Problem With Piping "Lift Off"

I am not an expert in the field, but I think you should not let that piping sag.

why of why do you keep posting when you clearly know nothing about the subject matter being discussed. Well I suppose this time you did not tell the OP to Google "Problem with Piping "Lift Off"", so perhaps you are learning (albeit very slowly).

Why do you post anon when you are a regular?

I am not sure this poster is a regular. I suspect his various identities are being banned one after another. It is an endless game of whack-a-mole for the administrators to keep up with multiple email accounts all originating from the same sphincter.

Several things could cause this "lift-off":

1. A nearby valve or heavy piping component that is inadequately supported, causing the pipe to sag between the nearest hangers, but to bow upward from the next hangers away. In this case, support the heavy item better.

2. Thermal expansion in a section of pipe "trapped" between rigid mountings, causing the pipe to buckle sideways or upwards, depending on how it is free to move. For this, design the pipe with expansion loops or joints, and support with spring or roller hangers.

3. Mechanical damage, such as raising a forklift into the piping. For this, the piping can be protected with a guard frame or railings.

Bojo....

By piping "lift-off" are you referring to the movement of an actual pipe, or "lift-off" as indicated by the results of a piping stress analysis. ?

What to piping seems to be telling you is that it wants a spring hanger in that location.

I suggest a detailed computer analysis of the system.....with actual as-built conditions and temperatures/pressures.

If the analysis indicates that the "piping lifts off" to the amount predicted by the analysis (+ or - 20%), you are spot on.

If the analysis indicates that the piping is within allowable code stress limits......I would do nothing.

Come back and tell us of your final solution

MJCronin,

Sir, I'm refering lift-off as indicated by the result in stress analysis since as far as I know(correct if I'm mistake) there is no such principle behind in the analysis when piping lift-off, It is the user judgement how to deal that kind of problem.

My concern in kind of problem is to gather some idea from some engineer in this forum who had experience in there analysis.

There some post in CAESAR II forum about this kind of problem but there such no solution with regards this problem.

Thank YOU!

Bojo one consideration is what is attached to the piping system. As MJ Cronin mentioned some type of spring hanger may be required. A variable spring can or constant support may be required to supply support or constant load to prevent stress to the attached components.

Hello bojo,

As for any conveying material, you should always take into consideration the density of the fluid/gas that your piping system will convey as these will have an effect on the performance of the pipe system. Temperature and pressure will have to be factored in when you design your system to allow for possible thermal expansions. Couple these data with the properties of the pipe material that you will use and results will give you an idea as to how much stress your system will be under, hence the idea as to how you'll need to support your pipe system. As a general rule, valves (since these are normally heavy set) will need to be supported individually to prevent additional stresses on your assembly due to its weight. The type and spacing of your props/supports will depend on the data that I already mentioned. If you project that there will be a considerable amount of expansion/contraction in your system due to temperatures, then by all means, provide room for your pipeline to move in order to avoid buckling. I hope I made sense.

Piping systems should always be sufficiently supported no matter what, whether it be pressure piping, heating pipe, fluid transfer pipe, etc...

The necessity of supports are principally to preventing unnecessary deflection particularly in horizontal runs and where couplings such as Viking Johnson (VJ) are being used to accommodate potential installation variations or simplicity of pipe run for fitters to be able to cut pipe to length on site. Equally, vertical pipework requires support; though it could be argued to a lesser degree because flanged pipes have good general compression characteristics.

The spacing of pipe supports in flanged systems should by rule of thumb be one per flange, though in certain circumstances this either is unecessary if a pumping system is incorporated in the pipe run, or if the pipe run is in a vertical repose.

In non-flanged pipe systems, supports should be provided at equal intervals or changes in direction so that no unnecessary forces are placed upon the joints whether they be threaded or socket connections.

Pipework that is working under high pressure could be argued needs little support - turn a hose on with full pressure, it will straighten up and become quite rigid; however, it equally becomes stressed, and thus movement or deflection is inevitable thus supports must be provided (fire hose is a classic example, if left unsupported by manual means, it will flail around and snake everywhere).

I have added a 3D generated image of a simple pumped pipework system to illustrate the point, you will notice pipes (whether flanged or not) are all supported from the floor, and in the vertical are supported from the pump discharge and eventually secured off the distribution tank above.

The use of couplings and valves are shown to good effect in the example, since from the suction point (encaste in the wall) to the pump there are control valves and hose couplings, yet support is unnecessary since the run is very short (however on the actual installation a support was added between the non-return valve and the tee), and from the pump to the " Y" branch, again no supports are necessary except between the "Y" branch and the VJ coupling. From the "Y" branch the run then turns vertically using a long radius bend and vertically upwards to the distribution tank and is secured off the tank support frame (ideally a support should be placed just beyond the long radius bend/VJ coupling, which was done on the actual installed site).

Hopefully you can see, even though the run is relatively short and is a pressure system (PN16), the need for supports is essential and should be provided where necessary; but depending upon the type of run of pipework, supports may not be necessary at every flange connection interval.

Hope this helps you understand things a little better.

Best regards,

apexmaster

Good day everybody

... I agree with some of the posts ,

lifting off in operating cases ( where all loads are combined ) means in may opinion piping is not supported at that specific location

This could happend for instance when you have a vertical leg expanding thermally upward onto a horizontal leg , with in that horizontal leg the displacement induced by thermal Higher than displacement du to weight , so the vertical movement is up and the piping is not touching his support at that location

This also means that some other load cases including Sustained and expansion ones have different type of supporting

Where you have a lift off there is now friction, the model could not reflect reality

It is obvious that a good system is the one for which alll load case have their supports working

As a guideline, what I use where I work is =

Normally one use a +Y ( single acting rest) at support , if you discover later that you have a lift off at that support , thus with reaction FY = 0 , then =

try again but this time with Y (double acting ) , check then the reaction FY , if it is say less than 300 N to 500 N than this ok,

By the way check also loads on at equipment if you have any around this support

Note also = if you do dynamic all supports are closed , because most of pipestress software is Linear, means double acting ,.. but this is another topic

Ramadan Mubarak

Fathi

guest,

"try again but this time with Y (double acting )"

I agree in this statement...but one clariffication regarding this statement "check then the reaction FY , if it is say less than 300 N to 500 N than this ok," correct me if I'm mis-interpret,..you mean if the load less than that stated value, so no problem with your support from +Y to Y..but f your load is more than your suggest value, how can you evaluate?

BTW, you have a document as a basis for your evaluation that load in your support from +Y to Y that says ok when your load limit to 300 N to 500 N?

We're not sure as to what the sizes are in the query that Bojo raised. I guess limiting the figures at 300N - 500N is not an idea that I would go with. If you have larger pipe sizes, I'm pretty sure that the figures would be even higher. The baseline would be, gather all the data that you need from fluid/gas to be conveyed, working/service temperatures, working/service pressures, materials for the pipeworks, roughness coefficients for each of the materials that you'll use. factor them all in and start your calculations. I'd go with apexmaster's explanation of the practicalities of support location as well...

Line size, temperature, pressure and what the pipe is carrying are not mentioned - all critical factors.

The system needs to be analyzed as a whole - discussing one section alone is meaningless and may well not solve your problem.