Internal lining for water pipes: spin-applied epoxy, polyurea or mortar

To line the inside of a water pipe, the choice depends on diameter, service and wall condition: spin-applied epoxy for non-man-entry pipes with a sound wall, sprayed polyurea when a thick layer and fast cure are needed, cement mortar for some water networks, and manual application in large man-entry pipes such as penstocks. In every case, the result depends on cleaning, preparation and inspection, and a lining does not replace a pipe that has lost its strength.

Internal corrosion of a steel or cast iron pipe causes tuberculation, leaks, loss of flow and sometimes poorer water quality. Replacing the pipe often means excavating, a long outage or dismantling structures. An internal lining applied in place can, when the wall is still sound, restore a durable barrier. This guide is for managers of plants, networks and hydroelectric facilities in Quebec and Ontario. It complements our pipe coating page.

Which internal lining methods are available?

There are four main families of methods, which differ by accessible diameter, achievable thickness and return-to-service time. The table summarizes their usual fields of use; the specification and the manufacturer's data sheet set the precise limits.

A structural liner, which takes over the mechanical function of the pipe, belongs to another family of work. It becomes necessary when the wall is too thin or perforated.

The first decision is therefore not the product but the condition of the wall. An ultrasonic thickness survey at representative points, or samples taken during a planned cut, shows whether the pipe still carries its loads. If it does, a barrier lining is enough; if it does not, lining alone only hides the problem for a while.

When is spin-applied epoxy the right choice?

Spin-applied epoxy is the right choice when the pipe is not man-entry, the wall is still sound and you want a smooth barrier with little section loss. A rotating head fed with two-component epoxy is pulled at controlled speed; thickness depends on product flow and pulling speed.

• Advantages. Work without continuous excavation, a smooth surface that improves flow, little section loss.
• Limits. Tight bends, valves and reducers interrupt the run; joints and fittings are treated separately.
• Standards. AWWA C210 covers liquid epoxy coatings for steel water pipe; for potable water, the product must comply with NSF/ANSI/CAN 61, as explained in our article on potable water tanks and NSF 61.

The time before refilling is read from the data sheet, and our article on epoxy coating service life in immersion explains what determines it.

When is polyurea preferable?

Polyurea is preferable when the goal is a thick, flexible layer and a quick return to service, for example in a raw water pipe exposed to abrasion or movement. It cures very quickly, which shortens the outage.

That fast cure has a trade-off: polyurea tolerates a damp or poorly prepared wall badly, and its adhesion has to be verified. For potable water, only a product complying with NSF/ANSI/CAN 61 is acceptable; AWWA C620 deals with spray-in-place polymeric linings for potable water pipelines, and AWWA C222 with polyurethane coatings. Our polyurea coatings service presents these systems.

How does the service change things: potable, raw or wastewater?

The service changes product choice, thickness and checks, because the attack and the health requirements are not the same. The starting point is always the water being carried.

• Potable water. NSF/ANSI/CAN 61 compliance of the applied product, cure conditions as required for that compliance, flushing and disinfection before return to service per AWWA C651.
• Raw and process water. Abrasion by sediment, fouling, temperature; thick, abrasion-resistant systems are preferred.
• Wastewater. Hydrogen sulfide attacks concrete and steel above the water line; see our article on H2S concrete corrosion in wastewater.

Treatment plant piping is often part of a package with basins and tanks; see our article on water treatment plant coatings.

How is a penstock treated?

A penstock is treated as a large man-entry structure: dewatering during an outage window, confined space access, abrasive blasting, manual application of a thick system and full thickness and holiday checks. Sediment abrasion and water velocity point to abrasion-resistant systems.

• Outage window. The schedule depends on generation and flows; the whole job is prepared before dewatering.
• Ambient conditions. A cold, damp wall encourages condensation: heating, ventilation and dehumidification keep the surface above dew point.
• Critical areas. Bends, bifurcations, inlets and outlets take more abrasion and receive particular attention.
• Safety. Entry follows the provincial confined space rules: atmosphere testing, continuous ventilation, rescue plan and isolation of the water supply upstream. Solvent-free products reduce vapour exposure inside the pipe.

Our hydroelectric coatings service covers penstocks, gates and scroll cases.

How is the inside of a pipe prepared?

Preparation has four steps: initial camera or walk-through inspection, removal of tubercles and deposits, blasting to the required grade, then drying and a cleanliness check. An internal lining only holds on a clean, dry, profiled wall.

• Initial inspection. CCTV inspection for small diameters, walk-through for large ones; survey of perforations, joints and fittings.
• Cleaning. Mechanical scraping or hydro-blasting to remove tubercles, deposits and loose old lining.
• Blasting. Centrifugal blast head in small diameters, manual blasting in man-entry pipes; the grade, often SSPC-SP 10 / NACE 2 for epoxy in immersion, comes from the specification. See our NACE 2 / SSPC-SP 10 guide.
• Drying. Ventilation and dehumidification until the wall meets the conditions on the data sheet.

Which checks and inspection should be required?

Checks are required before, during and after application, then an inspection before return to service. They form the pipe's record and make it possible to follow the asset afterward.

• Before. Cleanliness, surface profile, ambient conditions, dates and times recorded.
• During. Product flow and pulling speed for spin application, wet film thickness in man-entry pipes.
• After. CCTV inspection, dry film thickness where the wall is accessible, holiday testing per NACE SP0188 or ASTM D5162, adhesion per ASTM D4541 if the specification calls for it.
• Return to service. Cure verification, flushing and, for potable water, disinfection.

Our coating inspection service can handle these checks.

How do you get a quote?

Gather the diameter, length, material, service, known condition (CCTV inspection if available) and the outage window. Pricing is on consultation: it depends on access, cleaning, method, special points and the checks required. Our crews and qualified subcontractors work from LaSalle, including Montreal. For our protective coatings, send your information through the request a quote form: reply within 24 business hours.

Frequently asked questions

Can an internal lining repair a leaking pipe?

It can seal small pits on a wall that is still sound, but it does not replace the mechanical strength of a thinned or perforated pipe. In that case, a structural liner or replacement is needed.

How long is the pipe out of service?

The time depends on length, cleaning, method and product cure. Polyurea shortens the cure; epoxy needs a time set by its data sheet.

Can a potable water pipe be lined with epoxy?

Yes, with a product complying with NSF/ANSI/CAN 61, applied and cured under the conditions of that compliance, then flushed and disinfected before return to service.

Does the old internal lining have to be removed?

Yes if it is disbonded, friable or incompatible. A well-bonded, compatible old lining can sometimes be kept after preparation, but the specification and an adhesion test decide.