TL;DR
Increasing feedwater makeup is the earliest indicator of an HRSG tube leak. Confirm with an acoustic survey or infrared thermography from outside the casing. The unit must be shut down for any tube repair.
What you might see
- feedwater makeup demand rising with no change in load
- audible hissing or roaring noise from the HRSG casing
- localized rust staining on the HRSG casing exterior near a tube row
- flue gas CO or steam analyzer reading anomaly downstream of the leak location
Likely causes
Flow-accelerated corrosion (FAC) on economizer or LP evaporator tubes, especially at elbows with high fluid velocity
Thermal fatigue cracking at the tube-to-header weld from thermal cycling during frequent starts and stops
Under-deposit corrosion from poor feedwater chemistry allowing oxygen or iron to deposit
Erosion at tube support contacts from steam or gas velocity vibration
Required tools
- Feedwater makeup flow DCS trend
- Infrared thermal camera
- Acoustic detector or stethoscope probe
- Heat-resistant PPE for HRSG casing approach
Safety first
- The HRSG casing and steam piping are at elevated temperature. Maintain safe standoff distance during external surveys and wear heat-resistant PPE.
- An HRSG tube leak requires a controlled shutdown. Do not attempt to run the unit to failure.
Procedure
- 1
Trend feedwater makeup flow over the past 24 hours. A sustained increase of more than 5% above the baseline at the same load is a significant indicator.[1]
- 2
Walk down the HRSG casing exterior and listen for hissing. Inspect for rust staining or blistered paint, which indicates a wet area beneath the casing panel.
Warning: The HRSG casing surface can exceed 200 degrees C. Do not touch the casing without heat-resistant gloves and maintain 1-meter clearance from hot panels. - 3
Use an infrared thermal camera to scan the casing exterior from a safe distance. A cool spot (wet surface cooling) or a hot spot (steam impingement) pinpoints the leak location.
- 4
If the leak is confirmed, notify the shift supervisor and begin a controlled shutdown per the HRSG operating procedure.
- 5
After cooldown and isolation, perform an internal inspection to locate the leaking tube. Pressure test the suspect circuit to confirm the leak location.
- 6
Repair by tube plug-and-leave or tube section replacement per the ASME or OEM repair code. Restore water chemistry before restarting.
Sources
Vogt Power Vogt-Nemag HRSG (Heat Recovery Steam Generator) general technical documentation, Vogt Power
HRSG tube leak detection, flow-accelerated corrosion, and tube repair, general power generation references (general)
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