A NACE International paper, HRSG Tube Failures: Prediction, Diagnosis and Corrective Actions highlights the challenge of these failures:
Many HRSGs were originally designed for base load operation. Recent economic factors have led to drastically increased cycling of many units. This has exacerbated the rate of failures.
These leaks can lead to forced outages that create associated costs including fines, lost time and replacement power purchases, which can exceed $100,000 USD per incident.
Heat recovery steam generator (HRSG) tubes are stressed by thermal expansion and contraction of the tubes from the combustion turbine exhaust gas. Optimizing steam temperature control can extend the life of the tubes. Monitoring the tubes with acoustic sensors can also help provide early warning to address leaks before they lead to unplanned downtime.
I connected with Emerson’s Juan Panama who explained that fatigue and stress cracking can occur in welds or the tubes themselves, or that poor welds could cause pinhole leaks. Leaks in the tubes themselves (outside of a weld area) are typically caused by corrosion processes, localized overheating, or incorrect metallurgy.
Juan noted that small super heater and re-heater tube leaks are difficult to detect, as no visible indications are present.
Without sensors to detect leaks, plant staff traditionally has checked by going into an outage and shutting down the HRSG (to allow steam to condense back into water to make leaks more visible), or if a leak is large enough by observing an increase in water usage at the control system. Continue Reading ▶
