Gas Turbine and CCGT Plants

GT Outlet / HRSG Inlet Cycling Joint (Hot Casing)

Externally Insulated Ducts (Hot Casings)

DEKOMTE has many designs for hot casing exhaust systems of gas turbine systems. In order to establish a suitable design of casing, support, stiffeners and expansion joint, the stress calculations and fatigue of materials must be considered. Most significant in the calculation process is the cycling and types of starts that a plant will run.

The temperature gradient of the casing to the fabric clamping area will create high stresses, increasing fatigue and reducing life. Square ducts can have more serious problems with the corner regions due to high stresses.

In many plants the failure and replacement of fabric expansion joints is considered a normal and routine maintenance. With weld repairs to steel parts, adjacent stiffeners and duct cracks and regular outage activity.

DEKOMTE has more than two decades of experience in designing two shift, high cycling expansion joint systems. The goal is a complete solution which encompasses the whole scope of duct, frame, adjacent insulation and expansion joint to give a lifetime maintenance free solution.

DEKOMTE Belt expansion joint 10W as base load solution suitable for small GT applications; max. 320 cycles.

DEKOMTE Membrane expansion joint ME suitable for large axial movements; max. 10,500 cycles.

DEKOMTE 3WA Hightech expansion joint as cycling solution with ultra-long durability suitable for large axial and lateral movements.

Expansion joint design issues

  • Steel frame design
  • Fabric and bolster
  • Fixing system

Short term solution

  • Weld repairs to frame and duct
  • Regular replacement of fabric
  • External insulation

Long term solution

  • New steel part arrangement
  • Improved duct interface
  • New external insulation
  • New fabric and bolster design
  • New fixing and convector design
Dimension inside 7000 x 8000 mm
Temperature max. 670 °C
Pressure 50 mbar
Movement axial: -200 mm
lateral: 100 mm
Thermal transient cyclic operation
Maximum stress 400 N/mm²
Load cycles 250 000

Example of operating parameters for the hot casing design of a fabric expansion joint

Installed DEKOMTE expansion joint 3WA in operation.

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