Local loss in welded plastic pipeline
Local loss in welded plastic pipeline
(OP)
Hi,
Do you know something about losses in connection of butt welded plastic pipe?
For example in 3000 km long pipe there will be about 600 connections. Even if it is a small loss, for 600 joints losses will no longer be negligible.
How to determine the loss of joint plastic pipe?
Thanks in advance
Do you know something about losses in connection of butt welded plastic pipe?
For example in 3000 km long pipe there will be about 600 connections. Even if it is a small loss, for 600 joints losses will no longer be negligible.
How to determine the loss of joint plastic pipe?
Thanks in advance





RE: Local loss in welded plastic pipeline
RE: Local loss in welded plastic pipeline
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RE: Local loss in welded plastic pipeline
RE: Local loss in welded plastic pipeline
Just 'guesstimating' on thermal buttwelds, I would use something between the "Equivalent Length" for a gate valve and the 'run' side of a Tee. ione provided a small-bore pipe table. On a 4"NPS pipe this gives an Equivalent Length between an extra 3 to 8 feet. Meaning that the fluid friction of a thermal buttweld on 4"NPS pipe is the same as 3 to 8-ft of pipe.
This is *only* a SWAG, no experimental data to back it up.
SWAG = Scientific Wild-A$$ Guess
RE: Local loss in welded plastic pipeline
There is a mistake in example, I meant 3000 metres long pipeline, and when the pipe is welded every 5 metres, there will bee 600 joints. On each joint must be some pressure drop and I am asking how much it is.
I quess, then in large pipe (diameter) the pressure drop will be insignificant, but in smaller pipe could be indispensable.
Has anybody measured this pressure drop. Some experiments or verified data?
I apologize for my bad English
RE: Local loss in welded plastic pipeline
RE: Local loss in welded plastic pipeline
Good luck,
Latexman
RE: Local loss in welded plastic pipeline
As to the hdpe pipe vendors claims (I think basically going back many years) that the bead be "ignored", this appears to be disputed by some other folks (I believe also claimed to be far from ingénues in the polyethylene pipe field) at http://w
"Internal bead removal is fast becoming an important step in the pipe fusion process.
Why Remove the Internal Bead?
One of many great attributes of HDPE pipe is its low friction factor. HDPE pipe is less impaired by flow reduction or pressure loss from the fusion beads than the turbulence in a comparable system made of PVC push joints. Using a material that has less flow reduction and pressure loss doesn't mean that there isn't impairment. It is this impairment that we are completely removing. Removing the internal bead can remedy the following problems:
• The internal bead can cause problems when pigging for blockage and biofilm or when HDPE is used as a casing for telecommunication conduits.
• Sediment can build against a bead during a slow flow rate, this smaller blockage is a place where as large debris become embedded and cause more severe blockage.
• In the potable water industry biofilm can stage a footing from under the fusion bead where bacteria or other particle entrapment is of concern.
• With increased flow the bead creates a turbulence that generates wear when slurries of abrasive materials flow through the system. Even though the bead will finally wear away and turbulence decreases, the final effect is a thinner wall cross-section in that location."
I believe you will find, e.g. with a good web search of these and other forums that at least the above risks have not just been dreamed up, and the hdpe specialty bead removal company has not invested the design effort, money and tooling for nothing (I believe I remember a case e.g. reported not long ago on these forums where a small diameter hdpe pipeline had in fact unexpectedly gotten blocked with some sort of debris or detritus).
All that being said, I suspect a general answer to this question, like so many other questions on such forums, is "it depends". Not the least of the factors might be whether or not the designer has assumed a reasonably conservative, long-term design flow coefficient for actual field performance and the size pipeline involved (i.e. e.g. backed by a database involving a significant number of pipelines actually working in the service involved, not just laboratory tests or vendor promotions trying to compete with larger flow area pipes).
While I'm not exactly sure how it is effectively accomplished, e.g. with the remote access that might be involved and also with pipe ovalled by earth/ring loading or path bending etc. and without damaging the pipe wall?, the aforementioned folks claim to be able to do it, I'm sure FOR A PRICE.
RE: Local loss in welded plastic pipeline
RE: Local loss in welded plastic pipeline
Latexman: I used google a lot and found this article
htt
I don't agree with you, that fusion beads can be ignored.
Yes, best solution is remove internal beads, but sometimes you are not able to do this and then you have to calculate with some pressure drop (or it can have influence on total flow through pipe)
RE: Local loss in welded plastic pipeline
Using the bead dimensions given by PolyPipe in an orifice calculation gives much higher pressure drops than they claim. Where PolyPipe get a pressure drop of 0.005 psi for 25 beads in a 10" pipe, I calculate it to be 0.009 psi per bead or 0.225 psi for all 25.
In their example, the flow rate would not decrease from 1600 gpm to 1599 gpm but in fact would reduce to 1560 gpm - which is a 2.5% decrease. In a 4" line with welds every 20 ft (instead of the 40 ft assumed by PolyPipe) the reduction would be almost 12%.
The bead sizes measured by Veselsky are a bit smaller than those quoted by PolyPipe. This makes the effect a bit less than what my calculations above show, but the losses are still significant. Veselsky has published data which is very useful for standard pipeflow calculations. The values for ζ in Table 2 correspond with what Crane or most Western fluids authors would call "k" - the resistance coefficient - so thay can be plugged straight into a Darcy-Weisbach type calculation.
Unfortunately Veselsky's data is limited to pipes below 2" diameter. Using my orifice assumption as above I get k values of around 0.1 for a bead in a 4" line and 0.025 for a 10" line. These are small when taken alone, but mod23 has 600 of them which could become very significant, depending on the pipe ID.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Local loss in welded plastic pipeline
Good luck,
Latexman
RE: Local loss in welded plastic pipeline
How can the manufacturer maximise profit? Simply by using good measuring tools on line and a 3000m run can be made with the absolute minimum wall thickness and still be within standard tolerances. Hence your inside diameter will be larger than you think. Do the hydraulic calculations with the smallest wall thickness and see how drammatically the head reduces.
In fact this is one of the headaches with PE pipe. If friction is a major component of system losses you can end up running down the pump curve and operating at >115% of BEP. This will result in your pump vibrating and seals/bearings failing prematurely. Many a time I have had to machine the pump impeller to bring the performance back to the BEP.
Another thing to watch is when a manufacturer supplies a higher PN than ordered because it is in stock and he wants to shift it or meet a deadline that may incur penalties. The manufacturer has little understanding of power losses and your contractual obligations.
Lesson for all inpsect your PE pipe on site.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
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RE: Local loss in welded plastic pipeline
RE: Local loss in welded plastic pipeline
5-6 metres working distance with a automatised apparatus can reduce the cutting time. But I am not sure if there is a supplier for that. Therefore the HDPE pipe manufacturers might need to think about or do more research to eliminate the internal bead.
I think there are other HDPE pipe manufacturers that use welded fusion at the joints, but their welding is not butt welding, and the joint area wall thicknesses are larger than the pipe wall thickness. I was not directly involved in the discussion with manufacturer and do not know if this type joint gives the similar internal bead at the weld joint. It may be valuable to talk to them.
Kind regards,
Ibrahim Demir
RE: Local loss in welded plastic pipeline
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