Selection of Branch fittings 3

[Sachinkathe]

Hi
For branching as far as I know ther are following are the options
1) Equal Ts
2) reducing Ts
3) Stub ins ( With or Without reinforcement pads)
4) Half coupling
5) -- lets and ts for U/G services having 45Deg branches
ETC ETC
But which to use when is there any criteria? I know for a perticular combination there is only one option for selection as per the spec.

Thanks a lot
Sachin

 

[pennpiper]

Sachin,
You are close to the right answer but please allow me to modify your thoughts.
Choice for branch connection:
1) Equal Ts (Size to size branch)
2) Reducing Ts (Size to one size smaller branch)
3) Stub-ins Without reinforcement pad (Where design conditions allow)
4) Stub-ins With reinforcement pad (When design conditions require reinforcement)
5) Weld-O-Lets (for large sizes) where reinforcement is required.
6) Thread-O-Lets/Sock-O-Lets for small pipe sizes
7) Latro-Lets for 45Deg branches (All sizes)

Half Coupling are not recommended by most major Engineering companies or Owner/Operator/Clients

"But which to use when is there any criteria? "
I do not understand this question.

"I know for a particular combination there is only one option for selection as per the spec."
I do not understand this statement.

 

[JohnBreen]

For branch connections there are:

ASME/ANSI B16.9 welding fittings. Size-on-size Tees and Reducing Tee's and Laterals. The best choice for lower effective stresses (see B31.3 Appendix D). Pressure design not required (specify the same schedule as the matching pipe). Crotch radii provide better stress distribution and smoother flow characteristics. Only the butt welds need to be inspected.

Weld-in integrally reinforced fittings (sweep-o-lets) to MSS SP-97. Next best choice for stress consideration. Designed to include branch reinforcement needed for pressure design (specify by class of line). Crotch radii provide better stress distribution and smoother flow characteristics. Significant post weld NDE needed.

Weld-on integrally reinforced fittings (weld-o-lets)to MSS SP-97. More easily installed that "weld-in's". Next best choice for stress consideration. Designed to include branch reinforcement needed for pressure design (specify by class of line). Post weld NDE needed

Pad Reinforced fabricated branch connections (pad reinforcement is the only type recognized by ASME Codes). (AKA (in the vulgar) "stub-in") Next best choice for stress considerations. Require rigorous attention to fit-up and field fabrication. Require code calculations for pressure design (area replacement rules in B31.3 paragraph 304.3 and its sub-paragraphs, and see B31.3 Appendix H). Significant post weld NDE needed.

Unreinforced fabricated branch connections. (AKA (in the vulgar) "stub-in") Next best (worst) choice for stress considerations. Require rigorous attention to fit-up and field fabrication. Require code calculations for pressure design (area replacement rules in B31.3 paragraph 304.3 and its sub-paragraphs. Sometimes reinforcing pads NOT NEEDED for pressure design are added to lower SIS's. Significant post weld NDE needed.

Half couplings are not a good choice.

Extruded outlet branch connections are shop fabrications and require significant experience and NDE.

Saddle reinforcement, full encirclement and other types of "non-pad" reinforcement are used for very large diameter branches and for Penstocks (See AWWA Manual MS-11).

John

 

[moltenmetal]

Good advice has been given here.

Half couplings do see use limited use for non-moment connections such as instrument or sample taps. These are not piping branches per se, and are usually only permitted within a very limited size range (ie. a 1/4" NPT connection on a line 2" NPS or larger).

Some specs treat all branches as if they would see significant forces and moments, just to be safe, and hence eliminate the use of half couplings in favour of self-reinforced branch fittings (thread-o-lets and nip-o-lets etc.).

Good specs give the designer options via a branch table, specifying the branch types permitted for each run and branch size range. Sometimes the reducing tee is not available etc. There's no point telling someone to build a pipeline with components they can't obtain, or forcing them to use more components or welds than necessary.