Flanges yielding before the gasket is properly sealed? 

That is what you are risking when you allow Sfmax to govern the Selected Assembly Bolt Stress, Sbsel inside of the ASME PCC-1 Appendix O calculation. Please reconsider flange selection if the Maximum Permissible Bolt Stress before Flange Damage, Sfmax is limiting the bolt torque applied to the bolted flange joint assembly.

It is important to understand the seven load combinations included in the WRC 538 analysis. That is why Metalmark Engineering created this flange diagram to help visualize what each of the seven flange load combinations are checking for. I find it to be helpful when trying to investigate which load(s) is governing the Maximum Permissible Bolt Stress before Flange Damage, Sfmax. 

The Maximum Permissible Bolt Stress before Flange Damage, Sfmax governs the bolt stress applied to the bolted flange joint assembly for many Class 150 and Class 300 standard ASME B16.5/16.47 flanges. 𝐏𝐥𝐞𝐚𝐬𝐞 𝐝𝐨 𝐧𝐨𝐭 𝐨𝐯𝐞𝐫𝐥𝐨𝐨𝐤 𝐭𝐡𝐞 𝐒𝐟𝐦𝐚𝐱 𝐜𝐚𝐥𝐜𝐮𝐥𝐚𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 ASME standard 𝐟𝐥𝐚𝐧𝐠𝐞𝐬.

Does temperature matter for bolting flanges? 

I am often asked which flange yield stress value to use in the ASME PCC-1 Appendix O calculation. On one hand using the ambient air temperature makes perfect sense because it is the temperature the flange is assembled at. On the other hand using the operating temperature makes sense because higher temperatures can significantly lower the yield stress. The fact is that both need to be considered before selecting the Yield Stress (Sy) used in the determination of the Maximum Permissible Bolt Stress before Flange Damage, Sfmax.

The Modified Yield at Operating (S’yo) often governs over the Yield at Assembly (Sya) if:

1. Fraction of Gasket Load Remaining after Relaxation (ϕg) is close to 1

2. The the Yield at Operating (Syo) is 12.5% less than the Yield at Assembly (Sya)

This means that flanges with spiral wound gaskets and flanges operating at temperatures much greater than assembly temperature are susceptible to the Modified Yield at Operating (S’yo) governing over the Yield at Assembly (Sya). Please consider both assembly and operating temperatures when selecting the Yield Stress (Sy) used to find Sfmax.

When I think about phi, g, I think about relaxation. But have we been too relaxed about phi, g? 

ASME PCC-1 Appendix O allows a default Fraction of Gasket Load Remaining after Relaxation (ϕg) of 0.7 if no data is available. I have found that this statement leads designers to use the “default” value for too many gasket types. 0.7 is too high for some PTFE gaskets and other gaskets with high compressibility and can lead to leaky flanges over time. Please consider your gasket material before selecting the Fraction of Gasket Load Remaining after Relaxation (ϕg) needed in the ASME PCC-1 Appendix O calculation. 

Did you know that the Gasket Load Remaining after Relaxation (ϕg) may be lower for thicker gaskets? Please consider the possibility of using a lower Gasket Load Remaining after Relaxation (ϕg) value when increasing compressible gaskets from 1/16” to 1/8” thickness. 

Unsure what “default” Fraction of Gasket Load Remaining after Relaxation (ϕg) your internal spreadsheets are using? Metalmark Engineering offers on-site training to teach your team how to use modern software solutions.

Can you calculate gasket area?

Out of all of the complexities regarding modern gaskets, Gasket Area should not be something that designers are still getting wrong. 

And yet here we are…

I’ve met Owner/Operators who love to order gaskets with a larger outer diameter than the raised face outer diameter so they can “see the gasket”. That’s fine enough but using that outer gasket diameter in ASME Appendix 2 Flange and ASME PCC-1 Appendix O calculations is not. Please be careful not to include the gasket area outside of the raised face diameter. 

Another common calculation mistake arises when the gasket diameter fits within the flange raised face diameter. Many times designers use the gasket raised face diameter instead of the actual gasket diameter. This is usually because the raised face diameter is the “default” value in the spreadsheet they are using. Please be careful to use the actual gasket area when it resides within the flange raised face diameter.

Are the ASME Appendix 2 Flange and ASME PCC-1 Appendix O calculations causing difficulties for your overworked engineering department? Did you know Metalmark Engineering offers on-site training to teach your team how to use modern software solutions?

We need to have a heart-to-heart talk about the Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax. 

I see a lot of really high “default” values to make sure it never governs the Selected Assembly Bolt Stress, Sbsel inside of the ASME PCC-1 Appendix O calculation. This is an unconservative approach because it ignores the actual flange stresses that can be attributed to leaky gaskets. 

I prefer that the Target Assembly Gasket Stress, SgT governs the Selected Assembly Bolt Stress, Sbsel instead of Sfmax inside of the ASME PCC-1 Appendix O calculation. In other words, I do not want the flange to yield before the gasket seals properly. That is exactly why I like to make sure I calculate an accurate Maximum Permissible Bolt Stress Prior to Flange Damage, Sfmax value by iterating on all seven flange stress combinations. 

The Maximum Permissible Bolt Stress before Flange Damage, Sfmax governs the bolt stress applied to the bolted flange joint assembly for many Class 150 and Class 300 standard ASME B16.5/16.47 flanges. 𝐏𝐥𝐞𝐚𝐬𝐞 𝐝𝐨 𝐧𝐨𝐭 𝐨𝐯𝐞𝐫𝐥𝐨𝐨𝐤 𝐭𝐡𝐞 𝐒𝐟𝐦𝐚𝐱 𝐜𝐚𝐥𝐜𝐮𝐥𝐚𝐭𝐢𝐨𝐧 𝐟𝐨𝐫 𝐀𝐒𝐌𝐄 𝐬𝐭𝐚𝐧𝐝𝐚𝐫𝐝 𝐟𝐥𝐚𝐧𝐠𝐞𝐬.