dear sir,

how to model the 4 way tee junction?.

it is a natural gas pipe at a working pressure of 40bar(g) and design pressure of 50bar(g). May i use 4 way tee juction here? or any reinforcement is required at this junction?

Refer,
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=4282#Post4282
http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=265#Post265

I personally would recommend avoiding crosses in any pressure piping. I could consider using one in (B31.3) Category D fluid service, but even then only if some combination of regular tees and elbows could not work, and only if the cross were analyzed using FEA methods.

For your application, likely all sorts of reinforcement would be required. Consider that with a cross, sections of the fitting look more like a flat plate than a cylinder in terms of pressure containment.

Basker,
Just use a "Cross" fitting. No reinforcement is required. They are available in the same materials (Carbon Steel, Stainless Steel, etc.) as the other fittings.

http://www.pipelinesupply.com/tablecalculators/Weld_Fitting_Dimensions.pdf