Natural gas pipelines require routine maintenance such as internal cleaning and continual monitoring for leakage or other pipeline damage. While there are a number of ways to inspect and maintain a pipeline, one of the most important devices used is called a "pig." This device travels through the pipeline cleaning any matter that may have adhered to the inside of the pipe and removing any water. A "smart pig" goes one step further and transmits data regarding the internal condition of the pipeline back to the pipeline operator. Data smart pigs can gather include the existence of dents or gouges, metal loss due to corrosion or other causes, pits of corrosion, whether the pipe is still in an oval shape, and flaws in welds.
Pig launchers and receivers are installed at each end of a pipeline to allow the introduction or removal of a pig. Pigs are commonly forced through a pipe by the gas flow but are sometimes towed through the pipe by another device or a cable. Unfortunately, not all pipelines are capable of using pigs. Some older pipelines have bends that are too abrupt for pigs to pass.
There are two explanations for the naming of this device. The first is that early pigs made a squealing noise while traveling through the pipe, thus earning them the name “pigs.” The second somewhat less-creative explanation is that a pig is merely an acronym for the term “pipeline inspection gauge.”