A stupid ASME vs. ANSI question

[heaterguy]

I say stupid to kill myself before getting burnt from the flame throwing that's about to commence.

ASME requires a safety factor of 3.5 for yield strength design vs. actual, right?

Why then can ANSI flanges not have the same requirement? They seem to have a safety factor of one!

TYIA,

heaterguy

 

[metengr]

Well, ANSI is an accrediting organization and has nothing to do with evaluation of safety design margins, code rules, etc. They accredit Codes and Standards and both ASME B&PV Code and ASME B16.xx are accredited by ANSI.

Regarding design margins, this is left up to the respective committees that are responsible for their own code rules.

 

[jte]

heaterguy-

ASME requires a safety factor of 3.5 for yield strength design vs. actual, right?

Ummm... no. At a given temperature it would be 2/3 yield or 1/3.5 ultimate, or time dependent properties, whichever is lower. And that's just for the basic tensile stress. Unless you're dealing with local primary stresses, secondary stresses, or alternating stresses in which case you have a completely different set of factors to contend with.

Why then can ANSI flanges not have the same requirement? They seem to have a safety factor of one!

Yup, that's why they all break apart when we hydrotest them to 1.5 * MAP for piping. In fact, we have piles of flanges which have mysteriously broken or merely leaked sitting in the "boneyard". Ok, ok... when you say safety factor here, what do you mean for it to be against? Because the exceedingly large majority of the time a "flange failure" is not a physical tearing of the flange which would be possibly compared with a SMYS or SMUT but excessive (linear) deformation which has allowed the gasket to relax to the point at which fluid which should be inside the pipe... no longer is. Throw in a huge disparity in bolt torquing knowlege and techniques and its stinkin' amazing that they hold at all. Kudos to the ASME B16.5 (an American National standard accredited by ANSI) committee from me!

jt

 

[chicopee]

Most factors of safety I have experienced with ASME fired pressure vessel were of the order of four and five.