How to improve the accuracy of ultrasonic flaw detection in steel structure inspection?

Ultrasonic flaw detection as the core technology of non-destructive testing for steel structures, is widely used in weld quality assessment, internal defect positioning, and other fields. However, factors such as detection environment, operating procedures, and material characteristics often affect its accuracy. The following key measures are proposed from a professional perspective to improve the accuracy of ultrasonic flaw detection in steel.

1. Accurately calibrate instrument

The acoustic velocity, attenuation coefficient, and other characteristics of steel structure materials differ significantly from ordinary materials. The parameters of the flaw detector should be adjusted according to the specific grade. For example, the acoustic velocity of low-alloy high-strength steel is about 2% lower than that of carbon steel. If not recalibrated, the error of defects may exceed 5mm. At the same time, select the frequency of the probe that matches the surface roughness of the steel structure to avoid signal attenuation due to coupling.

2. Optimize couplant and scanning method

The steel structure surface often contains impurities such as scale and oil stains. A high-viscosity couplant be selected to ensure efficient sound wave transmission. During scanning, a "sawtooth rotation" composite method should be adopted to cover the heat-affected zone of the wel and the transition zone of the base metal, avoiding missed inspections of small defects due to a single scanning path. For complex structures such as T-shaped joints, the detection angle of oblique probe should be increased to compensate for the blind spots of single-angle detection.

 

 

3. Strictly control the timing and environment of detection

After welding the steel structure should wait for the weld to cool to room temperature before flaw detection to avoid the change in acoustic velocity caused by high temperature affecting positioning accuracy. When the ambient temperature 40℃ or falls below -10℃, temperature compensation calibration should be performed on the instrument. In addition, when the wind speed in the detection area exceeds 3/s, anti-wind measures should be taken to prevent the signal from being interrupted due to the rapid evaporation of the couplant.

From instrument calibration to environmental control, improving the accuracy of ultrasonic flaw detection in steel structures requires systematic management of each link. Through refined operation and parameter optimization, the detection rate of defects can be significantly improved, reliable protection for the safety of steel structures.