Hello All,

Currently I am doing stress analysis of Metering System.
All stresses are within limits with Liberal ON but restraint load at node 42 ( Refer attached CAESAR II file)is around 23476 PSI in Opearting case no.8 (W+T1+P1+U1)

I dont have feeling how high force( magnitude) we can permit going to the restraint. I would appriciate your valuable input on this. ............First Question

Also process data for this project is :

Design Temp (MAX) = 200 deg.F
Design Temp (MIN) = -20 deg.F
Operating Temp (MAX) = 120 deg.F
Operating Temp (MIN) = 80 deg.F

My second question is what temperature difference should I consider for thermal analysis. Is it mandatory to use Design temperature (and not the maximum operating temp)for analysis?


Regards,
Anant

Can I please get reply to my query ?

I would appriciate your quick responce as I am stuck and dont know what needs to be done.

Dear ASK,
Based on B31.3 code, you should consider temperature difference between maximum (or minimum) metal temperature and expected installation temperature to evaluate restraint reactions in a specified piping system.
If I remember correctly it must be specified in Para 319.3.1 (b).
As you know it may be difficult to specify the exact installation temperature based on the location of plant and time schedule of spool fabrication and construction at site so as a personnal experience I recommend you to evaluate your piping system for the maximum expected temperature difference. As a general, in each project you must have a specification for environmental parameters in which you can find maximum and minimum ambient temperatue measured at plant location.
Based on this specification you can evaluate your piping system, for example, between maximum metal temperature and minimum ambient temperatue.
To find out what is the maximum (or minimum) metal temperature, I strongly recommend you to consult with project responsible of process descipline. You should ask him (or her) to find out what is the maximum (or minimum) fluid temperatue and then based on that data and other information like line insulation and location and type of fluid you can simply calculate the maximum (or minimum) metal temperature for your flexibility calculations.
Now, I go to your first question.
First, you should specify that your restraint is a nozzle or not. If it is a nozzle your shall refer to allowable nozzle loads on static equipments or you shall refer to API standard for pumps, aircoolers, tanks, compressors, ... or you shall refer your calculated loads on nozzles to mechanical or machinary responsible for further evaluation.
But, if your restraint is a support you shall refer to your standard pipe support document in which you can find allowable loads for each support type you may use for your piping system. If your standard pipe support does not contain allowable loads you shall impose your calculated restraint loads from CAESAR flexibilty analysis to your support and investigate that your support can withstand under the loads or not. You can perform such calculations based on MSS SP58 or BS standard, or if you have enough time you can set up a finite element analysis.
At last, I aware you about some thing else. If you perform such a calculation to find out that your support will withstand under piping loads or not, you also need to make sure that your pipe will withstand under that load in places that it has contact with your support.
Be aware that integrity of your support and integrity of pipe (at places where pipe is in contact with support) is two different issues.

Anant,

The design high pressure requiring Sch 120 wall thickness results in little flexibility for the size Nps-18 and Nps-10 piping straight lengths. Some more offsets with elbows would have more flexibility to reduce the loads.

If the layout is fixed and the geometry cannot be changed then the guide restraint gaps might be opened up from the 0.75 inch as designed to maybe 1.0 inch gaps. The thermal expansion is closing the gaps at the guides from the 200 deg F design temperature. Yes, the 200 deg F should be used applied for the Code stress compliance evaluation. Sometimes the operating temperature could be lower to justify using a lower than design temperature to evaluate the loads at supports and equipment.

If there are equipment loads to consider at the piping connections then the larger 1.0 inch gaps might result in excessive loads at the connections. Some added flexibilty in the piping routing is probably then needed. Please have mentor or piping designer work with you on re-design.

Dear All,

Thanks a lot for your valuable input.



Regards,
Anant

anant,

Finally realized that the output was in ver 5.1 to be able to view it.

The very high restraint loads are actually occurring in the operating case 8 and 9 with large RX loads at node 122 ( from U1 where GX=1.0 ?) The guide restraint gaps are not closed in the thermal expansion cases.

Could you please explain the reason for GX=1.0 , GY=1.0 , GZ= 1.0 uniform loads? If these are for seismic loads, then I think you might need to revise the guide restraint gaps to the thermal displacement values (smaller - not larger gaps). I did not review all the 33 cases.