First, Preparatory Work Before Precision Steel Pipe Inspection
1. Pre-treatment of Precision Steel Pipes: Remove oil, rust, coatings, and other impurities from the surface of the precision steel pipe to avoid affecting measurement accuracy. For bent or deformed precision steel pipes, straightening treatment is required first to ensure that the measuring section is perpendicular to the axis of the precision steel pipe.
2. Tool Calibration:
- Mechanical measuring tools (e.g., micrometer, wall thickness micrometer): Calibrate with standard gauge blocks to ensure that the error is within the allowable range.
- Non-destructive testing equipment (e.g., ultrasonic thickness gauge): Calibrate using standard thickness test blocks, check the deviation between the equipment display value and the standard value, and correct if necessary.
3. Environmental Control: Maintain the testing environment temperature at 20±5℃ to avoid excessively high or low temperatures causing thermal expansion and contraction of the steel pipe, which would affect the measurement results; keep away from vibration sources, strong magnetic fields, and other interfering factors.

Second, Core Inspection Methods for Precision Steel Pipes
(1) Mechanical Measurement Method: Suitable for precision steel pipes with high accuracy requirements (deviation ≤ ±0.03mm), this is a commonly used arbitration inspection method in the industry.
- Tool Selection: A wall thickness micrometer is preferred. For large-diameter precision steel pipes, a combination of an inside gauge and an outside micrometer can be used.
- Measurement Steps:
- Selecting the Inspection Section: Select one section at each end and one in the middle of the steel pipe, for a total of three sections; evenly distribute eight measurement points along the circumference of each section.
- Single-Point Measurement: Vertically attach the measuring head of the wall thickness micrometer to the inner and outer walls of the steel pipe, ensuring complete contact between the measuring surface and the pipe surface without tilting; when reading the value, keep the line of sight perpendicular to the scale line and record the measurement result for each measurement.
- Repeated Verification: Repeat the measurement three times at each point, and take the average value as the actual wall thickness at that point. – Deviation Calculation: Wall thickness deviation = Actual measured wall thickness – Nominal wall thickness. The result must comply with relevant standards such as GB/T 3639 and ASTM A1011.
(2) Ultrasonic Testing Method: Suitable for batch testing, scenarios where samples cannot be damaged, or where direct contact with the inner wall of the steel pipe is difficult. The testing accuracy can reach ±0.02mm.
- Equipment and Coupling Agent: Use a digital ultrasonic thickness gauge with a coupling agent (such as glycerin or machine oil) to ensure no reflection loss of ultrasonic waves between the steel pipe surface and the probe.
- Measurement Procedure: Equipment Calibration: Calibrate using a standard test block with a material and nominal wall thickness similar to the steel pipe, and set the sound velocity parameters of the equipment.
- Measuring Point Arrangement: Same as the mechanical measurement method, select 3 sections, with 8 measuring points on each section, avoiding areas with defects such as welds and scratches on the steel pipe.
- Data Acquisition: After applying the coupling agent to the probe, press it vertically onto the measuring point. Record the data after the displayed value stabilizes. For measuring points with abnormal values, repeat the measurement and mark them. If necessary, combine with other methods for verification.
- Advantages and Precautions: Fast detection speed, non-destructive, and can penetrate coatings; however, the surface roughness of the steel pipe must be ≤Ra3.2μm, otherwise the coupling effect will be affected.
(3) Optical Inspection Method: Suitable for precision steel pipes with ultra-high precision requirements, such as those used in aerospace and high-end machinery.
- Equipment Selection: Laser thickness gauge, optical microscope, or X-ray thickness gauge.
- Measurement Principle and Procedure:
Laser Thickness Gauge: Utilizes a laser beam to illuminate the outer and inner walls of the steel pipe, respectively. The wall thickness is obtained by calculating the laser reflection time difference. During measurement, the steel pipe must be fixed and stable to avoid vibration.
Optical Microscope: After polishing the steel pipe cross-section, it is placed under a microscope. The wall thickness is directly measured through an image analysis system, allowing for direct observation of wall thickness uniformity.
- Applicable Scenarios: High-precision inspection of small-diameter precision steel pipes and thin-walled steel pipes, effectively identifying problems such as uneven wall thickness and eccentricity.

Third, Data Processing and Result Judgment for Precision Steel Pipes.
Data Statistics: Statistical analysis of wall thickness deviations at all measuring points is performed, calculating the maximum, minimum, average, and standard deviation to assess wall thickness uniformity.
- Result Judgment: If the wall thickness deviation at a single measuring point exceeds the standard allowable range, and the absolute value of the deviation is greater than 8% of the nominal wall thickness, it is considered unqualified. If the difference between the maximum and minimum wall thickness within the same cross-section is greater than 10% of the nominal wall thickness, it is considered uneven wall thickness, requiring further investigation into production process issues (such as rolling eccentricity or heat treatment deformation). During batch testing, if the proportion of unqualified measuring points is greater than 5%, the testing scope needs to be expanded, and full inspection may be necessary.

Fourth, Key Considerations for Precision Steel Pipe Measurement.
Measuring tools must be calibrated regularly (e.g., mechanical tools every 6 months, ultrasonic equipment annually) to ensure reliable accuracy.
For welded precision steel pipes, two additional measuring points should be added on each side of the weld. The wall thickness deviation at the weld needs to be evaluated separately (usually, the allowable deviation is 10% greater than in ordinary areas). After the inspection is completed, an inspection report must be filled out, specifying the steel pipe specifications, material, inspection method, measuring point data, deviation results, and judgment conclusions, and kept for traceability.