Analysis is to be done as per B31.3...
A 2" tapping is taken from a 24" elbow. The design temperature is 760 deg.C, so I have to consider analysis for the 2" piping.
The fitting is fabricated at site. Weldolet will be welded at site.

I have to model a weldolet at 30 deg to the Elbow.
1. Are there some special considerations for SIF ???
2. I am facing stress problem at the intersection by considering weldolet, so can I do FEA for the fitting and qualify the system.

Please advice...

Are you referring to elbolet?

FEM ( as per my knowledge) is the only solution.

Regards

I would simply make the 2" line flexible and forget about calculations in most cases. Only for critical applications I would do some calcs. If the fitting is done on site that means normally segmented elbow. Not critical line. Your line is 760 C, which is high - problem/critical line. Weldolet is not a good design most of the time on high temp lines due to big difference in thicknesses. Thermal stresses will crack the connecting weld with time. We have had better experience with DIN/EN connections. Segmented elbow on 760 C line? Add longitudinal welds, low allowable stress level and deep into creep. I hope your pressure is low.

As a general rule I do not like any items welded on the extrados of a bend. Very problematic.

FEA/FEM but you need to look into thermal stresses also, e.g. cooling and heating rates. To get bend FEA correct is not easy. Last attempt I saw had highest stress in intrados :-(((

B31.3 does not have a SIF for said fitting, the elbolet will restrict the elbows ability to ovalize due to applied bending moment. These structural reconsiderations over ride the designers desire to have a branch coming out of the elbow move the %^&#^^% branch off the elbow!

Without going into a FEA, in case of elbolets, we normally specify the said elbow as double flanged (to account for reduced flexibility) and specify weldolet SIF. And more importantly see to that the maximum stresses are away from the connection (elbow stresses are well below allowable limit) by including enough flexibility in the branch.

Thanks to everyone for their advice..

The temperature of 760 deg.C is reached during start-up condition only. The actual operating temp is 222 deg.C (well below creep range) for material A312 TP304H.
This is a low pressure line (5.2 kg/cm2)
Avoiding weldolet is the best option, but the process requirement, routing and space constraint must be taken into account.
I have considered Flanged elbow (considering reduced flexibility), because the elbow cannot ovalise.

FEA is the option left out and that is what I am working on now...

Thanks,

For this material creep starts around 1100 F. Look carefully into your heating and cooling rates. Flanges and other heawy items heat up and cool down slowly. You can easily have very high thermal stresses - rapid creep. I would limit all external stresses. Supports are one major source. No dummy branches or similar. Reinforcing pads are bad news also, see other current topic for my picture. That line is running only just above 500 C and is SS line.

If longitudinally welded NB600 pipe or bend fails on a 5 bar gas/steam line you do not want to be nearby. Generally they do not leak before failure. They simply blow up.