Hi,everybody
There are something disturbing me always in my stress analysis.Appreciate any suggestion and comments.
1)How to model the equipment?Assume the nozzle of the equipment one anchor point and calculate the displacement of the nozzle?Or model the equipment with a very large pipe?(The equipment maybe exchanger,maybe vessel)
2)No matter which way we model the equipment,the temperature of the equipment is a very important factor concerned our anaylsis.Which temperature will be used in the analysis?The average tem. of all inlet and outlet pipelines?Or the tem. from the data sheet of the eqipment?If from the data sheet,which one of the operating tem. and design tem. of the equipment should be used?

Thanks!

Hi Rockey,
1) There are 2 ways (as far as I know) that you can model the equipment... Try modelling a rigid body with zero weight from the nozzle to the center of the equipment (e.g. tower) and from there, down to the skirt of the tower using the tower temperature and diameter. This is followed by another rigid body, from skirt to base with temp slightly higher than ambient. The base of the tower should be anchor. The other method is to determine the thermal expansion of the equipment at the nozzle location (dL = thermal coefficient of expansion x Length x Temp)and input this as a displacement vector. Do remember that there is a radial dimensions as well. You should be able to find something in the Caesar Help file.

All the best in your modelling.

2) For checking if the piping has exceeded the code allowable, I always use the design conditions.

Hong-Joo,thank you very much!
Accoding B31.3 code,the most severe condition shall be taken into consideration.So it is reasonable to use the design conditons.But in some special place,for example,the vent header,the line maybe route very long destance.And its design tem. mostly very high.But actually,its operating tem. is just about ambient.If we calculate the line using the design tem.,there have to set many loops and many spring suppots.But in fact,it is not necessary.So,how to deal with this condition?

Appreciate any concerned information!

Hi Rockey,
I don't think there are 2 ways about it unless someone in the company wants to waive off the requirement of using design temperature. Typically for these long lines, you should have a number of elbows, these itself, also act as 'expansion loops' as it gives the piping additonal flexibilities.

You are incorrect when you state that B31.3 requires that the design temperature should be used for analysis purposes!

The terms design pressure and design temperature pertain solely to pressure design requirements.

By coincidence they may end up being used in analysis but this may be merely coincidence.

B31.3 requires you to analyze the maximum displacement stress range. For piping attached to thermally displaced equipment it may very well be a lower ambient temperature whereby the pipes growth would not match the equipments growth.

I strongly suggest you buy one of the various references listed here http://www.coade.com/support_reference.asp?varflag=Reference and in particular recommend the books by Woods, Becht, or Van Laan. It takes more than CAESARII to perform a credible analysis, the need for knowledge and experience can never be understated.

Also, be very careful with the rigid elements when modeling vessels. The vessel shell should be a large diameter pipe - not rigid, especially if the vessel is a tower. The reason is that if you put a wind load on the tower, a pipe element will deflect - a rigid won't.

The element from the nozzle to the centerline should be rigid, but all other tower elements should be normal pipe elements of the appropriate dimensions.