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Combined-cycle power stations are characterized by relatively high energy efficiency and are capable of operating flexibly. As a result, CCP stations are helping to drive the energy transition. However, this flexible mode of operation can present challenges for operators.

At a large US power producer, several cracks had been discovered on the HP attemperator spray lines. This was due to the attemperator spray water block valves developing undetected leak-by. The leak-by led to severe quenching of the steam pipe which eventually caused thermal fatigue cracking. The existing DP flow transmitters were unable to detect the leak-by, particularly when the fluid flows were low, as they are designed for relatively high flow under normal operation. In addition, when these plants are operating in low load conditions and during start-up and shutdown, the potential of tube stress is higher. This, in turn, means the risk of long-term damage is higher which is extremely costly for the plant.

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Site engineers, therefore, began to look for a solution that would determine when these block valves were starting to degrade. FLEXIM F601 ultrasonic flowmeters were installed on the HP and RH attemperator spray lines to evaluate flow detection effectiveness. The F601 flowmeter proved to have many advantages for this application: FLUXUS is able to capture the entire flow range and even leaks. It can replace the established DP flowmeter for process control purposes, providing reliable and continuous leakage detection. It is non-invasive which means it can be retrofitted easily without any process interruption, pipework, or subsequent inspection and documentation. There is no pressure loss and, therefore, no energy reduction. The non-invasive flowmeter does not come into any contact with the pressurized hot spray water which means there is no maintenance required. As a result, operating expenses are almost zero.

Since the installation of FLEXIM technology, the site engineers are now able to detect attemperator spray block valve leak-by and take corrective action to repair these important service valves as quickly as possible. Thanks to FLEXIM’s flowmeters, this US company can mitigate damage to their HRSG pressure parts ensuring lower replacement cost, more reliable unit operation, and avoiding unplanned downtime at all costs.

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The client is extremely satisfied with FLEXIM’s technology for spray water valve monitoring. They decided to equip their RH and HP spraywater lines with permanent devices to continuously measure the flow for process control and monitor leakage. They are now moving towards installing FLEXIM technology on their entire CCGT fleet. Once again, FLEXIM has proven to be the ideal solution.


  • Leakage detection due to low flow resolution down to 0,01m/s - NO blind spot
  • Extremely dynamic measurement
  • Cost-efficient and convenient retrofit without opening the pipe
  • Virtually free of maintenance (no parts in touch with spray water)
  • High accuracy and repeatability
  • No pressure, no energy loss
  • Outstanding zero-point stability