Optimizing PAUT for Stainless Steel: Addressing the Acoustic Challenges
Stainless steel’s well-known properties, such as high attenuation and elevated acoustic noise levels, present significant hurdles for inspections. The thin walls of small-diameter pipes further exacerbate these issues, making it difficult to achieve accurate beam propagation and flaw detection. The diverging surface of these pipes adds another layer of complexity, as the ultrasonic beam tends to spread more, reducing the accuracy of the inspection.
Given these challenges, the traditional go-to solutions for carbon steel do not translate well to stainless steel, where a more refined approach is required to ensure thorough inspection and reliable defect detection.
A Tailored Solution for Stainless Steel Welds
To address these unique challenges, Eddyfi Technologies developed the M15 probe, specifically engineered for inspecting thin-walled, small-diameter stainless steel piping welds. Unlike regular probes, the M15 probe incorporates design features that tackle stainless steel’s acoustic issues head-on, offering a significant leap forward in inspection accuracy.
Longitudinal Waves vs. Shear Waves: Selecting the Right Wave Mode
In stainless steel weld inspections, Longitudinal Waves (LW) in a Transmit Receive Longitudinal (TRL) configuration are sometimes considered due to their ability to mitigate beam attenuation and reduce noise. However, LW’s larger beam profiles and lower spatial resolution can limit their effectiveness, especially in thin-walled pipes where detecting fine details is crucial.
Eddyfi Technologies’ research shows that, despite the higher attenuation levels, pulsed-echo Shear Wave (SW) inspections are a better option for thin-walled stainless steel pipes. The improved spatial resolution of SW compensates for the higher attenuation, providing a clearer and more accurate view of potential defects, particularly for small, planar flaws.
The M15 Probe: Precision Engineered for Stainless Steel
The 7.5CCEV35-16-A15 probe, commonly used for carbon steel inspections, has proven effective for many applications, particularly in small-diameter, thin-walled pipes. However, its 7.5MHz frequency and 16-element linear array struggle when applied to stainless steel due to the material’s higher acoustic noise at these frequencies. To combat this, Eddyfi Technologies developed the M15 probe with a more suited 5MHz UT beam, which significantly reduces acoustic noise while maintaining the spatial resolution required for detecting small defects in stainless steel.
In carbon steel, the A15 probe’s curved surface (with a 35-millimeter fixed radius) effectively mitigates the diverging effect of the inspection surface across a range of pipe diameters, providing adequate results for carbon steel piping welds from ½ to 4 NPS. However, this configuration is still a compromise, offering non-ideal secondary-axis beam focusing to maintain 16 elements for compatibility with entry-level PAUT electronics. Coupled with the SA15-60S AOD wedges and the CIRC-IT scanner, the A15 probe remains the benchmark for thin-walled, small-diameter carbon steel pipe butt weld inspections.
Stainless steel presents a different challenge. The 7.5MHz frequency generates too much acoustic noise for effective inspection, even on thin-walled specimens. Reducing the frequency to 5MHz in the M15 probe helps to drastically cut noise while preserving the spatial resolution necessary for detecting critical defects. Additionally, optimizing the beam focus helps to further supress acoustic reflections from inter-granular boundaries, enhancing the Signal-to-Noise Ratio (SNR) and improving detection accuracy.
Eddyfi Technologies advanced this further by pioneering a 2D-matrix probe design for the M15 series. By using a 9x7 matrix configuration with 63 elements, the M15 probe achieves better beam focusing compared to conventional 1D-linear probes, enhancing inspection accuracy without compromising on low-clearance operation. This makes the M15 probe compatible with tight spaces, such as those typically found around small-diameter pipes, while still working seamlessly with the CIRC-IT scanner.
Versatility for Various Thicknesses
Available in small, medium, and large configurations to accommodate different wall thicknesses, the M15 probe line offers a versatile, high-performance solution specifically tailored for stainless steel weld inspections.
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Small (3.5mm ≤ T ˂ 5.5mm) |
Medium (5.5mm ≤ T ≤ 11.5mm) |
Large (11.5mm ˂ T) |
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5M9x7-M15S-8.1x6.3-2.5-IPEX |
5M9x7-M15-9.9x7.7-2.5-IPEX |
5M9x7-M15L-13.5x10.5-2.5-IPEX |
Conclusion: Elevating Weld Inspection for Stainless Steel Piping
Inspecting thin-walled, small-diameter stainless steel piping welds is a unique challenge that requires a specialized approach. While traditional RT methods struggle with detecting critical planar defects and create safety and operational disruptions,
Eddyfi Technologies' M15 probe line offers an advanced, reliable alternative. By optimizing PAUT for stainless steel’s acoustic properties and using an innovative 2D matrix probe design, Eddyfi Technologies has created a solution that overcomes the specific challenges of stainless steel, ensuring weld integrity in critical applications.
For industries looking to improve their inspection processes of thin-walled stainless steel piping welds, the M15 probe line represents the next generation of PAUT technology. Explore how our probes can meet your specific inspection needs by watching this webinar on PAUT Probe Development: From the Inspection Challenge Identification to the Final Product. For more information, contact us for expert advice.