I would suggest you run this by someone, but, have you tried melting it?
HDPE melts around what, 130°C? I guess that would also depend on the grade. You would probably have to check the melting point with the manufacturer?
How long of a piece are you looking at?
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Maybe cryogenic treatment would embrittle the HDPE and shrink it more than the pipe.
You do not say what the pipe is made of.
If the co-efficient of thermal expansion of the PE is higher than the pipe material, which I guess it most probably is, it can then be withdrawn as it contracts away. It could also be broken into smaller pieces as it em-brittles. The effect of temperature on the impact strength of the pipe vs the liner would need to be considered to determine the optimum temperature.
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Melting does sounds like a good choice as PE is so unreactive it would be hard to attack it chemically. There are solvents for PE (as used when doing GPC to determine the molecular weight of PE) but they are not nice, for example trichlorobenzene at 135°C. Thermal shock from pouring liquid nitrogen in the tube might work if you have access to the liquid nitrogen that is.
Most lined pipe is carbon steel. The liner protects the CS, which provides the strength.
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The piece that is stuck is approx. 2600ft in length.
The resin is Dow DGBD-2480 BK.
We have heated the pipeline to 70C and attempted to pull with no success.
If you heat it up too much, is there sufficient tensile strength to mechanically "pull it out"?
Even if you melt it, getting the melted plastic out would be tough too!
I was thinking like 20 feet when I suggested melting it. I don't know about 1/2 mile.
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As you heat it up, it will expand more than the pipe, increasing its grip until it softens, at which stage the tensile will be so low that it cannot be pulled out. It can be burned out, but you will need a lot of heat to get it burning, and you will need to pump in a lot of air to keep it burning. It will also leave a mess that will contaminate whatever is passed through the pipe unless you can get a wire brush all the way through.
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With a custom made gas tourch and an air tube and an air compressor.
It all depends on whether or not you can get straight access to each end.
Maybe get it burning and pump some oxygen in there to enhance the flamibility and purge the byproducts of combustion. I am presuming both ends are open so that and purge air or oxygen in from one end and exhaust out the other end.
I have no idea how much trouble and cost it can stand vs removing and replacing the entire pipe. You do have a very unique and difficult problem.
If you go the burning route, the biggest problem will be exhausting the smoke. If the pipe has fall, start the fire at the low end and exhaust out the high end.
I am also presuming this is a straight pipe.
Chemically PE is very similar to petrol and burns with a similar reaction. It just takes a lot more heat to vaporise it.
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Not to be a soggy noodle, but for 1/2 mile? How much pressure would you need to push that much air to combust, and remove the combustion product out the other end?
Have you done this before? With what size pipe?
ootpik did not mention size of pipe. I don't know if that would make a difference.
You are right, this is an unique problem.
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I suspect your problem is so unique that no one has done it before, at least not at anywhere near that scale.
If this has to be done, and the burning does not work, another method to simplify removal after shrinking it with liquid nitrogen would be to use something like a pipe cutter that expands out from the inside rather than squeezing down from the outside. Cut of a workable section of the liner and then freeze that section.
If you can get a short section of an identical pipe, you can do lab tests to see how much clearance and how each component em brittles at various temperatures.
I do not know if you can get internal expanding pipe cutters, but a half competent fitter should be able to knock one up for you.
HDPE should soften in the range of 110 to 130 deg C.
What is the internal finish. What is the ID. What is the access to each end. Is it straight and is there good straight access to each end
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Polyethylene burns like candle wax and will become pretty fluid when it gets hot. It is one of the cleanest burning plastics. Getting it lit would not be difficult. You would have to flare the vapors that exit the pipe and be prepared to contain the flowing molten polymer.
It might be possible to use controlled pyrolysis to remove the PE. I have removed saturated carbonaceous material from about 200' of 4" pipe. It may be possible to keep the line at 900°F and completely remove any organics. I think it might be worth a try.
We use this system to clean polymer (Nylon) piping and equipment on a routine basis as part of general maintenance and overhauls.
The first four are people that can supply portable gas burners and the last one is a description of the process.
