HRSG Tube Failure Diagnostic Guide (3rd Edition)

Heat Recovery Steam Generator (HRSG) tubes provide the media for extraction of useful energy from the waste heat in gas turbine exhaust at combined cycle power plants (GT-CCs) or from heat generated by process streams at petrochemical facilities.  HRSGs have undergone substantial changes in design over the past 15 years as the technology matured from small PURPA and Cogeneration units to today’s large power plants. HRSG tube failures are an infrequent occurrence at most units.  Typically, there is less than one failure per year.  However, the costs associated with unexpected forced outages for merchant units or for units in deregulated markets encourage efforts to anticipate problems.  Like boiler tubes in radiant boilers, HRSG tubes are subject to a variety of service related damage.  Damage mechanisms vary in severity based on materials selected, local operating temperatures and stresses, and the interaction between vibration and corrosion mechanisms. Because HRSGs have operated at generally lower metal temperatures than older radiant boilers, creep and creep fatigue have not been common failure causes.  Instead, corrosion fatigue, flow accelerated corrosion, and damage at locations with weld defects have occurred at many units.  Other corrosion mechanisms such as pitting and acid gas attack to cold end tubes have also contributed to premature HRSG tube failures.  In addition to fundamental design differences, modern HRSGs are also subject to a wider range of duty in power applications.  Baseload operation was normal for smaller HRSGs, but today’s deregulating electric power market will require many new large HRSGs to operate in cycling duty.

TFDG Front Cover

HRSG Inspection Planning Guide (2nd Edition)

Inspection is part of routine maintenance for any Heat Recovery Steam Generator (HRSG).  Visual inspections are performed at regular intervals in accordance with the requirements of regulatory bodies and insurers.  In the US statutory inspections are mandated typically every year although some jurisdictions allow justification for longer intervals.   Additional inspections are sometimes performed to establish the baseline condition of the HRSG (often early in life, but not always) or to perform less frequent special inspections to confirm component integrity. 

The high costs associated with unexpected forced outages for merchant units or for units in deregulated markets encourage efforts to anticipate problems in HRSG components that are susceptible to service related damage. Damage mechanisms vary in severity based on materials selected by the HRSG OEM, local operating stresses and the interaction between vibration and corrosion mechanisms.  In addition to fundamental design differences, modern HRSGs are also subject to a wider range of duty in power applications.  Baseload operation was normal for smaller HRSGs, but today’s deregulating electric power market requires many new large HRSGs to operate in cycling duty.  This has resulted in many units experiencing damage much sooner than would be expected with baseload operation.  Some cycled units have experienced tube failures and leaks after only a few thousand hours of operation.  The more severe duty from cycling operation reveals design weaknesses earlier at many newer combined cycle plants, as well as not infrequently fabrication-related deficiencies.

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Established in 1988, Tetra Engineering has more than 25 years experience providing solutions to the power industry. We specialize in solutions for HRSGs, conventional boilers & steam-cycle balance of plant.

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