A “king hole” is the lowest, southern most tube in a boiler tube sheet pattern. This spot should be identified on both sides of the vessel and will be the first tube that is removed. Essentially, the process calls for expanding the tube sheet hole and using the king hole to fish out cut tubes & stubs. It’s important to note that this style of tube removal will only work on a straight tube boiler without baffles. If baffles are present, the tubes will not be able to drop to the bottom of the unit for removal, so another method will need to be used.
The removal process consists of only a few steps. First, you’ll need a boiler tube cutter, pneumatic hammer or bump gun, an expander, and a small rod or pipe. When choosing an expander, it’s important to choose one that is ~1/16” undersized for the tube sheet hole ID. So, if the tube sheet hole is 2”, you’d want to use a 1-15/16” expander. Once you have the necessary tooling, cut both ends of the tube in the king hole location. This will drop the middle piece to the bottom of the vessel. Then, punch out the tube stubs using a knockout tool and bump gun. After the tube has been completely removed from the king hole, take the expander and roll the tube sheet hole on both sides. This will create an opening that is just slightly larger than the tube OD.
Using a rod or a smaller tube, an operator can fish out the loose tube and tube stubs through the king hole to pull them out. The cutting & retrieval process would be repeated for each tube, working from the bottom row up. It’s important not to cut too many tubes at one time, as it can make it more challenging to remove the tubes from inside the vessel.