What does scale or tuberculation mean on a sewer report?

Trenchlesspedia defines it as "the formation of mounds of reddish-brown iron-oxide on a pipe's interior," typically associated with older iron pipes. The mounds are called tubercles. McWane, an iron pipe maker, explains that older gray cast iron pipe was sold with no lining or with a thin bituminous coating, and that in soft or acidic water the inside surface built up iron oxide. Trenchlesspedia says the deposits eventually reduce the pipe's effective internal diameter, which lessens its flow capacity.

Much of the published writing on tuberculation is about water mains, where the cause is bacteria and water chemistry. Rust scale inside old iron drain lines is a related condition, and camera operators often use the same word for it. The effect is similar: a rougher, tighter pipe.

A rough, lumpy, brown-orange wall, sometimes with a much smaller opening than the pipe should have. Since the mounds reduce the effective diameter, a line with heavy scale can drain slowly or back up even though the pipe is not broken.

It depends on what the operator sees. In the PACP grading matrix we opened, which is an older edition and can differ from the one your report uses, hard buildup on the wall is an O&M item called Deposits Attached, Encrustation. Its grade depends on how much of the pipe cross-section it fills: up to 10 percent is a 2, up to 20 percent is a 3, up to 30 percent is a 4, and more than 30 percent is a 5. The same matrix has a structural code for metal pipes called Corrosion, graded 3.

That split matters. NASSCO's July 2023 tip says O&M defects "trigger routine maintenance and operational activities such as pipe cleaning, root removal and infiltration control," while high structural grades "typically require engineering assessment." Scale coded as deposits is a cleaning question. Corrosion coded on the wall is a pipe-strength question. A report may show both, so ask for both grades. Our page on what PACP coding is explains the system.

Because a deposit code describes the buildup, not the metal under it. The PACP matrix has separate codes for each, and NASSCO's July 2023 tip says a pipe "displaying both structural and operational failures would result in an engineering assessment as structural failures take precedence over conveyance issues and O&M defects are removed during repair or replacement activities." In other words, if the wall is corroded or cracked, cleaning is not the main question. That is the reason a camera report should say more than "scale present."

It can. NASSCO's tip notes that heavy deposits "may require heavier cleaning or several passes of a jetter." Whether an old, scaled cast iron line can take that kind of cleaning depends on the condition of the wall, which is why the order matters: look first with a camera, read both the deposit grade and the structural grade, then choose the method. Our pages on cast iron drain pipe lifespan and what hydro jetting is cover the tradeoffs.

• The percent of the pipe blocked by scale, and where along the run.
• The wall condition where scale was removed or thin, not only the deposit code.
• Any cracks, holes or corrosion coded as structural. See crack, fracture and break.
• The full video, so a second contractor can review it. See getting your inspection video.

If your report shows scale in an old iron line, HQ can review the footage with you and tell you what we see before anything gets cleaned. We are licensed and insured, run 24/7 emergency service, and give free estimates and upfront pricing on any repair. See hydro jetting or sewer repair.

For the current inspection service, see HQ’s sewer camera inspections.