Replace Rusty Nuts and Bolts

Do you reuse rusty nuts and bolts after opening a flange pair?

It’s true that a little surface rust is not going to reduce the bolt area enough to change the bolt properties in a significant way. However, surface rust greatly increases the Nut Factor K needed in the ASME PCC-1 Appendix O calculation. I do not like using large Nut Factor K values in my ASME PCC-1 Appendix O calculations so please replace your rusty nuts and bolts when opening flange pairs during your next turnaround. 

The applied torque required to meet the Selected Assembly Bolt Stress, Sbsel may vary wildly from bolt to bolt because breaking the frictional forces from rust varies from bolt to bolt. The only recourse for engineers is to increase the Nut Factor, K for all bolts to ensure the average applied torque is high enough to meet the Selected Assembly Bolt Stress, Sbsel. In a practical sense, this means a higher amount of torque is required to meet the Selected Assembly Bolt Stress, Sbsel to make up for this variation. I prefer to replace rusty nuts and bolts with new nuts and bolts because they make it easier to meet the Selected Assembly Bolt Stress, Sbsel. 

New nuts and bolts are an inexpensive way to help prevent leaky flanges.

Unsure where any of the values in your torque tables come from? Metalmark Engineering loves checking torque tables against the real world case to determine the source of flange leaks.