API steel pipe ultrasonic flaw sensitivity calibration steps
1. Comparison test block selection
Selection and steel pipe wall thickness of the comparison test block, need to comply with API SPEC 5L and SY/T 6423 standard requirements of the V-groove or flat bottom hole specimen.
If the wall thickness of the steel pipe ≤ 20mm, the priority choice of step test block; wall thickness > 20mm when the use of flat-bottomed hole test block.
2. Time baseline and zero calibration
Zero calibration: Use the R100 circular arc surface (inclined probe) or a large flat bottom with a depth of 100mm (straight probe) in the CSK-IA test block, and deduct the acoustic range delay of the protective film of the probe, coupling agent or wedge.
Sound velocity setting: Enter the correct ultrasonic propagation velocity according to the type of material (e.g. the longitudinal sound velocity of steel is about 5920m/s).
3. Core steps for sensitivity tuning
Place the bicrystal probe on the surface of the comparison test block, coupling agent to ensure good contact.
Adjust the instrument gain, so that the first bottom wave amplitude of the test block reaches 50% of the full scale of the fluorescent screen.
Gain compensation: add an extra 10dB on top of 50% as the final flaw detection sensitivity benchmark.
If a single crystal straight probe is used, the sensitivity needs to be verified based on the Bottom Wave Adjustment Method or Distance-Amplitude Curve (DAC).
4. Calibration verification and correction
Review the signal amplitude using a test block of other known reflectors (e.g., holes or slots of different depths) to ensure sensitivity consistency.
Automatic detection systems need to verify signal stability, and manual detection needs to periodically review the coupling status.
Cautions
Probe matching: double-crystal probe for thin-walled steel pipe (wall thickness ≤ 20mm), single-crystal straight probe for thick-walled steel pipe (wafer diameter φ14-20mm).
Environmental compensation: high temperature environment (≤70℃) need to recalibrate the speed of sound parameters to correct the temperature effect.
Record requirements: Calibration parameters (e.g. gain value, type of specimen) should be fully recorded in the test report, in accordance with API Q1 specification.
