maximum pipe deflection

[pongsapak]

Hi all

Do you know why all most recommend about maximum pipe deflection is 12.5 mm

Thanks

 

[BigInch]

Yes, its about the same as 1/2 inch.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

OK, I'll tell you.

If you have a 20 foot span, 1/2 inch is equal to L/240, a common limit for beam deflection where too much liquid pooling is avoided.

L/180 is a typical deflection limit for beams under motion sensitive floors and equipment.

L/360 is a typical maximum deflection limit for normal use floors.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ione]

Regards

http://www.awc.org/technical/spantables/tutorial.htm

 

[rconner]

Not sure exactly what the OP is looking at (this amount, or more or less, deflection in and of itself might not really mean much in an engineering sense, without knowing other details such as application/size/span etc.?), but of course liquid pooling can in some applications be eliminated by design gradient. According e.g. to AWWA Manual M11, “If intermittently supported pipelines are to drain freely, they must contain no sag pockets. To eliminate pockets, each downstream support level must be lower than its upstream neighbor by an amount that depends on the sag of the pipe between them.” This manual goes on with a simple calculation procedure to thus determine a “practical average gradient to achieve this, and then concludes, “The elevation of one end should be higher than the other by an amount equal to four times the deflection calculated at mid-span of the pipe.”

I guess aesthetics, stability or dynamics, as well as effects on specific coatings or linings involved might also be considerations in some at least local stipulations with regard to mid-span deflection.

 

[rneill]

I think aesthetics and perceived acceptability has as much to do with acceptable deflection limits as anything else. Myself, I've had situations where I had some piping that exceed the 1/2" deflection (but was still well within acceptable engineering limits) and it caused a lot of headaches with frequent requests to verify the design and acceptability.

It creates far fewer questions if the deflection is kept below limits where people don't really notice it.

 

[BigInch]

Same is true for structural work. A beam may perfectly well pass stress allowables, but deflection and vibratioin makes everyone walking on it worry far too much about a possible collapse.



**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[LSThill]

Team Members

NOTE: In most cases deflection will determine the span length. These span lengths are acceptable for horizontal runs of carbon, alloy or stainless steel pipe with the same O.D., equal or greater pipe wall thickness and for temperatures up to 750 degrees Fahrenheit. Piping with concentrated weights and risers require lesser span lengths and then allowables for stress and suggested deflection given in B31.1 Power Piping Code govern.

Span lengths may be found by inserting data in the unshaded areas.


L S THILL

 

[StressGuy]

To keep the span natural frequency >4HZ.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.