Why must pipe be jetted before it is lined?

Four things have to be true before a tube goes in.

A clear path. The tube has to travel the whole run. Wikipedia's summary of the method notes that obstructions in the existing pipeline, such as protruding laterals, must be removed before installation. Roots, chunks of scale, and hard grease can block or snag it.

A clean surface. The liner presses against the host pipe wall. Grease, rust scale, and mineral crust under it leave a soft, uneven surface. John Heisler of Pipe Lining Supply, writing in Cleaner, calls lining or coating over heavy tuberculation "the equivalent of painting over old exterior paint without any preparation" and says it sets the contractor up for failure. The preparation requirement depends on the rehabilitation system. A close-fitting structural CIPP liner is not universally dependent on adhesion to the host pipe; coatings and some other lining systems do require an appropriately prepared bonding surface. In either case, deposits can obstruct installation, affect fit and conceal defects.

The right measurements. The tube is manufactured to fit. NASSCO's guideline has the contractor accurately measure and document the diameter and length of the existing pipe before ordering tube materials, and the measuring is done after the pipe is cleaned enough to be measured. A pipe full of scale reads smaller than it is.

A true picture of the pipe. A camera cannot see through grease. Cleaning is how the operator finds out where the pipe is cracked, offset, or collapsed, and whether lining is even the right fix.

How a liner goes in, and why it cannot be rushed. A resin-impregnated felt or fiberglass tube is inserted or pulled through the damaged pipe, usually from an upstream access point. Water or air pressure moves it into position and presses it against the wall. Then the resin has to cure, by hot water or steam, or by UV light if the tube is fiberglass. Cure timing and installation limits depend on the liner, resin, dimensions and job conditions. Ask the installer for the chosen system's requirements. The pipe must be ready before installation starts. Once the resin is wet, the crew cannot stop and clean.

The same summary lists the tradeoffs: most tubes are custom manufactured to size, and lining leaves a smooth, jointless interior. After installation, use only maintenance tools and settings approved for the chosen liner; do not assume every cable or cutter is suitable.

NASSCO, the association behind many municipal sewer rehabilitation specifications, sets this out in its cured-in-place pipe guideline. It calls for a written installation plan that covers preparation work, cleaning operations, and pre-inspection by camera. The details:

• The contractor removes debris from inside the pipeline that would interfere with installation before ordering materials.
• Solid debris and deposits are removed and disposed of properly. Moving material from one section to the next is not allowed.
• Precautions are required with cleaning equipment to avoid damaging the existing pipe, and damage caused by cleaning equipment is the contractor's to repair.
• The contractor does post-cleaning video inspections using trained personnel, and provides the owner with the pre-cleaning and post-cleaning video for review before installation.
• Clearing obstructions that would hurt the liner's installation or long-term performance is the contractor's responsibility.

Those are municipal contract terms, but the logic carries into a building drain. If the spec for a city sewer calls for clean, inspect, and document, a property owner has good reason to expect the same.

Which tool depends on what is in the pipe:

• Grease, sludge, and light scale: hydro jetting. See what hydro jetting is and what the nozzles do.
• Roots: root-cutting nozzles or cutters. See whether jetting keeps roots from coming back.
• Heavy rust scale in cast iron: mechanical descaling with chain cutters. Cleaner's article argues that mechanical force does better than water pressure on tuberculation, and S1E lists grinding chains as the tool for large scale buildup in cast iron, concrete, and clay pipe. See cast iron descaling.

After cleaning, a camera pass confirms the pipe is ready. Old pipe needs care during cleaning too; read whether jetting can damage old cast iron or clay before anyone runs aggressive tools in a fragile line.

If the pre-lining pass turns up collapsed sections or breaks the liner cannot span, the answer changes. NASSCO's guideline covers this case: if pre-installation inspection reveals an obstruction, misalignment, broken or collapsed section, or sag that will prohibit proper installation, the owner may direct that the problem be corrected first, using open-cut repair. It also treats previously unknown obstructions as a changed condition, which is contract language for "the scope just changed."

For a building owner, the lesson is simple: get the cleaning and camera work done before you commit to a lining price, because that is when surprises show up. Trenchless options are compared in pipe bursting versus pipe lining, the scope question, full or partial, is covered in whether to reline the full sewer line, and trenchless versus dig covers the bigger comparison.

After lining, too. NASSCO's guideline has the contractor thoroughly clean the newly installed liner and clear standing water in sags before the final camera inspection, and remove debris and buildup that may have accumulated. So cleaning bookends the job: once to make the host pipe ready and once to show the finished pipe.

Cost and schedule follow from this too. Cleaning and inspection are real work that has to be planned into the job, and they are the step most likely to reveal the surprises that change the scope. A proposal that treats them as an afterthought is a proposal that may grow later. A proposal that spells them out is one you can compare with others on equal terms.

When you get a lining proposal, look for a line item or a description that covers cleaning, a pre-lining camera pass, and video you get to keep. The lining process also affects your building while it runs. NASSCO's guideline requires that flow around the section be plugged or bypassed before installation begins, and service connections may not remain plugged overnight, so ask how restrooms and kitchens will be handled during the work.

Questions worth asking any lining contractor:

• How will you clean the pipe, and with what tools?
• Will I get the before and after video?
• How will you measure the pipe, and what happens if it measures differently than expected?
• What happens if the camera finds a collapse or a break?
• How will my restrooms and kitchens be handled while the liner cures?

If a proposal skips cleaning, ask how the chosen system will be installed, fitted and inspected in a scaled or greasy pipe, and whether that particular product requires adhesion. HQ offers hydro jetting and commercial drain cleaning, with free estimates and the price given up front, before work starts.