Prompt Leak Detection for High Pressure Feedwater Heaters

I. THE NEED. A. In high pressure feedwater heaters, a tube leak quickly claims several neighboring tubes as collateral victims. B. Prompt detection of the initial leak would save the neighboring tubes from damage and preclude a potential turbine water induction incident. II. EXAMPLE. A. A Midwest generating station replaced 12 old high pressure heaters. The new heaters contained 304N SS tubes. In one of the new heaters, an unknown localized contaminant caused a single tube leak within the first year. This single leak went undetected until several surrounding tubes were lost due to impingement from the initial leak. And even the conservatively sized normal and emergency drains were overwhelmed, causing the heater to trip on high level. III. CAPABILITY OF SMART LEVEL CONTROLS. A. There are three known possibilities that would cause high drain-flow conditions in a feedwater heater. 1. High Unit Load. 2. The upstream feedwater heater is out of service. 3. A tube leak. B. Traditional Local level controls can sense high flow conditions, but cannot tell why. Most systems will alarm the opening of the emergency drain valve, but by that time, the collateral tube damage is usually severe. “Smart” Level Controls have the capability to distinguish between these conditions, thus allowing it to give early notification of a tube leak, before collateral damage becomes severe.