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Entrance effects are inconsistent and difficult to predict or estimate. Significant engineering judgment is required to incorporate them into an FAC program.
In a given power plant, several thousand piping components might be susceptible to FAC damage.
Without an accurate FAC analysis of the plant, inspection drawings and a piping database that includes examination and replacement histories, the only way to prevent leaks and ruptures is to examine every susceptible component during every outage — which would constitute a very costly examination program.
Early predictive tools
Tools for predicting FAC wear rates were first developed in the United States for nuclear power plants. In the late 1980s, a U.S. nuclear power plant experienced a rupture of a condensate system elbow, which resulted in 4 fatalities. The cause of the failure was found to be FAC. Subsequently, nuclear power plants expanded their inspection programs to reduce the risk of pipe ruptures caused by FAC.
To support the nuclear industry effort, EPRI developed
In the early 1990s, EPRI released a new computer code for nuclear plants called CHECWORKS. This program integrated and updated the capability of the previous codes, and was written to take full advantage of the recent advances in computer technology. Additionally, the capability was added to help utilities manage related plant data and to automate many of the analysis and reporting tasks conducted during an inspection outage.
In the mid-1990s, the rupture of a feedwater line in a midwestern fossil plant, later determined to be caused by FAC, led to many fossil plant owners expanding and refining their FAC inspection programs. In reaction to this, EPRI developed CHECUP to rank the relative rate of wall loss due to FAC at specific piping locations in fossil and co-generation power plants and industrial steam plants.
The program is designed to help utilities calculate wall loss of single-phase piping segments and components since plant start-up, and thereby increase the likelihood that damaged components will be identified, examined and repaired or replaced before component failure.
Fossil FAC advisor
In 2010, EPRI launched an effort to provide a new predictive tool for FAC in fossil plants. It was determined that a complete overhauling of the nuclear plant-based CHECWORKS code for fossil plant applications would be cost-prohibitive. As a result, a phased approach is under way in which CHECWORKS will be modified for fossil use to include several key capabilities.
The new software, released in August 2010, is Fossil FAC Advisor (FFA). Like CHECUP, FFA allows plant engineers to model the wall thickness of piping and other components, and to compare this modeling to historical data in order to identify areas susceptible to FAC and to plan repair and replacement.
However, FFA also offers a number of advantages compared to the previous CHECUP program. For example, FFA allows users to model both single- and two-phase flows. Unlike CHECUP, which was web-based, FFA also enables users to store inspection data. This capability allows utilities to refine future predictions based on historical data. Figure 2 shows the modeling feature; Figure 3 is an example of a typical wastage rate analysis.