What Is a Pipe Tee? Equal vs Reducing

Quick Answer

A pipe tee is a T-shaped buttweld fitting used to create a 90-degree branch connection from a main pipe (header) to a secondary pipe. Equal tees have the same diameter on all three ends. Reducing tees have a smaller branch outlet. Both are dimensioned per ASME B16.9 for sizes NPS 1/2 to NPS 48.

The tee is one of the most common fittings in process piping. It splits or combines flow streams, connects branch lines to headers, and provides access points for instrumentation taps. Tees are butt welded to the pipe using full-penetration welds, matching the pipe schedule and material grade.

Types of Pipe Tees

Type	Description	Use Case
Equal tee	All three ends same NPS	Header branch of equal size
Reducing tee	Branch outlet smaller than run	Branch takeoff to smaller pipe
Barred tee	Internal bars welded across branch	Piggable pipelines (prevents pig entry into branch)
Lateral tee	Branch at 45° instead of 90°	Low-pressure drop branching

Key Dimensions

ASME B16.9 defines two critical measurements for tees:

• C: Center-to-end distance along the run (both ends)
• M: Center-to-end distance of the branch outlet

For example, a 6 x 6 x 6 equal tee (NPS 6, SCH 40): C = 141.3 mm (5.563 in), M = 141.3 mm. A 6 x 6 x 4 reducing tee has the same C dimension but a smaller M value and branch bore.

Equal vs Reducing Tee Selection

Equal tees connect same-size pipes. They are straightforward to specify: one size, one schedule. Reducing tees handle mismatched diameters between the header and the branch. The size ratio between branch and run determines whether a reducing tee or an alternative fitting is more appropriate.

A practical rule: if the branch-to-run ratio is 0.5 or greater, a reducing tee is suitable. Below 0.5, a weldolet or other branch fitting is more economical and introduces less stress concentration.

Branch/Run Ratio	Preferred Connection
1.0	Equal tee
0.5 to < 1.0	Reducing tee
< 0.5	Weldolet, sockolet, or reinforced branch

Barred Tees

Barred tees (also called “pigging tees”) have restriction bars welded inside the branch opening to prevent pipeline pigs from entering the branch line during pigging operations. The bars are typically made from the same material as the tee body and are spaced to block the pig while maintaining full flow capacity through the branch.

Stress Considerations

Tee junctions concentrate stress at the intersection of the branch and run. ASME B31.3 applies stress intensification factors (SIFs) to tees in flexibility analysis. Reducing tees with large size reductions carry higher SIFs. For critical services, reinforced branch connections or full-encirclement saddles may be specified to distribute stress more evenly.

Read the full guide to pipe fittings