Pigs let NDT technicians perform inspections on buried pipelines.

Introduction

Throughout the United States, pipelines transporting water, oil, and natural gas cross the landscape like a massive web. Since pipelines are exposed to the natural elements, they will inevitably corrode and crack. If an oil or gas pipeline bursts, it can leak into the ground and harm the environment. In order to prevent this from happening, nondestructive testing is performed on pipelines to discover flaws before they pose an issue. In most places, pipelines are buried in the ground. So, how is NDT be performed on buried pipelines? The answer is pigs. No, not the kind that rolls in the mud!

What are Pigs?



Pigs, shown above, are cylindrical devices. Technicians insert the pig into buried pipelines to perform inspections and simultaneously clean the pipe. There are different types of pigs, and specialty pigs that can perform advanced testing methods are sometimes referred to as "Smart Pigs." Pigs come in all sizes depending on the diameter of the pipe being tested. In the pigging process, pigs are passed through the pipeline by the liquid or gas. Pigs can travel long distances. Inside the pig, a computer stores and transmits data for analysis or record keeping. The longest continuous inspection by a pig was performed in 1997 by the Trans Alaska crude oil pipeline with a distance of 1,055 km.



There are four main uses for pigs: Physical separation between different fluids flowing through the pipeline (product flow) Internal cleaning of pipelines Inspection of the condition of pipe walls

Capturing and recording geometric information relating to pipelines



What Nondestructive Testing Can Pigs Perform?

Pigs can perform several nondestructive testing methods. Magnetic Flux Leakage: Most commonly, pigs perform magnetic flux leakage testing. With magnetic flux, a strong magnetic field is used to discover damaged areas of the pipe. A sensor detects the magnetic flux leakage and records the area of damage.

Most commonly, pigs perform magnetic flux leakage testing. With magnetic flux, a strong magnetic field is used to discover damaged areas of the pipe. A sensor detects the magnetic flux leakage and records the area of damage. Ultrasonic Testing: Pigs can also perform ultrasonic testing. With this method, high frequency sound waves are used to determine wall thickness and detect cracks.

Pigs can also perform ultrasonic testing. With this method, high frequency sound waves are used to determine wall thickness and detect cracks. Visual Inspection: Many pigs can also be used for visual inspection. This is performed through a video feed where a remote operator reviews the video.



Conclusion

Thanks to pigs, nondestructive testing can be performed on buried pipelines to gather information and locate flaws in pipelines. Periodic inspections find flaws and damage before they become a major concern. As a result, leaks in pipelines are prevented and the environment is kept safe.

Citations

Pipeline Inspection. (n.d.). Retrieved December 2, 2019, from https://www.nde-ed.org/AboutNDT/SelectedApplications/PipelineInspection/PipelineInspection.htm.