Looking for References to Help Calculate the Thickness of a HDPE Pipe Hanging Down a Open Pit Wall 2

[Fyokou]

Hey Engineers,

I have a pump at the bottom of an Open Pit Mine (similar to sketch attached) that's going to discharge water up the pit wall to the nearest pond. Based on the Pump Size I can calculate the required thickness for the HDPE Pipe. However, I'm concerned with the fact that currently the client is only anchoring the HDPE Pipe on the Top and Bottom of the Pit Wall. Since the elevation is so great I would of thought that some intermediate support would be required due to the weight of the pipe and/or fluid hanging off the top support.

My thoughts are to check the Pipe based on the Hoop Stress (from the pumping) and Tensile Stress (from the hanging HDPE Pipe) but I would also think that the environmental issues should be considered (like wind, temperature growth and shrinkage, etc.).

Does anyone have references I could review to help in determining an appropriate Pipe Size and Thickness?

Also, any experience/knowledge to share is greatly appreciated!

Thanks!

 

[bimr]

That design is not going to work and may end up killing someone. HDPE pipe will snake around as it shrinks and expands with temperature.

Download the handbook:

http://plasticpipe.org/publications/pe_handbook.html

 

[cvg]

its commonly done but usually not more than a few hundred feet vertical without intermediate supports. use the heaviest drisco you can get, however do not place it tight down the slope as shown in the sketch. it needs to rest on all the benches and should definitely have intermediate anchors. You might want an intermediate pump and maybe an intermediate tank.

 

[Alex303]

HDPE is pretty forgiving and ~PN25 PE100 pipe is commonly used in this way around Western Australia, even though it's not ideal. Provided it's supported well at the top and the area is well suited to allow the movement of the pipe and a risk assessment is carried out, intermediate supports are not required. Often getting permission to install anything on those benches is impossible anyway.

One thing that should be considered (but often isn't) is the requirement for a maric valve or similar on the scour point to prevent unexpectedly high flow rates.

EDIT
If the risk is considered too great, the pipe can be installed on the pit ramp instead.

 

[LittleInch]

Fyouku, you seem to be thinking that PE is simply a different form of stereo. It isn't.

It comes in different sizes and doesn't act in the same manner – you don't get 12 3/4" pe pipe. For one thing it creeps under constant force and has a thermal expansion rate about 10 times that of steel. Long term strength starts to go down over 20C.

If this is on the surface in a hot place it will snake and also creep if it gets hot in the sun.

The links by bimr are a great start point.

Also you seem to thinking about SDR 5 pipe. Think about that for a minute, the Id will be 3/5 of the OD. That's crazy. There must be something else you can use.

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

 

[chicopee]

Just the static pressure of the water at the pump outlet wiildevelop a head of over 350 psi and that does not include back pressure from friction loss and start up inertia. I do not believe that hdpe pipe is manufactured with extra extra strong pipe wall, therefore, consider alternate material such as aluminum for pipes.

 

[miningman]

Well what exactly are we dealing with here?? Has the pipe already been installed by the mining crew and the OP is being asked for recommmendations on anchoring ?? Is the OP designing a system from scratch , with perhap;s limited mining knowledge?? Where is the proposed installation as temperature variations could have a really important role to play in making suitable suggestions??

 

[cvg]

i dont think aluminum is the answer due to constructability issues, but intermediate pumping with a good check valve and perhaps a break tank is more reasonable approach.

 

[Fyokou]

Hey Guys,

CVG is correct in that Constructablility is a concern. So in my opinion Aluminum is not the answer.

I'm in agreement with CVG that intermediate supports and/or pumping is a more likely better option.

For Miningman,

Currently the client (location in Northern Ontario, Canada) is already hanging DR7 HDPE down the pit wall similar to what is shown on the sketch but only approximately 180-190m down... flow rate at about 125m3/hr. A Pre-Feas was completed for a Pumping Station at a deeper elevation using DR 5 HDPE Pipe (quotation from a manufacturer - they will make it custom for the client). My task is to verify the "sales pitch" from the manufacturer is ok.

On a side note, the Pre-Feas. Looked into the option of using a PEXGOL pipe system but was not considered fully because of the high capital cost. I'll be bring this item back up with the client as a possible option again. Check out "[URL unfurl="true"]http://www.pexgol.com/mine-dewatering[/url]"

Have you seen this before Miningman?

Bimr,

I actually have a previous edition of this document... thanks for the link.

My main goal of this post is to trying to get feedback on people who have dealt with this similar issue and/or have references to help. Through my experiences I have seen what cvg described... intermediate supports and/or intermediate pumping typically NOT one straight shot up the pit wall.

Cheers!

 

[miningman]

Must admit this looks like a disaster in the making. I think the mine owner needs to answer how he is going to prevent the line freezing in the middle of winter. I hope they dont intend putting a check valve at the pump... flows to the pump will be a lot lower in January than in June. If HDPE is to be used, it will need a number of intermediate anchoring locations. Personally I would have thought that anything less than Sched 40 steel pipe for at least the lower sections would have been necessary. And at these operating pressures, use of victaulic clamps would be really marginal which implies flanged pipe. Id say anchor points are the least of the problems here.

 

[cvg]

it's way too difficult to hang steel pipe off a high wall plus it is too rigid, PE is flexible and can be easily installed or moved. all joints should be fusion welded, in other words, no joints at all. to move this stuff, attach to back of D-10 and pull... like I said it is quite commonly done due to ease of construction and relatively low maintenance. freezing is a concern for any pipe, PE can stand it, the valves and pump cant.

 

[cvg]

pH of the water may be as low a 2.0

 

[Fyokou]

To help prevent line for freezing in winter, they completely drain the line during the winter months...careful operation procedures when they start it back up in the spring thaw. This pipeline is for mine dewatering and mainly for storm water events.

Once again cvg is correct, the ease of installation of the PE is the main reasoning of using this material.

However, since the pit is getting deeper the mix of both steel and HDPE might have to be used.

Does anyone have technical reports/references based on hanging HDPE Pipe over the pit wall?

Cheers,

 

[Alex303]

Sorry mate I don't have anything technical regarding it specifically. What exactly are you concerned about mainly? Is it the expansion of the pipe during hot\cold? If so this is pretty easy to calculate. Or are you concerned about high stresses on joints or just failure of the pipe material?

Generally electrofusion joints are quite strong and I assume they are nearly as strong as the pipe itself (don't have the technical docs infront of me but that's my belief without checking).

If the pipe must hang off the pit wall just anchor it at the top based on weight of pipe and friction due to water running down the pipe (if the pipe is scoured) because the friction can be quite high depending upon your pipe size (i think it's maximum when the pipe is running half full?). The pipe manufacturer might be able to tell you the axial stress capacity of the pipe if you want this as well.

As said intermediate supports are desirable but not always practical.

This is nothing new, even though some would be surprised when they first see it because it is dangerous, but lots of other things in mining is dangerous too which is why you can never get out of the car when you are on site

 

[Fyokou]

Hey Alex303,

More concerned about the high stresses on joints and possible failure on due to axial stresses. I'm thinking at some point the length will be so large that the pipe will stretch out like a piece of bubblegum and snap. However, I can estimate that using the material data available.

No problems if there are no references. Sometimes I luck out and I find some technical reports on mining companies completing trial and errors on their systems. As an example, I found one on Pumpboxes vs. Frothing. Part of me was hoping maybe something would be out there.

I'll talk with different pipe manufacturers and this PEXGOL company to see what they have to say. After which I can discuss different options with the client.

I appreciate the discussion though!

Cheers,
Keith

 

[cvg]

the pit is stepped and you need to rest it on every step. so your maximum vertical hanging distance should only be the height of one step. I don't see axial force being significant unless it slips off the steps and this should be avoided. this could happen if there is not enough slack or there is surging and water hammer. surge and water hammer tends to be a problem for these systems due to the need for booster pumps with check valves. recommend spending the extra money to put in a tank at every booster to reduce the pressure and hopefully eliminate as many check valves as possible.