dar all!!

As far as I know any snubber requires a minimum velocity of the pipe before becoming rigid during a dynamic load.
I am doing a static calculation of a steam pipe with seismic forces and steam hammer.How can I modelize that lost motion? Perhaps with a gap? Is there any typical gap?
I am searching in LISEGA catalog (project's supplier) but it says that the response of the snubber is instantaneous but I think it is not real..

Thanks for any help.

regards

do a search on snubbers on this site you will find all the answers you may want and more!!!!

I recommend you look @ the gapped LISEGA Ebars which act a gapped limit strut with two distinct krates....

Hello,

I have been searching this site but I think I have not found it..

I see that there is a minimum speed of the pipe necessary for the snubber to become rigid. My problem is that I do not know how to include that data in my static analysis of the seismic forces and steam hmmer. I do not know, i.e, if the pipe is going to move 1, 2 or 5 mm before the snubber gets blocked.
Any suggestion?

Thank you all.

gap the support by your guess amount so that the line may displace freely by your guess amount...

what to guess???? beats me but if 1 mm overstresses the system your system is probably overstressed at any rate if you were to take into account local structural steel flexibilty....

frankly I suspect that local steel flexibilties (krates) will probably allow more displacement than the lockup rate of the snubber....


you are sharpening a very sharp edge with your efforts make sure you don't cut yourself....

Dear john C,Luf

I am not very clear about what you mean, you mean that we need not consider the 1,2 or 5mm gap before the snubber gets locked?

If actually the piping may overstress because of something such as the strural steal flexibilty and snubber gap, but the model don't know this, the model results will be ok, Does it is a disaster? Does those safety coefficient of the B31.1 code work here?

Regards,

Dear whm,

If you are determined to use snubber you do not need to define a gap in CAESAR II static analysis. Snubbers are active in the piping under sudden movement and acts as rigid support in the direction that you identify in the input window of CAESAR II. I do not believe that you need to introduce additional gap for the static analyses. It will not change anything. If my memory is right, the CAESAR II locks the gaps under the occasional loads. ( This needs verification from the CAESAR II user guide ). If so, there is no meaning of introducing a gap with snubber in the snubber acting direction under the occasional load cases.

In the load cases of static analysis, you need to make the snubber active under the occasional load case(s)as well.

The sensitivity of the snubber against sudden motion can only be given by the manufacturer or ( if the information available) by their catalogues. You need to go through the catalogs of several manufacturers to identify the suitable one against your need. I guess, if it gets more sensitive you may get more frictional forces into the piping system during the thermal expansion. This information on friction should be given by the manufacturer.
I do not think this is very effective in the calculation due to the heat rate applied to the system against the motion of snubbers. If the heating rate is high, you may have to think about.

Structural steel flexibility is an issue in any scenario. You need to introduce the flexibility in the support identification or model the structure with the piping to be able to simulate the response of piping properly.

Regards,

Ibrahim Demir

Dear Ibrahim Demir,

Thank you for your reply!

The manufacturer catalogues on my hand say that their snubber have a small mechanical gap, less than 3mm, and the stiffness of the snubber is about 40KN/mm, so once i worried that gap may lead to big change of calculate results if gap is introduced.

Best Regards,

Dear whm,

You must be dealing with very large pipes and large snubbers. I believe the stiffness rate that you are talking about is the dynamic stiffness ( spring rate) rate and you are able to use it in your calculation.

3 mm of mechanical gap looks very high. You need to find out the the source of the mechanical gap. The gap in one direction is definitely be filled by the thermal displacement of the piping.
The opposite direction is a question mark.

You had better talk to the manufacturer. I would like to hear about the result.

Regards,

Ibrahim Demir

Dear Ibrahim Demir,

Manufacturer explained that small movement(usually less than 3mm) is needed when the snubber load change from zero to nominal load. 3mm have included the mechanical gap factor. mechanical gap is very small, may less than 0.5mm.

So I misunderstood the manufacturer catalogues.

Regards,

Dear whm,

I would still ignore that small displacement until the snubber gets in action.

This is my opinion only.

Regards,

Ibrahim Demir