The ultrasonic flaw detector for civil air defense welds is a non-destructive testing equipment used to detect internal defects (such as cracks, pores, inclusions, etc.) in welds in civil air defense engineering. Its use must follow strict standard procedures. The following are detailed operating steps and precautions:
1、 Preparation before operation
Equipment inspection
Confirm that the appearance of the instrument is undamaged, the power cord and probe cable are securely connected, and the buttons and display screen functions are normal.
Check whether the probe type (commonly used angle probes such as K2 and K2.5) matches the thickness of the inspected workpiece, and whether the probe chip size and frequency (such as 2.5MHz and 5MHz) meet the testing requirements.
Prepare standard test blocks (such as CSK-IA, CSK-IIIA) for calibrating instrument parameters.
Workpiece preparation
Remove oil stains, rust, paint and other impurities from the inspection area on both sides of the weld (usually 20-30mm on each side of the weld), and if necessary, use sandpaper to polish until the metallic luster is exposed.
Mark the detection range, clarify the direction of the weld seam and key areas (such as heat affected zone and fusion line).
Coupling agent selection
Use glycerin, engine oil, or specialized ultrasonic coupling agent to ensure no impurities and moderate fluidity, in order to fill the air gap between the probe and the workpiece surface.
2、 Instrument calibration
Probe zero calibration
Couple the angle probe onto the flat surface of a standard test block (such as CSK-IA), and move the probe to find the reflected wave (bottom wave) on the bottom surface of the test block.
By using the "zero calibration" function of the instrument, the position of the bottom wave is matched with the known thickness of the test block, and the instrument automatically calculates and saves the zero point parameters of the probe.
K value (refractive angle) calibration
Place the probe at a specific angle marked position on the test block, and move the probe back and forth to find the echo peak of the large circular hole at the edge of the test block.
Record the K value aligned between the incident point and the test block, or calibrate by calculating the slope and input the actual K value into the instrument.
DAC curve production
Using the CSK-IIIA test block, move the probe to find the transverse hole reflection waves at different depths (such as 5mm, 10mm, 15mm, 20mm).
Calibrate each point in the instrument, generate a distance amplitude curve (DAC curve), and set the rejection line (+5dB), quantification line (-3dB), and evaluation line (-9dB).
3、 On site inspection
Probe placement and scanning method
Place the probe perpendicular to the direction of the weld seam and perform a zigzag scan along the direction of the weld seam (the probe's motion trajectory is zigzag), covering the entire detection area.
For complex welds such as T-joints and fillet welds, a combined scanning method of forward and backward movement+left and right swing can be used.
Parameter Settings
Enter the thickness of the workpiece and the sound velocity of the material (such as the sound velocity of steel, which is about 5900m/s).
Adjust the gain to display the complete DAC curve on the screen, ensuring that the detection sensitivity meets the standard requirements.
Defect identification and recording
Observing the waveform of the display screen: When there are no defects, the screen displays the initial wave (ultrasonic emission signal) and the bottom wave (reflection signal after penetrating the workpiece); If there is an abnormal wave (additional waveform between the initial wave and the bottom wave), the scanning should be stopped immediately.
Fine tune the probe position and confirm whether the abnormal wave is stable. If it occurs repeatedly, record its position (corresponding to the workpiece coordinates through the instrument scale), wave height (compared with the reference sensitivity), and depth (the instrument automatically calculates the depth of the defect burial).
Mark the specific location of defects on the weld seam for subsequent repair or re inspection.
4、 Defect interpretation and rating
Preliminary assessment of defect nature
Defect wave characteristics: sharp waveform, large amplitude (usually exceeding 50% of the bottom wave amplitude), and stable position as the probe moves.
Exclude false signals: Poor coupling can cause waveform disorder, requiring reapplication of coupling agent; Probe wear can cause waveform blurring, and the probe needs to be replaced.
Defect rating
Based on parameters such as defect wave height, location, and length, evaluate according to relevant standards (such as NB/T47013.3 "Non destructive Testing of Pressure Equipment Part 3: Ultrasonic Testing").
For example, if the defect is located in the center of the weld seam and its length exceeds 1/3 but is less than 2/3 of the thickness of the base metal, it may be rated as Grade II; If the length exceeds 2/3, it will be rated as Level III (requiring repair).
5、 Post operation maintenance
Equipment cleaning
After the detection is completed, wipe the probe and instrument surface with a clean cloth to remove residual coupling agent.
Organize and store the probes, test blocks, power cords, and other accessories in a dry and ventilated place.
Data storage and report generation
Store the detected waveforms and data in the instrument's memory or export them to a computer via USB.
Use specialized software to generate inspection reports, including workpiece information, inspection parameters, defect location, and rating results.
6、 Safety precautions
Operator Qualification
Operators need to undergo professional training and obtain a non-destructive testing qualification certificate (such as UT Level II or above).
protective measures
Wear protective goggles and gloves to avoid contact between the coupling agent and the skin or eyes.
The testing site should be kept away from flammable and explosive materials to ensure good ventilation.
Equipment safety
Avoid collision between the probe and hard objects to prevent damage to the chip.
When the instrument is not in use for a long time, conduct regular power on inspections to prevent internal components from getting damp.