Ultrasonic flaw detector is a non-destructive testing equipment that uses the propagation and reflection characteristics of ultrasonic waves in a medium to detect internal defects (such as cracks, pores, inclusions, etc.) in materials. The simple operation steps can be summarized as five core steps: "preparation → calibration → detection → interpretation → closure". The following provides a detailed explanation based on the operation logic of general-purpose instruments (digital):

1、 Preparation in advance: Ensure that the equipment is compatible with the environment

Preparation before operation is the foundation for ensuring detection accuracy, with a focus on checking equipment status, consumables compatibility, and workpiece conditions.

Equipment and consumables inspection

Turn on the device and confirm that the display screen, buttons, battery (or power) are functioning properly without any error prompts; If using batteries, ensure that the battery is fully charged (avoid sudden shutdown during testing).

Prepare the appropriate probe: Select the probe based on the workpiece material (such as steel, aluminum), thickness, and detection requirements (usually using a straight probe to measure internal defects and an angled probe to measure weld defects), check that the probe cable is not damaged and that the joint is in good contact.

Prepare coupling agent: The function of coupling agent is to fill the air on the surface of the probe and the workpiece (air strongly reflects ultrasonic waves, causing signals to be unable to enter the workpiece). Commonly used coupling agents include glycerin, engine oil, or specialized ultrasonic coupling agents to ensure no impurities and moderate fluidity.

Workpiece pre-processing

Clean the surface of the detection area: Remove oil stains, rust, paint, oxide scales, and other debris, and use sandpaper or cloth to polish until smooth (uneven surfaces can cause poor coupling and affect signal quality).

Clarify the scope of inspection: Based on the workpiece drawing or inspection standards, mark the areas that need to be inspected (such as both sides of the weld and stress concentration areas) to avoid missed inspections.

2、 Instrument calibration: Establish a "benchmark testing standard"

Calibration is a key step in eliminating instrument system errors, and the core is to adjust instrument parameters through standard test blocks (such as CSK-IA test blocks, IIW test blocks) to ensure accurate defect localization and quantification. (Note: Calibration is the core of operation, and uncalibrated instruments cannot obtain reliable results)

Basic parameter settings

Enter the "Parameter Settings" interface of the instrument and input basic parameters based on the workpiece and probe information:

Probe parameters: Input probe frequency (such as 2.5MHz, 5MHz), chip size, refractive angle (angle probe needs to be filled in, such as K2.5), and leading edge distance (angle probe refers to the distance from the front end of the probe to the center of the chip).

Workpiece parameters: Enter the thickness of the workpiece (key for direct probe detection), material sound velocity (such as steel sound velocity of about 5900m/s and aluminum sound velocity of about 6300m/s, which can be selected from the instrument preset library).

Zero point calibration (positioning calibration)

Purpose: To determine the propagation time of ultrasound inside the probe (i.e. "probe zero point") and avoid positioning deviation.

Operation: Couple the probe on the flat surface of the standard test block, move the probe to find the reflected wave on the bottom surface of the test block (the first large amplitude waveform displayed on the screen, called the "bottom wave"), use the "zero calibration" function of the instrument to correspond the bottom wave position with the known thickness of the test block, and the instrument automatically calculates and saves the probe zero point.

Sensitivity calibration (quantitative calibration)

Purpose: To ensure that the instrument can detect defects of the specified size in the workpiece (such as a Φ 2mm flat bottom hole), and can determine the size of defects based on wave height.

Operation: Couple the probe to the "artificial defect" position (such as the preset flat bottom hole or transverse hole) of the standard test block, find the reflected wave of the defect, adjust the instrument's "gain" knob (increasing gain=increasing sensitivity, waveform amplitude increases; decreasing it is the opposite), so that the defect wave reaches about 80% of the screen's full scale, and save the sensitivity parameter at this time (called "reference sensitivity").

3、 Formal testing: Scan and collect signals according to specifications

After calibration is completed, the workpiece can be inspected, with the core being to "make the probe move smoothly and observe the waveform changes on the screen".

Coupling and scanning

Apply a thin layer of coupling agent evenly on the surface of the detection area (the thickness should be sufficient to fill the gaps, too much will affect the movement of the probe).

Handheld probe, make the probe surface closely adhere to the surface of the workpiece, and scan along the detection direction at a slow and uniform speed (generally not exceeding 100mm/s to avoid missing defect signals); For complex parts such as welds, a scanning method of "sawtooth" or "forward and backward movement+left and right swing" can be used to ensure coverage of the entire inspection area.

Signal observation and recording

During the inspection process, keep a close eye on the instrument display screen: when there are no defects, the screen mainly displays the "initial wave" (the initial signal emitted by ultrasonic waves, located on the far left) and "bottom wave" (the signal reflected from the bottom surface after ultrasonic waves penetrate the workpiece, corresponding to the thickness of the workpiece).

If there is an abnormal wave (i.e. between the initial wave and the bottom wave, or an additional waveform that appears without a bottom wave), the scanning should be stopped immediately, the probe position should be fine tuned, and the stability of the abnormal wave should be confirmed:

If abnormal waves occur repeatedly, record their "position" (corresponding to the workpiece coordinates through the instrument scale), "wave height" (compared with the reference sensitivity to determine the size of the defect), and "depth" (the instrument automatically calculates the depth of the defect buried based on the sound speed).

4、 Defect interpretation: preliminary differentiation of defect nature (simplified version)

Non professional testing only requires a preliminary judgment of whether there are defects, and accurate qualitative analysis needs to be combined with standards and experience. The simple interpretation logic is as follows:

Typical characteristics of defect waves:

Sharp waveform with large amplitude (usually exceeding 50% of the bottom wave amplitude or exceeding the threshold specified by the standard);

When the probe moves, the position of the defect wave is stable (synchronously offset with the probe movement, corresponding to the actual position of the defect);

If the defect is large or deep, it may cause the bottom wave to weaken or disappear (ultrasonic waves are completely reflected by the defect and cannot reach the bottom surface).

Exclude 'false signals':

Poor coupling: The waveform is chaotic and unstable, and disappears after reapplying the coupling agent;

Uneven surface of workpiece: continuous small amplitude noise appears, which disappears after polishing the surface;

Probe wear: waveform blurred, restored to normal after replacing the probe.