1. Understand the Importance of Dwell Time
- Dwell time is the period between initial torque and retorques during flange joint installation. It addresses gasket short-term creep and embedment losses, which are critical for joint performance.
2. Select the Right Dwell Time Based on Gasket Type
- PTFE Gaskets: Expanded PTFE (ePTFE) greatly benefits from a short 15-minute dwell time, reducing stress loss to as low as 7.5%, Restructured PTFE (rPTFE), such as Tealon™, exhibits similar performance when allowed to relax 15 minutes to one hour, with minimal improvement beyond that. In contrast, skived PTFE (sPTFE) shows nearly twice as much relaxation with 4 times longer dwell time, making it a less reliable choice for long-term sealing performance.
- Compressed Fiber Gaskets (CFG): One hour is typically sufficient for these gaskets.
- Metallic Gaskets: Spiral wound and kamprofiled gaskets show minimal relaxation, even without retorque. Kamprofiled gaskets retain stress well over 24 hours.
3. Apply Appropriate Torque Levels
- For high-relaxation materials, proper torque is critical. Under-tightening leads to excessive stress loss and leakage, while over-tightening can cause gasket damage.
4. Consider Alternative Assembly Patterns
- The Alternative Assembly Pattern #3, as per ASME PCC-1, saves up to 45% of assembly time compared to the traditional cross-pattern method, without compromising gasket performance.
5. Balance Dwell Time and Maintenance Downtime
- Tailor dwell time to the specific gasket material and operational needs. Shorter dwell times, as brief as 15 minutes, can be effective for many gaskets, reducing downtime without sacrificing reliability. There is often little to no gain in waiting 24 hours to do a retorque.
By customizing dwell time to gasket type and installation conditions, you can improve plant efficiency, reduce maintenance downtime, and ensure reliable sealing performance.
For more information about Optimizing Dwell Time for Bolted Flanged Joint Installations, read the full technical article!
