Monitoring High-Pressure Spray Water in Overheated Steam Lines in Combined-Cycle Gas Turbine Power Plants

By installing Flexim flowmeters, we can now quickly detect leaks in high-pressure spray valve assemblies that regulate steam temperature and implement corrective measures to promptly replace critical valves. The installation of Flexim flowmeters minimizes damage to our HRSG system components, ensuring lower replacement costs and more reliable unit operation.
— Eugene Eagle, P.E., Heat Recovery Steam Generator Engineer.

Combined-Cycle Gas Turbine Power Plants

Combined-cycle gas turbine power plants are characterized by two key features in power generation:

• High Efficiency – Significantly better energy savings compared to other types of power plants.
• Flexible Operation Easily adjustable power output to meet electricity demand.

As a result, these plants are playing a vital role in advancing the global energy transition. However, flexible operation also introduces technical challenges, particularly pipeline degradation.

Common Issue: Steam Pipe Damage Due to Leaking Valves

In combined-cycle gas turbine and cogeneration power plants, heat recovery steam generators (HRSGs) and steam attemperators frequently experience premature damage due to inefficient valve performance.

A major energy company in the western United States (serving 8 million customers and operating over 110 power plants) has repeatedly encountered severe corrosion in the steam pipes of attemperators,leading to localized system shutdowns and extremely high repair costs.

Causes & Consequences:

• Leaking Valves: Cold water infiltrates the steam pipes instead of being sprayed as a mist (which would fully evaporate before reaching pipe bends). (hoàn toàn bốc hơi trước khi tới đoạn uốn cong).
• Thermal Shock: Cold water contacting hot pipes causes thermal shock, resulting in pipe cracking due to thermal fatigue.
• CHigh Remediation Costs:
  • Replacing a single attemperator steam pipe segment: $400,000 or more.
  • Replacing an entire tube module/harp due to end-of-life failure: Millions of USD.

Solution to solves challenges from EMERSON

Existing differential pressure (DP) flow sensors are unable to detect leaks, particularly at low liquid flow rates. Comparing inlet and outlet temperatures also lacks the precision needed to identify leaking valves. Consequently, plant engineers sought a more effective method to detect leaks early and prevent more severe damage.

Once again, Flexim’s non-invasive clamp-on flow measurement technology proved to be the ideal solution. The primary advantage of external ultrasonic technology (clamp-on ultrasonics) is the ability to conduct on-site testing to verify equipment reliability before purchase and deployment. This case was no exception.

Flexim engineers utilized the portable FLUXUS® F601 device to demonstrate accurate measurement capabilities directly on the system. The primary challenge was the constrained installation space, but the compact ultrasonic sensors of the FLUXUS® were adaptable to even the most complex positions.

Following a convincing demonstration, the plant decided to install the fixed FLUXUS® F731 system for the heat recovery steam generator. The installation required no system downtime, as the sensors are externally clamped onto the pipe, avoiding contact with the process fluid—resulting in no wear and virtually no maintenance.

Key Advantages of FLUXUS®:
✔ Ultra-Low Flow Detection: The inertia-free ultrasonic principle enables detection of even minimal leaks.
✔ Absolute Stability: Paired and specifically calibrated sensor sets ensure FLUXUS® accurately displays "0" when there is no flow.
✔ Early Warning System: Technicians can now instantly detect valve leaks and perform timely repairs, preventing severe system damage.

Results

The plant has planned to install FLUXUS® across all their combined heat and power (CHP) systems!

Key Benefits of FLEXIM (EMERSON) Clamp-On Ultrasonic Flow Measurement Solution

• Ultra-Small Leak Detection: Absolute zero-point stability and high resolution, even at low flow velocities (0.01 m/s).
• Easy Installation: No pipe cutting or system shutdown required.
• No Pressure Loss: Non-invasive design ensures no impact on system pressure.
• Lifecycle Cost Savings: No wear and virtually maintenance-free operation.