I will Probably get flamed for this, but here goes.

With respect to including sifs in B31.3 stress equations i have noticed the following 'apparent'
contradictions:
1.
Page 1-47 of Coade seminar notes suggests App D sifs (Ii,Io)be included in the calculation of the sustained loads Sl, and that the occasional loads be calculated likewise.
However, interpretation 6-03 specifically states that the application of sifs with respect to the sustained loads are not required.


2.Interpretation 1-34 would seem to contradict the reply given in interpretation 6-03 with respect to these sustained loads, stating that a sif factor of 0.75i-1i be used

3.Interpretation 6-03 whilst negating the use of sifs for the sustained loads, makes no mention of the occasional load.
However the Caesar help file SPECIFICALLY Quotes:
"B31.3 Code Interpretation 6-03 dated December 14, 1987 permitted users to ignore the stress intensification for sustained and OCCASIONAL loads.To comply with this interpretation, the user would enter 0.0."

The reason for my enquiry is thus, i have a prv system with operating pressures which are approaching the limits of the available pipe thickness.

do i apply sifs of 0.0,0.75 or 1.0 to the sustained and occasional loads?

my interpration is that a sif of 0i for the sustained and of 0.75i for the occasional are acceptable or have i misread the code?

i notice though that Caesar is not able to include
the varying sif factors as given above.

Please advise if possible

regards tim.

Sustained and Occasional loads are both "primary" and can lead to collapse. Therefore, what you do with one, you must do with the other.

The CAESAR II configuration option will allow you to completely ignore the SIF, use 0.75i, or 1.0i. Whatever setting you specify applies to both Sustained and Occasional load cases.

As to which one you should use is an engineering decision you must make. There is an article discussing this in the January 2001 edition of COADE's Mechanical Engineering News (page 12). This is an article worth reading.

Hurry up and do your analysis now before the code case that is up for ballot at the standards comittee is approved and comes out (if it is indeed approved), you will soon have little choice in the matter and will be applying 0.75 SIF in abscence of more applicable data to your SUS and OCC cases.

However you as a Superpiper may have more applicable data available on the collapsing phenomena of certain fitting geometries, and if you can justify the use of a value other than 0.75 SIF you may use it!

Also see my article in the M.E.N. January 2001....

The most important point was made by Rich Ay . It is an engineering decision.

John is correct that the B31.3 absence is leaving. The equation give in the part John mentions may be conservative in some situations. Which of course leads us back to engineering judgement.