Intelligent pigs are sophisticated devices that can be inserted into a pipeline at special pig launching chambers and transported along the pipeline with the flow at speeds of between 0.7 and 4 m/s for up to 100 kilometres. Intelligent pigs normally use a technology known as Magnetic flux leakage (MFL) to accurately detect circumferential and longitudinal cracks and metal loss due to corrosion.Application
Intelligent pigs have been used for assessing the condition of long distance oil and gas pipelines for many years now and this is still their main application. Intelligent pigs are rarely used on water or gas distribution pipes or sewage rising mains due to the cost and various other constraints outlined below.Technology Description
MFL only works in cast iron and steel pipes as it is based on the use of magnets to induce a D.C. magnetic field in the pipe wall. Wherever corrosion is present, a small amount of magnetic flux leaks from the pipe resulting in slight changes in the local magnetic field that are detected by sensors and recorded as the pig passes down the pipe. Although the technique can provide detailed information about the condition of metallic pipes, it is not feasible for use in water distribution mains for a number of reasons. First of all, because there must be close contact between the pig and the metallic pipe wall, it is not suitable for pipes lined with cement mortar, for example. Secondly as there must be a tight fit between the pipe and the pig any changes in diameter will either stop the progress of the pig or prevent close contact between pig and pipe. Thirdly, the progress of the pipe will also be prevented by control valves, air valves and tee connections. Finally, the cost of carrying out an intelligent pig survey is very expensive - around £400 per metre; whilst this may represent good value for maintaining the integrity of long distance oil pipelines it is unlikely to be economically feasible for water mains.
Pig Trap - Photo Courtesy of TRANSCO.