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#76965 - 02/16/23 05:47 AM SIF Multiplier for Sustained Stress Index
danb Offline
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Registered: 04/22/05
Posts: 1453
Loc: ...
I do not understand very well.

Related to the subject, I understand that now Caesar will not apply anymore the 0.75 multiplier for B31.3 2020 Edition. The Caesar help state that "When B31J is enabled (through Apply B31J SIFs and Flexibilities), the software ignores this configuration option."

However, there is something in B31.3 2020 S302.6.3 that makes me think that it still justified the 0.75 multiplier. This para state that the in-plane bending moment in the example is calculated by multiplying 0.75 times i inplane determined from ASME B31J, Table 1-1.
So it seems that the B31.3 itself believe that para 320.2 actually indicate the use of the 0.75 multiplier.
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Dan

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#76970 - 02/16/23 11:41 PM Re: SIF Multiplier for Sustained Stress Index [Re: danb]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 6226
Loc: Houston, Texas, USA
In our humble opinion, B31.3 contradicts itself here. Our interpretation for V13 is: if B31J is activated, then use the B31J SIFs and SSIs and NOT the 0.75i value. However, since the release of V13 a number of users have questioned this decision.

For V14, we are re-enabling the "0.75 Configuration Directive" you discuss above, even if B31J is activated.

(We were hoping the 2022 Edition cleaned this up, but that didn't happen.)
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Regards,
Richard Ay - Consultant

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#76971 - 02/17/23 01:56 AM Re: SIF Multiplier for Sustained Stress Index [Re: danb]
danb Offline
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Registered: 04/22/05
Posts: 1453
Loc: ...
At first view it seems to be as you interpreted.

But in the same time the i is the one in B31J because "may be considered as more applicable data" so this create confusion.

The intention of the code is shown in S302.6.3 of the same code done by the same members.

The clear intention was to impose the use of B31J as "more applicable data", leaving the code philosophy as it was.
In my humble opinion the phrasing doesn't show this in a straight manner.

Also in B31.1 2020 the appendix D was left inside (apparently without any reason) even the reference is to B31J.

My main problem now is that systems previously analyzed show overstress (SUS and OCC) in some critical points even the modifications are done in other area.

Right now I do not know how to solve this fake overstress. I can not wait for V14. Even if V14 would be out tomorrow let's say, it will take looong time to be used because of inertia. Showing the overstress to the client and trying to explain how the things are in reality is not the best idea.

The overstress is given part because of the mentioned problem, part of the SIF on reducers, also this issue being created by the famous B31J.

I wonder why for "eons" B31.3 considered the reducers being ok without SIF and now this not ok anymore.
One may say that the issues may be solved by a better supporting.
Of course, but this will lead to different configuration respect to the old one.
For example, many times the reducers are placed each side of the control valves.
The heavy valves and the new reducers sif will require additional supports near the valves. This will require some extra space since normally there is a drain that will have to be moved.

Imagine that the modifications will be requested and the senior layout checker will be stunned to hear that what was good for years is not valid anymore. How many times you were told "We have always done like this"

So will be the ability of the stress engineer to explain vs ability of checker to understand why.


Like I said before "better is the enemy of good"

I know that the intention was good.
_________________________
Dan

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#76973 - 02/17/23 09:16 AM Re: SIF Multiplier for Sustained Stress Index [Re: danb]
Richard Ay Offline
Member

Registered: 12/13/99
Posts: 6226
Loc: Houston, Texas, USA
Have you tried to manually define (input) the SIF/SSI computed from "0.75i"?
_________________________
Regards,
Richard Ay - Consultant

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#76975 - 02/17/23 10:28 AM Re: SIF Multiplier for Sustained Stress Index [Re: danb]
danb Offline
Member

Registered: 04/22/05
Posts: 1453
Loc: ...
Thank you!
Good idea. I will check and I will let you know.

Best regards,


Edited by danb (02/17/23 10:29 AM)
_________________________
Dan

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#76982 - 02/20/23 04:55 AM Re: SIF Multiplier for Sustained Stress Index [Re: danb]
danb Offline
Member

Registered: 04/22/05
Posts: 1453
Loc: ...
User SIFs are active only for EXP load cases.

Best regards,
_________________________
Dan

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