Which of the following is a recognized repair method for cast-iron pipes?

The use of a mechanical leak clamp is a recognized and effective method for repairing cast-iron pipes. This technique involves securing a clamp around the damaged area of the pipe, which creates a seal that prevents further leakage. Mechanical leak clamps are particularly useful as they can be quickly installed without requiring extensive excavation or pipe replacement, making them a practical solution in many situations. They work by applying uniform pressure around the circumference of the pipe, effectively sealing cracks or holes.

Repair methods like epoxy coating and concrete patching can be applicable in certain contexts but are less common for cast-iron pipes. Epoxy coatings are generally used for corrosion protection but may not suffice for structural integrity on their own, while concrete patching is not typically suitable for direct repairs on pipes. Screwing, while it might stabilize sections temporarily, is not a recognized method for effectively repairing pipes like a mechanical clamp is. Therefore, the mechanical leak clamp stands out as the most reliable and accepted method for addressing leaks in cast-iron piping systems.