A FEW TIPS ON CLOSED FEEDWATER HEATERS

In response to many inquiries about operating and troubleshooting closed feedwater heaters, we offer the following from the chapter "Achieving Reliability" of the course notes of our coppyrighted course, "Closed Feedwater Heaters-Mechanical Aspects":

Symptoms and Possible Causes of TTD and DCA Temperature Changes,

TTD Greater Than Design
A. Noncondensible buildup.  Check Operating Vents.
B. Excessive pressure drop in desuperheating zone of horizontal heater.
Check condensing zone pressure.
C. Water leaking into DSH zone.  Check for tube leaks or shroud leak in vertical channel head down heater.         .
D. Shell side tube corrosion.  Check for tube leaks.
E. Tubeside fouling.  Check for snake skins inside tubes.
F. Tubeside pass-partition leaks.  Check gasket on pass-partition covers or weld cracks at tubesheet.

DCA Greater Than Design
A. Low liquid leve. Check the liquid level.
B. Steam entering the drain cooler.  Check for water hammer caused by steam collapsing in DC,  It sounds like firecracker popping noise at the shroud welds and through tube holes at the end plate.
C. Horizontal split pass long drain cooler may have low liquid level or steam entering thrugh shoursd weld cracks,  Check the liquid level.  Check for shroud weld cracks.  Listen for water hammer noise.
D.  Vertical heater may have low liquid level or steam entering through shroud weld cracks.  Check for shroud weld cracks.  Listen for water hammer noise.

Check the Position of the Drain Valve Stem.
Knowing the position of the drain valve stem is useful because most drain lines and drain valve ststems are sized to carry much more flow than the normal drains flow rate.  Consequently, if a minor tube break occurs, the drain system will probably be able to handle the extra drain flows.  It is likely that the excessive drain flow will not have caused a noticable change in the DCA temperature, but it will be idicated by a cgange in the position of the drain valve stem.

Note:  The HEI Closed Feedwater Heater Specification requires that the valve stem position should be checjed ib every shift.

Following are failures that can be repaired and ones that cannot be repaired but which can be treated so as to slow the rate of deterioration:

Repairable Feedwater Heater Failures

A. Tube-to-tubesheet joint attachment.
B. Impingement plate failures and damage.
C. Vibration failure damage.
D. Shroud weld failures when the flat divider plate is welded to the arcuate section.

Failures that are Not Repairable But Can be Treated so as to Slow the Rate of Deterioration

A. Tube failure in the top row of the DC in horizontal heaters at the end plate caused by steam entering the DC through the annular spaces betweeb the tube ODs and the tube hole IDs.
B.  Tube failures in the top row of the DC in horizontal heaters at the back of the tubesheet caused by failure of the weld joining the DC flat divider plate to the back of the tubesheet.
C. Tube failures in the outer bends of U-tubes caused by vibration.
D. Tube failures in the inner bends of U-tubes caused by Stress Corrosion Cracking (SCC).
E. Tube failures at the back of the tubesheet caused by SCC and/or vibration.