I tried to search in the documentation of caesar II regarding blank gap wether it is the same with the zero gap but i could not found it.
If there is, what part of documentation in caesar II where it is stated?
Is it really the same meaning?
Because in the displacement, it is clearly stated that leaving it blank mean the pipe is free to move.

You do not need to specify a zero. For the gap field, a blank is the same as a zero.

Dear Mr. Richard

then either we will leave blank or put it zero . both result value should be same. BUt actually it is not correct when we analyse the system with gap field or with zero the analysis results are different.

can you tell me why is it? what Caesar under stand with blank and put it zero.

That makes no sense. Send the job in to TechSupport.

My suggestion, that for pipe 12 inch above, gap 3mm should be input to CAESAR II input, altough it is only construction tolerance. Because above 10 invh the stiffeness of pipe is more higher and little displacement can cause high force, especially if you have this guide near sensitive equipment.
Some of Client/owner want these 3mm gap to be modelling, some are not, but ithink like i said above it will be need for 12" above and if system have sensitive equipment.

Regards
Nalibsyah

Nalibsyah,

Quoting gaps is a project dependent parameter & varies from project to project. So , generalising this as 3 mm gap or applying it for 12" higher lines may be misleading to some.

As far as support gaps are considered, if the gap is defined as Construction Tolerance in Support Standard/Catalogue one is referring to , then this gap should be considered as zero .However, if this is not a construction tolerance & a real gap , then it should be specified as what it is in analysis.!!

The applicablity of gaps in supports is irrelevant with the pipe size.Whether its a 2" line or 20", support gap remains what it is.

Keep Smiling...

It always helps...

SJ

Thanks SJ,

What i mean here is situation like this, i have seen some company that doing their stress analysis during detail engineering by using Linier modelling approach, but here they are not considered gap at all in the model where actually in field they will be installed with 3 mm gap, so based on experience this will lead to a problem especially for large line near sensitive equipment.

I don't agree with you about you said that there is no relevance between gap and pipe size.
When you specified gap, then it means that you are allowed your pipe to move laterally, and remember from Stiffness formula : F=Kx, you can see if your pipe having bigger pipe then you have more stiffness ( K=3EI/L^3, and others according to beam stiffness formula), if you have more stiffness then you will have "More Load" if your pipe displaced from its normal position. 3mm displacement in 10" pipe will generate higher load than the same 3mm in 4" pipe.
I think you may have found in your experience where you must design your support with m,ore stiffness, and that is also why in vibration system gap should be avoided.

Thanks.

Dear Nalibsyah,
Providing gap in a stress calculation is a tricky thing. By saying so, no one can guarantee that the gap you mentioned in the calculation will be provided at site unless someone verifies it. I have seen locations where gaps were not provided at all despite of the 3mm gap mentioned in support standard. Also, it is a construction tolerance and not a deliberate gap. It can be anything between 0 to 3mm. That is why plant walk down before startup is considered to be a very important activity.
I do agree that the stiffness of a 10" pipe as compare to smaller pipe sizes is high and hence the loads generated are huge. But what about the stiffness of supporting structure? We do not consider the actual supporting structure stiffness in our calculation!
As per my understanding it's not necesasry to include the stangard 3mm gap in the calculation except near sensitive equipments. In case gaps are provided (even 3mm) near the vicinity of the equipment (3-4 supports from nozzle), it’s better to specify at the isometric. Also, if possible consider the structure stiffness in the calculation (if one is lucky to get it from civil/ structure department).

Regards

Nalibsyah,

Thanks for the information.

But what I meant is "if gap is not a construction tolerance , then it should be used in analysis."

I do agree for higher line sizes , the loads will be high. This is obvious.

But this should not be the reason for not using gaps for line sizes less than 12".

Just consider a situation where you have a lateral guide for a 10" line at 350 deg C in vicinity of a rotating equipment , say pump. Now if you use no gap (i.e 0) or standard gap of support, there will be significant difference on nozzle loadings as well as support loadings.

So this can't be generalised.

I too have seen some EPCs don't mention gap at all (but again the reason may be that the gaps are construction tolerances & not real gap !!!)

Keep Smiling...

It always helps...

SJ

Ok Thanks Rajind..i think i get your point..

I wonder if field supervisor have enough time to visit every support location for reviewing gaps!

With best regards,