Mr. Richard Ay, Mr. Dave and Forum members,

I am doing the Time history analysis for PRV reaction forces, i have doubt in mentioning the direction of the reaction forces.

Please find the attachment where i mentioned three cases in which the force directions are mentioned in each cases, please clarify which case is applicable, if all the three cases are not acceptable please provide the applicable case.

Waiting for your replies....

Sillyman,

From your attachment, my preference is Case-1.

Awaiting for additional comments from other members....

If you are entering a force based on the "Delta P" times area, then I would point my load upstream (towards the relief valve). This pressure front is adding to the line pressure at each elbow one at a time; the imbalance on each elbow-elbow pair is based on this delta P.

Mr. Dave,

Thanks for your reply, but i did not get an idea from it and it seems that you prefer the Case-1.

If i did not enter based on your assumption (i.e) "If you are entering a force based on the "Delta P" times area" what is your other option.

I am calculating the force (F) based on the set pressure times area. Bases on the ramp time, i calculate the load ratio and input in the Caesar model time history corresponding to the each bend and tee node.

Another option is to load each surface through the path with the current pressure times area load, updating these loads over time. The program will then do the delta P on its own.

So, use the delta P for each elbow-elbow pair you wish to load or load all elbows (or other changes in direction or changes in exposed surface perpendicular to flow).

Mr. Dave,

Thanks for your reply. Let me try to ask query in your way.

Please refer the attachment in my earlier post # 50434, where in Case-1 the forces are applied along the flow direction. In case-2 the forces are applied perpendicular direction.

From your first time reply, is seems that you prefer Case-1 (which is along the flow direction).

From your second time reply, it seems that you prefer Case-2 (which is perpendicular to flow direction).

For your information, i am loading all the elbows...

I am trying to provide a brief description of the thought process involved in setting these load vectors - something that you can offer to anyone reviewing your work. It appears you want verification of one of your three proposals. After a quick (and incomplete) review, I would use Case #2. But it's still up to you to justify this approach.

When PSV opens, there is a pressure disturbance in one end of PSV discharge line. The motion of that disturbance relative to fluid-through discharge line- is "a wave"; if you are able to describe that wave as "a pressure wave" you would say that there is a region of higher pressure and a region of lower pressure and there is a "front wave" which separates these two regions.

Wave moves through discharge piping, leg by leg; for limited time, each leg shall have a zone with higher pressure (upstream the wavefront) and a zone with lower pressure (downstream the wavefront). You may say that each piping leg will experience a "pressure imbalance" (limited in time) and the resulting force (that acts on piping leg) is upstream oriented.

IMO your reference to "Case-1 (which is along the flow direction)" and "Case-2 (which is perpendicular to flow direction)" is a forced one. The key words to define your case may be "each leg, flow direction, upstream oriented".

Best regards.

Thankyou Mr. Dave and Mr. Mariog for your replies.

Mariog,

Is your opinion is on Case-2.