The vast majority of pipelines running under our feet are well past their serviceable life. Thanks to sturdy materials used in the making of these pipelines, they have managed to live decades over their expected lifespan. However; it is the time for these pipelines, which are the backbone of a functioning society, to either replaced or repaired so that they continue to serve the purpose for which they have been laid. (Learn more in "The Lifespan of Steel, Clay, Plastic & Composite Pipes.")
The labyrinth of varied sizes of pipes carrying water, sewage, cables, gas, etc. traverse the underground serving different purposes, making it difficult to replace these pipes without causing damage to one or more of the neighboring pipelines. Traditionally, digging and replacing pipelines essentially meant disrupting an entire section of the road including the electric and gas connections that pass through the area to prevent a catastrophe in case of damage while digging.
Now that trenchless technology is being used for the repair of pipelines, the problem relating to dug up roads, traffic jams and the disruption of other service lines has been quietly eliminated. There are many forms of trenchless rehabilitation methods used for repairing water and sewer pipelines, such as mechanical spot repair, cured-in-place-pipe (CIPP), sliplining, shotcrete, spray-in-place pipe (SIPP) etc. These avoid disruption; they save time and cost less. Here we will take a closer look at the SIPP method of pipe rehabilitation.
Materials Used for SIPP
SIPP is not an entirely a new concept, for this method was followed in the early 1900’s with hand-applied cement mortar. A few decades later, cement mortar was applied using spray application in larger diameter pipes, and eventually, also in smaller diameter pipes.
For many decades, cement mortar was a popular choice for SIPP, however; cement mortar when hard lacks sufficient tensile strength to impart additional pressure capability and strength to a structurally deteriorated pipe, making it preferable only in pipes that still retained their structural integrity. Cement also requires sufficient setting time, thus requiring the pipeline to be out of service for a long period of time.
Other materials used for SIPP are polymers and epoxies that combine resin and a hardening agent, which are in a liquid state until combined and allowed to chemically react. Once the reaction is complete, they turn into 100% solids. Epoxy utilizes a resin – bisphenol A, and a hardening agent – epichlorohydrin. The reaction is initiated by introducing a catalyst and subjecting it to high temperatures. However, the setting time of certain epoxies requires an alternate service connection.
They do not add much to the structural strength of the host pipe and are best suited where cracks or gaps are to be filled in, and protection against corrosion is required. Polyurea and polyurethane are also lining materials that are very effective in SIPP lining methods because of their quick setting time and easy application.
These linings are produced using a compound of isocyanate, but each utilizes a different reacting resin. While polyurethane linings use a polyol ending blend, polyurea uses an amine ending blend as the resin.
Application of Polyurethane and Polyurea Liner
The process of rehabilitation using SIPP begins by identifying the region to be repaired. This is carried out by conducting an inspection using closed-circuit television camera (CCTV) mounted on robotic crawlers and connected to a monitor manned by an expert. Once the problem area is noted, access points are marked and excavation near valve junctions and other strategic points is carried out.
The ends of the host pipe are then dressed, and cleaning and carried out using different methods such as scraping, rack feed boring, foam swab, water jetting etc. The pipe is inspected once more to check for any leftover debris that may cause failure of the liner application.
The catalyst used in a polyurethane liner is similar to that used in epoxies and results in 100% solid material within minutes, which permits the addition of extra layers where high build-up is required. The application of polyurethane liner is done using a centrifugal system with an air driven spray head that advances through the pipe spraying the liner onto the pipe's surface in layers of 3-mm to 5-mm. These coatings are resistant to chemicals and corrosion but do not adhere well if the surface is wet.
Polyurea liners have a very short setting time and harden quickly, also producing 100% solid materials. The application process is different than polyurethane liners and does not necessarily require a catalyst, rather it requires high pressure and high temperature for application. The application system for polyurea lining is done either by a robot system or can be applied by hand to develop a pipe inside a pipe, with thickness varying from 0.5-mm to 25-mm.
These lining materials set quickly, eliminating the need for an alternate service line. They also possess excellent pressure ratings and are resistant to chemical abrasion, corrosion from hydrogen sulfide gas, acids, microbial buildup etc. making them an excellent choice for pipeline rehabilitation in the sewage, oil and gas industry, and even for potable water pipelines.
SIPP can be used in pipes installed horizontally or vertically with diameters ranging from as small as 1 ¼-inch to as large as 72-inches.
After the liners are installed, video inspection is carried to again to check for quality standards. If the liner has been placed appropriately, the pipe is restored to its original strength and design parameters, increasing the lifespan of the pipeline considerably. SIPP does not require reinstating laterals as may be needed in other lining methods such as CIPP.
The excavated holes near valves and other strategic points are closed up and restored to their original condition. Innovation in the field of trenchless rehabilitation has made inspecting, cleaning and repairing underground pipelines quick and effective. (Read on in "Trenchless Sewer Repair and Cleaning 101.")
Contractors are slowly catching up to the benefits of trenchless repair methods such as SIPP and CIPP and are making it an essential part of their toolkit. While repair takes place silently underground, pedestrians, commuters and homeowners no longer need to worry about unsightly scenes of dug up roads, sidewalks, gardens and driveways.