Butt Weld Tee

Equal Tees and Reducing Tees

An equal tee has a branch of the same nominal size as the run, and is used where a line splits into two lines of the same size. A reducing tee has a branch smaller than the run, and is the standard way to tap a smaller line off a larger header. When ordering a reducing tee, the specification must state the size in the order run by run by branch, for example 8 x 8 x 6 inch, which means an 8 inch run with a 6 inch branch. Reducing tees are available in two forms: with the run at full size throughout, or with a reduced run. The full run form is more common because it allows the tee to be welded into a line of uniform diameter, but the reduced run form gives a lighter, cheaper fitting where the flow permits.

Tee versus Olet for Branch Connections

A tee and an olet both create a branch, but they are used in different situations. A tee requires the main line to be cut and the tee welded in, which means two girth welds and a section of the run replaced. An olet is welded directly onto the outside of an uncut run pipe through a hole, which requires only one weld and no cutting of the main line. Olets are generally more economical for smaller branches off larger headers, and they are covered by MSS SP-97. Tees are preferred where the branch is close in size to the run, where the highest possible strength and stiffness are needed, or where a smooth internal bore without a protruding branch is important for pigging or for flow. In high pressure and critical service, a tee is normally the safer choice because its geometry is well understood and its reinforcement is integral.