Question 1: Wind direction
Wind is plane north and east. While major piping is 45 degree clockwise to the plane south. Subcontractor for stress ananlysis insist that if wind load case directing northeast and southeast respectively deso not exceed the allowable, the 45 degree wind(which is plane north and plane east) will also be OK. No oblique piping exists, i.e all lines are either paralle to southeast or north east.

Is there some theory backing up it? Basic wind speed is 150mph so I have to be very careful.

Question 2: ISO drawings
Becasue piping is not orthogonal to the plane direction, PDS model has to be rotate 45 degree to generate the ISO Drawings and make sure the N, E coordinate are true. So the iso drawing shows a lot of oblique lines which cause the drawing ugly-looking. I think it also hard for field installation.I am curious how you guys handle this situation.

Thanks for your advice.

Wei Rong,

Question 1: Wind direction
Your Stress Analysis subcontractor is WRONG. If you have significant skewed horizontal piping and the wind loads can be normal to the skewed piping then that case needs to be analized as well. Insist the subcontractor do your engineering correctly or find someone who will.

Good Luck,

Kevin, thanks for replying.
I just realize I was a little confused with direction in the previous post and just correct it. However, you guessed out the question I asked. Amazing!
In this project , there is no skewed line , all lines are either paralle to southeast or north east. In this case , true?
I think if only one element involved, maybe true, but a system with connective element , not really. I did not have full confidence on that. Please advise me. Thanks.

Wei Rong,

Wow, your really changed up your question. Now, I have to agree with the contractor. If your entire plant or unit is rotated as seems to be your case now, the wind should be run with the directions normal (perpendicular to) the pipe. This is the most conservative, there is no need to run N-S or E-W wind if you don't have any N-S or E-W piping. If your pipe is modeled skewed to your CAESAR axis, then you can get the correct wind directions with direction cosines.

Most plants that don't sit square to the world establish a 'Plant North' or 'Unit North' and drawings are based on that so at least the drawings are square.

I didn't comment on the PDS situation because I'm not a PDS expert but I have seen the way PDS treats skewed piping. Ouch! If your whole unit is like that, I feel for you.

Good luck,