UKSTT

Localised Repair Techniques

Resin injection systems involve the localised repair of pipes by resin injection into defects, the subsequent curing to prevent leakage and further deterioration.

RESIN INJECTION SYSTEMS: INFLATABLE PACKER, GROUNDWATER, EXFILTRATION, EPOXY RESIN

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. The technique may be considered for more serious defects, such as holes and circular fractures and 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 epoxy 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 inflatable 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 A thin internal collar of resin usually remains after the packer has been withdrawn.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.

PATCH REPAIR SYSTEMS: THERMAL CURE, THERMAL CURE SYSTEMS, INFLATABLE PACKER, SEWER, AMBIENT CURE SYSTEMS, POLYESTER RESIN

Localised pipe repair by positioning a short sleeve of resin-impregnated material within the host pipe and cured. Patch repair systems 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 systems and ambient cure systems are available. Resins are usually polyester resin (ambient temperatures) or epoxy resin (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.

ROBOTIC REPAIR SYSTEMS: GRAVITY PIPELINES, CCTV, EPOXY MORTAR, ROBOTIC REPAIR SYSTEMS, EPOXY RESIN

A remote control device with CCTV monitoring is used for the localised repair of defects and obstructions using grinding and filling tools. Robotic repair systems for gravity pipelines comprise of grinding robots and filler robots. Grinding robots remove 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. 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.

REROUNDING: HYDRAULIC MOLE, DEFORMED PIPE, HYDRAULIC RAMS

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. Rerounding 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. Deformed 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.