The only real benefit that I am aware of, is a reduction in cost. One saves the cost of cutting out a piece of the pipe, the cost of the fitting and the cost of making three welds instead of one.

As a general rule, one can make such joints, but only when the branch pipe is small compared to the main pipe into which it is being fitted. When the pipe starts getting a bit bigger, you need to add compensation. The relevant code you work to (ASME B31.3?) should guide you regarding what you may or may not do.

When it comes to ammonia piping, I would rather be more conservative, and go for the fittings. This will allow you to radiograph the butt joints to make sure they are sound. In addition, the chances of fatigue failure is greatly reduced when using fittings. It is possible that in a refrigeration system you may have some fatigue loading.

Keep in mind that ammonia can KILL.

Regards
Niekie Jooste

Disadvantages of using fittings

1) Lateral connections with angles other than 90 to the main line cannot be made with fittings.

2) 3 welds required for one branch vs 1

3) In some cases the one you need is not available at the jobsite (Especially reducing tees)


Disadvantages of not using fittings

1) Layout, cutting and weld prep of the pieces usually requires more skill.
2) In systems already operational,, cleanliness is harder to maintain.
3) Due to the amount of metal removed from the main pipe, reinforcing may be required.
4) It is more difficult to put a satisfactory weld in a fabricated branch connection with a CJP groove weld. This is my opinion based on my skill as a welder and may not seem true to all people.
5) NDE, (RT and UT) is more complicated.

Hope this helps

Gerald Austin
http://www.weldinginspectionsvcs.com/