Weld to weld clearence.

Hi,
As a convention the toe to toe distance between two welds ( circumferential or branch ) on a pipe should be 4 times the pipe wall thickness or 50 mm ( Some say 40 mm ) which ever is greater. Generally this is mentioned in the project specifications.
The question is where in the piping standards is it written. I went through B 31.3 but could not find any.
In section VIII , I found the mention but can that be generalised for piping ?

-Mandar. Received on Wed Oct 02 00:23:00 2002