Extraction Steam Line Expansion Joints
Features to look for to Assure Long Service Life in Extraction Steam Line Expansion Joints
PROBLEM: Bellows Failure In An Extraction Steam Line Causes A Severe Loss In Power Generating Effi ciency And
Revenue. The bellows failure is frequently due to one or more of the following:
- 1. The exhaust steam causes the cover to vibrate or resonate until it fails and disappears.*
- 2. The high velocity extraction steam causes the liner to vibrate or resonate until it fails and disappears.*
- 3. The high steam fl ow rates and proximity to rotating equipment can cause the extraction steam piping to
vibrate causing bellows fatigue failure.
- 4. Chloride stress corrosion cracking of the bellows.
- 5. When one expansion joint in the cluster fails the out rush of steam can destroy adjacent expansion
joints, particularly if they are not designed properly.
*Either 1. or 2. above will cause instant failure of the bellows.
SOLUTION: Senior Flexonics Pathway’s Recommended Design For Extraction Steam Line Expansion Joints Eliminates
- 1. Senior Flexonics Pathway recommends Inconel-625 bellows to eliminate the possibility of chloride
stress corrosion. This is inexpensive insurance
- 2. An alloy liner and cover to prevent erosion corrosion.
- 3. Minimum 1/8” thickness for the liner to resist vibration and fl utter due to high velocity extraction
- 4. Minimum 3/16” thickness cover to resist vibration and fl utter due to high velocity exhaust steam
and exhaust from any adjacent failed expansion joint.
- 5. Install an “Eddy Ring” at the downstream end of the cover to interrupt turbulence and eddy currents
that could cause bellows to vibrate and fail from fatigue.
- 6. Use multiple ply bellows to attenuate (deaden) vibration.
- 7. Weld all tie rod nuts to ensure that the nuts will not vibrate free.