We are designing the high pressure steam piping for a power station. The main steam design pressure is 120 Bar(g), design temperature is 550 deg.C, material is ASTM A335 Grade P91 and pipe size is 500 mm (20 inch) nominal. Near the turbine end, the main steam piping branches out by using a fabricated 45 degree Y- Lateral, having the size 500 X 500 X 400 mm. After this branching, the 500 mm pipe is reduced to 400 mm and therefore we are running two 400 mm branches to the steam turbine.

I am thinking to model this fabricated Y-Lateral fitting by a simple node point in Caesar-II, having three branches (500mm, 500mm and 400 mm) connected to it and having a suitable SIF at this node point.

My question is, what is a good number for the SIF for this Y-lateral? For this size, I do not have a Latrolet (or equal). Also ASME B31.1, mandatory appendix D does not list any Y-Lateral fitting.

How do I proceed? I will appreciate any suggestion.

Regards,
PSTRN
21 April 2008