Flexible joint as pump connector

Hi everyone, here i'm asking about how do we model a flexible joint in pump piping. I want to chek the system and the pump nozzle load. There is a flexible joint in pump suction after the strainer and in pump discharge there is also a flexible joint after the first elbow. So how do we model the flex. Joint here?

Hi Dylan

Check flexible joint you are suppose to use is Expansion bellow or hose.
1) If it is expansion bellow check material ( metallic/rubber) & bellow type ( tied/untied). Check caesar's application guide for modelling procedure of bellow. Ask vendor for stiffness & effective ID of bellow.
For technical know how about bellow refer EJMA ( Expansion joint manufacturing association)

2) If it is hose leave stress calculation before hose. Hose do not transmit force/moment from one point to other as piping.


Regards

Habib

A hose has the same problem as an untied bellow. It leaves the pressure*area force on the nozzle.

Hi corne

Hose can take care of pressure thrust itself. It don't act like untied bellow on pressure.
I think hose not recommended for high pressure service, vendor to specify the limit.

Regards

Habib

Ok thank you Habib, it is a hose. So in this case how i suppose to check the pump nozzle load? If we stop at the flex. Hose, it means we can't check the pump nozzle load.

Hi dylan

Still you may need to check dead weight on pump nozzle due to flange & valve weight. Check how hose is supported, may be pump nozzle have to take some portion of hose weight.

Regards

Habib

If we have to check dead weight that imposed to pump nozzle, we have to modelling the hose too, don't we? Correct me if i'm wrong. Thank you.

Please explain me how. If the hose is used as a flexible part, not all fibres of the hose will be in tension. How can it take care of the pressure thrust?

Hi corne
I think some vendor or some expert on hose can explain the issue better.
The way I understand, Expansion bellow act same like a spring ( with convolution). Both start point & end point of bellow must be in same axis with permissible allowable movement. It can not hold the pressure thrust itself. We need additional mechanism to hold pressure thrust.
Whereas hose is capable of holding pressure thrust itself that’s why start point of hose & end point of hose can be in any direction. If it could not hold pressure thrust then we had to put so many support in hose area wherever it change direction.
Not all hose require convolution in it.
If we cut a slice of hose & make free body diagram for longitudinal force it might be strong enough to hold that forces.
For easy understanding I compare hose with a strong nylon rope , which is flexible also & have high longitudinal strength capacity.
Attach hose connection for pressurized gas line –
http://www.zesco.com/products.cfm?PGroupID=ZP99139002&ref=rottext&subCatID=229

Regards
Habib

Hi dylan
You can make two different calculation. One from pump nozzle connection to start of hose. Other from end of hose to rest of piping. You may add addition weight for hose in your calculation.

Regards

Habib

@shr: I can understand the no-pressure-trust idea with the hose configuration as in the image you linked to. When you put a hose between a tank nozzle and a pipespool inline however, like a lateral bellow, I think the hose will give a pressure trust on the piping, unless you don't put a fixed support in the piping part.
If you don't put a fixed support there the hose will get all axial loads but won't be flexible anymore. I just see it as a (very) long rubber XJ.
Would like to hear some more opinions on this.

Hi corne
I think hose behavior in connection of tank to piping also be same.
In loading/unloading area where hose is connected between piping to truck anchor support is used ((as a minimum (holddown+guide) support & if possible limit support also added)) because some axial & lateral force is expected for hose handling.
Within piping also prefer rest+guide+axial stop support after hose.
I don't think Hose can be considered as long untied expansion bellow.

Let's some expert share their knowledge on the issue.

Regards

Habib

For Flex Hose I don't think that they are laterally stiff enough to apply pressure thrust. I believe they will deflect laterally (squirm) before they are able to apply large forces to nozzles. From ones I have seen installed on tanks for settlement the slack in the hose sags down until the brading on the bottom is in full tension. In my limited field experience I have never seen a hose push itself out straight the ones I have observed have alawys deflected laterally.

I never understand why people ONLY check the "dead weight". The B31 Codes require checking the WEIGHT (the sum of the dead weight and the live weight).

There are two sources of pressure thrust. IF you have bellows convolutions those convolutions are of a larger diameter than the ID of the pipe. The annular area (the area between the pipe ID and the ID of the bellows (beyond the pipe OD) times the internal pressure will place a force directly on the nozzle (the load path is from the bellows, through the connecting pipe to the nozzle. The "bore thrust" is the pipe ID times the pressure and that force will not impinge on the nozzle but will impinge upon the first surface it hits inside the pump. When desiging the pump bolts and foundations these two forces must be added to get the total force.

If you have a straight hose with an ID the same as the pipe no pressure force will be seen by the nozzle but the pressure force that is the ID times the the pressure will impinge upon the first surface it hits inside the pump. But you will have to support the pipe WEIGHT on the side away from the pump as that end will be virtually cantilevered from the adjacent support.

Regards, John.

Hi John

Thanks for Your comments. Yes I have to consider live weight also.

Pressure thrust on nozzle & inside pump what you mention is quite clear to me.
I understand this is applicable for untied expansion bellow.

If I have to consider ID* pressure for hose when if there is no convolution then how the hose is working in the gas line link I attached in previous post ?
I believe in that case hose try to deflected to much away from nozzle.
I think it will be difficult also if start point & end point of hose is in different axis.

Thanks for sharing your experience it really worth to us.


Regards

Habib

I try to model the flex. Hose as a rigid with additional weight and give the movement in displacement box and continue until the pump nozzle, and gives rest plus guides support at the end of flexible hose connection. Correct me if i am wrong doing this.

can anyone have caesar model for hose connection. i just want it for ref.

if anyone hvae that model . please send it.

thanks in advance.