Galvanized steel pipe was the standard for small drain branches, the 1.5 and 2 in lines from sinks, tubs and laundry fixtures, in houses built before about 1960, and in many houses it is still there behind the walls. It rusts. The zinc coating that protected it wears off within a couple of decades, and after that the steel corrodes from the inside, layer by layer, until a 2 in pipe has a 1 in hole through the middle and every threaded fitting has a lip of rust that catches whatever passes. A camera inspection of galvanized branches is less about finding a defect than about measuring how far along the rusting has gone, and the first challenge is getting a camera head into the pipe at all.
Quick answer: galvanized drain pipe shows on camera as a rough, rust-coloured wall with the bore visibly smaller than the fitting size, rust nodules and flakes on the wall, and a ridge of scale at every threaded fitting where the pipe end meets the fitting. The picture is dim because the rough brown wall absorbs light. A 17 mm head on a 5 mm rod is the only consumer camera that reliably enters it; a 23 mm head will stop at the first fitting. Narrowed galvanized branches are replaced, not cleaned, because the rust is the pipe wall.
Recognising galvanized pipe
Threaded fittings are the giveaway. Unlike the bells of clay, the hubs of cast iron or the glued sockets of plastic, galvanized pipe screws into its fittings, and on camera each joint shows as a sharp ridge where the pipe end stops inside the fitting, often with a step down into the fitting’s bore and a step back up into the next pipe. The wall is rough and brown to black. The pipe is small, 1.25 to 2 in nominal, and the bore is smaller than that. Galvanized is never the main lateral; if the camera is in a 3 or 4 in line, it is cast iron or something else. Identifying pipe material from the picture covers the others.
Rust narrowing
Steel corrodes into iron oxide, which takes up more space than the steel did, so the rust grows inward. The bore shrinks over decades until the pipe is nearly closed, and the shrinking is uneven: worst at the invert, worst near fittings, worst where water stands. On camera the wall looks like the inside of a rusty tin, with nodules, flakes and a bore that is clearly less than the fitting size. The narrowing is why galvanized branches drain slowly and block constantly, and why cabling them clears a hole through rust that closes again. The rust is the wall; removing it leaves a pipe with holes. Tuberculation in cast iron is the same chemistry in a larger pipe.
Scale lips at fittings
At every threaded joint the pipe end sits inside the fitting and the fitting bore is a step larger. Rust builds on both, and the result is a ridge, a lip of scale that catches paper, hair and camera heads. On camera the lip appears as a bright ring of rust that the head bumps against, and often the view beyond is through a hole smaller than the head. This is where cameras stop, where cables snag and where the picture in a galvanized branch usually ends. The lip is a sign that the fitting is corroding too, and that a branch replacement will involve the fittings and not just the pipe.
Getting a camera in
A 17 mm head on a 5 mm rod will enter a galvanized branch that still has a 1 in bore and will often make the first fitting. A 23 mm head will not. Even the small head will stop at a lip that has closed the bore below its diameter, and that is information: the distance at which the camera stops is the distance at which the pipe is effectively closed. Feed by hand, rotate at each fitting, and do not force; a head wedged in a rust lip inside a wall is an expensive extraction. The ranking of 17 mm sewer cameras and the guide on sewer cameras for older homes cover the equipment.
When to replace
When the bore is visibly narrowed, when lips are catching at fittings, when the branch blocks repeatedly, or when the camera cannot get in. Galvanized drain pipe at sixty or seventy years old is at or past the end of its life everywhere, and the usual decision is to replace the branch back to the stack with plastic rather than to clean it. A camera pass establishes how far the rust has gone and which fittings are involved, which sizes the job. For the main lateral in the same house, which will be cast iron or clay, the inspection is a separate question and the pre-1950 house guide covers it.
Common questions
Can galvanized drain pipe be cleaned?
A cable opens a hole through the rust. It closes again because the rust keeps growing. Cleaning buys time; it does not restore the pipe.
Can a 23 mm sewer camera inspect a galvanized branch?
Almost never. The bore is too small and the fitting lips stop it. Use a 17 mm head on a thin rod.
Does galvanized pipe leak?
Eventually, when the rust goes through the wall, usually at a fitting. Before that it blocks.
Related guides
See the best sewer cameras for 1.5 in pipe, camera inspection of a kitchen sink line, and why a sewer camera will not go around a bend.