United Kingdom Society for Trenchless Technology: UKSTT - Localised Repair Techniques
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Repair systems are used to address localised service problems or structural defects within a pipeline. The methods of localised repairs can be grouped as stabilisation or structural repair systems. The following sections describe a number of repair systems using trenchless technologies. In general, a stabilisation technique will address a localised problem, such as infiltration, without adding to the structural integrity of the pipeline. Typically, stabilisation techniques include chemical stabilisation, joint sealing and resin injection although in some circumstances the latter can also be classed as a structural repair. By definition, a defect addressed by a structural repair method will improve the structural integrity of a pipeline. Typical structural repair techniques include CIPP patch repair, robotic repairs and pipe re-rounding.
For more details see:Click here to view all UKSTT Members involved with Chemical Stabilisation.
Renovation of a pipeline and ancillary features by sealing, between two access points by the chemical reaction of added compounds to the surrounding ground.
The sealing of drainage systems can be achieved by chemical stabilisation 'fill and drain' techniques, which treat the main sewer, branches and manholes in one operation. Originating in Hungary, the system has been developed and is used quite widely as a 'non-destructive' sewer repair system.
The section to be sealed is isolated and then filled from a manhole with an environmentally safe chemical solution (usually sodium silicate). After a predetermined interval to allow the chemical to permeate through leaking joints and cracks, the solution is pumped out quickly. The section is then filled with a second proprietary chemical solution, which reacts with the residue of the first chemical to form a waterproof membrane. The second chemical is then pumped out and the pipe is cleaned to remove any residues.
The chemical reaction between the two solutions turns the material surrounding manholes and pipes into an impermeable mass, almost a weak concrete, around points of leakage. Due to the scale of plant requirements and the volumes of materials needed, these systems are more economical for large-scale leakage control projects than the treatment of isolated lengths. The greatest advantage of the method is to treat leaks throughout the whole system in a single operation.
Schematic courtesy of WRc
Click here to view all UKSTT Members involved with Joint Sealing & Testing.
The testing and sealing of defective pipe joints with a grout using a packer, all activities being from a single process.
A common method of sealing leaking joints in gravity pipelines is to use a packer, which combines the functions of leak testing and grout injection. Joint testing and sealing may or may not be 'localised', depending on how many joints fail.
A packer with inflatable end elements is positioned across a pipe joint and pressurised to isolate the joint. Air or water pressure is then applied to the centre section of the packer and the rate of pressure loss through the joint is measured. If the loss exceeds a specified limit, a sealing resin compound is injected into the joint through the packer and the joint is re-tested.
The packer design varies, using either a two-part acrylic grout or a water-active polyurethane resin. The grout combines with the ground around the leaking joint to form an impermeable mass, preventing leaks and enhancing structural stability.
Polyurethane grouts are hydrophobic and react either with free water in the soil or with a water solution injected through the packer at the same time as the grout. Generally, a ratio of 1 part grout to 8 parts water is recommended for pipe sealing, variations creating products of different strengths.
Click here to view all UKSTT Members involved with Resin Injection Systems.
The localised repair of pipes by injection of a resin formulation into defects subsequently curing to prevent leakage and further deterioration.
Resin injection systems, normally using an epoxy resin or mortar, are used to stabilise and re-bond the existing pipe structure, in addition to sealing against exfiltration and /or infiltration. Originally aimed at pipes where damage was not too severe or extensive, the technique has evolved and may be considered for more serious defects, such as holes and circular fractures. The technique is usually considered when infiltration / exfiltration problems have been identified. However care must be taken in areas of high groundwater levels particularly if water runs along the line of the pipeline thus removing the resin from the area of repair.
An inflatable packer is winched into position so that it is centred on the defect. The isolated defect is repaired by the injection of a rapid-setting epoxy resin into the crack, fracture or hole in the pipe wall. The packer is left in position until the resin has cured and is then deflated and removed. A thin internal collar of resin usually remains after the packer has been withdrawn.
Recent developments include the ability to produce an even, thicker lining to provide some stiffness thus approaching a structural repair. Although the technology does not provide a full structural repair it will stabilise a structure by preventing the creation or enlargement of voids in the pipe surround or by reinstating the ground support. Overlapping multiple repairs can achieve a longer repair length.
Click here to view all UKSTT Members involved with Patch Repair Systems.
Localised pipe repair by positioning a short sleeve of resin-impregnated material within the host pipe and cured.
Patch repair techniques involve impregnating a fabric with a suitable resin and positioned in place within the sewer around an inflatable packer. The packer filled with water, steam or air under pressure, presses the patch against the existing sewer wall while the resin cures.
Both thermal-cure and ambient-cure systems are available. Resins are usually polyester (ambient temperatures) or epoxy (thermal cure). Patch repairs are short versions of cured-in-place liners, using polyester needle-felt on its own or in combination with glass fibre.
Safe working practices are essential particularly when impregnation of the fabric is carried out on site since the spillage of chemicals and good ventilation is needed as polyester resins give off styrene.
For both systems, it is necessary to limit the rise in temperature of the materials until the patch is inflated within the pipe and avoid premature cure, which can cause failure.
The curing time depends on the resin formulation, the thickness of the patch, the temperature within the packer (in thermal-cure systems) and the temperature of the existing pipe wall. A high ground-water table will cool the outer surface of the patch and additional curing time should be allowed for hot cured systems. Ambient cured patches may not have sufficient thermo-energy to ensure a full cure.
After curing, the packer is deflated and removed. The patch should then be inspected by CCTV, any lateral connections being re-opened using the same techniques available for full-length liners
Click here to view all UKSTT Members involved with Robotic Repair Systems.
A remote control device with CCTV monitoring for the localised repair of defects and obstructions using grinding and filling tools.
Robotic repair systems for gravity pipelines comprise of grinding and filler robots. The former removes encrustation and intrusions and also mills out cracks to provide a good surface and key for the repair materials. The filler robot applies an epoxy mortar into the slot formed by the grinder and trowels off the material to a smooth finish.
Smaller robots will operate in diameters up to 200 to 400 mm; larger robots in diameters from 300 mm to 800 mm.
The hydraulically driven grinding head can be fitted with various shapes of cutter to cope with most pipe materials. Cutters are usually cooled by a water spray issuing from the central hub, providing a coolant and lubricant for the operation. Intruding laterals, grout deposits and hard encrustation can also be removed.
The operation of the self-propelled robots is monitored by a CCTV camera attached to the head.
Schematic courtesy of WRc
The two-part epoxy mortar may be mixed prior to filling the canister on board the filler robot. In some designs, the components are loaded into the robot separately and mixed at the outlet as they are used. The epoxy, applied by a system of remotely controlled nozzles and spatulas is injected through a flexible plate or former pressed against the pipe wall.
Defective lateral connections can be repaired by sealing the connections to the main pipe with epoxy resin to form a flush finish
Some filler robots can inject expandable foam into voids hydrophobic grout to stop infiltration.
Robotic repair systems are versatile but need a consistent programme of work to be economically viable.
Click here to view all UKSTT Members involved with Rerounding.
The insertion of an expansion device into a deformed pipe to return it to a circular shape prior to a permanent repair usually with a lining technique.
Re-rounding is not a stand-alone technique but is intended to re-shape a deformed pipe prior to patch repair or relining. An expander unit is used to re-round the pipe and install a metal or plastic clip, which holds the pipe fragments in position until a patch or liner is installed. Deformation of pipes between magnitudes of 10% to 35% is typical for this type of temporary repair.
The expander system is inflated with hydraulic pressure or, alternatively, a hydraulic mole forces steel 'petals' outwards by hydraulic rams. The plastic or metal clip is scrolled around the expander and secured prior to. After positioning under CCTV control, the clip is expanded with sufficient pressure to re-round the pipe.
Care must be taken with severely damaged pipes since the unit will take the path of least resistance when expanding. For example, if there is a void beneath the pipe invert (as a result of exfiltration / infiltration), the clip may be forced down when expanded, rather than re-shaping the soffit of the pipe. It is also important to follow the relining or patch repair as soon as possible after the re-rounding operation, (within 24 hours) since the clip has limited structural strength and may soon become misshapen if left without support.
Photo courtesy of WRc
Click here to view all UKSTT Members involved with Lateral Cutting.