Hi all;
i have a confusion weather i am doing right or wrong so i need some advice from seniors
if my pipe is along X-axis, vertical is Y axis. if my pipe is lying on steel structure with u bolts, i am using straint as
both y ( +,-)
z (+,-)
am i right and do i need to change stiffness value from 1.0E12 to any other in case of u bolt?

Hi sami

Yes you are doing right thing. Just cross check if your support standard mention any gap in that u both support detail.
You do not have to change stiffness only ensure that your system do not produce unacceptable huge horizontal load on that support.

Regards

Habib

Hi shr
maybe the gap of the U bolt SUPPORT is 2mm,if the pipe diameter is large,so we should think the expansion of the diameter direction, maybe the gap is 1 mm,should we input the 2mm gap or 1mm gap?

Regards
zzw

Hi zzw
Radial expansion of pipe is not considered in stress analysis.
Guide gap in Caesar again depends on company standard.
In some company support standard U bolt gap mention 2 mm but stress analysis is performed with no guide gap.
In fact zero mm or 2 mm gap is very difficult to ensure in site with common support standard.
Small gap difference do not make much difference in stress analysis.

When guide gap really make significant change in nozzle load like compressor, turbine it is advised to use rigid strut to ensure zero gap in horizontal direction.

Hi shr
i don't think zero mm or 2mm gap don't make much difference in stress analysis.beacause if the gap is 2mm,that is meanings the pipe can move 2mm in the transverse movement direction ,when the pipe stop to movement,the U bolt SUPPORT limit the pipe movement in the the transverse direction ,mabye the pipe stiffness is large,so the transverse force in the support is much difference between the zero mm gap and 2mm gap,because the two situations are different expansion!

Regards
zzw

Thanks habib for confirming me and that s nice that people are discussing more option in this topic it will increase knowledge of people like me

Hi zzw

I agree your point is correct.
But there are some practical aspect. Say we want exact 2 mm gap in particular support but at site it will not be possible to make that exact gap with common standard support. Gap at site may be 1 mm or 3mm.
Point is that we should not make a piping system where gap tolerance will seriously affect the system.
Some system still we require to maintain exact gap. Rigid strut is special piping attachment that can ensure exact zero mm gap. We can use it in critical system.

Hi shr
i agree with your opinion that at site it will not be possible to make that exact gap with common standard support,but for the support of the large diameter pipe it is difficult about how to design this limit support in the transverse direction ,please to see the attachments picture,we should input this 2mm gap in stress analysis with the caesar program?

Hi zzw

You are now concern of design of support.
we have to make conservative support design.
Say 2 mm gap support load is 10000 N
zero mm gap support load is 20000 N

we have to design the support for 20000 N load.

Hi shr
when you input 2mm gap,because the pipe stiffness is large ,but the transverse movement is less than 2mm,maybe 0.5mm,so the nearby nozzle maybe is large about the force and moment,i hope this gap is zero mm.at the same time this limit support may sustain very large force in some case(just as Say 2 mm gap support sustaining load may be 20000 N,zero mm gap support sustaining load may be 10000 N) .....
just you say"But there are some practical aspect. Say we want exact 2 mm gap in particular support but at site it will not be possible to make that exact gap with common standard support."
so i am confuseing that i should input this 2mm gap?the theory calculation is different from the fact installation,what do you think about it?

Regards
zzw

Hi zzw

"when you input 2mm gap, because the pipe stiffness is large"
No this is not the reason.

Do not be much serious of zero gap or 2 mm gap for most normal piping stress calculation just follow whatever your company practice says.

For highly critical system, sensitive nozzle or very large diameter make 2 report ,one with zero gap & another with 2 mm gap . Consider conservative result among both of two result in terms of support load, stress & nozzle load.

Hi shr
thanks your answers! but in some case ,the two results are very large different ,because the pipe stiffness is large and the pipe transform difficultly.when you use the guide support in the large diameter pipe,we must be carefull of the gap.after all the theory expansion 2mm is very different from the fact installtion 2mm.for the samll diameter pipe ,the zero mm or 2mm gaps do not make much difference in stress analysis!

Regards
zzw

Hello Muhammad-Sami,

The designation of Vertical Axis is interchangeable between Y & Z, always make sure that you have the right designation for your Vertical axis.

I would normally use GUIDE instead of z(+,-) for simplicity, if both sides are having the same gaps or properties. It is very convenient and to use especially for horizontally skewed lines.

I hope this helps...

hi i got your point and i have in my mind that we can use z as vertical axis too.i have used guide with no gap to act as restraint. in horizontal pipe at some degree from axis this method is working. i am attaching two pictures. what you say about using guide on vertical pipe to stop pipe moving backward due to skew pipe?
i hope attached image will explain what i want to say

There is a help function on CAESAR II. Try moving your cursor on the restraint type on your Caesar spreadsheet and click F1, you should be able to see this:

X (cosx, cosy, cosz) or X (vecx, vecy, vecz)
Translational skewed restraints. May be preceded by a (+) or (-). If a direction vector is entered, i.e. vecx, vecy, vecz, CAESAR II will convert the direction vector into the corresponding cosines.[/font]

oo thanks q361. it was not too clear in f1 help but in application guide it has been expalined with detail. i should have read it before. sorry for that.