Regarding SIF's for sustained and occ cases:
As Mr. Wright has written to you earlier, the SIF - Stress Intensification Factor, comes from fatigue tests, and is intended to allow the pipe stress analyst to predict peak stresses in piping components by knowing only the nominal stresses and pressure.
There has been some Code work suggesting that seismic loads should be checked for both fatigue and primary load failures. We feel like this theoretically can be true, but that for the vast majority of cases is unnecessary, and that the primary load failure checks currently implmented in the Code have served the industry well because they are safe and practical. Lower safety factors, increased cycles, and more inexperience of course, renders prior experience less germane.
E. Rodabaugh, and S. Moore's paper, "Background for the ASME Nuclear Code Simplified Method for Bounding Primary Loads in Piping Systems", sheds considerable light on the subject and shows that a part of the stress intensification factor is due to the gross discontinuity of the geometry, i.e. the cutting of a hole in the pipe at an intersection, and as such should be a part of a membrane stress evaluation for primary load concerns.
Whereas many analysts feel that SIF's should not be employed for primary or occasional loads, pipe stress programs apply them by default, and so the vast majority of primary stress analyses on piping systems have been conducted using them.
It is our feeling that certain systems are more susceptible to primary stress failures, and that these should be looked at more closely, meaning that SIF's should be applied. In general, this is true when the operating temperature is in the creep range, and when D/T is around 100 or greater, for in these cases the alignment of our analytical capability with reality is particularly poor.
Regards,
Tony Paulin
>
> I have seen many stress files where sif is ignored for sustained & occ
> (siesmic) cases.
> Is there any code interpretation to this? or can we ignore sif for
> fittings ( like weldolet, latrolet ) for sustained & siesmic
> cases ?
>
> Regards
> Sachin Bapat
>
>
>
>
>
> Texas Flange - a good source for information on industrial flanges, all
they ask is for referrals for designs they help with.
> 877-610-8924.
> www.texasflange.com
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Received on Sat Sep 28 12:28:00 2002
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