SIF OF LATERAL CONNECTIONS

Hello friends.

I have a query regarding the SIF for lateral connections.

Background:-
BP's spec on flexibility analysis states:-
Stress intensity at 45 degree fabricated tee is the same as for 90 degrees Tees provided the header thickness at the opening complies with paragraph 304.3.3 of ASME B31.3 using an enhanced design pressure as per the standard equivalent pressure calculation.
Otherwise the branch shall be checked for pressure containment(area containment) to ASME B31.3 para 304.3.3 using the design pressure, as per the line list, and checked for flexibility stresses sing the following enhanced stress raisers:-
90= SIF from B31.3 X1
60= SIF from B31.3 X1.25
45= SIF from B31.3 X2.25

Query:-
If my understanding is correct then,

1. We can use the same SIF for branch connections(other than 90 degree) if we evaluate the branch connection at pressure higher than design pressure.
However, I don't know the method of calculating "enhanced design pressure as per standard equivalent pressure calculation". Any ideas about this calculation?

2. We can evaluate the branch connection at design pressure only but we have to increase the SIF's with factors specified. Any rationale to increase the code SIF's? Maybe these modified values are coming based on BP's experience and verified by fatigue testing of branch connections per ASME B31J.

Neeraj
"The harder I work, the luckier I become"

Refer to this thread.

http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=3902

Hello Caesar III.

I referred to the above post but I noticed that people have conflicting opinions.
Some have advised to use a higher SIF value whereas some people advised to use SIF of 90 degree Tee only.

I am confused if SIF of 45 degree connection(Wrought Tee/Fabricated Tee) is higher/lower than 90 degree connection(Wrought Tee/Fabricated Tee).

Hi Neeraj,

People were debating, but Dr.Becht cleared it up. I'll just quote his reply here,

'Laterals have been found in testing and analysis to have a lower SIF than 90 degree branch connections. .... The B31.3 committee has discussed putting in a simple statement that the SIF for 90 degree branches can be conservatively used for laterals.'

I saw if we model the 30, 45, 60 degree lateral fitting, we get the 90 degree elbow's SIF in C2, but I'm B31.1 user. Maybe you could ask Moderator of this forum.

Hello Caesar III.

I think that SIF for a fabricated 45 degree Tee(Pipe to pipe connection by welding) will be much different from a wrought(mainly wrought) Tee.
I don't know as how to differentiate between the SIF based on method of construction.

Also, I don't know if Mr. Becht's explanation has been explicitly added in the code since I don't find any reference for Mr. Becht's statement.

Waiting for response from Moderators Richard and Dave.

Thanks

The B31 SIF formulas distinguish between fabricated intersections and forged fittings. But there is no distinction provided for the branch angle.

If you're using B31.1, c2 computes SIFs according to Appendix D. This appendix does not address laterals (of any angle), therefore the SIFs generated are indeed for 90 degree tees.

I hope everyone has been following the discussions and Webinars associated with FEATools? Invoking the "fea" option in FEATools does compute both the SIFs and (tee) flexibilities for laterals.

Yes FEAtools looks promising to slove these kinds of problems.

But unfortunately, my company has already been using the FE/pipe, so my chances to use the FEAtools are like winning the lottery since the limited budget.

Hello Richard.

Thanks for your reply.

I think that we can get a more reasonable SIF is we use FEM method. But I believe that FEM method can't distinguish between a forged 45 degree connection and fabricated 45 degree connection.

Is my understanding right?

Thanks