HRSGs and boilers |
HRSG preservation during shutdowns: a key issue often neglected
The preservation of HRSG fluid and steam systems during shutdown periods is an important objective at any power plant. However, this is often one of the most neglected aspects of HRSG operations. Improper layup will lead to increased corrosion, which can be the initiator of serious major failure mechanisms that will affect plant availability. Tetra Engineering has assisted plant owners and operators in developing practical preservation strategies tailored to the expected shutdown duration, equipment condition and available site infrastructure
Misha Gadher*, Mechanical and Thermal Process Engineer, and James Malloy**, Senior Consultant, Tetra Engineering Europe, Sophia-Antipolis, France
Plant preservation refers to a strategy used to limit corrosion and damage of power plant equipment during shutdown periods (or “layup”), including steam turbines, gas turbines, boilers, HRSGs and other steam-cycle BOP. The main objective is to isolate the critical equipment from corrosive environments. A well-considered and properly implemented preservation procedure protects plant reliability and ensures restart readiness during periods when the plant is not generating.
Why preservation matters more than ever
Preservation demand has increased in recent years as plant owners face greater uncertainty over when units may be required to operate. Although global electricity demand is increasing, the changing generation mix (increased generation by renewable sources) means that many fossil fuelled plants are operating less frequently. In some cases, operations have changed from baseload to cycling, and in others, plants are put on standby for extended periods before being called back into service. Protecting the boiler and steam cycle components from corrosion during these idle periods becomes increasingly important as the number and duration of the standby time grows.
The consequences of inadequate preservation Without adequate preservation, boiler and steam-cycle components can be exposed to corrosive conditions on both the gas-side and waterside. General corrosion, pitting, crevice corrosion, and under-deposit corrosion are common corrosion mechanisms that occur during layup. General corrosion during layup is often responsible for generation of large quantities of iron oxides. A thin layer of corrosion over the huge surface area of
Figure 1. External boiler tube corrosion Figure 2. Corrosion of HRSG pressure parts
Figure 3. Corrosion of steam turbine blades.
carbon steel creates a large volume of oxides. The oxides are transported to and deposited on heat transfer surfaces when the unit returns to operation. The deposits impede heat transfer and provide a crevice where chemical impurities can concentrate, further increasing corrosion. Pitting requires a stagnant fluid and therefore virtually only occurs when the unit is shut down. Again, oxygen provides a corrosive environment, especially if chlorides are present. Pitting can progress rapidly enough to penetrate a tube wall in a few weeks. For cycling units, a more common and more insidious failure scenario is that a pit will form and grow partially through the tube wall while the unit is shut down and in layup. Upon return to
*
misha.gadher@
tetra-eng.com **
james.malloy@
tetra-eng.com 16 | October 2026 |
www.modernpowersystems.com
Figure 4. Internal boiler tube corrosion.
service, the pit acts as a stress riser and a corrosion–fatigue crack forms and grows. The corrosion–fatigue crack eventually causes failure of the tube.
Tetra recently had experience with an HRSG that had been relocated and left without any preservation for several years. Advanced corrosion of the boiler, including pressure parts, was evident (Figures 1 and 2). Another instance showed heavy corrosion on turbine blades, see Figure 3, while other examples include severe internal boiler tube corrosion (Figure 4) and corroded external tube surface (Figure 5). Clearly this is not the ideal condition of the equipment for reliable service and resulted in high costs to assess and, where necessary, repair the damage.
All photographs: Tetra Engineering
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