Pipe descaling is a mechanical cleaning that removes hardened scale, rust, and mineral or grease buildup from the inside of a pipe, most often old cast iron. A flexible cable spins chains or a cutting head against the pipe walls, scraping the line back toward its full original diameter so water runs freely again.
This is different from ordinary snaking or basic drain cleaning. A snake, or auger, punches a hole through a clog so water can pass, but it leaves the hardened layer on the pipe walls in place. Descaling works the whole inner surface, so flow is restored across the full bore instead of through a narrow channel. On heavily scaled cast iron, high-pressure water alone often cannot cut the buildup back to bare metal, so a chain or cutting head is used.
Descaling is often a preparation step before trenchless pipe lining. A cured-in-place liner bonds to a clean pipe wall, so the scale and rust have to come off first. After the pipe is descaled, a camera inspection confirms the line is clear and shows whether the wall underneath is sound enough to line.
Descaling has a clear limit. It cleans a pipe; it does not repair one. If an inspection finds a crack, a hole, or a section where badly deteriorated cast iron has lost its wall, cleaning cannot fix that. Pipes in that condition need lining or replacement, and descaling is the step that gets the surface ready for it.