Pressure Thrust

[bogu]

Dear All

I am modelling a simple piping system in Autopipe which basically consists of a series of piping runs from a steam storage vessel to three headers i.e. three pipes separately exiting the vessel to each of the headers. In the middle of each of the piping runs is a valve. When I model the piping runs with two piping runs pressurised and one with a valve closed so that on the closed valve leg the vessel side of the pipe is pressurised and on the header side the pipe is a zero pressure do i need to place an applied load at the centre of the closed valve to simulate the pressure thrust on the closed valve.

Regards
Bogu

 

[BigInch]

I don't use Autopipe, but if it doesn't put a load there for you, you'll have to add the pressure "end cap" load yourself.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[europipe]

Do You use also the pipestresscalculation part of Autopipe?
I think it's neccesary.

Greetings

 

[DSB123]

bogu,
The answer is No.

 

[ColonelSanders83]

If you have any doubt you should join the forum linked below and post the question there

http://communities.bentley.com/forums/42936/ShowForum.aspx

This forum is run by Bentley and I have found it extremely usefull for such questions. There is nothing quite like getting the answer straight from the horses mouth.

DSB123: I believe your statement is only correct if you turn on the option to evaluate pressure extension and include axial force.

Just my two cents worth

Always remember, free advice is worth exactly what you pay for it!

 

[DSB123]

ColonelSanders83,
There is no difference between having a valve closed in a piping system and the end of a header blanked off with an end cap. You don't input a pressure thrust force at the end of a header. The internal pressure causes the longitudinal pressure in the pipe which is automatically calculated by any pipe stress program. If you input an axial pressure thrust force then you are "double dipping" on the effective axial stress in the pipe.

 

[BigInch]

If there was a different pressure on the other side of the valve, that statement is not true and the imbalance would have to be carried by axial force in the pipe to a reaction point.

If there is equal pressure, a pressure load on either side of the valve would effectively cancel and the result would be end cap loads at the end caps only.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[stanier]

I think DSB123 is correct here. The only time you would get a reaction would be in a dynamic event if someone closed the valve whilst the fluid is in motion. Otherwise the pressure is taken in the wall of the pipe in the form of longitudinal stress.

 

[LSThill]

Technical Reference

Tools Kit:
How to Predict Thermal-Hydrulic Loads on Pressure Vessel and Piping, Frederick J. Moody, Mechanical Engineering Department San Joes University

 

[DSB123]

stanier,
Thanks for the backup. You seem to be on the same wavelength as me.

LSThill,
What is a Hydrulic Load? and where is San Joes University? Also how does your post answer the question?

 

[BigInch]

Stanier,

No problem there. I used the term "axial force" rather than your "longitudinal stress". The only difference I can see between the two terms is your's is divided by Steel Area.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

In the case of end cap loads, those are always carried by longitudinal stress, although looking at what I wrote about that now, I certainly didn't make that clear.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[stanier]

I have this argument with civil engineers all the time. Tbey are used to using rubber ring joint pipes with thrust blocks, for underground pipes. When I suggest that a fully welded pipe does not need thrust blocks their eyes glaze over and they treat me like I am an imbercile. I point out to them that if the pipe was above ground would they need thrust blocks on a welded pipe. I even show them photos from refineries. They still dont get it!

It must be something they learn at university.

 

[BigInch]

They seem to dwell on the thrust block part of the picture, never noticing that the pipe has bell & spiggot joints.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/