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Pipespans HDPE lines
5

Pipespans HDPE lines

Pipespans HDPE lines

(OP)
Hello dear collegues,

Is there someone out there with a reference to a table of pipespans for HDPE pipelines?
My googling skills are appently not sufficient.
Thanks in advance.

Greetings

RE: Pipespans HDPE lines

Try the hdpe-pipe.com link attached.  Look for the engineering manual.  Span calculations are in the manual.

RE: Pipespans HDPE lines

2
While I believe I have seen a "table" or two like this relating to hdpe pipe in the past(e.g. in the Engineering Manual of Performance Pipe?), in much of the real world this is not a simple matter, particularly for prospective "exposed" pipe applications where supports are utilized. This is primarily due to the fact that both the (visco)elastic modulus or stiffness (that affects mid-span deflection) as well as effective tensile strength of the viscoelastic pipe beam are heavily influenced by both temperature and time. Even if installed in a climate controlled environment at roughly room temperature(not sure how many pipelines are like that?), it is indicated the bending modulus E might reduce from an already extremely low value of say 140,000 psi or so, to 30,000 psi or less in the "long-term". You will likely find when you rigorously examine this matter that you might well end up with very closely spaced supports, at least compared to long-standing, so to speak, metal pipe applications, drastically increasing support/hanger and installation costs.
While at least a few designers have in a sense overcome the issues of drastically increased support and installation costs by encasing the polyethylene pipe with a continuous, supporting  metallic "pipe beam", this kind of begs the question for many applications of why not simply install a properly designed system of stronger carrier pipe material?
Finally, I guess a designer must ask him or herself the question of what will be the potential service life of the installation to get the proper "long-term" modulus value for viscoelastic pipes (I ask this question in that I am aware of at least one installation of metallic pipe that included some sections on supports that ended up being in virtually continuous service for about 300 years or so, and as you might expect catalogs typically provide modulus values for much shorter service lives!)             
 

RE: Pipespans HDPE lines

(OP)
Thanks, mr. Speare, nice book, that are a lot of supports i've got to provide.

RE: Pipespans HDPE lines

europipe,

The HDPE manual will get you started.  But you really should carefully read the post by rconnor.  There is more to engineering practice than "just getting the pipe supports designed."  rconnor questions (correctly) the wisdom of spending a lot of money on supports for HDPE, when stiffer piping materials are available.  You have to look at the task more broadly, and consider other materials.

RE: Pipespans HDPE lines

(OP)
Thanks for the advice.
I'll go back to school again.

RE: Pipespans HDPE lines

A similar question came up a few months ago.  It was pretty much decided that, when spans are involved, you should use the most structurally sound pipe you can get your hands on.  There is no point in spending double building a pipe bridge and tressles, when a strong piece of XX steel pipe will make the span all on its own w/o any supports at all.  As rconner notes, that 30,000 psi will eventually put a stop to your free lunch, or rather ... free span.

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Pipespans HDPE lines

(OP)
B" the material isn't the issue.
HDPE meets the chemical resistance.
I really didn't ask the question how to design supporting and pressure items.
Maybe I've got to ask my 30 year yonger collegues about that.

 

RE: Pipespans HDPE lines

Wasn't it you that asked about ... pipespans.
HDPE being basically a no-span material in the long term, it begs the question of considering other materials, even as a casing (as was suggested by rconner, right), to make spanning possible, no.

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Pipespans HDPE lines

(OP)
I know, The pipespec I will propose is PP/GRE.
That's my favourite.
The pipespan of HDPE was my question.
I asked a table, not a studentbookintro, mr.Speare understood.

RE: Pipespans HDPE lines

Sometimes you get what you pay for, sometimes you get more.  At least here you always get your money's worth.

Let your acquaintances be many, but your advisors one in a thousand'  ...  Book of Ecclesiasticus

RE: Pipespans HDPE lines

While it is probably now obvious to some readers, I just realized my constant room temperature example in prior post doesn't really explain exactly what will happen when there is ANY temperature excursion in a viscoelastic pipeline's service life i.e. beyond that "room temperature", so I will provide a little more information. While it may not really make much if any difference what causes any particular higher temperature excursion, be it in normal process, a line or HVAC shutdown, change or accident in process, trash or worse fire in the facility, global warming or whatever, the result will be a reduction of actual elastic modulus and tensile strength with a corresponding increase in distortions of the beam (i.e. midspan deflection and otherwise).
What I also didn't mention is that with a coefficient of thermal expansion of maybe fifteen times or more that of e.g. some metal pipes, there will also be an attempted increase in length of an exposed or any other pipeline. While in some installations of such piping, provided e.g. on continuous flat supports or ground, designers/installers have attempted to compensate for this exagerrated movement by "snaking" the piping sideways, in a pipe-on-supports installation any extra snaking can unfortunately be additionally, preferentially and in exaggerated form (by the quite inexorable urging of gravity) in the downward direction between supports. Once a line starts to develop pronounced "sags" by such combined actions, I'm also not sure how much if at all it will be wont to "pop back up" if the temperature is brought back to room temperature, due to the also some characteristic creeping natures of such materials.
In conclusion, if an installation is not quite carefully considered in all respects, it is liable to end up looking in profile view like "Nessie", with aesthetic and maybe even related operational ramifications.

With regard to ad hominem or otherwise references of age in discourse, I don't know how it is in Europe or elsewhere, but in the good ol' US of A any discrimination with regard to advanced age is increasingly frowned upon. While I guess some of the reasons are legal, there is also the realization that society as a whole is getting older, with people also working longer, and there is additionally near universal hope that we may all get there someday. I will thus only provide positive comments with regard to age, and I will say "as to me and my house", we will (and have) even listen to a twelve year old (at least when he or she makes sense, and we can learn something from them!) Also, we will not hold any participant's youth and inexperience against them (to sort of borrow/paraphrase an ad lib from a past seasoned leader, in responding to a younger and eventually unsuccessful opponent's jab at his age, back in some days that preceded years of substantial positive economic expansion we envy today)!

As more and more of us are learning more and more about our world (e.g. through NGC and Discovery documentaries and other sources) it appears we are seeing many remarkable examples that indicate that at least some good quality Engineering principles and construction can be virtually ageless and durable. Whether it is the reportedly quite old structures at Göbekli Tepe (see at http://www.youtube.com/watch?v=Xo0ZkgqM1TE) or the Iron Pillar(s) of Delhi/Delphi et al, I guess we may not ever know exactly who the designers/builders were, exactly what the structures themselves are, how old the braintrust responsible was, or for that matter maybe even where they came from? We can perhaps only wonder about the eventual results of more "modern" designs, i.e. unless we quite thoroughly understand the principles, and/or directly see the results ourselves, and or have same related to us by trusted folks more expereinced than ourselves.

Everyone have a gerat weekend!                
 

RE: Pipespans HDPE lines

Design of thermoplastic piping is more complex than steel pipe as rconner has eloquently put it.

The other matter in regards to PE above ground is the type of support. Steel may be happy resting on a beam without a reinforcement saddle. PE on the other hand may buckle locally because of the loading. Hence the support may need to be a 120 degree saddle. Check out Roark & Young in terms how you design for local ring buckling.

If the PE buckles locally and them tries to move because of thermal strain the soft PE may be locally deformed (ie steel on plastic).

All that said there are many PE systems above ground performing well but they have been designed. the life cycle cost analysis has been done to show that it out performs steel or DI due to the corrosive envronment, no need to paint to avoid external corrosion, reduced surge pressures etc.

When designing thermoplastic systems I use a conventional stress analysis package. I build two identical models. One with materials properties that are instantaneous and one long term. I use the former for loads on equpipment and supports and the latter for deflection.

Generally the deflection is an aesthetic consideration and rarely a high stress situation, except for locaalised stresses. PE is often used in low cost mines that may have a design life of 3 -10 years. Gold mineral processing for instance. PE is rarely seen aboveground in water treatment plants with a desig life of 50 years or more. I have used PE & PP above ground in a zinc processing plant.

PE lined steel is a way around the deflection issue. You can procure from China a PE pipe with internal steel mesh. As to date I have  not got a satisfactory method of joining same.

The difficulty in design is that there is no standard that covers the materials such as for legacy products like steel & DI. ASME B31.3 has not gone into the complex behaviourof thermoplastic materials. other standards really only cover the materials properties but then fail to look at the time rate hisotry behaviour of visco elastic materials.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

RE: Pipespans HDPE lines

(OP)
Does someone know a reference to pipespans PP/GRP?
Greetings

RE: Pipespans HDPE lines

(OP)
Thanks Stanier, EN-14692-3 chapter 5.3.3.
 

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