Surge Loads in Pipework 2

[DSB123]

Hi There,
I have a general question regarding Surge Loads. If you were presented with the results from a hydraulic surge analysis and wanted to perform a Time History Analysis of the pipework system to ensure stress levels are acceptable and also to determine the support loads would it be relevant to apply a Dynamic Load Factor to the calculated loads. I ask because there are two schools of thought within my Company. I beleive a DLF is applicable whereas others seem to beleive the DLF is already taken care of within the Hydraulic analysis.

Regards

DSB123

 

[MortenA]

Stainer

In the AFT product range what is the difference between Impulse and Fathom?

Best regards

Morten

 

[DSB123]

All,
Thanks for the responses from everyone. There seems to be a lot of differing opinions on this - not a concise yes or no to the application of a DLF or not. Also when you look at the Caesar II applications guide then there seems to be two inputs that are required. The first is the forcing function (time history information from a hydraulics analysis) and a DLF spectrum input which applies Force Multipliers if I am not mistaken dependant on frequency. To me this suggests that the Caesar II software does apply a DLF to the basic Hydraulic time history input.

Any comments of what Caesar II actually does? Am I interpreting the application guide correctly?

Regards

DSB123

 

[BigInch]

I'm not sure what Caesar is doing these days, but it sounds like its handling things correctly. As I said, the LFs don't get applied in the hydraulic analysis. LFs are applied by the pipe stress and structural engineers.

http://virtualpipeline.spaces.msn.com

 

[DSB123]

BigInch,
Thanks for the quick response. So basically I am right when I say that you need to apply a DLF to the time history information (i.e. loads) when doing a pipe stress analysis.

 

[BigInch]

IMO, yes you are totally correct. (see above 11 Nov 07 17:31) The hydraulics guy probably doesn't know much about pipe stress other than S=PD/2/t/DF (where DF = design class factor, not dynamic factor), and if he does know more about stress, he usually doesn't care because stress is another department in the company matrix. Hydraulics analysis usually only sets the minimum wall thickness for pressure containment. At least that's the way its been at all the companies I've ever worked for (and that's a whole lot of companies).

http://virtualpipeline.spaces.msn.com

 

[stanier]

Hi Morten

These descriptions are off the top of my head. The website has more comprehensive descriptions. I run Fathom and Impulse but have used Arrow as well.

Fathom is a steady state analysis program with the capability of heat transfer, extended period simulation, goal seeking and costing. It handles Newtonian and non Newtonian incompressible fluids

Impulse is an unsteady state program for Newtonian and non Newtonian fluids. It does have the Fathom steady state engine as part of the software however does not have heat transfer, goal seeking and extended period simulation

Arrow is a steady state program for compressible fluids with the same functionality as Fathom.

Mercury is another even more sophisticated modelling program for a complete facility that is designed to critically model Capex and Opex costs with the ability to determine optimum line sizes, pumps operation and far more.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[BigInch]

I didn't see compressible Newtonian/non fluids with heat transfer.

http://virtualpipeline.spaces.msn.com

 

[eduardotano]

A DLF is used just to take approx. into account the dynamic response ("dynamic amplification") of a structure (piping system) to a given dynamic load, when the static (maximum) value of the load is applied to the structure and the system is solved statically. DLF may be defined as: "maximum dynamic response / static response". Due to the problem linearity, you can apply the amplification factor to the loads instead to the response, you will get the same results.
So, the answer to your question about if you have to apply a DLF in your mechanical analysis is: only is you are solving the problem statically. If you are solving an actual dynamic problem, i.e. you are applying a dynamic load (time history load vs. time at each loaded point of the system) and you are solving the problem dynamically (dynamic equilibrium: M d2u/dt + C du/dt + K u = P(t) ) you don´t have to apply a DLF, because the time history response of the problem ( u(t) ; F(t) = K u(t) ) will provide you the actual response of the structure, and obviously, its maximum values.
Regards.

 

[BigInch]

Anybody know what Caesar II is doing?

http://virtualpipeline.spaces.msn.com

 

[LSThill]

BigInch (Petroleum)

Yes, Anybody know what Caesar II is doing? Ask

http://WWW.COADE.COM

L S THILL

 

[BigInch]

CAESAR II includes a full range of the latest international piping codes. It provides static and dynamic analysis of pipe and piping systems and evaluates FRP (fiber reinforced plastic); buried piping; wind, wave, and earthquake loading; expansion joints, valves, flanges and vessel nozzles; pipe components; and nozzle flexibilities. The program automatically models structural steel and buried pipe and provides spectrum and time history analysis and automatic spring sizing. CAESAR II includes component databases and an extensive material database with allowable stress data. It also includes a bi-directional link to COADE`s CADWorx Plant drafting package.

So the capability for dynamic analysis is apparently there. Getting back to the original question, "I beleive a DLF is applicable whereas others seem to beleive the DLF is already taken care of within the Hydraulic analysis." I'd still say NO. Its not taken care of in the hydraulic analysis.

http://virtualpipeline.spaces.msn.com