Weldolet calculation

[Ing. Aponte]

Good morning,


I hope you are dong well. How MSS SP-97 evaluate the rating of a weldolet? They don't declare a design pressure and a design temperature. The only indication is that the weldolet is able to maintains the rating of the attached pipe. Another MSS indicate using B31 code to evaluate the design but here the problem is not the reinforcement area but the capacity of weldolet itself to keep the pressure.

Normally weldolet keep the same schedule on both run and branch pipe but my boss ask me to design a special piece with a similar shape of a weldolet but with a pipe run with schedule standard and branch pipe with schedule 10. II can use the finite element and ASME VIII div.2 part 5 but as input i need design pressure, design pressure and corrosion as a minimum.

Any ideas / advises?

Thanks Aponte

 

[IdanPV]

Table 1 of MSS-SP-97 provide the correlation of fittings class with schedule number.
For standard class fitting the pipe wall used for rating basis is "Standard (SCH. 40)"
If you were able to provide us with this "special weldolet" size, we might be able to help you.

As for the use of FEA:
If the Code of construction is B31.1 you may use 104.7.2(d), which permit the use of ASME VIII.2 and FEA.
Same goes with B31.3, you may use 304.7.2(d) to design the weldolet.

 

[LittleInch]

I don't understand the question here.

The run pipe is the key here as it is that pipe which is weakened by cutting a hole in it. The pressure rating is that of a std wall pipe of the same material and temperature.

That's the maximum pressure rating. If your branch pipe is only Sch 10 then its design pressure may be lower, hence it then restricts the design pressure.

Or its a small branch then maybe not. For a BW pipe you just weld the Sch 10 pipe onto the end of the weldolet if the connection weld is allowable in terms of internal bevel.

If its a SW then you just weld it.

You need to have the Design pressure and CA provided to you, otherwise how are you supposed to design anything?

Also why ASME VIII? B31.3 and B 31.1 both have calculations on how to design branch offtakes. A weldolet (which is a TM) - you should use the term "Integrally Reinforced Branch fittings" - is just a bit of metal where someone else has already done those calculations for you and proved them by testing and long service.

 

[Ing. Aponte]

Hi LittleInch,

thanks for your answer. What you said is correct and normally is exactly as you told.

I try explain better my problem: the Client of my boss is a small factory that want enter into the market of the "Integrally Reinforced Branch fittings" with an item that is basically a weldolet. As you know Weldolet is designed with same schedule on both run and branch. Till now, if you had different schedule between run and branch you have to adapt it: people in site do tapers on branch side if the branch pipe is thinner or use higher series if problem is on run side (for example if we have a run 20S weldolet is STD). System work bu some client don't accept fitting will be modified.

Idea of this factory is, starting from design of a weldolet, to solve this problem with new dedicated items. They are asking me to design it. This is the reason because I proposed ASME VIII: i have to prove that new design is safe.

Thanks

 

[LittleInch]

Ah.

That's better. But still hmmm.

Pressure rating though is quite simple.
Take the material and its SMYS at the max temp, calculate pressure using the equation in MSS SP 97 annex B and away you go as you know the wt due tot he schedule.

CA shouldn't come into this really.

Then make a few and test them.

The issue with doing this is how many variations you need to keep in stock or how many options you want to do the design work for.

You have sizes from 1" to 24" or more run size, then already there are three different run wt, (STD, XS and Sch 160, now you want to add even more options??

Or need to machine out a STD wall one each time?

Nice idea, but seems to be a solution to a problem which doesn't really exist, IMHO.

 

[Cobra17]

You have sizes from 1" to 24" or more run size, then already there are three different run wt, (STD, XS and Sch 160,

Don't forget that 1/2 - 6 NPS also has XXS

 

[Ing. Aponte]

Thanks to all for your replies. Tomorrow I will se the Client to speak about that.