Support Span Length Calculation

Dear all,
I have a 1 km straigth line-pipe over sleepers.
the first thing that I have to do, is to define the support span.
1)How can I define the max. support span length?
2) Which factor I have to consider for this purpose?
3) are there any admissible values for max bearing stress andmax deflection?

Thank you very much.

Dear,

As the code says, supports shall be directed toward preventing piping stresses in excess of those permited in the code.

So you can determine the maximum allowed span between supports using the the maximum bending stress theory (maximum stress from the corresponding code) and maximum allowed deflection.

Then, you can simply solve for span from equations, knowing the weight, diameter, momoent of inertia, etc.

Regards

Hi,
Use MSS SP69 for support span.
Regards,
R.K.

So Pablo GH,
Say the pipe is 36"nb then the allowable span is simply calculated by the beam bending equations allowing for the material properties and the allowable deflection (from where?) ?

So I can then rest the pipe directly onto the supports using this allowed pipe span can I?

What about local stresses at the supports/ buckling of the pipe cross section ?

Dear DSB1954UK,

The previously presented explanation was made in response to: "How can I define the max. support span length?". It was the "basics" to calculate the maximum allowed support span based, as explained before, ONLY AND EXCLUSIVELY on the maximum bending stress theory.

As stress analyst, you will fix the maximum allowed deflection (the media transported, the schedule and materials of the piping, ASME B31.1, ... "No rule, as along as it is under bending and combined stress allowables. You may want to limit it at times to allow free draining and even increase the stiffness for minimizing vibrations").

As you were perfectly setting out, much more considerations should be taken into account.

So, by using the determination of maximum span between pipe supports using maximum bending stress theory, you can find an starting point to define this distance between supports.

You will reduce this distance based on what previously said and, of course, on others factors an analyst should consider:
- Allowed maximum vertical deflection (as explained).
- Excessive stresses in the supporting elements and buckling (as you asked).
- Type of support.
- Excessive piping sag in piping requiring drainage slope.
- Resonance with imposed or fluid-induced vibrations.
- Avoiding excessive bending stresses from the uniform and concentrated loads between supports.
- Excessive thrusts and moments on connected equipment.
- A long Etcetera.

Regards.

I would be surprised if this information is not kept within your (client's) piping spec.

In addition to Pablo's list, I would expect to see a guide spacing, as a 1 km length of pipe could conceivably slide some number of meters in cross-wind conditions. Likewise, you would expect to see a number of expansion loops based on temperature - although admittedly, there are plenty of long lines that are working just fine without them, if they're allowed to buckle and curve.

There are some criteria and related formula mentioned in Sam Kannapan book for that. They are: stress limitation, vertical displacement limitation (refer to client spec for the value), also natural frequency.

For such value of span, you may pass the stress but not the displacement. Please take the shortest value of span which is the result of calc from the formula of those criteria.

Currently I am working on flow induced vibration (FIV). This for the case density x speed^2 value is high, which will generate big LOF.

By shorten the span (which is stiffer) will reduce LOF. By increasing ID (as followed by OD) will reduce LOF significantly as speed will drop. Only shorten the span could reduce LOF to low/ safe value.