Hi everybody,
I have a quesiton about pressure thrust, if i use an unrestrained expansion joint at a straight pipe and each pipe side has an anchor restraint, it will have a significant impact on the restraints, but looks upon the pipe and expansion joint as a force balance system , whether the pressure thrust act on each section of pipe as element internal force?

if the pressure thrust is only appear at where the blind plate placed , how to understand the existence of the force acting on the nozzle due to pressure in CII calculation?

One for you Dan !

Jackie,

Check out the attached bulletin on Pressure Thrust, I think it will give you the basics.

In regard to your question on straight pipe, an unrestrained EJ will generate large loads on the anchors upstream and downstream because the Pt is being applied at the EJ. The Pt actually occurs at the elbows / blanking plates but Pipe Stress Analysis programs don’t know where that is so they apply it at the EJ. In the vast majority of cases this is not a problem, however if you’re dealing with a very long line with a series of unrestrained EJ’s, the intermediate pipe & anchor loads will be inaccurate. Let me know if you want more info.

When we are calculating WRC-107, do we need to check Pressure thrust as True or False.
Please suggest if you have any reason False or True.

Can any one explain Why we need to check it as False or True in WRC 107 calculation.

Dear Jackie,

As discussed in the bulletin I sent you, the pressure thrust develops on the surface perpendicular to the axis of the unrestrained expansion joint, normally the first elbow up and downstream of the joint. In the event of the line running into a vessel, the pressure thrust is actually developing on the back side of the vessel and there is no tensile load in the nozzle due to the pressure thrust. Therefore, from a purely academic viewpoint, you should check “No” to not include pressure thrust. However, you should check the vessel stresses and stability for the pressure thrust which is developing on the wall 180° opposite to your nozzle.

Hello Dan,

I have a similar situation to Jackie.
I have a blower, roughly 10 psig max pressure at 250 deg F.
The discharge line is 12", and to minimize loads on the blower nozzle from the pipe's thermal expansion, an unrestrained bellow was installed just after the blower discharge nozzle.

The blower supplier has informed me that it's blower nozzles cannot handle any load (zero load criteria). Is this practical to design to? Would there always be some load acting on the blower (sustained loads from weight of discharge spool, pressure thrust or spring force from expansion joint)?

Thanks.

Dear Sir,

I have encountered manufacturer’s who want a zero reaction and my response has always been then put it in the middle of a field and don’t connect anything to it. It’s not possible and it is a sign of a cheap product. There will always be load on the equipment and that’s why Caesar has a number of calculations for evaluating loads on rotating equipment. Unfortunately, none of them specifically apply to blowers.

In the discussion above, we were talking about putting an unrestrained EJ on a vessel nozzle. Since vessels are normally very rigid compared to the pipe, it’s a simple matter. However, in your case you’re dealing with a piece of rotating equipment which is a lot more sensitive to the pressure thrust load. I would not recommend using an unrestrained EJ unless you receive agreement with the equipment manufacturer that their casing can take the pressure thrust load, which they probably won’t. So, I’d suggest you consider a restrained joint, ie tied, hinge or gimbal.

Thank you for the response Dan. I didn't mean to hijack the thread to a different topic. I didn't see where Jackie's initial message talked about connecting to a vessel.

I was thinking more in a general sense, any use of unrestrained expansion joint would transfer pressure thrust load to its upstream and downstream restraints/perpendicular surfaces.

In my case, was a blower. My main concern was to confirm that the manufacturer's zero allowable nozzle load was not practical. I did consider advising the owner to use a restrained joint, but even that will still impose a load onto the blower greater than zero.

Also just wanted to thank you as in my forum search, you've been the one responding to majority of the EJ questions.

Question:-

· If there is a vertical pump discharge line that turns horizontal after a short vertical run, should P X A force be added to the nozzle load of the pump? ( I believe the answer is NO because the pipes are in tension and system balances the forces )


· If there are flexible Victaulic coupling( like slip joint) on the vertical run, they will open up due to pr. thrust and remain open and, therefore, can transmit loads. Will the pressure thrust have to be added to the Pump Nozzle Load in this case? The question is whether P X A force will act like an external force on the nozzle similar to a untied EXJ?

Hi,

Question-01

Yes, no need to consider the P*A force in your calculation; since the pressure thrust on the pump will be there, against the pump internals, with or without the Victaulic coupling. So, no need to consider the effect of pressure on Pump nozzle for discharge pipe.

Question-02

There are two forces to consider here. One is the nozzle load or thrust which is the force due to the pressure head and change in momentum of the fluid through the pump. This load acts on the internal area of the pump. The Victaulic couplings introduce a second force or you can say load which will acts only on the pump flange (for vertical discharge system).

Do note that this coupling area will be slightly higher than your pipe ID, so while calculating the pressure thrust you have to be sure you are using a correct value.

Pump failures had seen when inadequately restrained flexible couplings have been used on the discharge side of the pump. The Victaulic coupling is having potential movement for the pair. This movement is restrained by the anchor and the pump, which brings up the concern over the use and calculation of magnitude of these forces.

Regards,
R.K.

Thanks for the response.

Let's discuss Question 2:

(a) Force-1, which is pressure thrust corresponding to the ID of pipe, will act as an external force on the anchor at pump base.

(b) Force-2, which is pressure thrust corresponding to annular area between OD of Vic. Ring and ID of pipe, will act as an external force on the pump nozzle.

This is known.

Now, going back to the original question:
Victaulic will open up due to pr. thrust and remain fully open and, therefore, can transmit loads. Under full open condition of the Vicaulic, which will remailn open due to pressure thrust on the elbow, it resembles a rigid pipe. Will the pressure thrust have to be added to the Pump Nozzle Load in this case? The question is whether P X A force ( as in (a) and (b) above) will act like an external force on the nozzle similar to a untied EXJ?

I'm not sure if my question is clear.

which type of victaulic coupling you are using?

Regards,
R.K.