Dear experts,

I am performing stress analysis for 4'' condensate line of 200 meters straight length with a depth of 1 meter from ground level running in underground. The Operating temperatures are 60 degree C (Maximum) and 4.4 degree C (Minimum), Operating Pressure = 81 bar with design code (ASME B 31.3).The system is getting failure in maximum stress range Expansion cases for all 90 degree Long radius and 45 degree elbow. I tried to increase the depth of the pipe but still there is a failure in case. The route changes cannot be done due to existing pipeline services .The Caesar II model is attached for your ready reference.
Kindly advise us alternate solution and please suggest me how to solve the issue.

Regards
R.Rajivgandhi

You have 4 variables:

1. Pipe route
2. Temperature
3. Pipe material
4. Pipe thickness

If you can't change 1, then you should question whether 2 makes sense for underground piping. If you can't change 1 or 2, then look at 3 or 4.

I would note that the amount of expected growth in the operating condition is some 85.4 cm for 200 m of 60C Carbon Steel. It has to go somewhere and bends are effectively anchored laterally on both ends.

What about adding an underground vault (or multiple vaults) with a bellows expansion joint? If you're routing is really that fixed there's not many options.

There's a good chance that you have a modeling problem and NOT an over stress problem.
The program will provide closely-spaced translational restraints before and after bends in your buried model. These extra restraints will knock out bending as you would expect in a buried line. CAESAR II will automatically add these restraints for those elements which frame (i.e., enter or exit) the bend. As a user, you are responsible for adding these extra restraints at other bearing points (e.g., tees). Unfortunately, your model does not show the full complement of added restraints because the length of the pipe into and out of your bends is too short. I see a few elbows in your model that have nodes explicitly defined at one or both ends of the elbow. For such modeling, it is up to you to tell the program to add these extra restraints on the neighboring elements. Do this by checking the "From End" and/or "To End" meshing checkbox. As an exercise, I suggest you check these boxes for all the contiguous, short runs around your bends. If this resolves your over stress issues, then go back and clean up your buried model.
In the future, be sure to have longer runs into and out of your bends.

Dear Dave Diehl,

Thank you for your reply, we have done detailed stress analysis with considering meshing checkbox option and found that the stresses are still exceeding the allowable limit.

We request you to check this option from our earlier attachment and give us your passable solution.

Kindly advice us how to sort-out this issue.

by
Rajiv

I am willing to answer specific questions about CAESAR II and its application but I am unable to provide specific design guidance for the safe design of your piping systems.

As Mr. Fletcher said, if you cannot adjust the routing or design conditions, you need to look into adjusting the piping material/thickness or potentially adding other equipment/devices to your design to accommodate the growth.