Dear Friends,

I am new to CAESAR II software & Stress analysis.

I understand, when a piping system without expansion joints is pressurized, the system will not move because the pipe is countering the force in tension. When an expansion joint is in the system, the pressure thrust force tends to pull the ends away from the expansion joint causing damage to itself and the pipe. This Pressure Thrust must be contained with main anchors which should carry the pressure thrust.

For a 36” pipe with pressure 150 psig, Pressure Thrust = 678817 N. Main anchors should resist these Pressure Thrust forces in the system when there is an expansion joint in the line. The same pressure thrust force should we consider (checking for support size) in a piping system where there is no expansion joint; will the pipe itself counter these pressure thrust forces. As the numbers are more I want to know it clearly. How high pressure piping can withstand this pressure thrust? Also please show me some reference standards. Kindly enlighten me.

Thanks in advance.

Internal pressure in an ordinary piece of pipe with closed ends will cause axial pressure stress due to the pipe wall resisting axial pressure.

Axial pressure stress = (pressure x internal area)/ metal area

Similarly hoop stress will be produced and resisted by the pipe wall in the circumferential direction.

Since hoop stress is numerically approximately twice axial stress, axial stress alone will never be the limiting factor on maximum pressure. Internal pressure will always be limited by the wall thickness exposed to hoop stress. Many factors such as allowable stress, corrosion allowance and manufacturing tolerance will have an impact on the allowed internal pressure for a given pipe diameter and wall tickness.

Have a look at ASME B31.3 section 3 or any decent applied mechanics textbook.

High pressure inside pipe will try to elongate pipe resulting in axial stresses. In case you are having elbow at pipe ends, pressure will stiffen the pipe bends resisting bend ovalization. This happens due to the pressure difference between pipe and atmosphere, typically known as Bourdon effect.
Pressure can affect the large diameter pipes having high D/t ratio. This is addressed in B31.3 Appendix D (Table D300 Note 7)
You can also refer peng paper on pressure elongation. Also, use search option.

And to be specific, the restrains will not see the pressure thrust loads. the force will be contained in the pipe wall withstanding the increased axial stress.

Thank you very much for you guidance.

I read Mr. Peng newsletter on pressure elongation and looked at ASME B31.3.

My senior and I had a discussion with client regarding a chilled water network. They are very much worried about the pressure thrust acts on the elbows & requirement of thrust blocks at each elbows with a capability of carrying heavy loads because of the pipe size (36”), flow rate (30,000 GPM) & pressure inside the pipe 150 psig.

My senior explained them “for metallic piping thrust blocks are not required at elbow as the displacement is very less, and if there is an expansion joint in the piping system it is significant to provide thrust blocks. Thrust blocks at each elbow are unnecessary and it requires enormous force to hold the pipe because of thermal growth or contraction moreover it is not advisable two anchors in a single line, so he placed an anchor in the middle of the line.” Also as like Mr. MoverZ mentioned, he clarified that the internal pressure at the elbow and pipe will cause axial/hoops pressure stress and this stress will be distributed overall piping as axial stress after this is compared with allowable stress limit.

Client hardly accepts this and they asked again the huge amount of force where it is distributed and how? And they need a manual calculation to prove this with CAESAR II results for a single line with elbow. Hope I may get valuable suggestions from our members to prove this and offer them better justification.

You could ask your client to find someone in their organisation with some engineering knowledge. In the nicest possible way of course.

If your piping system consists only of pipe and rigid bodies (ie: no expansion joints), then why are you concerned about pressure thrust?

You would only need extra restraints if you have concerns with pressure surge or slug flow, which your process group can assist you with.

For piping systems that contain no expansion joints, the axial loads include a longitudinal force calculated as Pressure X Internal Pipe Area.
Reporting this force to the pipe cross-sectional area, you obtain the stress due to axial loads.

The only thing your Client must understand is that the longitudinal stress calculated as above (and considering pressure as the only load) is not supplementary to the longitudinal stress calculated by a formula where "p" and pipe dimensions appears directly. It is the same "longitudinal stress due to pressure"!
Now, in practice a code may use a simplified conservative formula for circumferential stress and we may still count longitudinal stress as half of circumferential stress. In this case would be a difference between the results, but this is due to our approximations.

So the force may be huge but the longitudinal stress is reasonable for the reasons MoverZ explained you.

Regards.

Please read AWWA M-11.

You will be able to make your client happy.


Best regards,

Or visit this site: Water Agencies' Standards


http://www.sdwas.com/


Regards,

Hi,

Mr. Danb's reference can be shown as back up and manual calculation may not possible.

I Thank you everyone for assisting me. Your guidance helped us a lot to prove them and also helped me to know the concept better.

After explaining with few references, Client finally agreed with full Satisfaction.

Thank you for feedback. Glad to know that we were useful.

Regards

Dear
First differentiate between pressure thrust (dynamic presuure) and static pressure then we can have a clear picture.

Checkout this.
https://sites.google.com/view/pipingutilities