Methods for Measuring Wall Thickness of Small-Diameter Copper Tubes Using Ultrasonic Thickness Gauge

In the fields of industrial production and quality inspection, the wall thickness of small-diameter copper tubes is a critical parameter that directly affects their performance and service life. The ultrasonic thickness gauge, as an efficient and accurate measurement tool, has been widely used for wall thickness detection of small-diameter copper tubes. This article details the methodology for measuring the wall thickness of small-diameter copper tubes using an ultrasonic thickness gauge.

I. Measurement Principle
The ultrasonic thickness gauge measures the wall thickness of small-diameter copper tubes based on the ultrasonic pulse reflection principle. When the probe emits an ultrasonic pulse at a specific frequency and angle into the copper tube, the pulse reflects upon reaching the inner wall (the interface between the tube material and air). The reflected echo is then received by the probe. Since the propagation speed of ultrasonic waves in a specific material (e.g., copper) is known and stable, the wall thickness can be calculated using the formula:
Thickness = (Propagation Speed × Time) / 2,
where the time interval between pulse emission and reception is precisely measured. For small-diameter copper tubes, the curvature of the tube may affect the ultrasonic propagation path. Therefore, the probe must be tightly and vertically attached to the tube wall to ensure perpendicular propagation and minimize measurement errors caused by angular deviations.
 

II. Pre-Measurement Preparations
(1) Selection of Measurement Instruments
Small-diameter copper tubes require an ultrasonic thickness gauge with high precision (typically ±0.01 mm or higher) and a probe designed for small-diameter applications. For example, the PM5 Gen2 Ultrasonic Thickness Gauge produced by YUSHI INSTRUMENTS features a miniature probe and holder tailored to match the curvature of small-diameter tubes, ensuring optimal ultrasonic coupling and propagation. Verify that the instrument is functional, has sufficient battery power, and displays clear readings.
(2) Preparation of the Copper Tube

Surface Cleaning: Remove oil, rust, coatings, or welding slag from the tube surface using sandpaper, wire brushes, or cleaning agents. For coated tubes, strip the coating from the measurement area to expose the metal substrate.

Edge Treatment: If measuring near the tube end, trim the edge to eliminate burrs or chamfers, ensuring stable probe placement.

Couplant Selection: Use a couplant (e.g., glycerin, machine oil, or petroleum jelly) with moderate viscosity and good fluidity to eliminate air gaps between the probe and tube. Glycerin is recommended for small-diameter tubes due to its excellent wetting properties.

III. Measurement Procedure
(1) Instrument Calibration
Calibrate the gauge using a standard reference block of known thickness and material. Apply couplant to the probe, place it on the block, and adjust parameters (e.g., gain, sound velocity) until the displayed thickness matches the reference value. Ensure the probe remains stable during calibration.
 

(2) Selection of Measurement Points
Select multiple points evenly distributed along the tube. For straight sections, choose at least 3 points per cross-section (e.g., every 60° or 90°). For bent sections or complex geometries, increase the number of points. Avoid defects like welds, scratches, or dents.
 

(3) Probe Placement and Measurement
Apply couplant to the probe, position it perpendicular to the tube axis, and press gently to ensure full contact. Hold the probe steady until the reading stabilizes, then record the value. Clean the probe after each measurement.
 

(4) Repeated Measurements and Averaging
Perform at least 3 measurements per point and calculate the average. Maintain consistent probe placement and pressure. Investigate outliers caused by surface irregularities or improper coupling.
 

IV. Common Issues and Solutions
(1) Unstable Readings

Causes: Poor probe contact, uneven couplant, surface contamination, incorrect gain/sound velocity settings.

Solutions: Reclean the surface, adjust parameters, stabilize the probe.

(2) Abnormal Values (Too High/Low)

Causes: Incorrect calibration, wrong sound velocity, unsuitable probe, or internal defects.

Solutions: Recalibrate, replace the probe, or use supplementary testing (e.g., eddy current, radiography).

(3) Poor Probe Coupling

Causes: Unsuitable couplant viscosity or mismatched probe curvature.

Solutions: Change couplant types, use an adjustable-curvature probe, or add an elastic film for better contact.

V. Data Processing and Analysis
(1) Data Recording
Document all measurements, locations, timestamps, and tube specifications (diameter, design thickness, material grade, batch number). Include operator details and inspection dates.
(2) Result Evaluation
Compare measurements against standards (national, industry, or internal). If values fall within tolerance, the tube passes. For outliers, expand testing to determine defect severity.
(3) Handling Abnormalities
Notify relevant departments for non-conforming tubes (scrap, downgrade, or repair). Trace production issues (e.g., mold wear, improper parameters) and implement corrective actions.
 

Conclusion
Using an ultrasonic thickness gauge to measure small-diameter copper tube wall thickness is efficient and accurate. Proper instrument selection, preparation, standardized procedures, and thorough analysis ensure reliable quality control and safe industrial applications.