stress analysis

[zishan99]

A piping is designed to connect from compressor discharge and buffer storage tank.In case of compressor shutdown this piping will supplly nitrogen gas(as an alternate arrangement)to the plant,from the discharge piping of the compressor.The tie-in point at the discharge piping has a noticeable vibration duringf compressor is in operation.

The problem is that we have to install the piping as well as we have to do the stress analysis of this piping.What to do with this vibration and how to do the stress analysis?

Regards.
mechanical19k96@hotmail.com

 

[DSB123]

zishan99,
Suggest you approach a competent Pipe Stress Analyst who can perform a thermal and dynamic analysis of your pipework to ensure the design is acceptable and you do not get failure due to the vibrations.

 

[abba7114]

What is the size of the compressor discharge piping and the the branch connection? How far is the tie-in-point from the discharge nozzle and the length of the new pipe?
The vibration problem of compressor discharge must have been taken care of during the compressor piping design to protect the compressor nozzle(I assumed). As the discharge has been operating without failure I believe compressor vibration is not entirely transmitted to the discharge, hence if your tie-in is located at reasonable distance from the discarge nozzle, providing adequate support will solve your problem.

If the piping is a bit complex you may need ceaser or other similar software to model the system.

Though your information is complete I will suggest istallintg an anchor support very close to the tie-in on the new line.

 

[zishan99]

Thanks all.
The tie-in is not far from the compressor discharge nozzle and both tie-in and discharge piping having same size i.e 2incn NPS.

Regards.

 

[PAN]

zishan99,
Do you install the snubber at compressor discharge?

 

[zishan99]

PAN,The compressor piping already installed and buffer tank tie-in is taken in the previous annual turnaround.I did not see any snubber at compressor discharge.

Regards.

 

[StressGuy]

Is it a centrifugal or reciprocating compressor? I'd bet recip if you've got a vibration problem. With a 2" discharge, you are talking about a pretty small compressor, so I wouldn't be surprised if a formal stress review was ever done, even though it should hav been.

If the existing piping system was properly designed, you will see what commonly refered to as a "hold down" clamp like this:

http://www.pipingtech.com/products/ptpcat/support/holddown/hd1.htm

These clamp are used to tune the natural frequency of the piping system to be above the driving frequency of the recip compressor. A shorter span between clamps gives a higher natural frequency.

If you find no clamps in the discharge piping, chances are it was not properly designed to begin with and you will want to fix the existing piping system supports as part of your modifications.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[Cockroach]

Use rubber hose. This isolates the vibration and ensures your stresses are below maximum working pressure.

Have the rubber hose enforced with steel wrap or alternative inorder to gain radial strength.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada