B31.1 Branch Connection 1

[kryanl]

I'm working on determining the size of reinforcing pad required for a branch connection to an existing pipe. (10" into a 16" header.) With the temperature and pressure ratings, I have determined that each pipe wall, individually, is acceptably thick enough for operation. According to paragraph 104.3.1-C it seems like additional reinforcement is not required? Am I interpreting this correctly?

Anyhow, instinctively, I want to add a pad. So, just moving forward with calculations, my next roadblock is the vaiable 'A' in all referenced equations. this is defined in 104.1.2-A.6 as 'additional thickness' (due to several reasons). Now, as I mentioned above, my minimum required thickness for both the header and branch pipe is lower than the schedules of pipe we will be installing, but, this extra thickness can not be deemed as 'A', correct? Further, in 104.3.1.D.2.2, they define A7, the required reinforcement area, and that this shall be by combination of the other areas, A1, A2, etc. Do they mean that A7=A1+A2+A3+A4+A5?

So, as a summary, my questions are:
1) is a pad actually required?
2) what is A?
3) Does A7=A1+A2+A3+A4+A5?

I thank you for your assistance.

Kay

 

[NozzleTwister]

Hopefully you're aslo looking at Fig. 104.3.1(D), Reinforcement of Branch Connections. This figure shows these areas.

'A7' is the are that has been removed for the branch connection that you have to replace. This is called 'Area replacement for Pressure Design'. The figure shows the area that you have available and can use to count towards this area replacement. Add up the areas A1, A2, A3, A4 & A5 as they apply to your connection. These need to add up to A7 or more.

If A1, A2, & A3 total less than A7, then you need a re-pad or other reinforcement to satisfy the pressure design.

The extra pipe thickness IS used to count towards the required area within the zones shown in the figure mentioned above.

Take your selected pipe shedules, subtract out the mill tolerence, subtract the corrosion allowance, subtract the thickness required for pressure and the remaining thickness is used towards the required area replacement.

Note that you may want to add a re-pad or other reinforcement even if it is not required for pressure design. If bending occurs at the branch due to thermal displacements, adding reinforcement will lower the SIF's at the branch connection. consult with your Pipe Stress Analyst about this. He'll let you know if he needs reinforcement.

NozzleTwister
Houston, Texas

 

[MJCronin]

kay..

Is it absolutely necessary to use a pad ? They are expensive to fabricate, weld and inspect.

What materials, temeperatures and pressures are you dealing with ?

You seem to be working with standard pipe sizes,.... Why not consider a weldolet or sweepolet as manufactured by Bonney Forge (and many others?)

http://www.bonneyforge.com/branch_prod.cfm?id=2

....let us know more about the appliaction..??

-MJC

 

[kryanl]

Nozzle Twister: First off, thank you for reminding me to remove the corrosion thickness in my calculations. I'd totally skipped that step. Now, bringing up again my original questions, the 'A'referened to in D.2 would be the excess thickness alone, correct? (Nominal pipe size - tolerance - corrosion thickness- min.thickness per eqn. 3)
And, along those lines, in section D.2, where they define the variables, tmb and tmh would be the min.thickness per eqn. 3, without adding any tolerance or corrosion?


MJC: Yes, we must use a repad as opposed to a fitting. There is a long story behind the reasoning, coming from the field. Sometimes, we pick our battles (unless it is shown that the repad isn't large enough, of course).

Thank you,

 

[NozzleTwister]

kryanl, to quote you...

Now, bringing up again my original questions, the 'A'referened to in D.2 would be the excess thickness alone, correct? (Nominal pipe size - tolerance - corrosion thickness- min.thickness per eqn. 3)
And, along those lines, in section D.2, where they define the variables, tmb and tmh would be the min.thickness per eqn. 3, without adding any tolerance or corrosion?

You are CORRECT!

Good luck,

NozzleTwister
Houston, Texas