A stupid ASME vs. ANSI question
A stupid ASME vs. ANSI question
(OP)
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
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





RE: A stupid ASME vs. ANSI question
Regarding design margins, this is left up to the respective committees that are responsible for their own code rules.
RE: A stupid ASME vs. ANSI question
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
RE: A stupid ASME vs. ANSI question