HDPE Pipes - Transients (Roughness / MOP)

[Jack.C]

Hi all,

I'm looking for advice on best engineering practices for simulating a hydraulic pipeline, particularly regarding the maximum allowable pressure for HDPE pipes during transients.

I'm currently working with a PE100 PN16 water pipeline (SDR11) and have calculated a Maximum Operating Pressure (MOP) of 16 barg with a safety factor of 1.25. My MOP stands at 16 barg. I'm wondering if there's an established engineering practice that recommends ensuring the maximum pressure during a transient event does not exceed 1.1 times the MOP, which would be 17.2 barg. This concept is familiar in the context of steel pipes, where pressure during transients should not exceed 110% of the maximum allowable pressure (as per ASME B31.4).

Furthermore, when it comes to roughness values, I'm wondering about the commonly used values for HDPE pipes (idealy PE100 SDR11), both for pump design (where pressure losses are critical) and for transient analysis (for example, in surge vessel design). I've found different recommendations across various sources on the internet.

Best regards,
Jack

 

[EdStainless]

Just us roughness values from Cranes, these are some of the smoothest pipe that there is.

The duration of the transient is the biggest issue here.
For HDEP I sure wouldn't go anywhere near above MOP for a transient, and it is common for the magnitude of the transient to be limited to some fraction of the MOP. For various applications I have seen the transient itself limited to 1/3 or 1/2 or the MOP.

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P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

For PE I usually specify either 3 or 5 micron depending in part on whether you remove the internal weld bead or not.

Several of the vendors do their own nomographs and design manuals - look them up. e.g.

https://www.aliaxis.co.uk/en/downloads?type=396912

Due to its relatively low strength PE tends to "absorb" transients much better than steel pipe, but it depends on your design code for the information you're asking for.

Essentially the design code doesn't really care what you make the pipeline out of.

Ed - Why are you so wary? A transient is a transient - it's over pretty fast. PE is a great material for that really.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

https://ascelibrary.org/doi/10.1061/9780784413012.014[/URL]]

In the U.S., PE4710, PE3608, and PE3408 (previous generation material) pipes are used in water mains and forcemain sewers. These pipelines daily experience numerous pressure surges above their standard pumping pressure. For pipes operated at their rated pumping pressure, AWWA C901 and C906 allow "recurring" pressure surges equal to 0.5 times the pipe's Pressure Class (PC) and "occasional" surges to equal the pipe's Pressure Class. Thus, the surge allowance results in a total pressure (combined pumping pressure plus surge pressure) equal to 1.5 x PC during recurring surges and 2.0 x PC during occasional surges.

Roughness typically used is 0.0005 inches
If you derive it from actual pressure drop, it's likely to be half that, but being a little conservative is not a bad thing.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[EdStainless]

Transients can vary a lot, are we talking about a spike that peaks and drops in msec or few sec?

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P.E. Metallurgy, consulting work welcomed

 

[1503-44]

Since its only water ...

I would not be so liberal with hydrocarbons.
Evaluate your risks and select your overpressure factor accordingly.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Jack.C]

Thanks a lot for your valuable insights and sharing your expertise.

@EdStainless: Yes, indeed, we are discussing spikes with peaks lasting only a few seconds. This is why I raised the question regarding the potential impact on the pipes when we briefly exceed the design pressures. I assume that for HDPE pipes, such scenarios may have more significant consequences than for steel pipes. I will be able to provide more information once I have conducted detailed simulations of transient scenarios. It is possible that I may not exceed the design pressure limit, but if I do, I will explore appropriate measures to handle those pressure peaks.

 

[Gr8blu]

Be very aware of the difference between "recurring" and "occasional" transients. These are defined pretty much the same way across multiple standards, irrespective of whether the transient is electrical, mechanical, or chemical in nature.

In practice, an "occasional" transient happens exactly as often as you'd like to see a catastrophic failure of the part or process. Everything else is considered "recurring" or part of a duty cycle.

Converting energy to motion for more than half a century

 

[LittleInch]

I believe it's the opposite in that the MOP of the PE pipe is actually considerably below the yield point compared to steel pipes because of the creep effect you get with PE when it's stressed.

Temperature of the pipe though is critical - De-rating starts at 20C I think so pretty low. Stating an MOP without stating the temperature doesn't work. You need to know temp to state MOP.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.