Typically used for natural gas lines to water heaters, furnaces and other large appliances, black iron pipe is black in color and is often confused with galvanized iron pipes, which are used for other household supply lines. You can clean black iron the same way your clean most other types of iron, but since it's typically used for gas, stay away from flammable cleaners if possible.
Pour warm water over your black iron pipe. Use a plastic scrub brush to scrub the surface of the pipe and remove any built-up dirt. Pat the area dry with a dry paper towel.
Use steel wool or wet/dry sandpaper to clean your black iron pipe if a simple scrub doesn't do it. Wet the surface of the pipe with water. Scrub the surface of the iron with the steel wool or sandpaper until you remove any dirt or staining on the surface. Do not use steel wool to clean black iron pipes that are currently being used as a gas line. Scrubbing metal against metal can cause a spark, which may cause a fire if you have a slow gas leak.
Dry the area with a dry towel or paper towel once you've finished scrubbing.
Turn off any gas running to the black iron pipes. Unscrew the black iron pipes from one another using a wrench.
Fill a 5-gallon bucket or pail with water. Leave at least 6 to 8 inches or more between the water line and the top of the bucket so the water doesn't overflow when you put the pipes in the solution.
Add 1 tbsp. washing soda or lye per gallon of water to the bucket a little at a time to prevent any splashing. If you're using lye, wear goggles and gloves because lye can be caustic and burn your hands.
Place an old piece of metal, such as a piece of rebar or steel fence post, in the solution to use as an anode. An anode is the terminal that power or electricity flows into from an outside source. The end of the metal should stick out of the water and over the edge of the bucket. Use a squeeze clamp to keep it standing up straight and in the right position.
Use electrical squeeze clamps to connect a piece of 10- or 14-gauge copper wire to each piece of pipe from which you want to remove rust.
Attach the wires to the battery charger that is not yet plugged in. Hook the black wire from the battery charger to the copper wires running from your pipes. Hook the red wire from the battery charger to the anode in the bucket.
Place the pipes in the solution, making sure they don't touch the anode. Check your wires; the red and black wires must be attached correctly. If you have the wires backward, the iron pipes you're trying to clean can become corroded.
Plug in your battery charger.. After a few minutes, oxygen bubbles will rise to the surface if the process is working correctly. Leave the pipes in the solution with the power running for a few hours. The more rust on the pipes, the longer the pipes will need to stay in the solution. Make sure people and pets stay away from the bucket and charger.
Unplug the charger. Take the pipes out of the solution, place them under running water and scrub them with a scrub brush to remove any remaining rust. Allow the pipes to dry before reassembling them.