Difference between stubin and stubon branches

If you want to see a picture of a Stub-In/Stub-On then I recommend that you get your company's copy of the ASME B31.3 (or B31.1) and look it up. That way you will be sure to get the correct picture and not just someone's version of what they think it is.

In the meantime I will offer this description for you. This is from a related question.

Stub-in

The question:

What is it called when I weld a pipe to the side of another pipe instead of using a T fitting?"

My answer:

What you are doing is making a "Stub-in" branch. You have a header pipe (or run pipe) and a branch pipe. This is allowed in the ASME 31 Codes. There are two ways this is done. Both methods are commonly called a "Stub-in" but they are done in a different way.

One way is to cut the branch hole in the header pipe to the size of the outside diameter of the branch pipe. Then make the saddle cut of the branch pipe to fit the inside diameter of the header pipe. With this method the branch is inserted "into" the header pipe.

The second way is to cut the branch hole in the header pipe to the size of the inside diameter of the branch pipe. Then make the saddle cut of the branch pipe to fit the outside diameter of the header pipe. With this method the branch is sat "onto" the header pipe.

Both methods may be done with and without a reinforcing pad depending on the pressure and stress conditions.

With your case, considering the size of the header and the size of the branch I would recommend a full ring pad. The ring pad should be equal to (or greater than) the thickness of the header pipe and a minimum of 20" wide.

Additional information on Stub-in (Stub-on):

We have talked about using Straight Tees and Reducing Tees as a way to make branches from a line. For low pressure (or reasonably low pressure) there is another way to make branches from a line. This method uses only pipe. It is normally used only for low pressure/low temperature applications where the branch is reducing. The ASME B31.3 (and other piping B31 Code sections) recognizes two basic versions of the pipe to pipe branch.

One method is where the run pipe has a hole cut the outside diameter of the branch pipe. This opening is then beveled for a "full penetration weld" The branch pipe is saddle cut (with no bevel) to match the I. D. of the run pipe. They are then fitted together and welded.

The second method is where the diameter of the hole in the run pipe is the same I. D. as the I. D. of the branch pipe. This hole does not get a bevel. The end of the branch pipe is saddle cut to fit the run pipe and is then beveled for a full penetration weld.

With the first method, the branch pipe is inserted in the run pipe. With the second method, the branch pipe is set on the run pipe. Both are still commonly referred to as "Stub-ins"

Both of these can come non-reinforced (as described above) or reinforced. The reinforced version is normally only required for higher stress situations. The reinforcement is a "ring" plate cut from some scrape run pipe or the same material as the run pipe. At the center is a hole the same size as the branch pipe. If cut from flat plate it is then shaped to fit around the run pipe. The width of the ring is normally one half the diameter of the branch pipe. The ring is intended to replace the material that was removed when the hole was cut in the run pipe. A small diameter hole (1/4" NPT) is normally drilled (and tapped) in the ring to act as a vent during the welding process and to allow for Hydrotesting of the welds. The ring is then welded to the branch pipe and the run pipe with full penetration welds. The small hole is fitted with a plug after work is completed.