Good afternoon,

I need help for model rubber fittings as rubber bends and rubber reducing. Someone knows how can I simulate it? I think CAESAR II don't have rubber in material database, althought rubber fittings depends a lot of factors as how many turns have internal mesh for example.

I'm trying model rubber reducing as expasion joints using maximum displacement values. But how can I do the same method for bends? Impossible. If someone have another way to do it, please help me.

Regards,

Miyamoto

You need to be very specific on the system, piping materials, diameters when you ask a question to be able to get contribution. At the moment your question is open to interpretation, so it is discouraging to involve.

Many cases you do not need to involve with stress analysis when you use rubber fittings in the system intelligently, by watching the thermal expansion and putting the suitable supports to the right locations.

No one is able to give you any stiffness for stress analysis on the rubber products (as far as I know) because they are very low.

So do not push yourself uphill unless you need to.

Kind regards,

Ibrahim Demir

Thanks Ibrahim, but rubber fittings works in a lot of cases as a expasion joint once their stiffness is very low how you said. That's the problem.

So, I'll give you a simple example:

In this case, the system is made of a lenght of pipe of 2m, one side have a tank nozzle (atmospheric) and the oposite have a pump nozzle (sucction). DN 20", Temp: 30°C, Pressure: 0.8 bar. At the middle point of this system we are not using a expansion joint. We use a rubber reducing for this function.

Due low stiffness, this rubber fitting will absorb thermal expasion and the force that goes to both nozzle is just P * A. Sure, in this case I don't have problems with stress. But, imagine if this same system was compound by two pump nozzles, as series systems (discharge-suction). Now, the pressure of suction it's a lot of times more than a simple atmospheric pressure. And finally, the forces active in the nozzle will be very high.

I hope had cleared any doubt.

Awainting answers,

Miyamoto

So you are a miner.

For the first example you gave I would use the soft joint next to the tank nozzle, and support/guide pipe close to it as you do for the expansion joints.

In the second application; I am not sure if the pump discharge pressure can be taken by the soft rubber fittings. As far as I knor in the mining applications they keep the distance short between LP pump discharge and HP pump suction to reduce thermal problems. If you can reach WEIR pump handbook or in their brochures they do show exactly this applications.
You had better consult the pump suppliers about their input on the application.

In your application I do not expect the LP pump discharge pressure low due to high desired pressure in the end. Therefore rubber fittings can not provide the desired pressure between pumps. If you believe they can the first paragraph above is valid again.

Kind regras,

Ibrahim Demir

I forgot to mention, if you use rubber soft joint between pumps the pressure force in the pipe is to be taken by both pumps and their foundation.

Regards,

ibrahim Demir

Ok. Thanks for your help. But, forgetting a little bit of rubber joint and backing to rubber bends. If I can't select a material for a bend, how can I simulate it?

I do not understand your question about the rubber bend. If you need a specific answer you need to draw something with all the information required. So we can understand the system you are working on. Otherwise we may not be able to answer.

Hi all again,

Sorry for ressurrect an old thread, but I have some doubts about this issue yet.

(Please see image below)

May I consider a rubber bend as a flexible hose? Simply don't model and keep the pipe ends free?

Won't this kind of fitting transmitt any forces do fitting end (like a pump or tank nozzle)?

I think the bend tends to "open" when pressurized. So, in this case, due internal pressure it will work as a expansion joint untied. I tried to model it as a expansion joint with high stiffness (I will never get this values with vendors, unfortunately) which will have a lot of degrees of freedom and small displacements.

Can someone give some help?

Thanks in advance.

Sorry. Forgot the image. Follow.

Nobody have any idea?

Regards.

This is something CAESAR II cannot address. Your bend will of course transmit "some" magnitude of force or moment, but I expect this to be much much less than what the piping elements transmit. How much less I can't say.