Blog: Inline Inspections for Axial and Circumferential Cracks 

Author: Cory Wargacki, Regional Sales Manager

In the last five to six years, operators have taken greater steps to preserve the environment and are prioritizing a wider list of precautionary measures to ensure the prevention of pipeline failures. Part of their safety regimen includes conducting pipeline inspections that detect and size at-risk anomalies so they can make informed decisions to better preserve their pipelines.

As the demand has increased in Canada, NDT Global has become the go-to provider for these inline inspections. Specifically, crack inspections. Since I've started my career in the industry (16 years), a lot has changed. We have gone from being able to simply detect cracks in pipelines to having the ability to accurately size, locate, and apply attributes to crack-like features. We've made incredible strides with high-resolution data acquired from high-resolution tools and even more so with how that data is analyzed. 

NDT Global inspects for different types of crack-like features. There are various types of crack-like features that NDT Global inspects. In Canada, axial cracking is the most common feature, but the demand to also inspect circumferential cracks has increased steadily throughout the last few years.

Circumferential Cracking Versus Axial Cracking

Ten years ago, the idea of having circumferential cracking in your pipeline was mind boggling. But as technology advanced and as more inspections were conducted, it became apparent that circumferential cracks are very much a problem.

Circumferential cracking is not as age dependent as axial cracking but is primarily formed from the initiation of axial stress and not having the proper soil conditions. Whereas with axial cracking, cracks typically arise from low lack of fusion and poor welding practices, environmental conditions, stresses in the circumferential axis, and high rates of pressure cycling. If an operator suspects that both forms of cracks exist in their pipeline, it would be important to consider investing in both inspections as this is the only way (for now) for both feature types to be properly detected and sized.

Axial Crack Solution

At NDT Global, our ultrasonic crack inspection technology provides absolute depth sizing and crack depth profile for an accurate assessment. Due to NDT Global's high-resolution inspection tools, even minor cracks from approximately 1 mm (0.04 in.) in depth are detected and sized with tolerances as low as ±0.8 mm (±0.031 in.).

Key Benefits:

  • Industry-leading detection and sizing specifications

  • Full through-wall absolute depth sizing ability

  • High-density sensor spacing (5 mm resolution) provides a clear picture of every crack related anomaly

  • Eclipse ultrasonic crack technology specifically designed for challenging feature morphologies (hook cracks)

Circumferential Crack Solution

With NDT Global's circumferential crack solution, a diffracted shear-wave signal travels into the pipeline wall at a 45-degree angle and is reflected by an external or internal flaw. The inspection tool provides accurate data that is categorized into several properties such as a flaw property, length, width, crack type, and depth.

Due to the nature of initiation and propagation of circumferential cracking, it can be very challenging to assess the severity of the features. NDT Global's 15 years of circumferential inspection experience coupled with more than half a million analyzed and reported circumferential features has enabled our inspection and analysis teams to gain tremendous amounts of experience and a better understanding of circumferential feature characteristics.

Key Benefits:

  • Can be combined with an IMU to overlay areas of bending strain and circumferential cracking for identification of areas with potential axial strain

  • Detection of features as shallow as 1 mm (0.04 in.) depth with a sizing accuracy of ±1.0 mm (±0.04 in.)

  • High-density sensor spacing (5 mm resolution) provides a clear picture of every crack-related anomaly

Key Takeaways:

When investing in an ILI crack inspection, the 'right' solution is rarely based on just a few factors. It’s always smart to look at an inline inspection with a holistic approach to ensure you can save costs and increase operational value for years to come. While axial and circumferential crack inspections are both highly beneficial as separate inspections, operators often combine these inspections to identify more complex crack-like features that can be compromising to pipelines. As we continue to innovate our technological environments, NDT Global is committed to further enhancing both axial and circumferential technologies so operators can continue to sustain both durability and longevity for the life of their pipelines.

If you wish to learn more about crack inspection technologies, you can shoot me an email at

Discover the Power of Clarity.

Whether you’re ready to schedule an inspection or have questions about our process, our team can help get you started.

Contact Us