Hello All,

I am analyzing a hydro test case and I notice that when you are considering the spring hangers as rigid, everything works fine, but the F type supports. These spring hangers should behave as “+y” supports not as “y” support, as they are behaving. What I’m trying to say is that if an F type spring hanger is locked during hydro test and the pipe tends to lift off in that point it (the pipe) will.
Is there a way to let this point to lift off during hydro test?
Can I work around this problem living that only spring “As Design”, but living the others as Rigid? (I’m thinking to give instructions to field to unlock only this spring hanger during the hydro test)

Can you give any suggestions?

Thanks in advance.

CAESAR II locks all springs for the hydrotest case. There is no facility to lock some and unlock others.

Are you planing to let these F type springs to have a lift off when considered as rigid? Because tha fact that an F type is lock doesn't prevent the pipe from lifting off the support.

Regards

Mr. Massabie,

Your comments puzzle me.

You seem to believe F Type springs behave different than the others when locked.

I don't know of any commonly used springs that restrain upward movement when locked. Please educate me.

I do have another suggestion. Since you have this situation, you might review your support scheme again to make sure you have a well balanced support system. Your spring support point lifting off for hydro is an indication that maybe you don't.

Also, to analize your situation, you can always create your CAESAR model they way we did before CAESAR had the Hydrotest feature.

Good luck,

Well, if an F type spring hanger has a lift off, then the pipe will move freely upwards. (I know that opinions are divided between who cares and who doesn’t care about this lift off). And I don’t want to start an argument about this lift off. But in the other hand if this is happening in a, lets say, A type spring hanger then you know that your rod hangers are in compression and they shouldn't. In this case provisions should be taken to prevent this rod hangers to be in compression.
I am not saying that its Ok to have this lift off, and I have to agree that the system is quite unbalanced as you noted, (I knew that someone would notice, congratulations) but late construction changes makes this to happen: is unavoidable and we have to live with the consequences. We already tried different approaches such as not having that spring at all.
That’s why I was so interested in work around this lift off: I need to know the consequences of this unbalance, and as you pointed the solution was to treat this case in a separate file with this spring hanger as a “+y” support and investigate what is happening with the remaining supports. That’s also why would be interesting to let this spring hanger to be unlocked during hydro test, since in this case the spring will be “following” the pipe upwards, and I would like to see what would be the reaction of the system…

Best regards

At the moment, CAESAR II doesn't really care what "type" of spring you have. All the software cares about is the spring rate and the preload.

Now, it is true that you can specify a "spring can" by specifying a negative allowable space. However, this is used only for plotting the hanger icon on the graphics. There are no analytical changes made based on this input.

I'll note this request on the developement list, and we will study this idea for possible inclusion in Version 5.10.

Mr. Massabie,

CAESAR can analize the Hydro situation you want, it's just not going to be automatic.

1. Copy your file to a new file name for HYDRO.
2. Change all of your springs to rigid supports EXCEPT for the spring that you want active.
3. Also add any supports that may not have been active in your other analysis but will be in dead weight or hydro.
4. Change the pressure to your hydrotest pressure.
5. Manually change or compare your stresses to what you are using for your hydrotest allowable.
6. Run this case: WW+P?+H
P?= P1, P2 whatever is the Pressure case for hydro

Also, consider adding some temporary supports for hydrotest.

About the locked spring hangers in compression.... I recommend that you get a spring catalog and review all of the components used in a spring hanger assembly. Check the pin sizes and corresponding support lug hole sizes, eye nut opening etc. Also get a small sample spring or go to a shop or the field and study how the rod is supported on the spring coil inside the spring. What you will find is that a spring hanger, Type A, B, C, D, whatever, will not resist any compressive load. If that support point moves upward, your hanger assembly will become slack.

Thanks Mr. Monroe,

That’s the most closest analysis to my situation, I will give it a try…good old times when we had to think twice before entering data in the software!
About spring hangers in compression, that’s what I meant with “…provisions should be taken to prevent these rod hangers to be in compression.” Yes, none of the hangers would take any compressive loads but, and you have to agree with me, the F type is the exception to that statement.

Best regards, and thanks again.

Mr. Massabie,

I don't agree with you at all!

There is no exception with F Type springs. When the springs are locked and the pipe moves vertically upwards at that point, the pipe will lift off the load flange for an F Type and for the hanger type springs, the support disengages. There is no difference in the behavior.

It's pretty rare that a spring support location wants to lift off during hydro and when it does, it's usaully the result of poor piping and support design. Personally, I don't feel CAESAR should be modified to accomodate this situation, especially since CAESAR can easily perform this analysis even though you may have to think twice to do it.

Speaking of that, I don't understand you comment "…good old times when we had to think twice before entering data in the software!" If you're not thinking about what you're doing, you're dangerous! You can't just model it up, push the button and accept the results. There is a lot of difference between knowing how to RUN software and knowing how to USE software. You need to be thinking every minute, otherwise it's just garbage in, garbage out and you need to recognize the difference between garbage and meaningful results.

Mr Monroe,

This is becoming long,
"...For an F Type and for the hanger type springs, the support disengages..." That is exactly what I'm saying. But, for an A type the rod will be on compression, and that's different from disengaging. For an F type there is no danger in that, for an A type would.

"It's pretty rare that a spring support location wants to lift off during hydro..." I said that late changes in construction made this to happen and now we have to live with that, and see what would happen. Part of this job is to look if something not quite right or not totally wrong is still in the safe side of the design.

I think that CAESAR II and any software should be flexible and powerful enough to accept as many situations as possible, (and my feeling is that people from COADE are doing their best to achieve it). The judgement about “poor” or “not poor” should be made by the responsible of the analysis not by the software.

“…I don't understand you comment "…good old times..." Just an expression, don’t take it wrong, however let me explain my self: Long ago, for example, you had to look in the B31 codes after your SH for each case, now the software does that for you. (Now you barely think if the number used is correct or not) .The software is becoming more powerful (CAESAR II and many others). The tendency is to rely more and more in the software. In fact, the Hydro test had to be prepared in a different file, now is a matter of introducing the Hydro test pressure in a field. Analysts are divided between how much is too much for a tool to do part of the thinking or “all” the thinking. And someone with the feeling of "now is too much" would have said that. In a way, that comment was an acknowledgment to yours.

“…If you're not thinking about what you're doing, you're dangerous…” finally, we should stop making comments like this one. In each side of this forum are professionals (engineers or not) doing their best in their jobs. The fact that they are coming to this forum, asking and answering its a prove by itself. (Don’t take it personal Mr Monroe; I’ve seen these from many others). This kind of comments might be pushing away people that are looking for solutions or that might have a different opinion than ours.

Best regards

How does the hanger rod compress????? These do not compress per se because they usually have slop in the pivot points etc. they move freely up some limited amount.

That is why sway struts are sold... because they carry compression and tension loads!!!

Take a close look at a hanger rod assembly or call a vendor and ask them what their rod hanger assemblies are load rated to in compression!

Perhaps this is a quicker fix for your hydro case.

Again, it is a second pass through the analysis once you find some F types holding the pipe down (and increasing load on other supports).

Supply a CNode for the supports in question. (The CNode is a CAESAR II item that essentially defines the "other end" of the hanger.) Then add +Y restraints at those CNodes and re-run the hydro case. The spring may be locked but the +Y will lift off.

This is my last post on this thread ... I Promise!

My comments:

DAVE DIEHL's solution is the best to meet the needs of your hydrotest case.

I didn't mean to get your shorts in a bunch, but I felt some of your comments were a little nonchalant and I felt the need to address that.

I STILL LOOK UP Sh and verify that CAESAR and I agree. The data base in CAESAR may not be the same values as those for the Code version for my job. Also, some stress values for some materials differ depending on the material thickness, CAESAR doesn't make that selection for you.

Lastly, the A Type spring will still disengage just like the others. The only difference in a A Type and Types B or C is that a A Type has a nut welded on the top to thread a rod into as opposed to a lug and pin. The design for supporting the load on the coil inside the spring is the same and when the spring is locked, it will disengage with upward displacement. I suggest that you call you local spring salesman and ask him to bring some samples by your office.

Best Regards,