교량 부재의 T자형 관절 용접부 검사

General Description of the Application

During the manufacture of bridge structures, a lot of automated welding is used to rapidly and efficiently build multiple parts. One of these welding processes is a system that uses opposing arcs to weld stiffeners to webs on the bridge parts. This welding process produces horizontal fillet welds simultaneously on both sides of a tee-joint.
One problem with this technique is that on thin stiffeners, the heat exchange on vertical parts causes the parts to crack in the upper part of the weld.

The best method to inspect this particular defect without doing false calls on non-rejectable defects is to use an ultrasonic phased-array technique. The multiple-element probe can scan from 40 to 70 degrees simultaneously, allowing a user to inspect the complete volume of the weld in a single pass. When combined with the portable phased-array unit and the appropriate probe, the technique offers fast inspection and exact positioning of defects. Compared to conventional UT, this technique enables any inspector, with a few hours of training, to operate at least five times faster and present more reliable results.

Typical Inspection Requirements

• Thickness of the stiffeners: 10 mm (0.375 in.) to 16 mm (0.629 in.) (or more)
• Material: steel
• 38.1 mm (1.5 in.) of free space over the weld on the stiffeners
• Real-time A-scan and sectorial scan imaging
• User-friendly operating system

Defects Detected

• Crack
• Porosity
• Lack of fusion

Description of the Solution

• Manual inspection using one small phased-array probe
• One-line scan at around 25 mm/s (1 in.), one side at a time
• Inspection with 40- to 70-degree refracted angle
• Real-time display of sectorial scan and A-scan

Material Requirements

• Any //OmniScan SX or phased array instrument
• 5-MHz, 16-element probe
• Rexolite® wedge
• Couplant

Inspection Method

The setup is configured to perform an azimuthal scan from 40 to 70 degrees. The display and gain level are adjusted using a representable calibration standard.

The scan then performs one longitudinal scan about 2 mm (0.078 in.) over the weld on each side of the stiffeners. Data is displayed in real time and can be logged into a report sheet or marked directly on the part for immediate repair.

Note

Due to the multiple angles and the focusing capabilities, this technique is not based on amplitude detection, but on signal recognition of each type of defect, added to an accurate positioning of the defect in the weld.

Client´s Comments

With this method, we have been able to improve the efficiency, the precision, and the quality of our inspections. Furthermore, this new technique allows the technician to evaluate defects more easily. Now, the phased-array ultrasound technology is helping us evolve as ultrasonography did for medicine.