Hub Length Impacts Sfmax

Flange hub length has a big impact on the Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax. Make sure you get it right.

I’ve presented ASME PCC-1 Appendix O to facilities all across the United States. One not-so-obvious mistake I’ve found reviewing their torque tables pertains to the flange hub length. Let’s go over a couple of issues:

One facility assumed no flange hubs in the Sfmax calculation for their welding neck flanges. This ensures that the effect of Longitudinal Hub Stress, SH and Radial Flange Stress, SR cannot govern (because they are not calculated). This approach is not recommended as it does not represent reality and is unconservative. 

Another facility assumed full length hubs for their ASME B16.5 flanges in the Sfmax calculation when shorter hubs were actually used in the plant. The shorter flange hubs still complied with ASME B16.5 but meant they could not rely on the standard torque tables they were using. 

Is anyone reviewing the torque tables at your facility? Today is a great day to get your review started.