Hello Tushar,

Sam is correct, actually there is a Standard, and it is referenced in B31.3, paragraph 304.3.(e), Multiple Branches - it says "Consult PFI Standard ES-7 for detailed recommendations on spacing of welded nozzles".

You should look for Pipe Fabrication Institute Standard ES-7, ("ES" means "engineering standard"). The title is:

"Minimum Length and Spacing for Welded Nozzles"

and the web site is:

http://www.pfi-institute.org/Product.htm

Look in B31.3 Appendix "E" for Reference Documents and you will find this document listed under "PFI".

Regards, John.