jbirdphoenix
Mechanical
- Jan 7, 2025
- 1
Regards best practices for hot bolt torquing and general questions on how different companies approach torque values for a Plant site and any rules of thumb applied.
First question: When do you apply hot torquing? My experience says the rule of thumb is when processes hit the 400F mark. This is specific to un-insulated flange joints.
Second question: Dual threat, sealing at ambient temperatures and then heat-up. The yield stress of the bolted assembly changes with temperature; at about 400F the change is dramatic. You still need to maintain gasket crush to seat the gasket, however, there is a risk, upon heat-up of yielding the bolt at temperature. How do you address this? Do you use the yield stress value at temperature when hot torquing?
Third question: General rule of thumb for bolt stress is to keep it between 40-70% of yield. I've heard many reasons for this, but the answers sometimes conflict. Example: if you go too low, you don't get bolt stretching and may be prone to loosening. If you go too high, there is a risk of overtightening and yielding the bolt due to variations inherent with torquing.
Thanks in advance.
First question: When do you apply hot torquing? My experience says the rule of thumb is when processes hit the 400F mark. This is specific to un-insulated flange joints.
Second question: Dual threat, sealing at ambient temperatures and then heat-up. The yield stress of the bolted assembly changes with temperature; at about 400F the change is dramatic. You still need to maintain gasket crush to seat the gasket, however, there is a risk, upon heat-up of yielding the bolt at temperature. How do you address this? Do you use the yield stress value at temperature when hot torquing?
Third question: General rule of thumb for bolt stress is to keep it between 40-70% of yield. I've heard many reasons for this, but the answers sometimes conflict. Example: if you go too low, you don't get bolt stretching and may be prone to loosening. If you go too high, there is a risk of overtightening and yielding the bolt due to variations inherent with torquing.
Thanks in advance.
