Guys,

I have one question to clarify.
In order to keep model size reasonable for a branch pipe analysis ,can an existing main header pipe connected may be ignored in the model with limiting the branch point as a fixed anchor point.

For example, considering the analysis of anew 4" branch line connected to the large size existing header pipe 16",the tee/ branch point can be assumed as a fixed point and approximated to an anchor.

This approach may not affect the accuracy for the stress analysis and may suffice for the intended requirement.Is this approach be true.


Moreover , if the above approach is OK then is there any rule of thumb on restriction for header/branch pipe size ratios where this assumption can be reasonbaly applied.

Is there any other factor governs on this assumption as well.

Thanks.

Not really. At the junction there will be forces and moments transferred from the header to the branch. Even though your branch is smaller than the header, it (the branch) may affect the header depending on the loading conditions.

You can safely split a system at an (external) anchor, or a nozzle connection to a fixed piece of equipment. By separating the system elsewhere you miss or ignore the interaction between the two parts. Sometimes this could be insignificant, othertimes very important.

I would really try to avoid splitting the system.

Many Thanks Richard,

I have seen some engineer advice/suggest to develop the pipe header model upto 3 -4 pipe supports that may come through the pipe route either on side of tee/Branch point.Any external anchor point or equipment nozzle connection may be on far point along the header. Is this assumption/approach is reasonable or not.

Your advice would to build the model as a complete system to possible extent with out splitting thus reflecting actual scenario ...isnt it.

Regards

no more thumb rule for header and branch analysis. Yes your approach is true. Normally we consider ANC.

Do a search on "decoupling". There are some good posts.

Regards,

Yes the 3-4 supports is a rule of thumb. You still need to assess the situation because, again, you're missing the interaction between the two systems.

(What kind of supports? If they are just vertical supports, how does that affect the behavior in the horizontal plane?)

Thanks for response ,Richard.
I understood.

These supports may be,for example, simple Shoes or Guides...but there is no axial restraint/limit stop or anchor support on the main header until it is connected to equipment on the far side.

Sometimes the expansion (and hence forces) from branches can affect the header. Normally we tend to model the complete system up to the anchors in the system. Very small branches like 1", 3/4" and the like can be ignored. No need to model 4" drain with valve. But be careful. You have to check if the connecting lines are really affecting this header (being analyzed) or not.
"4" branch line connected to the large size existing header pipe 16",the tee/ branch point can be assumed as a fixed point and approximated to an anchor."
No I would not go for it and try to locate anchors or combination of limit stops and guides on the 16" header. In this case the 16" line can affect the NEW 4" branch line....

If you have a controlled movement(guides) you can stop the model and insert a estimated displacement after one or two guides. The point is that you make sure that there is no other influence from outside.

Regards,