This paper references slide 12 of the slide presentation for explaining further the Ameren "5%-Rule" expected remaining service life criteria evaluation for the AmerenUE Labadie unit 4, 5A LP feedwater heater.
A practical industry operating record criteria is proposed as a general guideline as to when to plan scheduling the re-sleeving of cuprous alloy tubed feedwater heaters, both high-pressure and low-pressure.
With longer time spans between major generating unit outages to plan a re-bundling, time-to-failure for a heat exchanger with advanced pluggage may not time well with those opportunities. So a predictive tube-failure rate model of remaining service life becomes invaluable; for instance, as to when to take a Spring mini-outage for interim measures such as a low-cost re-sleeving to avert larger losses. In the case of the Labadie 4-5A LPFWH, an avoided additional -16mw de-rate which otherwise may have occurred by Sept. 16, 2009. The 4-5A's re-sleeving decision was enacted by March of 2009, and in-service by June of 2009. Sleeve delivery was about 8 weeks.