triform branch reinforcement

[JeroenPh]

Hello people,

I have to calculate a reinforcement for a 36"x36" pipe to pipe connection under a angle of 30 degrees. I found out this should be done with a triform reinforcement. Does anybody know how to calculate the dimensions of the plates to use?

 

[prex]

If I correctly understand your description, you need to build a so called miter bend: they are treated by codes ASME B31.1 and B31.3, where rules are given for calculating the maximum allowable pressure as a function of miter angle and thickness.
The usual way to reinforce such components is to increase the pipe thickness in the proximity of the miter. Never heard about a triform reinforcement.

prex

http://www.xcalcs.com

Online tools for structural design

 

[zeven]

Tri-forms, as I know them, are a set of 3 rib stiffeners.
1 going around the underside of the main, and the other 2
wrapping around the top of the Main and Branch Crotch. Where they meet (either side of the tee in the saddle region) all 3 are connected to each other using a solid bars.
Calcs we have are based on very old (1960) office standard.

They used to common in high pressure pipes along time ago, but I mainly see them in large diam, thin walled, cooling water pipes. I would suggest that someone involved in this industy would have better software.

 

[JeroenPh]

Hello zeven,

The form you describe is what I mean. I found a method for calculation that is called "Pressure Strength Ratio - P.S.R". I used it and the outcome seems ok but I do not know if it is reliable.

 

[arto]

If memory serves me, I think the old Dutch Stoomwezen & British BS5500 Codes had methods ti calculate triform reinforcement.

 

[MJCronin]

jero,

"Prex" seems to misunderstand your question....."tri-forms" do not apply to mitered bends or elbows, they apply to large "tees" and other piping intersections.

Most modern industrial piping system designs do not use this method of intersection reinforcement. "Tri-forms" require a lot of careful hand work and fit-up....they are quality labor intensive. You are asking about a piping fabrication method that is at least 40 years old.

There is a very old text by Kellogg (1950s,I believe) called "Design of Piping Systems".... Balanced Tri-forms were discussed in it...(My god I am getting old...)


My recollections only


MJC

 

[zeven]

I still see new examples on large diameter (2 to 5 meter)
pipes on cooling water systems.
Prehaps the material saving of using very thin walled pipes
with triforms on tees and ring stiffeners on straight pipes
justifies the cost and difficulties.
It may be worth contacting a company that designs and supplies large cooling systems.

 

[Bushbaby]

Depending on your application, the american water works association code (AWWA) M11 covers the design and reinforcement of large branches

 

[rversteg]

Hi Jeroen,

Your question shows ressemblance with alike questions I received ...
My personal feeling about this tri-from reinforcement is that this is an out-of-date approach (as mentioned before by others) to the basic of the actual problem here.
As ASME B31.3 limits the standard branch connection calculations upto angles of min 45 degrees the ASME B31.3 requires an integral reinforcement or a full encirclement reinforcement or alike.
On these large diameters (36 inch) no integrally reinforced branch connection fittings appear in my mind as feasible.
This leads to the justifiable design approach of designing the run pipe having sufficient reinforcement available to compensate for the required reinforcement area by making this branch i.e. pipe-to-pipe.
From a point of stiffness I would suggest welding a plate between header and branch (30 deg side) to prevent additional bending moments on the branch connection welds.
The latter upon approval of a stress engineer as this additional stiffness obviously results in another stress calculation for this line than when having a plain pipe-to-pipe connection.

 

[carthago]

I winder if you have Stoomwezen (Dutch Rules).
In their Volume 3 , Section W0201 paragraph 5 ( Page 4)
you have the details for a triform reinforcement).

In the same rules, volume 1 , design , section D0501 ,paragr.7.1.3 ,page 16 , you have the way on how to calculate the reinforcement.

Please note , that triform act as stress risers, and will
increase the stress intensification factor : i,

They also introduce a lot of weld concentration if not designed with caution.
--------------------
The old Kellog piping book mention this design,...(area
compensation )