None that I am aware of. You have not defined the welding process, but keep in mind that you need to provide sufficient access for the welding apparatus as well as a direct line of sight and access for the welder's head, helmet, hands, filler metal, etc., around the entire circumference of the pipe joint. You can't weld it if you can't see it.
Limited access will make it that more difficult to weld. Not that there are no welders with the skills needed to weld where there is limited access, it just makes it that much more difficult to deposit a sound weld.
Al
Mark,
WELCOME TO THE AWS WELDING FORUM!!
As I don't do a lot of pipe welding nor pipe inspections I purposely awaited another response before welcoming you and chiming in.
Now, as to only the question of access with no consideration of weld code, application, joint, process then AISC makes some comments in the same venue as Al expressed. There is a definite need and, on the part of the engineer/detailer, a responsibility to provide adequate clearance for the work to be performed. AISC deals with both welding and bolting in designing of joints that allow for the needed clearances. If you can't get to it then it can't be done to a level that would instill confidence in the product and insure the public safety.
So, while I tend to agree with Al that there is no specific applicable code or standard that would provide the answer and/or direction you request, there is the common sense factor, safety factor, quality factor, and direction by one standard that would verify the obligation to provide a reasonable amount of clearance.
He Is In Control, Have a Great Day, Brent
If you gotta think about how close you CAN get it, you probably need to look at it in real life and see how its gonna be to weld. Do all you can to make the joint weldable. If its as easy as you can get it, then it is what it is.
The standard is sometimes mentioned in the field its the DU 1.1 "Specification for those who didn't have a clue.". As with many welding terms, the slang version is "I'd like to meet the idiot that drew this"
Have a good one.
Gerald