I have 6" pipe coming off a nozzle in the +Y direction for 3 feet and then it turns in to horizontal direction. The nozzle has a displacement in the +Y direction. I have a spring hanger on the horizontal length of pipe at 18 inches away from the bend.

My problem is that when I run my expansion case, the hanger is seeing a positive Y load where i need it to be negative. What i think is happening is that the hanger is being designed by Caesar in the sustained case so when the pipe displaces in the + Y direction, the spring compresses and is actually pushing on the pipe.

Is there a way for Caesar to automatically design the hanger so that it is over supporting in the sustained case, so that when the pipe heats up and displaces it's still supporting the pipe rather than pushing on it?

Right now when i install the hanger, it is making my expansion case worse (larger -Y load on nozzle). I figured i can manually do it by making the cold load larger than what is actually is, so that the hot load is closer to the real cold load.

The equipment is up in the air, so a spring can wouldnt work, but even if i did model it as a spring can, it would be somewhat of the same problem. The spring would decompress in the expansion case and wouldnt support enough of the weight and the nozzle would be overloaded again.

Any help would be greatly appreciated.

Did you release that nozzle for the hanger design?

You can also enter the spring's "operating load" as hanger sizing input to dial in exactly the operating load you wish.

I'm not sure what you are referring to when you say the expansion case shows a +Y load at the hanger. Typically, expansion is (operating-installed) and since your spring node moves up, the operating load is smaller than the installed load and (L1-L2) should show a negative hanger load. Is there something else going on here? Like some nonlinear liftoff nearby?

thanks for the replies guys. iv been sick the past week and just got a chance to look at my thread again.

I have released the nozzles. Freeing the nozzles did help the stress out Relative to not freeing the nozzles but it still made the expansion case worse off than when it was unrestrained.

When I wrote that the expansion case is seeing a +Y load, I was trying to say that the Spring hangers were actually making the expansion case worse. They were being compressed when the pipe thermally grew up. The spring hangers were then pushing on the pipe rather than trying to support it up thus causing and even greater -Y force on the nozzle.

I was thinking that the spring hanger had to be over designed for the cold case in order for it to still be in tension when it was in the hot case.

Ill try entering in an operating load next, but i was hoping Caesar would determine the best possible spring for me with out having to enter my own numbers

By default CAESAR II will design the spring so that the weight of the system is balanced in the "hot" condition. The "hot" condition used to design the spring is close to the Operating condition, but not exactly the same (I'm assuming only one temperature case here). So you can see a difference between the hanger report and the OPE restraint/displacement reports.

This means that the hanger/system is unbalanced in all other load cases. Potentially, if the spring stiffness is large compared to the system stiffness at the hanger location, then the spring may pull the system around in these non-balanced load cases. When this happens, you start tweaking things on the hanger dialog, as you indicate you're about to do.

The hanger design is based only on the HGR load cases. The design procedure is unaware of any other load cases that you may need to analyze.

So after a lot of messing around with Caesar, I realized in need a cold spring. It seems as if I should try to find an alternate method to fix my problem rather than using a cold spring (or a spring with "cold pull") but I'm not sure if i have another option.

I basically want my spring to be designed so that it's stable position is Installed hot and the spring is in tension in the cold position. My nozzle allowable loads are so low that I cant for the life of me come up with another solution.

I'm having trouble getting the "long cut" and "short cut" to work in caesar and it seems like a very odd way to go about what i am trying to do.

Is there any other way i can manipulate my spring hanger to have a cold pull?

I might of misinterpreted a cold spring in Caesar 2. From what i understand, a cold spring is how you cut a specific length of pipe with puts an initial load on the pipe while it is in the cold condition.

Im trying to achieve this with a spring hanger. I cant make caesar model a spring hanger to have a cold pull( where it is over designed so that a spring hanger is pulling on a piece of pipe that has been displaced in the +Y direction rather than pushing on it ) i want my nozzle load to see a +Y force rather than a -Y force in the cold case and then in the hot case see a Y force that is close to zero with a max of -66 pounds.

Richard, your previous post is pretty much summarizing what i want to do, but i cant seem to tweak my hanger dialog box in the proper way to achieve this.

Any help would be greatly appreciated

No you can't put "cold spring" on a spring hanger. However, you can specify your own OPE load on the hanger dialog. Perhaps this will get you where you want to go.

As Rich suggests, the "cold pull" that you want on your hanger IS the preload. If you are entering a spring in the model you enter this preload as a "Theoretical Cold Load" (typically the hot, design, load plus the spring rate times the expected thermal displacement) along with the spring rate. If you are having CAESAR II size the spring , this load is (as Rich says) entered as the "operating load" in the input.
It sounds to me like you are instead modeling your hanger as a restraint stiffness with no preload.

skrif

I know this will not help you, but just want to bring to your attention

The spring is always under compression. The Spring is preset so that during travel from cold-hot and hot-cold it is within the compression range.

and for reactions if you look at exp case (as dave says) L1-L2 would
give the difference and the direction might be misleading

*******When I wrote that the expansion case is seeing a +Y load, I was trying to say that the Spring hangers were actually making the expansion case worse. They were being compressed when the pipe thermally grew up. The spring hangers were then pushing on the pipe rather than trying to support it up thus causing and even greater -Y force on the nozzle.*******




Hi Skrif

Yes spring can produce more operating load on nozzle ( Like your case).
You need to check flexibility beyond the spring. Probable case when you put a hold down or anchor support after spring. You may need to add one more spring support or need to add more elbow after first spring.

You may attached sketch or Caesar file so that I can offer your more help.
Mind that cold spring is very difficult & dangerous option, should be avoided as best as possible.

Regards

Habib
habibur21@gmail.com