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Remove an Aluminum Tube

  1. Jul 31, 2018 #1
    Any ideas on how I would remove an Aluminum drop tube from a gasoline or diesel tank? The tube goes thru a 4" steel pipe that extends 3' to 4' above the tank.

    The problem is that after years of being in the tank the aluminum has seized to the steel pipe. I am thinking about trying to melt the aluminum or put a rubber plug in and fill it with dry ice or liquid nitrogen and hope it breaks loose.

    I've seen a caustic bucket on the rig make an aluminum hard hat disappear in a matter of minutes so I started researching a possible method of using caustic to strip the tube out but I don't know how to clean up the mess or what would happen to the gasoline if the chemical fell down into the tank. (I can't imagine it would be good) but maybe I could melt it suck it out somehow then neutralize it.

    I think I could use a rubber plumbers plug down to tank top to hold the chemical and once neutralized and removed or cleaned remove the plug and the bottom of the tube would just fall into the tank. right now we have to take a metal bar and try to cut it away from the steel pipe and just work our way down to tank top and then fight it to get it out.

    Any suggestions? At least can someone tell me what happens to the chemical if it hits the gasoline/methanol and how worried do I need to be about the fumes the reaction will create. Thank you for any help>
     
    Last edited by a moderator: Jul 31, 2018
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  3. Jul 31, 2018 #2

    anorlunda

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    Does the tank still have fuel or fumes in it?
     
  4. Aug 1, 2018 #3

    Tom.G

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    I like your idea of Dry Ice or Liquid Nitrogen as they are the least dangerous approaches, and no aftermath if they fail! That's assuming the steel pipe is malleable, not cast.

    Of course the other approach is remove the steel pipe from the tank, then either repair or replace it with a new assembly. If the pipe is welded on the tank, and it being a fuel tank, you would have to use a manual pipe cutter (similiar to a tubing cutter) for removal. Re-attaching afterwards is a seperate problem left as an exercise to the reader. :wink:

    Alternatively, can you just put a slightly smaller Aluminium tube down the pipe and leave the old one in place?

    What is the plan to avoid a repeat of the situation in the future?

    Cheers,
    Tom
     
  5. Aug 2, 2018 #4
    These are 10 to 20k tanks at a regular gas station. New EPA mandates that we check the overfill protection on the tanks. The tanks are buried 3 to 4 feet in the ground thus the steel riser. The drop tube is an industry standard part that has been used for 50 years or more. It is basically an aluminum sleeve that runs from grade to the bottom of the tank to prevent static build up, splashing and in some cases vapors from escaping. Those have to be removed to introduce a new product that has a flapper valve cut in which has a float that raises with the level of fuel and when the tank reaches 90% full the flow from the transport is stopped thus creating an overfill safety device. When the steel riser was new and the aluminum sleeve was new it all slid together very easily but over the years scale, dirt and of course our issue of dissimilar metals bonding has occurred. And yes the new tubes are exactly the same tubes they just have an overfill device cut in at about 10inches below tank top.
     
  6. Aug 2, 2018 #5
    Just to mention that removing the riser from the tank is an option but the cost associated with removing a 4'x4' chunk of concrete plus removing and shoring 3' of pea gravel backfill material not to mention permits and such is about 3k and then add the price of the new drop tube $1,500 and the top spill bucket that gets ruined and all the new brass adapters and caps and the cost of adding the overfill device just went from about $1,800 to about $5,000. I think we need to figure out a way to remove as many of these as we can without breaking ground so any ideas will be helpful - my little contract alone is for 500 stores times average 3 tanks per site so about 1500 of these new tubes need to be installed and about 50 percent of the old ones coming out are stuck. We currently hook things to the bottom to try and pull up and if that doesn't work we try a long bar and bend the tube in and pound the bar down to tank top and sometimes we get lucky but usually not and at that point we have a tank that cannot take a drop until we do construction. These are active gas stations and if the transports can't drop they can't sell fuel and everyone is angry.
     
  7. Aug 2, 2018 #6

    anorlunda

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    Wow, that is a good engineering problem. I have not thought this through yet, but I have had problems with the sacrifice of aluminum in a bimetal contact because of galvanic currents. I wonder if you can harness that?

    Do you have a time constraint, such that you must remove the tube in minutes once you start work, or could it wait several days?
     
  8. Aug 2, 2018 #7
    Depending on the solution, we could conceivably pre visit the sites with the solution as long as it did not interrupt the normal course of operation for the tank or the site.
     
  9. Aug 2, 2018 #8

    Borg

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    I missed the original comments about dry ice but, that was also my first thought since the different expansion coefficients of aluminum and steel should allow the aluminum to shrink more than the steel. This also may be why they're stuck in the first place.
    Just to be sure, I Googled - how to remove a rusted aluminum sleeve from a steel pipe
    A few results down had nearly the identical question - https://www.practicalmachinist.com/...-post-stuck-steel-tube-best-way-remove-93604/
    One of the comments in that thread pointed to an extended article on removing stuck seat posts on a bicycle.
    Cure #10 involves dry ice.
    Good luck. That's a lot of tanks to upgrade.
     
  10. Aug 2, 2018 #9

    CWatters

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    Perhaps...

    Some sort of expanding bung or balloon that can be put down the pipe and expanded. Test for leaks into the tank by filling with gasoline. Remove gas and flush with ??. Fill with Sodium Hydroxide? Think that dissolves aluminium but not steel. Keep circulating the Sodium Hydroxide. Flush out and remove bung. Would leave a short lenght of the aluminium pipe where the bung was but perhaps that's ok?
     
  11. Aug 2, 2018 #10
    How thick is the aluminum tube wall?

    Is there other tank access which would allow removal of the part of the aluminum tube that extends beyond the steel entry pipe (assuming that it was cut off just inside the tank)?
     
  12. Aug 2, 2018 #11

    jedishrfu

    Staff: Mentor

    Perhaps you could build a pipe probe with a circulating loop inside that you then insert into the aluminum sleeve. From there you could start circulating freon or some other freezing agent through the loop freezing the aluminum pipe insert. The aluminum insert might shrink enough to attach to the probe and perhaps allow you to break it away from the outer pipe.

    The idea of circulating the freon would keep it constantly cold preventing dissipation of the coldness as would happen if you used dry ice in the hole. Then again using the same pipe idea filled with dry ice might work too with no need for a circulating loop.

    I'm not a mechanical engineer and so this idea maybe crap but I thought I'd mention it. If it works it could be a useful tool for other stuck sleeves.
     
  13. Aug 2, 2018 #12
    I am ok with leaving the bottom of the tube floating in the gas. I have rubber plumbers plugs that I can blow up to seal the tube. What I really need to know is how can I recover the Sodium Hydroxide and does the aluminum turn to gas or will I have a pipe full of melted aluminum and Sodium Hydroxide. If so when I pull the plug will the Sodium Hydroxide react in an unfavorable way with the gasoline or Diesel fuel? I think it should be ok since I believe it is used in the refining process at some point but not sure.
     
  14. Aug 2, 2018 #13
    If I use liquid Nitrogen would I be able to put in in the tube in large quantities? Could I suck it out after a few seconds and put it in the second and third tubes at a site. Since all tanks will be buried the same depth it would take the same amount of liquid to fill each riser. What would happen if the plug broke and the liquid nitrogen fell into the fuel?
     
  15. Aug 2, 2018 #14

    Borek

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    Gas that will be produced during the reaction is hydrogen, after that you will be left with a caustic solution in a tube, aluminum will be dissolved in that solution.

    Not more than the tube volume :)

    Highly doubtful, but after few minutes there will be no liquid nitrogen left, it will quickly evaporate.

    Nothing more dangerous than the the buildup of a pressure because of the nitrogen boiling (which, depending on the presence of other holes in the tank, can be, or can be not a problem). Plus, some of the gasoline will temporarily solidify (just like freezing water), but I don't think it will change its properties once it melts back.
     
  16. Aug 2, 2018 #15
    Does the Caustic solution remain useable for the next tube or will it become less potent. Can I fill the pipe with water to flush the solution up and out into the containment bucket where I would remove it with something? Is there a way to neutralize the chemical?
     
  17. Aug 2, 2018 #16

    Tom.G

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    Can you explain, or better yet a drawing or photo of, the new float valve assembly and how it blocks the flow?

    I'm thinking perhaps the old Alumunium sleeve doesn't necessarily need removal. For instance a smaller diameter assembly could be inserted, or maybe the existing tube could be modified in situ to accept a float valve. For working down-hole, there are video cameras available on a long lead so you can see what you are doing, Plumbers commonly have them for sewer inspections.

    Another possibility for tube removal is a variation of a tubing cutter. Instead of cutting the outer circumference, you could make three (or maybe two) longitudinal (length wise) slits of the lining, collapse and remove a piece to give 'wiggle room' to easily remove the rest. You may have to make a few circumferential cuts from the inside to pull things out in sections. I have no idea if such tooling is commercially available, but the economics you mentioned would easily cover custom design and fabrication.

    Edit: Instead of longitudinal cuts, you could make a long spiral cut and collapse the tube by twisting it as it is pulled out.

    Cheers,
    Tom


    Edit 2: p.s. Please try to avoid a chemical approach. Would you want to fill the gas tank of your truck with the residual compounds?
     
    Last edited: Aug 2, 2018
  18. Aug 2, 2018 #17
    Some thoughts:
    1) I would try liquid CO2 before liquid nitrogen. It's readily available from any welding supplier and does not boil off in the container.
    2) Pouring liquid CO2 or nitrogen won't work. Inject it through a pipe with radial holes in the end so it sprays directly on the aluminum.
    3) Be prepared for noise and a big cloud of vapor. That cloud will not have oxygen in it. And you need really thick gloves to hold the pipe.
    4) Do you have access to drill it out? Something like a big reamer with replaceable carbide teeth driven by a drill like this: https://www.milwaukeetool.com/Products/Power-Tools/Drilling/Right-Angle-Drills/1854-1. Be advised that a drill that powerful needs to be braced because it has enough torque to break an arm or leg if the bit catches. Correction, when the bit catches.
    5) Can you get a cold chisel between the aluminum and steel to buckle the aluminum inward? You can weld an extension to a hardware store cold chisel, just make sure to preheat the cold chisel before welding. You would need to pound with at least a 3 pound hand sledge, a little tiny 1 pound hammer will just make noise. Is the steel pipe strong enough to stand up to the pounding?
    6) You can neutralize the caustic with acid. Sodium hydroxide plus hydrochloric acid makes sodium chloride (table salt) plus water plus heat. Bases (caustic) react with acids to make salts.
     
  19. Aug 2, 2018 #18

    jedishrfu

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    Is there a danger of sparks using this approach?
     
  20. Aug 2, 2018 #19

    Tom.G

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    Not in any part of it that I'm aware of. The cutting is done by displacing the Aluminium, not removing it with a grit wheel, so there is little heat generated even if the tubing-cutter bites into outer the steel pipe. For the removal stage, Aluminium does not spark, its softening temperature is well below incandescence.

    For those not familiar with tubing/pipe cutters, see this youtube video at the 3:00min mark:
    (if the ad repeats, hit the F5 key on your keyboard to refresh.)

    The approach I'm suggesting is essentially to turn a tubing cutter "inside out" so the rollers and cutting wheel are facing outward to cut the Aluminium tube from the inside.

    If there is still a sparking concern, fill the tank with CO2 or Nitrogen first. CO2 would be preferable because it is dense enough to stay in the tank, and readily available.

    Cheers,
    Tom
     
  21. Aug 3, 2018 #20

    Borek

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    Less potent, but - depending on the concentration - it could be probably used several times.

    Should work in principle, although you may need plenty of water to be sure the base was removed. Plus, when flushed solution becomes diluted and can't be reused.

    Any acid will do, even sodium bicarbonate (baking soda).

    That all being said (and despite being a PF's chemist on duty) I am with @Tom.G here - I would treat chemical approach as the last resort, when all mechanical solutions fail.
     
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