Stop Using Class 1 Bolts

I’m still seeing too many low strength bolts in the field. Please check your bolts to make sure they are the high strength version. 

It is difficult for engineers like me to fix bolted flange leaks caused by low strength bolts without first replacing the bolts with the high strength version. There can be a 70 ksi (480 MPa) yield strength difference between the two. 

Why can’t the bolted flange assembly seal? Well the bolts yield before the Minimum Gasket Seating Stress, Sgmin-S is reached. This is especially common for the folks that are still using air impact wrenches to torque their bolts. Adding more bolt load, which is the first solution tried in the field, does not help because the bolts keep stretching as more load is applied. 

I like to have enough bolt load to reach the Target Assembly Gasket Stress, SgT. This is almost always impossible with low strength bolts.