Use ASME PCC-1 Appendix O to Fix Leaky Flanges
What is ASME PCC-1 Appendix O?
It’s all about fixing your leaky flanges by taking a deeper look at the flange assembly bolt stress and ensuring the gasket is sealing properly. ASME PCC-1 Appendix O has a lot of stress values to look up (or calculate) and using “defaults” isn’t going to help you solve real world problems. It is important to know where to get some of the stress values you will need in order to properly determine bolt torque values using ASME PCC-1 Appendix O.
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.
ASME PCC-1 Appendix O Required by PIP
Did you know that ASME PCC-1 Appendix O is required by Process Industry Practices (PIP)?
Yes, everyone knows that using ASME PCC-1 Appendix O reduces leaks and emissions.
Yes, everyone knows that using ASME PCC-1 Appendix O makes your facility safer.
Yes, everyone knows that using ASME PCC-1 Appendix O saves you money.
But not everyone knows that ASME PCC-1 Appendix O is required by PIP. Appendix O definitions like Target Assembly Gasket Stress, Sgt and Assembly Bolt Torque, Sb are being mentioned in courtroom arguments. It is a great time to start learning more about bolted flange joint assembly.
Please review PIP VESV1002 Part 4.4.3 Nozzles, Manways, and Flanges for more information regarding this PIP Specification for Vessels.
Stop Blaming the Gasket for Bad Flange Designs
Stop blaming the gasket manufacturer for your bad flange designs.
I’ve noticed the gasket manufacturers always get the blame for leaky flanges. But did the designer even consider that the flange could be governing the bolted flange joint assembly? Or did they just grab an off-the-shelf ASME B16.5/16.47 flange and assume everything would happen to work out?
There are many cases for ASME B16.5/16.47 flanges where the Target Assembly Gasket Stress, SgT, is difficult to achieve without exceeding the Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax. This means that the flange may yield and start leaking before the gasket ever reaches its optimal stress condition for sealing!
There is not much the gasket manufacturer can do for your damaged flange.
Please refer to Table O-4.2-1 inside ASME PCC-1 Appendix O for a list of ASME B16.5/16.47 governed by the Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax.
Please refer to WRC 538 to better understand which flange stresses are governing the Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax in your designs.
Change Gasket with Service Change
Thinking about changing the service of existing equipment or piping? Don’t forget the gaskets!
I’m not a big fan of changing from methane service to hydrogen service, but I also understand that changes like these are becoming more and more popular as new construction costs rise. There may be some cost savings converting existing equipment and pipelines compared to building new. However, differences in the service conditions, such as molecule size, can have a big impact on gasket selection.
Please note differences in the PCC-1 Appendix O definitions for the new gaskets including:
Target Assembly Gasket Stress, SgT
Maximum Permissible Gasket Stress, Sgmax
Minimum Gasket Operating Stress, Sgmin-O
Minimum Gasket Seating Stress, Sgmin-S
Changing the gasket Target Assembly Gasket Stress, SgT directly impacts the Selected Assembly Bolt Stress, Sbsel in ASME PCC-1 Appendix O so a complete PCC-1 Appendix O recalculation is required!