What is one common method to remove a pipe that will not unscrew from a cast iron fitting?

Using heat to loosen a stubborn joint is a widely accepted method in plumbing, especially with cast iron fittings. When cast iron fittings and pipes are subjected to heat, the thermal expansion can help break the bond between the fitting and the pipe. Heating the joint causes the metal to expand and can create enough differential expansion that may allow the pipe to be unscrewed more easily. This method is particularly effective for fittings that have become corroded or have had sealants applied.

It's important to apply heat carefully and evenly, often using a torch, to prevent damaging the cast iron or affecting nearby materials. Always ensure that flammable materials are kept away from the heat source during this process, and consider the use of appropriate personal protective equipment.

Other methods may not be as effective or suitable for the specific needs of cast iron fittings. For example, using a pipe cutter is more appropriate for cutting through the pipe rather than removing it from a fitting. Hitting the fitting with a hammer could cause damage to the fitting or the surrounding area, and applying lubrication may not be effective for a joint that is excessively rusted or corroded.