Hello Gents!
I need your advice.
I have to carry out stress analysis for HDPE plastic pipework. My question is what is the applicable code in the Caesar II input?
Do you know also yield strength and elastic modulus value for this material? Please consider this as urgent issue.
Isometrics is attached fya.

B31.3 has some provisions in appendix B, but it appears this is for pressure stresses only. While I've done both metallic analysis and FRP analysis in CAESAR, I don't think plastic analysis is available.

I would suggest looking at the Plastic Pipe Institute's handboook for PE here.

Sorry I cannot help further.

Thank You Michael!
Unfortunately, I cannot find relative article which may describe analysis methodology of HDPE plastic pipe. I asked here supposedly, if someone would have experienced it at past.
Now alternatively, i am trying to gather mechanical properties(elastic modulus, Poisson ratio, yield strength) of this plastic material to create user defined material profile and run the simple analysis to check basics failures in stress and displacement results.
I hope this will help anyway.

Please take note to consider short term and long term elastic modulus. Plastic piping degrade in the course of time so design for both long term and short term and usually the long term elastic modulus will govern the design in terms of support span. You can also read some design guidelines as what Michael have given. I remember when you put a pad for HDPE make sure the edge are rounded and I think the reason is to not cause dent on the main pipe if the edge is sharp. Although I've done an analysis using Autopipe but what I have read from some forums the result using beam analysis may not be so accurate due to large displacement in which case may invalidate the assumption for beam analysis so that's why mostly HDPE pipes are just done using some simple manual calculation based from manufacturer's guidelines. But if you will qualify nozzle loads, then the forces and moments is hard to obtain using simple manual calculation and it's too expensive also to consider 3D Finite Element Analysis to consider large displacement so I think modeling using beam element software may still be used just take note of the limitations (maybe limit the displacement, correct me if I'm wrong with this approach). But if you don't have sensitive equipment like pump connected to HDPE then simple manual calculation is enough to check sizing of loops or support loads and support span calculation. HDPE Manufacturers usually include this simple manual calculation in their catalogue.

Any other experience on this field is greatly appreciated.

Cheers!!!

In terms of what Code to use I think there is no specific answer, so what I've done is I check both using simple manual calculation based from manufacturer's catalogue and also perform beam element analysis and tweak some numbers (I already forget how I come up with ASME B31.3 Code Allowable). Actually my purpose to do beam element analysis is get the forces and moments acting on the nozzle not more on stresses since manual calculation can verify if the piping is flexible enough. Not sure if there is really an official code to check flexibility for HDPE Piping like for metallic and FRP Piping. So that's the approach I can advise for now.

Any other opinion is greatly appreciated especially in terms of what official code to use for flexibility analysis.

Cheers!!

Thank you very much Borzki, for sharing your experience and recomendations above. It is deeply appreciated!
The matter is, i don't have any of manufacturer catalog provided by client either. That is why, i am struggling to find out eligible material properties to my case and it is differing as well.
I will take into consideration of short/long term elastic modulus values as you recommend above.
I am a little bit disappointed that Caesar II is not addressing directly to this analysis by having ready material properties and applicable code option. Hope to be available for this in near future

If you had got proper link or document about material properties of HDPE that would be helpful for me. As such, I could check my value against it.

See page 5 here for an example of stress versus time to failure for HDPE.

The information provided is specifically for burst (hoop stress), but you could apply it to bending stress and axial stresses, too, combining for a total stress.

I would urge you to check with the supplier in question for specific properties of his pipe material.

Raab,
B31.3 makes it clear that flexibility analysis used in evaluating metallic systems is not well suited for plastic materials/components.

Hi raab,

Unfortunately for plastic piping same as FRP and GRE Pipes, the material properties varies from Vendor to Vendor, so the recommendation of Michael to get the material properties from your Vendor is advisable. If you're working in EPC company the best work around is to coordinate with your material engineer and procurement people. What I usually do is request our material engineer to include in their requisition the stress analysis and support design of plastic piping. If cost permits, this will be the best way to execute it. You just need to cater man hour on your side to review their stress report. I have done this in one of my project around 2 years ago. The experience I had where I have done a lot of digging information is where I cannot convince the management to give the stress analysis to Vendor so the minimum I ask them is to request from Vendor their catalogue that includes guidelines for stress analysis.

Dave is also correct, ASME B31.3 does not address flexibility calculation of plastic piping. So as a stress engineer your on your own to decide what to do, so the approach that I've done is to use Vendor guidelines for stress analysis (loop sizing, support span, support design guidelines, etc.). I only used the software whenever I have some sensitive equipment to extract forces and moments for comparison purposes. I tweak some numbers and come up with some allowable stress and unofficially put it so that I have something in my stress report where it shows pass, since officially it's not a Code requirement. The official is from Vendor guideline which I recommend to request to your vendor thru your material engineer. In this case, you avoid assuming something which at later stage the official vendor may give different numbers.

You can do it.

Cheers!!!

When working with HDPE pipes take note that Modulus of Elasticity varies significantly by the temperature and duration of loading. I've performed the stress analysis of two major water treatment plants and as Borzki mentioned, you need to expect large displacements in the system due to it's high expansion rate. The de-rating of HDPE with Temperature is very important as well. Especially for the pipework installed outdoor exposed to solar radiation (when empty), the surface temperature could rise up to 60+ deg C.
the expansion rate for a PE100 material is about 2.4mm/m/10degC. so for a 50m header pipe installed outdoor you should expect (50mx2.4mm/mx3)=360mm where 3 is (50deg C-20deg C)/10degC assuming pipe being installed @20deg C and reaches to 50deg C in the sun.
Here in Australia there are some good guidelines handling PE pipework. You may simply go to www.PIPA.com.au for a broad range of technical information regarding such material. for example for derating of HDPE you may see this page (https://www.pipa.com.au/sites/default/files/document/attachment/pop013.pdf)
In applying modulus of elasticity, since it changes a lot, you'd need to know where you need this parameter for. For pipe support and span calcs I used the long term about 20yrs and for thermal stress I used 1hr as I assumed the temperature changes is not as quick as 3min or as long as 5 hrs. You may find some values from a supplier in Australia in here: http://www.vinidex.com.au/technical/pe-pressure-pipe/e-modulus/

Hi Borzki,
Thanks for your recommendation.
Which software did you use to evaluate the stresses in plastic piping?

What methodology did you consider to work out allowable stresses to compare them against?

Best Regards,
raab

Hi Dave,

Recently, I have seen a PSA software which directly address to HDPE and other plastic piping stress analysis.

I would look forward to seeing the similar features/options with Caesar II as well, as it could have actually prevented the users to have any wrong assumptions or any of unnecessary interfaces with non-official information about plastic piping systems.

I have found this article about HDPE analysis http://www.whatispiping.com/stress-analy...stress-analysis
Is it possible to create HDPE piping in CAESAR II?

Hello,

You can try using custom material in Caesar II using the data from HDPE vendor such as Elastic modulus (short term & long term?),poisson's ratio, expansion rate, density, etc. The only question will be establishing the allowable stress and Code to use. You can follow maybe the link you've provided regarding setting up the Code Allowable. I haven't read in detail the contents of the article but fundamentally Caesar II can also calculate beam stresses same as the all other beam type analysis software is doing. Maybe you can post process in excel the output from Caesar II and set-up your allowables. Anyway, this is just my general thought. It takes some man-hour to study and set-up this type of analysis.

Please correct if I have made any wrong statement.

Cheers!!