What are the pros and cons of using film-forming products versus a more traditional treatment program? What recommendations do you have for HRSG module replacements? How will cycling the gas turbine impact the life expectancy of the HRSG? What are the most common problems on HRSGs for a peaking unit?
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Amines are often used to lower corrosion in the water or wet steam phase of the water steam cycles by forming a hydrophobic and pH buffering layer on top of the steel surfaces. A part of the dosed amines will be flushed with feedwater into the evaporator sections, where they are thermally cracked into organic acids and carbon dioxide. These organic acids could result in elevated cation conductivity of the steam, rendering the control of steam purity difficult. These acids might also result in lowering the pH and could increase potential for corrosion, especially at locations where the organic acids are accumulated. In GE’s experience, film forming amines should only be used in plants that are equipped with a condensate polishing system.
For users experiencing FAC, our typical recommendation is to upgrade certain sections with FAC-resistant alloys (such as P11 or P22). For units that are experiencing creep and fatigue-related damage, we would consider recommending geometry modifications to reduce stresses in the most critical areas. Some users have an HRSG life monitor system installed. We are able to collect valuable information regarding remaining lifetime of critical components, which we can use to provide pertinent recommendations about the most cost-effective upgrade.
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In principle, cycling GT operation can result in accelerated lifetime consumption of pressure parts, control valves and desuperheaters. The most common problems we see on HRSGs behind cycling gas turbines are:
Cracks and weld failures due to premature fatigue damage on pressure parts, especially on High Pressure Superheater and Reheater headers and manifolds.
Cracks on desuperheater liners and erosion on water injection control valves.
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