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Precision  measurements of hidden carcass pitch in flexible offshore pipes

Non-destructive mapping of a steel carcass structure enclosed in a thick polymer layer — in collaboration with NOV Flexibles

Thorsten Bæk headshot
Thorsten Bæk
24 June 2024

Introduction

Flexible offshorepipes must endure immense external pressure while maintaining flexibility, making precise control and accurate knowledge during production critical to ensure optimal performance. Deviations in manufacturing can lead to the pipe being out-of-specifications. One key parameter, the "pitch" of the innermost steel carcass, measures the distance between structural repetitions along the pipe's length. This pitch must remain within a specific range to maintain the necessary collapse strength and flexibility of the carcass. Traditionally, monitoring pitch variations during production has not been possible once the polymer pressure sheath has been extruded on top of the carcass.

GLAZE Technologies' device and analysis software enables non-destructive detection of the carcass pitch directly through the polymer pressure sheath. This method has been rigorously validated by comparing our measurements with those obtained from destructive tests, where the polymer pressure sheath was removed and a manual calliper was used to measure the exposed carcass pitches, confirming the accuracy and reliability of our approach.

Key advantages

  • Non-Destructive Measurement:
    Enables accurate monitoring of carcass pitch without the need for destructive testing, preserving the integrity of the pipe throughout the production process.
  • Real-Time Data:
    Provides immediate feedback on the pitch condition, allowing for timely adjustments during manufacturing to ensure the product meets quality standards.
  • Cost-Effective:
    Reduces the expense associated with destructive testing methods and potential material wastage, offering a more economical solution for quality assurance.
  • Enhanced Safety:
    By ensuring the pitch remains within specified parameters, the technology contributes to a better quality of the end-product, reducing the risk of failures in demanding operational environments.
  • Ease of Integration:
    Designed to seamlessly integrate into existing production lines without significant modifications, facilitating easy adoption and minimal disruption.

Economic impact

  • Reduction in Waste:
    Minimizes material waste by identifying production errors early, saving costs on raw materials and reducing environmental impact.

  • Decreased Downtime:
    Improves production efficiency by eliminating the time-consuming process of destructive testing, thus reducing downtime and enhancing throughput.
  • Lower Testing Costs:
    Cuts down on the expenses associated with traditional destructive testing methods, such as labor, equipment maintenance, and setup.
  • Extended Equipment Lifespan:
    By preventing overuse and unnecessary stress testing on samples, the technology can help extend the lifespan of both the testing equipment and the pipes themselves.

  • Enhanced Product Value:
    Increases the market value of the pipes by ensuring higher compliance with safety and quality standards, making them more appealing to discerning customers.
Testimonial logo

"GLAZE has enabled NOV to do non-destructive inspections of a critical pipe parameter, which otherwise is nearly impossible to access in detail"

Thorsten Holst
Senior Development Engineer
NOV Flexibles

Technical solution

The metal carcass acts as a near perfect mirror for our terahertz pulse, reflecting a strong signal even after penetrating approximately 8-10 mm of polymer. The arrival time of the reflected pulse changes along the structure of the carcass. By tracking the arrival time of the reflection as we scan along the pipe, we can map out the corrugated structure of the carcass surface. A subsequent analysis of the structure allows for automatic extraction of the pitch distance, either as a single pitch or an average over several pitches for better statistics. 

The measurements were performed on a stationary cut-out segment of a flexible pipe at NOVs facilities. Using a linear stage, we conducted a line scan along the length of the pipe in sections of 30 cm.

Results

By tracking the distance to the metal carcass at the point of measurement along the pipe, a topological profile can be recreated. We adjust for misalignment between thestage and the pipe and apply smoothing. A repeating and identifiable feature is chosen and the distance between said feature can be calculated. In the plot below, the result of the analysis is shown with annotated individual and averaged pitch.The resulting pitch, for this section of the pipe, ranges between 37.4 mm and 38.4mm. The spatial resolution is limited by the scanning step size used and not by GLAZE's technology.

Thorsten Bæk headshot
Thorsten Bæk
1 June 2024
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