Mistras Group
Addressing Stainless Steel and Dissimilar Metal Weld Inspection with Advanced Phased Array Ultrasonic Techniques
By: Eddyfi Technologies
Source: Eddyfi Technologies
Phased array ultrasonic testing is a mature and widely adopted technology that allows for the inspection of critical components in various industries. Over the last five years, new techniques like full matrix capture and live total focusing method have been available on most high-end phased array ultrasonic testing units. They have been introduced in ASME codes and ISO standards with dedicated training courses, as prescribed by the codes, offered by large training centers.

However, innovation is ongoing and non-destructive testing equipment vendors are constantly working to make the inspection process as seamless as possible. There is always a desire to make inspections easier to setup, faster to perform, and inspection data imaging quality improved for best informed decisions—especially when it comes to the unique factors presented with stainless steel and dissimilar metal weld inspection.

The Problem

Industry recognizes that it is increasingly challenging to inspect complex materials like dissimilar metal welds which typically consist of at least two different materials, mostly involving Inconel alloys, often used to connect clad carbon steel vessels to stainless steel piping. Misoriented or branched cracks can easily be missed and undersized. In fact, for some inspection configurations and damage mechanisms, standard phased array probe and wedge combinations will not provide the required inspection capability to achieve the desired results. Therefore, Eddyfi Technologies presents the better solution employing advanced focusing techniques such as total-focusing method to help improve detection.

The Solution

The most common advanced focusing algorithm, total focusing method, sums the elementary A-scan signals from all elements in the array to generate a frame of pixels where each pixel is computed using a dedicated focused focal law. The frames can be used for "live" interpretation, or they can be stored for each position of the probe, very similar to a "dynamic" merge view in regular phased array. The process results in nearly ideal focusing on each point of the near-field zone of the active aperture, and this improved image resolution allows for better characterization and sizing of challenging flaws found in stainless steel and dissimilar metal welds.

A recently introduced feature, the total focusing method envelope obtains the image from the magnitude of the summed analytic signals through a Hilbert transform. The resulting live total focusing method images look like phased array signals with a smoothing filter applied. This delivers the same amplitude fidelity as the regular reconstruction while using a larger pixel size. This means that a lower resolution can be used, increasing the scanning speed without any loss in inspection quality.

Read the full article at Eddyfi.

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