Rice. 1. Stainless Steel Weld Manufacturing Inspection Method: Double 2D Matrix Assembly in TRL Mode.
Codes, stanadards, and methods have evolved to allow the use of phased array ultrasonic testing (PAUT) instead of RT for testing austenitic welds. First widely used in nuclear power plants almost 15 years ago, the use of dual (2D) array sensor assemblies has spread to the oil and gas and other industries where fast, reliable and safe inspection of high attenuation austenitic welds is required.
The latest portable phased array devices are equipped with powerful built-in software that allows you to quickly and efficiently set up, deploy and interpret 2D matrix array scans without having to import focus law files created with external calculators or remote control systems using advanced software. software for PC.
Today, inspection technologies based on 2D array transducers provide superior capabilities for detecting girth and axial defects in stainless steel and dissimilar metal welds. The standardized 2D dual matrix configuration can effectively cover the inspection volume of stainless steel welds and can detect flat and bulk defects.
Ultrasound inspection procedures typically involve dual arrays of two-dimensional matrices placed on replaceable wedge-shaped components whose contours match the outer diameter of the component under consideration. Use low frequencies – 1.5 MHz for dissimilar metal welds and other attenuation reducing materials, 2 MHz to 3.5 MHz for uniform wrought stainless steel substrates and welds.
The dual T/R configuration (transmit/receive) offers the following advantages: no near-surface “dead zone”, elimination of “phantom echoes” caused by internal reflections in the wedge, and ultimately better sensitivity and signal-to-noise ratio (ratio signal/noise). noise figure) ) due to the convolution of the T and R beams.
Let’s take a look at the PA UT method for controlling the fabrication of austenitic stainless steel welds.
When conducting production control, instead of RT, the control should cover the volume of the weld and the entire wall thickness of the heat-affected zone. In most cases, the solder cap will be in place. In carbon steel welds, it is recommended to use shear waves to sonicate the controlled volume on both sides, while the last half wave is usually used to obtain specular reflections from defects on the weld bevel.
At lower frequencies, a similar shear wave method can be used to test the proximal bevel of stainless steel welds, but is not reliable for testing through austenitic weld material. In addition, for the so-called CRA welds, there is a corrosion-resistant alloy coating on the inside diameter of the carbon steel pipe, and the last half of the wire jumper of the cross beam cannot be effectively used.
Let’s look at sample detection methods using a portable UT instrument and software, as shown in Figure 1.
Dual 2D array transducers that produce 30 to 85 degree P-wave refracted beams that can be used for full volume coverage. For wall thicknesses from 15 to 50 mm, frequencies from 1.5 to 2.25 MHz are considered suitable, depending on the attenuation of the substrate.
By optimizing the wedge angle and configuration of the array probe elements, a wide range of refractive angle scans can be efficiently generated without associated side lobes (Fig. 2). The footprint of the wedge node in the plane of incidence is minimized, allowing the beam exit point to be located as close to the weld as possible.
The performance of a standard 2.25 MHz 10 x 3 dual array array in TRL mode was evaluated on a 25 mm wall thickness 304 stainless steel plate weld. The test specimens had a typical V-shaped slope and “as-welded” surface condition and contained real and well-documented weld defects parallel to the weld.
Rice. 3. Combined phased array data for a standard 2.25 MHz 10 x 3 Dual Array (TRL) array on a 304 stainless steel plate weld.
On fig. 3 shows images of the combined PAR data for all angles of refraction (from 30° to 85° LW) along the entire length of the weld. Data acquisition was performed at a low gain level to avoid saturation of highly reflective defects. 16-bit data resolution allows appropriate soft gain settings for different types of defects. Data interpretation can be facilitated by properly positioning the projection shutter.
An image of a single defect created using the same merged dataset is shown in Figure 4. Check the result:
If you don’t want to remove the plug before inspection, another method of inspection can be used to detect axial (transverse) cracks in pipe welds: a single array array probe can be used in pulse echo mode to “tilt” the weld plug Sound beam from below As the sound beam propagates mainly in the substrate, shear waves can reliably detect defects on the near side of the weld.
Ideally, welds should be inspected in four beam directions (Figure 5) and require two symmetrical wedges to be inspected from opposite directions, clockwise and counterclockwise. Depending on the frequency and size of the individual elements of the array, the wedge assembly can be optimized to obtain angles of refraction from 40° to 65° relative to the direction of the scan axis. More than 50 rays fall on each search cell. A sophisticated US PA instrument with a built-in calculator can easily deal with the definition of sets of focusing laws with different skews, as shown in Figure 6.
Usually, a two-line sequence of checks is used to fully cover the amount of a check. The axial positions of the two scan lines are determined from the pipe thickness and the width of the weld tip. The first scan line runs as close as possible to the edge of the weld, revealing defects located at the root of the weld, and the second scan line completes the coverage of the HAZ. The base area of the probe node will be optimized so that the beam exit point is as close as possible to the toe of the crown without significant internal reflections in the wedge.
This inspection method has been found to be very effective in detecting misdirected axial defects. On fig. 7 shows a phased array image taken on an axial crack in a stainless steel weld: defects were found at various angles of inclination and a high SNR could be observed.
Figure 7: Combined phased array data for axial cracks in stainless steel welding (various SW angles and inclinations): conventional projection (left) and polar projection (right).
The benefits of advanced PA UT as an alternative to radiography continue to gain attention in the oil and gas, power generation, manufacturing and other industries that rely on reliable inspection of austenitic welds. Likewise, fully integrated PA UT instruments, powerful firmware and 2D array probes continue to make these inspections more cost-effective and efficient.
Guy Maes is Zetec’s director of sales for UT. More than 25 years of experience in the development and implementation of advanced ultrasound methods, competency assessment and software development. For more information, call (425) 974-2700 or visit www.zetec.com.
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