Water freezing in an Overland Pipeline

[ECD40]

We have a problem to solve with an overland water pipeline in very cold weather (minus 40 degrees). The pipe will be a 14" diameter DR11 HDPE material and 19,000 feet long. The flowrate will be 2,500 USgpm at a velocity of about 7.3 fps. The question is whether or not to insulate the pipe with the water flowing and how long will it take to freeze if the water slops flowing, with or without insulation. If we insulate the pipe, there will be a differential expansion between the HDPE pipe and the insulation material. The maximum summer outside temperature will average 75 degrees F. The pipe cannot be buried.
Can anyone help with this problem?
Thanks,
ECD40

 

[itsmoked]

Could smaller parallel line, say 4", heavily insulated be used to recirculate the contents of the main line thru a water heater? This would be an emergency/plant-maintence system to keep the mainline in service.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LittleInch]

Maybe the OP's keyboard has frozen solid....

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

 

[cvg]

he's stuck somewhere out on I-70

 

[georgeverghese]

It may be possible to obtain a narrow operating window for the case when the pipeline is above ground and uninsulated, with some credit taken for operator response time. Suspect it may involve maintaining a minimum flow even when there is no consumption. This may be a heated and insulated storage tank at the end of this line with say 2-3 days storage at min flow. Detailed heat transfer calcs required to establish what this min flow is.

 

[GD2]

Imagine this situation. There is no heat trace. There is an unplanned shutdown. Emergency crews respond to drain the system in 12 hours. Guess what, the vent and the drain valves can’t be cracked open, it’s frozen with ice formation.
What do you do? The screw uses force and break the valve. it’s winter at -40c.
My recommendation is at least trace the vents, drains and other dead legs.

GDD
Canada

 

[georgeverghese]

@GD2, My current thought on this unplanned shutdown is to pig the line clear into the downstream storage tank after a given period of time after shutdown, or when the end of the pipeline reads close to zero degC. An electric heater in a say 700m3 insulated storage tank maybe cheaper and less challenging than having to insulate and heat trace the entire line.
Another option is to insulate (but not heat trace) and include the heated storage tank - this may allow a wider flow turndown, and also allow a longer response time before having to pig for the case of an unplanned shutdown.

 

[miningman]

What downstream storage tank????????????????? I have a strong suspicion this line discharges into a tailing pond, AND the point of discharge has to move periodically. The line is almost 6000 metres long, and is therefore probably that far away from the nearest source of power. Snow and white out conditions will make it impossible to access the end of the line for days at a time.

Unless the OP provides more details, some of these suggestions are extremely impractical.

 

[cvg]

the mine sites I have been on have no shortage of power, but unlikely it will be distributed to warm a tailings pipeline. but this could be a water delivery pipeline to a mill with crusher, mill and flotation and could very well be river water or well water, pit dewatering water, reclaimed from leaching, etc. from any number of locations. no way of knowing without more information

 

[ECD40]

I'd like to thank you all for your valued input and comments.
After much deliberation and calculations (and listening to what has been said by you all in this Forum), the pipe will be insulated with 2" of polyurethane on a 14" diameter DR11 HDPE pipe, with no heat tracing. The entering temperature of the tailings slurry into the pipe has now been established to be 4 degrees C in the winter (39 degrees F). The temperature drop in the pipeline over the 19,000 feet with 2" of insulation is less than 1 degree F according to the website referenced below. Without insulation at minus 40 degrees and a 15 mph wind, the temperature drop would be about 17 degrees F, which will freeze the pipeline. Heat tracing is not an option.
The pipeline is transferring mine tailings slurry (waste) from one mine plant to another mine plant, 19,000 feet away, to make what we call 'mine backfill' to send underground to fill the cavities in the orebody after part extraction of the ore.
I've consulted with many sources regarding what other mines have done regarding pipeline freezing and found differing solutions, which were largely dependent on specific requirements. Anyway, I now have a safe path forward.
Thank you all again for your interest and participation.
ECD40

https://www.wbdg.org/guides-specifi...s/temperature-drop-calculator-hydronic-piping

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[miningman]

hmm, well now that we've got a bit more relevant info, I offer the following to allow the OP to revisit his calculations and possibly avoid professional embarassment. I cannot replicate his calculations using his attached website but less than 1 degree F sounds VERY low to me. Littleinch's computed 3-4 degrees C would be at the low end of what I would expect. I offer the following

Are we dealing with USGM or imperial gallons???. I cannot get a balance with 11.3 inches internal diameter and 7.3 feet per second.
Now that we know it is mine tailings and not clean water, what is the effect of a much increased slurry density on the heat calculations??
What will be the effect of the solids settling out in the low spots , even if only over say a 30 minute shut down??

It is a long time since I worked with HDPE tailings lines but from memory, the ability to maintain the exterior insulation is problematic at locations where the pipe lengths are butt welded. Has this been taken into account?? or is my memory faulty??

Perhaps heat trace must be installed but only energised infrequently. Regardless of cost , lack of power etc, a plant shut down over a period of weeks might be the alternative risk.

The drop in the assumed temperature of material entering the system from 10 to 4 degrees C, is a major change to the risk profile of this exercise.

 

[georgeverghese]

I get a total temp drop of 0.22degC with this 2inch polyurethane insulation at max flow. Strictly speaking, my calcs are based on still air, but the answer should still be good, since the insulation layer is the controlling resistance for the overall heat transfer. Permissible turndown on flow is approx 15:1 ( end temp = 0.6degC at min flow). But you havent said what you'll do when there is a no flow situation, the worst case being unplanned shutdown after operating at min flow.