In the field of industrial production and quality inspection, the wall thickness of small-diameter copper tube is a key parameter that directly affects its performance and service life. Ultrasonic thickness gauge as an efficient and accurate measurement tool, has been widely used in small diameter copper tube wall thickness detection. This paper describes in detail the use of ultrasonic thickness gauge to measure the wall thickness of small diameter copper tube.

The Principle of Measurement 

Ultrasonic thickness gauges measure the wall thickness of small diameter copper tubes based on the principle of reflection of ultrasonic pulses. When the probe emits ultrasonic pulses at a specific frequency and angle into the copper pipe, the pulses are reflected as they reach the inner wall (the interface between the copper pipe material and the air). The probe then receives the reflected echo. Since the velocity of ultrasound propagation in a given material (e.g., copper) is known and stable, the wall thickness can be calculated using the formula:

Thickness = (Propagation Velocity × Time) / 2

For small diameter copper tubes, the curvature of the tube may affect the propagation path of the ultrasound. Therefore, the probe must be vertically tight against the tube wall to ensure vertical propagation and minimize measurement errors caused by angular deviations.

Measurement Procedure

(1) Instrument calibration

Calibrate the instrument using a standard reference block of known thickness and material. Apply couplant to the probe, place it on the block, and adjust the parameters (e.g., gain, speed of sound) until the displayed thickness matches the reference value. Ensure that the probe remains stable during calibration.

(2) Select measurement points

Select multiple points evenly distributed along the pipe. For straight pipe sections, select at least 3 points per cross-section (e.g., every 60° or 90°). For curved sections or complex geometries, the number of points should be increased. Avoid defects such as welds, scratches or dents.

(3) Probe placement and measurement

Apply couplant to the probe so that it is perpendicular to the catheter axis and press gently to ensure complete contact. Hold the probe steady until the reading stabilizes, then record the value. Clean the probe after each measurement.

(4) Repeat measurement and averaging

Take at least 3 measurements at each point and calculate the average. Maintain consistent probe position and pressure. Investigate outliers due to surface irregularities or improper coupling.

Used Accessory-Probe Bracket

The measured workpiece has a small measuring surface, and the sharp narrow end of the delay block makes it difficult to keep the probe perpendicular to the surface of the measured material, which can result in a reduction of the signal amplitude, or even a complete loss of signal. It is inconvenient during the measurement process and requires the inspector to keep moving the probe to find the optimal measurement angle. In response to this measurement problem, it is effective for us to provide these probes with spring-equipped holders with a V-shaped groove at the front end of the holder, which makes it easy to keep the probe in a stable and perpendicular state during the inspection process.

Measurement Results

YUSHI PM5 Gen2 Ultrasonic Thickness Gauge can measure the small diameter metal tubes with probe brackets. The measurement results have excellent repeatability and accuracy.