How Can I Safely Remove a Seized Aluminum Tube from a Gasoline or Diesel Tank?

[James Demers]

Rather than caustic, which is going to be messy and dangerous, how about salt water, with a DC voltage applied to the two pipes? You should be able to drive oxidation of the aluminum, while protecting the steel. It's how sacrificial anodes work to protect ships' hulls (and water heaters), but with a bit of a boost from an external voltage. The method is called impressed current cathodic protection; it's used on pipelines. You'd want something like 1% salt, so the aluminum doesn't passivate. DC from an automotive battery charger should be sufficient.
This won't work if there's metal-to-metal contact (short-circuiting the setup), but there may not be much contact in an old, corroded system. A quick check with an ohmmeter will tell you if there's contact. Potential downside is salt water accelerating corrosion of the tank, if it gets inside. A mild acid (vinegar) should work as well, but you're getting into R&D land there.
Once the aluminum is sufficiently corroded, you can probably rip out the remainder with a reaming tool of some sort.

Further thought: rather than the steel pipe, you can provide your own cathode in the form of a steel or iron rod inserted down the middle of the aluminum tube. Wrap it in burlap, or slide some rubber rings onto it, so it doesn't contact the aluminum.

 

[sysprog]

Rather than caustic, which is going to be messy and dangerous, how about salt water, with a DC voltage applied to the two pipes? You should be able to drive oxidation of the aluminum, while protecting the steel. It's how sacrificial anodes work to protect ships' hulls (and water heaters), but with a bit of a boost from an external voltage. The method is called impressed current cathodic protection; it's used on pipelines. You'd want something like 1% salt, so the aluminum doesn't passivate. DC from an automotive battery charger should be sufficient.
This won't work if there's metal-to-metal contact (short-circuiting the setup), but there may not be much contact in an old, corroded system. A quick check with an ohmmeter will tell you if there's contact. Potential downside is salt water accelerating corrosion of the tank, if it gets inside. A mild acid (vinegar) should work as well, but you're getting into R&D land there.
Once the aluminum is sufficiently corroded, you can probably rip out the remainder with a reaming tool of some sort.

Further thought: rather than the steel pipe, you can provide your own cathode in the form of a steel or iron rod inserted down the middle of the aluminum tube. Wrap it in burlap, or slide some rubber rings onto it, so it doesn't contact the aluminum.

The electrolytical process is too slow, the energy cost is too high, the emission of hydrogen is too much, and the risk of spark production is too great. Other than methods which begin with removing all the fuel and fuel vapor in advance, the safest alternatives proposed here so far are those involving extreme cooling, which disbonds the two metals by virtue of the fact of the aluminum contraction being sufficiently more than the steel contraction. Again, it's advisable to not be without a been-there-done-that advisor (a licensed professional engineer who has specific-to-the-task experence) on the groundbreaking frontiers of novel methods when a big underground tank containing gasoline is involved.

 

[HILSONHS]

I think this is being over thought. Here is my suggestion:

Purchase a 5 foot length of black iron pipe of an outer diamether that will easily slip into the 4 in. diameter tank pipe. The
iron pipe must have in inner diameter to easily accommodate the aluminum drop pipe.

Using a rotary tool (Dremel, hand drill, etc) grind a bevel on the _inside_ of the iron pipe so that it takes the shape of cold chisel.
You should only need to grind a quarter of the inner diameter of the iron pipe. Don't grind the outermost lip of this semi-circular chisel
edge too thin. Dress the the outside edge of this cutting end so that it is smooth (no burrs).

Tie a rope or wire around the other end of the pipe that is long enough that if you accidently drop it in the 4' pipe you and retrieve it.

Now, if you can reach the aluminum drop tube try to separate it from the outer tube for a couple of inches using a hand held
cold chisel (coated with a litte axel grease to decrease the chance of sparks). Again, tie a string around the hand held cold chisel
in case you drop it.

(This is optional depending on how long the aluminum drop tube is: tie a string around the end of the aluminum drop tube and
thread the string through the previously prepared iron pipe. Make the string long enought that if the aluminum tube drops
into the tank you can retrieve it.)

Now the fun part: grease the ouside of the first foot or so of the iron pipe (spark prevention), slide it down over the aluminum
drop tube with the sharpend inner edge between the drop tube and the outher 4 in pipe. Raise and lower the iron pipe with
sufficient force to progressively "chisel" or separate the aluminum drop tube from the outer pipe. If you get all the way down
the aluminum tube you can pull it and the iron pipe chisel out.