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The Specifications:
The customer, a tube manufacturer in India, faced difficulties when it came to performing electromagnetic testing on larger tubes, with diameters ranging from 180 mm to 250 mm. Their previous testing system, which was based on eddy current testing (ECT) with an encircling coil, was effective for tubes with diameters up to 180 mm. However, the sensitivity of the system, which is inversely proportional to the tube diameter, significantly decreased when testing larger tubes. The customer needed a solution that would maintain the same level of defect detection sensitivity while accommodating the increased tube diameter. This posed a challenge for achieving the required test defect size, through drilled holes (TDH), consistency and defect sensitivity with heavier wall thicknesses.
Technical Specifications:
Tube Diameter: 80 – 250 mm
Wall Thickness 5- 16.5 mm
(some heavy wall with D/t ratio <5)
Testing Speed: High Speed Operation
(exact speed varies by application)
Flaw Detection: Weld Defects & Through-Drilled Holes (TDH)
Channels/Transducers: 24 Detectors in Each Array
Figure 1 MFL tester to detect through drilled holes.
The MAC® Solution:
To address these specifications, MAC® proposed the use of a Magnetic Flux Leakage (MFL) testing system, which provides superior sensitivity for the TDH reference defect and increased sensitivity for volumetric defects in thicker-walled tubes, as compared to the traditional eddy current approach. The MFL system uses a DC magnetic field to saturate the material of the tube, detecting defects such as cracks, voids, and corrosion throughout the entire cross-section of the tube. This method contrasts with eddy current testing, which is limited to detecting surface and some sub-surface defects.
The MFL system was adapted to the customer's existing plant setup. Since the tubes would be moving and rotating as part of the ultrasonic testing process, MAC utilized an existing design for a Magnetic Flux Leakage end-tester head and rotated it 90° to accommodate testing along the length of the moving tube, instead of just the tube’s ends. The material enters from the straightening process and is sent through rotating angulated rolls that drive and spin the tube through the test maintaining the correct pitch throughout the progression. These are controlled by the HMI and automatically set by the PLC. As the tube enters the test heads, an Automatic Pitch Control (APC) system that adjusts surface ride rolls for optimal sensitivity, ensuring effective flaw detection in various tube sizes and wall thicknesses (5-16.5mm). The first test head on the system is the flux leakage tester which detects through-drilled holes. After moving past the MFL tester the material spins above the Echomac® UT test transducers that detect longitudinal and transverse flaws, weld defects, wall thickness, and laminations. The test results are all collected and showcased in one test screen via MAC’s Multicollector software.
The custom system can detect both internal and external discontinuities, making it particularly effective for thicker-walled tubes. The system's design allowed for real-time adjustment of sensitivity, enabling dynamic detection of defects throughout the tube’s volume, rather than just near the surface. This is an efficient identification of defects in ERW pipes that could otherwise compromise the structural integrity of the mill’s products.
The Results:
MAC's custom Spin-the-Tube system utilizing Magnetic Flux Leakage (MFL) successfully addressed the customer's need to inspect larger tubes while maintaining high defect detection sensitivity. The MFL system has proven to be a flexible, efficient, and reliable solution for testing a wide range of tube sizes (customer specification was up to 250mm in diameter range) with enhanced sensitivity to volumetric defects and wall thicknesses, allowing the customer to maintain high-quality production standards while increasing operational efficiency.
Key results include:
- MFL testing was able to detect volumetric defects across the entire wall cross-section of the tube, including internal and external defects, which traditional eddy current methods could not reliably detect at larger diameters.
- The solution leveraged the existing MFL end-tester head design with a simple modification to rotate it, saving on costs and installation time while still achieving optimal testing performance.
- The integration of this advanced testing method into the customer's operations ensured that only tubes meeting strict quality standards—free of defects that could compromise structural integrity—continued through the production line.
- The system maintained high-speed operation, suitable for large-scale production, ensuring minimal impact on throughput while maintaining rigorous inspection standards.
Casey Powers, Director of Asia-Pacific Operations at MAC®, who handled the installation notes, “As the only worldwide supplier capable of delivering Spin the Tube ultrasonic and MFL system solutions, utilizing both technologies developed in-house, we offer unmatched precision and performance. This unique capability ensures seamless integration, optimized inspection accuracy, and long-term reliability for our customers. By combining decades of engineering excellence with cutting-edge advancements, we remain committed to providing superior NDT solutions that meet the evolving demands of the industry.” The world-class team at MAC stands ready to help provide innovative solutions to your most challenging problems. With 95+ years of experience, MAC has and will continue to be driven by cutting-edge engineering to deliver solutions that positively impact metal manufacturers worldwide.
