Cast-iron water main embrittlement and cracking

Field-observation aside on how cast iron water mains are cut: sledgehammers, not saws. Tom describes 36-inch diameter water main repairs as a brittle-fracture demonstration. Used to anchor the "gray cast iron is brittle but tougher than glass" framing. ## Figures referenced (recurring numeric anchors, not cases)

Cast iron pipes, pots is gray cast iron. If I took a sledgehammer to a cast iron pot — put your safety glasses on, wear your shin guards and other things, because shrapnel can go flying. If you want to break one — well, you probably haven't seen it, but I've been there when they're digging up an old cast iron pipe in the street. They just get down there with sledgehammers and wham, and break it apart. Because it's too hard to cut with a saw. It's easier to cut steel than it is to cut cast iron with all the hard particles and impurities. Good soft cast iron cuts like butter compared to steel. But the old dirty stuff with all the impurities has got hard particles and just dulls saw blades. They often use carbide saw blades to cut cast iron, believe it or not, for cast iron pipe. But big 36-inch diameter water mains, when they have a break or something, they just go in there with the sledgehammers and these guys beat it to death. Wear your goggles and stuff, because when it breaks it will shatter. It won't shatter like glass because it's tougher than glass, but it'll give off big brittle fractures.