Would it be possible to weld a 2" olet onto the back of an 8" equal tee and calling it a special item? This would essentially make it a 4-way intersection. I can't really why it wouldn't be allowed but I've never seen it before.
I need to make a bypass line over a control valve and the only options I have downstream the valve is a spool with only fittings welded to fittings.
I've seen connections like this all the time, It's basically dictated by piping configuration limitations. I don't see a need to call it a specialty item, unless you pre-fab a number of them in advance and have them ready to use by any other designers on the project? ...It's just an assembly of spec driven piping components.
I agree with 11echo and I have done this same thing before with Tees and Reducers.
After all, if you can attach an o-let to pipe, than why can't you attache it to a Tee?
The Tee wall is possible thicker than the pipe.
Never tried such arrangement before but have seen several on existing plant built by one respected EPC contractor during the 90s (not sure though if this is still in their current practice). In my opinion, such can be applied for olet on ordinary process drains. However, if the purpose of providing the olet is for some pressure or temperature instrument which might need an stable flow for proper read-out, then I think you should avoid placing olet on tee.
Generally this sort of configuration is not allowed under most codes as it would invalidate the warranty of the fitting and you could potentially get in to some serious legal issues if there is an accident caused by failure at this joint. Most manufacturers cover the fittings with something similar to "This Limited Warranty will not apply if: The Products have been the subject of modification; misuse; misapplication; improper maintenance or repair".........Best to find another solution if you can.