Prior to the introduction of plastic pipe many gas utilities used cast iron to build their gas distribution network. Currently, there is approximately forty thousand kilometres of cast iron pipe in service in North America and a further two hundred thousand kilometres in Europe. Mostly found in dense urban locations, the cost of replacing these systems can be significantly high, such that extending the life of these systems is now a common strategy. The main problem has been leakage from bell and spigot joints caused by road vibration, freeze/thaw cycles of the ground, and the swelling and drying of clay soils.
Repair technologies have evolved from mechanical joint clamps, to elastomeric seals, to shrink sleeves, to encapsulants and finally to anaerobics. The most advanced of these technologies involve the use of anaerobic sealants which are injected into the jute packing by drilling into the pipe bells. These sealants have been studied at Cornell University for longevity, and are predicted to withstand many years of service.
The use of anaerobics has been adapted to work with robotics that allows the injection to take place from the inside of the pipeline while the gas main is in operation. This technology allows 24 joints to be sealed from a single excavation. The robot is a tethered electro-mechanical device that allows visual location of the joint, internal drilling into the jute packing, and injection of the sealant. A semi-rigid umbilical cable contains the electrical, hydraulic, and communication lines, and a unique drive mechanism that allows for remote operation and positioning.
The development of this prototype technology was conducted by Engineering Services Inc. (ESI) of Toronto at the request of Enbridge Consumers Gas and was co-funded by Consolidated Edison of New York. Over 2000 joints have been successfully sealed in the last two years and the system is expected to be commercially available within the next year. Internal robotic repair of live mains is an industry first and has the potential to significantly reduce both costs and disruption of road excavations in urban areas.