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.
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.
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.
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.
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