What can happen, if we remove friction balanced intermediate anchor inbetween loops in low seismic zone?


regards,

sam

Well, I am definitely a convert to occasional anchors and guides... something to do with the piping system I'm looking at that has no guides or anchors -- and the shoes on one part of the line are dangling in mid air about 1-1/2" from the support beams. So, I'm all for them just so that in 30 years when someone wants to add something to the plant, the pipe is where they think it is...

not to mention when analyzing connecting piping they make nice easy places to stop the model (grin).

-Shanno

Yes, it is true that without any intermediate anchor, the adjacent piping systems will not be structurally isolated and it is possible to have actual axial displacement differing somewhat from the same postulated from piping stress analysis.

But, applying risk-management methods, one can provide long shoes to avoid shoes falling from supporting beams. If piping stress analysis is not predicting enough (thermal expansion & friction) axial load at an intermediate anchor,why not provide a support & guide there, just for a change to economise on strucural bracing ?

regards,

sam

Sam,

I'm with SLH, I too have seen lines where the shoes have slipped off the rack. As far as I'm concerned just one is one too many.

You talk about economics, how much do you actually save by providing extra long shoes at every support instead of some structural bracing? Is it worth designing for the additional spacing between nested loops and branch connections as well as additional flexibility for the additional movements? Can you predict this possible movement?

My idea of 'applying risk-management methods' is that I control my pipe movements from thermal, wind, seismic, etc. by physically restraining my pipe using anchors, line stops and guides. This way I manage where my pipe is going when it heats up and where it’s going when it cools down. That way, I don't take no risks!

Caesar analysis with and without friction are just theoretical. If you don't control your pipe movements, you don't have a clue were it's going. In an uncontrolled system, too many things can stop a shoe; Paint, glue, weld spatter, a burr on the steel or shoe, guide too tight or shoe locked in guide due to rotation, etc. Also, there is no control over which directions you're pipe may creep after several thermal cycles or restraint from unexpected slug flow.

Speaking of risks, where are the risks with your proposal?
Structural: 0%, completely off the hook.
Piping (Sam): 100%, continuous for the entire life of the line.

If a Line Stop and Bracing IS installed as I feel it should be, the only time Structural would be at risk is the occurrence of a seismic event and the risk to Piping during the normal operation would go to zero.

I really don't have much sympathy for whining Structural Engineers. No product is going to leak out of deformed structural steel, but it's certainly possible from deformed pipe.

That's my 2 cents on risk management.

Many years ago on a job in an active seismic zone there were numerous lines that neeeded to be controlled thermally, to validate the basis of the analysis. However nobody cared if thay broke free and slapped all over the place in a seismic event.

So in order to retsrain the line thermally I designed a break away longitudinal stop. The stop was designed for the minimal thermal forces and yet would break in a seismic event thereby not overloading the local member during seismic events.

The plant has since undergone numerous seismic events sometimes the stops broke and lines jumped, requiring some repair work but overall the stops have done what everybody wanted. So design a break away longitudinal stop and place it at your point of balanced thermal strains.

Thanks to You Sirs JCL,KLM & SLH. In fact, I wanted to have a response from my mentors and know about the pros and cons of such a bizarre idea.

Regarding the design of break away longitudinal stop I have some curiosity. What is the method of this design, any code or document for reference ?

regards,

sam

Additional points:

1. Do not forget that the piping and in particular the elbow wall thickness will vary, thus negating your "thermally balanced" loops in addition to Kevin's comments.

2. For seismic designs on larger or relatively heavy lines, a stop can be added in the middle of the loop to help share the seismic load (3 stops vs 2). This is obviously more feasible on new construction, since an additional structure is required outside of the rack. Check the rotation about the vertical axis at this new support to ensure the stops do not bind up against the beam (normal installation gaps may be OK).

3. Since the plant is in a low seismc zone the loads should not be too bad. Query structural if the rack or structures were originally designed for ANY seismic loads. If not then structural has much more to worry about than your loops.

Break Away stops are not code items they are rather a bit of imagination on my part.....

Two plates with a small bolt between them... the plates are allowed to slide and create a shear across the bolt.

Its suprising how much load a small diameter low strength bolt can take in shear.

One other thought on thermally balanced lines.... How are they heated up???? If they become heated by the fluid inside them, then initially one side will be hotter than the other negating a portion of the balance.....

Sir,

To take care of heating up by the fluid, even for thermally balanced stop, we design with 1/3 the thermal expansion and friction load from one side.

As you wrote, your break away stop worked as you wanted it to perform - like a fuse in an electric circuit or a safety plug in a pressure cooker. It is a good idea indeed!

It is just opposite of a snubber, upto some load, it will have high stiffness & zero afterwords. A snubber works based on accleration as a restraint for fast transients only.

regards,

sam

What if the restrain breaks and the pipe falls off the slippers?

This entirely depends on the catagory of fluid flowing through the pipe. For non-lifeline/safety-related piping, some distortion/ even collapse may be acceptable where only we can ignore seismic loading in design, if design basis permits.

regards,

sam