unsupported span

[bhart192]

need a little help here, we're planning a pipe support system and looking for some info on unsuppported spans , we will have a 6" sch 40 pipe carrying sand (100 pcf) at 500F , I see a lot of data on pipe filled with H20 , thanks Bob

 

[ione]

The principle is the same: just replace water with sand. Calculate the max bending stress considering the pipe is loaded with a uniformly distributed weigh (pipe weight + sand weight). You must keep the calculated value lower than allowable stress for your pipe material at your reference conditions.

 

[MiketheEngineer]

Bingo!!

 

[SNORGY]

Most of the tabulated pipe span data, I think, reflect the maximum support spacing to keep the piping natural frequency above a certain value to avoid resonance due to wind loading, so bending stresses might not limit the span length.

You might evaluate the span lengths and support spacing using a base case for water-filled pipe, compute the corresponding bending stress, hold that bending stress constant, and shorten the span according to the higher density of the slurry.

Regards,

SNORGY.

 

[BigInch]

No, usually the span is limited by deflection criteria of some kind, maximum 1/2 inch at the centerline, which is generally also less than what approaching the bending max stress would give.

Natural frequency criteria gives very different answers, depending on if they are filled with liquid or gas.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[SNORGY]

You are probably correct, BigInch.

I read this thread a while back, and perhaps took a lot of what's in it out of context.

thread378-49424


Regards,

SNORGY.

 

[BigInch]

Probably. It's a big thread. If you actually check the span tables, you will very seldom see any results from stress limits. Maybe on the 2" thin wall pipes. Floor beams in buildings do not often see stress limits either. Deflection limits almost always pick the beam section size for you.

Standard pipe rack distance beteen rack bents for pipes containing water (hydrotest load) is 20 ft and has been ever since I remember. U-Bolt any small lines to a bracket and U-bolt the bracket to the pipe next to it. Trying to save money with exact span distances is proven false economy in petroleum piping & refineries. Water plants may be another story entirely.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[MJCronin]

I agree with BigInch. Deflection will usually govern piping spans.

If your contained "fluid" is ~100 pcf. I would simply halve the spans for water (~62 pcf) and then check defelections based on the modulus of your piping material at your 500F operating temperature.

Do not forget to evaluate your pipe support loadings based on your new spans and watch out for huge loadings developed at any riser supports!

This is the type of system where I believe that a detailed pipe stress analysis would be useful.

My opinion only