valve performance problems caused by improper valve re-assembly. Also, a program based solely on disassembly doesn’t necessarily guarantee reliable operation. For example, a US plant with a mature disassembly-and-inspect program recently reported four unexpected failures not captured by their tracking and trending program. Valve disassembly on a sampling basis will always play a key role in assuring the reliability of a check valve population; however, this method requires that it be applied judiciously. A “red, yellow and green light” graded approach to valve disassembly would shift the focus to the inspection of valves in the “yellow light” stage prior to the onset of incipient failure. The plant can reallocate maintenance resources by not performing unnecessary disassemblies on valves in a "green light" good condition. Plant safety and reliability will improve because incipient failures will be intercepted before they enter a "red light" failed condition QUALITATIVE VS. QUANTITATIVE PERFORMANCE PREDICTION On the most fundamental level, all check valve populations, regardless of the program they are classified under, can be thought of as requiring three key activities: 1. Screening and evaluation to identify bad actors 2. Performance improvement activities. 3. Re-prioritization based on performance feedback. All three tasks require a mix of qualitative and quantitative data to determine valve condition. For example, the approach underlying the Check Valve Analysis and

International thesis/dissertation

Autore: Dr Gurudutt Sahni Contatta »

Composta da 44 pagine.


Questa tesi ha raggiunto 525 click dal 04/05/2007.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.