Any one have an equation which gives the maximum required distance between supports so that a sloping line does not pocket.

i believe kellogg may have a few pointers to this.

the distance (l) may be a function of slope,E,I,W

regards

Hi, there!

Here is a general formula that I use for maximum span calculation when the pocket occurence should be limited/avoided:

Lmax = [ 384/a * (kappa/m) * (E*I) / q ] ^ (1/4) ,

where:

a = non-dimensional coefficient: a = 5 for full anchored beam model, and a = 1 for simple supported beam model; you may consider an average value of 2 ... 3;

kappa = the required/adopted slope (i.e. 1/1000 ... 1/100 for instance);

m = the minimum (adopted) ratio between the erection height for one span, and the maximum deflection throughout that span; m > 1, generally m = 3 ... 4;

E = longitudinal elasticity (Young) modulus of the material (under hot conditions, for conservative reasons);

I = pipe cross-section axial moment (I use to perform this calculation both for nominal and corroded pipe section dimensions);

q = linear distributed pipe weight load; generally, I use this checking formula for empty-pipe conditions, because this is the actual operating situation when condensate should flow through the sloped pipe;

" ^ " represents the power operator.


I hope this formula will be useful for you.

Regards,

Dorin Popescu

Dear T.J.N.,

If you provide a node number in the middle of span, you can get it verified within Caesar-II results whether pocket is occuring middle of span
in no contents sustained loadcase.

regards,

sam

Referring to page 64 of 82 of the following booklet,

http://www.anvilintl.com/db/datasheets/Pipe_Hanger_Design-05.pdf,

the minimum slope required to avoid pocketing for condensation is 4 * delta(empty pipe)/span. We consider this to be 2 * delta(empty pipe)/span.

For example, for a 8" empty pipe having 20 ft span has 0.05" midpoint sustained deflection. Minimum Slope to avoid pocketing should be 4*0.5"/20' i.e. 1"/100'. We consider it as 1"/200'. Is Anvil right ?

At first, I went by herd mentality - accepted the printed words over reason of ourselves! We are getting conditioned to accept without reasoning!


regards,

sam

Dear All,

i just want to know:

a) Is it necessary that we should consider piping slopes within stress analysis.

what i think it is not so important since slope will not much effect the stress analysis results.

any comments?

Thanks

When modelling a larger system with several tie ins between different pipelines you will not be able to make all pipes line up properly if you dont include slopes in your modell. On smaller systems you can get away with not including the slopes I guess, but for larger systems you'll be better off including them from the beginning.

Per Magne

The original question was in relation to a Purified water line which absolutly had to have full draining when hot.
Caesar was used as a tool to asses the effects of expansion on drainabillity as well as stress the tubing during steam out.

Tim