DTE Energy : uses pigs to probe pipes to help ensure pipeline safety

I'll bet you've never seen an eight-foot pig, but you may have been near one and never knew it. Synonymous with swine, pig is also a nickname for a sophisticated internal pipeline inspection device that's used to verify the condition of underground steel natural gas and oil pipelines. DTE Energy uses pigs to inspect its gas transmission lines from eight inches to 36 inches in diameter.

One of the largest pigs used is more than eight feet long and weighs about 3,800 pounds. There are several pipeline inspection options allowed, but the company prefers pigs because they provide the most data.

The smart pig, which looks like something NASA would launch into space, is inserted into DTE transmission lines and pushed through pipes by the flow of natural gas. Along the way, it emits a strong magnetic field. Sensors on the device gather data on the effect the magnetic field has on the steel pipe. The data is captured by the pig and analyzed by a computer program.

The analysis indicates where there may be anomalies in the metal, such as dents that could cause a problem later, corrosion or a manufacturing defect in the pipe that went undetected.

Prior to using the smart pig, several runs are made with cleaning pigs to remove liquids and deposits from the inner walls of the pipeline. The pigs are inserted into the lines and retrieved at above ground access points. The units travel about five miles per hour. The longest DTE pigging run is 130 miles.

Customers are unaware of the inspection procedure because it has no impact on their service. DTE typically performs pigging from April through June, because the analytical report can take from 30 to 120 days to receive. If it indicates areas requiring further investigation, the company wants to allow time to excavate and make any necessary repairs, which may impact service if not performed before the heating season.

DTE pigs about half of its 2,200 miles of transmission lines - exceeding federal requirements - and plans to add more lines to the inspection program over the next several years. While pigging won't guarantee a trouble-free natural gas transmission system, the company feels it's the best available technology to help ensure safe and reliable service to its customers.