Tee Connections in Piping: Equal Tee, Reducing Tee

Piping Tees are used either for dividing main flow in two streams or for combining flow from two streams. The term most probably comes from the resemblance of the English letter Tee.

The main run pipe is often termed as Header and the other as a branch. Branch size may be smaller or equal to run pipe size but it cannot be larger. Tees having branch size equal to run size are called equal tees & other as unequal tees or reducing tees.

Tees are normally designed based on ASME B 16.9 or ASME B 16.11. Tee is always normal or perpendicular to the pipe axis and normally produced by forging.

Types of Piping Tee Connections

Piping tee connections are classified according to the branch size and end connection.

Based on the branch size, there are two types of piping tee connections. They are:

  • Equal Tee, and
  • Reducing Tee

Equal Piping Tee: When the branch size is equal to the run pipe it is called Equal Tee pipe fitting.

Reducing Piping Tee: In case of reducing tee, the branch size is smaller than the run pipe size. there is a limitation of the branch size. It can not be sufficiently smaller. For example, Reducing tee from 16″ pipe is available up to 6″ branch size. 16″ X 4″ piping tee is not manufactured. Usually reducing piping tee connections are manufactured till a branch pipe size of one size lower than 1/2 the parent pipe size. This rule is valid till 28″.

Equal Tee vs Reducing Tee
Fig. 1: Equal Tee vs Reducing Tee

Based on end connections, tees are classified as follows:

  • Socket Welded Tees
  • Screwed-End Tees
  • Butt Welding Tees
  • Flanged Tees

Socket Welded Tees

  • These are usually forged and used up to 2” run size on services where socket welded connections are permitted.
  • The applicable dimensional standard is ASME B16.11 and material standards including ratings are the same as those for socket welded elbows.
  • Normal industry practice is to use socket welded tees up to 1 1/2” run size.

Screwed-end Tees

Their use including rating, dimensional and material standards are the same as applicable to screwed elbows.

Butt welding Tees

  •  The dimensional standard applicable for equal and unequal tees is ANSI B16.9. These are available from 1/2” through 48”.
  • Unequal butt welding tees are available having branches up to one size lower than half run size e.g. If the run size is 8”, unequal tees are available in sizes 8” × 6”, 8” × 5”, 8” × 4” & 8” × 3 1/2”.
  • Applicable Pressure temperature rating and material standards are the same as those for butt-welding elbows.
  • Butt welding tees are usually used for size 2” and above and in smaller sizes for services where the use of socket weld joints is prohibited.

Flanged Tees

Their use including pressure rating, dimensional & material standards are the same as applicable to flanged elbows.

In normal large-bore pressure piping most often Butt-welded Tee connections are used. The ASME B 31.3 (Appendix D) provides a formula for calculating the SIF value at tee connections which Caesar automatically calculates when Tee is defined. The Tee connections are normally defined in Caesar as shown in the attached figure.

Tee modeling in Caesar II
Fig. 2: Tee modeling in Caesar II

For pipeline systems a special type of tee is used, known as Barred Tee.

Few more related articles for you.

Difference between Tee and Barred Tee
Smart Tee Model considerations in START-PROF
Inspection & Test, Marking & Colour Coding and Packing Requirements for Pipes & Fittings
Technical requirements for Pipes & Fittings for preparation of Purchase Requisition
Piping Elbows vs Bends: A useful literature for piping engineers

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

4 thoughts on “Tee Connections in Piping: Equal Tee, Reducing Tee

  1. Hi,you give very good explaintion about tee connection and you also classified a connection,Nice article!!

  2. Hi Anup! This blog is really working for me. And I am really inspired by your passion to share knowledge. I am working on CEASAR-II 2016 since last one year but I need some help to clear some functional doubts. So can you share your no. here or ping me on 07228051832.

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