The Benefits of NDT in a Gas Pipeline

Nondestructive testing (NDT) is preferred in the oil and gas industry—especially in gas pipelines. Petroleum and natural gas pose an environmental hazard to pipeline welds. Hydrogen and carbon dioxide in oil and gas, along with sulfides and other chemicals found, can cause embrittlement and corrosion of steel. Using NDT in gas pipelines can detect these issues before they become a larger problem.

The question for gas and oil companies isn’t whether to use NDT; it’s what sort of NDT is best for each purpose. Ideally, NDT in gas pipeline inspections will be quick, easy to analyze, and accurate both during welding and initial construction. It will also be portable and allow for NDT inspections to be conducted easily and routinely in the remote areas that gas pipelines often cross.

Improving Inspection in the Petroleum Industry with NDT

Oil and gas pipeline welding can be challenging and requires multiple passes, strict standards, and with the welder having to change position, the potential for flaws becomes greater. Hydrocarbons are corrosive towards metals, especially when under pressure, and flaws provide a point for these corrosive effects to take hold. NDT in gas pipelines plays a critical role in the early detection of corrosion in pipelines before it can do any harm. 

Inspection of welds has traditionally been conducted with dye penetrant tests and radiological testing. These two techniques have drawbacks both in terms of what they detect and their accuracy. 

• Dye penetrant testing may only penetrate into surface cracks and pinholes. If there are flaws deeper in the weld—like lack of fusion or a crack that does not penetrate the outer surface—it will likely go undetected. This method can also be time-consuming. 
• Radiographic testing using X-rays can see within the weld and detect inclusion, but it can struggle to detect planar flaws. There is also a radiation hazard that comes along with using X-rays. Taking the necessary precautions to protect inspection technicians makes an already time-consuming and unwieldy process more so. 

Corrosion inspection has traditionally relied on indirect measurements of volume and flow compared to the length of the pipe to infer if corrosion was occurring—a technique that often proved unreliable. Another approach was taking a pipeline out of service to insert a camera to conduct a visual inspection. Increasingly, these techniques are being replaced by NDT inspections that can detect and display corrosion occurring inside of an oil or gas pipeline.

Modern NDT in Gas Pipeline Inspections

For the most part, weld inspections and corrosion detection can be completed using phased array ultrasonic testing (PAUT). PAUT uses high-frequency sound waves to build a picture of the interior volume of a weld. 

Advances in NDT technologies have improved image resolution and introduced advanced focusing techniques in PAUT instruments, allowing for improved detection of flaws during long seam weld inspection even if their orientation inside the weld isn’t conducive to detection. Improvements in display technology make it intuitive to interpret these images, while batteries make these devices highly portable so they can be used in remote areas.

This allows for more accurate inspections of long seam and other weld inspections using NDT in gas pipeline manufacturing and during the pipeline’s service. Phased array ultrasound for corrosion mapping allows for an in-depth look at the interior surfaces of pipelines that can allow accurate detection of corrosion problems before they affect flow and without taking the pipeline out of service. These devices can also be used for NDT of a gas pipeline, even in inaccessible areas where there are no ports that allow access. Modern NDT testing techniques are scalable testing solutions for the oil and natural gas industry that ultimately saves both time and money.

Zetec is a nondestructive equipment manufacturer with over 50 years of experience providing NDT gas pipeline inspection and other solutions for the petroleum industry. To find out more, contact Zetec.