Inline Inspection using a tethered UTWM Crawler in an 8-inch flowline

By Pipecare Group

Introduction: Inline Inspection Using a Tethered UTWM Crawler in an 8-Inch Flowline

Inline inspection (ILI) using a tethered Ultrasonic Thickness Wall Thickness (UTWM) crawler is a highly specialized process that requires comprehensive planning before tool deployment.

The success of the inspection begins with collecting maximum information about the pipeline’s design parameters. Key details such as pipeline length, wall thickness, minimum bend radius, entry and exit locations, and elevation profile directly influence tool configuration and operational strategy.

Understanding the product to be used during inspection, the client’s expectations, and the scope of work is equally essential in defining inspection feasibility and performance criteria.

Crawler Design and Configuration

In parallel, the crawler tool must be carefully designed to meet the operational demands of the specific pipeline.

This includes a clear understanding of the modules to be integrated—sensor carriers, electronics housings, drive units, configuration, and tracking components. Each component’s weight, dimensions, and functionality contribute to calculating the required pulling and dragging forces. Proper sizing of the crawler motor ensures the tool can navigate bends, overcome frictional forces, and maintain consistent movement to capture high-quality ultrasonic data.

Case Study: UTWM Crawler Run in an 8-Inch, 200-Meter Flowline

A crawler-based UTWM inspection was conducted in a 200-meter-long, 8-inch flowline with moderate elevation changes.

Prior to the run, the line was filled with Liquid to allow ultrasonic coupling; however, slight variations in elevation resulted in persistent air pockets remaining inside the pipeline.

It was noticed that the presence of trapped air can disturb the ultrasonic transmission, which can lead to echo loss and, consequently, poor or unacceptable data quality.

During the inspection, extended zones exhibited echo loss due to these air pockets, demonstrating that even minor elevation differences can affect ultrasonic performance. Addressing this challenge required both design improvements and operational adjustments.

Crawler design for Improved Air Displacement

The crawler was modified to enhance its ability to push and displace air ahead of the tool.

Tool Performance Demonstration in a Test Pipe

Prior to the actual run, the tool was tested in a controlled pipe setup to validate the new design.

This confirmed that the updated configuration could effectively move trapped air pockets during forward movement.

BI-DI Tool Run Before UTWM Inspection

A bi-directional swabbing tool run was conducted ahead of the UTWM crawler.

This preparatory run helped sweep out remaining air pockets and stabilized internal fluid conditions, significantly improving the UT coupling environment.

Conclusion

There is no universal solution

Every pipeline is unique and requires a tailored inspection strategy. The more detailed the information collected regarding the pipeline’s design, geometry, and operating conditions, the higher the likelihood of achieving a successful ILI run.

Thorough pre-engineering, proper crawler configuration, and proactive mitigation of fluid-related risks—such as air pockets—are essential to ensuring accurate, reliable, and high-quality ultrasonic data.

PIPECARE Group Inline Inspection using a tethered UTWM Crawler