Fibre-optic temperature monitoring of a steam mixer

Reheat steam mixer


  • Vertical reheat steam mixer at a Finnish power station


  • Proving of optical fibre distributed-temperature monitor by field trial
  • To determine the global temperature distribution around the drain of the mixer, where previous failures have occurred


  • Extremely small window of opportunity to install equipment
  • Large mixer mass requires several days to cool to allow access


  • Optical fibre system and replacement insulation system produced in advance of plant shutdown
  • Armoured fibre spot-welded using techniques developed beforehand

Fibre optic system


  • Installation completed and tested within shutdown timescales
  • Successful monitoring of start-up and automatic drain operation achieved
  • Demonstrated that automatic drain operation leads to large temperature variations between top and bottom of the drain
  • Change in drain procedure shown largely to eliminate this thermal gradient


  • Global temperature distribution provided information as to the root cause of the problem
  • Minor changes to drain procedure eliminated thermal stress and hence fatigue damage
  • Extremely low cost of residuals left on plant

Plant Integrity